MCB L4

Question 1

What are the 6 phases of M Phase?

Describe them.

Answer 1

1- Prophase
M: Chromosomes condense
M: Mitotic spindles form
S:Intact nuclear envelope, centrosome, forming mitotic spindle, condensing chromosome, kinetochore
2- Prometaphase
M: Nuclear membrane disintegrates
M: Spindles attach to kinetochores
S: Spindle pole, kinetochore microtubule, fragments of nuclear envelope, chromosome in motion
3- Metaphase
M: Chromosomes align at equator
S: spindle pole, astral microtubule, kinetochore microtubule, spindle pole, kinetochores of all chromosomes aligned in a plane midway between 2 spindle poles
4- Anaphase
M: Sister chromatids Separate
M: Pulled towards spindle poles
S: Chromosomes, spindle pole moving outwards, shortening kentochore microtubule
5- Telophase
M:Chromosomes arrive at poles
M:Nuclear envelopes reform
S: set of chromosome at spindle pole, contractile ring starting to form, spindle pole, interpolar microtubules, nuclear envelope reassembling around individual chromosomes
6 - Cytokinese
M: Cytoplasm divides resulting in 2 genetically near-identical cells.
S: Completed nuclear envelope surrounds decondensing chromosomes, contractile ring creating cleavage furrow, re-formation of interphase array of microtubules nucleated by the centrosome
PPMATC
People procrastinate mainly at cornfields

Question 2

What is the cell cycle controlled by?

Answer 2

Cyclins and protein kinases (Cdks) - phosphorylation of cdk/cyclin complexes.

Question 3

Where do chemotherapy drugs target?

Answer 3

Target S and M phases - kill rapidly replicating cells.

Question 4

Where are nucleotides added, and what direction is DNA synthesised in?

Answer 4

Nucleotides are added to the 3’ end

DNA is synthesised in the 5’ to 3’ end.

Question 5

what is the difference between the leading and lagging strand?

Answer 5

Leading strand - Continuous synthesis in the 5’ to 3’ direction.
Lagging strand - Discontinuous synthesis in okazaki fragments, 5’to3’ direction.

Question 6

Explain how the following effects DNA replication:
RNA primer
Okazaki fragment
DNA primase
DNA helicase
DNA polymerase 
Nucleoase

Answer 6

DNA polymerase: adds nucleotides to 3’ of leading and lagging strand

DNA helicase: unwinds the DNA

DNA primase: adds RNA primer the polymerase can bind to synthesised in 5’ to 3’

Nucleoase: removes primer

okazaki fragment: lagging strand

DNA ligase: joins small gaps together

Question 7

What is Werner Syndrome?

Answer 7

Mutation to mitosis/DNA replication. AKA the premature aging disorder.

Question 8

How can we prevent the accumulation of mutations? 2 things.

Answer 8

1. Proof-reading capacity of DNA polymerase during DNA replication.
2. Excision repair systems act throughout cell life repairing DNA damage

Question 9

What can cause DNA damage? internal and external

Answer 9

Internal: Products of normal cell function
External: Mutagenic chemicals
UV
Ionizing radiation

Question 10

What is Xeroderma pigmentosum?

Answer 10

SUNLIGHT DISORDER.
Mutation in UV repair
Unable to remove thymine dimers 
Autosomal recessive disorder
Causes: Mental retardation, cancer, and severe burns in the sun