1
Q
What are the three filament structures of the cytoskeleton
A
- Microtubules (direct movement within the cell)
- Actin filaments (support cell shape. mobility and intracellular transport)
- Intermediate filaments (provide structural support and mechanical strength
2
Q
What is the role of the cytoskeleton
A
- Skeletal system of a eukaryotic cell
- Structural support, cell shape maintenance
- Intracellular transport
3
Q
How are microtubules different from actin filaments and intermediate filaments
A
- Microtubules have GTPase activity
- Actin filaments have ATPase activity
- Intermediate filaments have no enzymatic activity
4
Q
Explain the dis/assembly of tubulin dimers
A
- A GTP molecule + ß-tubulin, GTP -> GDP when the dimer is incorporated & GTP remains bound
- Dis: GDP is replaced with a new GTP, which allows polymerization
5
Q
What major groups are associated proteins are linked to microtubules, intermediate filaments and actin filaments
A
- MAPs (microtubule- associated tubules) for microtubules, plakins for intermediate filaments and actin-binding proteins for actin filaments
6
Q
What is the basic structure of microtubules
A
- Hollow, rigid tubular structure with 13 protofilaments with alpha and ß-tubulin arranged in a circular pattern
7
Q
What is the polarity of microtubules
A
- The plus end is the ß-tubulin and the minus-end is the alpha-tubulin
- This is critical for intracellular transport
8
Q
What is the function of MAPs?
A
- MAPs increase the stability of microtubules and promote their assemble by linking subunits together
- High levels of phosphorylation in Tau = Alzheimer’s disease
9
Q
What is the function of kinesins and dyneins
A
- They are motor proteins that move cargo along microtubles
- Kinesins move towards the plus end and the dyneins move towards the minus end
10
Q
Describe the structure of kinesin
A
- They’re tetramers with two heavy chains and two light chains.
- The globular heads bind microtubules and hydrolyze ATP for nrg
11
Q
What happens when there are motor protein defects
A
- They can result in neurological diseases bcos of sucky transport
12
Q
What is a microtubule-organizing center (MTOC)
A
- They’re cellular structures that nucleate and organize microtubules, such as centrosomes in animal cells
13
Q
Centrosome structure
A
- A pair of centrioles surrounded by a pericentriolar material (PCM) to nucleate the MT growth
- Centrioles help to organize the PCM and contribute to the formation of cilia and flagella
- They position themselves to direct microtubules, influencing of organelles and proteins
14
Q
What is the function of y-tubulin ring complex (y-TuRC)
A
- The y-TuRc is within the pericentriolar material
- Acts as a template for microtubules nucleation, specifying the minus end
15
Q
How do microtubules contribute to mitotic spindle formation
A
- During cell division, they reorganize to form mitotic spindle, which separates chr into daughter cells
16
Q
What is the structural polarity of actin filaments
A
- Actin filaments have fast-growing (+) end (barbed end) and a slow-growing (-) end (pointed end) that’s critical for directional growth and assembly
17
Q
What is the core structure of cilia and flagella
A
- Axoneme with a 9+2 microtubule arrangement
- Nine outer doublets with two central singlet microtubules
- They are anchored on the basal body (MTOC) of their assembly
18
Q
What is the primary fxn of cilia and flagella
A
- Cilia move fluid, mucus or particles over a cell’s surface (back-and-forth beating motion)
- Flagella are used for locomotion, propelling cells like sperm (in a whip-like motion)
19
Q
What protein is responsible for cilia and flagella movement
A
- Dynein, generates force for sliding of microtubules in the axoneme
- ATP gives dynein nrg to drive the sliding of microtubules, which causes the bending motion of cilia and flagella
20
Q
What is the structural difference between basal body and axoneme
A
- The basal body has 9+0 arrangement
- The axoneme has 9+2 arrangement
21
Q
What are radial spokes in the axoneme
A
- Radial spokes are protein complexes extending from the outer doublets to the central pair to coordinate cilia and flagella movement
22
Q
What is the role of nexin in ciliary and flagella motion
A
- It links adjacent microtubules doublets and helps regulate sliding, converting it into bending movements
23
Q
Cilia and flagella assembly
A
- IFT proteins => IFT particles => IFT trains
- They carry cargo proteins out for assembly, inhibition of IFT prevents cilia and flagella assembly
24
Q
Flagella and cilia locomotion
A
- Dynein anchors then a-tubule of the lower doublet and the b-tubule of the upper doublet
- Lower end slides towards the basal end of the upper end
- dynein detached from thr upper doublet, reattached and another cycle begins
25
Assembly process of intermediate filaments
- They **lack polarity & enzymatic activity** and they are not involved in **intracellular transport**
26
Two types of intermediate filaments
- Keratin (epithelial cells)
- Neurofilament (cytoplasm of neurons)
27
What is the role of intermediate filaments**(keratin)** in cell-cell junctions
- They link to desmosomes which will anchor cells to each other and the ECM
28
IF architecture
- Monomer: pair of globular terminal domains separated by a long å-helical region
- monomers => parallel dimers
- Dimers => antiparallel and staggered **tetramers**
- 8 tetramers = a **unit**
29
What are **actin-binding proteins (ABPs)**
- They regulate actin filaments, controlling **nucleation, elongation, capping and severing** to adapt the cytoskeleton to cellular needs
30
What is treadmilling
- The point during simultaneous addition of actin monomers at the **barbed end** and a **loss at the pointed end**, where both reactions are balanced
31
Actin cell mobility
- Actin filaments form structures like **lamellipodia**, enabling cells to **crawl** by pushing the plasma membrane forward
32
Actin and myosin relation
- The actin filaments are like **tracks** for the **myosin** motor proteins
- They help with **cytokinesis and muscle contraction**
33
What is the difference between lamellipodia and filopodia
- lamellipodia: broad sheets made from **dense actin networks**
- Filopodia: thin, fingers made from **bundled actin filaments**
34
Functions of **focal adhesions** in cell motility
- They connect actin cytoskeleton to the ECM
35
Function of myosin
- It is a **motor protein** that uses **ATP hydrolysis** to move along actin filaments
- ATP **binding** causes myosin to release actin, ATP **hydrolysis** causes myosin to reposition its head for the next power stroke
36
Structural components of myosin II
- It has a globular head **(ATPase activity)**, a lever arm **(regulatory light chain)**, and a long tail **(for dimeration and filament formation)**
- The tails point to the center and the heads point outside (bipolar)
- They generate contractile forces at the basal end of the cell = retraction/propulsion during **cell motility**
37
Unconventional myosin
- (Myosin I, V & VI)
- V: moves in a **hand-over-hand** fashion to the **kinesin** so two head are on the filament at all times
- They’re localized within hair cells of the **inner ear**
- VI: moves towards the **pointed end** of the actin filaments **(reverse)**
38
What is the **basic unit** of muscle contraction
- The sarcomere, a repeating unit of **myofibrils** with actin (thin) and myosin (thick) filaments
39
What are the roles of **Z, A and I bands** in sarcomeres
- Z line: Anchors thin filaments and marks sarcomere boundaries
- A: contains **thick** filaments and regions that overlap with **thin** filaments
- I: contains **only thin** filaments
H zone: only **thick** filaments
40
What triggers muscle contraction
- Ca2+ ions bind to **troponin**, causing **tropomysoin** to move (expose actin binding sites for myosin)
- **Sliding filament model**: thin ones slide past thick ones (sarcomere shortens, each filament is still the same length)
41
How is ATP replenished in muscle cells during contraction
- Creatine phosphate
- Glycolysis
- Oxidative phosphorylation
42
Excitation-contraction coupling
- Contact at the **neuromuscular junction** that shortens the sarcomere
- AP in the muscles are propagated by **transverse (T) tubules** that terminate where Ca2+ is stored (sarcoplasmic reticulum)
43
What is the purpose of studying muscle biometrics
- To understand how muscles convert **biochemical nrg** to mechanical work
- Key propertied of muscles studied is **elasticity**, allowing muscles to store/release nrg during movement
44
How do researchers apply muscle biometrics in technology
- Electromyography: measures **AP** within muscle tissue
- Fucntional electrical stimulation: stimulates/mimis muscle activity
45
name the three classes of actin-binding proteins
- **Nucleating** proteins: promote actin **polymerization** (Arp2/3 complex)
- **Severing** proteins: **cut** actin filaments into smaller fragments to prevent further polymerization (gelsolin)
- **Capping** proteins: **stabilize** filament ends they bind to the **(+/-)** end oif the filament to prevent the **addition/loss** of actin monomers (CapZ)
46
How do cross-linking proteins contribute to actin organization
- They bind multiple filaments = 3-D networks that give structural integrity (filamin)
47
What is the role of RHO GTPases in cellular motility
- They regulate actin dynamics by promoting **lamellipodia, filopodia or stress fibers** to coordinate cell movement
48
What are the main components of the bacterial cytoskeleton
- FtsZ, CreS, ParM (homologous of tubulin and actin)
49
The roles of bacterial components
- FtsZ: forms a contractile ring at the site of cell division - septum formation in binary fusion
- ParM: segregates plasmids during cell division by **polymerizing into filaments** that push plasmids to **opposite poles** of the cell
- CreS: **polymerizes** proximal to the membrane, plays a key role in **cell shape**
BIOL-3221
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