Epigenetics and DNA Replication

Examine the role of histone modification and DNA modification in shaping phenotypes across generations • Interpret EWAS plots

Epigenetics

heritable changes in gene expression or function that can’t be explained by changes in DNA sequence

Characteristics of epigenetic

affects chromatin structure

• effects accessibility of DNA for transcription

• can be long lasting, pass to daughter cells and sometimes to gametes

• allows organizmz to respond in longer term way to environmental conditions

Common mechanisms of epigenetic regulation

DNA methylation (a methyl group is added)

Chemical modifications to histone tails (adding chem groups)

• can inc. gene expression if acetyl group is added

• Histone and DNA modification can change chromatin conformation

Experiment: learned fear response in mice

Took F0 male mice and exposed them to an odor (acetophenone aka ACE) and an electrical shock so they learned to associate the shock with the odor

ACE is sensed by mice via their olfactory 151 receptor (Olfr151 gene)

F0 mice showed decreased methylation of Olfr151 gene

F1 gametes also had decreased methylation of Olfr151 gene

EWAS plot (epigenome-wide association study)

Scientists can look at rates of methylation at sites across the genome and look for association with phenotypes

Just like GWAS plots but instead of looking at SNPs they look at methylation status

What does an EWAS peak indicate?

Significant differences in genome modifications

Which DNA base is methylated?

Cytosine

What are histone tails? What modifications occur on histones?

Extensions of histone proteins subject to modification

modifications: Acetylation, methylation, phosphorylation

How do DNA/histone modifications affect gene expression?

They increase or decrease accessibility to RNA polymerase

Where is a gene more highly expressed?

Euchromatin

What proteins regulate eukaryotic transcription?

Transcription factors

Central Dogma of Biology

DNA must be replicated before mitosis

DNA-DNA → DNA-RNA → RNA-protein

RNA polymerases need what to work?

1 thing A template strand to copy

DNA polymerase needs what to work?

2 things:

a template strand to copy

a free 3’OH to ad onto

How does DNA replication get started?

An initiator protein will bind and open DNA

(Origin of replication sequence)

looks like a bubble in the middle of your ladder

_____________|. bubble |____

_____________|. |____

What happens after the bubble binds/initial start?

Helicase binds to the fork and unzips the 2 template dna strands

What happens after the DNA is unzipped by helicase?

Primase: a special RNA polymerase

• will use the template DNA to make short copies of RNA that we call primers can attach (they only needed access to the template)

How do we label the primers that attach thanks to primase?

Antiparallel to their respective DNA strands

If top strand is 5’ to 3’

RNA primer is 3’ to 5’

if DNA pol 1 was missing

unstable genome with RNA in it

If DNA pol 3 was missing

No replication occurs except for some primase

If helicase was missing

No replication would start

If ligase was missing

DNA would be fragmented/ newly synthesized fragments would be unjoined

primase was missing

no replication would start at all

No RNA primers would be synthesized

Which enzyme carries out proofreading

DNA pol 3