Cell Cycle + Replication Flashcards
Mitosis Promoting Factor (MPF)
Present in the cytoplasm of M cells
Induces mitosis
Activates protein kinase
Why is MPF found in all eukaryotes?
it is highly conserved and essential for promoting mitosis
Cyclin dependent kinase
an enzyme that catalyzes the transfer of a phosphate group
from ATP to a target protein
Phospholyzation
the transfer of ATP to a target protein
catalyzed by protein kinase
target proteins need energy input to begin mitosis
What happens when more cyclin is present?
MPF concentrations in the cytoplasm rise
target proteins are phospholyzed which initates mitosis
When do MPF concentrations peak?
During M phase
When do MPF concentrations rise?
During interphase
What is the MPF composed of?
Cyclin and cyclin-dependent kinase bound together
Cyclin
a regulatory protein that fluctuates in order to initiate M phase
it attaches to cdk’s to form MPF
therefore, when cyclin rises, MPF rises
Concentration of cdk’s
remain constant
only cyclin fluctuates since cdk’s are hard to reproduce
How many cyclin/cdk combos are there?
There are many combos that regulate the cell cycle for each phase
G1 checkpoint
pass if cell size is adaquent, DNA is undamaged, nutrients are sufficient
G0
mature cells do not pass the G1 checkpoint and enter into the G0 phase
G2 checkpoint
pass if DNA is undamaged and has replicated successfully
activated MPF is present
M checkpoint
chromosomes attatched to spindle apparatus
chromosomes have properly segregated and MPF is absent
When do checkpoints occur?
At the end of phases
Make sure work supposedly to be done in certain phases is complete
origin of replication
replication bubbles form at specific sequences of bases
How many origins of replications do bacteria have?
Only one
That this why their DNA is circular
How many origins of replications do eukaryotes have?
Many
Speeds up replication
Where does active DNA synthesis take place?
At the replication fork
Replication fork
Y-shaped region where the parental DNA double helix is separated into single strands and copied
What direction does DNA have to be copied in?
5’ to 3’
Why is DNA synthesis bidirectional?
2 replication forks going in both directions at the same time
Helicase
breaks the hydrogen bonds between base pairs and opens the double helix at the replication fork
Single-stranded DNA binding proteins
prevent the separated DNA strands from snapping back into place
topiomerase
an enzyme that prevents supercoiling of DNA
primer
an RNA strand that forms complimentary base pairs with the DNA template strand
provides DNA polymerase with a 3’ -OH group that can be used to form phosphodiester bonds
Leading strand
strand that is synthesized toward the replication fork
synthesized continuously
Lagging strand
synthesized in a direction that is away from the moving replication fork
synthesized in short Okazaki fragments
has to readjust to go in 5’ to 3’ direction
Primase
synthesizes a short stretch of RNA that works as a primer
DNA polymerase I
removes the RNA primer and replaces it with DNA
the end replication problem
there is no primer for DNA
telomere
protective end of chromosomes
TTAGG strand that is okay to loose due to end replication problem
Is DNA polymerase bidirectional?
No. It is unidirectional
Ligase
connects the fragments with phosphodiester bonds
works on BOTH the leading and lagging strands
How does telomerase work?
it extends the unreplicated end of DNA
lays down a primer and following the primer TTAGG cap
DNA is replicated to primer and the TTAGG cap is lost behind it, but that is alright
When are telomeres added in the cell cycle?
during the S phase
When are telomeres created?
During pre-natal development
born with all the telomeres we get
as we age, DNA becomes shorter
