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Cell Biology > Lecture 4 - The cytoskeleton (part 2) > Flashcards

Lecture 4 - The cytoskeleton (part 2) Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are two key intermediate filaments and what roles do they play in the cell#?

A

-keratin
makes up the cytosolic intermediate filaments that extend from the nuclear membrane to the cell membrane e.g. in skin epithelial cells
-laminin
makes up nuclear intermediate filaments

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2
Q

What are key features of intermediate filaments?

A
  • divergent in sequence and size (unline microfilament and microtubules)
  • large diversity (unlike mf and mt)
  • 5 major classes based on sequence similarities, includes hard keratins from skin and nails
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3
Q

What are features of the keratins, and what type are they?

A

Intermediate Type I (acidic keratins) and Type II (basic keratins) filaments

  • in epithelia
  • heterodimers of basic and acidic subunits
  • prominent in skin hair and nails
  • mutations are involved in skin disease
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4
Q

What are the features of Vimentin and what type of intermediate filament are they?

A

Type III
-widely distributed (lymphocytes, endothelial cells and fibroblasts)
-role in structure to support the cell membranes and keep nucleus and organelles in place
-

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5
Q

What are the features of Neuronal IF proteins and what type of intermediate filament are they?

A

Type IV

  • Found in neuronal neurofilaments
  • determine the axon diameter and therefore the speed of conductance
  • have a structural role in axons
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6
Q

What are the features of laminins and what type of intermediate filament are they?

A

Type V

  • found in the nucleus
  • fibrous network
  • role in regulating and supporting nuclear shape and organisation
  • role in organising and packaging DNA
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7
Q

What is the process of intermediate filament assembly?

A

1- Monomer forms a hetero or homo dimer with another monomer, forming a parallel dimer with C and N terminal ends
2- These are stacked in an antiparallel arrangement to form an antiparallel tetramer
3- Antiparallel tetramers are stacked end on end to form an elongated filamentous structure = protofilament
4- 2 protofilaments come together to form a protofibril
5- Four protofibrils wrap around each other to form an intermediate filament

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8
Q

What is the structure of an intermediate filament monomer?

A
  • globular NH2 head
  • globular COOH tail
  • 48nm
  • Central alpha helical rod domain
  • spacers in the alpha helical rod region between (non helical)
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9
Q

What are the features of intermediate filament assembly?

A
  • does not requite ATP or GTP hydrolysis
  • spontaneous
  • coil domains wrap around each other to form a coiled coil
  • globular domains project away from the intermediate filament
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10
Q

What is the structure of the epidermis and the keratins involved in the cells of the epidermis?

A 
outer epithelial layer
Stratum corneum layer
stratum granulosum layer
stratum spinosum layer
statum basale (basement membrane)
dermis

cells in stratum basale layer express K5/14 heterodimers, expressed less as cells leave layer. Begin to express K1 and K10 as they leave reflects changing activity

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11
Q

Give an example of a disease associated with mutations in keratins

A

Epidermolysis Bullosa Simplex (EBS) - Blistering disease

  • autosomal dominant muation
  • caused by mutations in K5/14, aggregates of keratin found in the cytoplasm
  • epiidermis no longer attached to the basement membrane and dermis
  • N- or C- terminal muations means cells are unable to form protofilaments and the entire intermediate filament cannot form completely
  • cells at the base of the epidermis are weakened
  • epidermis and dermis easily separated
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12
Q

Give an example of a disease associated with Laminin

A

Hutchinson-Gilford progeria syndrome

  • rare premature again disease
  • caused by mutations in the LMNA gene (150bp deletion) produces an abnormal form of the nuclear intermediate filament laminin A
  • nuclear envelope becomes unstable and prone to damage
  • > bone disease, hair loss, cardiovascular disorders, diabetes and muscle atrophy
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13
Q

What are microtubules and how are they arranged?

A
  • polymers of globulun tubular dimers
  • arranged into tube ~24nm diameter,
  • role in transport - cellular tracks for transporting vesicles, organelles and chromosomes
  • used by microtubule motor proteins, kinesin and dynein
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14
Q

What are microtubules composed of?

A

Alpha-tubulin and Beta-tubulin subunits
Alpha-tubulin binds GTP irreversibley can cannot be hydrolysed (non-exchangable GTP)
Beta-tubulin binds GTP reversibly and can be hydrolysed to GDP (exchangable GTP, done as tubulin grows)

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15
Q

What is Taxotene and what does it do?

A

Anti-cancer drug which targets the B tubulin found in microtubules to allow crystallisation of the tubulin dimer

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16
Q

What is the process of assembly of microtubules?

A
  1. Tubulin dimers assemble longitudinally into short protofilaments
  2. The protofilaments associate laterally into a curved sheet, increasing its stability
  3. Tubulin dimers continue to associate with the tubular structure
    - Beta tubulin associates with the (+) end
    - Alpha tubulin assocaites with the (-)
  4. As the dimers bind, the GTP on B tubulin is hydrolysed, creating a GDP microtubule
  5. If the rate of addition is greater than the GTP hydrolysis then a GTP cap is produced. As the rate of assembly is faster at the (+) end
17
Q

What is a microtubule GTP cap?

A

an area at the (+) end of a microtubule where GTP is maintained by alpha and beta tubulin
provides stability to growing structure and regulates length

18
Q

What are some similarities between microtubules and microfilaments?

A
  • dynamic interaction dependent on the Cc of the subunits within a cell
  • GTP cap/capping proteins
19
Q

What is the rate of microtubule growth dependent on?

A

the availability of dimers in the cell, the Cc of alpha and beta tubulin

  • once Cc is reached tubulin dimers can be converted into microtubules
  • if tubulin dimers are more than the critical concentration there is preferential addition of tubulin at the (+) end
  • if tubulin dimers are less than the Cc there is preferential loss of tubulin at the (+) end
20
Q

How are microtubules stabilised?

A

-GTP cap

21
Q

How is microtubule stability regulated?

A 
By 'dynamic instability'
series of 'catashtopihe and 'rescue' events
-Catastrophe - loss, quicker
-Rescue regrowth
Dependent on cell Cc of tubulin dimers
22
Q

What is the structure of the centrosome?

A

2 centrioles

  • organised at right angles
  • made up of 9 sets of triplet microtubules
  • surrounded by a percentriolar matrix = acts as a nucleation point and contains, gamma tubulin and pericentrin, centroles interact with the PC
23
Q

What is the MTOC?

A 
the microtubule organising centre
-structure used to organise tubules in the cell
-located near the nucleus
-directs assembly and orientation of microtubules
-directs vesicle traffic
-directs orientation of organelles
Animals = centrosome 
Plant = nuclear membrane, no MTOC
24
Q

What is the process of nucleation by microtubules at MTOCs?

A

gamma tubulin rings acts as nucleation points
growth from the (-) to the (+) end
(+) end can be capped for stability

25
Q

Where can the MTOC be found?

A
  • near nucleus

- at the base of cell extensions e.g. cillia, flagella, dendrites (basal body, acts as an MTOC, structurally similar)

26
Q

What are the importances of MTOCs?

A

Cell division

  • allow spindle apparatus to form and organise microtubules and for the division of chromosomes
  • In nerve cell, long extensions of dendrites have microtubules with mixed polarity for transport
27
Q

What are the types of micrtubule motor proteins and what is their mode of transport?

A 
Kinesins (Anterograde transport)
-membrane vesicles out
-mitochondrion in
Dyneins (Retrograde transport)
-lysosomes for degradation 
-organelles in for degradation

Can be regions in the cells with little of either microtubules or microfilaments and so single vesicles may have both kinesins and myosin motors attached

28
Q

What is the structure of kinesins?

A
  • dimer
  • two globular head with ATP binding site for binding to microtubules
  • coiled alpha helix
  • tail end contains two light chains which bind to the transported vesicle
29
Q

What are the similarites between kinesins and myosin?

A
  • both have ATP binding regions
  • both have interacting regions (Actin binding site/Microtubule binding site)
  • head, neck and tail region
  • made up of heavy and light chains

Cell Biology (15 decks)

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