DNA Replication, RNA Synthesis, Protein Synthesis

Question 1

3 DNA Repair mechanism:

Answer 1

1. Proofreading (during replication)
2. Mismatch repair (after)
3. Excision repair (after)

Question 2

Brief description of proofreading, mismatch repair & excision repair:

Answer 2

Proofreading: during replication, if a wrong base is added to the growing chain, the replication complex will excise the incorrect base which is followed by the addition of a correct base by DNA polymerase.

Mismatch repair: if there’s a mismatched base pair after replication is done, mismatch repair proteins will excise the mismatched base pair (along with some adjacent bases) and then addition of correct bases by DNA polymerase.

Excision repair: if there’s a damaged (hence non functional) base, excision repair proteins will excise the damaged base (& some adjacent bases) which is followed by addition of correct bases by DNA polymerase.

Question 3

What are the few kinds of information that genomic sequencing can provide?

Answer 3

• coding regions of genes
• regulatory sequences
• non coding sequences
• changes in sequences

Question 4

Types of RNA processing:

Answer 4

• splicing of introns

- end tail and cap processing

Question 5

Function of polymerase I, II &. III:

Answer 5

Poly. I : hydrolysed the primer (during dna replication) and replaces it with dna bases.

Poly. II : adds nucleotides to the forming dna strand during dna replication

Poly. III : adds nucleotides to Okazaki fragments during dna replication

Question 6

3 steps in dna transcription:

Answer 6

1. Initiation
2. Elongation
3. Termination

Question 7

3 post-transcriptional control:

Answer 7

1. Alternative splicing of exons
2. Breakdown by enzymes
3. MicroRNAs

Question 8

Translational & post-translational control:

Answer 8

Translational: binding of repressor proteins to the mRNA to inhibit translation

Post-translational: proteasome degrades protein targeted for breakdown

Question 9

Wobble base:

Answer 9

• first base at 5’ of anticodon (which pairs with first 3’ base on codon)
• allows non Watson-Crick base pairing with 3rd base in mRNA codon
• allows redundancy in genetic code (several codons coding for one amino acid)
• wobble base is the reason why there is not 61 tRNA

Question 10

Post-translational events:

Answer 10

• protein may be retained in ER or sent to lysosomes or plasma membrane (sent to other organelles within the cell)
• proteins with no signals are passed from ER to Golgi apparatus and then secreted out of the cell
• COVALENT MODIFICATIONS

Question 11

3 types of covalent modification:

Answer 11

1. Proteolysis: cleavage of protein
2. Glycosylation: addition of sugars
3. Phosphorylation: addition of phosphate group