Gene Transcription and Translation

Question 1

Define transcription and translation

Answer 1

Transcription - the process during which a sequence of DNA is used to produce messenger RNA sequences

Translation - the process by which mRNA determines the final amino acid sequence via transfer RNA within a ribosome.

Question 2

What enzyme ‘uncoils’ DNA. Describe the type of bonds pulled apart and the process

Answer 2

DNA strands are ‘unzipped’ by RNA polymerase and Hydrogen bonds between nucleoside pairs are pulled apart.

Question 3

Which strand provides the template for mRNA

Answer 3

The anti-sense strand (not the sense strand).

Question 4

Which nucleoside is replaced in RNA (versus DNA)

Answer 4

Uracil replaces Thymine which both bind to Adenine

Question 5

What is the function of transfer RNA

Answer 5

To bring the peptides to the Ribosome-mRNA complex.

Question 6

What initiates translation?

Answer 6

Formation of an initiation complex including

1. Smaller ribosomal subunit
2. First amino-acid tRNA
3. mRNA

The larger ribosomal subunit then binds to this complex

Question 7

Name and describe the function of the tRNA sites on the 70S ribosome

Answer 7

P-site –> Peptidyl site

A-site –> Acceptor site

Question 8

Describe the process of translation and how this process is terminated

Answer 8

The peptide chain is transferred from the A site to the P site and continues to grow until a stop codon (which does not code for any amino acid) is reached.

Question 9

Define a codon? and an anti-codon?

Answer 9

A sequence of 3 nucleotide bases which then codes for a specific amino acid on the resulting protein.

An anti-codon is the corresponding sequence of bases on tRNA which are complementary to the codon sequence of mRNA bases.

Question 10

What is a start codon

Answer 10

The start codon is A - U - G and codes for methionine. If it is the first AUG of an mRNA coding area, it acts as the start codon.

Question 11

In which direction is the mRNA read during translation

Answer 11

5’ to 3’ end

Question 12

What is a stop codon

Answer 12

The codon sequence that signals the end of translation: UAA, UAG, UGA.

Question 13

What type of bond is there between tRNA and its associated amino acid

Answer 13

Covalent bond

Question 14

How does tRNA get loaded with its amino acid

Answer 14

Aminoacyl tRNA synthetases

Question 15

Differentiate primary, secondary, tertiary and quaternary structure of proteins

Answer 15

1. Primary - product of translation –> polypeptide chains
2. Secondary - H-bonds –> alpha helices and beta pleated sheets
3. Tertiary - Folded 3D structure various bonding arrangements
4. Quaternary - More than one protein/polypeptide chain joined together e.g. haemoglobin

Question 16

Describe the point mutation that occurs in sickle cell disease

Answer 16

Chromosome 11
Adenine becomes Thymine at position 6 aa chain
codon GAG becomes codon GTG
This means that Glutamic acid becomes Valine

Question 17

Give two examples of hormones that alter gene expression and state where these receptors are found

Answer 17

Oestrogen - cytosol receptor - this complex moves into nucleus attaches to a specific region of DNA to affect gene expression (activation or repression).

Thyroid hormone - nuclear receptor –> affects gene expression.

These are essentially ‘transcription factors’.