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24 terms

Biology: Protein synthesis, enzymes, mutations, genetic engineering.

Biology terms, definitions, processes, etc.
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Transcription
Occurs in the nucleus, and is process by which a DNA molecule is read and rewritten as an mRNA molecule.
1. DNA uncoils with the assistance of RNA polymerase, exposing nucleotide bases.
2. RNA polymerase assists the RNA nucleotides attaching to the exposed DNA nucleotides.
3. The RNA polymerase recognises the start codon (AUG), and begins the production of the mRNA molecule until a stop codon is reached.
4. Once transcription has completed, the DNA returns to its double helix structure, and mRNA leaves the nucleus.
Translation
Occurs at the ribosomes, and is the process by which an mRNA molecule is translated into a sequence of amino acids.
1. The tRNA molecule brings its specific amino acid to the ribosome according to the mRNA codon.
2. Once the tRNA molecule has unloaded its amino acid, it is referred to as 'unloaded,' and is sent to retrieve another amino acid.
3. The amino acids are brought alongside one another and they are joined by a peptide bond.
4. When the polypeptide chain has been created, it leaves the ribosomes and folds into a 3D shape.
Polymerase Chain Reaction
Firstly, DNA is heated to separate the the double stranded molecule into two single strands. A mixture of DNA polymerase, nucleotides, and primer is added to the DNA. Upon cooling, the primer attaches to the single strands, and DNA polymerase synthesises the nucleotides attaching to the single strands according to base pairing. This can be repeated to produce thousands of DNA copies.
Isolating and identifying a gene
Firstly, the nucleotide sequence of the G.O.I needs to be known. Then, the DNA containing the G.O.I is cut using restriction enzymes. From this, a radioactively labelled DNA Probe can be created that is complementary to the G.O.I. A solution containing the G.O.I is heated to separate the double strands, upon cooling, the DNA probe will bind to the G.O.I, thereby isolating and identifying the gene.
Cloning a gene
The G.O.I is identified and isolated using a radioactively labelled DNA Probe. When the G.O.I has been isolated, it is removed from the DNA sequence, and inserted into a plasmid which has been cut with the same restriction enzyme that the G.O.I was cut with. The G.O.I is inserted into the plasmid, which is inserted into the bacterial cell. This cell reproduces, producing many copies of the gene.
DNA Probe
Before using a DNA probe, the nucleotide sequence of the G.O.I needs to be known. When this is known, the DNA probe can be created that is complementary to the G.O.I. The probe can then be added to the mixture containing the G.O.I, thereby locating it.
TI Plasmids
TI Plasmids are bacterium that cause tumours. The Ti plasmid is removed from the bacterium, and the desired gene is added to it. The plasmid is inserted into the bacterium, which is inserted into plant cells. The cells divide rapidly, creating a tumour.
Viral Vectors
Are particles made up of nucleic acid core and protein coat. They introduce their genetic material into a host cell, causing it to manufacture viral proteins.
Gene Guns
Tungsten and Gold are coated with DNA, and shot using a helium gun through the cell walls of plants.
Micro-injection
A desired gene is inserted directly into the nucleus of a fertilised ovum. The resulting animal will then contain its own genes, and the foreign gene.
Gel electrophoresis
The process of separating DNA fragments by size, shape, and charge. Firstly, DNA is cut up using restriction enzymes. This restriction fragmented DNA is then added to the gel. Since DNA has a negative charge, the fragments move toward the positive terminal. Larger DNA fragments are located toward the negative terminal, whereas smaller DNA fragments are located toward the positive terminal.
DNA Fingerprinting
The creation of an autoradiograph using gel electrophoresis. When the DNA fragments have been separated, the gel can be transferred onto a filter sheet. This filter sheet is then removed and immersed into radioactively labelled DNA probes. An autoradiograph has been created: the dark bands are where the DNA probes have attached. Each DNA fingerprint is specific to an individual, as the DNA used is a 'junk repeat' located in the centromere that does not code for anything - the frequency of non coding repeats is specific to an individual.
Enzyme
A biological catalyst that speeds up the rate of a reaction.
Types of chemical reactions
Anabolic: Energy is used - complex molecules are synthesised and energy is used to create bonds that hold reactants together.
Catabolic: Energy is released - complex molecules are broken down.
Active site
Enzymes have active sites on their surface to which the substrate binds to. The active site and the substrate are complementary.
Induced fit model
When a substrate binds to the active site, and the enzyme changes shape slightly to fit onto the substrate better.
Changes in enzymes
As enzymes are proteins, they are very sensitive to their environments. There is an optimum temperature and pH to which an enzyme works best. If the temperature or pH surpass this optimum, then the active site on the enzyme changes, making it impossible for the complementary substrate to fit there.
Inhibitors
Non competitive: When a molecule will attach to the enzyme changing the shape of the active site.
Competitive: When a molecule with a similar shape to the substrate attaches to the enzyme at the active site, the substrate is no longer able to bind to the active sire.
Activation energy
Reactant molecules must absorb energy for chemical bonds to break. The energy needed to break these bonds is called activation energy. An enzyme can decrease this activation energy required by stressing the bonds of the substrate, making it more likely to react. Also, as there is already stress on the bonds, there is less energy needed to begin the reaction as the bonds will be easier to break.
Mutations
Changes in the DNA sequence
Mutation rate
The rate at which mutations can occur is increased by certain environmental factors: UV light, heat, and certain chemicals.
Types of mutations
Substitution: When one base takes the place of another.
Insertion: When bases are added. which results in an overall movement of all codons, ultimately causing a change in the amino acid sequence.
Deletion: When bases are deleted, resulting in an overall movement of codons, causing a change in amino acid sequence.
Inversion: When sequences of bases are swapped, changing mRNA and amino acid order.
Codons
Triplets of bases on mRNA molecules. Complementary to DNA, however uracil replaces thymine. The number of codon is equal to the number of amino acids. The number of bases divided by three is equal to the number of amino acids.
Anticodon
Triplet bases on tRNA molecules. Complementary to the codon on mRNA molecules.