B3 Revision:Protein Synthesis

DNA controls production of proteins in a cell

Proteins made of a chain of amino acids which fold up to give each protein a specific shape and function

Gene

A section of DNA that codes for a specific protein

Order of the bases in a gene decides the order of amino acids in a protein

Amino acids coded for by a sequence of 3 bases in a gene:Base triplet

Non-coding regions of DNA

Don't code for any amino acids

Some can switch genes on and off so controls if a gene is expressed

Mutations:

Random changes to an organism's DNA which can be inherited

Produces a genetic variant (different version of a gene)

May change amino acid which may change the shape of the final protein

Causes a change in activity which could change characteristics of an organism

Process:

Transcription

Translation:

DNA can't move out of the nucleus as it's really big

RNA polymerase joined RNA nucleotides to make mRNA

RNA polymerase binds to a region of non-coding DNA in front of a gene causing the DNA to unzip

RNA polymerase moves along one of the strands of DNA

Uses coding DNA in the gene as a template to make mRNA so that mRNA complements the gene

mRNA moves out of nucleus and joins with a ribosome in the cytoplasm

After transcription

Amino acids brought to ribosome by tRNA (transfer)

Order in which they are brought matches the order of base triplets in mRNA

The pairing of the codon and anticodon makes sure the amino acids are brought to the ribosome in the correct order

Amino acids are joined together by the ribosome making polypeptide (protein) and empty tRNA move away

Codon (mRNA)

Anticodon (tRNA structure)

Base triplets in mRNA

Complimentary to codon for amino acid

Variants in non-coding regions of DNA can also affect phenotype of an organism

Variants in non-coding parts of DNA affect the ability of RNA polymerase to bind to it, making it easier or harder

Affects how much mRNA is transcribed so how much protein is produced which could affect the phenotype