Lec 11-13 Flashcards
Nucleic acid
-Macromolecule
-DNA & RNA are nucleic acids
Differences between DNA & RNA
RNA: C, G, U, A, ribose, single stranded
DNA: C, G, T, A, deoxyribose, doubled stranded
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.
A
DNA replication
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
Leading and lagging strands
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
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.
B
Repair systems
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
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.
D
DNA in the cell cycle
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
Mitosis phases
Prophase: DNA condenses, spindle apparatus forms
Metaphase: chromosomes line up at metaphase plate
Anaphase: sister chromatids pull apart
Telophase: sister chromatids reach opposite poles
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
A
Nerve cells (almost) never divide. Which
phase are the cells (almost) always in?
G1/G0
In G1 phase, there is no DNA replication. The cell just performs normal function. Cells that never/rarely divide enter G0 phase
Checkpoints
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
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.
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
Regulator molecules of the cell cycle
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