Trafficking, Life and Death of the Cell Flashcards
(180 cards)
1
Q
What is an example of a cell that enters G0 “resting phase”?
A
Neuron
2
Q
What is the G1 phase of the cell cycle?
A
The start of the cell cycle - The cell grows and synthesises mRNA and proteins for DNA replication
3
Q
What is the S phase of the cell cycle?
A
The phase during which DNA replication occurs
4
Q
What is the G2 phase of the cell cycle?
A
Pre-mitotis phase - The cells undergoes rapid growth and protein synthesis
5
Q
Which phases make up interphase?
A
G0, G1, S and G2
6
Q
What is prophase?
A
First stage of mitosis - Nuclear envelope is breaking down, DNA is condensing into chromosomes and spindle poles form and positioned
7
Q
What is prometaphase?
A
Second stage of mitosis - Spindle poles connecting to chromosomes and repositioning them at the metaphasal plate
8
Q
What is metaphase?
A
Third stage of mitosis - Chromosomes line up at the metaphasal plate
9
Q
What is anaphase?
A
Fourth stage of mitosis - Chromatids are separated and pulled to opposite poles by spindles
10
Q
What is telophase?
A
The fifth stage of mitosis - The DNA decondenses, the nuclear envelope reforms and the spindle poles disassemble
11
Q
What is cytokinesis and when does it begin occuring?
A
The pinching and separation of the cell membrane, resulting in one cell being turned into 2. It starts to occur during anaphase but does not finish until after telophase
12
Q
When are chromosomes at their most condensed state?
A
Anaphase
13
Q
How long does mitosis take to occur?
A
Less than one hour
14
Q
At what point are chromatids connected?
A
A region of centromeric DNA called the kinetichore
15
Q
At what point on the chromosome does the spindles attach to during mitosis?
A
Kinetichore
16
Q
What amino acids in a protein can be phsophorylated?
A
Serine and threonine (sometimes tyrosine)
17
Q
How does phosphorylation activate/deactivate a protein?
A
The addition of a negative phosphate group causes a conformational change to that protein either making it active or deactivating it
18
Q
True or False:
Kinases activate proteins
A
False
Kinases can activate proteins but they can also deactivate them
19
Q
What type of kinases control the cell cycle?
A
Cyclin dependent kinases
20
Q
How are cyclin dependent kinases activated?
A
Binding to a cyclin protein - Cyclin pulls the activation group towards it, revealing the ATP
21
Q
How are cyclin dependent kinases controlled?
A
Different cyclins are specifically expressed at different stages of the cell cycle
22
Q
What is actin?
A
a protein that forms (together with myosin) the contractile filaments of muscle cells, and is also involved in motion in other types of cells
23
Q
What is anaphase?
A
the stage of meiotic or mitotic cell division in which the chromosomes move away from one another to opposite poles of the spindle
24
Q
What is the anaphase promoting complex (APC)?
A
an ubiquitin ligase that targets key mitotic proteins such as cyclins and directs them to the proteosome to initiate anaphase
25
What does aneuploidy mean?
the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46
26
What is the apoptosome?
a large quaternary protein structure formed in the process of apoptosis. Its formation is triggered by the release of cytochrome c from the mitochondria in response to an internal (intrinsic) or external (extrinsic) cell death stimulus
27
What are astral microtubules?
a subpopulation of microtubules, which only exist during and immediately before mitosis. They are defined as any microtubule originating from the centrosome which does not connect to a kinetochore. They help anchor/position the spindle pole
28
What are Bax and Bak?
proapoptotic proteins belonging to the Bcl-2 protein family which are activated by BH3-only proteins and inhibited by prosurvival Bcl-2 proteins via direct interactions
29
What is Bcl-2?
an antiapoptotic protein belonging to the Bcl-2 protein family that bind to BH3-only proteins and prevents them from activating the proapoptotic proteins Bax and Bak, preventing apoptosis
30
What is Bcl-xl?
a transmembrane molecule in the mitochondria that is a member of the Bcl-2 protein family. It acts as a antiapoptotic protein by preventing the release of mitochondrial contents such as cytochrome c
31
What are BH3-only proteins?
a subset of the Bcl-3 family of proteins that contain only a single BH3-domain. These proteins play a key role in promoting apoptosis and include BAD
32
What are caspases?
a family of cysteine proteases that serve as primary effectors during apoptosis to proteolytically dismantle most cellular structures, including the cytoskeleton, cell junctions, mitochondria, endoplasmic reticulum, Golgi, and the nucleus
33
What is cyclin-dependent kinase (CDK)?
an enzyme that activates upon binding to a cyclin that affects the progression of the cell cycle
34
What is CFTR protein?
a membrane protein and chloride channel that conducts chloride and thicyanate ions across epithelial cell membranes. Mutations of the CFTR gene can lead to dysregulation of epithelial fluid transport in the lung (and other organs) resulting in cystic fibrosis
35
What is clathrin?
a protein that plays a major role in the formation of coated vesicles.
36
What is condensin?
large protein complexes that play a central role in chromosome assembly and segregation during mitosis and meiosis
37
What is a constitutive secretory pathway?
a type of exocytosis where the contents of the vesicles are secreted automatically
38
What is COPI?
a protein complex that coats vesicles from the cis end of the golgi complex back to the rough ER where they were originally synthesised and between golgi compartments
39
What is COPII?
a type of vesicle coat protein that transports proteins from the rough ER to the golgi
40
What is cyclin?
a family of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (Cdk) enzymes
41
What is cystic fibrosis?
a genetic disorder that affects mostly the lungs, but also the pancreas, liver, kidneys, and intestine. Long-term issues include difficulty breathing and coughing up mucus as a result of frequent lung infections
42
What is cytochrome c?
a small protein usually located on the inner membrane of the mitochondrion. When cytochrome c is released from the mitochondrial in activates caspase 9 which activates other caspases which are responsible for destroying the cell from within
43
What is cytokinesis?
the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells
44
What is a death induced signalling complex (DISC)?
A protein complex formed by the association of signaling proteins with a death receptor upon ligand binding. The complex includes procaspases and death domain-containing proteins in addition to the ligand-bound receptor, and may control the activation of caspases 8 and 10
45
What are death ligands?
ligands that bind to death receptors on the surface of the cell membrane that once bound to their receptor will cause a conformational change and initiate a cascade of different kinases and caspases that will ultimately function to demolish the cell in a controlled manner. Their main role would be to initiate the external pathway of apoptosis, such as the activation of caspase-8
46
What are dyneins?
an ATPase that cross-links adjacent microtubules and that by controlling their relative sliding motion regulates the movement of cellular organelles and structures (as the beating of cilia and flagella and the movement of chromosomes to the poles of the spindle)
47
What is dynamic instability?
the switching between microtubule growing (polymerising) and shrinking (depolymerising) states
48
What is an ER signal sequence?
a sequence of amino acids located at the N-terminus of a protein that directs the protein across the ER membrane. It consists of one or more positively charged amino acids followed by a continuous stretch of 6-12 hydrophobic residues
49
What is an executioner (effector) caspase?
a type of caspases which includes caspases 3, 6 and 7 that are activated by their own cleavage and once activated cleaves multiple substrates leading to apoptosis of the cell
50
What is familial hypercholerterolaemia?
an inherited condition that results in high levels of low-density lipoprotein (LDL) cholesterol which may be caused by an absence of or faulty LDL receptors or inability for LDL to be internalised
51
What is the Fas death receptor?
a receptor on the surface of cells that leads to programmed cell death that forms a death inducing signalling complex (DISC) upon ligand binding.
52
What is G1 phase?
the first of four phases of the cell cycle where the cell synthesises mRNA and proteins in preparation for subsequent steps leading to mitosis
53
What is G2 phase?
the third of four phases of the cell cycle where the cell rapidly grows and synthesise proteins to prepare for mitosis. Cancer cells often skip G2
54
What is GlcNAc phosphtransferase?
an enzyme responsible for the addition of a mannose-6-phosphate to an enzyme destined for a lysosome
55
What is I-cell disease?
a condition caused by a deficiency in the GlcNAc phosphotransferase which means that lysosomal hydrolase enzymes are not targeted to lysosomes, and are instead secreted from cells. This causes cells to fill up with dense inclusion bodies filled with macromolecules that would usually be broken down
56
What are importins?
a protein complex that transports protein molecule into the nucleus by binding to specific recognition sequences, called nuclear localisation sequences (NLS)
57
What is an initiator caspase?
a type of caspase which includes caspases 8 and 9 that are activated by dimerisation and once activated activates executioner caspases through cleavage
58
What are interpolar microtubules?
a type of microtubule that make links with interpolar microtubules radiating from the other pole. They centeralise mitotic apparatus and define the location of the metaphasal plate
59
What is a karyotype?
the number and visual appearance of the chromosomes in the cell nuclei of an organism or species
60
What is KDEL?
a target peptide sequence in a protein that prevents it from leaving the endoplasmic reticulum. A protein with a functional KDEL motif will be retrieved from the Golgi apparatus by retrograde transport to the ER lumen. K - lysine, D - aspartic acid, E - glutamic acid, L - leucine
61
What is kinesins?
a protein belonging to a class of motor proteins found in eukaryotic cells. Kinesins move along microtubule (MT) filaments, and are powered by the hydrolysis of adenosine triphosphate (ATP) (thus kinesins are ATPases)
62
What is a kinetochore?
a complex of proteins associated with the centromere of a chromosome during cell division, to which the microtubules of the spindle attach
63
What are kinetochore microtubules?
a type of microtubule that radiate out from the pole and contact kinetochores. They undergo rapid polymerisation/depolymerisation events
64
What is Mad2?
an essential spindle checkpoint protein that sits at free kinetochores and blocks anaphase promoting complex (APC) action.
65
What is mannose-6-phosphate?
a molecule added to lysosomal enzymes by GlcNAc phosphotransferase that allows them to enter and remain in the lysosomes
66
What is metaphase?
a stage of mitosis during which chromosomes are at their second-most condensed and coiled stage. During metaphase the chromosomes align in the equator of the cell before being separated into each of the two daughter cells
67
What is a microtubule?
components of the cell cytoskeleton found throughout the cytoplasm which are tubular polymers of tubulin. The microtubule cytoskeleton is involved in the transport of material within cells, carried out by motor proteins that move on the surface of the microtubule
68
What are microtubule associated proteins (MAPs)?
proteins that bind to the tubulin subunits that makeup microtubules to regulate their stability
69
What is the microtubule organising centre (MTOC)?
a structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions: the organization of eukaryotic flagella and cilia and the organization of the mitotic and meiotic spindle apparatus, which separate the chromosomes during cell division
70
What is a mitochondrial matrix signal?
a sequence of amino acids located at the N-terminus of the protein that is a basic, amphipathic α-helix that is recognised by the TOM complex in the outer membrane and the TIM complex in the inner mitochondrial membrane
71
What is mitosis?
a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth
72
What are motor proteins?
a type of protein that slide along the microtubules and generate forces to move organelles through the hydrolysis of ATP. The three important types include myosin, kinesin and dynein
73
What is myosin?
a type of motor protein important for muscle contraction and a wide range of other motility processes in cells. During cytokinesis it combines with actin to create the contractile ring
74
What is navitoclax?
an anti-cancer drug that binds to and inactivated most anti-apoptotic Bcl-2 family members, however it also blocks Bcl-xl activity causing decreased platelet lifespan
75
What is NF-AT?
a transcription factor that activates gene transcription
76
What is a nuclear localisation signal (NLS)?
an amino acid sequence that 'tags' a protein for import into the cell nucleus by nuclear transport. Typically, this signal consists of one or more short sequences of positively charged lysines or arginines exposed on the protein surface
77
What is a nuclear pore complex (NPC)?
large protein complexes that cross the nuclear envelope, which is the double membrane surrounding the eukaryotic cell nucleus
78
What are oncogenes?
a gene that has the potential to cause cancer. In tumour cells, they are often mutated and/or expressed at high levels. Activated oncogenes can cause those cells designated for apoptosis to survive and proliferate instead, leading to cancer.
79
What is peptidase?
an enzyme that performs proteolysis: protein catabolism by hydrolysis of peptide bonds
80
What is prometaphase?
the second phase of mitosis, the process that separates the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells. During prometaphase, the physical barrier that encloses the nucleus, called the nuclear envelope, breaks down
81
What is prophase?
the first phase of mitosis and meiosis where the chromatin condensed and the nucleolus disappears
82
What is a proteasome?
protein complexes which degrade unneeded or damaged proteins tagged by ubiquitin molecules by proteolysis
83
What is Ran protein?
a small G protein that is essential for the translocation of RNA and proteins through the nuclear pore complex. It binds to importin after it has brought molecules into the nucleus, allowing importin to be shuttled out into the cytoplasm
84
What is a regulated secretory pathway?
a type of secretion where the molecules packaged in vesicles are only released after a signal is received. An example of this is neurotransmitters released into a synapse
85
What is S phase?
the part of the cell cycle in which DNA is replicated, occurring between G1 phase and G2 phase
86
What is a signal recognition particle (SRP)?
a ribonucleoprotein that recognises and targets specific proteins to the ER. SRP binds to the signal sequence of the protein being translated causing a pause in translation. The protein is then directly translated into the ER
87
What is Taxol?
an anti-cancer drug that acts by stabilising microtubles. It causes cells to arrest at metaphase due to defects in spindle microtubule dynamics resulting in chromosome missegregation and cell death
88
What is tBID?
a protein that activates the mitochondrial apoptotic pathway when it is created through the cleavage of BiD by active caspase 8
89
What is telophase?
the final stage of mitosis and meiosis where the two daughter nuclei form in each daughter cells and the nuclear envelopes reform
90
What is the TIM/TOM complex?
a protein complex which translocates proteins with a specific signal sequence at the N-terminus produced from nuclear DNA through the mitochondrial membrane
91
What is a TNF receptor?
a cytokine receptor able to bind to TNFs (including Fas) that play an important role in appotosis
92
What is ubiquitin?
a molecule that is often added to a substrate protein that can mark them for degradation via the proteasome
93
What is Venetoclax?
an anti-cancer drug that is a selective Bcl-2 inhibitor while sparing platelets by binding to Bcl-xl three times weaker than Bcl-2
94
What is whole chromosomal instability?
the persistent inability of a cell to accurately segregate its genome (alters the dosage of oncogenes) - with deletion/mutation of tumour suppressor p53
95
What are the substrates of the cyclin-Cdk complex?
Nuclear lamins and the nuclear pore complexes
Microtubule-associated proteins (MAPs)
Motor proteins
Anaphase promoting complex (APC)
96
What molecule is responsible for stabilising chromatids?
Cohesins
97
What allow cytosolic condensin proteins to contact DNA and induce chromatin condensation?
The opening of the nucleus
98
What happens when the cyclin-Cdk complex interacts with the nuclear lamins?
The nuclear lamins are phosphorylated causing the breakdown of the nuclear envelope
99
What happens when the cyclin-Cdk complex interacts with the MAPs?
The MAPs that stabilise interphase are inactivated. They reform as mitotic spindles
100
What happens when the cyclin-Cdk complex interacts with APC?
It activates it
101
What does APC do?
It targets ubiquitinated securin molecule bound to separase and breaks it down, activating the separase.
It also causes the degradation of M-Cdk
102
What does separase do?
It cleaves the cohesins that keeps sister chromatid joined
103
What is the structure of microtubules?
Microtubules consist of two monomers (α and β: form a tubulin heterodimer). 13 strands of tubulin heterodimers surround a central lumen. Microtubules have a negative end and a positive end
104
What does a GTP cap do for microtubules?
It slows the depolymerisation of the microtubule allowing it to grow
105
How are microtubules arranged during interphase?
Microtubules are attached to the microtubule organising centre (MTOC) from there negative end. The positive end grows to the cell periphery
106
What are kinesins?
A type of motor protein that is responsible for positive end movement along the microtubule
107
What are dyneins?
A type of motor protein that is responsible for negative end movement along the microtubule
108
What is different about kinesin-5?
It is double-headed; it contains 2 motor domains allowing it to push the poles apart
109
What attaches the kinetochore to the positive end of the microtubule?
Ndc80 complex
110
What makes up the contractile rile during cytokinesis?
Actin and myosin
111
What protein is responsible for ensuring that all kineotchores are attached by the spindle microtubles?
Mad2
112
How does Mad2 work?
It binds to free kinetochores and blocks APC action so the chromatids can't be separated
113
What effect does Taxol have on filaments and what is its mechanism?
It stabilises filaments by binding alongside them preventing dynamic instability. This leads to chromosome missegregation and eventually apoptosis
114
What are the three main methods of protein transport across membranes?
Gated transport
Transmembrane transport
Vesicular transport
115
What is a feature of the amino acid sequence that signals import into the nucleus?
It is a basic stretch of amino acids found within the protein
116
What is a feature of the amino acid sequence that signals import into the mitochondria?
It is found at the N-terminal of the protein and forms a positively charge amphipathic α-helix
117
What is a feature of the amino acid sequence that signals import into the peroxisomes?
It is found at the c-terminal of the protein
118
What is a feature of the amino acid sequence that signals import into the ER?
It is a hydrophobic stretch of amino acids followed by a basic stretch
119
What is the maximum size of proteins that can diffuse across nuclear pore complexes?
50kDa
120
How would a 100kDa protein pass into the nucleus?
Active transport
121
How does a prospective nuclear protein pass through a nuclear pore complex?
Importin binds to the protein and causes a configurational change in the NPC allowing the protein to pass through. In the nucleus importin binds to Ran protein and releases the nuclear protein before Importin-Ran are shuttle out into the cytosol
122
In what ways can the nuclear localisation signal be blocked and hence regulate the import of proteins into the nucleus?
An inhibitor protein may bind to the nuclear protein.
| The NLS may be modified (i.e. phosphorylation)
123
True or False:
| Proteins are imported into the nucleus in a folded conformation
True
124
True or False:
| The mitochondria matrix signal is a very strict unique sequence
False
| It is variable but is always a basic, amphipathic α-helix
125
What is the mechanism for the import of protein into the mitochondrial matrix?
The precursor protein binds to the TOM complex of the outer membrane by the matrix signal sequence. The TOM complex then aligns with a TIM23 complex of the inner membrane. The protein is then able to pass through the complexes unfolded into the matrix space
126
What does the TIM complex require to import a protein?
A membrane potential. The space between the membranes is positive and the matrix space is negative
127
What is the mechanism of protein import into the ER?
As the protein is being translated the SRP sequence is recognised by an SRP molecule which docks the ribosome onto the membrane. The protein is then translated directly into the ER through a protein translocator
128
What is added to most proteins synthesised in the Rough ER?
Most proteins synthesised in the rough ER are glycosylated by the addition of a common N-linked oligosaccharide
129
What is the role of protein glycosylation?
```
Folding/quality control
Structural/protective/stabilising
Organisational/barrier function
Protection from microorganisms
Targeting
```
130
How are oligosaccharides used as tags to mark the state of protein folding?
A semi-folded protein undergoes glucose trimming until the oligosaccharide is recognised by calnexin (a chaperone). Calnexin assists in the folding of the protein. If it is incorrectly folded glucosyl transferase bind to it and prevents it from leaving the ER, calnexin can then correct it. Once the N-linked oligsaccharide is correct signalling that the protein is correct, it can leave the ER
131
What is the cause of cystic fibrosis?
It is caused by gene mutations that result in deficient or dysfunctional cystic fibrosis transmembrane conductance regulator (CFTR) protein
132
What is CFTR?
CFTR is an anion channel normally present on the plasma membrane of epithelial cells
133
What type of coat protein surrounds vesicles leaving the ER?
COPII
134
What type of coat protein surrounds vesicles leaving the golgi?
COPI
135
How does clathrin allow vesicles to form?
Clathrin triskeleton monomers bind to activated receptors and causes the membrane to bend. Once the receptor are almost fully enclosed in the membrane dynamin (a GTPase) polymerises and constricts the neck of the vesicle until it breaks of from the cell membrane. The clathrin then uncoat from the vesicle
136
What is the pathway of molecules that have been phagocytosed?
Early endosome to Late endosome. They are then either sent to the lysosome (for breakdown) or to the golgi (for relocation)
137
What is the pathway of lysosomal enzymes synthesised in the ER?
ER to golgi to late endosome to lysosome
138
What does a KDEL sequence do?
Prevents soluble ER resident proteins from being excreted. When proteins with a KDEL sequence are exported from the ER they are recognised by KDEL receptors and sent back to the ER
139
What amino acids make up the KDEL sequence?
Lys-Asp-Glu-Leu
140
What are the three pathways for protein sorting through the trans Golgi network?
Signal-mediated diversion to lysosomes
Signal-mediated diversion to secretory vesicles
Constitutive secretory pathway
141
How are lysosomes always so acidic?
The lumen is maintained at an acidic pH by an H ATPase that pumps H ions into the lume
142
What prevents lysosomal enzymes from breaking down molecules while being transported to the lysosome?
They are not active when being transported. The only activate under acidic conditions such as that in the lysosome
143
How are lysosomal proteins recognised?
Lysosomal enzymes are glycosylated with a mannose in the ER and then phosphorylated in the golgi. So they have a mannose-6-phosphate
144
Which enzyme is responsible for adding a phosphate to the mannose of a lysosomal enzyme?
GlcNAc phosphotransferase
145
What does a deficiency in GlcNAc phosphotransferase cause?
I-cell disease
146
A protein has an ER signal sequence, no transmembrane anchor and no other signal sequences. Its final destination is most likely...
a) The ER
b) The golgi
c) Lysosome
d) Mitochondria
e) Outside the cell
f) In the plasma membrane
e) Outside the cell
147
A protein has an ER signal sequence and a transmembrane anchor but no other signal sequences. Its final destination is most likely...
a) The ER
b) The golgi
c) Lysosome
d) Mitochondria
e) Outside the cell
f) In the plasma membrane
f) In the plasma membrane
148
What happens when necrosis occurs?
Necrotic cells trigger inflamation by cells of innate immune system.
149
What are the type of signals that can elicit apoptosis?
Inside the cell:
DNA damage, oxidative stress, cytosolic calcium overload, unfolded protein accumulation
Outside the cell:
Death ligands
150
What activates executioner caspases?
Initiator caspases
151
Where are caspases found in the cell?
Cytosol and nucleus
152
What molecules do executioner caspases react with?
```
ICAD
eIFs
MST1
Nuclear lamins
Proteins at cell adhesion sites
```
153
What do eIFs do?
Block proten translation
154
What does MST1 do?
Phosphorylates histones causing chromatin condensation
155
What causes PS to flip? What is the point of it?
Effector caspase activation; it signals to other cells that is needs to be endocytosed
156
What are the two caspase activation pathways?
Intrinsic (mitochondrial) pathway
| Extrinsic (death receptor) pathway
157
What occurs in the Intrinsic (mitochondrial) pathway?
An apoptotic stimulus signals the release of cytochrome c from the mitochondria. Cytochrome c then binds to and activates Apaf1, causing activated Apaf1 molecules to combine to form the apoptosome. Caspase-9 is then recruited into the apoptosome which activates the caspase
158
What family of proteins regulates cytochrome c release?
Bcl-2
159
Where is Bcl-2 found?
It is anchored in the mitochondrial outer membrane
160
How does Bcl-2 regulate cytochrome c release?
Bcl-2 prevents Bak/Bax action which are responsible for cytochrome c release
161
What protein family blocks Bcl-2?
BH3-only proteins
162
Where is Bax usually found?
Cytosol, it is targeted to the mitochondrial outer membrane after activation
163
How to Bak/Bax release cytochrome c?
They combine to form oligomers (membrane pores) that allows cyt c to pass through the membrane
164
How does Navitoclax work?
It binds to and activates most anti-apoptotic Bcl-2 family members but it reduces the number of platelets circulating
165
Why does Navitoclax reduce platelet counts?
The life-span of platelets are regulated by Bcl-xl which is bound and blocked by Navitoclax causing decreased platelet lifespan
166
How does the extrinsic pathway cause cell death?
A death ligand (such as Fas) binds to a death receptor which causes the assembly of the death induced signalling complex (DISC). This facilitates the activation of the caspase
167
What makes up the DISC?
Adapter proteins (e.g. FADD) and initiator caspases
168
How does the two apoptotic pathways overlap?
Caspase 8 (initator) directly activates effector caspases. It also cleaves BiD to tBiD which is an active BH3-only protein. tBiD activates the mitochondrial apoptotic pathway
169
```
In a proliferating (cycling) mammalian cell, the order of phases in the cell cycle is
Select one:
a. G1, G2, S, M
b. G1, S, G2, M
c. M, G0, G1, S, G2
d. G2, S, G1, M
e. G0, G1, G2, M, S
```
b. G1, S, G2, M
170
Proteasomes:
Select one:
a. glycosylate proteins in the endoplasmic reticulum
b. cleave proteins at a single specific site
c. are ATP dependent proteases
d. add mannose-6-phosphate to lysosomal proteins
e. are large enzymes involved in the ubiquination of proteins
c. are ATP dependent proteases
171
CDK:
Select one:
a. Becomes an active kinase upon binding by cyclin
b. Becomes an active kinase upon degradation by cyclin
c. Becomes an active phosphatase upon degradation by cyclin
d. Becomes an active phosphatase upon binding by cyclin
a. Becomes an active kinase upon binding by cyclin
172
The mitotic spindle:
Select one or more:
a. must align all chromosomes properly before mitosis can be completed
b. emanates from four centrosomes
c. aligns each chromosome by attachments to the telomeres
d. is arranged so that both sister chromatids of a particular chromosome move towards the same pole
e. is composed of astral, kinetochore and polar microtubules
a. must align all chromosomes properly before mitosis can be completed
AND
e. is composed of astral, kinetochore and polar microtubules
173
The targeting signal that directs proteins into the mitochondrial matrix is:
Select one:
a. A C-terminal KDEL signal
b. An N-terminal basic, amphipathic alpha helix
c. A stretch of basic amino acids exposed on the folded protein
d. A mannose 6-phosphate
e. An N-terminal stretch of hydrophobic amino acids followed by a basic amino acid
b. An N-terminal basic, amphipathic alpha helix
174
The targeting signal that directs proteins into the nucleus is:
Select one:
a. An N-terminal basic, amphipathic alpha helix
b. A C-terminal KDEL signal
c. An N-terminal stretch of hydrophobic amino acids followed by a basic amino acid
d. A stretch of basic amino acids exposed on the folded protein
e. A mannose 6-phosphate
d. A stretch of basic amino acids exposed on the folded protein
175
The signal recognition particle (SRP).
Select one:
a. binds to ER signal sequences and blocks protein translation
b. binds to the mRNAs encoding ER proteins
c. is a complex consisting of the ribosome and the ER translocation machinery
d. binds to KDEL signals
e. recognizes signal sequences and translocates them across the ER
a. binds to ER signal sequences and blocks protein translation
176
Proteins found in the nucleus:
Select one:
a. May diffuse across the nuclear pore complex without a targeting signal if they are smaller than ~50 kDa
b. A C-terminal KDEL signal
c. Contain a basic stretch of amino acids in the protein that is cleaved upon entry
d. Must bind to importins in order to cross the nuclear pore complex
e. Must first be unfolded before they cross the nuclear pore complex
a. May diffuse across the nuclear pore complex without a targeting signal if they are smaller than ~50 kDa
177
Receptor mediated endocytosis of LDL
Select one or more:
a. requires vesicle formation mediated by clathrin and dynamin
b. leads to both the LDL particle and LDL receptor being degraded in the lysosome;
c. leads to the degradation of the LDL receptor in the lysosome and degradation of the LDL particle by the proteasome
d. involves the LDL receptor binding to the LDL particle at the plasma membrane; Correct
e. leads to the transport of the LDL particle to the ER;
a. requires vesicle formation mediated by clathrin and dynamin
AND
d. involves the LDL receptor binding to the LDL particle at the plasma membrane
178
N-glycosylation of proteins
Select one or more:
a. is a feature of many proteins imported into the ER
b. occurs in the Golgi and lysosomes
c. is a modification that has a role in folding and quality control
d. is the covalent attachment of oligosaccharides to the N-terminus of the protein
a. is a feature of many proteins imported into the ER
AND
c. is a modification that has a role in folding and quality control
179
New drugs that target the apoptotic pathway to treat chronic lymphoid leukemia are designed to:
Select one:
a. Bind and inactivate all members of the Bcl-2 family
b. Bind to BH3-only proteins
c. Inactivate caspases
d. Act as BH3 mimetics
e. Block pro-apoptotic proteins Bax and Bak
d. Act as BH3 mimetics
180
```
In the apoptosis hierarchy, which circumstance most directly leads to activation of pro-caspase 9?
Select one:
a. Assembly of the apoptosome
b. DISC formation
c. The activation of Bid
d. Activation of caspase 3
e. Treatment of cells with death ligand
```
a. Assembly of the apoptosome
