4.2- Protein Synthesis

Question 1

What is a ‘genome

Answer 1

1. The complete set of genes in a cell

Question 2

What is a ‘proteome’

Answer 2

1. The full range of different proteins that a cell is able to produce

Question 3

1. What is tRNA?

Answer 3

A folded strand of RNA which is held in a clover shape due to H-bonds. Each tRNA carries a specific amino acid.

Question 4

1. What is mRNA?

Answer 4

A linear strand of RNA which is transcribed from a DNA template and has no H-bonds. Its length depends on the length of the gene. (NOTE: in eukaryotes, pre-mRNA is transcribed from DNA)

Question 5

mRNA

Answer 5

mRNA
Linear
No hydrogen bonds
Doesn’t have a binding site for an amino acid
Length can vary
Has codons

Question 6

tRNA

Answer 6

Folded and clover shaped
Has hydrogen bonds
Has a binding site for a specific amino acid
Always the same length
Has an anticodon

Question 7

DNA triplet

Answer 7

three bases on DNA which code for an amino acid

Question 8

Codon = t

Answer 8

three bases on mRNA which code for an amino acid

Question 9

Anticodon

Answer 9

three bases on tRNA which are complementary to a codon. Each tRNA carries a specific amino acid

Question 10

1. What is transcription?

Answer 10

In eukaryotes: The formation of pre-mRNA using DNA as a template
In prokaryotes: The formation of mRNA using DNA as a template

Question 11

1. Describe how mRNA is formed:

Answer 11

1. DNA Helicase breaks hydrogen bonds between DNA strands so that they separate (using energy from ATP)
2. Only one DNA strand acts as template;
3. RNA nucleotides attracted to exposed bases;
4. (Attraction) according to base pairing rule;
5. (Complementary) base pairing so A→U, T→A, C→G, G→C;
6. RNA polymerase joins (RNA) nucleotides together;
7. Pre-mRNA spliced to remove introns;

Question 12

1. What is splicing?

Answer 12

The removal of introns from the pre-mRNA to form mRNA

Question 13

1. How and why is transcription in prokaryotes different to eukaryotes?

Answer 13

In eukaryotes pre-mRNA is formed and then splicing occurs to remove introns and form mRNA
In prokaryotes mRNA is formed and it doesn’t contain any introns so there is no splicing

Question 14

What is translation?

Answer 14

The production of polypeptides at ribosomes, using information in the sequence of codons carried by mRNA

Question 15

Describe how a protein is formed from the mRNA template

Answer 15

1. mRNA leaves (nucleus) through nuclear pore
2. mRNA associates with a ribosome;

3. Ribosomes moves to find the start codon/AUG
4. tRNA brings a specific amino acid;
5. The anticodon on tRNA is complementary to the codon on mRNA
6. Ribosome moves along to the next codon on mRNA (it can fit two tRNAs)
7. Another tRNA binds to the 2nd binding site in the ribosome (bringing another specific amino acid)
8. The process continues and a peptide bond forms between the amino acids in a condensation reaction (using energy from ATP) to form a polypeptide chain
9. the tRNA detaches and collects another amino acid and the process continues
10. The sequence of codons determines the order of amino acids in the polypeptide