B8 - DNA, genes and protein synthesis

Question 1

Describe how mRNA is formed by transcription in eukaryotes.

Answer 1

1. Hydrogen bonds break
2. One DNA strand acts as a template
3. Free RNA nucleotides align to complementary base pairing
4. Uracil (RNA nucleotide) base pairs align with adenine (DNA nucleotide)
5. RNA polymerase joins adjacent nucleotides
6. Pre-mRNA is spliced (introns are removed) to form mRNA

Question 2

Describe how a polypeptide is formed by translation of mRNA.

Answer 2

1. mRNA attaches to ribosomes
2. tRNA anticodons bind to complementary mRNA codons
3. tRNA brings a specific amino acid
4. Amino acids joined by peptide bonds
5. with the use of ATP
6. tRNA released (after amino acid is joined to polypeptide
7. Ribosome moves along the mRNA to form a polypeptide

Question 3

Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide. Do not include descriptions of transcription and splicing in your answer.

Answer 3

1. mRNA associates with a ribosome
2. Ribosome moves to start codon
3. tRNA brings specific amino acid
4. Anticodon on tRNA is complementary to mRNA codon
5. Ribosome moves along mRNA molecule to next codon OR Ribosome fits to two tRNA molecules
6. (Process is repeated and) amino acid are joined by peptide bonds/ condensation reactions (to form a polypeptide) OR (process is repeated and) amino acids joined using ATP (to form polypeptide)

Question 4

Describe how mRNA is produced in a plant cell.

Answer 4

1. The DNA strands separate by breaking the hydrogen bonds OR hydrogen bonds broken between complementary DNA bases
2. Only one strand/ template strand is used to make mRNA/ transcribe)
3. Complementary base pairings AU, TA, CG, GC
4. RNA nucleotides joined by RNA polymerase
5. Pre-mRNA formed
6. Splicing/ introns removed to form mRNA