Lecture 16 - Chromosome Structure and Dynamics

Genetic information in DNA is passed to the next generation by

• DNA replication

• Cell division

2 (or 3) genomes found in cells

nuclear, mitochondrial, chloroplast

Genome is a _____ copy of all the genetic information of an organism or virus

complete

Cell nucleus diameter

5-8 um

_____ are the most abundant proteins in chromosomes

Histones

Most abundant amino acids in histones

lysine and arginine

Histones are responsible for the first and most fundamental level of chromatin packing in the ______

nucleosome

Histone October forms the ______ ______ ______ (made of eight histone particles)

nucleosome core particle

4 core particles of histones

• H2A

• H2B

• H3

• H4

Histones are ____ charged

positively

Each of the histones in the octamer have long _______ amino acid tails

N-terminal

Further packing of the nucleosome relies on ______ ___ which pulls nucleosomes together

histone H1

purpose of packaging DNA in chromosomes

• allows cell to accommodate huge genomes

• protects DNA from nucleases

• enhances the regulation of gene expression

extended chromosome material

euchromatin

condensed chromosome material

heterochromatin

Heterochromatin regions are found throughout the chromosome but are most concentrated near _____ and _____

centromeres; telomeres

Heterochromatin corresponds to _____ genes

quiescent

What happens to genes that accidentally become packaged into heterochromatin

fail to express

_____ is transcriptionally active DNA

euchromatin

(T or F) a cell can adjust its chromatin structure to expose specific regions of DNA to give access to other proteins

true

Adjusting of chromatin structure by ____ _____ ______

chromatin remodling complexes

chromatin remodeling complexes can both ____ and _____ chromatin

unwind; condense

Chromatin structure adjustment occurs via _____ ______

histone modifications

the ____ of all 4 core histones are subject to covalent modifications

tails

3 types of covalent modifications used in histone modifications

acetylation, methylation, phosphorylation

How do covalent modifications adjust histones

• reduce/increase affinity of tails for DNA

• create docking sites for regulatory proteins

Epigenetic modifications do not alter the ___ ______, but can alter gene expression patterns in a cell

DNA sequence

Dynamic adjustment of local chromatin packing by chromatin remolding complexes and histone modifications results in ___-_____ packing of interphase chromosomes

non-uniform

Example of useful heterochromatin

telomeres

Do telomeres code for proteins?

no

Telomeres are found on ___ ends of the chromosome

both