Topic 2 Molecular Genetics: DNA Organization

Question 1

• DNA can’t just be a jumbled mess in the cell — we need organization! The key structure responsible for this is the nucleosome

Answer 1

Note

Question 2

• Structure formed when DNA is coiled around bundles of 8-9 histone proteins, kind of like beads on a string
• During cell division (interphase), however, chromatin exists as two types:

Answer 2

1. Nucleosome

Question 3

a. Euchromatin

b. Heterochromatin

Answer 3

Types of Nucleosome

Question 4

• Chromatin is loosely bound to nucleosomes; present when DNA is actively being transcribed

Answer 4

a. Euchromatin

Question 5

• Areas of tightly packed nucleosomes where DNA is inactive and appears darker.
• Heterochromatin contains lots of satellite DNA (large tandem repeats of noncoding DNA concentrated at centromeres and ends of chromosomes)

Answer 5

b. Heterochromatin

Question 6

• DNA segments that can move to a new location on either the same or different chromosome. There are a two types of transposons:
• Insertion sequences that consist of only one gene that codes just for the enzyme that transports it (transposase)
• Complex transposons code for extra features: replication, antibiotic resistance
• If either type of these transposons were inserted into another region, mutation results, which could have any degree of effect to the overall expression of the gene.

Answer 6

2. Transposons (jumping genes)

Question 7

• The human genome contains many types of DNA that do not actually code for proteins or RNA, and because most of the genome appears to be repetitive DNA, there are lots of transposable elements present as well.
• Pseudogenes are former genes that have accumulated mutations over a long time and no longer produce a functional protein

Answer 7

3. Pseudogenes

Question 8

• There are ~24,000 genes in the human genome, with a majority of the genome consisting of repetitive DNA

Answer 8

Note