PROTEIN SYNTHESIS DEFINITIONS

Gene expression

information from one gene is used to make a functional protein through transcription and translation – including protein folding.

Function of DNA

carries the genetic code of an organism in the base sequence of DNA.

Gene

 a section of DNA that codes for a particular polypeptide chain / protein that determines a characteristic (e.g. a certain enzyme)

Coding strand

the DNA strand that contains the genetic information which is exactly what the mRNA copy of the template DNA will be. 

template strand

 the DNA strand from which the mRNA strand is created and is complementary to the mRNA strand due to the complementary base pairing rules.

Transcription

 the process whereby one DNA strand is used as a template in order to create a mRNA molecule that is an exact copy of the coding strand.

Translation

 process where the mRNA is translated to produce the specific sequence of amino acids in a polypeptide chain or protein.

mutation

a permanent but random change in the base sequence of DNA (which produces a new or different protein/new allele)

Mutagen

- A mutagen is a substance or an environmental factor (e.g. UV radiation) that changes the DNA base sequence (genotype) or increases the rate of mutations.

triplet

 3 consecutive bases on the DNA strand is called a triplet

codon

three consecutive bases on the mRNA is called a codon

anti codon

three consecutive bases on tRNA that code for an amino acid 

frameshift

 A frame shift is where after an insertion or deletion mutation, all the triplets are incorrect because of a shift in the reading frame of the codons in mRNA (as they are not “read” in their correct threes).

mRNA

mRNA is “messenger” RNA and is the short single strand of RNA that is made off the template DNA strand.

tRNA

tRNA is “transfer” RNA that is complementary to the mRNA codons. Its anticodon ensures that the correct amino acid is added to the growing polypeptide chain (as the Ribosome reads the mRNA).

Ribosome

The Ribosome is the structure that “reads” the mRNA and, through the use of tRNA, adds amino acids that correspond to each codon on the mRNA until a stop codon is reached. Made up of rRNA and protein. 

Polypeptide chain

The polypeptide chain is the name for the chain of Amino acids which is held together with peptide bonds which will fold together to make a functional protein

Genotype

The genotype is the alleles that the individual (organism) possesses for a particular trait or gene.

enzyme

proteins that catalyse (speed up) reactions in living things (e.g. in metabolic pathways enzymes work by speeding up the series of reactions by building up or breaking down chemicals, making the substrate for the next reaction in the series). 

metabolic pathway

 a series of enzyme-controlled biochemical reactions where the product of one reaction becomes the substrate for the next reaction (intermediates).

degenerate code

The genetic code is degenerate because some codons code for the same amino acid. This means the genetic code is degenerate and redundant. Redundant codons are usually different at the 3rd base.

point/gene mutation

 a point or gene mutation occurs where there is a change to the base sequence of a gene. Bases are either inserted or deleted or substituted into the gene causing a point mutation.

Deletion mutation

A deletion mutation is when a base is taken out or removed from the DNA sequence of a gene. Causes a frameshift.

Insertion Mutation

 An insertion mutation is when a base is inserted into the DNA sequence. Causes a frameshift.

Substitution mutation

Substitution mutation is where a single nucleotide (base) is changed or swapped by another base.

mis-sense mutation

if the substituted base causes a change in the amino acid sequence but may not cause a change in the shape or function of the protein this is a mis-sense mutation.

non-sense mutation

 if the substituted bases results in the production of a stop codon it will have a severe impact on the protein formed - nonsense mutation.

amino acid

 the building blocks of proteins / polypeptides. 

protein synthesis

to make a protein (polypeptide) from the DNA / gene. 

base pairing rule

 states that A can only bind with T (on the DNA) or U (on the RNA), T (DNA) or U (RNA) can only bind with A, and C can only bind with G. 

redundancy

 the genetic code has redundancy due to the fact that 2 or more codons can code (specify) the same amino acid