PNB 2274 Exam 2| QUESTIONS WITH COMPLETE SOLUTIONS 100% VERIFIED| LATEST UPDATE
GRADED A+
Explain the structure of a sarcomere: a sarcomere is the functional contractile unit in a
skeletal muscle fiber
- Z discs are at end = where actin attaches
- M line is in the middle = myosin filaments anchored here
- H zone contains only the myosin (middle)
* 1 sarcomere = A band + 1/2 I band + 1/2 I band
What happens when a sarcomere contracts? - H band narrows
- overlap of A band proteins
- z lines are coming together
What is the molecular structure of thin filaments? - made of actin subunits
- actin is a polymer
- G-actin is a monomer
- F-actin is a polymer
- protein double helix
- 2 types of accessory proteins wrapped around thin filaments : 1. tropomyosin, 2. troponin
How do tropomyosin and troponin behave? calcium ions flow into the sarcoplasm, calcium
binds to troponin, troponin undergoes a conformational change which then results in pulling
tropomyosin out of the way (off of the actin active site), myosin is thus able to bind to actin!
What is the molecule struck of thick filaments? composed of myosin filaments
,What are the actions of the sliding filament theory? actin filaments come together to
produce a myosin contraction
- myosin head is in the "cocked" position = ready to go + bound to the actin active site
- phosphorylation (ADP-->ATP) releases the myosin head creating a "power stroke"
- ATPase activity hydrolyzes ATP to ADP in order to cock the myosin head once again
Mechanisms of the response loop in muscles: response = contraction
stimulus = calcium @ cellular level
sensor for calcium = troponin
signal = conformational change + movement of tropomyosin off of binding site
control center = calcium detecting and release system
output = calcium release, ATP, contracting of myosin
target cells = protein filaments
What are the physical properties of smooth muscles? 1. found in the walls of viscera and
blood vessels
2. short fusiform cells (widest in the middle and tapered at each end)
3. one centrally-located nucleus
4. no striations
5. thin filaments are attached to dense bodies (in skeletal are attached to Z lines)
6. under involuntary control
What is an important similarity between smooth and skeletal muscle? smooth and skeletal
muscle share the same fundamental mechanism for contraction
- scrunches up with it contracts
- filaments of actin and myosin are present
, - myosin is still pulling actin
What is the mechanism for smooth muscle contraction? thin filaments are being pulled in
opposite directions
- myosin pulling on the actin pulls together the dense bodies
1. calcium enters the cell via ryanodine receptors or IP3R
- calcium is brought in not just from the sarcoplasm but also the outside of the cell
2. calcium binds to calmodulin
3. the binding of calcium to calmodulin activates myosin light chain kinase
4. the MLC kinase phosphorylates the light chains in myosin heads and increases myosin ATPase
activity
5. active myosin cross bridges slide on actin and create muscle tension
How is the role of DhpR different in smooth muscles? in skeletal muscle, DhPR was
mechanically-gated calcium channel, in smooth muscle it responds to voltage to allow calcium
in
(positive feedback loop)
What is the major receptor in smooth muscle and how does it operate? IP3R is the major
receptor for calcium in smooth muscle
- does not open mechanically
- calcium acts as the ligand
- IP3 is activated by G protein-couple receptors
What is the role of phosphatase? anytime you have a kinase, a phosphatase is necessary to
to remove the phosphate in order to inactive the protein
- phosphorylation dictates protein shape, activity, stability, binding partners, localization
(kinases activate protein "on")
GRADED A+
Explain the structure of a sarcomere: a sarcomere is the functional contractile unit in a
skeletal muscle fiber
- Z discs are at end = where actin attaches
- M line is in the middle = myosin filaments anchored here
- H zone contains only the myosin (middle)
* 1 sarcomere = A band + 1/2 I band + 1/2 I band
What happens when a sarcomere contracts? - H band narrows
- overlap of A band proteins
- z lines are coming together
What is the molecular structure of thin filaments? - made of actin subunits
- actin is a polymer
- G-actin is a monomer
- F-actin is a polymer
- protein double helix
- 2 types of accessory proteins wrapped around thin filaments : 1. tropomyosin, 2. troponin
How do tropomyosin and troponin behave? calcium ions flow into the sarcoplasm, calcium
binds to troponin, troponin undergoes a conformational change which then results in pulling
tropomyosin out of the way (off of the actin active site), myosin is thus able to bind to actin!
What is the molecule struck of thick filaments? composed of myosin filaments
,What are the actions of the sliding filament theory? actin filaments come together to
produce a myosin contraction
- myosin head is in the "cocked" position = ready to go + bound to the actin active site
- phosphorylation (ADP-->ATP) releases the myosin head creating a "power stroke"
- ATPase activity hydrolyzes ATP to ADP in order to cock the myosin head once again
Mechanisms of the response loop in muscles: response = contraction
stimulus = calcium @ cellular level
sensor for calcium = troponin
signal = conformational change + movement of tropomyosin off of binding site
control center = calcium detecting and release system
output = calcium release, ATP, contracting of myosin
target cells = protein filaments
What are the physical properties of smooth muscles? 1. found in the walls of viscera and
blood vessels
2. short fusiform cells (widest in the middle and tapered at each end)
3. one centrally-located nucleus
4. no striations
5. thin filaments are attached to dense bodies (in skeletal are attached to Z lines)
6. under involuntary control
What is an important similarity between smooth and skeletal muscle? smooth and skeletal
muscle share the same fundamental mechanism for contraction
- scrunches up with it contracts
- filaments of actin and myosin are present
, - myosin is still pulling actin
What is the mechanism for smooth muscle contraction? thin filaments are being pulled in
opposite directions
- myosin pulling on the actin pulls together the dense bodies
1. calcium enters the cell via ryanodine receptors or IP3R
- calcium is brought in not just from the sarcoplasm but also the outside of the cell
2. calcium binds to calmodulin
3. the binding of calcium to calmodulin activates myosin light chain kinase
4. the MLC kinase phosphorylates the light chains in myosin heads and increases myosin ATPase
activity
5. active myosin cross bridges slide on actin and create muscle tension
How is the role of DhpR different in smooth muscles? in skeletal muscle, DhPR was
mechanically-gated calcium channel, in smooth muscle it responds to voltage to allow calcium
in
(positive feedback loop)
What is the major receptor in smooth muscle and how does it operate? IP3R is the major
receptor for calcium in smooth muscle
- does not open mechanically
- calcium acts as the ligand
- IP3 is activated by G protein-couple receptors
What is the role of phosphatase? anytime you have a kinase, a phosphatase is necessary to
to remove the phosphate in order to inactive the protein
- phosphorylation dictates protein shape, activity, stability, binding partners, localization
(kinases activate protein "on")
