Nucleic Acids

Question 1

Why were bacteria and viruses used in early DNA studies?

Answer 1

Rapid growth

Easily manipulated experimentally

Mutations can be induced easily and selected

Question 2

Describe Griffith’s transformation experiments.

Answer 2

Avirulent and virulent strains of Diplococcus pneumoniae used

Treatment of mouse with heat-killed virulent and avirulent strain resulted in death

Transfer of DNA must have occurred (as neither strain can cause death alone)

Question 3

What is the main difference between avirulent and virulent strains of Diplococcus pneumoniae and why is this important?

Answer 3

Avirulent = no capsule

Virulent = capsule –> able to escape immune system

Question 4

How was it discovered that DNA (not proteins) contained genetic material?

Answer 4

Avery et al mixed heat-treated virulents with avirulents to create virulents

When the heat-treated virulents were treated with DNAses before mixing, no virulents were produced (but with proteases they were)

Question 5

What was the Hershey-Chase experiment?

Answer 5

Radioactively labelled DNA (32P) and protein (35S) showed that viral DNA from T2 bacteriophages was entering E.coli (not protein)

Hence it must be DNA coding for new viruses

Question 6

How was the structure of DNA discovered?

Answer 6

Maurice and Wilkins - X-ray crystallography (X-ray diffraction data) showed double stranded and antiparallel

Chargaff’s rule - equal numbers of A and T, G and C regardless of organism

Watson and Crick solved it with the data

Question 7

What are the three components of a nucleotide?

Answer 7

Nitrogenous base

Pentose sugar

1, 2 or 3 phosphates

Question 8

What gives the acidic nature of nucleic acids?

Answer 8

Phosphate groups

Question 9

What are the two types of pentose sugar in genetic material?

Answer 9

Ribose

Deoxyribose

Question 10

Which bases are the purines?

Answer 10

Adenine

Guanine

Question 11

Which bases are the pyrimidines?

Answer 11

Thymine

Cytosine

Uracil

Question 12

What is the main difference in structure between purines and pyrimidines?

Answer 12

Purines have two rings but pyrimidines have one

Question 13

What is the difference between the structures of ribose and deoxyribose?

Answer 13

Ribose has an OH group on the 2’ carbon whereas deoxyribose has a H on the 2’ carbon

Question 14

What does a nucleoside consist of?

Answer 14

Base and sugar

Question 15

How do nucleosides become nucleotides?

Answer 15

Phosphorylation by kinases

Question 16

What is a dNTP and what is it made up of?

Answer 16

Deoxyribonucleoside triphosphate - building block of DNA

Base + deoxyribose + 3 phosphates

Question 17

Why do nucleic acids display polarity?

Answer 17

Phosphodiester bonds/phosphates

Question 18

How many base pairs are in human DNA?

Answer 18

3.5 x 10^9

Question 19

Which direction is DNA formed?

Answer 19

5’ to 3’

Question 20

Describe the structure of DNA.

Answer 20

Complementary strands form a right-handed double helix

Antiparallel

Coiled around a central axis of symmetry

Hydrophobic bases inside and backbone outside

Major and minor grooves

Question 21

How many nucleotides are there per turn of the double helix?

Answer 21

10

Question 22

What is the pitch of DNA?

Answer 22

3.4nm

Question 23

What is the diameter of the DNA helix?

Answer 23

2nm

Question 24

Where are the bases accessible from in DNA?

Answer 24

Major and minor grooves

Question 25

What are the complementary base pairings?

Answer 25

A + T/U G + C

Question 26

What is the bond formed between complementary base pairs?

Answer 26

Hydrogen bonds

Question 27

How many hydrogen bonds form between the complementary bases?

Answer 27

2 between A + T/U 3 between G + C

Question 28

What is the orientation of the hydrogen bonds in relation to the central axis of the helix?

Answer 28

Perpendicular

Question 29

What is the name of the process of separating the DNA strands?

Answer 29

Denaturation

Question 30

What is the 'melting temperature' (Tm)?

Answer 30

Temperature at which the hydrogen bonds between bases break

Question 31

Areas rich in which base pairing will have a higher Tm?

Answer 31

G-C

Question 32

Which of single or double stranded DNA has a higher relative absorbance?

Answer 32

Single (260nm)

Question 33

What are the three main forms of DNA?

Answer 33

B A Z

Question 34

Describe the B form of genetic material.

Answer 34

Right-handed helix 10 residues per turn Bases are perpendicular to the central axis

Question 35

Describe the A form of genetic material.

Answer 35

Right-handed helix 11 residues per turn Base pairs are tilted at 20° to the axis

Question 36

Where is the A form of genetic material found?

Answer 36

DNA:RNA RNA:RNA

Question 37

How is the A form of genetic material related to the B form?

Answer 37

A form is a moderately dehydrated B form

Question 38

Describe the Z form of genetic material.

Answer 38

Left-handed helix ~12 residues per turn Sugar-phosphate backbone zigzags

Question 39

What types of regions of DNA display the Z form?

Answer 39

Regions with alternating purines and pyrimidines

Question 40

Where is the DNA located in eukaryotic organisms?

Answer 40

Nucleus Mitochondria Chloroplasts (plants)

Question 41

Where is the DNA located in bacteria?

Answer 41

Cytoplasm

Question 42

Describe DNA in eukaryotes.

Answer 42

Long, linear, double-stranded DNA bound to protein to form chromatin Closed circular DNA molecules in mitochondria and chloroplasts

Question 43

Describe DNA in prokaryotes.

Answer 43

Typically one double-stranded, supercoiled, circular chromosome complexed with proteins to form nucleoids Plasmids - small, circular extra-chromosomal molecules in bacteria

Question 44

What is the genome?

Answer 44

Entire set of genes in the chromosomes of an organism