Unit 1- Gene Expression And Protein Synthesis

Question 1

What are the three types of RNA ?

Answer 1

tRNA. mRNA. Ribosomal RNA

Question 2

What is the function of tRNA?

Answer 2

Carries its specific amino acid from the cytoplasm to the ribosome.

Question 3

What is the function of mRNA?

Answer 3

Carries a copy of DNA code from the nucleus to the ribosome.

Question 4

What is the function of Ribosomal RNA?

Answer 4

Along with protein it forms the ribosome.

Question 5

Describe the structure of RNA

Answer 5

Phosphate, Ribose sugar, Base. Uracil instead of thymine (binds with adenine). One strand.

Question 6

What stages are in protein synthesis? What comes first?

Answer 6

Transcription, splicing, translation. Trancription is first (C -> L).

Question 7

Describe the process of transcription.

Answer 7

1. RNA polymerase moves along DNA unwinding the double helix and breaking the hydrogen bonds between the bases.
2. RNA polymerase synthesises a primary transcript of mRNA from RNA by complementary base pairing.
3. Uracil is complementary to adenine.

Question 8

Describe splicing.

Answer 8

The mRNA strand produced during transcription is called a primary transcript. It contains coding regions called exons and non-coding regions called introns. The introns are removed by splicing and the exons join to form a mature transcript.

Question 9

Describe the structure of tRNA.

Answer 9

tRNA folds due to hydrogen bonds between it’s complementary bases. The folding produces the anticodon and a specific amino acid binding site. The amino acid binding site is specific to one type of amino acid. The anticodon is complementary to to one codon ensuring the amino acids are added in the right sequence.

Question 10

Describe translation.

Answer 10

1. mRNA attaches to the ribosome.
2. Start codon indicates where the first amino acid should be placed.
3. Each tRNA molecule carries a specific amino acid to the ribosome.
4. Anticodons on each tRNA align with their codons on the mRNA by complementary base pairing.
5. Amino acids join by peptide bond.
6. Each tRNA then leaves the ribosome as the polypeptide is formed.
7. Translating genetic code into a sequence of amino acids.
8. Stop codon is reached preventing further addition of amino acids.

Question 11

Describe alternative RNA splicing.

Answer 11

Different proteins can be expressed from only one gene as a result of alternative RNA splicing. Different mature RNA transcripts are produced from the same primary transcript depending on which exons are retained and joined together.