Final Exam Flashcards
(156 cards)
1
Q
What are the microtubule associated motor proteins?
A
kinesin
dynein
myosin I
2
Q
What is the function of kinesin?
A
plus end directed motor moves along the microtubule towards the (+) end of the filament
3
Q
What is an example of the function of kinesin?
A
movement of chromosomes during mitosis
intracellular vesicle transport
4
Q
What is the function of dynein?
A
minus end directed motor that moves along the microtubule towards the (-) end of the filament
5
Q
what are examples of the function of dynein?
A
movement of chromosomes during mitosis
movement of sperm flagella is a dynein-based motor process
6
Q
What is the function of myosin I?
A
plus end directed motor that moves along the microtubule towards the (+) end of the filament
movement mediated by ATP hydrolysis
7
Q
What is the overall function of microtubules (with associated proteins)?
A
guide intracellular transport
anchor intracellular organelles
form mitotic spindle
function in chromosome segregation during cell division
8
Q
What do microtubules form?
A
mitotic spindle
9
Q
where do microtubules radiate from?
A
centrosome (minus end is embedded in the centrosome)
10
Q
what is a centrosome?
A
the poles
11
Q
what is a centromere?
A
holds chromosomes/chromatids together and connects chromosome to spindle fibers via the kinetochore
12
Q
How does cleavage furrow formation work in animal cells?
A
cleavage furrow is formed by a belt-like bundle of actin filaments called the contractile ring
as cleavage progresses, the ring of actin tightens around the cytoplasm eventually pinching the cell in two
entire contractile ring is dismantled shortly after cytokinesis is complete
13
Q
when does the contractile ring form in cleavage furrow formation?
A
contractile ring forms just beneath the plasma membrane in early anaphase
14
Q
How is the actin ring in cleavage furrow formation tightened?
A
tightening of the actin ring involves interactions between actin filaments and myosin II
movement of myosin along the actin causes the contraction and tightening of the actin filaments
15
Q
How does cytokinesis occur in plant cells?
A
during late anaphase a group of small vesicles derived from the golgi complex align themselves across the equatorial region of the spindle
vesicles contain polysaccharides and glycoproteins required for cell wall formation
16
Q
what guides vesicles to the spindle equator in plant cells?
A
vesicles are guided to the spindle equator by an array of microtubules (and associated mictotubule motor proteins)
vesicles fuse together to produce a cell plate which represents the cell wall in the process of formation
17
Q
what is cell locomotion?
A
cells move by protruding a portion of the cytoplasm
18
Q
what types of cells need to move?
A
amoeba, macrophages, fibroblasts, embryonic cells during development etc
19
Q
What are the three steps in cell movement?
A
protrusion, adhesion, contraction
20
Q
describe protrusion
A
front of cell pushes out an extension called a lamellipodium
21
Q
describe lamellipodium
A
extension cell pushes out during protrusion
filled with actin filaments that have a (+) end facing towards the plasma membrane
22
Q
how are lamellipodium formed?
A
actin assembly is required for protrusion (assembly pushes on leading edge of cell membrane to form protrusion)
myosin I moves along actin filaments causing them to slide past one another
BOTH OF THESE TOGETHER FORM THE LAMELLIPODIUM
23
Q
describe the second step of cell movement, adhesion
A
cells must adhere to substrate in order to move
adhesion is mediated by integrin protein
24
Q
what is an integrin protein?
A
transmembrane adhesion protein
bound to an intracellular bundle of actin filaments
bound to extracellular matrix
25
describe the 3rd step of cell movement: contraction
back of cell contracts to move the front of the cell forwards
maybe myosin based since myosin II has been localized to the rear of the cell
26
Describe the cell motility of disease-causing organisms
disease causing microorganisms can use the cell's normal cell adhesion and cell motility systems to enter a cell
27
Describe the example of disease-causing organisms using cell motility that was discussed
Listeria monocytogenes: gram positive bacteria
infects cells by binding to a cell and entering the cell (phagocytosis) [not destroyed by lysosome]
once inside, the bacterium moves in the cytoplasm where it can divide rapidly
the bacterium moves inside the cell by producing a "comet tail" of polymerized actin [using the cytoplasmic g-actin of the host cell]
28
What is a kinetochore?
complex of proteins and RNA molecules attached to the centromere
29
What are astral microtubules?
face away from the poles toward the membrane
30
what are polar (interpolar) microtubules?
face center of cell
31
what are kinetochore microtubules?
face the center of the cell and contact the chromosomes
32
How do chromosomes move?
microtubules can change length while attached to the kinetochore
tubulin subunits add to the (+) end
tubulin subunits can be removed at the kinetochore or at the pole
33
How do microtubules change length?
microtubules lengthen as subunits are added to the (+) end
lengthens from the pole to capture the kinetochore
34
what does dynein do as a microtubule motor in chromosome movement?
dynein located at kinetochore is trying to move along the filament towards the (-) end
chromosomes move towards the pole
tubulin subunits are lost where filament connects to kinetochore
35
what does kinesin do as a microtubule motor in chromosome movement?
kinesin is located at the poles and is trying to move along the filament towards the (+) end
subunits are removed at pole region (overall shortening of microtubule)
36
What two microtubule motors move chromosomes during anaphase together?
dynein and kinesin
36
what is the role of katanin?
Severing microtubules associated protein
Causes microtubules to lose subunits
Has been localized to pole region of spindle
37
Describe what happens in metaphase (in regards to the microtubules)
balance between forces exerted by kinesin at poles and dynein at kinetochore
no overall loss of subunits results in chromosome alignment
*PROCESS NOT CLEARLY UNDERSTOOD*
38
Briefly outline an experiment that you could do to show the involvement of kinesin and dynein in cell division
loss of function (knock-out) experiment [kinesin/dynein]
knock out or block protein function
look at position of the chromosomes
look for a chromosome shift or absence of chromatid segregation
39
What is p53?
tumor suppressor gene that encodes a transcription factor
40
what can a mutation in a transcription factor do?
prevent activation of gene expression (DNA repair enzymes or proteins involved in cell cycle checkpoints)
41
what is the function of p53?
activates DNA repair enzymes
can halt a cell at G1/S (regulation point- halts growth and DNA replication)
activate apoptosis (programmed cell death)
42
what is apoptosis (programmed cell death)
biochemical events lead to changes in cell morphology and cell death
changes include cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation
dependent on family of proteins called caspases
43
what do caspases do?
cleave nuclear lamins causing the break down of the nuclear envelope
cleave inactive forms of Dnase to create an active form (Dnase degrades DNA)
Ethidium bromide stains degrading DNA
44
How do elephants avoid cancer?
large mammals that have more cellular DNA (more mutations) and numerous rounds of cell division (more chances for DNA errors)
can survive up to 60 years in the wild
don't develop cancer because they evolved to have 40 copies of the p53 gene (humans have 2), cells with damaged DNA are repaired or apoptosis is triggered
45
What are anti-mitotic drugs?
used to treat cancer (don't target only cancer cells)
46
What are the 2 types of anti-mitotic drugs discussed?
vinblastine: binds to tubulin and prevents microtubule formation
taxol: binds to microtubule and prevents disassembly
47
How is taxol able to stop division/mitosis?
chromosome movement during cell division requires disassembly
if it cant disassemble, chromosomes cant segregate during anaphase
48
What is metastasis?
migration of cancer cells
mechanism unknown (actin??)
cells break cell adhesion
49
what do neurodegenerative diseases such as Alzheimer's and Parkinson's do?
cause a change in the shape of the axon of neurons microtubules collapse into a constricted structure (not clearly understood)
abundant abnormal aggregates of cytoskeletal proteins in neurons and glial cells of CNS (ex. tau proteins)
50
Why is it odd that in neurodegenerative disorders microtubules collapse?
axons of neurons contain bundles of microtubules WITHOUT dynamic instability
51
what does the constriction of microtubules in the neuron do?
prevent or decrease vesicle transport within an axon (vesicles most likely carrying neurotransmitters)
52
what are tau proteins?
microtubule associated proteins for stabilization
abundant in CNS cells
defective tau proteins has been linked to Alzheimer's
53
What is intracellular transport?
proteins made in the cytoplasm must be transported to different compartments in the cell
54
how do proteins find the correct target in intracellular transport?
signal sequences: a stretch of amino acids that specifies a destination
55
describe the nuclear envelope
double membrane
contains nuclear pore complexes
56
describe the structure of the nuclear pore
octagonal structure of repeating subunits that forms a channel through the membrane
57
what are nucleoporins?
repeating subunits that make up the structure of the nuclear pore
58
what is the nuclear cage?
fibrils that extend into the cytoplasm and nucleus
provides support to nuclear pore
59
how are small molecules transported across the nuclear envelope?
small molecules move through the aqueous channel by diffusion
60
how are large molecules transported across the nuclear envelope?
move through the channel by active transport (requires energy)
proteins to be imported require a nuclear localization signal
61
what are examples of small molecules transported across the nuclear envelope? large?
small: H2O, small ions
large: mRNA, histone proteins, ribosomes, DNA replication/transcription enzymes
62
what is a nuclear localization signal?
amino acid sequence that directs a nuclear protein to the nucleus for transport
63
How are large molecules imported?
active transport
64
Describe nuclear import receptors
soluble cytoplasmic proteins (importins)
recognize the nuclear localization signal on the protein to be transported
recognize the nucleoporin structure (FG repeats)
guide the transport of proteins through the pore (post-translational)
65
What are FG repeats?
repeats of glycine and phenylalanine
66
Explain how hydrolysis of a GTP molecule would power a protein across the nuclear envelope
transport is powered by the hydrolysis of GTP: GTP binds to the import receptor and pore
hydrolysis of GTP causes a conformational change in pore structure
67
How does export across the nuclear envelope occur?
*SAME PROCESS AS FOR IMPORT*
nuclear export signals located on molecules to be exported
nuclear export receptors: soluble proteins
export receptors bind to the export signal and the nucleoporin to guide the cargo through the pore to the cytoplasm
export powered by the hydrolysis of GTP
68
Where are proteins destined for the ER initially synthesized and how are they directed to the ER?
cytosolic ribosomes
ER signal sequence directs the protein to the endoplasmic reticulim
69
What does a signal recognition particle (SRP) do in the ER?
recognizes and binds to the ER signal sequence
70
what is a signal recognition particle (SRP)?
composed of 6 polypeptides and an RNA molecule
binds to the signal sequence on the protein being synthesized
71
Describe the protein transport in the ER
1. binding of SRP temporarily halts translation of the protein
2. SRP/ribosome complex is transported to the ER membrane
3. SRP binds to a receptor on the ER membrane
4. SRP is released from the complex and translation resumes
5. as the protein is translated, it is threaded through a pore in the ER membrane (hydrolysis of GTP)
72
How are soluble/secretory proteins transported?
ER signal sequence acts as a start transport sequence
ER signal sequence is cleaved off by the signal peptidase enzyme
protein is released into the ER
73
What are single pass transmembrane proteins?
cross the membrane once, span width of membrane
74
what are multi-pass transmembrane proteins?
cross the membrane more than once
75
How are single-pass transmembrane proteins transported?
ER protein: signal sequence initiates translocation
stop transfer signal anchors the protein in the membrane (located in middle of protein sequence)
76
where is the signal sequence found in single-pass transmembrane proteins?
found at amino terminal end of protein or in middle of sequence
77
How are multi-pass transmembrane proteins transported?
protein signal sequence initiates translocation
protein is threaded through the membrane until the stop transfer sequence
78
where is the protein signal sequence located in multi-pass transmembrane proteins?
located in the middle of the polypeptide sequence (serves as the start transfer sequence)
79
How do ER soluble proteins arrive?
passed through the membrane unfolded and must refold inside the lumen of the ER
80
What are binding proteins?
class of proteins that bind to incoming soluble proteins and aid in protein folding (ER)
chaperone protein
81
How do chaperone proteins work?
*PROCESS NOT WELL UNDERSTOOD*
some chaperones bind to proteins to be folded and protect the protein from degradation by forming large aggregate with the protein
once the protein is properly folded the chaperone releases
82
WHat are examples of other chaperone proteins?
heat shock proteins Hsp60 and Hsp70
83
what do abnormalities in chaperone proteins cause?
disruption of folding process can affect cell development and growth
can cause: photoreceptor degeneration in the eye, CNS abnormalities and male infertility
84
What are the two steps of the degradation of a protein via the Ubiquitin Proteasome Pathway (UPP)
1. tagging of the substrate protein by the covalent attachment of multiple ubiquitin molecules (conjugation)
2. subsequent degradation of the tagged protein by the proteasome
85
what types of proteins are targeted by the Ubiquitin Proteasome Pathway?
short lived proteins
regulatory proteins (ex. cyclin: cell cycle regulator)
86
Describe protein import in mitochondria and chloroplasts?
proteins destined for mitochondria and chloroplasts are synthesized in the cytoplasm on cytosolic ribosomes
contain a signal sequence that specifies their destination
transported into the organelles posttranslationally
signal sequence is cleaved by peptidases following import
87
What are the functions of the cell membrane?
form a cell boundary- confine biochemical reactions
sense external signals
protection
transport
cell shape
cell signaling
88
WHat is the structure of the cell membrane?
composed of lipids and proteins
described by fluid mosaic model
89
what is the fluid mosaic model?
membrane lipids are arranged in a bilayer
proteins are embedded in the bilayer
90
what does cell membrane fluidity mean?
lipid molecules able to move and behave more like a liquid than a solid
lipids can diffuse laterally in the membrane
91
What are the reasons for cell membrane fluidity?
1. phospholipid tails are short
2. phospholipid tails contain double bonds
92
why do short phospholipid tails increase fluidity?
short tails reduce the tendency of the lipids to interact with one another
93
why do double bonds in phospholipid tails increase fluidity?
Presence of double bonds in fatty acid tail: unsaturated
double bonds create kinks in the fatty acid tail
presence of kinks prevents packing together of phospholipids
94
what are the 3 types of membrane lipids?
phospholipids, glycolipids, cholesterol
95
describe phospholipids
polar head group (hydophilic) and nonpolar tails (hydrophobic)
amphipathic
most abundant lipid in the membrane
can move laterally
96
what does amphipathic mean?
contains hydrophilic and hydrophobic regions
97
what example of a phospholipid was given?
phosphotidylcholine
head group of glycerol, choline, phosphate group
tail region of fatty acid tails
98
describe glycolipids
lipids with a carbohydrate side chain (sugar side chain is exposed at cell surface)
99
what is the function of glycolipids
protection of cell from harsh conditions, cell recognition, and cell signaling
Harsh conditions=pH change, presence of lipases/proteases
100
where are glycolipids prominent?
membranes of nerve cells (brain) and epithelial cells that line the intestine
101
What is vibrio cholerae?
a bacteria that can occur in both marine and freshwater habitats that is pathogenic to humans and produces cholera toxin (enterotoxin)
102
How does vibrio cholerae harm its host?
the toxin acts on the mucosal epithelium of the digestive tract
causes sudden onset of massive diarrhea causing the individual to lose gallons of protein-free fluid and associated electrolytes, bicarbonates, and ions
103
what does vibrio cholerae have to do with glycolipids?
enterotoxin binds to glycolipids on the surface of intestinal cells
binding activates the adenylate cyclase enzyme in the cells converting the enzyme into pumps which extract water and electrolytes from blood and tissues and pump it into the lumen of the intestine (dehydration)
104
describe cholesterol
found in some membranes
steroid ring structure
ring interacts with tails of phospholipids
presence of cholesterol decreases the fluidity of the membrane
Provides support and stability to the membrane
105
what are the three types of membrane proteins?
integral
peripheral
lipid-anchored
106
describe integral membrane proteins
contain one or more hydrophobic regions embedded in the lipid bilayer
most integral proteins are transmembrane proteins
Amphipathic
107
give an example of an integral protein
transmembrane protein: membrane protein that extends through the lipid bilayer
both single-pass and multi-pass
multi-subunit proteins
composed of several polypeptide chains
108
Describe peripheral membrane proteins
found on the periphery of the membrane attached to phospholipid head groups or other adjacent proteins
attach to membrane by electrostatic interactions and H bonds
109
Describe lipid-anchored membrane proteins
form of peripheral protein
covalently bound to lipid molecules that are embedded in the lipid bilayer
110
How are lipid-anchored membrane proteins linked to the outer membrane surface?
attached by GPI anchor (glycosylphosphatidylinositol)
111
how are lipid-anchored membrane proteins linked to the inner membrane surface?
attached by a fatty acid group
112
Describe the fluidity of membrane proteins
proteins can rotate in the membrane
proteins can diffuse laterally in the membrane
113
What are the two experiments to show protein mobility?
1: mouse/human cell fusion experiment
-- mixing of mouse cell membrane proteins and human cell membrane proteins after cell fusion
2: FRAP (fluorescent redistribution after photobleaching)
--label a membrane proteins with a fluorescent antibody
--bleach the fluorescent molecules in a small area using a high intensity laser beam
--fluorescence intensity recovers as the bleached molecules diffuse away and unbleached molecules diffuse into the irradiated area
114
What might prevent the movement of membrane proteins?
proteins are linked to the extracellular matrix
proteins are linked to membrane components
cellular junctions (cell-cell interactions): proteins can diffuse up to a cell junction but not past it
115
WHat are the types of cell junctions?
tight junctions
gap junctions
anchoring junctions
116
what are tight junctions
bind cells in a tissue layer
prevent the "leaking" of materials between cells
117
what are gap junctions
tunnels that connect cells allowing for exchange of materials between cells
opening and closing of gap junctions is a regulated process (controlled by levels of intracellular calcium)
118
what are anchoring junctions
connect cells to each other and to extracellular matrix
can be connected to the cytoskeleton
119
how are peripheral proteins isolated?
extracted from the membrane by changes in pH or ionic strength
120
how are integral proteins isolated?
removed by mild detergents which disrupt the hydrophobic interactions between lipids in the bilayer (Ex: Triton X, NP40)
121
How are isolated proteins separated?
SDS-PAGE: separates proteins based on size
122
how are isolated proteins detected?
western blot
ELISA (enzyme linked immunosorbent assay)
123
What does SDS stand for and what does it do?
sodium dodecyl sulfate
denatures proteins and coats them with a negative charge
124
What does PAGE stand for and what does it do?
polyacrylamide gel
negatively charged proteins migrate in the gel towards the (+) electrode
migration rare dependent on size of proteins
125
Describe the connection between HPV and cervical cancer
HPV= human papilloma virus
Causes services cancer
E6 protein binds to the p53 and inactivates the protein
126
What are adaptor proteins?
Form a bridge between nuclear localization signals and nuclear pore
Large number in cytoplasm that can recognize multiple nuclear localization signals
127
What are the two populations of cellular ribosomes
Cytoplasm: synthesis of structural proteins (actin, tubulin) and enzymes
Membranes of endoplasmic reticulum
128
ER protein synthesis is what?
Cotranslational: synthesis and transport occur together
129
Nuclear protein transport is what?
Post-translational: transport after synthesis
130
Membrane transport is affected by what?
Size and polarity of the molecules
131
Give examples of how size and polarity impact membrane transport
Small, nonpolar molecules can diffuse rapidly across the lipid bilayer (oxygen, carbon dioxide)
Small, uncharged, polar molecules such as water and urea will slowly diffuse across the lipid bilayer
132
What is diffusion of water called
Osmosis
133
What are lipid bilayers impermeable to
Charged molecules
The charge on the molecule and the molecules degree of hydration prevents it from entering the bilayer
134
What are examples of molecules that cannot enter the bilayer
Na+, Ca2+, K+
135
What mediates membrane transport
Membrane proteins
2 main classes: carrier proteins and channel proteins
136
Describe carrier proteins
Bind to molecule to be transported
Undergo a series of conformational changes to transfer the bound molecule across the membrane
137
What are the 3 types of carrier proteins
Uniport
Symport
Antiport
138
Describe uniport proteins
Transport a single ,molecule
Ex. Calcium ion transport
139
Describe symport proteins
Transport of two molecules, coupled transport
Transport occurs in a single direction
Ex. Na+ / glucose transport
140
Describe antiport proteins
Transport of two molecules, coupled transport
Occur in opposite direction
Ex. Na+/K+ pump
141
What is passive transport?
Occurs by diffusion
142
What are the two types of passive transport
Simple
Facilitated
143
Describe simple diffusion
Concentration gradient drives transport
Diffusion occurs from area of high concentration to area of low concentration
144
Describe facilitated diffusion
Diffusion of molecules occurs through the use of carriers or channels in the membrane
145
Describe coupled carriers
Free energy released during the movement of one molecule down an electrochemical gradient is used as a force to pump the other molecule against the electrochemical gradient
Energy stored in the electrochemical gradient of one molecule is used to drive the movement of the other molecule
Ex. Na+/ glucose
146
What are the 3 types of active transport
Coupled carriers
ATP driven pump
Light driven pump
147
Describe ATP driven pumps
Uses hydrolysis of ATP to pumpmolecules across the membrane
Hydrolysis of ATP powers transport
148
Give an example of an ATP pump
Na+/K+ pump found in the plasma membrane of most animal cells
Na+ is pumped out of cell against its electrochemical gradient
K+ is pumped into the cell
149
Describe light driven pumps
Mainly found in bacteria (halophilic baxteria)
Couples transport against an electrochemical gradient to an input of light energy
Carrier proteins are light gated
Absorption of light causes conformational change in the carrier proteins
150
What do light driven pumps play a role in
Phototaxis
151
What are channel proteins
For, aqueous pores that extend across the lipid bilayer
When pores open, molecules can pass
Transport occurs quickly
Can be channel protein or gated channel protein
Gated requires stimuli to open the channel
152
What are stimuli that can open membrane channels
Voltage change across the membrane
Mechanical stress
Ligand mediated
153
What kind of channel does voltage change open?
Voltage-gated channels
Ex. Muscle contraction and nerve function
154
What kind of channels does mechanical stress open
Mechanically gated channels
Many of the channels have cytoplasmic extensions that link the channel to the cytoskeleton
155
What is a ligand mediated channel
Binding of a ligand opens the channel
Ligand can be an extracellular mediator (ex. Neurotransmitter)
Ligand can be an intracellular mediator (ex. Nucleotide-ATP)
