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Biochemistry > L11 > Flashcards

L11 Flashcards

1
Q

What are the 3 types of muscles?. briefly describe each.

A

skeletal : striated , moves voluntarily , each skeletal muscle is supple with its own nerves , vein and artery . there are 640 skeletal muscles in the body

cardiac :also striated , is involuntary , found in the heart

smooth muscle : not striated , found in visceral organs where movement is involuntary .

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2
Q

what is the electrically excitable plasma membrane that surrounds individual muscle fibers ?

A

sarcolemma

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3
Q

what are myofibrils?

A

unit arranged in parallel . they are embedded in intracellular fluid .forms muscle fibers

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4
Q

what is the intracellular fluid that myofibrils are embedded in called?

A

sarcoplasm

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5
Q

what is the functional unit of the muscle called?

A

sarcomere

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6
Q

what is the sarcoplasmatic reticulum?

A

the muscle cells own version of endoplasmic reticulum , it is the cells transport and storage system . it’s walls are loaded with calcium pumps which use ATP to save up calcium ions

also studded with calcium channels that are linked to protein in the membrane of the muscle cell

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7
Q

what does the sarcoplasmic reticulum surround ?

A

The sarcoplasmic reticulum with its transverse (T) tubules and terminal cisterns surrounds each myofibril. The T tubules invaginate from the sarcolemma.

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8
Q

describe what is seen under the electron microscope when veiwing the myofibril.

A

alternating dark and light bands can be seen. these bands are referred to as I and A bands.

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9
Q

what are A and I bands of the myofibril?

A

A bands are dark bands while I bands are light bands

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10
Q

what part of the A band is least dense ?

A

– central region of the A band ( the H zone ) appears less dense than the rest of the band

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11
Q

which band Is bisected by the z line?

A

I band

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12
Q

where do thin filaments exist ?

A

In the I band , it also exists in parts of the A band but not the H zone

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13
Q

what proteins do thin filaments contain ?

A

actin , tropomyosin , and troponin

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14
Q

how is the thin filament arranged ?

A

around the thick filament as a hexagonal array

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15
Q

where are the thick bands present?

A

in the A bands

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16
Q

what protein does the thick fillaments have ?

A

myosin

17
Q

how are thick filaments arranged ?

A

cross section as a hexagonal array

18
Q

what is G-actin?

A

monomeric actin that is globular and makes 25% of muscle protein by weight

19
Q

what does G-actin do in presence of Mg2+?

A

polymerizes to form an insoluable double helical fillament called F actin

20
Q

what is myosin ?

A

constitue a family of proteins

contributes 55% to muscle protein by weight and it forms thick filaments

21
Q

describe the structure of myosin .

A

has fibrous tail consisting of 2 intertwined helices

each helix has a globular head portion at one end

22
Q

what are the chains that myosin consists of?

A

2 heavy chains (H chains ) and 4 light chains (L chains )

23
Q

what so tropomyosin and troponin do?

A

complex present in thin filaments that block myosin from attaching to actin , this blockage is removed when it is bonded with calcium

24
Q

what is tropomyosin?

A

fibrous molecule that consists of two chains , alpha and beta , that attach to f actin in the groove between the filaments

it is present in all muscular and muscle like structure

25
Q

describe the troponin complex .

A

unique to strained muscles and consists of three polypeptides .

26
Q

what are the three polypeptides that troponin consists of?

A

TpT: Binds to tropomyosin as well as other 2 troponin components

TpI: inhibits F actin- myosin interaction and also binds to other components of troponin

TpC:calcium binding polypeptide . 4 molecules of calcium ion are bound per molecule of troponin C

27
Q

When highly sensitive assays are used, cardiac-specific isoforms both troponin I and troponin T are detectable in serum as early as 2 hours after Acute Myocardial Infarction.

Levels reach their peak at 12 hours and remain elevated for 7 to 10 days.

Troponin can therefore be used even for patients with delayed presentations.

A

0-0

28
Q

list the sequence of events in contraction.(study fromCB yabn el 7alal)

A

discharge of motor neuron and release of acetylcholine

binding of acetylcholine to nicotinic acetylcholine receptors

generation of action potential in muscle fibers

release of Ca2+ from terminal cisterns of sarcoplasmic reticulum and diffusion to thick and thin filaments

binding of ca 2+ to troponin C , uncovering myosin binding sites of actin

formation of cross linkages between actin and myosin and sliding of thin on thick filaments producing shortening

29
Q

steps of relaxation :

CB yabni

A

Ca2+ pumped back into sarcoplasmic reticulum

Release of Ca2+ from troponin

Cessation of interaction between actin and myosin

30
Q

what is malignant hyperthermia ?

A

body temp rises when exposed to certain drugs

reaction consists primarily of rigidity of skeletal muscles , hyper metabolism and high fever

31
Q

why does mutation in calcium channel protein (RYR1) cause high cytosolic concentration of CA2+ in skeletal muscle ?

A

when a mutation on the RYR1 gene occurs the mutated channel opens up more easily and stays open for longer , flooding the cytosol with cA2+

32
Q

What does high levels of ca2+ stimulate ?

A

sustained muscle contraction (rigidity ). it also stimulates breakdown of glycogen , glycosides and eorobic metabolism( resulting in excessive production of heat)

33
Q

what is dystrophin and what is its function?

A

it is a cytoskeleton protein that connects F-actin to dystroglycan complex

34
Q

what is a dystrophin complex ?

A

The dystrophin complex acts as an anchor, connecting each muscle cell’s cytoskeleton with the framework of extracellular matrix proteins. Also play a role in cell signalling by interacting with chemical signals.

absence of dystrophin, plasma membrane of muscle cells gets damaged during contractile process leading to muscle cell death.

35
Q

what diseases is the term muscle dystrophy applied too ?

A

The term muscular dystrophy is applied to diseases that cause progressive weakness of skeletal muscle.

36
Q

what is Duchenne muscular dystrophy

A

a serious form of dystrophy in which the dystrophin protein is absent from muscle. It is X-linked

37
Q

what is beer muscular dystrophy ?

A

Dystrophin is present but altered or reduced in amount.

38
Q

what is sarcopenia ?

A

Loss of skeletal muscle mass with age
Mainly after 5th decade of life
Can lead to frailty and loss of functional capacity

Regular exercise during middle age reduces sarcopenia

Biochemistry (15 decks)

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