Topic 1

Question 1

What experiment did Griffith do in 1928?

Answer 1

First experiment suggesting that bacteria are capable of transferring genetic information through a process known as transformation.

Question 2

What experiment did Avery do in 1944?

Answer 2

Found out that it is DNA that is the transforming agent

Question 3

What experiment did Hershey and Chase do in 1952?

Answer 3

Radioactively labelled isotopes (phosphate and sulphur to show that it is DNA and not protein that contains genetic material.

Question 4

How many bonds do a) AT b) CG form

Answer 4

AT form Two ; CG form 3

Question 5

In what direction does DNA run?

Answer 5

DNA template is read in 3’ to 5’ direction BUT a new strand is synthesized in the 5’ to 3’ direction.

Question 6

Meselson and Stahl experiment

Answer 6

Worked out DNA replication is semi-conservative.

Question 7

Role of DNA primase

Answer 7

DNA primase: lays down a short strand of RNA to act as a primer for DNA synthesis (DNA primase is an RNA polymerase) . So Ozakaki fragments can form

Question 8

Role of DNA polymerase I

Answer 8

DNA polymerase I: This enzyme synthesizes new DNA strands on the lagging strand and during DNA repair

Question 9

Role of DNA polymerase III

Answer 9

DNA polymerase III: This enzyme synthesizes new DNA strands on the leading strand

Question 10

Role of single stranded binding proteins

Answer 10

Single stranded binding proteins: These proteins bind to single stranded DNA at the replication fork to stabilize the single strands (ie stop them reannealing)

Question 11

Role of DNA helicase

Answer 11

DNA helicase: This enzyme unzips the two strands of DNA at the replication fork.

Question 12

What are Okazaki fragments

Answer 12

The short fragments of DNA synthesized on the lagging strand of DNA as the replication fork progresses.
They contain an RNA primer. The primer is subsequently removed by DNA polymerase I (or eukaryotic equivalent) and fragments joined by DNA ligase.

Question 13

How does the DNA polymerase reduce the frequency of errors from 1 in 105 to 1 in 107?

Answer 13

The polymerase has a 3′ to 5′ proofreading activity that checks if the correct base has been inserted before the next base is inserted. If an error has been made, the base is excised and replaced. The accuracy of this proof reading is 1 error in 100 base insertions.

Question 14

Role of DNA ligase during DNA repair

Answer 14

Joins fragments of DNA together (eg Okazaki fragments on the lagging strand, or newly synthesized DNA strands during repair of DNA).

Question 15

Function of uracil N-glycosylase. How’s this help reduce mutation in DNA

Answer 15

Uracil-N-glycosylase cuts (excises) uracil from DNA.
Uracil can arise in DNA by the deamination of cytosine. If the uracil is not removed it will base pair with adenine during replication, resulting in a C to T mutation (also called GC to AT if giving the base on both strands of the DNA).

Question 16

How many base pairs of DNA

Answer 16

About 3 billion base pairs in the whole sequence (or 6 billion altogether).

Question 17

In Sanger DNA sequencing how is the growing chain of DNA terminated?

Answer 17

When a dideoxynucleotide (ddNTP) is inserted; as it has no free 3′-OH group, the polymerase cannot continue adding bases.

Question 18

What is needed in each reaction mix for Sanger sequencing?

Answer 18

The polymerase enzyme, a gene specific primer, all four dNTPs, one specific ddNTP

Question 19

Define polymorphism

Answer 19

A sequence variation that occurs in at least 1% of the population.

Question 20

SNP

Answer 20

Single nucleotide polymorphism

Question 21

Define: DNA microarray

Answer 21

An array of thousands of different DNA sequences laid out in a grid on a microchip (glass slide)

Question 22

Give 2examples of what microarrays could be used to investigate.

Answer 22

Occurrence of different SNPs in an individual

Differences in gene expression between eg different samples, tumour vs normal tissue, etc.

Question 23

Is the mRNA a replica of the sense or anti-sense strand of DNA?

Answer 23

The sense strand (ie carries the message). Makes sense…

Question 24

Which enzyme carries out transcription?

Answer 24

RNA polymerase (forms mRNA)

Question 25

3 mRNA modifications

Answer 25

5′- cap, polyA tail, splicing out introns.

Question 26

Define intron and exon

Answer 26

Introns: non-coding sequences in DNA (e.g. remain in the DNA)
Exon: coding parts of the gene that are transcribed into protein

Question 27

Which a.a. is always 1st

Answer 27

Methionine (AUG) (STOP codons are UAG, UGA, UAA)

Question 28

Which end of tRNA molecule is a.a attached

Answer 28

3’ end (just as the free OH- group is on the 3’ end of DNA)

Question 29

Role of A, P and E sites on ribosome

Answer 29

A: newly arrived tRNA docks in the A site
P: growing polypeptide is attached to the tRNA in P-site
E: after next polymerisation reaction, uncharged tRNA moves to E site and exits

Question 30

3 antibiotics that target prokaryotic ribosomes

Answer 30

tetracycline, streptomycin and chloramphenicol

Question 31

What are monoamine oxidase inhibitors treat?

Answer 31

Depression

Question 32

Experiment where AT go together

Answer 32

Erwin Chargaff (1952)

Question 33

Barr body

Answer 33

the inactive X chromosome in a female somatic cell, rendered inactive by a process called lyonization

Question 34

What are pseudogenes

Answer 34

non-functional genes

Question 35

What is a TATA box?

Answer 35

run of T and A bases. Region of the promoter where transcription factors bind to initiate transcription by binding the RNA polymerase to the region of the gene where transcription begins.

Question 36

Transcripts are…

Answer 36

capped, spliced, polyadenylated and then exit the nucelus.

Question 37

What is polyadenylation

Answer 37

Polyadenylation is the addition of a poly(A) tail to a messenger RNA. The poly(A) tail consists of multiple adenosine monophosphates; in other words, it is a stretch of RNA that has only adenine bases. In eukaryotes, polyadenylation is part of the process that produces mature messenger RNA (mRNA) for translation.