Genes & The Genome

Question 1

What is the difference between the DNA packaging of genes that are expressed vs not expressed?

Answer 1

• Genes expressed - euchromatin: beads on a string

- Genes not expressed - heterochromatin: solenoid fibre

Question 2

Give an example of a disease involving deficient DNA packaging/expression.

Answer 2

• RETT’S DISEASE
• Neurological development disorder (loss of hand coordination, mobility & speech).
• Mutation in methyl-CpG-binding protein 2 (silences transcription of certain genes) - inability to bind to correct DNA regions, or inability to recruit histone binding complexes - modifying complexes can’t repress gene - abnormal gene activation.

Question 3

What are genes? How many do humans have?

Answer 3

• The fundamental unit of heredity, carrying the code for proteins.
• 25,000

Question 4

What is the genome? How many chromosomes do humans have?

Answer 4

• The entire DNA sequence.

- Composed of 24 chromosomes (22 autosomes + 2 sex chromosomes X & Y).

Question 5

Describe the classical X-shape of chromosomes.

Answer 5

• X shape is a replicated chromosome containing 2 identical DNA molecules (sister chromatids).
• Each chromatid has a p (short) arm and a q (long) arm.
• Telomeres are present at each end.
• Centromere (consisting of repeated sequences) links the sister chromatids - can be at different positions.

Question 6

What are telomeres?

Answer 6

• Repeated sequences (TTAGGG) at each end of chromosomes.

- Protects the DNA molecule from degradation.

Question 7

What is telomeric ageing?

Answer 7

Shortening of telomere every time the cell divides.

Question 8

Describe 3 types of centromere positions.

Answer 8

• Metacentric: centromere in middle of chromosome
• Submetacentric: centromere 2/3 up chromosome
• Acrocentric: centromere close to the end of chromosome