Lecture 26 Flashcards
1
Q
Cells come in different forms:
A
- 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)
2
Q
Stem cells:
A
- 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
3
Q
Liver regeneration:
A
- 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
4
Q
Cell cycle:
A
- 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
5
Q
Yeast: sachromyces cerevisiae:
A
- Budding yeast, a new daughter cell grows from the mother cell
- During cell division everything within the cell are duplicated (endosomes, ribosomes, nucelus etc)
6
Q
Yeast: pombe:
A
- Divide by fission
- Once the cell reaches a certain size a septum forms and the cells divide
7
Q
Cell growth:
A
- 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
8
Q
Cell signals promote either cell growth or cell division:
A
- Cell growth and cell division can occur simultaneously, separately or consecutively, depending on the signal they receive from growth factors, mitogens and external factors
9
Q
Growth gives shape, how?
A
- 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)
10
Q
Example of mitosis (cell division) without cell growth:
A
- In amphibians the oocyte grows without dividing until fertilization
- After fertilisation the cell divides without growth for some time
11
Q
Apoptosis:
A
- 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)
12
Q
cdc mutants in S. cerevisiae:
A
- cell cycle mutants
13
Q
Wee-1 gene:
A
- leads to very small cells
-
14
Q
Cell cycle, M phase:
A
- 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)
15
Q
Cell cycle, G1 phase:
A
- Is the cell cycle ready to be entered?
- Start checkpoint
- Is the environment favourable?
16
Q
S phase:
A
- Mitosis occurs, nuclear separation occurs here
17
Q
G2 phase:
A
- At the end we went mitosis, so we check if the cell is ready to divide
- Is the DNA properly replicted?
- Is the environment
18
Q
The discovery of cyclins:
A
- 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
19
Q
MFP:
A
- 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
20
Q
Cyclins:
A
- 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
21
Q
The activity of Cdks is dependent on what?
A
- 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
