Stages of Cell cycle

Question 1

Name the 6 stages of the cell cycle?

Answer 1

Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis

Question 2

What happens to the chromosomes and mitotic spindle in prophase?

Answer 2

Replicated Chromosomes, consisting of 2 sister chromatids condense and move appart
Outside the nucleus the mitotic spindle assembles between the 2 chromosomes which have replicated

Question 3

What happens in prometaphase?

Answer 3

Nuclear envelope breakdown

Chromosomes attach to spindle microtubules via their kinetochores and undergos active movement

Question 4

When does open and close mitosis occur?

Answer 4

Open= when nuclei dissolves before cell division
Close= nuclei remains intact

Question 5

What happens in metaphase?

Answer 5

Chromosomes align at the equator of spindle. midway between spindle poles
Kinetochore microtubules attach sister chromatids to opposite poles of the spindle

Question 6

What happens in anaphase?

Answer 6

Sister chromatids synchronously seperate to form 2 daughter chromosomes and each s pulled towards a spindle pole.
Kinetochore microtubules get shorter and spindle poles move appart

Question 7

What happens in telophase?

Answer 7

2 sets of daughter chromosomes arrive at the poles of the spindle and decondense
A new nuclear envelope forms
Central spindle is formed
Division of cytoplasm begins with contraction of contractile ring

Question 8

What happens during cytokinesis?

Answer 8

Cytoplasm is divided into two by a contractile ring of actin and myosin filaments

This pinches the cell in 2 to create 2 daughter cells

Mitotic cyclins are destroyed and proteins are dephosphorylated

Question 9

What are kinetochores?

Answer 9

multiprotein complexes that are responsible for the attachment of chromosomes to the microtubules of the mitotic spindle, are assembled on the centromeric chromatin

Question 10

When are kinetochores assembled?

Answer 10

assembled early during mitosis on centromeres (centromeric chromatin)

Question 11

Define centromere

Answer 11

part of the chromosome where the primary constriction is; a fragment of DNA, which allows for chromatid segregation during mitosis; a region on the chromosome where kinetochore is assembled

Question 12

How are chromosomes attached to the mitotic spindle?

Answer 12

Attached via kinetochores

Question 13

How does plant cell cell cycle differ?

Answer 13

Plant cells do NOT contain centrosomes but they have fully functional mitotic spindle

Question 14

In which phase is the DNA and centrosome replicated?

What is established immediately after this and what is responsible for this?

Answer 14

S phase

Sister chromatid cohesion is established by cohesin (mostly) and DNA catenation

Question 15

Give 3 reasons why spindle checkpoints are useful

Answer 15

1) detects incorrect attachment at kinetochores
2) Arrests cells in metaphase
3) provides more time to correct improper attachments When SAC is satisfied (meaning: all kinetochores are properly attached to the microtubules of the mitotic spindle), APC/C becomes activated.

Question 16

What keeps APC/C inactive and when does it become active?

Answer 16

APC/C remains inactive, until all kinetochores are attached properly to microtubules. Spindle Assembly Checkpoint (SAC) keeps APC/C inactive

Question 17

What are the two major functions of APC/C

Answer 17

❶ Ubiquitinates Securin, which – after Securin destruction – releases (activates) Separase. Separase removes cohesin from centromeres, which triggers anaphase.
❷ Ubiquitinates Cyclin B, what – after Cyclin B destruction – inactivates Cdk1, which in turn leads to the mitotic exit

Question 18

What has inherent polarity?

Answer 18

Mitotic spindle assembly Microtubules have an inherent polarity.

Dynamic nature of microtubules: slowly depolymerising at (-) ends, rapidly polymerising or depolymerising at (+) ends.

Metaphase .The plus ends of the microtubules project away from the spindle pole, while minus ends anchored at spindle poles,

Question 19

Explain how colchicine blocks microtubule dynamicity

Answer 19

Colchicine binds at the alpha/beta tublin interface and blocks polymerisation of microtubules.
Leds to shortening and depolymerisation of microtubules and unattached kinetochores and trigger SAC

Question 20

Define Cancer

Answer 20

A cancer is an abnormal type of tissue growth in which some cells divide and accumulate in an uncontrolled, relatively autonomous way.

Question 21

What are the 3 categories of external factors on extracellular signalling molecules?

Answer 21

Mitogens
Growth Factors
Survial Factors

Question 22

Describe Mitogens

Answer 22

stimulate cell division, primarily by triggering a wave of G1/S-Cdk activity that relieves intracellular negative controls that otherwise block progress through the cell cycle.

Question 23

Describe Growth factors

Answer 23

stimulate cell growth (an increase in cell mass) by promoting the synthesis of proteins and other macromolecules and by inhibiting their degradation

Question 24

Describe survival factors

Answer 24

promote cell survival by suppressing the form of programmed cell death known as apoptosis. All of them, via specific receptors, induce particular signaling pathways/cascades that affect the cell cycle progression

Question 25

What causes cell proliferation

Answer 25

G1 cyclin–Cdk complexes trigger the activation of gene regulatory proteins that stimulate the expression of numerous G1/S genes, including genes encoding G1/S cyclins, S cyclins and the proteins that carry out the events of the early cell cycle. The resulting waves of G1/S– and S–Cdk activities result in irreversible commitment to cell division.

Question 26

Describe the difference between Receptor Tyrosine Kinases in normal and cancer cells.

Answer 26

(a) Normal receptors exhibit tyrosine kinase activity only after a growth factor has bound to them, (b) Some oncogenes encode mutant receptors whose tyrosine kinase is permanently activated, (c) Other oncogenes produce normal receptors but in excessive quantities, which leads to excessive receptor activity.

Question 27

Define oncogene

Answer 27

: a gene whose protein product promotes cancer, generally because mutations or rearrangements in a normal gene (the proto-oncogene) have resulted in a protein that is overactive or overproduced.

Question 28

Define protoncogene

Answer 28

generally regulate cell growth, cell division, cell survival, or cell differentiation

Question 29

Define tumour suppressor gene

Answer 29

: a gene that encodes a protein that normally restrains cell proliferation or tumorigenesis, such that loss of the gene increases the likelihood of cancer formation

Question 30

What is the role of p53 protein?

Answer 30

a cellular stress sensor. In response to hyper-proliferative signals, DNA damage, hypoxia, telomere shortening, and various other stresses, the p53 levels in the cell rise

Question 31

Name 5 features of cancers

Answer 31

They can bypass normal proliferation controls, this includes independence of mitogens, suppression of apoptosis
They can colonise other tissues
Most cancers derive from a single abnormal cell
Cancer cells contain and accumulate somatic mutations
A single mutation is not enough to change a normal cell into a cancer cell
Cancers develop gradually from increasingly aberrant cells
Cancer cells display an altered control of growth (e.g. they are not contact inhibited) Cancer cells have an altered sugar metabolism
Cancer cells have an abnormal ability to survive stress and DNA damage They can escape a built-in limit to cell proliferation
Cancer cell are genetically unstable
Cancer cells create their own micro-environment (niche), where they evolve → Check MBOC pages 1091 through 1103 for detail

Question 32

Define genetic instability

Answer 32

an abnormal increase in the rate at which genes and chromosomes are mutated, rearranged or lost.

Question 33

Define chromosomal instability

Answer 33

Chromosomal instability (CIN) – an abnormally high incidence of defects in chromosome number or chromosome structure