Structure of DNA

Question 0

H-bonds between Guanine and Cytosine

Answer 0

3 - three

Question 1

How many H-bonds between Adenine and thymine

Answer 1

Two - 2

Question 2

Chargoff’s rule

Answer 2

There is a 1:1 ratio between base pairs in DNA.

Eg. If there are 36 thymines in a DNA molecule there must also be 36 adenines in this molecules.

Question 3

What are the three forms of DNA?

Answer 3

1. A-DNA
2. B-DNA - most common
3. Z-DNA - very rare

Question 4

What forces contribute to the structure and stability of DNA?

Answer 4

1. Hydrogen bonds
2. Covalent bonds
3. Ionic interactions
4. Van der Waals interactions

Question 5

Which of the forms of atomic bonding is the weakest?
A. Hydrogen bonding
B. Covalent bonding
C. van der Waals interactions
D. Ionic interactions

Answer 5

C

Question 6

What base binds with adenine?

Answer 6

Thymine

Question 7

What base binds with cytosine?

Answer 7

Guanine

Question 8

Which double stranded DNA is more stable?
A. 8A-T, 1C-G
B. 5A-T, 4C-G

Answer 8

B. this is because guanine forms three hydrogen bonds with cytosine while adenine only forms two hydrogen bonds with thymine.

Question 9

Why does salt stabilize DNA?

Answer 9

Ions the form salt neutralize charges found in DNA.

-> less repulsion -> more compact -> more stability

Question 10

Heterochromatin

Answer 10

Highly condensed - no gene expression

Question 11

Euchromatin

Answer 11

Less compact - gene expression

Question 12

In what phase of the cell cycle would you expect to see all of the DNA as heterochromatin?
A. Interphase
B. Mitosis
C. Meiosis

Answer 12

B and C

Cell division occurs in mitosis and meiosis and DNA must be compact and non-expressive to occur

Question 13

What is the term for inactive X-chromosome?

Answer 13

Barr body

Question 14

What overall charges do arginine and lysine have?

Answer 14

Positive

Question 15

How to does DNA wrap around histones and stay stable?

Answer 15

1. Phosphates are negatively charges
2. Histones contain positively charged amino acids, arginine and lysine
3. these amino acids neutralize negative charges from phosphates
4. This allows less repulsion so that DNA wrap around
5. Histones also form hydrogen bonds with DNA backbone and DNA bases in the minor groove
6. These features allow great stability for DNA.

Question 16

Why are there minor and major grooves?

Answer 16

Strands are not directly opposite each other and so form unequal grooves

Question 17

What interacts with major groove?

Answer 17

Proteins
Modifying enzymes
Transcription factors
Restriction enzymes

Question 18

What interacted with minor groove?

Answer 18

Not sure

Question 19

What do bacteria do to protect DNA?

Answer 19

Have methylated to add a methyl group to DNA

Question 20

Type 1 restriction enzymes

Answer 20

Multi-subunit REs that cut at random positions far from their recognition site

Question 21

Type 2 restriction enzymes

Answer 21

REs that cut at defined positions close to or within their recognition site

Most useful

Question 22

Type 3 restriction enzymes

Answer 22

REs that cut about 25 base pairs away from their recognition site

Can be useful

Question 23

Application examples of RE use in lab

Answer 23

1. Creating plasmid vectors during gene cloning and protein expression experiments
2. Used to distinguish gene alleles by specifically recognizing single base changes in DNA known as single nucleotide polymorphisms (SNPs) - genotyping
3. Used to digest genomic DNA for gene analysis by southern blot - allows researchers to identify how many copies of a gene are present in the genome of one individual, or how many gene mutations have occurred within a population