Chapter 17 Flashcards
Three classes of transcriptional activators
- General TXN Factors (GTF)
- Activators
- Co-Activators
What type of compound is an activator
Protein
Where do activators bind
distal enhancer sequences
What do GTFs do?
Bind to TATA Box (core promoter region) and recruit RNA pol
What do activators stimulate?
transcription initiation
DNA binding proteins are composed of?
- DNA binding domain
- activation domain
Do co-activators bind to DNA
No couples action of activator to GTFs
What is a co-activator
large multi-protein complex
What do repressors do
Inhibit activator from starting transcription initiation (block function of activator)
Ways that the repressor can inhibit the activator
- Repressor binding site may overlap with activator binding site
- The repressor domain interacts with the activation domain
- Can recruit corepressors (prevent co-activators)
The two domains of a repressor
- DNA binding
- repression domain
Combinatorial control
the strategy of controlling TXN in which any gene is controlled by a combination of factors
TXN factors
bind to DNA and recruit RNA pol to the promoter.
Structural motifs possessed by DNA binding domains
- Helix-turn-Helix
- Zinc Finger
- Leucine zipper
Hormone
effector module produced by a cell affects another cell
Three major types of hormones
- Protein hormones
- steroid hormones
- amine hormones
Protein hormones
- composed of Amino Acids
Steroid hormones
- composed of lipids
Amine hormones
- composed of amino acids with modified groups
Function of polypeptide hormones
bind to receptors in plasma membrane of the cell and trigger a cascade of signal transduction pathway responses.
Function of steroid hormone
diffuses through plasma membrane and binds to the cytoplasmic receptor SHR.
What happens after the steroid hormone binds to the SHR
The complex binds to the genome and alters gene expression.
Why are certain cells targetted by hormones but not other
Only cells with that specific hormone receptor can be affected by that hormone
Why are steroid hormone receptors located inside the target cells
Steroid hormones are non-polar and can easily diffuse through the plasma membrane
Why are peptide hormone receptors located on the surfaces of cells
peptide hormones cannot diffuse through the cell without a transport channel.
Chromatin remodeling epigenetic changes
- gene silencing
- genomic imprinting
Euchromatin
- TXN active
- Interphase of cell cycle (S-phase)
- DNase accessible (cuts DNA)
Heterochromatin
- TXN Inactive
- Mitosis
- DNase inaccessible
What protein binds the DNA and condenses it?
Histones
What is a nucleosome?
Histone + DNA
What does histone binding repress?
Gene expression
Nucleosome-free regions are:
DNase 1 hypersensitive sites (first to be cut by DNase 1)
Lysine acetylation
transfer of an acetyl group from acetyl-CoA to the primary amine of the lysine chain
These compounds Add acetyl groups to the histone tail
- Histone acetyltransferases (HATs)
-lysine acetyltransferases (KATs)
Chromatin Remodeling steps (lysine acetylation)
- recruited to chromatin by activators
- acetylates lysines of amino-terminal tails of histones
Histone deacetylase (HDACs)
removes acetyl groups from histone tails
Nucleosome remodeling complexes
- ATP-dependent
- Similar to KAT complexes
Steps to Chromatin remodeling (Nucleosome)
- Complexes recruited by activators
- Complexes remodel/ move nucleosomes to permit transcription
Function of Nucleosome remodeling complexes
- Slide nucleosome
- restructure the nucleosome in place
- transfer nucleosome to another DNA
Gene Silencing
regulation of gene expression in a cell to prevent the expression of a certain gene
Why does gene silencing occur?
Occurs because of the location of the gene
Example of gene silencing
telomeres
Telomeres
- heterochromatin
- ends of chromosomes
- tandem repeat DNA sequences
Telomere position causes
Gene silenicng (genes to be turned off)
Telomere position effect is caused by
Silent Information Regulation Proteins (SIR)
SIR Steps
- Rap 1 protein binds to tandem repeat in telomere
- Rap 1 protein recruits SIR silencing complex
- SIR2p deacetylates, which leads to heterochromatin condensation and transcriptional inactivation
