DNA & protein synthesis

Question 1

What is genome & proteome?

Answer 1

• genome - the complete set of genes in a cell
• proteome -the full range of proteins that a cell can produce

Question 2

What are the 2 stages of protein synthesis?

Answer 2

• transcription - production of mRNA from DNA in the nucleus
• translation - production of polypeptides from the sequence of codons carried by mRNA at ribosomes

Question 3

What are the similarities & differences between the structure of tRNA & mRNA?

Answer 3

Similarities:
- both single polynucleotide strand
Differences:
- tRNA is folded into a ‘clover leaf shape’ whereas mRNA is linear
- tRNA has H bonds between base pairs, mRNA doesn’t
- tRNA is a shorter fixed length whereas mRNA is a longer variable length
- tRNA has an anticodon, mRNA has codons
- tRNA has an amino acid binding site, mRNA doesn’t

Question 4

How is mRNA formed by transcription in eukaryotic cells?

Answer 4

1. H bonds between DNA base pairs break
2. only 1 DNA strand acts a template
3. free RNA nucleotides align with their complementary bases on the template strand - in RNA uracil replaces thymine
4. RNA polymerase joins adjacent nucleotides
5. forms phosphodiester bonds by a condensation reaction
6. pre-mRNA is formed & needs to be spliced to remove introns to form mature mRNA

Question 5

How is production of mRNA in a eukaryotic cell different from the production of mRNA in a prokaryotic cell?

Answer 5

• pre-mRNA is produced in eukaryotes whereas mRNA is produced directly in prokaryotes
• this is because genes in prokaryotes don’t contain introns so there is no splicing in prokaryotes

Question 6

How does translation lead to the production of a polypeptide?

Answer 6

1. mRNA attached to ribosome which moves to a start codon
2. tRNA brings a specific amino acid
3. tRNA anticodon binds to complementary mRNA codon
4. ribosome moves along to the next codon & another tRNA binds so 2 amino acids are joined by a condensation reaction forming a peptide bond using energy from the hydrolysis of ATP
5. tRNA is released after amino acid joined polypeptide
6. ribosome moves along mRNA to form polypeptide until it reaches a stop codon

Question 7

What is the role of ATP in translation?

Answer 7

• hydrolysis of ATP into ADP + Pi releases energy
• amino acids join to tRNAs & peptide bonds form between amino acids

Question 8

What is the role of tRNA in translation?

Answer 8

• attached to 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

Question 9

What is the role of ribosomes in translation?

Answer 9

• mRNA binds to ribosome with space for 2 codons
• allows tRNA with anticodons to bind
• catalyses formation of peptide bond between amino acids
• moves along mRNA to next codon

Question 10

How is the base sequence of nucleic acids related to the amino acid sequence of polypeptides when provided with suitable data?

Answer 10

• genetic code if provided for where triplet/ codons produce specific amino acids
• tRNA anticodons are complementary to mRNA codons
• sequence of codons on mRNA are complementary to sequence of triplets on DNA template strand
• in RNA uracil replaces thymine