Cell Determination + Gene Expression

Question 1

What is cell differentiation?

Answer 1

Production of different cell types within an organism

Question 2

What is determination?

Answer 2

Memory of differentiation

Stability of cell differentiation even after cessation of any inducing signal

Question 3

What is cell lineage?

Answer 3

Series of successive cell types leading from zygote to a particular mature cell type

Question 4

How can cell type become different?

Answer 4

Different cell types express different sets of genes
Gene expression
Different cell types make very different sets of gene products thus makes cells different

Question 5

What is modulation?

Answer 5

Dependent on external stimuli
Simple reversible change to gene expression with no change in cell type
Also called adaptation

Question 6

State similarities between cell differentiation and modulation

Answer 6

Both involve changes in gene expression

Question 7

State differences between differentiation and modulation

Answer 7

Differentiation= stable, complex change 
Modulation= temporary, simple change

Question 8

Differentiation is complex

Answer 8

Diverse set of cell-type specific genes is generally activated in expression during one step in lineage + others are repressed
New expression pattern is called program of differentiation and it is largely controlled at level of mRNA transcription

Question 9

Differential transcription is detected by…..

What does this reveal?

Answer 9

Using individual probes

This reveals many mRNA difference between any 2 cell types

Question 10

What are two main levels of control of transcription?

Answer 10

Chromatin remodelling or folding

Specific transcriptional regulation of individual genes

Question 11

What is one mechanism of remodelling?

What happens ?

Answer 11

DNA methylation=> adding methyl groups to cytosine
Methylation of gene has effect of increasing folding + silencing transcription
Occurs on cytosine with CG pair=> cytosine converted to methylcytosine
It’s copied to opposite strand by maintenance methyltransferase

Question 12

What is de novo methylation?

Answer 12

CG are not always methylated

Unmethylatd pairs can become methylated by de novo methyltransferase

Question 13

What is master gene regulator?

Answer 13

Are kind of transcription factor

Regulate transcription of whole set of lineage specific genes for given cell type

Question 14

Give an example of master gene regulator

Answer 14

MYOD(myogenic differentiation) in skeletal muscle can activate a program of muscle specific genes

Question 15

Mature differentiated cell types have 3 main division patterns

Answer 15

1) Cells may divide very little but can divide to repair damage
2) Cells that cannot divide= terminal differentiation. Some are not replaced when lost
3) Terminally differentiated cells may be constantly replaced by division of precursor cells called somatic stem cells

Question 16

Are there any diseases of cell differentiation?

Answer 16

Some uncommon non-lethal birth defects such as:
Aniridia= lack of iris of eye due to mutation in TF PAX6
Congenital anaemia
Thrombocytopenia= platelet deficiency due to mutation in TF GATA-1 needed for differentiation of erythrocytes and platelets

Question 17

What is a household gene?

Answer 17

Gene expressed in all or nearly all cell types

Question 18

What is luxury gene?

Answer 18

Gene expressed in only one or few cell types

Question 19

What is a precursor/ progenitor?

Answer 19

Any immature cell type able to differentiate into another cell types

Question 20

What is transit cell?

Answer 20

A cell that is undergoing terminal differentiation towards functional cell type but is still itself able to divide