Lecture 26 Flashcards Preview

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Flashcards in Lecture 26 Deck (21):

Cells come in different forms:

- 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)


Stem cells:

- 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


Liver regeneration:

- 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


Cell cycle:

- 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


Yeast: sachromyces cerevisiae:

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


Yeast: pombe:

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


Cell growth:

- 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


Cell signals promote either cell growth or cell division:

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


Growth gives shape, how?

- 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)


Example of mitosis (cell division) without cell growth:

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



- 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)


cdc mutants in S. cerevisiae:

- cell cycle mutants


Wee-1 gene:

- leads to very small cells


Cell cycle, M phase:

- 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)


Cell cycle, G1 phase:

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


S phase:

- Mitosis occurs, nuclear separation occurs here


G2 phase:

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


The discovery of cyclins:

- 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



- 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



- 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


The activity of Cdks is dependent on what?

- 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