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BMSC 220 CELL BIOL > AbuArish Section > Flashcards

AbuArish Section Flashcards

1
Q

What three structures make up the cytoskeleton?

A

Microtubules
Actin filaments
Intermediate filaments

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2
Q

What are microtubules made of?

A

Tubulin

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3
Q

How are microtubules arranged?

A

Longitudinal rows af 13 protofilaments

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4
Q

What two components make up protofilaments?

A

a tubulin and B tubulin
- + end by b tubulin and - end by a tubulin

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5
Q

What are MAPs and what do they do?

A

Microtubule associated proteins
- increase stability and promote microtubule assembly by linking tubulin subunits together

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6
Q

What determines the shape of the cell?

A

Microtubules

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7
Q

What are the three kinds of motor proteins?

A

Kinesin and Dyein which move along microtubules
- Myosin which moves along actin filaments

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8
Q

Which direction do motor proteins move?

A

Unidirectionally

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9
Q

Explain what kinesins do

A

Superfamily of 14 motor proteins
- tetramer of 2 heavy and 2 light chains
- most move outwardly from - to +

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10
Q

Does kinesin movement require ATP?

A

yes, one per step

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11
Q

What does kinesins being highly processive mean?

A

Means they can walk along microtubules for a long time without falling off because one of the kinesin heads is always attached to the microtubule

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12
Q

Explain what dyneins do?

A
  • Massive protein
  • two identical heavy chains
  • varying intermediate and light chains
  • moves from + to - end, opposite of kinesins
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13
Q

What is cytoplasmic dynein responsible for?

A

moving spindle and positioning chromosomes during mitosis

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14
Q

What are MTOCs? Give an example of one

A

Microtubule organizing centers - where nucleation of microtubules occurs
- control number and polarity of microtubules
- control numberof protofilaments
- control the time and location of assembly
- Centrosome is an MTOC

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15
Q

What is the centrosome?

A

MTOC
- two barrel shaped centrioles surrounded by electron dense PCM
- major site of microtubule initiation in animal cells

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16
Q

What is a basal body?

A

MTOC
- forms at the base of cilia and flagella
- identical to centrioles - can swap between them

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17
Q

What is the common factor all MTOCs share?

A

y-tubulin - protein for microtubule nucleation
- pcm serves as attachment point for y tubulin

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18
Q

What can cause the disassembly of microtubules?

A
  • posttranslational modification
  • cold
  • hydrostatic pressure
  • elevated Ca
  • variety of chemicals
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19
Q

What happens during assembly of tubulin dimers?

A

GTP is bound to Btubulin
- GTP hydrolyzed to GDP after dimer is incorportated

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20
Q

What happens during disassembly of tubulin dimers?

A

Dimer enters the soluble pool, GDP replaced by GTP- nucleotide exchange allows it to recharge to become a building block again

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21
Q

What is dynamic instability of microtubules?

A

explains that growth and shrinkage of microtubules can coexist in the same region
- any given microtubule can flip between growing and shrinking unpredictably
- property of the plus end

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22
Q

What are cilia?

A

Hairlike, sometimes motile organelles
- on many eukaryotic cells?

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23
Q

What does the single nonmotile cilia do on cells?

A

Acts as a sensory organ monitoring changes in environment

24
Q

Are cilia and flagella structurally identical?

A

yes

25
Q

Do cilia and flagella have a plasma membrane?

A

yes, shared with the cell just extended

26
Q

What is the axoneme? What is the array

A

core of the cilia
-array of microtubules running thru entire organelle
- axoneme consists of 9 peripheral doublet microtubules surrounding a pair of single microtubules (9+2 array)

27
Q

What is intraflagellar transport (IFT)

A

Process through which material is transported along cilia or flagella
- assemble into a protein complex called IFT particle
- multiple IFT particles lign up to form IFT trains
- Carry cargo proteins like tubulin out to + tip for assembly
- inhibiting IFT prevents cilia and flagella from forming

28
Q

Which motor protein generates swinging movement for ciliary movement?

A

Dynein

29
Q

should you go back and look at the complicated shit for cilia movement?

A

probably

30
Q

What are ciliopathies?

A

diseases that result from primary cilia defects
- Polycystic kidney disease
- Bardet Biedl syndrome

31
Q

What are intermediate filaments?

A

Strong ropelike fibers 10-12nm
- provide mechanical strength to cells under physical stress
- chemically heterogenous - 70 genes
- divided into 5 classes
-4 classes are cytoplasmic, 1 is on the nuclear envelope (Lamins)

32
Q

What connects intermediate filaments to other cytoskeletal filaements?

A

Plectin - wispy bridges
- each plectin has a binding site for IF at one end and for any one of the three at the other end

33
Q

5 common points for IF structure? 1 2 4 8

A
  • each monomer has a pair of globular terminal domains sperated by a long fibrous alpha helical region
  • pairs of monomers are associated in parallel orientation to form dimers (polar)
  • dimers associate in an anti parallel staggered fashion to form tetramers (basic subunit) (nonpolar)
  • 8 tetramers associate to form a unit length of IF
  • Elongated IFs are formed from the end to end associated of the unit lengths
34
Q

Does IF assembly require ATP or GTP?

A

No

35
Q

What is different about IFs from the other cytoskeleton elements?

A

Assembly and disassembly are controlled by subunit phosphorylation and dephosphorylation

36
Q

What are keratin containing IFs

A

IFs that contain keratin
- structural proteins of epithelial cells
- radiate through cytoplasm attached to nuclear envelope
- anchored by desmosomes
- also connected to the other 2 elements
- function to absorb mechanical stress

37
Q

What are neurofilaments?

A

Bundles of IFs located in cytoplasm of neurons - parallel to axons

38
Q

What is F-actin?

A

Third major cytoskeletal element
- flexible helical filament composed of actin monomers
- two stranded structure with two helical grooves

39
Q

What can actin filaments be organized into (3)

A
  • ordered arrays
  • highly branched networks
  • tghtly anchored bundles
40
Q

How are actin monomers arranged in an actin filament?

A

Pointing in the same direction - polar filament with barbed + end and pointed - end

41
Q

How is an actin filament assembled and disassembled?

A

Actin monomer binds to ATP
- actin is an ATPase
- ATP is hydrolyzed to ADP after incorporation
- initial nucleation occurs slowly - elongation is quick tho
- both ends are labelled - barbed end grows 10x faster

42
Q

What are the 5 steps in actin assembly? Type of exercise

A
  • Actin filaments are added w atp
  • if ATP is high, subunits are added
  • as monomers are consumed, ATP drops until addition only continues as barbed end
  • as filament elongation continues free monomers drop, starts taking from pointed end to give to barbed
  • ## eventually growth and concentration become constant - treadmilling
43
Q

What is myosin?

A

molecular motors of factin
- protein superfamily
- two groups
– conventional type ii muscle cells
– unconventional in other cells
- operate with actin
- move towards barbed end of actin
- all share head domain
- head domain contains two sites - one that drives myosin motor by hydrolyzing ATP and one that binds the actin
- tails are divergent

44
Q

What are type ii myosins?

A

primary motors for muscle contraction
- move towards + barbed end
- required for cell splitting, generating tension and cell migration

45
Q

Myosin filaments are bipolar, what does this mean?

A

reversal of polarity in center
- myosin heads at the opposite ends of a myosin filament can pull actin filaments together

46
Q

What is myosin V?

A

unconventional myosin
- moves in a hand over hand motion similar to kinesin
- transports various types of cytoplasmic vescicles and organelles

47
Q

What is the structure of a skeletal muscle fiber?

A
  • muscle fiber is a multinucleate cell
  • each fiber has many myofibrils
    -each myofibril consists of repeating arrays of sarcomeres
48
Q

What is a sarcomere?

A
  • exends from one Z line to the next Z line
  • dense M line in the H zone
  • I band has only thin filaments
  • ## H zone has only thick filaments
49
Q

What is the sliding model of muscle contraction?

A

shortening of sarcomeres consists of thin and thick filaments sliding over eachother
- A band remains constant
-H and I bands decrease
- Z lines move inwards

50
Q

What are the thin filaments composed of?

A

actin, tropomyosin and troponin

51
Q

What is tropomyosin?

A

elongated molecule that fits into thin filament grooves and associates w 7 subunits

52
Q

What is troponin?

A

globular protein complex composed of 3 subunits spaced apart, touches actin and tropomyosin

53
Q

What are the 8 categories of actin binding proteins?

A
  • nucleating
  • monomer sequestering
  • end blocking
  • monomer polymerizing
  • actin filament depolymerizing
  • cross linking and bundling
  • filament severing
  • membrane binding
54
Q

What are actin binding proteins?

A

determins organization and behavior of actin filaments in cells

55
Q

How do cell fibroblasts move?

A

flattens itself close to substratum and becomes fan shaped
- extends small protrusion called lamellipodium from cell which adheres to substratum at focal adhesions providing anchor sites to pull itself forwards

56
Q
A

BMSC 220 CELL BIOL (6 decks)

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