12 The Cell Cycle

Question 1

What are the functions of cell cycle?

Answer 1

Reproduction
Growth and development
Tissue renewal

Question 2

What takes place before the cell can divide?

Answer 2

The duplication of the genetic material

Question 3

Define a somatic cell. How many chromsomes does it have?

Answer 3

IT’s any cell in an organism besides the sex cells. It has 46 chromosomes or two sets of 23

Question 4

How many chromosomes does a gamete cell have?

Answer 4

One set of 23

Question 5

What is a sister chromatid. Describe its structure and a pair’s parts.

Answer 5

A sister chromatid is one of two that make up a chromosome. It has a centromere, a region where the pair attach, and an arm, the part on each side of the centromere

Question 6

Differentiate between mitosis and cytokenesis

Answer 6

Mitosis is the division of the genetic material while cytokenesis is the division of the cytoplasm

Question 7

What accounts for 90% of the cell cycle? What are its subphases? What is the shortest phase?

Answer 7

The interphase. Its subphases are G1, S phase, and G2. Mitosis is the shortest phase of the cell cycle

Question 8

What occurs during all three subphases? What occurs solely in S phase? What happens during both G phases?

Answer 8

In all three, growth is taking place, and mitochondria and Er are produced. In S phase, genetic material is duplicated. In both G phases, many metabolic processes are taking place readying the cell for division

Question 9

List the phases of mitosis and what happens in each phase

Answer 9

Prophase - chromatin condenses to chromsomes/mitotic spindle begins to form/centrosomes move away from each other, and asters begin to form
Prometaphase - nucleur envelope dissolves/chromosomes condense/kinetochores form on chromatids/ kinetochore microtubules form
Metaphase - centrosomes reach opposite poles of cell/chromosomes line up on metaphase plate
Anaphase - shortest stage/cell elongates/daughter chromsomes begin moving to opposite ends
Telophase - 2 new nucleur envelopes arise/nucleoli reappear/chromsomes unwind/spindle micrtubules depolymerize
Cytokenesis - division of the cytoplasm

Question 10

Define aster, mitotic spindles,metaphase plate, and cleavage furrow.

Answer 10

Aster- shorter micrtubules that extend from each centrosome extending towards cell membrane
Mitotic spindles - structure that begins to form in the cytoplasm during prophase made of the cell’s cytoskeleton.
Metaphase plate - imaginary plane in the centre of the cell where centromeres of chromosomes line up
Cleavage furrow - first sign of cleavage, a groove in the cell surface where the metaphase plate used to be

Question 11

When is anaphase launched?

Answer 11

When the cohesin proteins attaching the chromatids are cleaved

Question 12

What is the purpose of nonkinetochore spindle. Explain how they do it.

Answer 12

They interact with those from the other side which makes them responsible for elongating the whole cell during anaphase. Motor proteins attached to the microtubules walk the region of overlap away from each other. As they push apart, they elongate the cell.

Question 13

Define kinetochore & kinetochore spindle

Answer 13

Kinetochore is a structure on certain regions of the DNA at each centromere
A kinetochore spindle is a spindle microtubule attached to a kinetochore

Question 14

Describe the 2 mechanisms involved in the poleward movement of chromosomes

Answer 14

• Motor proteins on kinetochores walk the chromosomes along microtubules
• Motor proteins at the spindle poles reel in the chromosomes

Question 15

How do microtubules elongate/polymerize and shorten/depolymerize?

Answer 15

They elongate by adding sub-units of tubulin and shorten by losing them

Question 16

How does cytokineses occur in animal cells VS plant cells?

Answer 16

In an animal cell, the cytoplasmic side of the cleavage furrow has a contractile ring of actin microfilaments. When they interact with the protein myosin mlcls, the ring contracts
In a plant cell, vesicles from the golgi apparatus move to the cell’s centre via microtubules forming a cell plate. It enlarges until it can merge with the cell wall of parent cell/

Question 17

Define binary fission

Answer 17

Type of reprouction prokaryotes and single celled eukaryotes undergo in which a cell doubles its size then divides. In the latter, mitosis is needed.

Question 18

Define origin of replication

Answer 18

when the DNA begins to replicate at a specific part on a bacterial chromosome, producing 2 copies of origin. One copy moves to each end of cell through polymerization of actins

Question 19

What is the hypothesis about the origins of mitosis? How is this supported?

Answer 19

Mitosis evolved from simpler prokaryotic mechanisms of reproduction. Some of the proteins involved in cellular fusion also function in mitosis

Question 20

List the variations of cell division

Answer 20

Bacteria- binary fusion
Most eukaryotes- mitosis
Unicellular protists (dinoflagelletes) - chromosomes attach to nucleur envelope which remains intact, microtubules pass through tunnels in the nulceus, and the nucleus divides through binary fusion
Diatomes/some yeasts - nuclear envelope remains intact, mitosis is roughly the same

Question 21

Compare role of actin and tubulin in mitosis to their role in binary fusion

Answer 21

Mitosis - tubulin is involved in spindle formation and chromosome movement while actin helps the contractile ring of cytokineses
Binary fusion - it’s the opposite; actin-like mlcls move the bacterial daughter chromosomes to opposite ends of the cell while tubulin-like mlcls are involved in daughter cell seperation

Question 22

What is the cell cycle directed by?

Answer 22

The cell cycle control system - a cycle of mlcls in the cell that trigger and coordinate its events

Question 23

Define a checkpoint. List the three major ones in the cell cycle

Answer 23

A control point in a cycle where stop and go-ahead signals can regulate the cycle. The three major ones are found in the G1, at the end of G2, and through M.

Question 24

Which checkpoint is dubbed the restriction point and is considered the most important in a mammalian cell? Why?

Answer 24

The G1 checkpoint. If a cell receives the go-ahead signal here, it will continue division. If it doesn’t, it will exit the cycle and enter G0 phase, the nondividing state.

Question 25

Two types of proteins that act as regulatory mlcls in the cycle control system:

Answer 25

Protein kinases - signalling enzymes that activate or inactivate proteins by phosphorylating them, allowing them to give particular go-ahead signals

Cyclins - protein that has fluctuating concentrations within the cell cycle

Question 26

Define Cdks and MPFs.

Answer 26

Cdks - Cyclin dpeendant kinases; protein Kinases can only enter the active form after binding with cyclin

MPF - maturation/M-phase promoting factor; it triggers cell’s passage past the G2 checkpoint into M phase.

Question 27

Discuss the levels of concentration of cyclin as it corresponds to MPF activity.

Answer 27

The peaks of MPF actiivty correlate to peaks of cyclni concentration. Cyclin levels rise during S and G2 phases and then falls steeply during M.

Question 28

List four factors that can influence cell division

Answer 28

Growth factors
Availability of nutrients
contact with neighboring cells
anchorage dependence

Question 29

Define growth factor; give an example

Answer 29

Protein released by certain cells that cause other cells to divide. Platelet-derived growth factor (PDGF)

Question 30

Describe a situation in which density dependent inihbition takes place

Answer 30

Cultured mammalian cells divide only till they fill a single layer of cells in the culture container

Question 31

Define anchorage depdance and substratum

Answer 31

Anchorage dependence is a cell’s need to be attached to a substratum

Question 32

What properties do cancer cells not exhibit? I.e Why do they continue growing even when growth factors are depleted?

Answer 32

They lack anchorage dependence, density-dependent inhibition, and they either make growth factors themselves or have an abnormality in that signal transduction pathway that conveys the GF’s signal even in its absence.

Question 33

Give an example of an immortal cell line.

Answer 33

The HeLa cells. Removed from a cancerous cervical tumour in 1951 from a woman called Henrietta Lacks.

Question 34

What do you call cells in culture that have taken the ability to divide infinitely and behave like cancer cells?

Answer 34

We say these cells have undergone transformation

Question 35

Define benign tumour

Answer 35

A mass of abnormal cells that remain at the original site because they have too few genetic and cellular changes to survive in another site

Question 36

Define malignant tumour

Answer 36

A mass of abnormal cells that has undergone genetic and cellular cahnges enabling them to spread to new tissue, impairing the function of one or more organs

Question 37

Define metastatis

Answer 37

After cancer cells release signals cuasing blood vessels to grow toward the tumour, few tumour cells may seperate, enter the vessel/lymph node and travel to other body parts