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BIO130 Final > Lecture 4 > Flashcards

Lecture 4 Flashcards

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
Q

What kind of bonds hold tubulin together in a microtubule protofilament?

A

all bonds between the individual subunits are noncovalent, but the bonds between protofilaments are weaker than the bonds within each protofilament

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26
Q

What happens to the growth of isolated cilium microtubules incubated with a high concentration of tubulin and GTP?

A

faster growth of microtubules at the plus end, but there is still a little growth at the minus end

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27
Q

What drives dynamic instability in microtubules?

A

driven by the hydrolysis of GTP (guanosine triphosphate) in tubulin dimers, which leads to the addition or loss of tubulin subunits.

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28
Q

How does dynamic instability contribute to microtubule function?

A

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
Q

What is a microtubule organizing center (MTOCs)?

A

the place where microtubules grow out from
the minus ends are stabilized at MTOCs and plus ends grow out

30
Q

When does the mitotic spindle start to assemble?

A

begins forming during prophase. The assembly relies on the properties of microtubules, including their dynamic instability.

31
Q

What would happen if only GDP were present without GTP in regards to microtubule stability?

A

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
Q

How does the growth of microtubules occur?

A
  • 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
Q

How does the shrinkage of microtubules occur?

A
  • 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
Q

Is alpha tubulin hydrolyzed during dynamic instability?

A

no, it’s tightly bound to beta-tubulin, which gets hydrolyzed

35
Q

What are the organizing centers for microtubules in cells?

A

in cells include centrosomes, the two poles of a mitotic spindle, and basal bodies of cilia and flagella

36
Q

What is the function of microtubule organizing centers?

A

they have nucleating sites for microtubule growth to start assembling new microtubules
(ex. centrosomes)

37
Q

What is an example of a nucleation site?

A

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
Q

What are some microtubule-associated proteins that help microtubule regulation?

A
  • 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
Q

How do neurotransmitters synthesized in the ER get to the axon terminals?

A

by motor proteins on microtubules

40
Q

What are some motor proteins that work on microtubules?

A
  • kinesins
  • dyneins
41
Q

What direction does kinesin move along microtubules?

A

moves along microtubules from the minus end toward the plus end

42
Q

What direction does dyneins move along microtubules

A

moves along microtubules from plus end towards the minus end

42
Q

How do motor proteins like kinesin and dynein contribute to cellular processes?

A

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
Q

What does kinesin 1 do?

A

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
Q

What does cytoplasmic dynein do?

A

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
Q

Where are microtubules located in an animal cell?

A

extend from the centrosome to the cell periphery

46
Q

Where is the ER located in an animal cell and how did it get there?

A

from the nuclear envelope to the cell periphery
by kinesin-1

47
Q

Where is the Golgi located in an animal cell and how did it get there?

A

near the centrosome
by cytoplasmic dynein

48
Q

What are actin filaments also referred to as?

A

microfilaments

49
Q

What are actin filaments made of and their properties?

A
  • actin monomers
  • flexible, inextensible (bend but can’t stretch)
50
Q

What are the functions of actin filaments?

A
  • stiff, stable structure
  • contractile activity
  • cell motility (crawling)
  • cytokinesis (contractile ring)
51
Q

What motor proteins are associated with actin filaments?

A

myosins

52
Q

What is the structure of an actin filament?

A

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
Q

Do actin filaments have polarity?

A

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
Q

What role does ATP play in actin filament assembly?

A

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
Q

What happens when there is a rapid addition of actin monomer?

A

when actin is added on faster than ATP hydrolysis in newly added actin monomer, an ATP cap is created, which promotes growth

56
Q

How do actin-binding proteins influence actin filament dynamics?

A

regulate the length and stability of actin filaments by promoting polymerization or depolymerization

57
Q

What are the different phases of actin polymerization in a test tube?

A
  • 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
Q

How does an actin filament grow?

A

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
Q

What is actin filament treadmilling?

A

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
Q

What is the role of actin-binding proteins in treadmilling?

A

regulate treadmilling by promoting polymerization at the plus end or depolymerization at the minus end of actin filaments

61
Q

Why is actin filament polarity important for treadmilling?

A

enables polarized treadmilling, with forward propulsion occurring at the plus-end-rich leading edge and disassembly happening at the lagging edge

62
Q

How does treadmilling occur?

A
  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
Q

What is an example of actin filaments undergoing treadmilling?

A

cell crawling, dynamic changes in actin filaments
They assemble at the leading edge and disassemble further back to push the leading edge

64
Q

How are actin filaments regulated?

A

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
Q

What direction does myosin move?

A

the head moves along the actin filament from the minus end towards the plus end by using ATP hydrolysis to move

66
Q

What types of myosin is there?

A

myosin 1 and myosin 2

67
Q

What is myosin 1?

A

head - binds to actin
tail - bind to cargo (vesicles to regulate secretion and plasma membrane to shape the cell)

68
Q

What is myosin 2, with an example?

A

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

BIO130 Final (7 decks)

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