Lecture 3 Flashcards
what is the job of extracellular signals?
they are required by cells to divide, grow and survive
what do growth factors do?
stimulate growth by promoting synthesis and inhibiting degradation of macromolecules
what is the difference between death and survival factors?
death factors promote apoptosis and survival factors suppress apoptosis
how are states of a stem cell maintained?
by receiving external signals to define its ‘state’
what are the 2 things the external signals defining the stem cells ‘state’ could be?
1) soluble ligands for receptors
2) internally generated signals
what has to be done for a cell to differentiate?
you have to turn genes on and off and lock those changes in i.e chromatin has to be altered to allow or close down transcription
what are 3 types of chromatin modification?
1) DNA methylation
2) Histone acetylation
3) phosphorylation
what are 2 ways to control transcription?
Alternative splicing
Degradation of mRNA – siRNA , miRNA
what are 3 methods of blockage of translation?
Protein processing - transport
Control of enzyme activity by effectors and inhibitors
Proteasome degradation – turning signals on and off
what are the building blocks of chromatin?
nucleosomes and histones
what is heterochromatin?
closed chromatin - inaccessible to transcription factors
with is euchromatin?
open chromatin - accessible to transcription factors
what are the 2 ways methylation of DNA can block transcription?
1) direct blocking of TF11D (TATA binding protein)
2) recruitment of histone deacteylases
what defines a cell type?
by expressing specific proteins such as transcription factors in different cell types only a certain repertoire of genes are switched on - this repertoire is what defines a cell type
what do mediator complexes do and why are they important?
they are bridges of activators between transcription factors holding structures together and promoting transcription - the 3D structure is very important giving the protein shape and controlling cell fate decisions
what do tissue specific enhancers do?
drive expression differently in different cell types and times - Enhancers allow the same gene to be used in diverse processes in space and time
what do siRNA and miRNA do?
1) degradation of mRNA
2) block translation
what do ubiquitin proteins do?
tag other proteins for destruction by proteasomes - if you can control this you can control the turnover of a protein and therefore cellular processes
what are the 3 decisions stem cells can make?
1) self renewal - making a copy of onself
2) differentiation
3) death - active process - death factors promote apoptosis
describe the structure of nucleosomes
the N-terminal lysine-rich tails of core histones project radially from the nucleosomal core and are covalently modified
what is a TATA box?
binding site of:
1) general transcription factors
2) histones
- binding of a transcription factor blocks the binding of a histone and vice versa
