Lecture 3

Question 1

what is the job of extracellular signals?

Answer 1

they are required by cells to divide, grow and survive

Question 2

what do growth factors do?

Answer 2

stimulate growth by promoting synthesis and inhibiting degradation of macromolecules

Question 3

what is the difference between death and survival factors?

Answer 3

death factors promote apoptosis and survival factors suppress apoptosis

Question 4

how are states of a stem cell maintained?

Answer 4

by receiving external signals to define its ‘state’

Question 5

what are the 2 things the external signals defining the stem cells ‘state’ could be?

Answer 5

1) soluble ligands for receptors

2) internally generated signals

Question 6

what has to be done for a cell to differentiate?

Answer 6

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

Question 7

what are 3 types of chromatin modification?

Answer 7

1) DNA methylation
2) Histone acetylation
3) phosphorylation

Question 8

what are 2 ways to control transcription?

Answer 8

Alternative splicing

Degradation of mRNA – siRNA , miRNA

Question 9

what are 3 methods of blockage of translation?

Answer 9

Protein processing - transport
Control of enzyme activity by effectors and inhibitors
Proteasome degradation – turning signals on and off

Question 10

what are the building blocks of chromatin?

Answer 10

nucleosomes and histones

Question 11

what is heterochromatin?

Answer 11

closed chromatin - inaccessible to transcription factors

Question 12

with is euchromatin?

Answer 12

open chromatin - accessible to transcription factors

Question 13

what are the 2 ways methylation of DNA can block transcription?

Answer 13

1) direct blocking of TF11D (TATA binding protein)

2) recruitment of histone deacteylases

Question 14

what defines a cell type?

Answer 14

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

Question 15

what do mediator complexes do and why are they important?

Answer 15

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

Question 16

what do tissue specific enhancers do?

Answer 16

drive expression differently in different cell types and times - Enhancers allow the same gene to be used in diverse processes in space and time

Question 17

what do siRNA and miRNA do?

Answer 17

1) degradation of mRNA

2) block translation

Question 18

what do ubiquitin proteins do?

Answer 18

tag other proteins for destruction by proteasomes - if you can control this you can control the turnover of a protein and therefore cellular processes

Question 19

what are the 3 decisions stem cells can make?

Answer 19

1) self renewal - making a copy of onself
2) differentiation
3) death - active process - death factors promote apoptosis

Question 20

describe the structure of nucleosomes

Answer 20

the N-terminal lysine-rich tails of core histones project radially from the nucleosomal core and are covalently modified

Question 21

what is a TATA box?

Answer 21

binding site of:

1) general transcription factors
2) histones
- binding of a transcription factor blocks the binding of a histone and vice versa