Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Year 2 - Cancer > Cell cycle and control > Flashcards

Cell cycle and control Flashcards

1
Q

What factors influence the rate at which a cell needs to divide?

A
  1. Embryonic cells divide at a much faster rate than adult cells (early frog embryo cells: 30 min)
  2. Complexity of systems: a less complex system will divide more rapidly (yeast cells: 1.5-3 hours)
  3. Necessity for renewal: in the body, certain cell types must divide more rapidly to replenish lost cells e.g.
    intestinal epithelial cells are shed very often so need quick replenishment: 20 hours but hepatocytes don’t need frequent renewal: 1 year
  4. State of differentiation: some cells never divide – such as neurones and cardiac myocytes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why must cell division be properly controlled?

What is abnormal in cancers in terms of proteins, chromosomes etc?

A
  • Premature, aberrant mitosis will result in cell death
  • In addition to mutations in oncogenes and tumour suppressor genes, most solid tumours are aneuploid
  • Various cancer cell lines show chromosome instability (lose/gain whole chromosomes during division)
  • Cell cycle regulators are either at higher or lower levels in different tumours
  • Normal cells have contact inhibition of growth – cells grow by sensing neighbouring cells (tumours lose this)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the cell cycle?

A
  • The cell cycle is an orderly sequence of events in which a cell duplicates its contents and divides in two.
  • It involves both duplication and division: cells cannot divide before they duplicate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the 2 main processes in a cell cycle?

A

interphase and mitosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the different phases in mitosis?

A

prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What happens in mitosis and what happens in interphase?

A
  • Interphase (duplication): DNA, organelles, protein synthesis
  • Mitosis (division): Nuclear division, cell division (cytokinesis)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the most vulnerable period in the cell cycle and why?

A
  • Mitosis: very important but vulnerable so has to occur very fast
  • Cells are more easily killed during mitosis (manipulated clinically: irradiation, heat shock, chemicals)
  • DNA damage occurring during mitosis cannot be repaired -> mutation may be carried over in DNA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are some things which happen during mitosis to the cell functioning?

A
  • Gene transcription is silenced

- There is a slow down in the metabolism of the cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the stages of interphase and what happens is them?

A

G0: cells are resting here, cycle cycle machinery is dismantled, just doing normal functions such as secretion etc

G1: Cells decide to divide, decision point

S: DNA and protein synthesis occurs, everything is duplicated

G2: Cell is checked, it is another decision point, everything must be fine to progress to mitosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What happens in the S phase?

A
  • DNA replication
  • Protein synthesis: initiation of translational proteins, and elongation is increased
  • Capacity for translation is also increased
  • Replication of organelles must take place (centrosomes, mitochondria, Golgi, etc.)
  • Mitochondria DNA replication must be coordinated with the nuclear DNA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the centrosome?

A

Consists of 2 centrioles (barrels of 9 triplet microtubules)

There is a mother and daughter centriole and they align at 180 degrees

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the 2 functions of the centrosome?

A
  • Microtubule organising centre (MTOC) Controls the polymerisation of microtubules
  • Coordinate the mitotic spindle
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why are centrosomes important?

A

Because they are the organiser of a highway, in which the chromosomes will slide around the cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What happens in G1 to the centrosome?

A

It separates into the mother and daughter centriole as normally they are stuck together.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What happens to the centrioles in the S phase?

A

They duplicate - they mother produces a daughter and the daughter produces a mother

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What happens once the centrioles have duplicated?

A

They start to organise the microtubules which should occur before mitotic phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What do the centrosomes have around them?
What is nucleation?
What are nucleating sites?

A
  • There is a cloud of protein complexes around them
  • There are points on them where they make nucleating sites for the microtubules
  • When you put tubulins together to make microtubules it is called nucleation
  • As the cell encounters a need for mitosis, the microtubules start to grow from these points and form an array of microtubules (looks like a sea urchin)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How is DNA condensed into chromosomes - what is the arrangement?

A

DNA strand -> wrapped around beads to form beads on a string (involving histone proteins) -> further compaction and folding-> chromosome scaffold -> scaffold condenses and folds -> eventually becomes a chromosome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What happens in prophase?

A
  • In prophase, the cell must protect the chromosomes against breakage
  • This is why DNA must be packed up and compacted into chromosomes (condensed)
  • The centrosome has been duplicated by late prophase
  • During late prophase, the nuclear envelope breaks down and by doing so, the chromosomes come out into the cytoplasm
  • As the nuclear envelope breaks down, the centrosomes migrate to opposite sides
  • They then begin to organise the spindle
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Describe how the DNA is condensed in terms of size changing at each stage

A
  • The double helices are wrapped around histones to forms ‘beads-on-a-string’ form of chromatin: DNA goes from being 2 nm wide to 11 nm wide
  • The string is then further wrapped around itself to form 30 nm wide fibres
  • The 30 nm fibres are then extended as a scaffold forming a chromosome scaffold – 300 nm
  • Further folding and it become 700 nm
  • Chromosome is 1400 nm
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Describe the structure of a chromosome at prophase - what is the centromere and kinetochore?

A
  • Each consists of 2 sister chromatids, with a centromere and each with a kinetochore
  • The centromere is a constriction around the chromosome, acting like a belt
  • The kinetochore is a lot of protein complexes around the centromere
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the importance of the kinetochore?

A

IS A FUNCTIONAL UNIT FOR THE SEGREGATION OF THE CHROMOSOMES.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are the two types of microtubules?

A

Radial microtubule arrays (asters): These form around each centrosome. As soon as the nucleus starts to break down, they start to form around the MTOC

Polar microtubules: When the nucleus breaks down, the radial arrays still grow and they meet in the middle. They hook to each other in the opposite direction. These are then called polar microtubules - they form to stabilise structures.

24
Q

What happens in metaphase?

A

Chromosomes align at the equator of the spindle.

25
Q

What is prometaphase made of?

A

Early and late prometaphase

26
Q

What happens in early prometaphase?

A
  • Breakdown of nuclear membrane is finalised
  • Spindle formation is largely complete
  • Attachment of chromosomes to spindle via kinetochores
  • One microtubule array will attach to the kinetochore on one side, and another microtubule array will attach on the other side
27
Q

What happens in late prometaphase?

A
  • Chromosomes attached to each pole congress to the middle
  • Chromosome slides rapidly towards centre along microtubules
  • ## In the kinetochores there are specialised proteins, which sense the attachment of microtubules
28
Q

What is CENP-E?

A

CENP-E = centromere protein E (kinetochore tension sensing)

it senses whether the kinetochore is attached to microtubules or not

29
Q

What can anaphase be split into?

A

A and B

30
Q

What happens in anaphase A?

A
  • Cohesin is broken down and the microtubules get shorter (cohesin is a protein complex holding to sister chromatids together)
  • The chromatids start moving towards the centrosomes
  • The daughter chromatids are pulled towards opposite spindle poles
31
Q

What happens in anaphase B?

A

The daughter chromosomes can reach the opposite poles by two methods:

  • Due to the shortening of the microtubules that form the spindles
  • By the spindle poles migrate away from each other pulling the chromatids with them
32
Q

What happens in telophase?

What is the cleavage furrow?

A
  • Daughter chromosomes arrive at the pole
  • Nuclear envelope reassembles at each pole
  • Cells try to revert to their normal size
  • You get the assembly of a contractile ring of actin and myosin filaments
  • The contractile ring squeezes the cell so that it divides into 2 daughter cells
  • The cleavage furrow is where the cells are going to be cleaved
33
Q

What is cytokinesis?

What is the midbody?

A

Cells dividing - they round up
Once the cells divide you can see where the cells were once joined (this piece is called the midbody. With time membrane is inserted here and cells become completely separated. The midbody is where is the actin and myosin ring was formed - a connection between the two cells.

34
Q

Why are the checkpoints in spindle assembly?

A

The cells have to ensure that each duplicated chromosome is attached to the microtubules. Unless this is the case, the cell division cannot progress to anaphase.

35
Q

What is checked for during the spindle assembly checkpoints? How is this done?

A
  • Senses the completion of chromosome alignment and also checks for spindle assembly
  • The kinetochore has proteins that emit a signal when the kinetochore is not attached to microtubules, once the kinetochore attaches to microtubules, it stops emitting the signal
  • At metaphase, when all the kinetochores will stop sending signals, the cell can proceed to anaphase
36
Q

What are the kinetochore signalling proteins?

A

CENP-E

BUB Protein Kinase (BUBs dissociate from the kinetochore when chromatids are properly attached to the spindle. When all dissociated, they go on to signal progression to anaphase

37
Q

What is normal chromosome attachment to the microtubules?

A

Normally, you have a chromosome made up of 2 sister chromatids. There is normal attachment (amphelic attachment), where the microtubule array of one centrosome is attached to the kinetochore of one sister chromatid, and the microtubule array of another centrosome is attached to the kinetochore of the other chromatid. This type of attachment will allow the sister chromatids to be split apart and go to opposite poles.

38
Q

What are some abnormal microtubule attachments that can result in aneuploidy?

A

Syntelic Attachment: both the kinetochores are hooked by two microtubule arrays from the same centrosome

Merotelic Attachment: there is more than one microtubule array attached to the same kinetochore – this means that one of the chromatids is being pulled in two different directions

Monotelic Attachment: only one of the kinetochores of one chromatid is attached to a microtubule array, the other kinetochore is unattached

39
Q

What happens if a cell loses both chromosomes?

A

it will die

40
Q

How may aneuploidy occur due to defects in centrosome and DNA replication?

A
  • You can also have aberrant centrosome or DNA duplication

The centrosome is meant to duplicate only once, and then separates to the two pole. If this duplication is defective, there may be a situation in which you end up with 4 centrosomes. This can lead to very abnormal attachment of the microtubule arrays to the kinetochores leading to abnormal cytokinesis, When the cells divide, the result is 4 daughter cells

There can also be a situation where there is over-replication of the DNA. You end up with aberrant cytokinesis, where there are two normal daughter cells, two cells with a single chromosome, and one cell without ANY chromosome.

41
Q

What can be targetting to reduce tumour cell proliferation?

A
  • One mechanism of cancer therapy is exploiting checkpoint control
  • The kinetochore signalling tells the cell when metaphase is complete so if you have an inhibitor for this checkpoint, you can make the nucleus think that it is correctly hooked onto microtubules and it will move to anaphase and as it isn’t ready to divide will die
42
Q

Which checkpoints are targetted and what is done?

A

Checkpoint kinase (CHKE1 and CHKE2) – serine threonine kinase.

Activation of this kinase holds cells in G2 phase until all is ready. Inhibition of these checkpoint kinases leads to untimely cell transition to mitosis.

The cell thinks that everything is aligned, so anaphase takes place -> loss of chromosomes and cell death in tumour cells

43
Q

What are the 2 things that can happen if there are errors in the cell cycle?

A
  1. Cell cycle arrest
    - This usually happens at the checkpoints (G1 and spindle check point)
    - This may be due to the detection of DNA damage
    - Can be temporary
  2. Programmed cell death (apoptosis) – if something is very wrong in the cell
    - DNA damage is too great and cannot be repaired (or if damage is irreversible)
    - Chromosomal abnormalities
    - Toxic agents
44
Q

Where are the checkpoints in the interphase and mitosis?

A
  • G1 and G2

- There is an anaphase-metaphase checkpoint

45
Q

What do tumours do at checkpoints?

A
  • Tumours develop means by which they can bypass these checkpoints
  • Tumours exploit the first checkpoint by hyper-activating growth factors
  • Tumours can also block the DNA damage machinery, inducing cells to enter mitosis when they shouldn’t
  • During tumorigenesis, tumours can also operate at the exit of the cell cycle. When the cells divide, they pause and enter the G0 phase. Tumour cells can block this so once cells exit mitosis, the cycle is initiated again to continue cell division
46
Q

What can tumours do following mitosis that leads to hyperproliferation?

A

When normal cells divide, they pause and enter the G0 phase. Tumour cells can block this so once cells exit mitosis, the cycle is initiated again to continue cell division

47
Q

What triggers a cell to enter the cell cycle and divide?

A
  • In the absence of a stimulus, cells go into G0 (quiescent phase)
  • The exit from G0 is highly regulated, and requires growth factors and intracellular signalling cascades
  • The signalling cascades convey the message to the cell that the should divide
48
Q

What do signalling cascades involve?

A
  • Response to extracellular factors
  • Signal amplification
  • Signal integration
  • Modulation (via other pathways)
  • Regulation of responses.
49
Q

Give examples of ligands that bind and activate receptors that are involved in cell signalling

A
  • Epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) both signal through their respective receptor protein tyrosine kinases
  • They are dimeric ligands
  • Respective receptors are monomeric and found in the inactive state
50
Q

What happens when EGF and PDGF bind to their receptors?

A

The intracellular domain will be linked to a kinase domain

  • When the dimeric ligand binds, it induces dimerization of the monomeric receptors
  • This is the signalling unit– dimerization activates the kinase domain (inside the cell)
  • There is cross-phosphorylation of receptors due to kinase domains being brought close together
  • We see phosphorylated amino acid residues in the kinase domain -> activation and they can affect other proteins in the cell
51
Q

How does the protein kinase domain phsophorylate?

A
  • The protein kinase picks up an ATP and transfers a phosphate group to the hydroxyl group (ATP -> ADP)
  • The serine is phosphorylated – this phosphorylation is a signalling trigger
  • This is reversed by protein phosphatases (they remove phosphate groups to restore the OH group)
52
Q

What are the two types of kinases?

A
  • One type can phosphorylate serine and threonine residues

- The other type can phosphorylate tyrosine residues

53
Q

How does adding a phosphate group (-ve) charge alter the function of the protein?

A
  • Causing a change in shape (conformation) leading to a change in activity
  • Creating a docking site for another protein
54
Q

What happens when the EGF receptor is activated?

A

Once the kinase is activated, it phosphorylates proteins in the tail of the EGF receptor. This activated form is highly expressed in tumour cells. Receptor activation triggers kinase cascaded and binding of adapter proteins.

55
Q

What are protein kinase cascades?

How are they regulated?

A

The first kinase is activated by phosphorylation, and then further kinases are activated by the activated kinases and so on. These kinases are all switched off by phosphatases (they are regulatory).

56
Q

What does a protein kinase cascade result in?

A 
The proteins regulated by the kinases are often other kinases and so activation of one kinase activates another to activate another
Results in:
- Signal amplification
- Signal diversification
- Opportunity for regulation
57
Q

What other kinds of proteins can be phosphorylated besides kinases?

A

This includes scaffolding proteins and transcription factors. This leads to signal amplification, diversification and opportunity for regulation.

Year 2 - Cancer (9 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions