4.2 Protein Synthesis

Question 1

What is a genome.

Answer 1

The complete set of genes present in a cell.

Question 2

What is a proteome.

Answer 2

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

Question 3

Structure of mRNA.

Answer 3

• mRNA is a single-stranded molecule
• made up of a sugar-phosphate backbone and exposed unpaired bases
• uracil bases are present instead of thymine bases
• small linear strand

Question 4

Structure of tRNA.

Answer 4

• tRNA is a single-stranded molecule
• has a sugar-phosphate backbone
• has a folded shape (there are hydrogen bonds between some of the complementary bases)
• amino acids bind to a specific region of the molecule
• the specific anticodon found on the tRNA molecule is complementary to a specific codon on an mRNA molecule

Question 5

Compare the structure of mRNA and tRNA.

Answer 5

1. tRNA has hydrogen bonds whereas mRNA does not.
2. tRNA is folded (has a clover leaf shape) whereas mRNA is linear.
3. tRNA has an anticodon whereas mRNA has a codon.
4. tRNA has an amino acid binding site whereas mRNA does not.

Question 6

Where is mRNA found?

Answer 6

Synthesised in the nucleus and then moves to the cytoplasm where it sits between the two subunits of ribosomes.

Question 7

Where is tRNA found?

Answer 7

The cytoplasm

Question 8

Describe the process of transcription.

Answer 8

1. DNA helicase unzips DNA, breaking the H-bonds between the bases.
2. One strand of DNA acts as a template.
3. RNA nucleotides align by complementary base pairing.
4. In RNA uracil base pairs with adenine on DNA.
5. RNA polymerase joins adjacent RNA nucleotides by phosphodiester bonds.
6. At a stop codon the RNA detaches.

Prokaryotes: forms mRNA
Eukaryotes: forms pre-mRNA

Question 9

What happens in eukaryotes after transcription?

Answer 9

Splicing → removal of introns from pre-mRNA to form mRNA that leaves via the nuclear pores and released into the cytoplasm.

Question 10

Describe the process of translation.

Answer 10

1. The mRNA is attached to ribosome.
2. Anticodons bind to the complementary codon on the mRNA.
3. The tRNA brings the specific amino acid that the mRNA codon codes for.
4. Amino acids join by peptide bonds.
5. The formation of the peptide bond requires the use of ATP and an enzyme.
6. The tRNA is released after amino acid is joined to the polypeptide.
7. The ribosome moves along the mRNA to form the polypeptide.

Question 11

Give the two types of molecule from which a ribosome is made.

Answer 11

1. ribosomal RNA (rRNA)
2. ribosomal protein