BMM 339: lecture 37

What holds each strand of DNA together?

Phosphodiester bonds

What are the ends of DNA called?

5' end (phosphate group) and 3' end (OH group)

What types of base pairs are found in DNA?

A-T and G-C

What stabilizes the base pairs in DNA?

Hydrogen bonding between the bases

How are the two strands of DNA oriented?

Anti-parallel: 5' to 3' and 3' to 5'

How are DNA sequences typically written?

5' to 3'

How do proteins interact with DNA?

Via the major groove of the DNA

What maximizes stacking energy in DNA?

A helical twist

What occurs during DNA strand separation?

DNA underwinding and supercoil formation

What enzymes control supercoiling in DNA?

Topoisomerase enzymes

What is chromatin made of?

DNA wrapped around nucleosomes

What do nucleosomes contain?

An octamer of 4 histones: H2A, H2B, H3, and H4

What is the role of H1 in nucleosomes?

It is the linker between nucleosomes

What are the two types of chromatin?

Heterochromatin (inactive) and euchromatin (potentially active)

What affects chromatin compaction and structure?

Modifications of histone tails and DNA methylation

What can temporarily displace nucleosomes?

Remodeling complexes

What is one mechanism for forming heterochromatin?

The association of some chromosome regions with nuclear lamin

What fraction of the human genome contains functional genes?

Only a small fraction

What are exons and introns?

Exons encode proteins; introns are spliced out RNA segments

What is required to constrain large chromosomes in a small space?

Multiple layers and modes of tertiary structure

What proteins maintain chromosome structure?

Histones, condensins, and cohesins

What role do cohesins play in chromosome structure?

They hold recently replicated DNAs together

What do condensins do during mitosis?

Cause chromatin condensation