DNA and protein synthesis

Question 1

Genome

Answer 1

The complete set of genes in a cell

Question 2

Proteome

Answer 2

The full range of proteins that a cell can produce

Question 3

Transcription

Answer 3

Production of messenger RNA (mRNA) from DNA, in the nucleus

Question 4

Translation

Answer 4

Production of polypeptides from the sequence of codons carried by mRNA, at ribosomes

Question 5

Compare and contrast the structure of tRNA and mRNA

Answer 5

Comparison (similarities):
● Both single polynucleotide strand

Contrast (differences):
● tRNA is folded into a ‘clover leaf shape’
, whereas mRNA is linear / straight
● tRNA has hydrogen bonds between paired bases, mRNA doesn’t
● tRNA is a shorter, fixed length, whereas mRNA is a longer, variable length (more nucleotides)
● tRNA has an anticodon, mRNA has codons
● tRNA has an amino acid binding site, mRNA doesn’t

Question 6

Describe how mRNA is formed by transcription in eukaryotic cells

Answer 6

Hydrogen bonds between DNA bases break
Only one DNA strand acts as a template
Free RNA nucleotides align next to their complementary bases on the template strand
○ In RNA, uracil is paired with adenine
RNA polymerase joins adjacent RNA nucleotides
This forms phosphodiester bonds via condensation reactions
Pre-mRNA is formed and this is spliced to remove introns, forming mRNa

Question 7

Describe how production of messenger RNA (mRNA) in a eukaryotic cell is
different from the production of mRNA in a prokaryotic cell

Answer 7

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

Question 8

Describe how translation leads to the production of a polypeptide

Answer 8

mRNA attaches to a ribosome
tRNA anticodons bind to complementary mRNA codons
tRNA brings a specific amino acids
Amino acids join by peptide bonds with the use of ATP
tRNA released after amino acid joined to form, a polypeptide
The ribosome moves along the mRNA to form the polypeptide

Question 9

Describe the role of ATP, tRNA and ribosomes in translation

Answer 9

ATP:
● Hydrolysis of ATP to ADP + Pi releases energy
So amino acids join to tRNAs and peptide bonds form between amino acids

tRNA:
Attaches to / transports a specific amino acid, in relation to its anticodon
tRNA anticodon complementary base pairs to mRNA codon, forming hydrogen bonds
2 tRNAs bring amino acids together so peptide bond can form

Ribosomes:
mRNA binds to ribosome, with space for 2 codons
Allows tRNA with anticodons to bind
Catalyses formation of peptide bond between amino acids (held by tRNA molecules)
Moves along (mRNA to the next codon) / translocation