Module 4: Lecture 2

Question 1

True or False
Titin is the largest protein in the body

Answer 1

True

Question 2

Titin contains how many amino acids?

Answer 2

27,000

Question 3

What is the molecular weight of Titin?

Answer 3

3 million daltons

Question 4

Which description of the sarcomere organization is correct?

a) The A- band contains no thin filaments
b) The H-zone contains no thin filaments
c) The z-discs are contained within the A-band
d) The I-band contains some thick filaments

Answer 4

B

Question 5

How is your A-band defined?

Answer 5

based on the length of your thick filaments however there is an overlap of thin filaments as well

Question 6

The Z-discs are contained in which band A or I?

Answer 6

I

Question 7

What does your I-band contain?

Answer 7

it goes from one thick filament of one sarcomere to another thick filament of a second sarcomere

• z-line is included

Question 8

What is the H-band

Answer 8

• From M-line to thick filaments where there is no overlap of thin filaments
• ONLY THICK FILAMENTS

Question 9

True or False
Muscle contraction does not necessarily cause “shortening” of the muscle

Answer 9

True because of isometric contractions

Question 10

What does the state of contraction refer to?

Answer 10

state in which your actin and myosin are forming cross bridges and generating force

Question 11

What happens after a contraction of a muscle

Answer 11

relaxation of a muscle

Question 12

True or False
The overlap for your thick and thin filaments in necessary for your cross-bridges to actually form

Answer 12

True

Question 13

What is the signal that allows for the process of muscle contraction?

Answer 13

• the action potential from the neuromuscular junction

Question 14

What molecule is the key that signals your actin and myosin cross-bridges to form?

Answer 14

increase in cytosolic calcium

Question 15

What are your thin filaments made up of?

Answer 15

• quaternary structure (made up of multiple different protein chains)
• Globular actin

Question 16

If we polymerize G-actin into a long chain we will form what?

Answer 16

• Filamentous actin
• aka F-actin

Question 17

If we take 2 F-actin filaments and intertwine them what do we get?

Answer 17

Actin helix

Question 18

How do we regulate the binding site on the actin filaments?

Answer 18

• tropomyosin
  (regulatory protein)
• they are intertwined on that actin helix physically blocking the binding site for myosin

Question 19

What does troponin do?

Answer 19

regulates tropomyosin

• sensor about when the muscles is activated or not

Question 20

What are the 2 key regulatory molecules that will allow muscles to contract or not?

Answer 20

1. Troponin
2. Tropomyosin

Question 21

A single tropomyosin molecule can block how many actin molecules?

Answer 21

about 7 actin molecules

Question 22

How many troponin molecules is needed to regulate a single tropomyosin

Answer 22

1

Question 23

Troponin has 3 subunits which are what?

Answer 23

1. T, Tropomyosin
2. I, Inhibitory
3. C, Calcium

Question 24

What does the first subunit of troponin (T) do?

Answer 24

physically interacting with the tropomyosin molecule itself

• holding it in close proximity to the actual tropomyosin molecule

Question 25

What does the second subunit of troponin (I) do?

Answer 25

keeps it in that inhibitory state and ensures that those binding sites are blocked

Question 26

What does the third subunit of troponin (C) do?

Answer 26

responsible for sensing when a muscle contraction should be occurring - calcium binds to troponin C and induces the conformational change, which removes inhibition

Question 27

What is the thick filament made up of?

Answer 27

- lots of myosin molecules

Question 28

A single myosin molecule is made up of what?

Answer 28

- 2 heavy chains - 4 light chains

Question 29

what does dimer mean?

Answer 29

composed of two heavy chains that are intertwined with their tail regions in this helical form

Question 30

Within the head of a myosin molecule what are the 2 binding sites?

Answer 30

1. Actin binding site - binds to the thin filament to form the cross-bridge 2. ATP binding site - where we hydrolyze ATP to perform a cross-bridge cycle

Question 31

True or False The myosin heads are coming out from both directions away from the M-line

Answer 31

True

Question 32

One heavy chain contains what?

Answer 32

- 1 tail - 1 head

Question 33

What do light chain contain?

Answer 33

specialized protein that stabilize the head (also a site for regulation) - essential light chain - regulatory light chain

Question 34

One heavy chain has how many accompanying light chains?

Answer 34

2

Question 35

What enzyme is also found at the ATP binding site?

Answer 35

ATPase

Question 36

What are the 4 steps of the cross-bridge cycle?

Answer 36

1. Binding between the myosin head and the thin filament 2. Movement of the cross-bridges (Power stroke) 3. Detachment of the cross-bridges: detach myosin from thin filament 4. Re-energize the myosin head so it can re-attach to a thin filament repeating the cycle

Question 37

What is a Power Stroke?

Answer 37

step in which the myosin head physically pulls the myofilament inwards towards the M-line

Question 38

From rest to contracted sarcomere, what happens to the A-band, I-band, H-zone and overall sarcomere length?

Answer 38

A-band: no change - pull thin filaments towards M-line I-band: Shorten - will decrease as the thin filaments are being pulled the thick filaments will get closer to the z-line H-zone: Shorten - as thin filaments come closer to M-line the H-zone will decrease as thin filaments overlap thick filaments Sarcomere: Shorten - Z-lines are getting closer to eachother

Question 39

True or False When we are contracting our thin and thick filaments will not actually change in length but their overlapping distances will be affected

Answer 39

True