4/21/16
PhasesoftheCellCycle
• Thecell cycleconsists of
• theMitotic phase (M)
• Interphase (G1,S, G2)
Repetition
Summary of last lecture
•
•
INTERPHASE
Interphas e c an be
div ided into s ubphas es
–
G1 phas e
–
S phas e
–
G2 phas e
S
(DNA synthesis)
G1
G2
The mitotic phas e
–
is made up of
mitos is and
c y tok ines is
A closer look to the Cyclins and Cdks
TheCellCycleControl System
• Thesequentialeventsofthecellcycle
• aredirected byadistinct cell cyclecontrolsystem, which is similar to a
clock
RB-E2F
G1 c h e c k p o i n t
Co n tro l
s y s te m
S
E2F
G1
M
-RB-p–E2F-complex
----RB-ppp + E2F released
G2
Du ri n g G1 p h a s e p ro g re s s i o n , a c ti v a ti o n o f c y c il n
M c hec k point
G2 c h e c k p o i n t
D/c d k 4 a n d c y c l i n E/c d k 2 c o mp l e x e s b y c y c il n
a c ti v a ti n g k i n a s e (CAK) l e a d s to s e q u e n ti a l
p h o s p h o ry l a ti o n o f th e tra n s c ri p ti o n fa c to r RB.
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4/21/16
TheCellCycleClock:Cyclins andCyclin-DependentKinases
• two types of regulatory proteins are involved in cell cycle control: cyclins and cyclindependent kinases (Cdks)
theactivity of cyclins and Cdks fluctuates during thecell cycle
(a ) Fluc tua tion of MPF
G1 S G2 M
M
• Thehumanlifecycle
Ke y
during meiosis
meiocytes produce
haploid cells
Tim e
Sy n th e s i s o f c y c l i n b e g i n s i n
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Du ri n g G1, c o n d i ti o n s i n th e c e l l
Cdk
Cyclin
G2
checkpoint
Cdk
is
degr aded
Du ri n g a n a p h a s e , th e c y c l i n c o mp o n e n t
o f MPF i s d e g ra d e d , te rmi n a ti n g th e M
p h a s e . Th e c e l l e n te rs th e G1 p h a s e .
FERTILIZATION
Ov a ry
Di p l o i d
z y g o te
(2 n = 4 6 )
Te s ti s
Ac c u mu l a te d c y c l i n mo l e c u l e s
Degr aded
Cyclin
Sp e rm
Ce l l (n )
MEIOSIS
1 l a te S p h a s e a n d c o n ti n u e s
th ro u g h G2. Be c a u s e c y c l i n i s
p ro te c te d fro m d e g ra d a ti o n
d u ri n g th i s s ta g e , i t
a c c u mu l a te s .
he lp re gula te the c e ll c y c le
4
Ov u m (n )
Cyclin
(b) Mole c ula r m e c ha nis m s tha t
fa v o r d e g ra d a ti o n o f c y c l i n , a n d
th e Cd k c o mp o n e n t o f MPF i s
re c y c l e d .
Ha p l o i d g a me te s (n = 2 3 )
Ha p l o i d (n )
Di p l o i d (2 n )
G1 S G2 M
M PF act ivit y
(Mitos is Prom oting
Fa c tor, MPF) a c tiv ity a nd
c y c lin c onc e ntra tion
during the c e ll c y c le
M PF
Cyclin
c o mb i n e wi th re c y c l e d Cd k
2
mo l e c u l e s , p ro d u c i n g e n o u g h
mo l e c u l e s o f MPF to p a s s th e
G2 c h e c k p o i n t a n d i n i ti a te th e
e v e n ts o f mi to s i s .
Mitos is a nd
de v e lopm e nt
Mu l ti c e l l u l a r di p o
l id
a d u l ts (2 n = 46 )
3 MPF p ro mo te s mi to s i s b y p h o s p h o ry l a ti n g
v a ri o u s p ro te i n s . MPF‘ s a c ti v i ty p e a k s d u ri n g
me ta p h a s e .
• Meiosis reduces the number ofchromosome sets from diploid
to haploid
• Meiosis takesplacein two sets
• InterphaseandmeiosisI
I nt er phase
Hom ologous pair
of chr om osom es
ofdivisions,
meiosis Iand meiosis II
in diploid par ent cell
MEIOSIS I: Se pa ra te s hom ologous c hromos ome s
INTERPHASE
2n
PROPHASE I
METAPHASE I
ANAPHASE I
Chr om osom es
r eplicat e
TheStagesofMeiosis
Hom ologous
pair of r eplicat ed chr om osom es
Sist er
chr om at ids
Ce n tro s o me s
(wi th c e n tri o l e p a irs )
Si s te r
c h ro ma ti d s
Diploid cell wit h
r eplicat ed
• An overview of meiosis
Ch i a s ma ta
Si s te r c h ro ma ti d s
re ma i n a tta c h e d
Ce n tro me re
(wi th k i n e to c ho re )
Sp i n d l e
Me ta p h a s e
p l a te
chr om osom es
M ei osi s I
• Meiosis I reduces the
number of chromosomes
from diploid to haploid
1 Hom ologous
chr om osom es
separ at e
n
Haploid cells wit h
r eplicat ed chr om osom es
Ch ro ma ti n
M ei osi s I I
• Meiosis II produces four
haploid daughter cells
Haploid cells
wit h unr eplicat ed chr om osom es
Nu c l e a r
e n v e l o p eTe tra d
Ho mo l o g o u s
Mi c ro tu b u l e
c h ro mo s o me s
a tta c h e d to
s e p a ra te
re p l i c a te d (ho mo l o go u s)k i n e to c h o re
Pa irs of hom ologous
Te tra ds line up
c h ro mo s o me s
c hrom os om e s s plit up
Hom ologous c hrom os ome s
(re d a nd blue ) pa ir a nd e x cha nge
s e gm e nts ; 2 n = 6 in this e xa m ple
Chrom os om e s duplic ate
2 Sist er chr om at ids
separ at e
n
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4/21/16
• Acomparisonofmitosisandmeiosis
• TelophaseI,cytokinesis,andmeiosisII
MITOSIS
MEIOSIS
TELOPHASE I AND
CYTOKINESIS
METAPHASE II
PROPHASE II
ANAPHASE II
MEIOSIS
TELOPHASE II AND
CYTOKINESIS
Pr ophase I
Chr om osom e
r eplicat ion
Haploid
chr om at ids
daught er
f or m ing
separ at e
Chr om osom e
r eplicat ion
Tet r ad f or m ed by
synapsis of hom ologous
chr om osom es
2n = 6
diploid c ell
Chr om osom es
posit ioned at t he
M et aphase
Sist er
M EI O SI S I
Pr ophase
Duplicat ed chr om osom e
( t wo sist er chr om at ids)
Cleavage
f ur r ow
Chiasm a ( sit e of
cr ossing over )
Par ent cel l
( bef or e chr om osom e r eplicat ion)
( hom ologous
chr . )
II: Se pa ra te s s is te r c hrom a tids
m et aphase plat e
Tet r ads
posit ioned at t he
m et aphase plat e
M et aphase I
cells
Sist er chr om at ids
separ at e dur ing
anaphase
Anaphase
Tel ophase
Hom ologues
separ at e
dur ing
anaphase I ;
Anaphase I
Tel ophase I
sist er
chr om at ids
r em ain t oget her
2n
Haploid
n = 3
haploid c ells
Daught er
cel l s of
m ei osi s I
wi th re p l i c a te d c h r
2n
M EI O SI S I I
Daught er cel l s
of m i t osi s
n = 3
Tw o hapl oi d cel l s
f or m ; chr om osom es
Dur i ng
ar e st i l l doubl e
f our
re p l i c a te d
c h ro mo s o me s
anot her
r ound of cel l di vi si on,
hapl oi d daught er
t he si st er
cel l s r esul t , cont ai ni ng
chr om at i ds
f i nal l y separ at e;
si ngl e chr om osom es
n
diploid cells
n
n
Daught er cel l s of m ei osi s I I
Sist er chr om at ids separ at e dur ing anaphase I I
n
haploid c ells
wi th s i n g l e c h r
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