Lec 11-13

Question 1

Nucleic acid

Answer 1

-Macromolecule
-DNA & RNA are nucleic acids

Question 2

Differences between DNA & RNA

Answer 2

RNA: C, G, U, A, ribose, single stranded

DNA: C, G, T, A, deoxyribose, doubled stranded

Question 3

What is the result of DNA synthesis?

a. Two identical DNA double helices, each with one new
and one old strand.
b. Two identical DNA double helices, one with two new
strands and one with two old strands.

Answer 3

A

Question 4

DNA replication

Answer 4

DNA helicase opens double helix, topoisomerase binds to relieve twisting forces further down helix

Binding proteins keep strands apart

Primase lays down primer on both sides, forms complimentary base pairs, 10 nucleotides long

DNA polymerase alpha or epsilon synthesizes leading

DNA polymerase delta synthesizes lagging

Question 5

Leading and lagging strands

Answer 5

Leading: synthesized toward the fork

Lagging: synthesized away from fork, gaps sealed with ligase

Both are synthesized 3’ to 5’ on template strand, 5’ to 3’ on daughter strands

Question 6

Would DNA ligase inhibition affect the process of DNA synthesis?

a. Yes. Both the leading and lagging strands would not be synthesized properly.
b. Yes. The lagging strand would not be synthesized properly.
c. No. Ligase is not necessary to bind Okazaki fragments together.
d. No. DNA polymerase can fix any mistakes caused by ligase inhibition.

Answer 6

B

Question 7

Repair systems

Answer 7

Proofreading: DNA polymerase detects its mistake, pauses, then removes and replaces base

Mismatch: detected after DNA synthesis, section with mismatch cut out, replaces, ligase seals gap

Nucleotide excision: fixes damage done by UV light, section of DNA is removed and replaced, ligase seals gaps

Question 8

Breast cancer cells have a faulty mismatch repair system. Mismatch repair fixes mutations caused by _______. First, ______ is removed
and then DNA polymerase adds the correct nucleotide(s).

a) Environmental damage. Just the incorrect nucleotide.
b) Environmental damage. A section that includes the incorrect nucleotide.
c) DNA synthesis (replication). Just the incorrect nucleotide.
d) DNA synthesis (replication). A section that includes the incorrect nucleotide.

Answer 8

D

Question 9

DNA in the cell cycle

Answer 9

G1: unreplicated, uncondensed DNA, fulfilling normal function

S/G2: replicated, uncondensed, sister chromatids

M phase: replicated, condensed, homologous chromosomes

Cytokinesis: unreplicated, condensed, chromatids pulled apart

Question 10

Mitosis phases

Answer 10

Prophase: DNA condenses, spindle apparatus forms

Metaphase: chromosomes line up at metaphase plate

Anaphase: sister chromatids pull apart

Telophase: sister chromatids reach opposite poles

Question 11

In which phase of mitosis would a cell get stuck if replicated DNA condenses into chromosomes
but the spindle apparatus fails to form properly.

a) Prophase (including prometaphase)
b) Metaphase
c) Anaphase
d) Telophase
e) Cytokinesis

Answer 11

A

Question 12

Nerve cells (almost) never divide. Which
phase are the cells (almost) always in?

Answer 12

G1/G0

In G1 phase, there is no DNA replication. The cell just performs normal function. Cells that never/rarely divide enter G0 phase

Question 13

Checkpoints

Answer 13

G1 cp: Pass if -cell size is adequate -nutrients are sufficient -DNA is undamaged

G2 cp: Pass if -chromosomes replicate successfully -DNA is undamaged -activated MPF is present

M-phase cp: Pass if -chromosomes attach to spindle fibers -chromosomes separate - no MPF

Question 14

DNA damage in thyroid cells caused by insufficient iodine consumption is usually fixed by a repair system called direct reversal repair, which operates similarly to nucleotide excision repair. If someone consumes insufficient iodine but still does not develop thyroid cancer, direct reversal repair must be

a) working optimally at M1 checkpoint.
b) working sub-optimally at M1 checkpoint.
c) working optimally at G1 checkpoint.
d) working sub-optimally at G1 checkpoint.
e) working optimally at G1 and G2 checkpoint.

Answer 14

C

The G1 checkpoint is where DNA damage is detected and where nucleotide excision repair would occur. If someone is at risk of developing thyroid cancer but hasn’t, the G1 checkpoint is working

Question 15

Regulator molecules of the cell cycle

Answer 15

Cyclins: move cells from one phase to the next

Cdks: phosphorylates target proteins making them more of less active

MPF: starts M phase

APC/C: destroys proteins

p53: detects DNA damage, fixes damage or destroys cell

Question 16

Healthy thyroid cells usually only undergo mitosis in the presence of a growth factor hormone binding to the growth factor receptor on their cell membrane. However, thyroid cancer cells will replicate even in the absence of this growth factor. Considering only this, a thyroid cancer cell divides in the absence of growth factor because _____ and ___ checkpoint is faulty.

a) S cyclin is underexpressed; M1
b) P53 is mutated; G2
c) G1/S cyclin is overexpressed; G1
d) P53 is mutated; G1

Answer 16

C

The cells keep replicating, regardless of the missing hormone meaning there is too much cyclin that keeps pushing the cell through G1 checkpoint