Chapter 7,8,9 Flashcards
(82 cards)
1
Q
What is a cytoskeleton?
A
- a network of proteins extending throughout cytosol.
- continually changing
- more dynamic than vertebrae skeleton
2
Q
What is the cytoskeleton involved in?
A
- cell shape
- organelle positioning (organization/holds things in place)
- interactions with environment (can disassemble then reassemble)
- movement
3
Q
What are the functions of the cytoskeleton?
A
- muscle movement
- wound healing
- sperm movement
- immune system response
- development of tissues (ex. embryos)
4
Q
What are the 3 types of cytoskeletal elements?
A
- Intermediate filaments (for strengthening cells)
- Microtubules (for cell division)
- Actin Filaments (for muscle movements)
5
Q
What is the advantage for cytoskeletal filament subunits being joined non-covalently?
A
-easily broken so can be rearranged (dynamic)
6
Q
What do the proteins that cytoskeletal subunits interact with do?
A
-regulate assembly and disassembly
7
Q
What are the shapes of the subunits of microtubules and actin?
A
- globular subunits
- microtubules: forms hollow tube
- actin: coiled coils
8
Q
What are the shapes of the subunits that make up intermediate filaments?
A
-elongated, fibrous subunits (very strong)
9
Q
Function of intermediate filaments?
A
-help cell withstand mechanical forces (prevent damage to cell)
10
Q
Characteristics of intermediate filaments?
A
- network of keratin-like filaments
- family of protein
- very high tensile strength
- often surrounds nucleus and extends throughout rest of cytoplasm to plasma membrane
11
Q
What are the 4 types of IF?
A
Cytoplasmic:
1. keratins: in epithelial cells (skin, hair, gut lining)
2. vimentin: in connective tissue cells, muscle cells, and glial cells
3. neurofilaments: in nerve cells
Nuclear:
4. nuclear lamin: in all animal cells (strength to nuclear envelope)
12
Q
What is the function of a desmosome in regard to IF?
A
-they are spot-like adhesions that involve keratin that join cells to other cells (act like rivets)
13
Q
Why can intermediate typing be used to identify the origin of cancer cells when they metastasize?
A
-the IF in the cell doesn’t change when it moves locations so by detecting the IF type, we know where the cell came from
14
Q
What does a hemidesmosome do?
A
-anchors a basal cell to the surface of basal lamina
15
Q
What is Epidermolysis bullosa?
A
-a keratin mutation that results in faulty keratin in the epidermis (the dermis and epidermis are no longer attached so when the rub, blisters form)
16
Q
What are plakins (plectin) and what is their function?
A
- crosslink intermediate filaments to other cytoskeletal and membrane sites to provide flexible, intracytoplasmic resilience to external stresses
- aids bundling of IF’s
- can join IF’s to microtubules
17
Q
What happens when theres mutations in the gene for plectin?
A
- combined features of epidermolysis bulosis simplex and muscular dystrophy and neurodegeneration (neurofilament dissruption)
- shows how important cytoskeletal elements are
18
Q
What happens to the nuclear envelope during mitosis?
A
- gets broken down and reformed
- lamins are phosphorylated causing meshwork to fall apart
- nuclear envelope vesicles are transported to different sides of the two reforming cells
- to reform the nucleus, nuclear lamins are dephosphorylated
19
Q
How do IF protect against stretching forces?
A
-found where there is mechanical pressure, it stops the cells from pulling apart and rupturing
20
Q
Why are IF’s so strong?
A
- have an N-terminus head and C-terminus tail with long middle alpha helical rod domain
- two monomers line up to form a coiled coil
- the two dimers associate to form a staggered tetramer
- the tetramers (8 of them) come together to form a strong rope-like filament
21
Q
Why don’t IF’s have polarity?
A
-the COOH and NH3 ends are staggered
22
Q
What are the functions of microtubules?
A
- form rail road tracks that anchor/position
- allow motor proteins carrying things down the track to position organelles
- divide components of cell in mitosis and meiosis
23
Q
What is the structure of microtubules?
A
- a and B tubulin heterodimers stack to form protofilament with alternating a and B subunits
- protofilaments line up and wrap around to form long tubes (13/tube)
24
Q
Why do microtubules have polarity?
A
-they are different on each end, have a plus and minus end
25
What subunit is at the growing end of the microtubule? Starting end?
- B at growing end (plus)
| - a at starting end (minus)
26
Why is polarity important for microtubules?
-defines direction in a cell (some motor proteins move towards minus, others plus)
27
What does the mitotic spindle (made of microtubules) do?
-aids cell division by directing chromosomes to the right location
28
What do cilia and flagella (made of microtubules) do?
-help move certain cells or move fluids around
29
Where do microtubules grow out of?
-nucleating sites made of y-tubulin ring complexes on centrosomes
30
How does B-tubulin have enzymatic activity?
- it can cleave a P off GTP
- the energy to assemble microtubules comes from GTP binding so cutting P can lead to microtubule disassembly which could lead to dynamic instability
31
What is dynamic instability of microtubules?
- microtubule growing and shrinking
| - this happens always unless stabilized at plus end
32
How can you stabilize a microtubule with dynamic instability?
-bind to protein to stabilize the plus end
33
When does a microtubule grow?
- if addition is faster than GTP hydrolysis, GTP cap forms
- allows new tubulin dimers to bind and the microtubule grows
- polymerization
34
When does a microtubule shrink?
- if GTP is hydrolyzed to GDP before GTP-cap can form (unless its stabilized by a protein)
- depolymerization
35
What does the colchicine drug do?
-binds to free tubulin and keeps it from polymerizing (stop microtubule growth)
36
What does the taxol drug do?
-binds to microtubule ends and keeps them from depolymerizing (shrinking)
37
How are microtubule drugs used for chemotherapy?
- mitosis gets arrested (cell division stopped)
| - called antimitotic drugs
38
Some microtubules are always stable, why and what do they do?
- they are tethered to proteins in cell cortex (capping proteins)
- help organize the cytoplasm
39
How does the ER get stretched out to the edge of a cell?
-kinesin stretches it out along microtubules
40
How does the golgi stay condensed and near centrosomes?
-dyenin keeps it stacked together
41
Most cells have polarity, what is this maintained by?
- microtubules
| ex. axons of nerve cells have microtubules that point in one direction to serve as tracks for transport of vesicles
42
What is a faster way to move cargo than diffusion?
- directed movement by axon transport (moved along MT's by motor proteins)
- 10cm/day
43
What is saltatory movement?
-small jerky steps that organelles and vesicles appear to take (occurs from the motor protein being attached to ATP, ATP hydrolysis occurring causing conformational change which makes the protein walk along MT track)
44
Which end do kinesin motor proteins move towards?
-plus end
45
Which end do dynein motor proteins move towards?
-minus end
46
Where is the cargo attached to on the motor protein?What about the ATP?
- tail domain
| - motor head
47
Are MT in cilia stable or do they grow and shrink?
-stable, they originate from centriole-like structures called basal bodies
48
What is the structure of cilia and flagella?
- they have 9 outer MT doublets and 2 inner MT's
- the MT's are held together by radial spokes and nexins
- there are dyenin arms attached to the outer doublets to move them relative to each other
49
What is the structure of a basal body?
-9 MT triplets and no central MT
50
How does a flagella create movement?
-ciliary dyenin attaches to one MT with its head domain and to another with its tail to hold two MT together and then uses ATP hydrolysis to generate movement and causes the flagella to bend
51
Where are microfilaments (actin) found in the cell?
-around the outside of a cell
52
What is the structure of an actin filament?
- made up of globular actin monomers
- have a plus and minus end (polarity)
- grow from either end but more often from plus end
53
Actin is an ATPase, what does this mean it can do?
- when bound to ATP its activated so the filament can grow
- if the ATP is hydrolyzed to ADP, the filament disassembles
- creates a treadmilling effect of actin being continuously bound and lost
54
What are the 8 actin binding proteins and what do they do?
1. nucleating protein: initiates actin filament (gives it something to start from
2. monomer sequestering proteins: bind to monomers and keep them from assembling until needed (prevents them from forming when they aren't supposed to)
- ex. tropomyosin, profilin
3. bundling protein: allows for many filaments to act together (crosslink)
4. motor proteins: actin and myosin work together in muscle tissue
5. side-binding proteins: prevent binding of myosin to actin (in muscle tissue we only want binding when muscle contracts)
- ex. tropomyosin
6. capping protein: block ends and keep actin filament stable
7. cross-linking protein: allow actin to provide case to stabilize membrane structure (in cell cortex)
8. serving protein: cut up actin filaments
- ex. cofilin, severin
55
In what to forms is actin found?
50% monomers
| 50% filaments
56
How is actin useful in RBC's?
-RBC's have to move through very narrow blood vessels so they need to be flexible and strong (actin and spectrin filaments attached to the plasma membrane allow this)
57
How does actin help a mobile cell move?
- nucleating proteins allow actin strands to start at the leading end of the cell which pushing out the leading end (extending pseudopodium)
- the protruding end makes contact with the surface of other cells and integrins
- actin disassembles from the trailing end of the cell
- the cell is pulled forward by myosin contraction
58
What does the drug Cytochalasin do?
-binds to free actin and prevents polymerization (fungus)
59
What does the drug Latrunculin A (Lat-A) do?
-provents actin polymerization (sponges)
60
What does the drug Jasplakinolide do?
-stabilizes actin filaments so they can't depolymerize (sea sponge) 🧽
61
The Rho protein family is a group of monomeric GTPases that affect the organization of the actin cytoskeleton, what are theses proteins?
- Rho: causes formation of long bundles of actin filaments that dont normally occur in the cell, when associated with myosin they can shorten the length of a cell
- Rac: results in lemellapodium which is a large edge that is trying to be pushed out
- Cdc42: stimulates protrusion of a forest of filapodia (projections of the cell)
62
What is the structure of myosin I?
- globular head, filamentous tail
- head interacts with actin
- tail interacts with different thing (vesicles, plasma membrane)
- found in all cells
- to move, it walks towards the plus end which drives the actin in the opposite direction
63
What is the structure of myosin II?
- dimer
- assembles into thick filamentous muscle cells
- ATPase activity in head region
- same globular head and filamentous tail as myosin I
64
How does myosin II cause actin filaments to be drawn together?
-myosin heads on either side of a bare region, both sides move opposite of each other to plus end of actin which results in actin being drawn together
65
How is myosin II involved in cytokinesis?
-splits the cell in two by forming a contractile band of myosin and actin
66
What is the structure of skeletal muscle fibers?
- very large (up to 30 cm)
- multinucleated
- striated
- made from fusion of myoblasts
67
What is a satellite cell on a muscle fiber?
-doesn't fuse to muscle fiber, remains separate providing a supportive function
68
What is a smallest contractile unit of a muscle?
-sarcomere
69
What are the units of a muscle from smallest to the actual muscle?
1. sarcomere
2. sarcomeres lined up end to end to form a myofibril
3. myofibrils line up side by side to make up muscle fiber
4. muscle fiber
5. fascicle (surrounded by sarcolemma)
6. muscle bundle
70
How are muscles attached to bone?
-by tendons
71
What are the striations from on muscles?
-individual sarcomeres
72
What is a Z disc in a muscle fiber?
- elastic filaments
- separations between sarcomeres
- made up of specialized proteins that actin and myosin filaments are attached to
73
What is the sarcoplasmic reticulum?
- similar to ER
- bound channel surrounding myofibril that is involved in calcium release (Ca2+ plays huge role in muscle contraction and stored inside SR)
74
What happens when Ca2+ needs to be released into muscle fiber?
-signal is sent in Transverse tubules from sarcolemma
75
What makes up a triad in skeletal muscle fibers?
- t tubules with terminal cisternae
| - allows intimate connection between t tubules and SR
76
Full cycle of how muscles move:
1. myosin head is attached to actin filament and lacks bound ATP: rigger conformation
2. as ATP is bound to myosin, myosin is released from actin
3. ATP is hydrolyzed to ADP (P is still bound to myosin head though), cocked formation occurs, cleft closes around ADP molecule that triggers a large shape change displacing myosin head by about 5nm
4. force generating step: myosin head is bound to new site on actin which causes ADP to be released
5. ADP release triggers power stroke where myosin head regains original conformation which moves actin filaments (towards minus end)
77
When do myosin and actin interact to cause muscle contraction?
- when Ca2+ gets to them
| - regulatory proteins prevent muscle contraction until signal comes for them to contract (tropomyosin and troponin)
78
What protein does Ca2+ bind to to allow actin and myosin to interact?
-Ca2+ binds to troponin complex which causes a conformational change which moves tropomyosin out of the way (it was lined up on myosin head stopping interaction)
79
How does myosin attach to the Z line?
titin
80
What are the A, I and H bands of muscles?
- I band: between myosins (gets shorter when muscle contracts)
- A band: region of thick filamentous myosin (doesn't change in length when muscle contracts)
- H band: between actin on either side (gets shorter too)
81
Steps of contraction of skeletal muscle:
1. neural control
2. excitation
3. release of Ca2+ from SR
4. contraction cycle begins
5. sarcomeres shorten
6. generation of muscle tension (pulls on tendons)
82
Features of smooth muscles:
- cells are not striated
- fibers smaller than those in skeletal muscle
- spindle-shaped; single, central nucleus
- more actin than myosin
- no sarcomeres
- dense bodies instead of Z disks
