BIO130 Final > Lecture 4 > Flashcards

Lecture 4 Flashcards

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1
Q

What is the cytoskeleton?

A

network of protein filaments that extends throughout the cytoplasm of eukaryotic cells

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2
Q

What is the main function of the cytoskeleton?

A
  • Structural support
  • internal organization of cell
  • cell division
  • Large-scale movements
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3
Q

What are the limits of light microscopes when viewing the cytoskeleton?

A
  • resolution limit is ~200nm (cytoskeleton filaments are 7 to 25 nm)
  • limits from wavelength of visible light
  • cannot resolve cytoskeletal filaments
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4
Q

What is a fluorescence microscope?

A

light microscope with the same resolution but fluorescent labels added to detect specific proteins. It can detect cytoskeletal filaments

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5
Q

What is a transmission electron microscope?

A
  • uses beams of electrons, very short wavelengths. The resolution limit is ~1nm and reveals detailed structures
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6
Q

What is immunofluorescence microscopy?

A

uses fluorescently labeled antibodies to detect specific molecules or antigens in cells or tissues

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7
Q

How does immunofluorescence microscopy work?

A
  • the binding of fluorescently labeled antibodies to target molecules or antigens in a sample
  • When excited by light of a specific wavelength, these antibodies emit fluorescence, allowing the visualization and localization of the target molecules under a fluorescence microscope
  • primary antibody used to bind to a specific protein
  • secondary protein (covalently tagged to a fluorescence marker) binds to the primary antibody
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8
Q

What are the three types of cytoskeletal filaments?

A
  • actin
  • intermediate
  • microtubules
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9
Q

What are intermediate filaments?

A

are structural proteins found in the cytoplasm of eukaryotic cells, providing mechanical strength and support to the cell

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10
Q

Where are intermediate filaments commonly found within a cell?

A

anchored to the plasma membrane at cell-cell junctions called desmosomes, as well as within the nucleus forming a meshwork called the nuclear lamina

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11
Q

What is the structure of intermediate filaments?

A

long strands twisted together like a rope. Each strand is made up of fibrous subunits containing a central elongated rod domain with unstructured domains at either end.

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12
Q

Which type of cells would you expect to contain a high density of intermediate filaments in their cytoplasm?

A
  • Skin epithelial cells: These cells form tight connections with each other through desmosomes, requiring strong mechanical support provided by intermediate filaments.
  • Smooth muscle cells in the digestive tract: These cells undergo frequent contractions and require robust structural support from intermediate filaments.
  • Nerve cells in the spinal cord: These long, thin cells need strong cytoskeletal elements like intermediate filaments for structural integrity.
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13
Q

Do intermediate filament strands have unique polarity? Can one end be distinguished from another by chemical or other means?

A

No, unlike microtubules and actin filaments, individual strands of an intermediate filament do not have distinct polarity or orientation that can be distinguished chemically or otherwise.

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14
Q

What happens to the nuclear lamina during cell division?

A

The nuclear lamina disassembles and reforms at each cell division; it breaks down during mitosis when the nuclear envelope disintegrates and then re-forms in each daughter cell.

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15
Q

Do cytoplasmic intermediate filaments also disassemble during mitosis?

A

yes

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16
Q

How are intermediate filaments organized within the nuclear envelope?

A

Intermediate filaments lining and strengthening the inside surface of the inner nuclear membrane are organized as a two-dimensional meshwork called the nuclear lamina, constructed from a class of proteins called lamins.

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17
Q

What are the different stages of a cytoplasmic intermediate filament?

A
  • alpha-helical region on monomer
  • 2 monomers (coiled-coil dimer)
  • 2 dimers (staggered antiparallel tetramer of two coiled-coil dimers)
  • 8 tetramers associate side by side and assemble into filament (held by noncovalent interactions)
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18
Q

What is an example of intermediate filaments in an epithelial cell?

A

keratin filaments form a network throughout cytoplasm out to cell periphery
It’s anchored in each cell at cell-cell junction (desmosomes), connect to neighboring cells. It provides mechanical strength

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19
Q

What is the basic structural unit of a microtubule?

A

the tubulin dimer, which consists of two subunits called alpha-tubulin and beta-tubulin to form a tubulin heterodimer bound to GTP

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20
Q

How do microtubules exhibit polarity?

A

through their structure, with one end termed the ‘plus end’ (usually more dynamic and where growth occurs) and the other termed the ‘minus end’ (usually anchored to structures like centrosomes)

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21
Q

What are some drugs that affect microtubule dynamics, and how do they work?

A

Drugs like Taxol stabilize microtubules by binding to them and preventing depolymerization. In contrast, drugs like colchicine bind to tubulin dimers and prevent their polymerization into microtubes.

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22
Q

What are microtubules involved in?

A
  • Cell organization (vesicle transport, organelle transport)
  • mitosis
  • structural support (cells, motile structures like cilia and flagella)
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23
Q

What is the structure of a microtubule protofilament?

A

composed of a linear arrangement of tubulin protein subunits (plus end is beta and minus end is alpha)

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24
Q

How does dynamic instability occur in microtubules?

A

refers to the ability of microtubules to alternate between periods of growth (polymerization) and shrinkage (depolymerization) at their plus ends

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25
What kind of bonds hold tubulin together in a microtubule protofilament?
all bonds between the individual subunits are noncovalent, but the bonds between protofilaments are weaker than the bonds within each protofilament
26
What happens to the growth of isolated cilium microtubules incubated with a high concentration of tubulin and GTP?
faster growth of microtubules at the plus end, but there is still a little growth at the minus end
27
What drives dynamic instability in microtubules?
driven by the hydrolysis of GTP (guanosine triphosphate) in tubulin dimers, which leads to the addition or loss of tubulin subunits.
28
How does dynamic instability contribute to microtubule function?
allows microtubules to undergo rapid remodeling, enabling them to explore different parts of the cell and establish stable links with other molecules or structures
29
What is a microtubule organizing center (MTOCs)?
the place where microtubules grow out from the minus ends are stabilized at MTOCs and plus ends grow out
30
When does the mitotic spindle start to assemble?
begins forming during prophase. The assembly relies on the properties of microtubules, including their dynamic instability.
31
What would happen if only GDP were present without GTP in regards to microtubule stability?
the microtubules would not be able to stabilize and grow since GTP-tubulin is necessary for adding new subunits at the plus end; thus, they would continue shrinking
32
How does the growth of microtubules occur?
- free alpha-beta tubulin dimer (bound to GTP) add to growing microtubule at the plus end - shortly after, beta-tubulin hydrolyzes GTP to GDP - rapid addition of alpha-beta tubulin dimers (happens quicker than GTP hydrolysis in newly added ab-tubulin dimers, which leads to the formation of GTP cap and stabilizes the plus end) - microtubule continues to grow
33
How does the shrinkage of microtubules occur?
- free alpha-beta tubulin dimer (bound to GTP) add to growing microtubule at the plus end - shortly after, beta-tubulin hydrolyzes GTP to GDP - slower addition of aB-tubulin dimers (happens slower than GTP hydrolysis in newly added aB-tubulin dimers, which leads to GTP cap lost and now GDP-tubulin at plus end) - microtubule disassembles due to weaker binding
34
Is alpha tubulin hydrolyzed during dynamic instability?
no, it's tightly bound to beta-tubulin, which gets hydrolyzed
35
What are the organizing centers for microtubules in cells?
in cells include centrosomes, the two poles of a mitotic spindle, and basal bodies of cilia and flagella
36
What is the function of microtubule organizing centers?
they have nucleating sites for microtubule growth to start assembling new microtubules (ex. centrosomes)
37
What is an example of a nucleation site?
y-Tubulin Ring Complex, which is a protein complex of y-tubulin and accessory proteins and has a ring of y-tubulin (which acts as an attachment site for aB-tubulin dimer)
38
What are some microtubule-associated proteins that help microtubule regulation?
- nucleate growth of new microtubules: nucleating proteins (y-tubulin ring complex) - promote microtubule polymerization: branching protein (augmin), polymerizing protein - promote microtubule disassembly: severing protein (katanin) - stabilize microtubules: stabilizing protein (bind to side), catastrophe-inducing motor protein (kinesin-13), plus-end linking protein
39
How do neurotransmitters synthesized in the ER get to the axon terminals?
by motor proteins on microtubules
40
What are some motor proteins that work on microtubules?
- kinesins - dyneins
41
What direction does kinesin move along microtubules?
moves along microtubules from the minus end toward the plus end
42
What direction does dyneins move along microtubules
moves along microtubules from plus end towards the minus end
42
How do motor proteins like kinesin and dynein contribute to cellular processes?
transport cellular cargo along microtubules, are involved in organelle positioning, and play critical roles in cell division by contributing to chromosome segregation and spindle dynamics
43
What does kinesin 1 do?
it's a dimer it's head moves along the microtubule towards the plus end to the axon terminus, while transporting cargo of organelles, vesicles, and macromolecules on their tails
44
What does cytoplasmic dynein do?
it's a dimer it's head moves along the microtubule towards the minus end to the cell body, while transporting cargo of worn-out mitochondria and endocytosed material on its tails
45
Where are microtubules located in an animal cell?
extend from the centrosome to the cell periphery
46
Where is the ER located in an animal cell and how did it get there?
from the nuclear envelope to the cell periphery by kinesin-1
47
Where is the Golgi located in an animal cell and how did it get there?
near the centrosome by cytoplasmic dynein
48
What are actin filaments also referred to as?
microfilaments
49
What are actin filaments made of and their properties?
- actin monomers - flexible, inextensible (bend but can't stretch)
50
What are the functions of actin filaments?
- stiff, stable structure - contractile activity - cell motility (crawling) - cytokinesis (contractile ring)
51
What motor proteins are associated with actin filaments?
myosins
52
What is the structure of an actin filament?
it's a helical filament, composed of actin monomers, held together by noncovalent interactions. These filaments have a double helical structure (two protofilaments twisted in a right-handed helix) with a plus end and a minus end
53
Do actin filaments have polarity?
yes, the plus end is different from the minus end actin monomers are in all the same orientation in each protofilament, but growth is faster at the plus end
54
What role does ATP play in actin filament assembly?
Free actin monomers bind ATP (in the center of the protein) before adding to a growing filament. After incorporation into the filament, ATP is hydrolyzed to ADP. This hydrolysis leads to decreased strength of binding between monomer in the filament
55
What happens when there is a rapid addition of actin monomer?
when actin is added on faster than ATP hydrolysis in newly added actin monomer, an ATP cap is created, which promotes growth
56
How do actin-binding proteins influence actin filament dynamics?
regulate the length and stability of actin filaments by promoting polymerization or depolymerization
57
What are the different phases of actin polymerization in a test tube?
- actin subunits and ATP added to test tube - nucleation (lag phase): small oligomers spontaneously form but are unstable - elongation (growth phase): some oligomers become more stable, leads to rapid filament elongation (faster at plus end) - steady state (equilibrium phase): decrease in actin subunits, rate of subunit addition = rate of subunit disassociation, treadmilling
58
How does an actin filament grow?
at the plus end, there is an addition of actin monomers, which leads to polymerization. shortly after, actin hydrolyzes ATP to ADP. When an ADP-actin is lost from the minus end it would be depolymerization
59
What is actin filament treadmilling?
a dynamic process where actin monomers are continuously added to the plus end and removed from the minus end of the filament, resulting in a net flow of actin subunits through the filament
60
What is the role of actin-binding proteins in treadmilling?
regulate treadmilling by promoting polymerization at the plus end or depolymerization at the minus end of actin filaments
61
Why is actin filament polarity important for treadmilling?
enables polarized treadmilling, with forward propulsion occurring at the plus-end-rich leading edge and disassembly happening at the lagging edge
62
How does treadmilling occur?
1. actin filament growth 2. at treadmilling concentration - actin filament remain the same size and looks "stable" but there is net addition at plus end and net loss at minus end - actin monomers move through the filament and are eventually replaced (a continuous supply of ATP is needed)
63
What is an example of actin filaments undergoing treadmilling?
cell crawling, dynamic changes in actin filaments They assemble at the leading edge and disassemble further back to push the leading edge
64
How are actin filaments regulated?
actin-binding proteins - sequester actin monomers (prevent polymerization): monomer-sequestering protein - promote nucleation to form filaments: nucleating protein - stabilize actin filaments (capping): capping protein, side-binding proteins - organize: bundle, cross-link filaments - severe actin filament
65
What direction does myosin move?
the head moves along the actin filament from the minus end towards the plus end by using ATP hydrolysis to move
66
What types of myosin is there?
myosin 1 and myosin 2
67
What is myosin 1?
head - binds to actin tail - bind to cargo (vesicles to regulate secretion and plasma membrane to shape the cell)
68
What is myosin 2, with an example?
dimer - 2 heads, 2 tails (organized in a coiled-coil) ex. bipolar myosin 2 filament - slide actin filaments in opposite directions (plus end of both actin) to generate a contractile force
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