Nucleic Acids & Chromatin

Question 1

Structure of Metaphase Chromosome

Answer 1

-Only visible; highly condensed
- Ends: called telomeres
- Centre: centromere
- Two identical copies of a chromosome after DNA replication
- Each copy; chromatid
-Centromere: site of assembly of kinetochore

Question 2

What is the Kinetochore?

Answer 2

Multiprotein structure responsible for actual events of chromosome segregation.

Question 3

What is at the 3’ and 5’ ends of a nucleotide?

Answer 3

• The sugar is the 3’ end
• The phosphate is the 5’ end

Question 4

What does the extra OH in RNA cause?

Answer 4

Makes it susceptible to alkaline degradation; and responsible for secondary structure.

Question 5

Define Histone

Answer 5

Protein; associates with DNA in the nucleus to condense DNA to smaller volume.

Question 6

Define chromatin

Answer 6

Complex of DNA and proteins that form chromosomes in the nucleus

Question 7

What are the two types of chromatin?

Answer 7

-EUCHROMATIN: less condensed; can be transcribed
-HETEROCHROMATIN: condensed and typically not transcribed

Question 8

What is a nucleosome?

Answer 8

-Subunit of chromatin
- 1.65 turn of DNA wrapped around a histone octamer
- Histones are positively charged; binds to negatively charged DNA backbone

Question 9

Types of chromatin remodelling

Answer 9

1) ATP-dependent: complexes that either move, eject or restructure the nucleosome
2) Covalent histone modifications: by enzymes.

Question 10

Histone Modification

Answer 10

• Lysine rich tails can be modified by: acetylation, methylation and phosphorylation
• Can act as binding sites of other regulatory proteins; can promote condensation or decondensation

Question 11

Epigenetic effect

Answer 11

• Influences phenotype without altering the genotype
• The result of modification after DNA replication
• Switches genes on or off
• Passed onto germ cells affecting F1 generation; can affect germ cells of foetuses in utero this affecting F2 generation
• Inherited changes but no change in genotype