4.2 DNA and protein synthesis

What is the genome?

The complete set of genes in a cell

What is the proteome?

The full range of proteins that a cell can produce

Describe the two stages of protein synthesis

Transcription - Production of mRN from DNA in the nucleus

Translation - Production of a polypeptide from the sequence of codons carried by mRNA at ribosomes

Describe the structure of mRNA

Linear

No hydrogen bonds between paired bases

Codons

No amino acid binding site

Describe the structure of tRNA

Clover leaf shape

Hydrogen bonds between paired bases

Anticodons

Amino acid binding site

Describe how mRNA is formed by transcription in eukaryotic cells

Hydrogen bonds between DNA bases break

One DNA strand acts as a template

Free RNA nucleotides align next to complimentary bases on template strand

RNA polymerase joins adjacent RNA nucleotides forming. phosphodiester bonds via condensation reactions

Pre-mRNA is formed and is spliced to remove introns forming mature mRNA

How is the production of mRNA in eukaryotic cells different to the production of mRNA in prokaryotic cells?

Pre-mRNA is produced in eukaryotic cells whereas mRNA is produced directly in prokaryotic cells because genes in prokaryotic cells don’t contain introns so no splicing occurs

Describe how translation leads to the production of a polypeptide

mRNA attaches to a ribosome

tRNA brings a specific amino acid

tRNA anticodon binds to complimentary mRNA codon

Ribosome moves along to next codon and another tRNA binds so two amino acids can be joined by a condensation reaction forming a peptide bond using energy from the hydrolysis of ATP

tRNA released after amino acids joined polypeptide

Ribosome moves along mRNA to form the polypeptide, until a stop codon is reached

Describe the role of ATP in translation

Hydrolysis of ATP to ADP + Pi releases energy used in condensation reaction to form a peptide bond between amino acids

Describe the role of tRNA in translation

Attaches to a specific amino acid

tRNA anticodon binds to mRNA codon, forming hydrogen bonds

Two tRNAs bring amino acids together so a peptide bond can form

Describe the role of mRNA in translation

mRNA binds to a ribosome

Allows tRNA with anticodons to bind

Catalyses formation of peptide bond between amino acids

Moves along to next codon