August 9 2019 Regulation gene Expression in Eukaryotes Flashcards
How does histone methylation affect gene expression?
Histone methylation suppresses gene expression
How do histone acetyltransferases affect gene expression?
They transfer an acetyl group from acetyl-CoA to a lysine on the histone tail of the nucleosome, thereby reducing its positive charge, and weaking the bond between negatively charged DNA and positively charged lysine on the histone tails.
How does SWI/SNF modify gene expression?
It regulates accessibility of DNA by sliding or eviction of nucleosomes.
How does methyltransferase modify chromatin structure?
It recognizes hemimethylated DNA, in which the parent strand is methylated and the daughter strand is not methylated, and fully methylates it
Which structural motif is commonly found in the DNA-binding domain of steroid hormone receptors?
zinc-finger motif
Which control regions of the eukaryotic gene do mediator proteins control?
general transcription factors, gene-specific regulatory factors, hormone receptor elements (HRE), and enhancer binding proteins
Explain the conformation of unbound glucocorticoid receptors in the cytosol, and how cortisol changes this conformation to regulate gene transcription.
The glucocorticoid receptor resides in the cytosol bound to heat-shock proteins. As cortisol binds, the receptor dissociates from the HSPs, exposing the nuclear localization signal. The receptors form homodimers that are translocated to the nucleus, where they bind to the hormone response elements (HRE) in the DNA control region of certain genes.
In what part of the cell is the inactive thyroid hormone receptor located, and what is its role there?
nucleus, forms a heterodimer with retinoid X receptor that binds to thyroid hormone response elements and to corepressors (including one with HDAC activity), thereby inhibiting expression of certain genes
What do regulatory proteins do and what and where do they gain access to?
Regulatory proteins possess DNA-binding motifs and they gain access to the bases of DNA at the major groove
What are HATs and what do they do?
HATs are histone acetyl transferases. They reduce the positive charge on lysines, making histones bind DNA less tightly. This type of acetylation leads to activation.
What are HDACs and what do they do?
HDACs are histone deacetylases. They remove the acetyl groups from an amino acid on histones and cause repression of gene expression.
What do master regulators do? What are they?
They are regulators of transcription factors. They are proteins that switch broad developmental or metabolic programs On or Off.
What are CpG islands? What is their impact on DNA expression?
CpG islands are where the methylated cytosines are located (@ the 5th nucleotide); CG-rich sequences. Since the DNA is methylated, it is transcriptionally silent.
Define zinc fingers sturcture and function.
Zinc fingers consist of an alpha helix and beta sheet where 4 cysteine and/or histidine residues coordinately bind a zinc ion. Zinc fingers are steroid hormoe receptors.
Describe the leucine zipper structure.
Two polypeptide helices with leucine residues exposed on each side, forming hydrophobic interactions with each other, causing dimerization. More positive charged to interact with DNA.
