Gene Expression

Biology Level 2 external

Amino Acid

Building Block of proteins

Anticodon

Three coding bases on tRNA, each specific for an amino acid

Autosomes

Chromosomes other than those concerned with sex linkage

Codon

Three bases on mRNA that code for an amino acid

Coding Strand

the untranscribed strand of DNA, where the triplets code for the amino acid sequence of a polypeptide

Complementary base pair rule

The bases always pair in the same way. thymnie to adenine, guanine to cytosine and uracil to adenine -  for RNA. 

Degeneracy of the code

Several codons can specify one amino acid due to redundancy, where 64 possible combinations of three bases code for only 20 amino acids.

Deletion mutation

A mutation where a base(s) is removed from the base sequence of a gene, usually resulting in a ‘frame shift’. 

DNA/ deoxyribonucleicacid

Genetic material in the form of a double-stranded molecule containing the genetic code. Contains a deoxyribose sugar and phosphate backbone, and bases A,T,G,C

Enzyme

A globular protein that acts as a biological catalyst to speed up the rate of a chemical reaction in an organism

Frameshift

Due to an insertion or deletion mutation, the sequence of the bases is shifted after the mutation point to new triplet combinations, resulting in a different amino acid sequence

Gene

A section of DNA that codes for a protein

Gene expression

The process whereby the genetic code on DNA is converted into a functional protein. Includes transcription, translation and protein folding. 

Genotype

the combination of alleles carried by an organism 

insertion mutation

A mutation on the DNA where a base(s) is added into the base sequence of a gene, usually resulting in a “frame shift”.

Metabolic pathway

A series of enzyme-controlled reactions, where the intermediate product of one reaction becomes the substrate of the next. 

Misense Mutation

A change of a base in DNA that results in coding for a different amino acid in the protein. This may (or may not) alter the shape of the protien and therefore it’s function. 

mRNA/ messenger RNA

a single stranded nucleic acid that carries the genetic code via codons from the nucleus to the ribosome to make a polypeptide chain

Mutagen 

an environmental factor that causes a mutation

mutation

a permeant change in the base sequence of DNA

non-sense mutation

A change of the baes on DNA which puts a stop codon in the wrong place. the resulting protein in non-functional 

nucleotide

building block of nucleic acids, made of deoxyribose sugar, phosphate, and nitrogenous base

peptide bond

a bond formed by the ribosome between two amino acids during translation to form a peptide

phenotype

How a gene is expressed as a protein/characteristic/trait

point mutation

a change of only one or a few bases in a DNA sequence

protein

A molecule made up of many amino acids that has a specific shape and function with a cell or organism

protein synthesis

the process whereby the genetic code on DNA is converted into a functional protein. Includes transcription, translation and protein folding

redundancy of the code

where several codons can code for the same amino acid. E.G, CCU, CCC, CCA  and CCG code for proline. 

RNA/ ribonucleic acid

single stranded nucleic acid, with the bases U,A,G,C and the sugar is ribose. Three types: tRNA, mRNA, rRNA.

Sex Linkage

Genes on the sex chromosomes that are expressed differently in the different sexes. 

Silent mutation (same-sense mutation) 

A change of a base in DNA, where the triplet still codes for the same amino acid. This is due to the redundancy of the genetic code

Start codon

the first AUG codon on mRNA signals the starting point for translation by the ribosome 

Stop codon

three codons on mRNA (UAA, UAG, UGA) that do not code for an amino acid and therefore signal the ribosome to stop translation 

Substitution mutation

a mutation where the base(s) on the DNA are swapped for another. For example, ATC - AAC

Template strand

the strand of DNA that is used during the synthesis of mRNA

transcription

the process where a strand of mRNA is synthesised using the bases of DNA as a template.

translation

the process whereby a ribosome ‘read’ the mRNA codon sequence and matches it with the correct tRNA anti-codons using the base pairing rule, ensuing that the amino acids carried by each tRNA are added in the correct order to form a polypeptide

Triplet

three consecutive bases on DNA that code for an amino acid

tRNA/ transfer RNA

carries an amino acid to the ribosome during translation