4.2 DNA and Protein synthesis

Question 1

Define genome and Proteome

Answer 1

Genome- The complete set of genes in a cell (including those of mitochondria and chloropasts)

Proteome- The full range of proteins that a cell can produce (coded for by the cells DNA/Genome

Question 2

Describe the two 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 ribosome

Question 3

Compare and contrast the structure of tRNA and mRNA

Answer 3

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 4

Describe how mRNA is formed by transcription in eukaryotic cells

Answer 4

1. Hydrogen bonds between DNA bases break
2. Only one DNA strand acts as a template
3. Free RNA nucleotides align next to their complementary bases on the template strand
   ○ In RNA, uracil is used in place of thymine (pairing with adenine in DNA)
4. RNA polymerase joins adjacent RNA nucleotides
5. This forms phosphodiester bonds via condensation reactions
6. Pre-mRNA is formed and this is spliced to remove introns, forming (mature) mRNA

Question 5

Describe how production of mRNA in a eukaryoti ccell is different from the production of mRNA in a prokaryotic cell

Answer 5

• Pre mrna produced in eukayotic cells whereas mRNA is produced directly in prokaryotic cells
• Because geenes in prokaryotic cells dont contain intromns so no splicng in prokaryoti cells

Question 6

Describe how translation leads to the production of a polypeptide

Answer 6

1. mRNA attaches to a ribosome and the ribosome moves to a start codon
2. tRNA brings a specific amino acid
3. tRNA anticodon binds to a complementary mRNA codon
4. Ribosomes move along to next codon and naother tRNA binds so 2 amino acids can be joined by a condensation reaction forming a peptide bond -using energy from hydrolysed atp
5. tRNA released after amino acid joined polypeptide
6. Ribosomes moves along mRNA to form the polypeptide, until a stop codon is reached

Question 7

Describe the role of ATP in translation

Answer 7

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

Question 8

Describe the role of tRNA in translation

Answer 8

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 bonds can form

Question 9

Describe 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 betweeb amino acids
Moves along (mRNA to the next codon)/Translocation

Question 10

Describe how the base sequence of nucleic acids can be related to the amino acid sequence of polypeptides when provided with suitable data

Answer 10

You may be provided with a genetic code to identify which triplets/codon produce amino acids
tRNA anticodons are complimentary to mRNA codons-e.g. mrna codon=ACG-trna anticodon= UGC
Sequence of codons on MRNA are complimentary to sequence of triplets on DNA template strand-e.g. mRNA base sequence= ACG UAG AAC –>DNA base sequence: TGC ATC TTG
In RNA uracil is replace dby thymine