12th Biology Study Material Chapter11(Biotechnology:Principles and processes) - Tamilyoungsters.
Chapter-11: BIOTECHNOLOGY: PRINCIPLES AND PROCESSES
Biotechnology is a broad area of science involving multiple disciplines designed to use living organisms or their products to perform valuable industrial or manufacturing processes or applications pertaining to human benefit.
Recombinant DNA technology:
An organism's genome contains virtually all the information necessary for its growth and development
Steps in producing recombinant DNA
1. The required gene is cut from a DNA molecule using a restriction enzyme.
2. A bacterial plasmid is isolated and cut with the same restriction enzyme. This ensures cut ends are complementary (same base sequence) to the ends of the required gene.
3. The required gene is joined to the plasmid using the enzyme DNA ligase in a process called ligation.
4. The resulting recombinant plasmid is returned to the bacterial cell.
5. The bacteria reproduce and the required gene is cloned.
How do we obtain DNA and how do we manipulate DNA?
Quite straightforward to isolate DNA For instance, to isolate genomic DNA
1. Remove tissue from organism
2. Homogenise in lysis buffer containing guanidine thiocyanate (denatures proteins)
3. Mix with phenol/chloroform - removes proteins
4. Keep aqueous phase (contains DNA)
5. Add alcohol (ethanol or isopropanol) to precipitate DNA from solution
6. Collect DNA pellet by centrifugation
7. Dry DNA pellet and resuspend in buffer
8. Store at 4°C
Each cell (with a few exceptions) carries a copy of the DNA sequences which make up the organism's genome. How do we manipulate DNA? It used to be difficult to isolate enough of a particular DNA sequence to carry out further manipulation and/or characterisation of its molecular sequence
Recombinant DNA Technology
Techniques for - Isolation - Digestion - Fractionation - Purification of the TARGET fragment - Cloning into vectors - Transformation of host cell and selection - Replication - Analysis - Expression of DNA DNA is manipulated using various enzymes that modify and/or synthesise it Until 1970 there were no convenient methods available for cutting DNA into discrete, manageable fragments. 1970 - The Beginning of the Revolution Discovery of a restriction enzyme in the bacterium Haemophilus influenzae Restriction enzymes . Restriction enzymes are endonucleases Bacterial enzymes Different bacterial strains express different restriction enzymes The names of restriction enzymes are derived from the name of the bacterial strain they are isolated from Cut (hydrolyse) DNA into defined and REPRODUCIBLE fragments Basic tools of gene cloning
Names of restriction endonucleases
Titles of restriction enzymes are derived from the first letter of the genus + the first two letters of the species of organism from which they were isolated.
The product of each reaction is two double stranded DNA fragments
Restriction enzymes do not discriminate between DNA from different organisms
Restriction endonucleases are a natural part of the bacterial defence system Part of the restriction/modification system found in many bacteria These enzymes RESTRICT the ability of foreign DNA (such as bacteriophage DNA) to infect/invade the host bacterial cell by cutting it up (degrading it) The host DNA is MODIFIED by METHYLATION of the sequences these enzymes recognise
o Methyl groups are added to C or A nucleotides in order to protect the bacterial host DNA from degradation by its own enzymes
Types of restriction enzymes Type I Recognise specific sequences·but then track along DNA (~1000-5000 bases) before cutting one of the strands and releasing a number of nucleotides (~75) where the cut is made. A second molecule of the endonuclease is required to cut the 2nd strand of the DNA
o e.g. EcoK.
o Require Mg2+, ATP and SAM (S-adenosyl methionine) cofactors for function Type II Recognise a specific target sequence in DNA, and then break the DNA (both strands), within or close to, the recognition site
o e.g. EcoRI
o Usually require Mg2+ Type III Intermediate properties between type I and type II. Break both DNA strands at a defined distance from a recognition site
o e.g. HgaI
o Require Mg2+ and ATP
Hundreds of restriction enzymes have been isolated and characterised Enables DNA to be cut into discrete, manageable fragments Type II enzymes are those used in the vast majority of molecular biology techniques Many are now commercially available
Many Type II restriction endonucleases recognise PALINDROMIC sequences (From Greek palindromos, running back again, recurring : palin, again)
A segment of double-stranded DNA in which the nucleotide sequence of one strand reads in reverse order to that of the complementary strand. (always read from the same direction)
For example, EcoRI recognises the sequence 5'-G A A T T C-3'
3'-C T T A A G-5'
What are cloning vectors?
Cloning vectors are extra-chromosomal 'replicons' of DNA which can be isolated and can replicate independently of the chromosome. Vectors usually contain a selectable marker - a gene that allows selection of cells carrying the vector e.g. by conferring resistance to a toxin. DNA of interest can be cloned into the vector and replicated in host cells, usually one which has been well characterised.
Commonly used vector systems Bacterial plasmids Bacteriophages Cosmids Yeast artificial chromosomes (YACs) Ti plasmid (plants) Eukaryotic viruses such as baculovirus (insect cells), SV40 virus and retroviruses.
Characteristics of a Cloning Vector
Origin of replication (ORI)
This process marks autonomous replication in vector. ORI is a specific sequence of nucleotide in DNA from where replication starts. When foreign DNA is linked to this sequence then along with vector replication, foreign (desirable) DNA also starts replicating within host cell.
Selectable Marker
Charecteristics of Selectable marker: A gene whose expression allows one to identify cells that have been transforrned or transfected with a vector containing the marker gene. A marker gene is used to determine if a piece of DNA has been successfully inserted into the host organism.. A gene, usually encoding resistance to an antibiotic,.A selectable marker will protect the organism from a selective agent that would normally kill it or prevent its growth.
Restriction sites
It should have restriction sites, to allow cleavage of specific sequence by specific Restriction Endonuclease. Restriction sites in E.coli cloning vector pBR322 include HindIII , EcoRI , BamHI , SalI, PvuI, PstI, ClaI etc. Refer NCERT text book diagram of pBR322
A Cloning Vector that Works with Plant Cells
Most commonly used plant cloning vector "Ti" plasmid, or tumor-inducing plasmid. Found in cells of the bacterium known as Agrobacterium tumefaciens, normally lives in soil. Bacterium has ability to infect plants and cause a crown gall, or tumorous lump, to form at the site of infection. Ti plasmid - called T DNA - separates from the plasmid and incorporates into the host cell genome. This aspect of Ti plasmid function has made it useful as a plant cloning vector (natural genetic engineer).
Plasmids are the most commonly used vector system. Several types available for cloning of foreign DNA in the host organism Escherichia coli. Many E. coli plasmids allow the expression of proteins encoded by the cloned DNA Bacteriophage another common vector system used for cloning DNA. These are viruses which 'infect' E. coli. The M13 bacteriophage is a single-stranded DNA virus which replicates in E. coli in a double-stranded form that can be manipulated like a plasmid. It can be used to produce single-stranded DNA copies which are useful for DNA sequencing. Bacteriophage is another bacteriophage which is commonly used to make DNA libraries. It allows the cloning of larger fragments of DNA than can be incorporated into plasmids. Transformation is the process by which plasmids (or other DNA) can be introduced into a cell. For E. coli transformation with plasmids is quite straightforward, plasmids can be introduced by electroporation or by incubation in the presence of divalent cations (usually Ca2+) and a brief heat shock (42°C) which induces the E. coli cells to take up the foreign DNA
1. two antibiotic selection and replica plating
2. color selection: blue/white selection using the lacz gene
Insertional inactivation - Subcloning a DNA fragment into an active gene (usually a marker gene whose function can be easily detected) will disrupt the function of that gene. This can be detected by looking for colonies that no longer display that phenotype. Colour selection A more common method to determine which transformants contain plasmids with inserts is to use colour selection. For E. coli, this involves the lac complex and blue/white screening. Colonies carrying plasmid with no insert will be coloured blue whereas colonies carrying recombinant plasmid will be white. For plasmids such as pBR322, which contains two antibiotic resistance genes, cloning an insert into one of these will disrupt that gene and inactivate the resistance to that antibiotic. Southern/Northern Blotting Analysis Analysing complex nucleic acid mixtures (DNA or RNA) The total cellular DNA of an organism (genome) or the cellular content of RNA are complex mixtures of different nucleic acid sequences. Restriction digest of a complex genome can generate millions of specific restriction fragments and there can be several fragments of exactly the same size which will not be separated from each other by electrophoresis. Techniques have been devised to identify specific nucleic acids in these complex mixtures Southern blotting - DNA Northern blotting - RNA
Southern blotting Technique devised by Ed Southern in 1975, is a commonly used method for the identification of DNA fragments that are complementary to a know DNA sequence. Allows a comparison between the genome of a particular organism and that of an available gene or gene fragment (the probe). It can tell us whether an organism contains a particular gene(DNA fragment) or not In Southern blotting, 1 Chromosomal DNA is isolated from the organism of interest, and digested to completion with a restriction endonuclease enzyme. 2 The restriction fragments are then subjected to electrophoresis on an agarose gel, which separates the fragments on the basis of size. 3 DNA fragments in the gel are denatured (i.e. separated into single strands) using an alkaline solution. 4 Transfer fragments from the gel onto nitrocellulose filter or nylon membrane.
Fig 7-32, Lodish et al (4th ed.)
DNA is bound irreversibly to the filter/membrane by baking at high temperature (nitrocellulose) or cross-linking through exposure to UV light (nylon). Final step is to immerse the membrane in a solution containing the probe - either a DNA (cDNA clone, genomic fragment, oligonucleotide) or RNA probe can be used. This is DNA hybridisation The membrane is washed to remove non-specifically bound probe, and is then exposed to X-ray film - a process called autoradiography. The principle of Southern blotting
PCR(Polymerase Chain Reaction): PCR is a technique for the in vitro amplification of a desired sequence of DNA. PCR allows the generation of a large quantity of DNA product (up to several g) from only a few starting copies. It has been shown that PCR can be used to generate a detectable quantity of DNA from only one starting target (or template) molecule. PCR developed in the mid-1980's, has found multiple applications, such as:
1. Rapid amplification of intact genes or gene fragments
2. Generation of large amounts of DNA for sequencing
3. Generation of probes specific for uncloned genes by selective amplification of a specific segment of cDNA
4. Analysis of mutations for medical applications
5. Detection of minute amounts of DNA for forensic purposes
6. Amplification of chromosomal regions adjacent to genes of known sequence and many more·
Development of PCR won the Nobel prize for Kary Mullis and co-workers. PCR principle PCR reaction is a DNA synthesis reaction that depends on the extension of primers annealed to opposite strands of a dsDNA template that has been denatured (melted apart) at temperatures near boiling. By repeating the melting, annealing and extension steps, several copies of the original template DNA can be generated. The amount of starting material (target) needed is very small Not necessary to isolate the desired sequence, because it will be defined by the primers that are used in the reaction. The primers are oligonucleotides complementary to different regions on the 2 strands of DNA template (flanking the region to be amplified). The primer acts as a starting point for DNA synthesis. The oligo is extended from its 3' end by DNA polymerase.
Primer design The stages of a PCR reaction PCR is a cycle of three steps:
1. DENATURATION - the strands of the DNA are melted apart by heating to 95°C
2. ANNEALING - the temperature is reduced to ~ 55°C to allow the primers to anneal to the target DNA
3. POLYMERISATION/EXTENSION - the temperature is changed to the optimum temperature in order for the DNA polymerase to catalyse extension of the primers, i.e. to copy the DNA between the primers.
The cycle is repeated over and over again - as many times as needed to produce a detectable amount of product. Discovery of a thermostable DNA polymerase The breakthrough came with the discovery of the thermostable DNA polymerase Taq polymerase, from the thermophilic bacterium, Thermus aquaticus, which lives in hot springs. Taq polymerase enzyme can resist high temperatures required to melt the template DNA apart without denaturation (loss of activity) and works best at high temperatures (72°C). This led to improved specificity & sensitivity. Annealing of primers to sites other than the target sequence is significantly reduced at the higher temperatures used for Taq polymerase.
Applications of PCR 1) Cloning a gene encoding a known protein 2) Amplifying 'old DNA' 3) Amplifying cloned DNA from vectors 4) Creating mutations in cloned genes 5) Rapid amplification of cDNA ends - RACE 6) Detecting bacterial or viral infection * AIDs infection * Tuberculosis (Mycobacterium tuberculosis) 7) Cancer Detecting mutations that occur in cancer and monitoring cancer therapy. Determining if a patient is free of malignant cells 8) Genetic diagnosis a. Diagnosing inherited disorders * Cystic fibrosis * Muscular dystrophy * Haemophilia A and B * Sickle cell anaemia b. Diagnosing cancer - certain cancers are caused by specific and reproducible mutations: e,g. Retinoblastoma - childhood cancer of the eye. The heritable form (germ line mutation of one of the two retinoblastoma allelles): mutation is detected in all cells. Spontaneous form: only detected in tumour tissue. c. Blood group typing d. Prenatal diagnosis – eg determining the sex of foetus for those at risk of X-linked disorders PCR is one of the most versatile techniques invented, and has so many applications that this list could go on for quite some time. Downstream processing It refers to the recovery and purification of biosynthetic products, particularly pharmaceuticals, from natural sources such as animal or plant tissue or fermentation broth
Stages in Downstream Processing
A widely recognized heuristic for categorizing downstream processing operations divides them into four groups which are applied in order to bring a product from its natural state as a component of a tissue, cell or fermentation broth through progressive improvements in purity and concentration.
Removal of insolubles Product Isolation ProductPurification Product Polishing
GLOSSARY:
Amplification
An increase in the number of copies of a specific DNA fragment; can be in vivo or in vitro. See also: cloning, polymerase chain reaction Annotation Adding pertinent information such as gene coded for, amino acid sequence, or other commentary to the database entry of raw sequence of DNA bases. Antisense Nucleic acid that has a sequence exactly opposite to an mRNA molecule made by the body; binds to the mRNA molecule to prevent a protein from being made. Autoradiography A technique that uses X-ray film to visualize radioactively labeled molecules or fragments of molecules; used in analyzing length and number of DNA fragments after they are separated by gel electrophoresis. Bacterial artificial chromosome (BAC) A vector used to clone DNA fragments (100 to 300 kb insert size; average, 150 kb) in Escherichia coli cells. Based on naturally occurring F-factor plasmid found in the bacterium E. coli. Base sequence The order of nucleotide bases in a DNA molecule; determines structure of proteins encoded by that DNA. Bioinformatics The science of managing and analyzing biological data using advanced computing techniques. Especially important in analyzing genomic research data. Biotechnology A set of biological techniques developed through basic research and now applied to research and product development. In particular, biotechnology refers to the use by industry of recombinant DNA, cell fusion, and new bioprocessing techniques. Cancer
Diseases in which abnormal cells divide and grow unchecked. Cancer can spread from its original site to other parts of the body and can be fatal. See also: hereditary cancer, sporadic cancer Carcinogen Something which causes cancer to occur by causing changes in a cell's DNA. See also: mutagen Carrier An individual who possesses an unexpressed, recessive trait. cDNA library
A collection of DNA sequences that code for genes. The sequences are generated in the laboratory from mRNA sequences. See also: messenger RNA Cell The basic unit of any living organism that carries on the biochemical processes of life. Chromosome The self-replicating genetic structure of cells containing the cellular DNA that bears in its nucleotide sequence the linear array of genes. In prokaryotes, chromosomal DNA is circular, and the entire genome is carried on one chromosome. Eukaryotic genomes consist of a number of chromosomes whose DNA is associated with different kinds of proteins.
Clone An exact copy made of biological material such as a DNA segment (e.g., a gene or other region), a whole cell, or complete organism. Cloning Using specialized DNA technology to produce multiple, exact copies of a single gene or other segment of DNA to obtain enough material for further study. Process, used by researchers in the Human Genome Project, referred to as cloning DNA. Resulting cloned (copied) collections of DNA molecules constitute clone libraries. Second type of cloning exploits the natural process of cell division to make many copies of an entire cell. The genetic makeup of these cloned cells, called cell line, is identical to the original cell. Third type of cloning produces complete, genetically identical animals such as the famous Scottish sheep, Dolly. Cloning vector DNA molecule originating from a virus, a plasmid, or the cell of a higher organism into which another DNA fragment of appropriate size can be integrated without loss of the vector's capacity for self-replication; vectors introduce foreign DNA into host cells, where the DNA can be reproduced in large quantities. Examples are plasmids, cosmids, and yeast artificial chromosomes; vectors are often recombinant molecules containing DNA sequences from several sources. Complementary DNA (cDNA) DNA that is synthesized in the laboratory from a messenger RNA template. Complementary sequence Nucleic acid base sequence that can form a double-stranded structure with another DNA fragment by following base-pairing rules (A pairs with T and C with G). The complementary sequence to GTAC for example, is CATG. Cosmid Artificially constructed cloning vector containing the cos gene of phage lambda. Cosmids can be packaged in lambda phage particles for infection into E. coli; Permits cloning of larger DNA fragments (up to 45kb) than can be introduced into bacterial hosts in plasmid vectors. Crossing over The breaking during meiosis of one maternal and one paternal chromosome, the exchange of corresponding sections of DNA, and the rejoining of the chromosomes. This process can result in an exchange of alleles between chromosomes.
See also: recombination DNA (deoxyribonucleic acid) The molecule that encodes genetic information. DNA is a double-stranded molecule held together by weak bonds between base pairs of nucleotides. The four nucleotides in DNA contain the bases adenine (A), guanine (G), cytosine (C), and thymine (T). In nature, base pairs form only between A and T and between G and C; thus the base sequence of each single strand can be deduced from that of its partner. DNA bank A service that stores DNA extracted from blood samples or other human tissue. DNA repair genes Genes encoding proteins that correct errors in DNA sequencing. DNA replication The use of existing DNA as a template for the synthesis of new DNA strands. In humans and other eukaryotes, replication occurs in the cell nucleus. DNA sequence.
The relative order of base pairs, whether in a DNA fragment, gene, chromosome, or an entire genome. See also: base sequence analysis
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Double helix The twisted-ladder shape that two linear strands of DNA assume when complementary nucleotides on opposing strands bond together. Electrophoresis A method of separating large molecules (such as DNA fragments or proteins) from a mixture of similar molecules. An electric current is passed through a medium containing the mixture, and each kind of molecule travels through the medium at a different rate, depending on its electrical charge and size. Agarose and acrylamide gels are the media commonly used for electrophoresis of proteins and nucleic acids. Electroporation A process using high-voltage current to make cell membranes permeable to allow the introduction of new DNA; commonly used in recombinant DNA technology.
See also: transfection Embryonic stem (ES) cells An embryonic cell that can replicate indefinitely, transform into other types of cells, and serve as a continuous source of new cells. Endonuclease See: restriction enzyme Escherichia coli Common bacterium that has been studied intensively by geneticists because of its small genome size, normal lack of pathogenicity, and ease of growth in the laboratory. Eugenics Study of improving a species by artificial selection; usually refers to the selective breeding of humans. Exogenous DNA DNA originating outside an organism that has been introduced into the organism. Exon
The protein-coding DNA sequence of a gene. See also: intron Exonuclease An enzyme that cleaves nucleotides sequentially from free ends of a linear nucleic acid substrate. Expressed sequence tag (EST) A short strand of DNA that is part of cDNA molecule and can act as identifier of a gene. Used in locating and mapping genes.
See also: cDNA, sequence tagged site Fingerprinting
In genetics, the identification of multiple specific alleles on a person's DNA to produce a unique identifier for that person. See also: forensics Fluorescence in situ hybridization (FISH) A Physical mapping approach that uses fluorescein tags to detect hybridization of probes with metaphase chromosomes and with the less-condensed somatic interphase chromatin. Forensics Use of DNA for identification. Some examples of DNA use are to establish paternity in child support cases; establish the presence of a suspect at a crime scene, and identify accident victims. Functional genomics Study of genes, their resulting proteins, the role played by proteins in the body's biochemical processes.
Gel electrophoresis
See: electrophoresis Gene The fundamental physical and functional unit of heredity. A gene is an ordered sequence of nucleotides located in a particular position on a particular chromosome that encodes a specific functional product (i.e., a protein or RNA molecule)
See also: gene expression Gene expression The process by which a gene's coded information is converted into the structures present and operating in the cell. Expressed genes include those that are transcribed into mRNA and then translated into protein and those that are transcribed into RNA but not translated into protein (e.g., transfer and ribosomal RNAs). Gene library
See: genomic library Gene mapping Determination of the relative positions of genes on a DNA molecule (chromosome or plasmid) and of the distance, in linkage units or physical units, between them. Gene pool
All the variations of genes in a species. See also: allele, gene, polymorphism Gene therapy Experimental procedure aimed at replacing, manipulating, or supplementing nonfunctional or misfunctioning genes with healthy genes.
See also: gene, inherit, somatic cell gene therapy, germ line gene therapy Gene transfer
Incorporation of new DNA into an organism's cells, usually by a vector such as a modified virus. Used in gene therapy. See also: mutation, gene therapy, vector Genetic engineering Altering the genetic material of cells or organisms to enable them to make new substances or perform new functions. Genetic engineering technology
See: recombinant DNA technology Genetic marker
A gene or other identifiable portion of DNA whose inheritance can be followed. See also: chromosome, DNA, gene, inherit Genetic material
See: genome Genetic polymorphism Difference in DNA sequence among individuals, groups, or populations (e.g., genes for blue eyes versus brown eyes). Genetic screening Testing a group of people to identify individuals at high risk of having or passing on a specific genetic disorder. Genetic testing Analyzing an individual's genetic material to determine predisposition to a particular health condition or to confirm a diagnosis of genetic disease.
Genetics The study of inheritance patterns of specific traits. Genome All the genetic material in the chromosomes of a particular organism; its size is generally given as its total number of base pairs. Genome project
Research and technology-development effort aimed at mapping and sequencing the genome of human beings and certain model organisms. See also: Human Genome Initiative Genomic library A collection of clones made from a set of randomly generated overlapping DNA fragments that represent the entire genome of an organism. Genotype The genetic constitution of an organism, as distinguished from its physical appearance (its phenotype).
Human Genome Project (HGP)
Formerly titled Human Genome Initiative. See also: Human Genome Initiative In situ hybridization Use of a DNA or RNA probe to detect the presence of the complementary DNA sequence in cloned bacterial or cultured eukaryotic cells. In vitro Studies performed outside a living organism such as in a laboratory. In vivo Studies carried out in living organisms. Independent assortment
During meiosis each of the two copies of a gene is distributed to the germ cells independently of the distribution of other genes. See also: linkage Informatics
See: bioinformatics Karyotype Photomicrograph of an individual's chromosomes arranged in standard format showing the number, size, and shape of each chromosome type; used in low-resolution physical mapping to correlate gross chromosomal abnormalities with the characteristics of specific diseases. Knockout
Deactivation of specific genes; used in laboratory organisms to study gene function. See also: gene, locus, model organisms Marker
See: genetic marker Microinjection A technique for introducing a solution of DNA into a cell using a fine microcapillary pipette. Mitochondrial DNA Nitrogenous base
A nitrogen-containing molecule having the chemical properties of a base. DNA contains the nitrogenous bases adenine (A), guanine (G), cytosine (C), and thymine (T). See also: DNA
Northern blot A gel-based laboratory procedure that locates mRNA sequences on a gel that are complementary to a piece of DNA used as a probe. Nucleotide
A subunit of DNA or RNA consisting of a nitrogenous base (adenine, guanine, thymine, or cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA), a phosphate molecule, and a sugar molecule (deoxyribose in DNA and ribose in RNA). Thousands of nucleotides are linked to form a DNA or RNA molecule. See also: DNA, base pair, RNA Nucleus The cellular organelle in eukaryotes that contains most of the genetic material. Phage A virus for which the natural host is a bacterial cell. Plasmid Autonomously replicating extra-chromosomal circular DNA molecules, distinct from the normal bacterial genome and nonessential for cell survival under nonselective conditions. Some plasmids are capable of integrating into the host genome. Number of artificially constructed plasmids are used as cloning vectors. Polymerase chain reaction (PCR) A method for amplifying a DNA base sequence using heat-stable polymerase and two 20-base primers, one complementary to the (+) strand at one end of the sequence to be amplified and one complementary to the (-) strand at the other end. Because the newly synthesized DNA strands can subsequently serve as additional templates for the same primer sequences, successive rounds of primer annealing, strand elongation, and dissociation produce rapid and highly specific amplification of the desired sequence. PCR also can be used to detect the existence of the defined sequence in a DNA sample. Polymerase, DNA or RNA Enzyme that catalyzes the synthesis of nucleic acids on preexisting nucleic acid templates, assembling RNA from ribonucleotides or DNA from deoxyribonucleotides. Primer Short preexisting polynucleotide chain to which new deoxyribonucleotides can be added by DNA polymerase. Probe Single-stranded DNA or RNA molecules of specific base sequence, labeled either radioactively or immunologically. Used to detect the complementary base sequence by hybridization. Restriction enzyme, endonuclease
Protein that recognizes specific, short nucleotide sequences and cuts DNA at those sites. Bacteria contain over 400 such enzymes that recognize and cut more than 100 different DNA sequences. See also: restriction enzyme cutting site Restriction fragment length polymorphism (RFLP) Variation between individuals in DNA fragment sizes cut by specific restriction enzymes; polymorphic sequences that result in RFLPs are used as markers on both physical maps and genetic linkage maps. RFLPs are usually caused by mutation at a cutting site.
See also: marker, polymorphism
Restriction-enzyme cutting site Specific nucleotide sequence of DNA at which a particular restriction enzyme cuts the DNA. Some sites occur frequently in DNA (e.g., every several hundred base pairs); others much less frequently (rare-cutter; e.g., every 10,000 base pairs). Retroviral infection Presence of retroviral vectors, such as some viruses, which use their recombinant DNA to insert their genetic material into the chromosomes of the host's cells. The virus is then propogated by the host cell. Reverse transcriptase Enzyme used by retroviruses to form a complementary DNA sequence (cDNA) from their RNA. The resulting DNA is then inserted into the chromosome of the host cell. Ribonucleotide
See: nucleotide Ribose
The five-carbon sugar that serves as a component of RNA. See also: ribonucleic acid, deoxyribose Ribosomal RNA (rRNA) A class of RNA found in the ribosomes of cells. RNA (Ribonucleic acid) Chemical found in nucleus and cytoplasm of cells. Plays important role in protein synthesis and other chemical activities of the cell. Structure of RNA similar to that of DNA. There are several classes of RNA molecules, including messenger RNA, transfer RNA, ribosomal RNA, and other small RNAs, each serving a different purpose. Sanger sequencing
A widely used method of determining the order of bases in DNA. See also: sequencing, shotgun sequencing Satellite Chromosomal segment that branches off from the rest of the chromosome but is still connected by a thin filament or stalk. Scaffold In genomic mapping, a series of contigs that are in the right order but not necessarily connected in one continuous stretch of sequence. Segregation The normal biological process whereby the two pieces of a chromosome pair are separated during meiosis and randomly distributed to the germ cells. Sequencing Determination of order of nucleotides (base sequences) in a DNA or RNA molecule or the order of amino acids in a protein. The X or Y chromosome in human beings that determines the sex of an individual. Females have two X chromosomes in diploid cells; males have an X and a Y chromosome. The sex chromosomes comprise the 23rd chromosome pair in a karyotype.
Shotgun method Sequencing method that involves randomly sequenced cloned pieces of the genome, with no foreknowledge of where the piece originally came from. This can be contrasted with "directed" strategies, in which pieces of DNA from known chromosomal locations are sequenced. Because there are advantages to both strategies, researchers use both random (or shotgun) and directed strategies in combination to sequence the human genome. Single nucleotide polymorphism (SNP) DNA sequence variations that occur when a single nucleotide (A, T, C, or G) in the genome sequence is altered. Single-gene disorder Hereditary disorder caused by a mutant allele of a single gene (e.g., Duchenne muscular dystrophy, retinoblastoma, sickle cell disease).
See also: polygenic disorders Somatic cell Any cell in the body except gametes and their precursors. Southern blotting Transfer by absorption of DNA fragments separated in electrophoretic gels to membrane filters for detection of specific base sequences by radio-labeled complementary probes. Transfer RNA (tRNA) A class of RNA having structures with triplet nucleotide sequences that are complementary to the triplet nucleotide coding sequences of mRNA. The role of tRNAs in protein synthesis is to bond with amino acids and transfer them to the ribosomes, where proteins are assembled according to the genetic code carried by mRNA. Transgenic An experimentally produced organism in which DNA has been artificially introduced and incorporated into the organism's germ line.
See also: cell, DNA, gene, nucleus, germ line Transposable element A class of DNA sequences that can move from one chromosomal site to another. Trisomy
Possessing three copies of a particular chromosome instead of the normal two copies. See also: cell, gene, gene expression, chromosome Virus
Noncellular biological entity that can reproduce only within a host cell. Viruses consist of nucleic acid covered by protein; some animal viruses are also surrounded by membrane. Inside the infected cell, the virus uses the synthetic capability of the host to produce progeny virus. See also: cloning vector Western blot
A technique used to identify and locate proteins based on their ability to bind to specific antibodies. See also: DNA, Northern blot, protein, RNA, Southern blotting Wild type The form of an organism that occurs most frequently in nature. Yeast artificial chromosome (YAC) Constructed from yeast DNA, it is a vector used to clone large DNA fragments.
See also: cloning vector, cosmid
Outline of molecular biology Questions
1 Mark Questions
1) What is biotechnology?
2) Define plasmid.
3) What are molecular scissors?
4) What do you mean by recognition sequence?
5) Which enzymes act as molecular glue?
6) What is elution?
7) What are cloning vectors?
8) Name the sequence within a cloning vector from where the replication commences.
9) Mention the bacteria that acts as natural genetic engineer.
10) Name any two processes by which alien DNA is introduced into the host cell.
11) Expand the term PCR.
12) Name the microorganism from which the thermostable DNA polymerase required for PCR is obtained?
13) What is a bioreactor?
14) What are the two main processes involved in downstream processing?
HINTS: 1) Large scale production and marketing of products and processes using living organisms, cells or enzymes.
2) Autonomously replicating circular , extra-chromosomal bacterial DNA used in gene manipulation.
3) Restriction enzymes.
4) Restriction endonucleases always cut DNA at a specific point by recognizing a specific sequences of base pair known as recognition sequence.
5) DNA ligases
6) The ultimate step in the separation and isolation of DNA fragments through gel electrophoresis in which separated bands of DNAs are cut out from the gel and extracted from the gel piece.
7) Cloning vectors are extra-chromosomal 'replicons' of DNA which can be isolated and can replicate independently of the chromosome. DNA of interest can be cloned into the vector and replicated in host cells
8) ORI point
9) Agrobacterium tumefaciens
10) Microinjection,biolistics(gene gun)
11) Polymerase Chain Reaction
12) Thermusaquaticus
13) Large scale biotechnological product involves the use of bioreactor.
14) Separation and purification.
2-Marks Questions
1) Enlist the core techniques that pave the way for modern biotechnology.
2) What is gene cloning?
3) Mention the three steps involve in genetically modifying an organism.
4) Why do bacteria possesses restriction enzyme ?
5) Mention one basic difference between restriction endonucleases and exonucleases.
6) What is a palindromic sequence? Give example.
7) What are ― sticky ends‖ and ―blind ends ?
8) Mention the role of selectable marker in cloning vector.
9) What is insertional inactivation?
10) How can you make a bacterial cell competent to take up foreign DNA ?
HINTS:
1) ( a) Genetic engineering (b) maintenance of sterile ambience.
2) The process of cloning multiple copies of a gene.
3) (a) identification of DNA with desirable genes (b) introduction of the identified DNA into the host and (c) maintenance of introduced DNA in the host and transfer of DNA to its progeny.
4) By restriction enzyme bacteria can attack and destroy the phage DNA in case of viral attack and thereby prevent viral attack.
5) Exonucleases digest DNA from the flank ( beginning/end) of the DNA strands. Whereas endonucleases catalyses the hydrolytic cleavage of DNA in the middle.
6) A segment of double-stranded DNA in which the nucleotide sequence of one strand reads same in reverse order to that of the complementary strand. (always read from the same direction)
7) Double stranded ends of a DNA molecule (without any overhangings) produced by the action of certain restriction enzymes .-[blunt ends)/ Sticky ends - Double stranded ends] of a DNA molecule (with overhangings) produced by the action of certain restriction enzymes
8) The selectable marker genes in a cloning vector allow for the selection and identification of bacteria that have been transformed with a recombinant plasmid compared to nontransformed cells. Some of the most common selectable markers are genes for ampicillin resistance (ampR) and tetracycline resistance (tetR ) and the lacZ gene used for blue white selection.
9) Insertional inactivation refers to the loss of activity of the selectable marker genes due to the insertion of foreign DNA within the coding sequence of the marker gene in a transfected bacteria.
3-Marks Questions:
1)Enlist the major steps in recombinant DNA technology. 2)Mention the steps involved in the separation and isolation of DNA fragments through agarose gel electrophoresis.
3)Describe in brief the principle of DNA isolation through gel electrophoresis.
4)Highlight the salient features that are required to facilitate cloning into a vector.
5) Enumerate the major steps for isolation of DNA.
6) Draw a neat ,labeled diagram of (a) simple stirred tank bioreactor/ (b) sparged tank bioreactor. Answers: 1) R-DNA Technology: Restriction enzyme cuts double stranded DNA at its particular recognition sequence. The cuts produce DNA fragments with cohesive ends DNA from a plasmid was also cut by the same restriction enzyme When two of the above mentioned DNA come together they can join by base pairing. DNA ligase enzyme used to unite the backbones of the two DNA fragments ,producing R-DNA 2) Agarose gel electrophoresis:
3) DNA When charged molecules are placed in an electric field, they migrate toward either the positive or negative pole according to their charge. In contrast to proteins, which can have either a net positive or net negative charge, nucleic acids have a consistent negative charge imparted by their phosphate backbone, and migrate toward the anode DNA is electrophoresed through the agarose gel from the cathode (negative) to the anode (positive) when a voltage is applied, due to the net negative charge carried on DNA
4)Salient features of a DNA cloning Vectors:
Size: small enough to be easily separated from the chromosomal DNA of the host bacteria.
Ori site; must have the site for DNA replication that allows the plasmid to replicate separately from the host cell‘s chromosome. Multiple Cloning sites :a stretch of DNA with recognition sequence for many different commonb restriction enzymes. Selectable marker genes
RNApolymerase promoter sequence
5) Major steps for isolation of DNA: Cell containing DNA is treated with lysozyme/cellulose/chitinase DNA along with RNA,Protein,lipid are released Treatment with RNAase,protease to remove RNA and Protein Appropriate treatment to remove other impurities Addition of chilled ethanol to get precipitation of purified DNA
6) Consult NCERT Textbook page number 204
5-Marks Questions:
1) What do you mean by PCR? Briefly enumerate the major steps of PCR. Mention the utility of PCR.
Ans: PCR is a cycle of three steps:
DENATURATION - the strands of the DNA are melted apart by heating to 95°C.
ANNEALING - the temperature is reduced to ~ 55°C to allow the primers to anneal to the target DNA
POLYMERISATION/EXTENSION - the temperature is changed to the optimum temperature in order for the DNA polymerase to catalyse extension of the primers, i.e. to copy the DNA between the primers. The cycle is repeated over and over again - as many times as needed to produce a detectable amount of product (DNA)
