Exam 3 Flashcards
What molecules do vesicles carry between compartments?
soluble proteins and membrane proteins
What is vesicle budding driven by?
assembly of a protein coat
What does vesicle docking depend on?
Tethers and SNAREs
Where do transport vesicles carry proteins?
Golgi apparatus
What part of the cell is responsible for lipid production?
smooth ER
True or false, lipid proteins are transported by transport vesicles to the Golgi.
true
What secretes from the Golgi?
hormones
Can the endomembrane system be modified?
yes, depending on the cell type
Transport occurs between compartments in what?
endomembrane system and the plasma membrane
Endocytotic mechanisms are destined for what?
lysosomes
What protein coats vesicles?
Clathrin
What shape do clathrin molecules assemble into?
basket like cages
What do clathrin molecules do?
help shape membranes into vesicles
Formation of baskets on the membrane leads to what?
reformation and internalization
Where does clathrin form baskets?
endocytotic site
Why do vesicles form?
to internalize things outside of the cell
What pinches the vesicle from the membrane?
Dynamin (GTPase)
What does clathrin bind to?
adaptin
The binding of clathrin and adoption do what?
buds the vesicle until its pinched off by Dynamin
The vesicle distorts, doing what?
allows clathrin and adaptin to fall off leaving carboxy terminal domains of receptors
Where is the initial site of adaptin assembly?
carboxy terminal domains of the receptors
What are Tethers and SNAREs?
proteins
What does vesicle docking involve?
membrane proteins, v-snares, and t-snares
Where are V-SNARES?
on vesicles
here are T-SNAREs?
on target membrane
What does the RAB protein bind to?
vesicles containing cargo
What initiates membrane fusion?
t-snare binding to v-snare
What releases vesicle cargo to next compartment?
membrane fusion
RAB binding to a tethering protein pulls what?
v-snares and t-snares
Where are most proteins modified?
in the ER
What controls the size of the ER?
demand for protein folding
Where are proteins further modified and sorted?
Golgi
Secretory proteins are released from the cell by what process?
exocytosis
What event happens before proteins are sent to the Golgi?
glycosylation event
What amino acid are many proteins glycosylated on in the ER?
asparagine
What membrane lipid delivers Oligosaccharide to a protein?
Dolichol
What catalyzes the transfer of oligosaccharides from Dolichol to Asparagine?
the enzyme oligosaccharyl transferase
Where do ER proteins enter the Golgi?
the cis face
Proteins are glycosylated as they travel through what?
Golgi Cisternae
Where do proteins exit the Golgi?
trans face
The Golgi consists of what?
stack of flattened membrane enclosed sacs
What part of the Golgi does most glycosylation happen?
medial cisterna
What element triggers the release of secretory proteins?
Calcium
What are the 2 pathways of exocytosis?
regulated and constitutive
Where do the regulated and constitutive pathways diverge?
trans Golgi network
Is the constitutive pathway regulated?
no
What do secretory vesicles do?
store and release concentrated proteins
What do specialized phagocytic cells ingest?
large particles
Pinocytosis takes up what?
fluid and macromolecules
Receptor-mediated endocytosis provides what into animal cells?
specific route
Where are endocytose macromolecules sorted?
endosomes
Lysosomes are the principle site of what?
intracellular digestion
Is pinocytosis constantly happening?
yes
Is phagocytosis a triggered process?
yes
Is receptor mediated cytosine triggered?
yes
What does phagocytosis do?
completely changes the cell membrane and completely envelopes an invader
What do pseudopods do?
wrap and surround the particle to be digested
In what process does the cell membrane fold and create small pockets and captures the cellular fluid and dissolved substances?
pinocytosis
What are some examples of pinocytosis?
microvilli of the small intestines and ducts of the kidneys
What is a example of receptor mediated endocytosis?
cholesterol internalization from the blood stream
Where does LDL enter the cells?
via receptor-mediated endocytosis
Where can viruses enter cells?
receptor0mediated cytosis
Lysosomes contain a variety of what that are only active under acidic conditions?
hydrolytic enzymes
Do lysosomes originate from the Golgi?
no
Lysosomes are the result of what?
endocytic chamber forming
What pathways do materials destined for degradation follow?
endocytosis, phagocytosis, and autophagy (auto phagocytosis)
Delivery of vesicle to the lysosomes comes from where?
the Golgi
Can cell signals act over a long or short range?
yes
What do all responses depend on?
a signal from the cell
What do receptors trigger in a cell?
molecular switches
What are the purpose of cell-surface receptors?
relay extracellular signals via intracellular signaling pathways
What molecules act as molecular switches?
some intracellular signaling proteins
What do ion-channel-coupled receptors convert?
chemical signals into electrical signals
What is signal transduction?
process where one type of signal is converted into another. example chemical into electrical
What are the 2 mechanisms of extracellular signaling molecules?
bind to cell-surface receptors or bind to intracellular receptors (hydrophobic)
What is Acetylcholine an example of?
a signaling molecule that can induce different responses in different target cells
What cellular signals have multiple different functions?
cell survival, division of cell, different structures and functions of cells, cell death trigger
How do fast extracellular signals act?
through existing protein function
How do slow extracellular signals act?
through changes in transcription or protein synthesis
Describe cell-surface receptors.
on plasma membrane (are membrane proteins)
synthesized on the rough ER
enter vesicle transport to Golgi
goes through glycolysis
alpha helical shape
Signaling molecules eventually interact with what kind of protein?
specific effector proteins
What do altered effector proteins do?
change the behavior of the cell
Signaling molecules can effect final response elements (proteins), this has what sort of effect?
metabolism, shape, genes expression
What is Protein Phosphorylation and GTP binding proteins an example of?
intracellular signaling proteins that can act as molecular switches
Explain protein phosphorylation.
transfers phosphates to initial target, signal is now being transducted. keeps target dephosphorylated
Explain GTP proteins.
when they are in a state v fund to GTP they are off, hydrolysis of GTP turns the signal on (these are 2 different pathways)
What are the 3 main classes of cell-surface receptors?
ion-channel coupled
G protein coupled
enzyme coupled
What is a GCPR?
Guanine Protein Coupled Receptor
What does stimulation of GCPR’s do?
activates G protein subunits
What can the Cyclic AMP Signaling Pathway do?
activate enzymes and turn on genes
What does the Inositol Phospholipid Pathway trigger?
rise in intracellular Ca2+
In a GCPR signaling pathway what dissolved gas is generated to carry a signal to the adjacent cells?
NO (nitrous oxide)
Activation of G protein subunits is also known as what?
G protein coupled signaling
How does GCPR activate G proteins?
by inducing the exchange of GDP for GTP at the alpha subunit
The G protein alpha subunit is switched of by…
hydrolyzing its bound GTP to GDP
Do some G proteins directly regulate ion channels?
yes
What enzyme is Cyclic AMP synthesized by?
Adenylyl Cyclase
What enzyme degrades Cyclic AMP?
Cyclic AMP phosphodiesterase
True or False. Nucleotides can be coenzymes or signaling molecules.
true
Do Cyclic AMP level rise or lower rapidly in response to an extracellular signal?
rise
A rise in intracellular cyclic AMP can activate what?
gene transcription
Epinephrine stimulates the breakdown of what in skeletal muscles?
glycogen
What triggers the release of Ca2+ from internal storage sites into the cytosol?
inositol phospholipid pathway
Elevtaed cytosolic Ca2+ can activate what?
calmodulin dependent pathways
Calmodulin dependent pathways activate via what?
calmodulin dependent kinase (CAM-kinase)
Fertilization of an egg leads to what happening?
results in a wave of calcium along the whole cell
Where is a major calcium storage site?
in the cellular ER
The inositol phospholipid signaling pathway is what kind of signaling cascade?
heterogemeric
What is the result of IP3 being triggered by the GPCR system?
calcium will constantly be dumping out of the ER
What are the first 2 steps in the Inositol Phospholipid pathway?
- ligand binds to GPCR activating G-proteins and activating Phospholipase C
- Phospholipase C activates 2 signaling pathways
What are steps 3 & 4 of the Inositol Phospholipid pathway?
- Phospholipase C dissociates IP3 and Diacyl Glycerol from a membrane bound Inositol phospholipid
- IP3 binds to Ca2+ channels on the ER, this triggers Ca2+ release from the ER
What are steps 5 & 6 of the Inositol Phospholipid pathways?
- elevated cytosolic Ca2+ and released diacyglycerol work together to activate Protein Kinase C (PKC)
- PKC phosphorylates numerous protein targets to generate cell response
What is phospholipase?
hydrolyzed phospholipids
What changes the shape of the calmodulin protein?
calcium binding
How many calciums bind to calmodulin?
4
What is chemotaxis?
movement of cell or molecule with the concentration gradient
The activation of RTK stimulates what?
the assembly of an intracellular signaling complex
Active phosphorylated RTKs provide what for other signaling proteins?
docking sites
What are inactive RTKs?
membrane proteins
What are some examples of signals in a cell?
local, cell cell, ion, long range diffusible, and neurotransmitters
What controls nerve cell production in the fruit fly Drosophila?
notch signaling
What is the signal protein in a Drosophila called? receptor protein?
delta; notch
Are delta and notch proteins transmembrane?
yes
What results in the binding of delta to notch?
proteolysis of the receptor
When delta notch complex is cut off it floats, then what happens?
the GDP system transports it to the nucleus
Does notch serve in binding and transcription factors?
yes
Explain steroid signaling.
small hydrophobic hormones bind to intracellular receptor that act as transcription regulators
What do all steroid hormones have?
cholesterol backbone
Are steroid hormones amphipathic?
yes
What does amphipathic mean?
they can just pass through
Explain the steroid hormone cortisol.
acts by activating a transcription regulator in cytosol
cortisol receptor protein complex moves to the nucleus
it controls gene transcription
Explain signaling integration “crosstalk”.
intracellular signaling proteins serve to integrate multiple external incoming signals
What are the 3 filaments in the cytoskeleton?
intermediate filaments
actin
microtubules
Describe there cytoskeleton.
gives a cell shape
allows cell to organize internal compartments
allows generation of force for movements
What is the Golgi structured around?
microtubules
Explain intermediate filaments.
very fibrous, like ropes
form net/meshwork throughout cell
associate with cell cell contact points
has high tensile strength
How big are intermediate filaments?
10 nm
Explain microtubules.
not solid
helical distribution
more rigid than actin
more dynamic than filament proteins
not very strong
How big are microtubules?
25 nm
What is actin also known as?
microfilaments
What is actin the main component of?
muscle
Explain actin.
helical polymer
undergoes dynamic assembly and disassembly constantly
concentrated around cell periphrie
fingerlike extensions
How big are actin?
7 nm
Are intermediate filaments found in plants and lower vertebrate animals?
no
Are intermediate filaments, microtubules, and actin all tissue specific?
no, only intermediate filaments
What is the nuclear lamina?
meshwork of intermediate filaments that support the nuclear envelope
Explain how intermediate filaments are formed.
8 thinner strands twisted into a rope
dimers then arranged in opposite orientations
tetramers link end to end
8 tetramers twist into the rope like filament
What are intermediate filaments associated with?
desmosomes
Are intermediate filaments good for transport?
no, they do not have direction
Is there energy required to form an intermediate filament?
no energy is required
What are the 2 types of intermediate filaments?
cytoplasmic and nuclear
What are the subclasses of cytoplasmic filaments?
keratin filaments- epithelial cells
vimentin and vimentin related- connective tissue cells. muscle cells, and glial cells
neurofilaments- nerve cells
What is the subclass of nuclear filaments?
nuclear lamins- in all animal cells
What makes skin more prone to blistering?
mutant form of keratin
What are lamins?
intermediate filaments that support snd strengthen the nuclear envelope
form network at base of nuclear envelope
provide attachment site for chromosomes
What is progeria?
premature aging
What causes progeria?
mutations in lamin A
Describe plectin.
protein that aids in bundling of intermerdiate filaments
What is plectins function?
links intermediate filaments to other cytoskeleton components such as actin and microtubules
What are KASH proteins?
on cytoplasmic membrane on outer nuclear envelope
What are SUN proteins?
anchored on the inner nuclear envelope
Does plectin affect KASH and SUN if disrupted?
yes
What is the function of KASH?
binds microtubules, motors, plectins, or actin
What is the function of SUN?
bind chromatin or nuclear lamina
Wha6tis the major microtubule organizing center?
the centrosome
Where do microtubules originate from?
the centrosome
What happens if microtubules are depolymerized?
the Golgi disorganizes
What are cilia and flagella important for?
cell motility
Are centrosomes organizing centers?
yes
How many centrosomes do cells normally have?
one
Do plants have centrosomes?
no, most of them do not
Are microtubules hollow tubes?
yes
What are microtubules made out of?
globular tubular subunits (alpha beta dimers)
How many subunits are in a microtubule cross section?
13 subunits
How many GTP binding sites do microtubules have?
two
What do protofilaments do for microtubules?
give them their helical structure
Is the beta tubular end positive or negative?
positive
Is the alpha tubular end positive or negative?
negative
Where does tubular polymerize on a centrosome?
nucleation sites
Describe y-Tubulin.
embedded in pericentriolar centrosome matrix as “ring complexes”
Where does nucleation take place?
negative end of the tubule
Describe microtubule dynamic insability.
not permanent when it polymerizes
Does each microtubule grow and shrink independently of its neighbor?
yes
How are microtubules stabilized?
capping proteins that bind to the ends of the positive ends
What happens during polymerization of microtubules?
alpha beta dimers GTP adds to positive end forming a GTP cap
Loss of the GTP cap results in what?
microtubule polymerization
What does the Kinesin motor do?
hydrolyzes ATP and moves toward MT plus end
at does the Dynein motor do?
hydrolyzes ATP and moves toward MT minus end
What drives intracellular transport?
motor proteins
How do motor proteins move along microtubules?
using their globular heads
Where are ATPase domains?
glubular heads
What is the lagging foot and can lift?
ATP
What is the front foot and is bound?
ADP
What do adaptors signal for?
binding of kinesins or dyneins
How are microtubules in a cilium or flagellum arranged?
“9 + 2” array (9 doublet microtubules, 2 center microtubules)
What does the movement of Dynein cause?
cilia and flagellum to bend
Describe actin filaments.
thin and flexible
Do actin and tubular polymerize by different mechanisms or the same?
similar mechanisms
What underlies the plasma membrane in most eukaryotic cells?
a cortex rich in actin filaments
What can alter the arrangement of actin filaments?
extracellular signals
What influences the type of protrusions formed at the leading edge?
actin binding proteins
What allows animal cells to adopt a variety of shapes to perform a variety of functions?
actin filaments
What do actin monomers polymerize into?
filaments
Do actin filaments have polarity?
yes, they have a + end and - end
What does actin polymerization require?
ATP, actin ATP monomer adds to plus end of polymer
What can actin filaments undergo?
tread milling
What controls the behavior of actin filaments?
actin binding proteins
How does actin help the cells move forward?
forces generated in the actin filament rich cortex
What pushes the leading edge of the lamellipodium forward?
web of polymerizing actin filaments
How is the plus end of newly polymerized actin stabilized?
capping protein
What does the stabilization of a polymerized actin filament result in?
branching structures that push the plasma membrane forward
What does actin associate with to form contractile structures?
myosin
What is involved in organelle movement?
myosin 1
What is involved in muscle contraction?
myosin 2
Does myosin 1 contain a tail region?
no
Does myosin 2 contain a tail region? if so what does it form?
yes myosin 2 filaments
What are the 4 phases of the eukaryotic cell cycle?
G1, S, G2, M
What triggers the major processes of the cell cycle?
a cell cycle control system
What happens in the M phase?
division
What happens in the G1 phase?
longest phase, is the growth phase
What happens in the S phase?
DNA synthesis
What happens in the G2 phase?
gap phase between S and M
What do checkpoints do in the cell cycle?
won’t allow the next phase to start until specific things are checked off
What do checkpoints in the cell cycle measure?
tension
What does the cell cycle control system (checkpoints) depend on?
cyclically activate protein kinases called CDKs (cyclin dependent kinases)
How are cyclin concentrations regulated?
transcription and proteolysis
What does the activity of cyclin-CDK depend on?
phosphorylation and dephosphorylation
What can block CDK activity?
CDK inhibitor proteins
How can the protein cyclin be controlled?
by synthesis, disruption, or post translational modification
How was MPF discovered?
discovered by injecting fertilized Xenopus egg cytoplasm into Xenopus oocytes
What does progression through the cell cycle depend on?
CDKs
Kinase is only active when what is present?
cyclin
Cyclin responds to what sort of activity?
MPF
Cyclins are destroyed as mitosis stops, this corresponds with what?
metaphase anaphase transition
What does S-cyclin do?
initiates DNA replication cycle and hangs on until M phase
What is the regulator in the cell cycle control system?
timed destruction
What is cyclin degradation through?
ubiquitin dependent proteasome
What is the signal for the destruction of cyclin?
ubiquitylation
What is ubiquitin?
small protein
Polyubiquitin forms on proteins targeted for what?
destruction
What enzyme gives polyubiquitin?
E3 ligase
What does APC (E3 ligase complex) do?
targets cyclin, initiates destruction, and promotes metaphase to anaphase transition
Can CTK kinase work without cyclin?
no
What post translational modification can prevent CTK from working?
phosphorylation
What is the response element to DNA damage?
P27
What can control the CTK?
protein binding
What is Mitosis?
nuclear division
What is Cytokinesis?
cytoplasmic divison
What are the 4 phases of Mitosis?
prophase
metaphase
anaphase
telophase
What is the result yielded from Cytokinesis?
2 identical daughter cells
Describe a cell cycle checkpoint.
ensures that key processes in the cycle occur in the proper sequence
What drives the cell cycle?
synthesis and degradation of cyclin proteins
Does DNA need to be replicated multiple times or only once?
only once
What is stably inactivated in G1?
CDKs
Mitogens promote what that stimulates cell division?
the production of cyclins
What is something that can temporarily halt the progression through G1?
DNA damage
How can cells delay division for prolonged periods?
by entering specialized nondividing states
What is one way to stimulate cell proliferation?
inhibiting the Rb protein (retinoblastoma)
What is the Rb protein?
tumor suppressor that inhibits cell cycle progression
How does the Rb protein inhibit progression in the cell cycle?
binds to transcription factors that promote cell replication
What enzyme is constantly surveying to make sure that DNA is continuous?
ligase
What is the “guardian of the genome”?
P53
What happens to P53 is DNA damage isnt present?
it gets degraded in the proteasome
What does P2bind to in order to block it from working?
cyclin CDK complex
What activates and stabilizes P53?
DNA damage
What stimulates the transcription of P21?
activation and accumulation of P53
What does P21 inhibit?
G1/S phases and S-CDKs
What happens if P53 is mutated?
damaged DNA will be replicated through mitosis
DNA damage activates what that phosphorylates P53?
kinases
Is phosphorylated P53 degraded by proteolysis?
no
What does S-CDK do?
initiates DNA replication and blocks re-replication
What can incomplete replication do to the cell cycle in G2?
arrest it
What are the 4 steps in the G1 phase of mitosis?
- ORC (origin of replication complex) is loaded onto DNA
- CDC6 binds to the ORC
- Helicase displaces ORC to form a pre replication complex
- ORC is loaded
What are the 4 steps in the replication part of S phase?
- ORC is activated to initiate DNA replication
- S-CDK kinase phosphorylates & activates helicase
- S-CDK kinase phosphorylates & guides assembly of DNA polymerase & other proteins at replication fork
- DNA replication machinery is activated
What are the 4 steps in S phase where DNA re-replication is blocked?
- S-CDK phosphorylates CDK
- CDC6 phosphorylation blocks reloading of helicase & assembly of ORC pre-replication complex
- helicase isn’t recruited, replication machinery is not assembled
- re-replication is prevented
What is a signal for the ORC site?
CDC6
What is destroyed at the metaphase anaphase transition?
S cyclin
What drives the entry into mitosis?
M-CDK
What helps configure duplicated chromosomes for separation?
cohesins and condensins
How do you convert DNA histone complexes into supercoiled structures?
through interactions of cohesins and condensins
M-cyclin activates what?
M-CDK
What inhibits M-CDK?
phosphorylation
M-CDK phosphorylates what?
CDC25 phosphatase
How does M-CDK create a positive feedback loop?
activated M-CDK indirectly activates more M-CDK
Cohesins for m rings that do what?
tie together 2 adjacent sister chromatids by forming until the rings are broken in late mitosis
What do condensins do in terms of chromosome formation?
coil each sister chromatids into compact structures
Does the nuclear envelope have to breakdown in M phase?
yes
What proteins are responsible for the structure of the nuclear envelope?
lamin proteins
What happens in lamin is phosphorylated?
the nuclear envelope falls apart
How many transient cytoskeletal structures mediate M phase in animal cells?
2
What helps form the 2 poles of the mitotic spindle?
G2/M transition centrosomes duplicated during S/G2
What happens in prophase?
the mitotic spindle starts to assemble
What attaches to the mitotic spindle?
pro metaphase chromosomes
How do chromosomes assist in the assembly of the mitotic spindle?
via kinetochores
What occurs in metaphase?
chromosomes line up at the spindle equator
What happens in anaphase?
proteolysis triggers sister chromatid separation
What happens in anaphase A?
chromosomes segregate and moves to poles
What happens in anaphase B?
spindles elongate to further separate poles
What spindle checkpoint prevent sister chromatid seperation and stop the metaphase anaphase transition?
unattached chromosome
When does the nuclear envelope disassemble?
G2/M phase transition (lamins are phosphorylated)
When does the nuclear envelope reform?
telophase (lamins are dephosphorylated)
What is the key to the spindle assembly checkpoint?
kinetochores
What keeps the lamin phosphorylated?
CDK
Do kinetochores stay attached in anaphase A?
yes
How is force generated in anaphase B?
sliding overlapping microtubules that increase the pole to pole seperation
What helps form the 2 poles of the mitotic spindle?
duplicated chromosomes
When does the mitotic spindle start to assemble?
in prophase
When do chromosomes attach to the mitotic spindle?
prometaphase
Do chromosomes assist in the assembly of the mitotic spindle?
yes
When does centrosome duplication occur?
during interphase
How do chromosomes assist in the assembly of the mitotic spindle?
through kinetochore microtubule interactions
Where do kinetochores assemble?
chromosome centromere region
Do kinetochores attach to the plus or minus end of the microtubule?
plus
Do kinetochores contain proteins that send cell cycle stop signals in the absence of microtubule attachmetns?
yes
Why are chromosome centromere regions very planar?
they are ATP rich
What are the 3 classes of microtubules that make up the mitotic spindle?
astral, kinetochore, and interpolar microtubules
How are interpolar microtubules stabilized?
by motors and microtubule associated proteins
What do Dynein motor proteins deplete?
kinetochores of stop signal proteins, when a checkpoint is released
What is APC (anaphase promoting complex)?
ubiquitin proteasome
What does APC trigger?
cyclin degradation & loss of CDK activity
What triggers sister chromatid seperation at anaphase?
proteolysis of cohesins
What are sister chromatids held together by?
cohesin proteins
What promotes the destruction of cohesin proteins?
APC
Can the spindle assembly checkpoint be regulated by only one kinetochore?
yes
What determines the plane of cytoplasmic cleavage?
the position of the mitotic spindle
What is the contractile ring of animal cells made of?
actin and myosin
Cytokinesis in plant cells involves the formation of what?
a new cell wall- phragmoplast
Astral overlap creates opportunity for what to form?
cleavage furrow
What shrinks the cleavage furrow?
actomyosin contraction
What forms a new cell wall in plant cells?
vesicle fusion at equator
What is cytokinesis in plants guided by?
phragmoplast
