Week 12 Textbook Flashcards

1
Q

what is the cell cycle

A

the orderly sequence of events by which a cell duplicates its contents and divides into 2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is cytokinesis

A

when the cell splits itself into 2 new daughter cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is the M phase

A

where the nucleus and cytoplasm divide to produce 2 daughter cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what phases does interphase include

A

g1, s phase, g2 phase

S phase = synthesis, the dna is replicated

G1 phase = falls between the end of cytokinesis and the start of DNA synthesis

G2 phase = falls between the end of DNA synthesis and the beginning of mitosis

  • during the gap phases, it monitors the internal and external environment so that it has the proper conditions for reproduction and if they should continue to the next phase or allow more time to prepare
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what happens during interphase

A

A cell grows, transcribes genes, synthesizes proteins, grows in mass
the phases allow the cell to enlarge, duplicate
- without the phases, the cell would not have enough time to double in mass before it divided

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is the first division after fertilization called

A

cleavage division

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

can you explain the cell cycle control system

A

to make sure that the dna is replicated and divide properly

  • regulated via feedback from certain points in the cycle = checkpoints so that the control system does not trigger the next step in the cycle unless the cell is properly prepared
    EX: the completion of the S phase must trigger the beginning of the M
    if dna is damaged, the cycle = on hold
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what happens if the environment is unfavourable for cell proliferation

A

needs sufficient nutrients and specific sigal molecules in the extracellular environment
if = unfavourable = delay enter in the cell cycle and can enter a specialized resting state known as G zero = can be referred to as the start
- start is the important transition state and it happens at the end of g1 as it continues to the S phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is the second major transition state

A

between G2 to M phase
making sure all DNA is replicated from the S phase and making sure all the DNA that was damaged is fixed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is the third transition state

A

midway thru mitosis
confirms that the duplicated chromosomes are properly attached to a cytoskeletal machine called the mitotic spindle - before it pulls them apart and puts them into 2 daughter cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

how does the cell cycle control system prevent cancer

A

the Start transition in late G1 - the signals from the other cells if needed will stimulate the cell proliferation and if they do not need more cells they will block cell proliferation which prevent it from moving to the next phase
it regulates the cell number in the tissue of the body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

t/f all eukaryotic cells have similar machinery and control mechanisms

A

true
this is why we can study a wide variety of organisms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

how do u switch a protein on and off

A

by phosphorylating and dephosphorylating
phosphorylating = protein kinase
deephosphorylation = protein phosphatases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

explain the function of protein kinases in the cell cycle control system

A

they are activated when needed and quickly inactivated
become active toward the end of the g1 phase and are responsible for driving the cell into S phase
the other kinase becomes active just before the M phase and drives the cells into mitosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

the progression of the cell cycle depends on _____

A

cyclin-dependent protein kinases (Cdks)
Cdk is attached to a cyclin molecule = activation to initiate particular steps
the cyclin molecules also helps direct the Cdk to the target proteins that the Cdk phosphylates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what are cyclins

A

they have no enzyme activity on their own but they need to bind to the cell cycle kinases before they can become active
= cyclin-dependent protein kinases or Cdks

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

why is it called cyclins

A

because the concentratoin change are cyclical
the cyclical changes in the cyclic concentrations help drive the cyclic assembly and activation of the cyclic-Cdk complexes

  • more concentration during mitosis rather than interphase
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

explain in detail the G1 phase

A

depending on the extracellular signals reflecting conditions in the environment, the control machinery can either hold the cell in g1, g zero or into another cell cycle or terminally differentiation

once it passes the start state it usually contines smoothly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

the cell is filled with active cyclin-cdk complexes - specially S-Cdks and M-Cdks. These complexes must be turned off by the end of mitosis. Why?

A

to allow the cell to properly finish dividing
prevent the cell from immediately starting another division without taking a break in the g1 phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

how does the cell transition from M phase to G1 phse

A

destroying all exisiting cyclins so that cdks cannot be activated

stop making new cyclinc - to prevent new cdks from being activated

use cdks inhibitor proteins to block any remaining activity

this ensures that it doesn’t rush into dividing again before it is ready

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is the origins of replication and what does it do for the cell cycle

A

serves as landing pads for the proteins and protein complexes that control and carry out DNA synthesis
- it recruits a protein called Cdc6 whose concentration rises early in g1
together these proteins position the helicase
- the signal to commence replication comes from s-cdk - the cyclin-cdk complex that triggers s phase

s-cdk is assembled and activated at the end of g1 - triggers the binding of all the other proteins needed for replication
- also prevents the re-replication
it does this be phosphorylating both cdc6 and ORC - inactivating the proteins prevents helicases from reloading onto the origin of replication pads
when Cdks are inactiviated in the next g1 phase, the ORC and Cdc6 are reactivated - this allows the origins to be prepared for the s phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

how does the cell keep from dividing with DNA that is incorrectly replicated

A

the cell cycle control system delays entry into the M phase
the activity of m-cdk is inhibited by phosphorylation at particular sites - to progess into mitosis these inhibitiry phosphates must be removed by an activating protein phosphatase called cdc25
if dna replication stalls the presence of single stranded dna at the replication fork triggers a dna damage response = inhibition of the phosphatase cdc25 - this prevents the rmoval of the M-cdk
therefore, m-cdk remains inactive and M phase is delayed until the dna is complete and fixed –> g2 -> m phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

t/f the activation of s-cdk helps prevent the onset of M phase

A

false
the activation of s-cdk does not prevent hte onset of M phase
it is the inactivation of m-cdk which prevents the onset of Mpahse

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what are sister chromatids

A

when a chromosomes is duplicated and the eo copies remain tighly bound together
held together by cohesins - these assemble along the length of each chromatid as the DNA is replicated
without proper cohesins = issues with segragation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

explain how chromosomes condensation occurs via condensins

A

the condensin = ring shaped SMC protein that compacts duplicated chromosomes for segregation by forming both loops and loops within loops
- assemble along each individual sister chromatid helping each of these double helices to coil up

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what is the contractile ring

A

divides the entire cell into 2 = cytokinesis
- based on actin and myosin
- arranged at the equator of the cell
starts to assemble just beneath the plasma membrane toward the end of mitosis

27
Q

mitotic spindle is based on actin t/f

A

false
it is based on microtubules

28
Q

what are the 5 stages in mitosis

A

prophase
prometaphase
metaphase
anaphase
telophase - cytokinesis

29
Q

before m phase begins - what are the 2 critical events that need to be completed

A

dna needs to be fully replicated
the centrosome must be duplicated

30
Q

what is the centrosome

A

it is the principal microtubule organizing center in animal cells
the duplication is necessaet for the centrosome to be able to form the 2 poles of the mitotic spindle which allows each daugther cell to recieve its own centrosome

31
Q

when does centrosome duplication occur

A

at the same time as dna replication
the process is triggered by the cdks which initiate the dna replication
as mitorsis begins the centrosomes that were formed only on one side move to the opposite ends
- each of them nucleate a radical array of microbtubules called aster
- rapdily growing and shrinking microtubules extend in all directions from the 2 centrosomes

32
Q

what is a kinetochore

A

some microtubules may attach to a chromosome at its kinetochore
a protein complex associated with each sister chromatid - the kinetochore microtubules are central players in chromosome segregation

33
Q

what are interpolar/non-kinetochore microtubules

A

short microtubules in constact elgonation and collaspsing, making and breakign connections - driven in part by interactions with motor proteins and other microtubules form a dense gel like meshwork which is the basic framwork of the mitotic spindle

34
Q

t/f the centrosomes on either side of the cell become called the spindle poles

A

true
and they have astral micotubules coming out from it

35
Q

what are the 3 kinds of microtubule that come out of the mitotic spindle

A

kinetochore microtubule
non-kinetochore microtubule which are sacttered arround the spindle
astral microtubules

36
Q

overview of prophase

A

duplicated chromosomes each consisiting of 2 sister chromatics = condense
mitotic spindles assembles and move apart

37
Q

overview of prometaphase

A

breakdown of the nuclear envelope
chromosomes can now attach to the spindle microtubules via their kinetochores

the process of the dissolving of the envelope is triggered by the phosphorylation and disassemble of the nuclear pore proteins and the intermediate filament proteins of the nuclear lamina

38
Q

overview of metaphase

A

chromosomes are aligned at the equator of the cell
midway between the spindle poles
the kinetochore micotubules on each sister chromatic attach to the oppoiste poles of the spindle

39
Q

overview of anaphase

A

sister chromatics are separated and pulled slowly towards the spindle poles that they are attached to the kinetochore microtubules get shorter and the spindle poles move further apart
- breakage of the cohesin linkages that hold the chromosomes together
- the cohesin is destroyed by a protease called separase
- separase = inactive state by an inhibitory protein called securin - once securin has been destroyed (ubiquitylation), the separase is free to sever the cohesin linkages (now active)

40
Q

overview of telophase

A

the two sets of chromosomes arrive at the poles of the spindle
new nuclear membrane forms around each set
this completes the formation of 2 nuclei and marking the end mitosis
the division of cytoplasm begins starting with the assembly of the contractile ring

41
Q

overview of cytokinesis

A

in the animal cell
the cytoplsma is divided by the contractile ring of actin and myosin filaments

42
Q

t/f the kinetochore binds to the plus end of the microtubule

A

true
the kinetochore is binded to the centromere part of the chromosome and has the kinetochore microtubules to bind to it at the plus end

43
Q

what happens if the centrosome dna sequence is altered

A

no kinetochore binding
fail to segregate

44
Q

what does bi orientation mean

A

when the attachment is opposite poles
this generates tension on the kinetochores which are pulled in opposite directions
(remember the kinetochores are attached to either sister chromatid at their centromere (the dip in the middle of the chromosome)

45
Q

t/f a continuous balanced addition and loss of tubulin subunits is needed to maintain the metaphase spindle

46
Q

what happens when the drug colchicine blocks the addition of tubulin

A

no more tubulin addition
tubulin loss continues until the metaphase spindle disappears

47
Q

what happens if one end of the kinetochore attachments are severed during metaphase

A

the entire chromosomes immediately moves towards the pole to which is remain attached

48
Q

what would happen if the attachment between 2 sister chromatids is cut

A

the two opposite chromosomes separate and move toward opposite poles
shows that they are moved to the middle = metaphase plate under tension

49
Q

explain the differences in anaphase A and anaphase B

A

anaphase A = kinetochore microtubules shorten and the attached chromosomes move poleward - the chromatids are pulled to the poles
- the driving force = the loss of tubulin subunits from both ends of the kinetochore microtubules

anaphase B = the spindle poles themselves move apart - further segregating the 2 sets of chromosomes
- microtubule growth at plus end of non-kinetochore microtubules also help push the poles apart
- driving force = motor proteins in the kinesin and dynein families
kinesins proteins act on the overlapping non-kinetochore microtubules
dynein proteins anchored the plasma membrane, move along the astra microtubules to pull the poles apart

50
Q

what happens if the cell were to proceed into anaphase before all chromosomes were connected to the spindle

A

one cell would = less chromosomes
one cell = surplus
to make sure - the cell makes use of a negative signal - the kinetochores of unattached chromosomes send a stop signal to the cell cycle control system
the signal inhibits further progress of mitosis by blocking the activation of APC/C
- the spindle assembly checkpoint thereby controls the onset of anaphase as well as the exit from mitosis

51
Q

explain the reformation of the nuclear envelope in telophase

A

vesicles of nuclear membrane surround these chromosome clusters and then fuse to re-form the nuclear envelope
the nuclear pore proteins and nuclear lamins were phosphorylated during prometaphase, now they are dephosphorylated which allows them to reassemble and rebuild the nuclear envelope and lamina
inside the nucleus contains decondensed chromosomes

52
Q

what is APC/C

A

anaphase-promoting complex OR cyclosome
it triggers the anaphase by activating separase - which is a protease that cleaves the cohesins that hold the sister chromatids

53
Q

what is the cleavage furrow

A

cuts between the two groups of segregated chromosomes
so that each daughter cell receives an identical and complete set of chromosomes
- formed by the contractile ring underneath the plasma membrane

54
Q

how does the mitotic spindle dictate the position of the cleavage furrow

A

during anaphase, the overlapping microtubules that form the central spindle recruit and activate proteins that signal to the cell cortex to initiate the assembly of the contractile ring

55
Q

what is the contractile ring made out of

A

made of overlapping array of actin filaments and myosin filaments
assembles in anaphase - and is attached to membrane-associated proteins on the cytosolic face of the plasma membrane
large force produced

56
Q

what is the substratum

A

the surface that cells grow on or attach to
the cell changes shape and adhesion during divison - in interphase they have strong adhesive contacts with the substratum, in M phase, they round upd
integrins are responsible for sticking the cell to the substratum and during M phase, the integrins get phosphorylated which weaken their attachment ability

57
Q

what is phragmoplast

A

in a dividing plant cell, the structure containing microtubules and membrane vesicles (dervied from the golgi apparatus) that guides the formation of the new cell wall
- they are specialized microtubule-based structure

58
Q

how are the organelles separated into the daughter cells

A

mitochondria and chloroplasts are abundant
- the ER is cut into 2 during cytokinesis
- the golgi apparatus fragments during mitosis and the fragments associate with the spindle microtubules via motor proteins - they hitch a ride into the daughter cells as the spindle elongates in anaphase

59
Q

what are centrioles

A

cylindrical array of microtubules usually found as pairs in the centrosome in animal cells
- the other pair is sitting perp to the other one
surrounded by a gel like matrix of proteins
- inside gel = special forms of tubulin = g-tubulin = nucleation site for the growth of one microtubule

although the centrioles do not have roles in nucleation of microtubules - centrioles found in cilia and flagella do nucleate growth in microtubules

60
Q

what initiates microtubule growth

A

all of them use y-tubulin ring complexes
by using nucleation sites and keeping concentrations of free alpha/beta tubulin dimers below the concentration that would allow microtubules to form spontaneously

61
Q

explain meiosis

A

in specialized germ line cells
somatic cells = diploid which contains 2 copies of every chromosome from the dad and mom
all the chromosomes are duplicated, then they get paired - allows the segregation of homologous chromosomes during the first division
- the 2 duplicated chromosomes within each homolog are then separated during the second meiotic division - this produces 4 haploid nuclei
- the separation = random - each haploid gets a different mixture of mom and dad chromosomes

62
Q

what is a bivalent

A

structures formed when a duplicated chromosome pairs with its homolog at the beginning of meiosis
= 4 sister chromatids
2 sister from homologous chromosome 1
2 sister from homologous chromosome 2
- these structures are very stable

63
Q

how do homologs recognize each other during pairing

A

not fully understood
probably matching dna sequences on the maternal and paternal chromosomes