Theme 3 - Mod 3 - Eukaryotic Transcriptional Regulation

How many distinct cell types do adults have

200

What are transcription factors

Proteins that bind to specific DNA sequences and allow them to interact with the DNA and control transcription

Difference in gene regulation between eukaryotes and prokaryotes

Prokaryotic genes are expressed as operons by a single promoter

Eukaryotic genes are expressed by its own promoters and enhancers (DNA also packed in chromatin)

Nucleosomes

Contains octamer of 8 histones with approx 150 base pairs

Process of chromatin remodeling

1. Begins when an activator protein or transcription factor binds to an enhancer site

2. This leads to further recruitment of proteins that can lead to further chromatin remodeling

Process of how histone modification alter DNA winding

1. Positively charged tails of histone proteins interact with negatively charged phosphates of DNA

2. Acetylation via HAT of tails weakens their interaction with DNA and permit some transcription factors to bind to DNA

What happens when acetylation and methylation with a single methyl group is added

Leads to transcriptional activation

What happens when three methyl groups are added

Repression of transcript

What are the 4 DNA binding motifs/trans-acting factors

Basic Helix-loop-helix

Helix-turn-helix

Zinc finger

Leucine zipper

What do DNA motifs/trans-acting factors do

They bind to DNA by molecular interactions that occur between the amino acid in the alpha helix and the functional group of the nitrogenous base

Core promoter

Binding site that is required for binding of RNA polymerase and associated transcription factors

What is the TATA box recognized by

Recognized by the TATA-binding protein (TBP) subunit of the transcription factor TFIID

What is the BRE region recognized by?

Recognized by the TFIIB transcription factor

TFIID and TFIIB

Binding transcription factors that are able to make protein to protein interactions that assist with the assembly of the transcription complex

Enhancer sequences

Able to bind to cell or region specific transcription factor

This facilitates the formation of the transcriptional complex by enhancing transcription

Difference in prokaryotes and eukaryotes enhancer regions

Enhancer region in eukaryotes is much further from the promoter region

Why is the enhancer region so far from promoter

Flexible nature of DNA allows for the assembled transcription factors and RNA polymerase to come to close proximity by looping of DNA

Adaptor/Mediator proteins

Connect the proteins bound to the enhancer site with the proteins bound to the promoter

Silencer

A sequence that codes to combine transcriptional repressors to inhibit transcription

Upstream from target gene

Hemoglobin protein in fetus and adult

Fetus - Alpha and gamma globins

Adult - Alpha and beta globins

Why do fetus need gamma globins and adults don't

Gamma globins can bind to oxygen more strongly than beta globins

Hemoglobin gene expression in adult and fetus

Fetus - A, Y is on, B is off

Adult - A, B is on, Y is off

What does it mean when the gene is off

The nucleosomes and histones aren't unwinded so transcription cannot occur

What happens when there is undermethylation of CpG island

DNA binding proteins will recognize promoter sequence and transcription occurs

What happens when there is heavy methylation of CpG island

DNA binding proteins can't bind to promoter sequence therefore inhibiting transcription

HDAC

Binds to methylated DNA and promotes the removal of acetyl groups from neighbouring histones

Importance of HDAC

Allows for nucleosomes in histones to reassemble and therefore repressing transcription

Default state of transcription in prokaryotes and eukaryotes

Prokaryotes - on

Eukaryotes - off