Nucleic Acids

Question 1

What characteristics should genetic material have?

Answer 1

• replication
• storage of information
• expression of information
• variation by mutation

Question 2

Give some information on bacteria and viruses on the early study of DNA

Answer 2

They are capable of rapid growth and complete life cycle within hours. They can be easily manipulated experimentally. Mutations can be induced early and selected.

Question 3

What are 2 key experiments for DNA discovery?

Answer 3

Griffith’s experiment
Injecting a mouse with active bacteria and it dies and then heating the bacteria and it dies so the mouse does not get infected.

Avery transformation experiment
Treatment of heat killed virulent strain with proteases had no effect but DNAase removed the transformation effect. Showed that DNA is needed for translation to occur

Question 4

What were the two sets of evidence that were used to solve the structure of DNA?

Answer 4

• Base composition analysis if hydrolysed samples of DNA (showed it was double stranded and anti-parallel)
• Xray diffraction studies

Question 5

What did Charguff discover?

Answer 5

That A and T were bonded and C and G as there were equal amounts of each pair

Question 6

What are the 3 parts of a nucleotide?

Answer 6

1. Nitrogenous base
2. Pentose sugar (deoxyribose)
3. Phosphate (1,2 or 3)

Question 7

What makes pyrimidines and purines different?

Answer 7

Purines have a double carbon-nitrogen ring and pyrimidines have a single one

Question 8

In adenine (the base), what number nitrogen is bound to what number carbon?

Answer 8

Nitrogen 9 to carbon 1

Question 9

What carbon is the phosphate group bound to in deoxyribose?

Answer 9

5 (5 prime bond)

Question 10

What can the sugar in nucleotides be phosphorylated by? What does this produce?

Answer 10

By specific kinases, producing nucleotides

Question 11

How many phosphates are there on a nucleotide?

Answer 11

3

Question 12

What is a nucleoside?

Answer 12

A nucleotide with no phosphate groups on it

Question 13

Where does a phosphodiester bond form in DNA?

Answer 13

Between the phosphate and the deoxyribose sugar

Question 14

What gives a DNA strand polarity?

How does the phosphate group attach two sugars together?

Answer 14

The phosphodiester bonds

It joins to one sugar at carbon 3 and another at carbon 5 (3 to 5 prime)

Question 15

What part of the nucleotide is facing inwards and what is facing outwards?

Answer 15

Bases face inwards and the phosphate sits on the outside.

Question 16

Give some information on the DNS molecule being a double helix

Answer 16

• 2 DNA chains which are complementary to each other are coiled around a central helix of symmetry
• The chains are paired in an anti-parallel manner, ie.e the 3’ end of one strand is paired with the 5’ end of the other
• The deoxyribose-phosphate backbone is on the outside of the molecules and the hydrophobic bases are stacked on the inside
• The spatial relationship gives a major (wide) and minor (narrow) groove. The bases are accessible from these grooves (how enzymes enter)

Question 17

Is DNA a left or right handed helix?
How many nucleotides per turn?
How long is each turn?
How long is the helix diameter?

Answer 17

Right

10

3.4nm

2nm

Question 18

The base pairs are — to the axis of the helix?

Answer 18

Perpendicular

Question 19

Why is the GC bond harder to denature than AT?

Answer 19

GC has 3 bonds and AT has 2

Question 20

Give some information on denaturing DNA?

Answer 20

2 strands separate when the hydrogen bonds between the bases are disrupted.
The temperature at which half the helical structure is lost is defined at the melting temperature.
Single stranded DNA has a higher relative absorbance at 260nm then double stranded DNA

Question 21

Give some brief information on the 3 types of DNA

Answer 21

B form - right handed, 10 residues per turn, perpendicular bases to axis, most common
A form - dehydrated B form, 11 bases per turn
Z form - left handed, 12 base pairs per turn

Question 22

Where is DNA found in eukaryotes?
Bacteria?
Plants?

Answer 22

Eukaryotes - In the nucleus and mitochondria
Bacteria - cytoplasm
Plants - nucleus and chloroplasts

Question 23

Compare the structure of DNA in eukaryotes and prokaryotes

Answer 23

Eukaryotes - long linear molecules of dsDNA, bound to proteins to found chromatin.
They have closed circular DNA molecules in the mitochondria.

Prokaryotes - typically contain and single stranded, supercoiled circular chromosome . Their DNA is complexed with proteins to form nucleoids. Bacteria carry small circular extra-chromosomal molecules called plasmids.

Question 24

What does a genome look like?

How many base pairs is the human genome?

Answer 24

DNA tightly packed into chromosomes and is stored at 10,000x shorter than its length achieved by supercoiling.
DNA plus proteins (histones) are called chromatin which is packed into nucleosomes which are then condensed into chromosomes. It can be RNA or DNA.

3.5 x 10 ^ 9

Question 25

Give 4 pieces on information on replication/storage/expression/variation

Answer 25

By replication, DNA can form a copy of itself.

DNA is stores, carefully packaged into chromosomes.

Nucleic acids have a structure that is perfect to allow expression of gene products.

Mutations can lead to variation but are carefully controlled.