Medical Genetic Overview

Question 1

Define the cell cycle

Answer 1

• The cell cycle is the lifespan of somatic cells.
It describes the sequence of cell growth and cell
division. Somatic cells continuously undergo cell division

Question 2

The interphase represents the phase of

Answer 2

cell growth

Question 3

the longest phase in the cell cycle.

Answer 3

The interphase

where several metabolic reactions take place.

takes place in the cytoplasm & the cell nucleus.

Question 4

G1

Answer 4

cell grows in size
organelles replicated & after syntheses of enough ribosomes cells move to S phase.

If the cell can not divide again
, it enters G0

Question 5

S

Answer 5

• cells replicate DNA
  2n - 4n
  Histone synthesis is linked to DNA synthesis
  in S phase

Question 6

G2 phase of cell cycle

Answer 6

Cell grows in size
- Synthesis of proteins associated with mitosis,

Question 7

M phase of cell cycle

Answer 7

• mitosis
• Chromatin condenses - chromosomes, Cell death 4
  segregate to opposite poles of the cell prior
  to cytokinesis (cell division)

Question 8

What dictates whether cells progress from
one cell cycle to the next?

Answer 8

Cyclin-dependent kinases (CdKs)
- Protein kinases
- phosphorylate specific proteins,
- 6CdKs

Cyclins - specify protein targets for CdKs to
phosphorylate
- Amounts of cyclins vary ín the cell cycle
- Decline in amount controlled by. l death
degradation in the 26s proteasome

Question 9

Regulation of cell cycle progression
Cdk(s) and Cyclins

Answer 9

• Cyclins D and E (G1/S) activate
  Cdk
  • phosphorylate proteins in G1 that
  will be needed for DNA replication
  in S phase
• Cyclin A (S phase)
  • sustains DNA replication
• Cyclin B (G2/M)
  • regulates phosphorylation of
  proteins in G2 - assures DNA
  replication complete before cell
  division.

Question 10

Rb with regulated gene needed for DNA synthesis (…..)

What is phosphorylat the Rb?

Answer 10

E2F Transcription factor

D/Cdk4/6,

Question 11

Mitosis
4 sub-phases:

Answer 11

1st - Prophase
2nd - Metaphase
3rd - Anaphase
4th - Telophase
followed by
Cytokinesis

Question 12

Prophase

Answer 12

3 Major Events
1- chromosomes condense
2 - spindle fibers form (spindle fibers are specialized
radiating out from centrioles)
3 - chromosomes are
captured by spindle

Question 13

Metaphase

Answer 13

chromosomes align along equator of the cell, with one kinetochore facing each pole

Question 14

Anaphase

Answer 14

sister chromatids separate

spindle fibers attached to kinetochores shorten and
Pull chromatids towards the poles.

free spindle fibers lengthen- and push poles of cell apart

Question 15

Telophase

Answer 15

• spindle fibers disintegrate
• nuclear envelopes form around both groups of chromosomes
•chromosomes revert to their extended state

Question 16

• A single germ cell divides into four unique daughter cells.
  Called

Answer 16

Meiosis
In meiosis, there
are 2 divisions
of the nucleus:
meiosis I
meiosis II

Question 17

Crossing over

Answer 17

of homologous chromosomes in prophase 1 is exchange of part of genetic material between homologous chromosomes, switching parts of them forming recombinant chromosomes, allowing genetic variation in gametes.

Question 18

Morphologically chromosomes are classified according to the position of the centromere
Centrally localized:
…..
Terminally localized:

Intermediate position:

Answer 18

METACENTRIC I

ACROCENTRIC

SUBMETACENTRIC

Question 19

• the gene sequence is always
written

Answer 19

5’ → 3’

Question 20

coding sequence (……..)
are interrupted by
noncoding DNA (……..).

Answer 20

exons

introns

Question 21

Gene Expression

Answer 21

Definition: It is the process by which the information
encoded in a gene converted into protein
It briefly consists of 2 major processes,
First DNA transcription to RNA, Then RNA translation
into proteins

Question 22

Post Transcriptional Modifications of mRNA

Answer 22

1-5’ “Capping”: The cap is a 7-methyl-guanosine attached to the S’-terminal end of the mRNA.
This cap permits the initiation of translation and stabilize the mRNA.
2-Addition of a poly-A tail: about 40-200 adenine
nucleotides attached to the 3’-end. These tails help
stabilize the mRNAs against
Exonucleases and facilitate their exit from the nucleus.
3-Excision (splicing) of introns, and ligation of the exons.
Now, mature mRNA is ready to be transferred to the
cytosol where protein synthesis occurs on ribosomes.

Question 23

tRNA processing

Answer 23

1- Excision of intron in the anticodon loop.
2- Excision of sequence at 5’- end
3-The acceptor arm: addition of sequence CCA to the 3’- end.
4- Bases modifications: Uracil is reduced to form dihydrouracil.
Uracil is methylated to thymine.
Pseudouridine is formed.
Dihydrouracil and pseudouridine are
unusual bases.

Question 24

Targets for cyclin B/ Cdkl include

Answer 24

histone H1 and lamin
• Phosphorylation of H1
•Chromatin condensation into mitotic chromosomes as cells enter M phase
• Phosphorylation of lamin
• nuclear envelope disintegration, an event that occurs as cens enter M

Question 25

Programmed cell death

Answer 25

apoptosis

Question 26

Intrinsic pathway
pro-apototic and anti-apoptotic

Answer 26

Bcl2 - anti-apoptotic protein blocks activity of pro-apoptotic proteins Bax and Bak

→ Pro-apoptatic :Bax and Bak change mitochondrial membrane integrity, allowing release of cytochrome c
Release of cytochrome C triggers formation of an apoptosome complex that activates a procaspase (9) to a caspase (9, initiating apoptosis

P53 transcription factor - stimulates synthesis PUMA and NOXA; tie up BcL2, allows Bax and Bak to promote apoptosis.

Question 27

Extrinsic pathway

Answer 27

•signal molecules (e.g. TNFa) binds to a cell surface receptor - the “death receptor”
•Causes recruitment of an adaptor protein that triggers activation of procaspase 8
•by proteolytic cleavage and association of mnonomer subunits
•subsequent activation of other caspases
•Also activates Bid which activates Bax and
Bak
• Growth factors inhibit apoptosis

through receptors and activation of the Akt
athway, inhibit Bad; Bad is another activator
+ Bax and Bak.

Question 28

Protein attached to the centromere

Answer 28

Kinetochore

Question 29

Number of sets of a chromosomes in cells

Answer 29

Ploidy

Question 30

Strands of DNA wrap around a protein (histone) forming
……………..

Answer 30

Nucleosomes/coil together forming chromatin.
Chromatin loops and coils together forming supercoils,
Supercoils bunch together forming chromsomes.

Question 31

Def of A Gene

Answer 31

• a specific DNA sequence that
contains genetic information
• information required to make a specific type of protein
• that information is stored in the
sequence on the ‘sense’ strand