Mitotic Cell Cycle & Stem Cells

Question 1

Events of mitotic cell cycle

Answer 1

Interphase: G1, S, G2,
Mitosis

Question 2

What occurs during interphase ?

Answer 2

G1: cell synthesis organelles such as mitochondria and ribosomes. Manufacture proteins. Builds up large store of energy.

S: DNA replication. Centrosome duplicated

G2: cell continues to store energy and manufacture organelles and proteins

Question 3

What is a centrosome ?

Answer 3

Nonmembranous organelles found only in animal cell.
Function as the microtubule organising centre (MTOC) to organise th cels microtubule through the cell cycle.

Question 4

What are centrioles ?

Answer 4

Centrioles is where microtubule extend from, forming spindle fibres.
Some spindle fibres attach to the kinetochore of the chromosome forming kinetochore microtubules.

Question 5

What protein makes up spindle fibres ?

Answer 5

Tubulin

Question 6

Outline prophase

Answer 6

Behaviour of chromosomes:
- Chromatin condense into chromsomes (making it visible under light microscope)
- Centrosome moves to opposite ends of the cell developing a pair of centrioles.

Behaviours of nuclear envelope:
- Nucleolus disappears
- nuclear envelope disintegrates

Behaviour of centrioles:
- microtubules extend from centrioles to form spindle fibres
- kinetochore assembles at centromere of chromosome
- some spindle fibres attach to kinetochore

Question 7

Outline metaphase

Answer 7

Behaviour of chromosomes
- chromosomes align on the metaphase plate

Question 8

Outline anaphase

Answer 8

Behaviour of chromsome
- Centrosome of each chromosome divides and two sister chromatids separates
- daughter chromosome formed
- daughter chromosome move to opposite poles of the spindle as kinetochore microtubules shorten

Cell elongates as the non kinetochore microtubules lengthen

Question 8

Outline telophase

Answer 8

Behaviour of chromsomes;
- chromosome uncoil into chromatin

Behaviours of centrioles:
Spindle fibres disintegrate

Behaviour of nuclear ecnelope:
- reforms around chromosome at each pole
- nucleolus reappears

Question 10

Outline cytokinesis in animal cells

Answer 10

• cleavage furrow developed in cell membrane, eventually joining up and separating 2 daughter nuclei

Question 11

Outline cytokinesis in plant cells

Answer 11

• Series of golgi vesicles line in middle of parent cell and fuse to firm cell plate.
• Content of golgi vesicles contributes to the cell wall. Membrane of golgi vesicles form cell membrane.
• cell plate fuse with parent cell separating 2 daughter nuclei

Question 12

Significance of Mitosis

Answer 12

Ensures 2 daughter nuclei formed contained genetically identical sets of chromosomes so that daughter cell is genetically identical to parent cell after cytokinesis.

Maintains genetic stability
- growth, single cell to multicellular organism
- repair
- asexual reproduction

Question 13

Whatn are the Cell cycle checkpoints

Answer 13

G1
G2
M

Question 14

What is Checked at G1 checkpoint ?

Answer 14

Size of cell
Nutrients availability
DNA integrity
Appropriate growth signals

Question 15

What is checked at G2 checkpoint ?

Answer 15

DNA integrity and replication

DNA damage —> stall for repair
DNA damage beyond repair —> p53 triggers cell to undergo apoptosis

Question 16

What is called at M checkpoint ?

Answer 16

All chromsomes attached to spindle fibres
Proper tension on paired kinetochores

Question 17

What are the unique features of stem cells ?

Answer 17

1. unspecialised cells
2. able to differentiate into various cell types under certain conditions to form
   specialised cells
3. capable of dividing and renewing themselves (self-renewal) for long periods via
   mitotic divisions

Question 18

What is differentiation of stem cells ?

Answer 18

Stem cells do not have tissue-specific strictures that allow it to perform superfic functions.

Question 19

What are levels of potency ?

Answer 19

Totipotent: diff to any cell type for form a whole organism

Pluripotent: diff into almost any cell type to form any organ

Multipotent: give rise to limited range of cellls and tissues appropriate to their location

Unipotent: give rise to only one type of cell

Question 20

Example of diff potency level

Answer 20

Toti: zygotic stem cells

Pluri: embryonic stem cells

Multi: adult stem cells

Question 21

Sugggest how a cell differentiates to firm a specialised cell

Answer 21

1. Receives signal to switch on certain sets of genes ad switch off other sets of gens
2. Result in different proteins being produced giving rise to different tissue-specific structures

Question 22

Ethical implications of stem cells research

Answer 22

1. Human embryonic stem cellls require destruction of the embryo. Some believe that an embryo has the same moral status as live-born human, which interest ad rights that must be respected. Hence derstruction of the embryo is tantamount to murder
2. Donors of the coyotes or embryos may not uave consented for theirs to be used for research
3. Underlying medical completions and risks exist regardless whether donors are fully informed of them

Question 23

What are the major sources of blood stem cells

Answer 23

Bone marrow
Umbilical cord

Question 24

Pros and cons of using umbilical cord stem cells for treating diseases in the same individual

Answer 24

Pro: 1. No foreign antigens on cell membrane hence recipients immune system will not reject 2. Can be converted into specialised cells to treats specific diseases Cons: 1. Storage capacity limited and high costs involved 2. Freezer failure cause ells to be damaged or mutated

Question 25

Why do stem cells harvested from burn patients skin need to be treated with chemicals to stimulate proliferation

Answer 25

1. When stem cells are removed from skin, there are no natural growth hormones to stimulate cell division. 2. Addition of chemicals is necessary to stimulate cell division by binding to cell receptors and stimulating cell division

Question 26

Why is it important that scientist ensure high telomerase activities in the iPS cells ?

Answer 26

1. iPS cells need to undergo continuous cell division 2. Telomerase must be present to elongate the telomeres which are shortened after every round of cell division 3. This maintains telomere length to prevent loss of genes through erosion at chromosomal ends

Question 27

Describe role of centromeres:

Answer 27

1. Attach sister chromatids together 2. Site of kinetichore assembly, allowing spidle fibres to attach 3. Alllow separation of homologous chromsomes or sister chromatids