Cell Cycle: Start/Restriction Point & S Phase Flashcards
1
Q
The presence of each cyclin rises and falls at distinct points of the cell cycle. True or false?
A
True
2
Q
Which cyclin is highest during S phase?
A
S-cyclin (Cyclin A)
3
Q
Which cyclin is highest during G1?
A
G1/S-cyclin (cyclin E)
4
Q
Which cyclin is highest during M phase?
A
M-cyclin (cyclin B) and decreasing S-cyclin (cyclin A)
5
Q
Which cyclin is highest during G2?
A
S-cyclin (cyclin A) with M-cycling (cyclin B) rising
6
Q
Familiarize yourself with this figure.
A
7
Q
There are ___ classes of cyclins, each of which binds and activates specific ______..
A
Four
Cyclin-dependent kinases (Cdks)
8
Q
There are four classes of cyclins: ____, ______, ______, and _____.
A
G1
G1/S
S
M
9
Q
The cyclin and cyclin-dependent kinase complex G1-CDK in yeast is composed of ___________ and _________.
A
Cyclin 3 (Cln3)
Cyclin-dependent kinase 1 (CDK1)
10
Q
The G1-CDK complex in mammals is composed of ____________ and _______________.
A
Cyclin D
Cyclin-dependent kinase 4 (CDK4) and cyclin-dependent kinase 6 (CDK6)
11
Q
The G1/S-CDK complex for yeast is composed of ________ and/or ___________ and ____________.
A
Cyclin 1 and cyclin 2 (Cln1, Cln2)
CDK1
12
Q
The G1/S-CDK complex in mammals is composed of ________ and _____________.
A
Cyclin E
CDK2
13
Q
The G1-Cdk complex in vertebrates is composed of cyclin ___ and cyclin-dependent kinases ____ and ____. In yeast, this same complex is composed of cyclin (Cln) _____ and cyclin-dependent kinase _____.
A
Cyclin D
Cdk4 &Cdk6
Cln3
Cdk1
14
Q
The G1/S-Cdk complex in verebrates is composed of cyclin ____ and cyclin-dependent kinase _____ while in yeast it is composed of cylcin (Cln) _____ and cyclin-dependent kinase ____.
A
Cyclin E
Cdk2
Cln1, 2
Cdk1
15
Q
In yeast, G1 cyclin synthesis is stimulated by _________________ and ________________.
A
Nutrient accumulation and availability
Cell growth (i.e., size)
16
Q
In mammalian cells, G1 cyclin synthesis is stimulated by __________, ________________, and ___________.
A
Nutrient accumulation and availability
Cellular growth (size)
Growth factor stimulation
17
Q
The S-Cdk complex is composed of cyclin _____ and Cdk ____ and ____ in vertebrates and cyclin (Clb) ______ and Cdk1 in yeast.
A
Cyclin A
Cdk2 & Cdk1
Clb5, 6
18
Q
Complete the table.
A
G1-Cdk, Cdk 4 & Cdk6
Cyclin A
Cdk1
19
Q
Complete the table
A
G1-Cdk, Cdk4 & Cdk6
Cyclin E
Cyclin A, Cdk2 & Cdk1
M-Cdk, Cdk1
20
Q
Complete the table.
A
G1-CDK, Cyclin D, Cdk4 & Cdk6, Cln3, Cdk1
Cyclin E, Cdk1
Cyclin A, Cdk2 & Cdk1, Cdk1
M-Cdk, Cdk1
21
Q
Complete the table.
A
G1-Cdk, Cyclin D, Cdk4 & Cdk6, Cln3, Cdk1
G1/S-Cdk, Cyclin E, Cdk2, Cln1, 2, Cdk1
S-Cdk, Cyclin A,Cdk2 & Cdk1, Clb5, 6, Cdk1
M-Cdk, Cyclin B, Cdk1, Clb1, 2, 3, 4, Cdk1
22
Q
In the M-Cdk complex, cyclin _____ and cdk _____ are present in vertebrates and cyclin ________ and cdk ____ in yeast.
A
Cyclin B
Cdk1
Clb 1, 2, 3, 4
Cdk1
23
Q
The G1/S boundary is the “start” or _______________ point.
A
Restriction
24
Q
What do cyclin dependent kinases do?
A
Regulate progression of the cell cycle at distinct stages
25
Cyclin-dependent kinases regulate progression at distinct stages of the _______ cycle.
Cell
26
Cyclin-dependent kinases can be regulated by _________ binding, \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, and ________________ binding.
Cyclin
Phosphorylation
CDK inhibitory proteins (CKIs)
27
What are three ways in which cyclin-dependent kinases (CDKs) are regulated?
(1) Binding of their respective **cyclins**,
(2) **phosphorylation**, which can activate or deactive them, and
(3) binding of **CDK inhibitory proteins** (CKIs)
28
What does CKI stand for?
Cyclin-dependent kinase (Cdk) inhibitory proteins
29
In yeast, G1 cyclin synthesis is stimulated by _________________ and \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.
Nutrient accumulation and availability
Cellular growth (increase in size)
30
In mammals, G1 cyclin (cyclin D) synthesis is stimulated by \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, and \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.
Nutrient accumulation and availability
Cellular growth
Growth factor stimulation
31
What is the primary difference between yeast and mammalian cells regarding G1 cyclin synthesis?
Mammalian cells require **growth factor stimulation**
32
For all other cyclins, each active _______ initiaties a wave of ____________ activity, which produces a new \_\_\_\_\_\_\_.
Cdk
Transcriptional
Cyclin
33
How are cyclins degraded in the cell?
**Ubiquitin-dependent proteolysis**
34
What is required for **ubiquitin-dependent proteolysis** during the cell cycle?
Two **E3 ubiquitin-ligases**:
1. **SCF complex**
2. **APC/C complex** (*a*naphase *p*romoting *c*omplex or *c*yclosome)
35
What does APC/C complex stand for?
**A**naphase **p**romoting **c**omplex or **c**yclosome
36
The SCF complex is active throughout the cell cycle but only recognizes _______________ targets.
Phosphorylated
37
What are two targets of the SCF complex?
**G1 cyclins** and **CKIs** (*c*yclin-dependent *k*inase *i*nhibitors)
38
How does the SCF complex recognize its targets G1 cyclins and CKIs (cyclin-dependent kinase inhibitors)?
Phosphorylation
39
When is APC/C (anaphase promoting complex or cyclosome) active?
When **phosphorylated** by the **M-cyclin/Cdk complex** at the *metaphase/anaphase* transition
40
What phosphorylates APC/C (anaphase promoting complex or cyclosome)?
The M-cyclin/Cdk complex (cyclin B/Cdk1)
41
What does APC/C target?
Proteins that possess **destruction box** motifs (recognition sites for APC/C)
42
What proteins have destruction boxes?
S-cyclin (cyclin A), M-cyclin (cyclin B), and proteins that connect sister chromatids
43
What are the three targets of APC/C?
1. S-cyclin (cyclin A)
2. M-cyclin (cyclin B)
3. Proteins that connect sister chromatids
44
In the absence of phosphorylation, ____________________________ (Cdks) still have activity but are much lower.
Cyclin-dependent kinases
45
Cyclin-dependent kinases (Cdks) are more active when \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.
Phosphorylated
46
CDKs are phosphorylated by \_\_\_\_\_\_\_\_\_\_\_\_.
***C*DK *a*ctivating *k*inases** (CAKs)
47
CAKs (CDK activating kinases) are active throughout the cell cycle and _________________ the amino acid ____________ at the active site.
Phosphorylate
Threonine
48
Phosphorylation of the amino acid threonine by CAKs (CDK activating kinases) at the active site of CDKs increases their activity but is not the ______________ step.
Rate-limiting
49
What kinase phosphorylate and inhibit mitotic CDKs?
**Wee1 kinases**
50
What do **Wee1** kinases phosphorylate on CDKs?
**Tyrosine** and **threonine** residues in the **ATP binding site** of CDK
51
Wee1 kinases phosphorylate a tyrosine and threonine residue in the _______________ site of CDK, which *potently* inhibits CDK activity.
ATP-binding site
52
How are phosphorylations completed by Wee1 kinases removed?
**Cdc25 phosphatases**
53
\_\_\_\_\_\_\_\_ phosphatases dephosphorylate and therefore ___________ mitotic CDKs inhibitied by Wee1 kinase phosphorylation.
Cdc25
Activate
54
How many classes of CKIs are present in mammalian cells?
4
55
What does CKI stand for?
**C**D**K** **i**nhibitors
56
What are the four classes of CKIs (CDK inhibitors) in mammalian cells?
1. **Wee1** kinases
2. **INK4** (G1 CDK inhibitors)
3. **p21CIP** (G1/S and S CDK inhibitors)
4. **p27**KIP1 (G1/S and S CDK inhibitors)
57
What does INK4 stand for?
***In*hibitors of *k*inase *4***
58
What inhibits G1 CDKs (CDKs 4 & 6)?
INK4 (*inhibitors of kinase 4*)
59
How does INK4 (inhibitors of kinase 4) (a CKI) inhibit CDK4 and CDK6 in the G1 phase?
INK4 binds them, preventing cyclin binding
60
When is INK4 most likely to be expressed?
In response to excessive growth stimulation because it inhibits CDKs 4 & 6 from binding cyclin D
61
What does the "p" stand for in p21CIP and p27KIP1?
Protein
62
What are the G1/S (CDK2) and S (CDK2 & 1) CDK inhibitors (CKIs)?
p21CIP and p27KIP1
63
How do p21CIP and p27KIP1 act as CKIs (CDK inhibitors)?
Binding G1/S and S cyclin/CDK complexes, inhibiting CDK activity
64
As the activity of a particular CDK begins to increase, one of its targets is the ___________ that is trying to inhibit it.
CKI (CDK inhibitor)
65
How do CDKs inactivate CKIs?
CDKs bind CKIs when CDK levels increase, and CDK binding to CKIs inhibits CKIs
66
What happens after a cyclin-dependent kinase (CDK) binds its CDK inhibitory protein (CKI) target?
**SCF complex** recognizes it via its substrate recognition partner, an **F-box protein**, and *ubiquinates* it
67
How does a CDK *inhibitor* (CKI) become degraded?
Binding by CDK, ubiquinated by **SCF complex** via help of its *substrate recgonition partner*, an **F-box protein**
68
What helps the **SCF complex** recognize CKIs (CDK inhibitors)?
**A substrate recognition partner**, an **F-box protein**
69
What is an **F-box protein**?
A substrate recognition partner for the SCF complex
70
How do cells commit to moving through the cell cycle?
Moving past the G1/S boundary
71
What is the **rate-limiting step** for the cell cycle?
The **G1/S boundary**
72
In yeast, the G1/S boundary is known as the "start" point whereas it is known as the "\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_" point in mammalian cells.
Restriction point
73
What do we mean by a "start" or "restriction point" in the cell cycle?
The cell is committed to moving through the cycle unless some significant problem occurs
74
What is required for start in yeast?
1. Sufficient nutrients and growth
2. Sufficient level of Cln3 (cyclin 3), the G1 cyclin
3. Synthesis of Cln1 and Cln2 (cyclin 1, cyclin 2), the G1/S cyclins
75
What three things are required for start in yeast?
1. Synthesis of Cln1 & 2
2. Synthesis of enough Cln3 (G1 cyclin)
3. Nutrient availability and appropriate cell size
76
Cln3/CDK1 phosphorylate the transcriptional co-repressor of Cln1 and Cln2, \_\_\_\_\_\_\_\_, thereby enabling transcription of Cln 1 & 2 required for start.
**Whi5**
77
What does Whi5 do?
It **represses** transcription of **Cln 1 & Cln 2** and thereby regulates start
78
What deactivates Whi5?
Phosphorylation by Cln3/CDK1, the G1 cyclin/CDK complex
79
Regulation of Cln3 occurs at what level?
The level of **translation**
80
The regulation of Cln 1 and Cln 2 occurs at what level?
The level of **transcription**
81
How is Cln3 regulated?
When nutrients are scarce, translation of all proteins is inhibited, and nutrient available is detected and relayed through the **Target of Rapamycin (TOR) kinase**
82
What is TOR kinase stand for?
Target of Rapamycin kinase
83
What does TOR kinase do?
Target of Rapamycin kinase detects nutrient levels in yeast cells, ultimately regulating whether the cell will translate Cln3
84
In mammalian cells, passing the _______________ point requires both growth factor signaling and sufficient nutrients.
Restriction
85
Nutrient availability and binding by growth factors are relayed through a kinase called _____________________ in mammalian cells.
Mammalian Target of Rapamycin (mTOR)
86
Which specific mTOR is involved in identifying nutrient availability and growth factoring binding?
mTOR complex 1 (mTORc1)
87
Active mTOR phosphorylates three key substrates. What are they?
1. S6 kinase
2. 4E binding protein
3. Transcription factors
88
mTOR phosphorylates ______ and activates it, which then phosphorylates its target \_\_\_\_\_\_\_\_\_\_\_.
S6 kinase
Ribosomal protein S6
89
mTOR phosphorylates S6 kinase, which then phosphorylates ribosomal protein S6 because ribosomal protein S6 must be phosphorylated for the _______________ to engage translation.
Ribosome
90
mTOR phosphorylates 4E binding protein, which normally binds eIF4E and ______________ eIF4E.
Inhibits
91
How does 4E binding protein inhibit eIF4E?
By binding and sequesting eIF4E
92
When 4E binding protein is phosphorylated by \_\_\_\_\_\_\_, it releases \_\_\_\_\_\_\_\_\_, allowing it to bind other eIFs and the 5' cap of mRNA.
mTOR
eIF4E
93
mTOR phosphorylates other transcription factors, too, which increase the _________________ synthesis.
Ribosomal subunit
94
What regulates mTOR?
1. Low ATP levels and environmental stress *inhibit* mTOR
2. High amino acid levels and growth factor stimulation *activate* mTOR
95
What two things *inhibit* mTOR?
1. Low ATP levels, specifically ATP/AMP rato
2. Environmental stress, like osmotic stress, oxidative stress, and high temperatures
96
\_\_\_\_\_ ATP levels, and specifically low ATP:AMP ratios, ___________ mTOR as do ______________ stressors.
Low
Inhibit
Environmental
97
What two things *stimulate* mTOR?
1. High amino acids levels, especially leucine
2. Growth factor stimulation
98
What amino acid is especially significant in activating mTOR?
Leucine
99
What G-protein activates mTOR?
Rheb
100
What protein acts as the GAP (GTPase activating protein) for Rheb, which functions as the G-protein for mTOR?
Tuberous sclerosis 1/2 (TSC1/TSC2)
101
What do TSC1/TSC2 stand for?
Tuberous sclerosis 1/2
102
When TSC1/TSC2 is active, it binds and activates the G-protein \_\_\_\_\_, stimulating the hydrolysis of GTP to GDP. This _______ the G-protein and thereby decreases its ability to activate \_\_\_\_\_\_. Thus, for cell growth to occur, we want TSC1/TSC2 to be \_\_\_\_\_\_\_\_\_\_.
Rheb
Deactivates
mTORc1
Inactive
103
What do tuberous sclerosis 1/2 (TSC1/TSC2) do regaring mTOR activation?
TSC1/TSC2 act as the GAP for **Rheb**, which is the G-protein that activates mTOR
104
What phosphorylates and inactivates TSC2 of the TSC1/2 complex?
Protein kinase B (PKB)
105
Under favorable conditions, Akt/PKB is activated. PKB then phosphorylates and _________ TSC2 of the _________ complex. Phosphorylation likely leads to the ___________ of the complex. As such, the complex can no longer function as the ______ for Rheb, so Rheb remains in its \_\_\_\_\_-bound state and active, thereby activating mTORc1 and increasing \_\_\_\_\_\_\_\_\_.
Inactivates
TSC1/TSC2
Dissociation
GAP (GTP-ase activating protein)
GTP-bound
Cell growth
106
Under unfavorable conditions, specifically low ATP/AMP ratios, **AMP kinase** is activated, which in turn phosphorylates and activates \_\_\_\_\_\_\_, which increaseTSC1/2 complex levels. This allows for Rheb to hydrolyze its GTP for \_\_\_\_, thereby inhibiting its ability to activate \_\_\_\_\_\_\_.
TSC2
GDP
mTORc1
107
\_\_\_\_\_\_ ATP/AMP ratios activate \_\_\_\_\_\_, which in turn phosphorylates and activates TSC2, which causes the association of the TSC1/2 complex. The TSC1/2 complex can now act as the GAP for \_\_\_\_, thereby hydrolyzing its GTP for GDP. This causes its deactivation and decreases mTOR activity.
Low
AMP kinase
Rheb
108
Which pathway mediates mTOR activation via growth factors?
PI3K via G-protein Rheb and its GAP TSC1/TSC2
109
Which pathway mediates mTORc1 activation via amino acid levels?
The **Rag** complex of G-proteins
110
When amino acid levels are high, mTORc1 is activated by ___________ G-proteins.
Rag complex
111
Which pair of the Rag complex is GTP bound under high amino acid levels?
A&B
112
Which pair of the Rag complex is GDP bound under high amino acid levels?
C&D
113
What acts as the GEF (guanine nucleotide exchange factor) for RagA&B?
**Ragulator**
114
Under low amino acid conditions, RagA&B are bound to \_\_\_\_\_\_\_\_\_\_\_\_\_\_.
GDP
115
Under low amino acid conditions, RagC&D are bound to \_\_\_\_\_\_\_\_\_\_\_\_.
GTP
116
What acts as the GAP (GTP-ase activating protein) for RagD?
Leucyl-tRNA synthetase
117
When can **leucyl-tRNA synthetase** act as the GAP for Rag D?
Upon **leucine** binding
118
Be able to describe the pathway that leads to mTORc1 activation via growth factor binding.
119
In the presence of amino acids, mTORc1 is activated by what pathway?
The Rag complex
120
How is mTORc1 activated by the Rag complex of G-proteins? In other words, what must be present in the cell for the pathway's activation?
Amino acids, especially leucine
121
How is mTORc1 activation different from other G-proteins we've encountered throughout the semester?
RagA/B must be **GTP** bound
Rag C/D must be **GDP** bound
122
mTORc1 is activated by the ____________ complex of G-proteins. Amino acids activate \_\_\_\_\_\_\_\_\_\_\_\_\_\_, the GEF for RagA/B, and leucine binds and activates \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, the GAP for RagC/D. This allows for RagA/B to become \_\_\_\_-bound and RagC/D to become \_\_\_\_-bound, which is required for mTORc1 activation.
Rag complex
Ragulator
leucyl tRNA synthetase
GTP-bound
GDP-bound
123
mTORc1 can be regulated by ATP levels when _____ kinase phosphorylates and activates TSC2.
AMP kinase
124
ATP levels can also regulate mTORc1 by \_\_\_\_\_\_\_\_\_\_.
Inhibition
125
\_\_\_\_ATP:AMP ratios activate AMP kinase to either phosphorylate and activate \_\_\_\_\_\_\_\_, thereby inhibiting mTORc1, or directly phosphorylate and inhibit _______ because ____ levels signal to the cell that there is not enough energy for cell growth.
Low
TSC2
mTORc1
Low
126
There are four cyclin/CDK pairs in \_\_\_\_\_\_\_\_\_\_\_, two in ___________ yeast, and three in budding yeast.
Mammals
Fission yeast
127
Be able to explain the major differences between cyclin/CDK complexes in fission yeast cells and mammalian cells.
128
The order of cyclin/CDK complexes from G1 to M phase in mammalian cells: D, E, A, B; 4&6, 2, 2, 1.
Cyclin D/CDK4&6
Cyclin E/CDK2
Cyclin A/CDK2
Cyclin B/CDK1
129
Growth factor binding its receptors activates the MAPK pathway. This results in transcription and translation of the G1 cyclin/CDK complex: \_\_\_\_\_\_\_\_\_. The G1 cyclin/CDK complex phosphorylates \_\_\_\_\_\_, which releases E2F, a ______________ that upregulates expression of S cyclin/CDK complex: \_\_\_\_\_\_\_\_\_\_\_\_\_.
Cyclin D/CDK 4&6
Rb (Retinoblastoma)
Transcription factor
Cyclin E/CDK2
130
\_\_\_\_\_ upregulates expression of cyclin E/CDK2, which then phosphorylates \_\_\_\_, releasing E2F and increasing its own expression.
E2F
Rb
131
When enough cyclin \_\_/CDK\_\_ is accumulated in the yeast cell, the cell moves past the ____________ point or ______ boundary.
Cyclin 3/CDK2
start point
G1/S boundary
132
At the beginning of G1 phase, Rb or _____________ binds and sequesters the transcription factor \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.
Retinoblastoma
E2F
133
What does Rb stand for?
Retinoblastoma
134
What happens when cyclin D/CDK4&6 phosphorylate Rb?
Rb releases transcription factor E2F
E2F then upregulates transcription of cyclin E and CDK2
Cyclin E/CDK2 are required for transition from G1 phase to S phase
135
What does Rb do in its unphosphorylated form?
Sequesters the transcription factor E2F
136
In mammalian cells, cyclin \_\_\_/CDK4&6 promote progression from G1 to ____ phase while cyclin \_\_\_/CDK2 initiate ________ in late G1 phase. Cyclin \_\_\_/CDK2 initiate ________ in S phase, again, and cyclin B/CDK1 promotes mitosis in late ____ phase.
Cyclin D/CDK4&6
S phase
Cyclin E/CDK2
Replication
Cyclin A/CDK2
Replication
G2
137
The transcription factor E2F, active G1/S cyclinE/CDK2 complex, and active S cyclinA/CDK2 complex all have a _______ feedback loop with E2F.
Positive
138
E2F increases transcription of cyclin \_\_\_\_. Cyclin E/CDK2 in turn phosphorylate \_\_\_\_, which releases E2F.
Cyclin E
Rb
139
Cyclin E/CDK2 or __________ phase complex increases the synthesis of the S-phase cyclin, cyclin \_\_\_\_.
G1/S phase
Cyclin A
140
As protein synthesis increases, cyclin D and CDK4&6 levels increase; cyclin D/CDK4&6 phosphorylate ____ (retinoblastoma), which then releases the transcription factor E2F in the cytosol.
Rb
141
The S phase is regulated in cells by regulating the S phase cyclin, which in yeast is ______ and in animals is \_\_\_\_\_\_. Initial S cyclin synthesis is stimulated by G1/S cyclin/CDK activity (i.e., cyclin E/CDK2). Upon its synthesis, the S chase cyclin is inhibited by _____ in yeast and _____ in animals. This keeps the cyclin inactivae until the correct time.
Clb5&6
Cyclin A
Sic1
p27KIP
142
The G1/S cyclin/CDK complex ultimately overcomes the inhibition of the S phase cyclin via ____ in yeast and ____ in animals. The G1/S cyclin/CDK complex phosphorylates these CDK inhibitory proteins, leading to their ubiquination and degradation by the _____ complex.
Sic1
p27KIP1
SCF complex
143
In yeast, Sic1 inhibits the S phase cyclin: \_\_\_\_\_\_\_\_\_. Once start occurs, the G1 cyclin/CDK complex (Cln3/CDK1) phosphorylates Sic1. This results in ubiquination and degradation of Sic1 by the SCF complex, which requires the help of _______ in identifying targets. Sic 1 must be phosphorylated ___ times in order for degradation to occur.
Clb5&6/CDK1
F-box protein
6 times
144
How many times must Sic1 be phosphorylated in __________ yeast before it can be recognized by _______ and ubiquinated by SCF complex?
Budding
F-BOX protein
6 times
145
Why must Sic1 be phosphorylated 6 times before it can be recognized by FBOX?
Poor affinity at some binding sites; requires high levels of G1/S cyclin/CDK (cyclin E/CDK2)
146
What is the significance of Sic1 requiring phosphorylation 6 times?
Provides a sharp transition between G1 and S phases
147
During _____ phase, replication of DNA occurs via multiple ________ of replication, but the pre-replication complex is assembled during _____ phase.
S phase
Origins of replication
G1
148
What makes up the pre-recognition complex?
Origin recognition complex
Helicase
Loading factors, Cdc6 and Cdt1
149
What three things are required for assembly of the pre-replication complex?
1. Origin recognition complex
2. Helicase
3. Loading factors, Cdc6 and Cdt1
150
**Initiation of replication** requires phosphorylation of the replication complex by two kinases: (1) \_\_\_\_\_\_\_\_\_, which phosphorylate **initiator proteins** that in turn recruit **helicase activating factors** and the **DNA polymerase complex**, and (2) \_\_\_\_\_\_\_\_\_\_, which phosphoryates MCM helicase.
CyclinA/CDK2
DDK
151
When do the kinases that phosphorylate the replication complex become active?
S phase; they assembly during G1 and wait
152
How does the cell ensure replication occurs only once?
1. Loading factor **Cdc6** is phosphorylated by **cyclin A/CDK2** and targeted for ubiquination and degradation by **SCF complex**
2. Loading factor **Cdt** detaches from pre-replication complex and bound by its inhibitor, **geminin**, which is later targeted by **APC/C complex** in M phase
3. **Helicase** only loads when DNA is **unphosphorylated**; following replication, phosphorylated helicase is exported from the nucleus and only reenters the nucleus following dephosphorylation by phosphatases active during G1
153
The loading factor ______ is phosphorylated by cyclin A/CDK2 and then targeted by ______ for degradation by the proteosome.
Cdc6
SCF complex
154
After it helps the pre-replication complex attach, loading factor _____ is bound by its inhibitor \_\_\_\_\_\_\_\_, which is later targeted for degradation by the ________ complex in M phase.
Cdt1
Geminin
APC/C
155
Helicase only loads onto DNA when it is phosphorylated or non-phosphorylated?
Non-phosphorylated
156
What links sister chromatids together?
Cohesins
157
Cohesins are made up of four subunits: two _____________ and two \_\_\_\_\_\_\_\_\_\_\_.
Coiled-coils
Globulars
158
Why are sufficient levels of Cln3 required in yeast for start to occur?
Cln3/CDK1 phosphorylate the transcriptional co-repressor Whi5, releasing its inhibition of Cln 1 and Cln2 transcription
159
In yeast, Cln3/CDK1 complex phosphorylates the transcriptional co-repressor \_\_\_\_\_\_\_, which releases from DNA and allows for transcription of the next round of cyclins: _____ and \_\_\_\_\_.
Whi5
Cln1
Cln2
160
For mTORc1 activation, RagA&B must be bound to _____ and RagC&D must be bound to \_\_\_\_.
GTP
GDP
161
For activation of mTORc1, RagA&B must be in its GTP form. This requires that its GDP be exchanged for GTP by its GEF \_\_\_\_\_\_\_\_\_\_\_\_\_\_. Simultaneously, RagC&D must be in its GDP form. This requires that its GTP be hydrolyzed to GTP by its GAP \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.
Ragulator
Leucyl-tRNA synthetase
162
For mTORc1 activation to occur under high amino acid conditions, __________ must bind leucyl-tRNA synthetase in the ___________ membrane. This activates the GAP function of leucyl-tRNA synthetase and results in RagC&D becoming _____ bound.
Leucine
Lysosomal
GDP-bound
