gene regulation Flashcards
What is epigenetics
the study of how cells control gene activity without changing the DNA sequence.
How do are cells, that have identical genes, appear and function so differently?
- Different gene expression
What are the main protein components of a Chromosome?
Histones: bind to Dna and give chromosomes shape and help activity of genes
8 histones come together to make a nucleosome
What structural similarities do these four proteins share
Each histone has
- 3 alpha regions
- N terminal tail (where regulation occurs as post-translational modifications) and c terminal tail
How do they interact with the DNA?
DNA can make two full warp around H3\H4 tetramer
H2.H2B tetramer comes in
Tails of histones stick out
In what region on the proteins do these modifications mainly occur?
Histone tails are the sites of active post-translational modifications
acetylation
removes positive charge on lysine
Methylation
methyl groups added to lysine side chains (larger positive charges)
Phosphorylation
makes tails of serine, threonine and tyrosine negative.
How do these proteins and DNA interact to give Chromosomes more condensed or relaxed states?
Histone acetyltransferase: relax the structure of chromosomes Histone De-acetylase: more condensed
How do HAT’s and HDAC’s alter gene expressio
HAT- by transferring acetyl groups to specific lysine
HDAC: removes acetyl groups from lysine to compact
chromatin remodeling limited to only acetylation of Histones?
no, Mainence Methyltransferase
DNA polymerase and methylation reproduce genome
What is the general model for methylation?
Addition of methyl group to DNA, proteins, or other molecules that can affect how cells act in the body
Methylation can turn off genes
methylation a permanent or transient way to turn off genes?
A temporary way to turn off genes.
reverse methylation
DNA methyltransferase inhibited
other factors that can influence DNA methylation levels?
nutrition
What exactly is a gene
Portion of DNA that is transcribed, has a promoter, a promoter-proximal element, and enhancers
PPE and enhancer
PPE: located near the promoter
Enhancer: located further away from gene
What is the difference between General and Specific Transcription Factors?
General: all genes have them in order to proceed with transcription
Specific: ex: PPE/ enhancer , specific for a particular gene
What is the “Combination Lock” model for Transcriptional Regulation?
Where co activations work with enhancer, PPE, and promoter region to initiate transcription
how Transcription Factors can bind and affect DNA at other points. what causes different gene expression
Enhancers can still be accessed on tightly packed DNA. These enhancers are transcription regulators. They recruit HAT proteins, not other transcription factors. Specific TF can bind and They can recruit HAT’s to relax condensed Chromatin allowing Transcription.
Different types of enhancers is what causes a different gene expression
Coordination can be enhanced/repressed with other signaling molecules
Just transcription factors can translate and will have slow rate of transcription
If a specific transcription factor binds with a specific signaling molecule, it can bind to multiple genes. Combination with a specific along with a common factor, it can amp up the rate of transcription
“Master TF” can cause the expression of multiple genes – MyoD
- A cell that doesn’t know what it is, will not express genes. They are off
- Reason: earlier gene, gene for MyoD, a specific transcription factor, is off.
- gene is necessary to turn muscle genes on.
- As cell becomes muscle cell, one of genes will start expressing, the myoD gene,
- Low level of expression to create MyoD protein
- As cell continues to actually becomes muscle cell, MyoD will be a transcription factor for itself.
- MyoD will come back and bind to MyoD gene and upregulate more MyoD
- Also a transcription factor for other genes, upregulate to make different transcription factors. (make more myosin
a. What is microRNA (miRNA) and how does it inhibit gene expression?
- miRNA: very small (22 bp) and interacts with a protein to form a miRNA protein complex.
- Goes out into cytoplasm and looks for mRNA that has a complementary sequence and can hybridize to mRNA, it can degrade mRNA strand.
- The more its complemented, the faster itll degrade. If its not that complement, itll inhibit the message.
- Depending on how long the message is in the cytoplasm, control how much of gene product is made.
