M 1.3 Flashcards
Muscle Proteins: Three Kinds?
- Contractile Proteins
- Regulatory Proteins
- Structural Proteins
Muscle Proteins: What kind?
- Generate force during contraction
Contractile Proteins
Muscle Proteins: Two Contractile Proteins?
- Myosin
- Actin
Muscle Proteins: What Contractile Protein?
- Makes up thick filament; a molecule consists of a tail and two myosin heads, which bind to myosin- binding sites on actin molecules of thin filament during muscle contraction
- Functions as a motor protein in all three types of muscle tissue
Myosin
Muscle Proteins: What Contractile Protein?
- The main component of thin filament; each actin molecule has a myosin-binding site where myosin head of thick filament binds during muscle contraction.
- Functions as a motor protein in all three types of muscle tissue
Actin
Muscle Proteins: What kind?
- Help switch the contraction process on and off
Regulatory Proteins
Muscle Proteins: Two Regulatory Proteins?
- Tropomyosin
- Troponin
Muscle Proteins: What Regulatory Protein?
- Component of thin filament; when skeletal muscle fiber is relaxed, this covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin
Tropomyosin
Muscle Proteins: What Regulatory Protein?
- Regulatory protein that is a component of thin filament; when calcium ions (Ca2+) bind to this, it changes shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin.
Troponin
Muscle Proteins: What kind?
- Keep thick and thin filaments of myofibrils in proper alignment, give myofibrils elasticity and extensibility, and link myofibrils to sarcolemma and extracellular matrix
Structural Proteins
Muscle Proteins: Five Structural Proteins?
- Titin
- α-Actinin
- Myomesin
- Nebulin
- Dystrophin
Muscle Proteins: What Structural Protein?
- Connects Z disc to M line of sarcomere, thereby helping to stabilize thick filament position; can stretch and then spring back unharmed, and thus accounts for much of the elasticity and extensibility of myofibrils
Titin
Muscle Proteins: What Structural Protein?
- Structural protein of Z discs that attaches to actin molecules of thin filaments and to titin molecules
α-Actinin
Muscle Proteins: What Structural Protein?
- Forms M line of sarcomere; binds to titin molecules and connects adjacent thick filaments to one another
Myomesin
Muscle Proteins: What Structural Protein?
- Wraps around entire length of each thin filament; helps anchor thin filaments to Z discs and regulates length of thin filaments during development
Nebulin
Muscle Proteins: What Structural Protein?
- Links thin filaments of sarcomere to integral membrane proteins in sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers; thought to help reinforce sarcolemma and help transmit tension generated by sarcomeres to tendons
Dystrophin
Three Types of Skeletal Muscle Fibers
- Slow Oxidative (SO) Fibers
- Fast Oxidative-Glycolytic (FOG) Fibers
- Fast Glycolytic (FG) Fibers
What Type of Skeletal Muscle Fibers?
- Fibers appear dark red because they contain large amounts of myoglobin and many blood capillaries
- Contains many large mitochondria therefore these fibers generate ATP mainly by aerobic respiration (that’s why they are called oxidative fibers)
- These fibers are said to be “slow” because the ATPase in the myosin heads hydrolyzes ATP relatively slowly and the contraction cycle proceeds at a slower pace than in “fast” fibers.
- these fibers have slow speed of contraction; twitch contractions last from 100 to 200 msec, and they take longer to reach peak tension; very resistant to fatigue and capable of prolonged, sustained contractions for many hours
- They are adapted for maintaining posture and for aerobic, endurance-type activities
Slow Oxidative (SO) Fibers
What Type of Skeletal Muscle Fibers?
- Largest and contain large amounts of myoglobin and many blood capillaries; appears dark red
- Can generate ATP by aerobic respiration giving them moderately high resistance to fatigue
- Can also generate ATP by anaerobic glycolysis due to high levels of intracellular glycogen level
- “Fast” because the ATPase in their myosin heads hydrolyzes ATP three to five times faster than the myosin ATPase in SO fibers making their speed of contraction faster
- Twitches of these fibers reach tension more quickly than those of SO fibers but are briefer in duration—less than 100 msec
- Contribute to activities like walking and sprinting
Fast Oxidative-Glycolytic (FOG) Fibers
What Type of Skeletal Muscle Fibers?
- Have low myoglobin content, few blood capillaries, few mitochondria, and appear white in color
- Contain large amounts of glycogen and generate ATP mainly by glycolysis
- these fibers contract strongly and quickly due to their ability to hydrolyze ATP rapidly
- Fast-twitch fibers are adopted for intense anaerobic movements of short duration; fatigues quickly
Fast Glycolytic (FG) Fibers
