TH- Mitosis and cell cycles

Question 1

What are the 3 functions of cell division?

Answer 1

• Reproduction
• growth
• repair

Question 2

what is a genome?

Answer 2

A cells genetic info packed as DNA

Question 3

what is a somatic cell?

Answer 3

any diploid biological cell forming the body of an organism; that is, in a multicellular organism, any cell other than a gamete.

Question 4

what is a gamete?

Answer 4

organism’s reproductive cells, haploid cells.

Question 5

What is chromatin?

Answer 5

DNA + associated protein

Question 6

what are genes?

Answer 6

units that specify an organism’s inherited traits

Question 7

what form is a chromatin in when cell is not dividing?

Answer 7

long, thin chromatin fiber

Question 8

what happens to chromatin before cell division?

Answer 8

During prophase, chromatin condenses into chromosomes

Question 9

Describe the structure of a chromosome

Answer 9

• 2 sister chromatids connected by a centromere

- each chromatid contains identical copies of DNA

Question 10

what is mitosis?

Answer 10

formation of 2 identical daughter nuclei from the parent nucleus

Question 11

what is cytokinesis?

Answer 11

division of the cytoplasm to form two seperate daughter cells

Question 12

what are the 2 cell cycle phases?

Answer 12

• interphase

- mitotic phase

Question 13

which 5 phases make up mitosis?

Answer 13

• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase(cytokinesis)

Question 14

which 3 phases make up interphase?

Answer 14

• G1
• S phase
• G2

Question 15

what happens in each phase of interphase?

Answer 15

• G1= growth phase, because this is the time in which a cell grows. cell synthesizes various enzymes and nutrients that are needed later on
• S= cell synthesizes a complete copy of the DNA in its nucleus. It also duplicates a microtubule-organizing structure called the centrosome.
• G2= The cell reproduces its organelles and makes sure everything is ready for the split.

Question 16

Describe the 5 phases of mitosis

Answer 16

-prophase= The chromatin is condensing.
The nucleolus is beginning to disappear
the mitotic spindle is starting to form.
The centrosomes move away from each other, apparently propelled by lengthening microtubules.

-prometaphase= We now see discrete chromosomes; each consists of two identical sister chromatids
nuclear envelope fragments, and microtubules from the spindle interact with the condensed chromosomes.
Kinetochore microtubules from each pole attach to one of two kinetochores.
Nonkinetochore microtubules interact with those from opposite ends of the spindle.
spindle fibers push the sister chromatids towards the metaphase plate

-metaphase= The spindle is complete,asters have grown and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate.

-anaphase= Anaphase commences when the proteins holding the sister chromatids together are inactivated.
centromeres divide, separating the sister chromatids.
Each is now pulled toward the pole to which it is attached by spindle fibers.
does that ^ by ‘walking back’ as kinetochore is essentially a motor protein
The microtubules shorten by depolymerizing at their kinetochore ends

-Telophase= . Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divide the cytoplasm in two or cleavage furrow for animal cells.

Question 17

How does the mitotic spindle elongate?

Answer 17

by incorporating more subunits of the protein tubulin.

Question 18

what is an aster?

Answer 18

radial array of short microtubules, extends from each centrosome

Question 19

How do the kinetochore microtubules go back towards their pole?

Answer 19

motor proteins on the kinetochore “walk” the attached chromosome along the microtubule toward the nearest pole.
Meanwhile, the excess microtubule sections depolymerize at their kinetochore ends.

Question 20

What is the function of the nonkinetochore microtubules?

Answer 20

responsible for lengthening the cell along the axis defined by the poles.

Question 21

describe the process of cytokinesis in animal cells

Answer 21

• occurs by a process called cleavage.
• first sign of cleavage is the appearance of a cleavage furrow in the cell surface near the old metaphase plate.
• On the cytoplasmic side of the cleavage furrow is a contractile ring of actin microfilaments associated with molecules of the motor protein myosin which causes the ring to contract
• the contraction deepens the furrow until the parent cell is pinched into 2 daughter cells

Question 22

describe the process of cytokinesis in plant cells

Answer 22

• vesicles from the Golgi coalesce at the metaphase plate, forming a cell plate.
• The plate enlarges until its membranes fuse with the plasma membrane at the perimeter.
• The contents of the vesicles form new cell wall material between the daughter cells.

Question 23

how do prokaryotes reproduce?

Answer 23

binary fission

Question 24

describe the process of binary fission

Answer 24

1- chromosome replication begins at one point in the circular chromosome, the origin of replication site, producing two origins.
2-Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell
3-As the chromosome continues to replicate, one origin moves toward each end of the cell.
4-While the chromosome is replicating, the cell elongates.
5-Replication finishes. The plasma membrane grows inward, and new cell wall is deposited.
6-Two daughter cells result.

Question 25

why do scientists believe that 'As eukaryotes evolved, the ancestral process of binary fission gave rise to mitosis'

Answer 25

- Certain protists exhibit types of cell division that seem intermediate between binary fission and mitosis - Since prokaryotes evolved before eukaryotes, mitosis probably evolved from binary fission

Question 26

What evidence is there for the hypothesis 'cell cycle appears to be driven by specific chemical signals' in terms of G1 and S phase.

Answer 26

Fusion of an S phase cell and a G1 phase cell induces the G1 nucleus to start S phase. This suggests that chemicals present in the S phase nucleus stimulated the fused cell.

Question 27

what are the sequential events of the cell cycle are directed by?

Answer 27

cell cycle control system.

Question 28

what is a checkpoint in a cell cycle?

Answer 28

critical control point where stop and go-ahead signals regulate the cycle.

Question 29

how are the signals transmitted within the cell?

Answer 29

by signal transduction pathways.

Question 30

where are the 3 major checkpoints?

Answer 30

G1, G2, M

Question 31

why is the G1 checkpoint considered the most important in most cells?

Answer 31

- If the cell receives a go-ahead signal at the G1 checkpoint, it usually completes the cell cycle and divides. - If it does not receive a go-ahead signal, the cell exits the cycle and switches to a nondividing state, the G0 phase.

Question 32

Define growth factors

Answer 32

is a naturally occurring substance capable of stimulating cell proliferation, wound healing, and occasionally cellular differentiation.

Question 33

which 2 proteins are involved in the cell cycle control?

Answer 33

cyclins and cyclin-dependent kinases (Cdks)

Question 34

what do kinases do to other proteins?

Answer 34

activate or deactivate other proteins by phosphorylating them.

Question 35

what is MPF?

Answer 35

- one cyclin-Cdk complex | - M-phase-promoting-factor

Question 36

Peaks in the activity of one cyclin-Cdk complex, MPF, correspond to peaks in ...

Answer 36

[cyclin]

Question 37

what does MPF trigger/cause?

Answer 37

triggers the cell’s passage past the G2 checkpoint to the M phase.

Question 38

What are the 3 changes MPF causes?

Answer 38

- MPF promotes mitosis by phosphorylating a variety of other protein kinases. - stimulates fragmentation of the nuclear envelope by phosphorylation of various proteins of the nuclear lamina. - triggers the breakdown of cyclin, dropping cyclin and MPF levels during mitosis and inactivating MPF.

Question 39

What does the M checkpoint ensure?

Answer 39

all the chromosomes are properly attached to the spindle at the metaphase plate before anaphase.

Question 40

what happens at kinetochores that have not yet attached to spindle microtubules?

Answer 40

- signal to delay anaphase originates at kinetochores - This keeps the anaphase-promoting complex (APC) in an inactive state. - When all kinetochores are attached, the APC activates, triggering breakdown of cyclin and inactivation of proteins holding sister chromatids together.

Question 41

What stimulates the division of human fibroblast cells in culture?

Answer 41

platelet-derived growth factor (PDGF)

Question 42

what does PDGF do at a site of injury?

Answer 42

- living organism, platelets release PDGF in the vicinity of an injury. - PDGF bind to tyrosine-kinase receptors of fibroblasts, a type of connective tissue cell. - This triggers a signal-transduction pathway that allows cells to pass the G1 checkpoint and divide. - this causes an increase in fibroblaststhat help heal the wound

Question 43

Describe density-dependant inhibition

Answer 43

- Cultured cells normally divide until they form a single layer on the inner surface of the culture container. - If a gap is created, the cells will grow to fill the gap. - At high densities, the amount of growth factors and nutrients is insufficient to allow continued cell growth.

Question 44

Describe anchorage dependence

Answer 44

- To divide, they must be anchored to a substratum, typically the extracellular matrix of a tissue. - Control appears to be mediated by pathways involving plasma membrane proteins and elements of the cytoskeleton linked to them.

Question 45

when does the abnormal behaviour of a cancer cell begin?

Answer 45

-when a single cell in a tissue undergoes a TRANSFORMATION that converts it from a normal cell to a cancer cell.

Question 46

What happens if the immune system doesnt destroy transformed cell?

Answer 46

cells that evade destruction proliferate to form a tumor, a mass of abnormal cells.

Question 47

what is a benign tumor?

Answer 47

abnormal cells that remain at the originating site and dont cause serious problems

Question 48

what is malignant tumor?

Answer 48

cells become invasive enough to impair the functions of one or more organs.

Question 49

What is metastisis

Answer 49

cancer cells often lose attachment to nearby cells, are carried by the blood and lymph system around the body to other tissues, and start more tumors

Question 50

What are the treatments for metastasizing cancers?

Answer 50

high-energy radiation and chemotherapy with toxic drugs.

Question 51

How do these cancer treatments work?

Answer 51

- These treatments target actively dividing cells. - Chemotherapeutic drugs interfere with specific steps in the cell cycle. - For example, Taxol prevents mitotic depolymerization, preventing cells from proceeding past metaphase.

Question 52

Why do we experience side effects from chemotherapy?

Answer 52

due to the drug’s effects on normal cells.