L1 - Introduction to DNA

Question 1

What is the chemical structure of a nucleotide?

Answer 1

5-carbon sugar (deoxyribose / ribose)
Phosphate
Nitrogenous base

Question 2

Which bases are purines and pyrimidines?

Answer 2

Purines = Adenine + Guanine
Pyrimidines = Thymine (Uracil in RNA) + Cytosine

Question 3

What is the difference between the two?

Answer 3

Purines have a two-ringed structure compared to pyrimidine which only has one

Question 4

Where is the phosphodiester bond found in the backbone?

Answer 4

5’ - 3’ phosphodiester linkage connects nucleotides. Between phosphate of a different nucleotide and sugar (pentose)

Question 5

Which end is a nucleotide added to DNA during replication?

Answer 5

3’ end

Question 6

Where is the attachment for the nucleotide on the 3’ strand?

Answer 6

Nucleophylic attachment by the 3’OH on alpha phosphate of incoming nucleotide

Question 7

What happens next?

Answer 7

Pyrophosphate is released which is carried out by pyrophosphatase to pull the reaction forward

Question 8

What is the difference between prokaryotic transcription and eukaryotic transcription?

Answer 8

Eukaryotic Transcription takes place inside of the Nucleus, while Prokaryotic Transcription takes place in the Cytoplasm. In Eukaryotic Transcription, proteins known as Transcriptional factors are needed, while In Prokaryotic Transcription, no such proteins are needed.

Question 9

What is the difference between prokaryotic translation and eukaryotic translation?

Answer 9

The key difference between eukaryotic and prokaryotic translation is that eukaryotic translation and transcription is an asynchronous process, whereas prokaryotic translation and transcription is a synchronous process.

Question 10

What is alternative splicing?

Answer 10

Alternative splicing is a cellular process in which exons from the same gene are joined in different combinations, leading to different, but related, mRNA transcripts.

Question 11

What is the common general cloning strategy? (3 steps)

Answer 11

1. Target DNA from donor organism extracted, cut with restriction endonuclease and ligated into cloning vectors
2. Recombinant constructs are transferred into the host cell
3. Host cells which do not take up construct are eliminated by selection protocol

Question 12

What does T4 DNA ligase do?

Answer 12

It can catalyse the joining of two blunt-ended strands of DNA.

Question 13

What are four important features of a cloning vector?

Answer 13

1. Origin of replication
2. Restriction site for insertion of target DNA
3. Selectable marker with an antibiotic resistance gene
4. Small in size so it can integrate into the host cell easily

Question 14

Role of reporter genes:

Answer 14

They can indicate transcriptional activity and their expression can be quantified (show activity levels of a promoter). Screening for successful transfections.