Protein synthesis

Stage 1 of translation

RNA polymerase binds to the promoter at the start of the gene, helped by transcription factors.

Sage 2 of translation

A helicase unzips the 2 DNA strands by breaking the hydrogen bonds between the bases.

Stage 3 of translation

Activated RNA nucleotides bind via hydrogen bonds to the exposed bases on the template stands forming complementary base pairs.

Stage 4 of translation

RNA polymerase catalyses the condensation reaction that joins the incoming RNA nucleotide to the growing RNA chain, forming a phosphodiester bond.

Stage 5 of translation

Two phosphates are released as pyrophosphate and hydrolysed to provide energy for the reaction.

Step 6 of translation

RNA polymerase stops transcription when it reaches a termination signal.

Step 7 of translation

mRNA is released from the template strand and leaves the nucleus through a nuclear pore.

Advantages of copying DNA into RNA

mRNA is a small molecule that can leave the nucleus via a nuclear pore.

Many copies of mRNA can be made and then translated to synthesise many polypeptides.

There are more steps that allows for more regulation.

What are the 3 stages of translation

Initiation, elongation and termination

Initiation

Initiator tRNA carrying methionine binds to AUG start codon and ribosome assembles.

Elongation

The next tRNA, carrying a specific activated amino acid, binds via its anticodon to the next exposed mRNA codon, forming hydrogen bonds between complementary bases. Ribosome catalyses the condensation reaction that joins adjacent amino acids by a peptide bond. Ribosome moves one codon along mRNA and empty tRNA is ejected.

Termination

Translation continues until a stop codon is reached. Since there is no corresponding tRNA, a protein release factor binds instead. The polypeptide is released and the ribosome dissociates.

How is ATP needed during protein synthesis

To attach a specific amino acid to its corresponding tRNA with the aid of an enzyme. When the bond between the tRNA and amino acid is broken, this provides the energy for peptide bond formation.

Role of mRNA

Single stranded RNA copy of a gene synthesised in the nucleus. Leaves nucleus through a nuclear pore and assembles with a ribosome in the cytoplasm. Sequence of bases determines the sequence of amino acids in the polypeptide.

Role of tRNA

Small, L-shaped molecule that functions as an adaptor to bring activated amino acids to the ribosome and align them in the correct order along the mRNA.

Role of rRNA

Transcribed in the nucleolus and assembles with proteins to form a ribosome. Catalyses peptide bond formation.

Chaperone proteins

Help the polypeptide to correctly fold into its final specific 3D shape (tertiary structure).

methionine amino peptidase

Enzyme that removes the initial methionine from polypeptide

where do later modifications to the polypeptide chain take place.

Golgi body