2 - Green - Muscle Physiology

Question 1

bHLH

Answer 1

Basic helix-loop-helix

Structural region on MyoD that is required for activity and dimerization

Question 2

E-box

Answer 2

Binding site in DNA for myogenic factors

Required to activate transcription

Question 3

Excitation-Contraction Coupling

Answer 3

Pysiological process of converting an electrical stimulus to the muscle into a contraction

Question 4

Power Stroke

Answer 4

Molecular intractions between actin and myosin that lead to muscle contraction

Question 5

Satellite Cells

Answer 5

Stem Cells found in skeletal muscle fibers that promote repair and regeneration

Question 6

SERCA

Answer 6

Sarcoendoplasmic reticulum calcium ATPase

Pump located in sarcoplasmic reticulum (SR) that transports Ca²⁺ from the cytoplasm into the SR

Question 7

Summation Contraction

Answer 7

Short duration contraction caused consecutive action potentials

Question 8

Tetanus Contraction

Answer 8

Steady, prolonged contraction caused by continuous stimulation

Question 9

Twitch Contraction

Answer 9

Single muscle contraction caused by one action potential

Question 10

How are myotubes formed? What is uniqe anout thoe organelle structure?

Answer 10

Single cell myoblasts fuse to form multinucleated myotubules

Question 11

What transcription factors drive fusion of myogenic cells?

Answer 11

MyoD

myogenin

myf-5

MRF-4/herculin/myf-6

Question 12

MyoD Structure

Answer 12

Nuclear phosphoprotein

Contains bHLH region

Question 13

How are transcription factors utilized to drive myogenic fusion?

Answer 13

Dimers

homodimers okay, but hetero-dimers with E2 proteins best

Question 14

What is present in most muscle-specific enhancers in multiple copies?

Answer 14

E-boxes

Question 15

E2 Family of Genes

Answer 15

E2A

E2-2

HEB

Question 16

How is transcription activated?

If no E-boxes are present, how are these regulated?

Where does specificity reside?

What affect doe MyoD initiate have on the regulatory regions?

Answer 16

MyoD complexes must bind two or more upstream E-Boxes

Intermediate proteins

Specificity resides in the basic region

MyoD initiates chromatin remodeling

Question 17

Do differentiated muscle cells continue to divide?

Answer 17

No

Question 18

What are the early and late myogenic proteins?

Answer 18

MyoD, Myf5 = Early

Myogenin, MRF4 = Late

Question 19

What can a loss of Myostatin result in?

Answer 19

Hughed Jacked Man

Yolked diesel cows

Question 20

What is the chief negative regulator of muscle growth?

By what mechanism does it work?

How is it activated?

Answer 20

Myostatin

Inhibits myoblast proliferation, inhibits progression of myoblasts from G1 to S

Activated by MyoD binding to E-box in myostatin promoter

Question 21

Gain of Function (GoF)

vs

Loss of Function (LoF)

[Myostatin]

Answer 21

GoF = Overexpression = Fewer Muscle Cells

LoF = Underexpression = Jacked and Tan

Question 22

What are recruited to repair and regenerate muscle?

What do they act on?

Where are they located?

Answer 22

Satellite cells are recruited to supply myoblasts for repair and regeneration

located on surfact of muscle fiber, beneath basal lamina

Question 23

What is the status of satellite cells on a regular basis?

How are they activated?

Answer 23

Quiescent until needed

Activated by immune response to injury

Question 24

How does weight training increase muscle mass?

What regulates this activity?

What androgen may play a role in this?

Answer 24

Microtrauma activates satellite cells

Growth factors and hormones regulate–stimulate increase in protein and glucose uptake

testosterone may have direct regulatory effect on satellite cells

Question 25

2 Light Chains 2 Heavy Chains

Answer 25

Essential and Regulatory Ea/ has globular head and filamentous tail

Question 26

Myosin Cross Bridge

Answer 26

Composed of head, project from thick filament, **links thick and thin myofilaments**

Question 27

What does myosin act as biologically? What does it bind to? Where are these properties located?

Answer 27

ATPase, releases chemical energy for contraction Binds to actin Globular head

Question 28

Tropomyosin

Answer 28

Lies in groove between two strands of actin ## Footnote **Regulatory function and provides structural rigidity to actin; blocks active sites**

Question 29

Troponin

Answer 29

Complex of three proteins: T - binds troponin to tropmyosin C - high/low affinity for Ca²⁺ I - Inhibits interaction between actin and myosin

Question 30

Titin

Answer 30

Spring like molecule that extends from M-line to Z-disc, keeps myosin filaments centered in sarcomere and maintain resting tension that allows muscle to snap back if overextended

Question 31

Nebulin

Answer 31

Associated with actin regulates assembly and alignment of actin filaments

Question 32

Free cytostolic Calcium levels in relaxed muscle? What happens upon stimulation? What does it bind to? Result?

Answer 32

Low Levels greatly rise Binds to **troponin C** to change conformation and open binding sites

Question 33

What leads to E-C Coupling? What does this result in?

Answer 33

Excitation of motor end plate by nerve leads to influx of sodium ions Results in depolarization of muscle plasma membrane (sarcolemma), open V.G. Sodium Channels.

Question 34

Once the action potential initiates a wave of depolarization, how does it travel? What do these contain? What is the result?

Answer 34

T-tubular system of sarcolemma Voltage gated **calcium channels (dihydropyridine - DHP)** **Calcium release**

Question 35

How is Calcium released from the sarcoplasmic reticulum? What causes these to open?

Answer 35

Through channels with Ruanodine receptor 1 or RyR1 Activated through protein-protein interaction with DHP channels in T-tubule membrane

Question 36

What recaptures Ca²⁺ in the cytoplasm? Where is it returned?

Answer 36

Sarcoendoplasmic Reticulum Calcium ATPase (**SERCA**) Terminal cisternae

Question 37

What "cocks" the myosin head?

Answer 37

Myosin-Actin + ATP -\> M-ATP + A ATPase on myosin hydrolzyes ATP Conformational change of M-ATP to M\*-ADP-Pi M\* = high energy state

Question 38

What are last two steps of myosin-actin interaction, and what is the result?

Answer 38

Pi and ADP are released sequentially, causing ratchet movement - **power stroke**

Question 39

Movements during power stroke?

Answer 39

Actin towards M-line of sarcomere Z-bands toward eachother Sarcomere shortening (contracting)

Question 40

Rigor mortis

Answer 40

No ATP Actin not released from myosin

Question 41

Analogy for Actin-Myosin interaction?

Answer 41

ATP Cocks Myosin trigger Actin+Myosin pulls trigger Stored energy released

Question 42

Chloride Channel (CIC-1)

Answer 42

Responsible for large resting chloride conductance of skeletal muscle ## Footnote **Stabilizes resting membrane potential preventing false action potentials** **Repolarizes membrane following contraction**

Question 43

Why is calcium readily pumped back into SR cisternae by SERCA during relaxation? What protein helps clear this calcium?

Answer 43

Ca²⁺ has higher affinity for pumps than for troponin C Calsequestrin

Question 44

What are three sources to replenish ATP?

Answer 44

(In this order) 1. Creatine Phosphate 2. Glycolysis 3. Oxidative Phosphorylation