chapter 4 - the cell cycle

Question 1

purpose of cell replication

Answer 1

growth and development
maintenance and repair
reproduction

Question 2

what rate do cells grow?

Answer 2

exponential growth, number of cells present double.

Question 3

binary fission

Answer 3

a type of asexual reproduction seen in prokaryotic cells

Question 4

process of binary fission

Answer 4

1. DNA and plasmids replicate
2. cell elongates. DNA moves to opposite sides.
3. cell undergoes cytokinesis, by pinching inward and creating a septum.
4. a new cell wall and membrane are formed down the centre of the cell.
5. two new genetically identical cells are formed.

D: DNA replication
E: elongation
S: septum formation
W: new cell wall and membrane formed
C: cell division

Question 5

cytokinesis

Answer 5

the division of the cytoplasm and formation of two daughter cells

Question 6

septum

Answer 6

a dividing wall formed during binary fission

Question 7

stages of the eukaryotic cell cycle

Answer 7

interphase: cellular growth and duplication of chromosomes
mitosis: separation of sister chromatids and formation of two new nuclei
cytokinesis: division of the cytoplasm and formation of two daughter cells

Question 8

interphase

Answer 8

cell synthesises necessary DNA, proteins, and organelles required for growth and replication
DNA in nucleus exists as long chromatin threads instead of discrete chromosomes.

Question 9

stages in interphase

Answer 9

G1, G0, S, G2

Question 10

G1 phase

Answer 10

cell grows by:
increasing the volume of cytosol
synthesising proteins for DNA replication
replicating its organelles

Question 11

G0 phase

Answer 11

cells that are not required to replicate rest in G0.
quiescent are dormant but have the ability to re-enter the cell.
terminally differentiated cells remain in G0 indefinitely.

Question 12

S (synthesis) phase

Answer 12

cell replicated its DNA, turning one chromosome into two identical sister chromatids

Question 13

G2 phase

Answer 13

cell grows and prepares for mitosis, synthesises proteins
increases volume of cytosol

Question 14

mitosis stages

Answer 14

-prophase (prepare)
-metaphase (meet in middle)
-anaphase (move apart)
-telophase (towards two)

Question 15

what happens during prophase?

Answer 15

-early stage: nucleolus disappears and chromatin starts to condense. centrioles separate from each other and form spindle fibres. centrioles move towards pole of cell.
-late stages: chromosomes are visible with 2 sister chromatids

Question 16

what happens during metaphase?

Answer 16

chromosomes are assembled along equator and the kinetochore at each chromosome’s centromere extends kinetochore fibres that attach to spindle fibres

Question 17

what happens during anaphase?

Answer 17

spindle fibres shorten, chromatids of each chromosome are dragged to opposite poles of the cell by their kinetochores

Question 18

what happens during telophase?

Answer 18

chromosomes begin to decondense back into the expanded chromatin that exists during telophase. the nuclear membrane re-forms around each nucleus

Question 19

cytokinesis in animals and plants

Answer 19

-in animals a cleavage furrow develops and pinches the plasma membrane into two cells
-in plants a cell plate first forms at the equator before separating to two cells

Question 20

regulation of cell cycle

Answer 20

cell can pause for repairs or undergoes programmed cell death.
G1 checkpoint: checks growth size, protein for DNA etc.
G2 checkpoint: checks DNA has replicated properly.
Metaphase checkpoint: cell checks formation of spindle fibres.

Question 21

pathways of apoptosis

Answer 21

mitochondrial
when internal components are damaged, mitochondria detects damage and releases cytochrome c into the cytosol

death receptor
death signalling molecules can be recognised by death receptor proteins on the surface of cells, often released by immune cells

both of these pathways lead to the activation of caspase enzymes

Question 22

stages of apoptosis

Answer 22

-activation of caspases
-digestion of cell contents: capases cleave intracellular proteins, which leads to the breakage of organelles
-cell shrinks: cell shrinks as intracellular materials are broken down
-membrane blebbing and breakage: membrane warps and detached from the cell in membrane enclosed vesicles (apoptotic bodies) which contains the broken down cellular material

-phagocytes engulf and digest the apoptotic bodies by phagocytosis (occurs after apoptosis)

Question 23

how do tumours occur?

Answer 23

when the rate of apoptosis decreases too much, cell growth increases exponentially, resulting in the form of tumours.

Question 24

types of tumours

Answer 24

benign: relatively slow-growing masses of cells that are generally enclosed within a capsule which prevents the abnormal cells from separating and invading other body parts

malignant: cells of these tumours can mutate further and become malignant when they gain the ability to invade nearby tissues and/or enter the bloodstream or lymphatic system

Question 25

characteristics of tumour cells

Answer 25

-blood supply formation -increased survival -tissue invasion and metastasis (unique to cancer cells) -antigrowth deactivation -self sufficiency (BIT AS)

Question 26

properties of stem cells

Answer 26

self-renewal: able to produce as differentiated cell and a copy of themselves when they replicate potency: stem cells are undifferentiated cells which give rise to differentiated cells with a specialised function

Question 27

potency of stem cells

Answer 27

totipotent: can differentiate into any cell type pluripotent: can differentiate into multiple cell types multipotent: can differentiate into a limited number of specialised cells