W4 Cell diff. + GE

Question 1

Cell differentiation

Answer 1

The production of different cell types within an organism. Also each step in the lineage

Question 2

Determination

Answer 2

The stability of cell differentiation even after the end of any inducing signal
Transmitted to daughter cells after division
Depends on cells environment

Question 3

Cell lineage

Answer 3

The series of successive cell types leading from the zygote to a particular mature cell type

Lineages can branch if precursor able to differentiate into more than one daughter cell type (branches do not represent cell division)

Question 4

Somite

Answer 4

Blocks of cells that are related to segments of evolutionary precursors
Each segment in embryo = somite

Question 5

Modulation

Answer 5

A simple, reversible change in gene expression, with no change in cell type

Example:
Upregulation of alcohol dehydrogenase in liver cells to detoxify alcohol to allow recovery

Question 6

Household gene

Answer 6

Gene expressed in all or nearly all cell types, e.g. tubulin

Question 7

Dolly the sheep

Answer 7

A whole differentiated (mammary epithelial) sheep cell was fused to the cytoplasm of a sheep oocyte (egg cell - big cell repeated a lot of times).
The resulting cell proliferated to form a whole early embryo, which was implanted in the uterus of a ewe and resulted in Dolly (born 1996)
Thus the differentiated mammary cell had all the genes needed to form a whole sheep
Dolly was also fertile

Question 8

Maturing lymphocytes

Answer 8

Lose DNA segments in generating immunoglobulin diversity as they make many different immunoglobin. So these are cells that do not contain all of human genome.

Question 9

Differential transcription

Answer 9

Detected by using individual “probes” (Synthetic DNA with a known sequence, complementary to the sequence you are looking for), or by microarrays or RNA-seq , (all mRNA in cell) which can test for thousands of RNA sequences at once.
This reveals many mRNA differences between any 2 cell types

Question 10

Chromatin remodelling

Answer 10

How DNA folded so the conformation of whole DNA in that area of a CS
Euchromatin (open + in use)
Heterochromatin (Folded + not in use + coiled)

Transcriptional machinery can’t access when coiled + folded

Question 11

Methylation

Answer 11

Methylation of a gene (especially its promoter or control sequence) has the effect of increasing folding and silencing transcription
Chemical change to DNA done by an enzyme

Question 12

Methylation process

Answer 12

Occurs on cytosine within a “CpG” pair (=CG). Cytosine converted to methylcytosine.
Copied to opposite strand (also CpG) by a maintenance methyltransferase
So at DNA replication we get the methylation copied so methylation pattern “remembered” (not all DNA sequence transmitted to daughter cells + also called plasma methylation)

DNA methylation tends to occur in whole stretches, rich in CpG pairs. (Coincide w/promoters of genes)
This methylated DNA becomes highly folded (heterochromatic).

Question 13

De novo methylation

Answer 13

CpG pairs not always methylated
Unmethylated pairs can become methylated (during cell differentiation, including gamete formation)
By a de novo methyltransferase
Directed by cations so can methylate the right cytosine

Question 14

Transcription factor

Answer 14

A regulator of transcription + a protein (often a dimer or multimer) that fits physically on to a specific DNA sequence

Question 15

Promoter

Answer 15

A regulatory region of DNA, 5’ or “upstream” of the start site for transcription of a gene. Regulates transcription of that gene by binding certain transcription factors

Question 16

Master gene regulators

Answer 16

A kind of transcription factor
that regulates transcription of a whole set of lineage-specific genes (a “program”) for a given cell type
e.g. MYOD (Myogenic Differentiation) in skeletal muscle – can activate a program of muscle-specific genes

Question 17

Mature, differentiated cell types patterns

Answer 17

Cells may divide very little but can divide to repair damage (e.g. endothelium, liver)
Cells that cannot divide - terminal differentiation. Some are not replaced when lost (e.g. neurons, lens)
Terminally differentiated cells may be constantly replaced by division of precursor cells called somatic stem cells (e.g. in bone marrow, gut epithelium, epidermis)

Question 18

Diseases of cell differentiation

Answer 18

Defects of differentiation are often lethal. But there are some (uncommon) non-lethal birth defects where differentiation of a particular cell type is affected E.g.:
Aniridia – lack of the iris of the eye, due to a mutation in the transcription factor PAX6

Congenital anaemia and thrombocytopenia (platelet deficiency), due to a mutation in transcription factor GATA1, needed for differentiation of erythrocytes and platelets

Question 19

Gene expression

Answer 19

Synthesis of the product of a given gene – a protein or a functional RNAs like a tRNA Involves transcription and (for proteins) translation

Question 20

Luxury gene

Answer 20

A gene expressed in only one or a few cell types

Question 21

Precursor or progenitor

Answer 21

Any immature cell type able to differentiate into another cell type(s)

Question 22

Terminal differentiation

Answer 22

Production of a mature functional cell type that cannot divide (e.g. neurons, skeletal muscle, granulocytes)

Question 23

Totipotent

Answer 23

Able to produce all cell types of both the body and the extra-embryonic parts (placenta, membranes)

Question 24

Transit cell

Answer 24

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