4.2: Transcription and Translation

Name the type of bonds between…

a) Complimentary base pairs

b) Adjacent nucleotides

[2 marks]

a) Hydrogen bonds

b) Phosphodiester bonds

Describe two differences between the structure of a tRNA molecule and the structure of an mRNA molecule [2 marks]

1. tRNA has a “clover leaf” shape”, mRNA is linear

2. tRNA has hydrogen bonds, mRNA does not

3. tRNA has an amino acid binding site, mRNA does not

4. tRNA has an anticodon, mRNA has codons

In a eukaryotic cell, the structure of the mRNA used in translation is different from the structure of the pre-mRNA produced by transcription.

Descrive and explain a difference in the structure of these mRNA molecules [2 marks]

1. mRNA has fewer nucleotides OR pre-mRNA has more nucleotides OR mRNA has no introns/only has exons OR pre-mRNA has exons and introns

2. because of splicing

Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation [3 marks]

1. tRNA brings specific amino acid to the ribosome

2. Anticodon on tRNA binds to codon on mRNA

3. Amino acids join by condensation reaction (using ATP) OR Amino acids join to form a peptide bond (using ATP)

Describe how mRNA is produced from an exposed template strand of DNA [3 marks]

Do not include DNA helicase or splicing in your answer

1. Free RNA nucleotides form complimentary base pairs

2. Phosphodiester bonds form

3. By action of RNA polymerase

Describe how mRNA is formed by transcription in eukaryotes [5 marks]

1. Hydrogen bonds between DNA bases break

2. Only one DNA strand acts as a template

3. Free RNA nucleotides align by complimentary base pairing

4. In RNA Uracil pairs with adenine on DNA OR in RNA, uracil is used in place of thymine

5. RNA polymerase joins adjacent RNA nucleotides

6. By phosphodiester bonds between adjacent nucleotides

7. Pre mRNA is spliced to form mRNA OR introns are removed (to form mRNA)

Describe how a polypeptide is formed by translation of mRNA [6 marks]

1. mRNA attached to ribosomes OR mRNA attaches to rough endoplasmic reticulum

2. tRNA anticodons bind to complementary mRNA codons

3. tRNA brings a specific amino acid

4. Amino acids join by peotide bonds

5. Amino acids join together qith ther use of ATP

6. tRNA released after amino acid joined to polypepide

7. The ribosone moves along the mRNA to form the polypeptide

What is the proteome of a cell? [1 mark]

The proteome is the full range of/number of different proteins that a cell is able to produce at a given time

OR

The proteome is the full range of/number of diffferent proteins in the genome/DNA is able to code for

Give the two types of molecule from which a ribosome is made [1 mark]

One of…

RNA/ribonucleic acid(s)/nucleotide(s)/nucleic acid(s)/rRNA/ribosomal RNA/ribosomal ribonucleic acid

And one of…

Protein(s)/polypeptide(s)/amino acid(s)/peptide(s)/ribosomal protein

Describe the role of a ribosome in the production of a polypeptide. Do not include transcription in your answer [3 marks]

1. mRNA binds to ribosome

2. Allows tRNA with anticodons to bind/associate

3. Catalyses formation of peptide ond between amino acids (held by tRNA molecules)

4. Moves along (mRNA to the next codon)

In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of the pre-mRNA. Explain why. [2 marks]

1. Introns in pre-mRNA

2. Removal of sections of pre-mRNA/splicing

(“introns removed” scores two marks)