molecular biology

Question 1

name the pyramidines and purines

Answer 1

pyramidines: cytosine, thymine (uracil in RNA)
purines: adenine, guanine.

Question 2

G&C or A&T rich DNA is more stable and why

Answer 2

G&C rich DNA, 3 H-bonds over 2 H-bonds btwn. A&T

Question 3

Name the differences between eukaryotic and prokaryotic DNA

Answer 3

Prokaryotes: single circular DNA; double helix looped into a circle
Eukaryotes: several linear chromosomes

Question 4

How to prokaryotes protect their DNA

Answer 4

Through DNA methylation or by packaging DNA in smaller units by supercoiling the DNA using DNA gyrase

Question 5

How does DNA coil in eukaryotes?

Answer 5

-DNA gets wrapped around 8 histones to make nucleosides
-nucleosides coil upon themselves to form chromatin

Question 6

What is a centromere and a telomere

Answer 6

centromere: region where chromatids attach
Telomere: ends of the chromosome; made of both single and double stranded DNA; consisting of short nucleotide repeats

Question 7

How to telomeres stabilize the ends of chromosomes

Answer 7

Telomeres cap the end of chromosomes stabilizing

Question 8

What is the central dogma

Answer 8

DNA —> RNA —> Proteins

Question 9

Name the start and stop codons

Answer 9

Start: AUG
Stop: UAA, UGA, UAG, UGG
(You are annoying, you go away, you are gone)
** remember that the first three do not code for a specific amino acid**
UGG codes for tryptophan

Question 10

What are point mutations and what protein makes the mistake that causes these?

Answer 10

Point mutations are single base pair changes caused by polymerase errors

Question 11

Name and define the three different point mutations

Answer 11

1) missense: codon for an amino acid becomes a different codon that specifies for a different amino acid
2) nonsense: codon for an amino acid becomes a STOP codon which creates a shortened protein
3) silent mutations: codon for an amino acid becomes a new codon for the same amino acid

Question 12

What are frameshift mutations and what are they caused by?

Answer 12

Frameshift mutations involve insertions or deletions of amino acids because of polymerase errors; this changes the reading frame

Question 13

What do transposons consist of?

Answer 13

Consists of Transposase ( cut & paste enzyme)

Question 14

What is the first type of Transposon? How does it work?

Answer 14

1. Invented sequence (IS) element

How it works: Code for “cut & paste” transposase enzyme

*Contributes to genomic variation

Question 15

What is the second type of Transposon? How does it work?

Answer 15

2. Complex Transposon: has genes included within IS

How it works: transposase cuts transposon out

*Contributes to genomic variation

Question 16

What is the third type of Transposon? How does it work?

Answer 16

3. Composite Transposon: Two transposons franking central region of DNA –>

a. if the 2 transposase run in the same direction they loop over each other, causing larger deletion of DNA and then chromosomal rearrangement,
b. if they are in opposite directions, DNA gets inverted, chromosomal rearrangement within same chromosome

How it works:
Transposase pastes transposon somewhere else
- if inserted in intergenic region(region of DNA in between 2 genes) : no problem
- if inserted in coding region(middle of gene): mutations

*Contributes to genomic variation

Question 17

Source of Mutation: Polymerase Errors

What are its effects on DNA and what is it repaired by?

Answer 17

Effects:
1. Point mutations
2. Small Repeats
3. Insertions/deletions(small, frameshift)

Repaired by:
1. mismatch repair pathway(after replication)
2. nucleotide excision repair(before replication)

Question 18

Source of Mutation: Endogenous Damage(reactive oxygen species and physical damage)

What are its effects on DNA and what is it repaired by?

Answer 18

Effects:
1. oxidized DNA
2. cross-linked bases
3. physical damage
4. these can lead to polymerase errors

Repaired by:
1. nucleotide excision repair
2. homologous/non-homologous end joining

Question 19

Source of Mutation: Exogenous damage(radiation, chemicals)

What are its effects on DNA and what is it repaired by?

Answer 19

Effects:
1. UV rad = pyrimidine dimers
2. X rays = double stranded breaks & translocations
3. chemicals = can lead to physical damage, intercalation & polymerase errors

Repaired by:
1. direct reversal by white light (dimers)
2. homologous/non-homologous end joining
3. nucleotide excision repair

Question 20

Source of Mutation: Transposons (jumping genes)

What are its effects on DNA and what is it repaired by?

Answer 20

Effects:
1. insertions/deletions (large)
2. inversions
3. duplications

Repaired By:
1. generally don’t lead to repair mechanisms

Question 21

What does a Mismatch Repair Pathway do? When is it detected? What is the problem and what is the solution?

Answer 21

• repairs bases due to DNA polymerase errors
• detected after replication is complete

Problem: which is original parent strand (correct) and daughter strand (mismatched)

Solution: methylation on parent strang for identification

Question 22

When does a nucelotide excision repair occur? why? How do you do this?

Answer 22

• occurs prior to replication because defective bases will lead to polymerase errors
• simply remove and replace