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ah bio > 1.5 > Flashcards

1.5 Flashcards

1
Q

Function of the cytoskeleton

A

Gives mechanical support and shape to the cell

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2
Q

What does the cytoskeleton consist of

A

The cytoskeleton consist of different protein structures including microtubules, which are found in all eukaryotic cells

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3
Q

What are microtubules and where do they come from

A

Microtubules are hollow cylinder is composed of the protein tubulin. The radiate from the microtubule organising centre (MTOC) or centrosome.

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4
Q

Functions of microtubules

A

Microtubules control the movement of membrane bound organelles and chromosomes.

Other major functions
- Determine cell shape
- involved in cell movement
- form the spindle fibres

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5
Q

What does cell division require of the cytoskeleton

A

Cell division requires remodelling of the cytoskeleton

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6
Q

What does formation and breakdown of microtubules involve

A

Formation and breakdown of microtubules involves polymerisation and depolymerisation of tubulin

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7
Q

What forms the spindle fibres

A

Microtubules form the spindle fibres that are active during cell division

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8
Q

When is the centrosome/MTOC duplicated?

A

Duplicated in non-dividing (interphase) cells

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9
Q

Products of the cell cycle

A

Two genetically identical daughter cells

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10
Q

What are the two main phases of the cell cycle

A

The cell cycle consist of interphase and mitotic (M) phase

Mitotic = mitosis

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11
Q

List the phase of interphase

A

G1: initial growth phase. Protein synthesis occurs and new organelles are formed

Synthesis (S): replication of nuclear DNA

G2: second phase of growth prior to mitosis. By the end of this phase the centrosome/MTOC has been duplicated

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12
Q

Describe G1

A

G1: initial growth phase. Protein synthesis occurs and new organelles are formed

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13
Q

Describe S phase

A

Synthesis (S): replication of nuclear DNA

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14
Q

Describe G2

A

G2: second phase of growth prior to mitosis. By the end of this phase the centrosome/MTOC has been duplicated

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15
Q

What does the mitotic phase involve

A

Mitosis and cytokinesis

In mitosis do chromosomal material is separated by the spindle microtubules. This is followed by cytokinesis, in which the cytoplasm is separated into two daughter cells

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16
Q

What does mitosis (M) phase consist of

A

Prophase
Metaphase
Anaphase
Telophase

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17
Q

Describe prophase

A

DNA condenses into chromosomes each consisting of two sister chromatids. The nuclear membrane breaks down; spindle microtubules extends from the MTOC by polymerisation and attach to chromosomes via their kinetochores in the centromere region.

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18
Q

During prophase why do chromosomes condense

A

Chromosomes condense to become visible, to stop transcription and to prevent tangling during separation

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19
Q

Describe metaphase

A

The chromosomes are aligned at the metaphase plate (equator of the cell)

They are held in place by microtubules from each pole attached to each centromere

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20
Q

Describe anaphase

A

As spindle microtubules shorten by depolymerisation, sister chromatids are separated, and the chromosomes are pulled to opposite poles of the cell

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21
Q

Describe telophase

A

The chromosomes decondense and nuclear membranes are formed around them.

22
Q

After what stage of mitosis does cytokinesis take place

A

Cytokinesis takes place at the end of telophase

23
Q

What is cytokinesis

A

Cytokinesis occurs at the end of telophase and involves the separation of the cell into two daughter cells

24
Q

Describe checkpoints in control of the cell cycle

A

Progression through the cell cycle is controlled by checkpoints at G1, G2 and M (metaphase in mitosis)

25
Q

What are checkpoints

A

Checkpoints are mechanisms within the cell that assess the condition of the cell during the cell cycle and halt progression to the next phase until certain requirements are met

26
Q

Describe the proteins that accumulate during cell growth

A

Cyclin proteins that accumulate during cell growth are involved in regulating the cell cycle.

Cyclins combine with and activate cyclin-dependent kinases (CDK’s). Active cyclin-CDK complexes phosphorylate proteins that regulate progression through the cycle. If sufficient phosphorylation is reached, progression occurs.

27
Q

Describe the G1 checkpoint

A

At the G1 checkpoint, retinoblastoma protein (Rb) acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication.

Phosphorylation by G1 cyclin-CDK inhibits the retinoblastoma protein (Rb). This allows transcription of the genes that code for proteins needed for DNA replication. Cells progress from G1 to S phase.

28
Q

During the G1 checkpoint, describe what happens by phosphorylation

A

Phosphorylation by G1 cyclin-CDK inhibits the retinoblastoma protein (Rb). This allows transcription of the genes that code for proteins needed for DNA replication. Cells progress from G1 to S phase.

29
Q

What is assessed during G1 checkpoint

A

Cell size

30
Q

Describe the G0 (nondividing state (interphase))

A

If a go ahead signal is not reached at the G1 checkpoint the cell may switch to a nondividing state called the G0 phase.

31
Q

Cyclin and cell size during G1

A

As the cell size increases during G1, Cyclin proteins accumulate and combine with regulatory proteins called CDKs and activate them.

Active CDKs cause the dephosphorylation of proteins that stimulate the cell cycle.

If a sufficient threshold of phosphorylation is reached the cell cycle moves on to the next stage. If an insufficient threshold is reached, the cell is held at G0.

32
Q

What has happened by the end of G2

A

DNA replication has occurred

33
Q

Describe the G2 checkpoint

A

At the G2 checkpoint, the success of DNA replication and any damage to DNA is assessed

34
Q

What happens once the checks are completed at G2

A

Once the checks are completed at checkpoint G2 the cell is ready for mitosis.

The start of mitosis is triggered by the complex called mitosis promoting factor (MPF) which itself is controlled by a number of other cell cycle signals

35
Q

How is the start of mitosis triggered

A

The start of mitosis is triggered by the complex called mitosis promoting factor (MPF) which itself is controlled by a number of other cell cycle signals

36
Q

What does DNA damage trigger

A

DNA damage triggers the activation of several proteins including p53 that can stimulate DNA repair, arrest the cell cycle or cause cell death

37
Q

2 main responses by active p53

A

Cell cycle arrest - DNA repair - cell cycle restart

Apoptosis - death and elimination of damaged cells

38
Q

Describe checkpoint 3 (known as the M checkpoint occurring during metaphase)

A

A metaphase checkpoint controls progression from metaphase to anaphase.

At the metaphase checkpoint, progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules

39
Q

What can an uncontrolled reduction in the rate of the cell cycle lead to

A

An uncontrolled reduction in the rate of the cell cycle may result in degenerative diseases such as Alzheimer’s or Parkinson’s disease.

40
Q

What can an uncontrolled increase in the rate of the cell cycle lead to

A

An uncontrolled increase in the rate of the cell cycle may result in tumour formation (cancer)

41
Q

What are proto-oncogenes

A

A proto-oncogene is a normal gene, usually involved in the control of cell growth or a division, which can mutate to form a tumour promoting oncogene.

These oncogenes can cause the cell to divide in an uncontrolled and unregulated manner.

42
Q

What triggers apoptosis

A

Apoptosis is triggered by cell death signals that can be external or internal

43
Q

Example of external death signal

A

The production of deaths signal molecules from lymphocytes

44
Q

Example of internal death signal

A

DNA damage

45
Q

What is apoptosis

A

Apoptosis is programmed cell death.

46
Q

Describe the mitochondrion and the caspade cascade

A

During apoptosis dependability of the mitochondria membrane increases allowing cytochrome C to exit the inter-membrane space and into the cytoplasm.

Cytochrome C activate executioner caspase enzymes which have a controlled cascade of action. These act a DNAase, protease and enzymes that destroy the cell.

It can also activate other types of enzymes in the body like nucleases that can break down DNA

47
Q

Describe how external death signal molecules work

A

External death signal molecules bind to a surface receptor protein and trigger a protein cascade within the cytoplasm

48
Q

Describe how internal death signals work

A

An internal (intrinsic) death signal resulting from DNA damage causes activation of p53 tumour-suppressor protein

49
Q

What do both types of death signal activate

A

Caspases (types of protease enzyme) that cause the destruction of the cell

50
Q

Why and when is it apoptosis essential

A

Apoptosis is essential during development of an organism to remove cells no longer required as development progresses or during metamorphosis.

51
Q

When may cells initiate apoptosis

A

Cells may initiate apoptosis in the absence of growth factors

ah bio (6 decks)

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