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Locomotor System > Biochemistry: Muscles > Flashcards

Biochemistry: Muscles Flashcards

1
Q

What are the functions of muscles?

A
  • body moving
  • respiration
  • digestion
  • vascular tone and blood circulation
  • excretion
  • kinetics (mechanical work)
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2
Q

What two groups are vertebrate muscles classified into?

A
  • skeletal muscles
  • smooth muscles
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3
Q

What three compounds play a major role in muscle contraction?

A
  • myofibril proteins
  • Ca2+
  • ATP
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4
Q

What is each muscle fiber covered by?

A

membrane (sarcolemma)

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5
Q

What does the sarcolemma consist of?

A

50-70% proteins:
- ion channels
- enzymes
- pumps
- structural proteins
- etc.

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6
Q

What follows the sarcolemma?

A

the sarcoplasm

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7
Q

What is the sarcoplasm? What is it composed of?

A

an intracellular fluid
- sarcoplasmic reticulum
- transverse pipe system
- myofibrils
- energy sources (lpids, glycogen molecules)
- enzymes

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8
Q

What are myofibrils?

A

complex of contractile proteins

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9
Q

What are skeletal muscles composed of?

A

72-80% water
20-28% dry matter

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10
Q

What do intracellular muscle proteins divide into?

A

sarcoplasma proteins (water soluble)
fibrillar myofibril proteins (insoluble in water)

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11
Q

What is the function of sarcoplasma proteins? Examples.

A

MYOGLOBIN:
accumulate oxygen in muscles
(the colour of the muscles depends on it)

CALCEZVESTRINE:
stimulate the onset of muscle contraction

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12
Q

State an example of a sarcoplasma protein.

A

myoglobin
calcezvestrine

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13
Q

What are myofibrils?

A

complex of contractile proteins

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14
Q

What are the two types of myofillaments that the myofibrils consist of? What do they consist of?

A

1) thick fillaments: 200-400 molecules of myosin
2) thin fillaments: complex of actin proteins, tropomyosin and troponin

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15
Q

What percentage of all proteins involved in muscle contraction does myosin, actin and troponin account for?

A

90%

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16
Q

What is myosin? What is it composed of?

A
  • a molecule
  • fibrillar “tail“: two identical twisted alpha helices (form a supercoil)
  • globular “head”
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17
Q

What is the function of myosin?

A

1) myosin mollecules bind to fillaments under physiological conditions.
400 myosin molecules make up a myosin fillament.

2) myosin has ATPase activity.
- hydrolyses ATP (used for muscle contraction)

3) myosin is a mechanoenzyme
- catalyses the conversion of energy from chemical bonds into mechanical energy

18
Q

What is actin?

A
  • monomeric, globular protein
  • composed of a single polypeptide chain of 374 amino acids
  • not specific (also present in other eukaryotic cells)
19
Q

What does the actin fillament consist of?

A
  • actin
  • tropomyosin (Tm)
  • troponin’s (3)
20
Q

What does the actin core consist of?

A

two twisted F-actin chains (fibrillar actin)

(each consisting of 400 polymerised G-actin molecules)

21
Q

What is attached to the F-actin fillament? By what joints? Where located?

A

2 chains of tropomyosin molecules
- by flexible joints
- located in a depression formed by two actin chains

22
Q

What is tropomyosin bound to?

A

3 troponin proteins:
- Troponin C (Ca2+ binding)
- Troponin I (inhibitory)
- Troponin T (tropomyosin binding)

23
Q

What is the name of the compound formed when the heads of the myosin molecule bind to the actin threads?

A

actomyosin

24
Q

What are muscle nitrogenous compounds? Explain their molecular weight. What is their function? Examples?

A
  • organic componds that contain nitrogen,
  • low molecular weight
  • regenerate ATP, reduce muscle fatigue, increase the amplitude of muscle contraction,
  • eg. amino acids, nucleotides, creatine
25
Q

What are muscle non-nitrogenous compounds? What is their function? Examples?

A
  • organic componds that do not contain nitrogen,
  • reserve source of energy (triglycerides), muscle contractions (ions)
  • eg. glucogen, milk, pyruvate, lipids, inorganic salts
26
Q

How does the electrical impulse reach the muscles?

A

through the junction of nerve and muscle in the sarcolemma

27
Q

What is the usual potential difference of the sarcolemma? What happens when there is an electrical impulse?

A
  • excess of politive charge on the outside
  • inside: -60mV

DEPOLARIZATION:
- sudden increase in membrane conductivity to K+, Na+ and Ca2+ ions.

28
Q

What ions are displaced into the sarcoplasm due to depolarization? What does this rapid displacement cause?

A

Ca2+ ions
- causes ATP to be hydrolysed (allowing for muscle contraction)

29
Q

What happens to myosin when tropomyosin changes its position?

A

the myosin head (containing ADP and Pi) rotates at a large angle to join the F-actin. to form an angle of 90 degrees.

30
Q

What happens during the ‘power stroke’? How does it occur?

A

fusion of myosin, ATP, and actin releases Pi.
- myosin changes angle from 90 degrees to 45 degrees, by pulling actin towards it

31
Q

Why does the myosin head position change to 45 degrees?

A

it is the conformation which requires the least energy

32
Q

What happens in stage 3? How is the myosin head detatched from the actin?

A

ATP binds to the myosin-F-actin complex

33
Q

What happens in step 4? Once the ATP attatches to myoactin complex?

A

the newly bound ATP is hydrolysed by myosin and a new interaction occurs without releasing ADP and Pi.
The cycle repeats.

34
Q

What is the function of ATP in the sliding fillament theory?

A

ATP seperates the myosin head from the thin fillament (F-actin) and is the driving force behind muscle contraction.

35
Q

What is the main factor regulating muscle contraction? What concentration of Ca2+ is there when?

A

Ca2+
- highest muscle contraction: 10^-6/5
- no contraction: 10^-7

36
Q

How is smooth muscle different from skeletal muscle?

A
  • NO TROPONIN COMPLEXES.
  • chains of MYOSIN differ (phosphorylated or dephosphorylated)
  • ACTIN > MYOSIN (reversed ratio in transverse muscles)
37
Q

What are the three types of smooth muscles?

A

1) individual unit
2) multiple muscle units
2) mixed forms

38
Q

Explain the individual muscle unit. State examples.

A
  • smooth cells connect through slit joints
  • react together as a seperate functional unit

eg. digective tract, bladder, ureter, uterus

39
Q

Explain multiple units of smooth muscle. Examples.

A
  • connected by the autonomic nervous system
  • actions are independent of other cells or groups of cells in the same muscle
  • eg. iris, dendate muscles
40
Q

Explain mixed forms of smooth muscle. Examples.

A
  • both types of properties
  • activity generated by the nervous system and smooth muscles themselves
  • eg. vascular

Locomotor System (19 decks)

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