Eukaryotic Chromosome Structure + Epigenetics

Question 1

what are the four levels of DNA packing and their size?

Answer 1

1. nucleosome 10 nm
2. solenoid 300 nm
3. looped domain
4. metaphase chromosome

Question 2

what are the components of a nucleosome

Answer 2

DNA and its core histones

it has two of each of the core histones:
- H2A
- H2B
- H3
- H4

H1 is not part of the nucleosome but is attached to the DNA near the nucleosome

Question 3

what is a histone? describe it

Answer 3

positively charged proteins around with DNA coild to form chromatin

it has positive R groups with bind to negatively charged DNA phosphate groups

Question 4

what is the difference between a core and linker histone

Answer 4

core histones are wrapped by hthe DNA whereas linker histones are on the outside

Question 5

describe solenoids

Answer 5

H1 histones come together causing 6 nucleosomes to coil together, they then stack on top of each other forming chromatin fiber

Question 6

describe the third level of packing, looped domains

Answer 6

the chromatin fibers form loops which attach to nonhistone proteins. The nonhistone proteins form a scaffold

Question 7

What DNA chromosome structures has active DNA?

Answer 7

it must be uncoiled

Question 8

what DNA chromosome structures have inactive DNA?

Answer 8

• DNA as it is most condensed so info is inaccessible
• interphase chromatin, still less condensed than during mitosis but order still exists

Question 9

interphase chromatin have both euchromatin and heterochromatin

Question 10

what is euchromatin

Answer 10

loosely packed region on chromatin, active transcription (light stain)

Question 11

what is heteochromatin

Answer 11

densely packed region on chromatin which is inactivated

Question 12

describe methylation

Answer 12

atttachment of methyl groups (CH3-) to DNA bases usually at cytosine which happens after DNA is replicated, it suppresses gene expression meaning it occurs on genes that are not expressed

once removed it turns genes one

Question 13

what is histone acetylation

Answer 13

attachment of an acetyl group (COCH3-) to histones

Question 14

how does histone acetylation impact gene expression?

Answer 14

changes histone shape reducing its grip on DNA, which results in more loosely packed DNA so it activates gene expression

deacetylation supresses gene expression

Question 15

epigenetics

Answer 15

study of heritable changes in gene expression caused by mechanisms other than the DNA sequence

Question 16

what are some environmental impacts on the epigenome

Answer 16

diet, stress, physical activity, exposure to toxins

Question 17

imprinting

Answer 17

supression of genes so that only 1 allele is expressed