Lecture 26

Question 1

Cells come in different forms:

Answer 1

• Size (2 - 3cm, 200 microns)
• Shape (highly structured, maintained by the cell wall in plants)
• Specificity (different types for different things, in different organisms, differing levels of complexity)

Question 2

Stem cells:

Answer 2

• Totipotent: can differentiate into anything
• Pluripotent: more limited, but still many possibilities
• Blood stem cells: will turn into some form of a blood cell
• Other stem cells: create muscle, nerves, bones etc

Question 3

Liver regeneration:

Answer 3

• A rat liver can regenerate itself, if part of a liver is chopped off, but will stop at a certain size so that the liver doesn’t take over the body
• The degree of regeneration varies across the kingdom of life

Question 4

Cell cycle:

Answer 4

• Cell growth occurs through chromosome duplication via mitosis
• Chromosomes duplicate, chromosomes segregate
• Cytokenesis: cells separate
• Interphase: the nucleus is present, gene activity and cellular metabolism
• Prophase: chromosomes become visible
• Prometaphase
• Metaphase: there is little gene activity as chromosomes are condensed, chromosomes duplicate
• Anapase: chromosomes separate
• Telophase

Question 5

Yeast: sachromyces cerevisiae:

Answer 5

• Budding yeast, a new daughter cell grows from the mother cell
• During cell division everything within the cell are duplicated (endosomes, ribosomes, nucelus etc)

Question 6

Yeast: pombe:

Answer 6

• Divide by fission

- Once the cell reaches a certain size a septum forms and the cells divide

Question 7

Cell growth:

Answer 7

• Cell growth is different from cell division
• G1: gap phase, the beginning of the cycle
• S: replication
• G2: mitosis,
• M:
• Cell division without growth means there is no G1 or G2 phase
• Must be an ordered process

Question 8

Cell signals promote either cell growth or cell division:

Answer 8

• Cell growth and cell division can occur simultaneously, separately or consecutively, depending on the signal they receive from growth factors, mitogens and external factors

Question 9

Growth gives shape, how?

Answer 9

• Growth in all directions are created by even growth (yeast growth)
• Hyphal growth occurs from one end (polarised growth)
• These two growth mechanisms can occur in different and in the same organisms (dimorphic organisms)

Question 10

Example of mitosis (cell division) without cell growth:

Answer 10

• In amphibians the oocyte grows without dividing until fertilization
• After fertilisation the cell divides without growth for some time

Question 11

Apoptosis:

Answer 11

• Some cells are destined to die
• The nucleus condenses and the cell is devoured by surrounding cells
• This is a response to cell damage or normal development (ie, digit formation in the human embryo)

Question 12

cdc mutants in S. cerevisiae:

Answer 12

• cell cycle mutants

Question 13

Wee-1 gene:

Answer 13

• leads to very small cells

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Question 14

Cell cycle, M phase:

Answer 14

• Mitosis is at the start and is nuclear division
• Is all DNA replicated?
• Is the environment stable?
• G2/M checkpoint
• Are all chromosomes attached to the spindle?
• Metaphase to anaphase transition, anaphase is triggered and the cell proceeds to cytokinesis (cell division)

Question 15

Cell cycle, G1 phase:

Answer 15

• Is the cell cycle ready to be entered?
• Start checkpoint
• Is the environment favourable?

Question 16

S phase:

Answer 16

• Mitosis occurs, nuclear separation occurs here

Question 17

G2 phase:

Answer 17

• At the end we went mitosis, so we check if the cell is ready to divide
• Is the DNA properly replicted?
• Is the environment

Question 18

The discovery of cyclins:

Answer 18

• Cyclin’s are key molecules in the cell cycle
• In amphibians like frogs there are huge eggs.
• Cell division can be synchronised by synchronising fertilisation with sperm
• ## Proteins at different levels of the cell cycle can be determines

Question 19

MFP:

Answer 19

• Mitosis promoting factor
• A cyclin plus cyclin dependent kinase
• This protein activity peaks at cell division in the middle of mitosis- This can be added to cells to stimulate mitosis

Question 20

Cyclins:

Answer 20

• Proteins that are synthesised and degraded throughout the cell cycle
• Cyclin is a kinase dependent on the presence of Cdk
• Cdk enzymes are inactive until bound by a cyclin, Cdk-activation kinase (CAK) makes it fully active by phosphorylation
• Activity is regulated by the presence of cyclins

Question 21

The activity of Cdks is dependent on what?

Answer 21

• The activity and specificity of Cdk is dependent on what type of cylin has phosphorylated the Cdk enzyme
• Different stages of the cell cycle have different cyclins present, so a different substrate protein acts at each state