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KINE2011: Human Physiology > Module 4: Lecture 2 > Flashcards

Module 4: Lecture 2 Flashcards

1
Q

what is the A band based on?

A

the thick filaments and how far they travel
- your thin filaments are within it as well

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2
Q

why is the I Band called the light band?

A

because there is no thick filaments in it so light is allowed through it

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3
Q

does muscle contraction always cause a ‘shortening’ of the muscle?

A

no

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4
Q

what does contraction refer to?

A

an active state in which your actin and myosin are forming cross bridges and generating force

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5
Q

what is the sliding filament mechanism caused by?

A

cross-bridge cycling

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6
Q

why can a cross bridge form?

A

because of the overlap of the filaments and the binding sites

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7
Q

what is the sliding filament mechanism a result of?

A

the action potential stimulating skeletal, smooth and cardiac muscles

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8
Q

what is linked to internal changes in calcium release and contraction?

A

changes in the membrane potential of muscles

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9
Q

what is the signal that allows your action and myosin cross bridges to begin to form and actually generate force?

A

when cytosolic calcium increases in a resting myofibre

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10
Q

what is the only purpose of the action potential in the muscle fiber?

A

to stimulate the release of calcium

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11
Q

are thin filaments a single polypeptide chain?

A

no, it is a quaternary structure, meaning it is made up of multiple different protein chains

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12
Q

what is the single polypeptide chain component of actin called?

A

globular actin (G-actin)

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13
Q

what is a single polypeptide chain?

A

a long chain of amino acids that fold back in on itself

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14
Q

how can ‘F-actin’ be formed?

A

if you polymerize a whole bunch of g-actins into a long chain

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15
Q

what is formed from two F-actins intertwining?

A

an actin helix
- the main structure of thin filaments

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16
Q

is there a binding site on every actin molecule?

A

yes, it is where the myosin head can physically attach to the actin molecule and where the cross bridge is formed

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17
Q

how do we make sure that myosin does not attach to the actin to form a cross bridge binding sites at rest?

A

we physically block the binding sites with tropomyosin that intertwine on the actin helix

18
Q

what is the sensor on the actin for when the muscle is activated or not?

A

troponin

19
Q

what are the regulatory molecules?

A

troponin and tropomyosin

20
Q

what does troponin regulate?

A

whether tropomyosin is blocking or not blocking that active site

21
Q

how many actin molecules can one single tropomyosin molecule block?

A

seven actin molecules
- all regulated by one single troponin protein

22
Q

each tropomyosin molecule is held in such _________ binding position by the _________ molecule.

A
  1. inhibitory
  2. troponin
23
Q

what are the three troponin subunits?

A
  1. T
  2. I
  3. C
24
Q

which troponin subunit is physically interacting with the tropomyosin molecule itself?

A

troponin T
- this is what is holding it in close proximity to the actual tropomyosin molecule

25
Q

which troponin subunit keeps it in the inhibitory state and ensures that the binding sites are blocked?

A

troponin I

26
Q

when we want muscle contraction, which subunit of troponin do we have a conformational change in?

A

troponin I subunit that removes inhibitory blocking

27
Q

which troponin subunit is responsible for sensing when a muscle contraction should be occuring?

A

troponin C
- calcium binds to troponin C and induces the conformational change to remove the inhibition

28
Q

what is our thick filament made up of?

A

a whole bunch of myosin molecules with the head regions in both directions away from M line

29
Q

what is a single myosin molecule composed of?

A

two large polypeptide heavy chains that are intertwined with their tail regions in this helix form and four smaller light chains
- they combine to generate a large molecule with two globular heads and one long tail
- two large polypeptide heavy chains and four smaller light chains

30
Q

where on a myosin molecule is the site for where a cross-bridge with actin forms?

A

globular heads

31
Q

what are the two binding sites on a single large polypeptide heavy chain globular head?

A
  1. actin binding site
  2. ATP binding site
32
Q

the light chains on the polypeptide heavy chains are for what?

A

they are specialized proteins that stabilize the head and also act as a site of regulation
- critical for stability
- they are meant to stabilize the myosin head and the interactions and regulate its activity

33
Q

what are the two light chains on the heavy chains called?

A

one is called the essential light chain and the other is called the regulatory light chain

34
Q

what energy is used for generating your cross bridges/contraction?

A

ATPase

35
Q

why are the myosin molecules in the two ends of each thick filament oriented in opposite directions?

A

so that the power stroke of the cross-bridges move the thin filaments toward the centre of the sarcomere

36
Q

what happens during the power stroke?

A

the head of the myosin physically bends and pulls the myosin head inward

37
Q

what is the sequence of events that allow for the cross-bridge cycle?

A
  1. binding between the myosin head and the thin filament
  2. movement of the cross-bridge through power stroke, cross bridge bends, pulling thin myofilament inward
  3. detachment of the cross-bridge: detach myosin from the thin filament
  4. re-energize the myosin head so it can re-attach to a thin filament to repeat the cycle
38
Q

every time a myosin undergoes power stroke, it is pulling ____________________________________.

A

that actin filament closer and closer towards the M line

39
Q

why do we have two heads on a single myosin molecule?

A

to generate more force than a single head

40
Q

what is the A Band defined as?

A

the width of your thick filaments

41
Q

from rest to contracted sarcomere, what happens to the A-band, I-band, H-zone, and overall sarcomere length?

A

A-band: no change
I-band: shorten
H-zone: shorten
Sarcomere: shorten

KINE2011: Human Physiology (29 decks)

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