L1 - DNA structure & function / Chromosome structure

Question 1

Friedrich Miescher

Answer 1

1868
Isolated nuclein from human pus
later renamed nucleic acid
had high molecular weight and was acidic (due to phosphorous)

Question 2

Avery, MacLeod and McCarty

Answer 2

1944
Streptococcus pneumoniae transformation experiments
2 populations
1 population was pathogenic with individual cell components separated

Question 3

Hershey and Chase

Answer 3

1953
Bacteriophage experiments with radioactive tag
A bacteriophage is DNA and protein coat only

Question 4

Structure of DNA

Answer 4

• Double helix of complementary antiparallel strands
• each strand in a linear polymer made of repeating units

Question 5

What is a nucleotide composed of?

Answer 5

sugar
base
phosphate(s)

Question 6

What is a nucleoside composed of?

Answer 6

sugar
base

Question 7

Deoxy adenosine

Answer 7

deoxyribose + adenine

Question 8

Deoxy guanosine

Answer 8

deoxyribose + guanine

Question 9

Deoxy cytidine

Answer 9

deoxyribose + cytosine

Question 10

Deoxy thymidine

Answer 10

deoxyribose + thymine

Question 11

How do DNA stands exhibit directionality?

Answer 11

• due to backbone
• strands run antiparallel
• base pairs are planar and stack
• 3’ has hydroxy group
• 5’ has nucleotide

Question 12

How are DNA strands held together?

Answer 12

Hydrogen bonds between complementary base pairs
- A large base (purine) pairs with a small base (pyrimidine)

• A & T (2 hydrogen bonds)
• G & C (3 hydrogen bonds)

Question 13

4 Requirements of genetic material to provide the mechanism for heredity

Answer 13

• Be stable over time (DNA is stable, lasts years, complementary strands)
• Be able to be faithfully replicated (semiconservative replication)
• Be able to change in a controlled way (point mutations)
• Be able to encode protein sequence for expression of traits

Question 14

What is the genome?

Answer 14

All the DNA in (the nucleus of) a cell or of an organelle

• mitochondria and chloroplasts have their own circular genomes

Question 15

How many base pairs in
1. haploid nuclear genome
2. human mitochondrial genome

Answer 15

3.0 x10 9 bp
1.5 x10 4 bp

Question 16

Chromosome structure (3)

Answer 16

• DNA wraps twice around 8 core histone proteins to form nucleosomes
• Histone H1 brings nucleosomes together to form a chromatic fibre
• Chromatin is further condensed by scaffold proteins into mitotic chromosomes

Question 17

What are the 8 core histones?

Answer 17

2x histone H2A
2x histone H2B
2x histone H3
2x histone H4

Question 18

Interphase chromosomes arrangement - 2 types of chromatin

Answer 18

euchromatin
heterochromatin

Question 19

Differences between euchromatin and heterochromatin

Answer 19

euchromatin:
- less compact DNA form
- contains genes that are frequently expressed (ie access is important)

heterochromatin
- more compact
- contains DNA that is not transcribed