Cell Differentiation & Gene Expression

Question 1

what is cell differentiation?

Answer 1

the process where cells undergo changes in gene expression and activity to specialise and take on specific roles in an organism

Question 2

what are stem cells?

Answer 2

• undifferentiated, unspecialised cells of the human body
• have the ability to differentiate into many cells
• ability to renew themselves by mitosis

Question 3

what are the types of stem cells?

Answer 3

• totipotent
• pluripotent
• multipotent
• unipotent

Question 4

describe totipotent cells and where are they found

Answer 4

• can differentiate into every single cell type (embryonic and non-embryonic)
• zygotes

Question 5

describe pluripotent cells and where they are found

Answer 5

• can differentiate into most cells but not embryonic cells

- cells in blastocyst

Question 6

what can multipoint cells differentiate into? where are they fund

Answer 6

• the can differentiate into limited types

- mesenchymal cells and and adult stem cells

Question 7

what re unipotent cells and give an example

Answer 7

• can only differentiate into one type of cell

- dermacytes

Question 8

what is the difference between differentiations and modulation?

Answer 8

differentiation : a stable complex change

modulation : a temporary simple change

Question 9

what are the two stem cell theories?

Answer 9

1) assymetric division: suggests that one stem cell produces one differentiated cell and one stem cell
2) symmetric division: either they produce two stem cells or two differentiated cells

Question 10

give an example of a pluripotent stem cell

Answer 10

• embryonic stem cells
• derived from 4-5 day old embryo in blastocyst phase
• shown to be transiently existing cells

Question 11

give an example of multipoint stem cells

Answer 11

• adult stem cells
• they are tissue specific, depending on their niche
• their purpose is to replace dead cells

Question 12

how does methylation occur?

Answer 12

• strands are separated and there is new strand synthesis, each methyl group gets separated.
• new strand synthesis happens and there are two new strands which are unmethylated
• maintenance methyltransferase adds new methyl groups onto the daughter strands.
• this is how the methylation pattern is remembered in daughter cells.

Question 13

where does DNA methylation occur and why?

Answer 13

DNA methylation occurs in stretches of DNA that are rich in CpG pairs which coincide with the promoter regions.

Question 14

how can unmethylated CpG pairs become methylated?

Answer 14

CpG pairs are not always methylated, unmethylated pairs can become methylated during gamete formation and this is done by de novo methyltransferase.

Question 15

what effect does methylation have and give an example of a gene that is mostly methylated and why

Answer 15

-increasing folding and silencing the gene.

• globin genes are only needed to make haemoglobin so these genes are methylated in all other cell types of the body
• the transcriptional machinery cannot access it.

Question 16

what is the difference between a promoter and an enhancer?

Answer 16

• enhancer increases the level of transcription of a gene

- promoter initiates transcription of a gene.

Question 17

what are master gene regulators?

Answer 17

regulate transcription of a whole set of lineage-specific genes (a ‘program’) for a given cell type.

Question 18

how do master gene regulators work?

Answer 18

• transcription of the gene for the master gene regulator occurs
• creating the regulatory proteins
• these proteins then bind to and activate the promoters of different genes coding for proteins that will differentiate the cell.
• these specialised proteins are made, and then proceed to work on the cell.

Question 19

what are some non lethal birth defects due to differentiation?

Answer 19

• aniridia - lack of the iris due to a mutation in PAX6
• congenital anaemia and thrombocytopenia (platelet deficiency) due to a mutation in a transcription factor called GATA 1

Question 20

how did the dolly the sheep experiment prove that all differentiated cells have the complete genome not just the genes they require?

Answer 20

a differentiated epithelial cell of the sheep was fused to the cytoplasm of the sheep oocyte and the cell proliferated to form an embryo. The differentiated cell had all the genes needed to form a sheep