Cell differentiation and gene expression

Question 1

Differentiation

Answer 1

The production of many cell types within an organism

A stable, complex change

Question 2

Determination

Answer 2

The stability of cell differentiation even after the end of any induced signal

Transmitted to daughter cells after division

Question 3

Cell lineage

Answer 3

Differentiation occurs in steps

At each step an immature cell type such as a precursor changes into a more mature cell type and this still may be a type of precursor 

The series of cell types evolving from a zygote to a mature cell type = lineage

Question 4

Branches

Answer 4

Particular precursors can divide into more than one daughter cell types (pluripotent)

Branches don’t represent cell division, just the possibilities of types of daughter cells that can be formed from precursor cells

Question 5

Gene expression

Answer 5

Different cell types express different genes

The whole process leading to the synthesis of the final product of the gene: 

Protein 

Functional RNAs 

Include processes like transcription and translation

Question 6

Modulation

Answer 6

Simple reversible change in gene expression, with no change in cell type

Also known as adaptation 

Temporary substitution

Question 7

Differentiation vs modulation

Answer 7

Differentiation:

Stable 

Complex change 

Modulation: 

Temporary  

Simple change 

Both involve gene expression

Question 8

Dolly the sheep

Answer 8

Differentiated mammary epithelial sheep cell fused into cytoplasm of sheep ococyte

Fused cell divided many times and proliferated forming an embryo 

Put in the uterus of an ewe 

Embryo had all the genes for a whole sheep 

Dolly was also fertile

Question 9

Differentiation

Answer 9

During one step of lineage, multiple genes that determine cell type are activated during expression while others are repressed

Program of differentiation: new gene expression pattern 

The program is largely controlled during mRNA transcription

Question 10

Differential transcription

Answer 10

Detected by using individual probes by RNA-seq

Reveals the differences in RNA between 2 cell types

Question 11

Control of transcription (Chromatin remodeling)

Answer 11

Euchromatin (open conformation)

Heterochromatin (coiled and folded) 

Folding interferes with transcription, as transcription machinery cannot access DNA 

Different cell types of different sections of genome are translated so gene expression varies

Question 12

Control of transcription (methylation)

Answer 12

Increases heterochromatin

A methyl group binds to a cytosine (in a CpG) becoming methylcytosine 

This is copied onto the opposite strand by maintenance methyl transferase  

DNA methylation occurs in whole stretches rich in CpG pairs 

Methylation causes folding of chromatin 

De nova methylation: 

CpG pairs are not always methylated  

Unmethylated pairs can become methylated by a de nova methyltransferase

Question 13

Specific transcriptional regulation of individual genes

Answer 13

Different genes are activated by different transcription factors (depending on binding elements)

Different cell types express different ranges of transcription factors  

So each cell transcribes in nearly all cell types

Question 14

Master gene regulators

Answer 14

A transcription factor that regulates transcription of a whole set of lineage specific genes, like a program

Question 15

Cancer

Answer 15

Cancer is not caused by faulty differentiation

However differentiation is often deficient in cancer cells 

Tumour cells look like precursors

Question 16

Defects from differentiation

Answer 16

Aniridia is the lack of the iris of the eye due to a mutation in the transcription factor PAX6

Thrombocytopenia is a platelet deficiency due to a mutation of GATA-1 which is needed for the differentiation of platele