Lecture 20 (11b) - Cell Communication Part 2 Flashcards
(66 cards)
1
Q
Record jumps
A
Frog - Rosie (6.5m)
Human - Jackie Joyner Kersee (7.m)
2
Q
three types of vertebrate muscle
A
- skeletal
- cardiac
- smooth
3
Q
Skeletal muscle
A
- voluntary movement, breathing, maintaining posture
* appear striped bc of regular arrangement of sarcomeres
4
Q
Cardiac muscle
A
- beating of heart
* cells interdigitate, forming a mesh
5
Q
Smooth muscle
A
- involuntary, movement of internal organs
* do NO have stripes of regularly arranged actin and myosin
6
Q
One muscle is composed of
A
hundreds of thousands of muscle cells (fibers) bundle together with connective tissue
7
Q
One cell is called a
A
muscle fiber - large and multinucleate
• comes from the fusion of many myoblasts during development)
8
Q
Each muscle cell (one fiber) consists of
A
several myofibrils
9
Q
1 muscle fiber = 1 cell
A
actin + myosin --> sarcomere --> myofibril --> muscle fiber + CT --> 1 muscle
10
Q
Muscle cells need lots of
A
mitochondria to make ATP
11
Q
Muscle cell membrane
A
sarcolema
12
Q
Muscle cell cytoplasm
A
sarcoplasm
13
Q
Each myofibril consists of repeating units called
A
sarcomeres
14
Q
Each sarcomere is made of
A
overlapping actin and myosin filaments
15
Q
1 sarcomere is from
A
Z line to Z line
16
Q
I band
A
actin
17
Q
A band
A
myosin with overlapping actin
• darker because myosin is thinner
18
Q
H zone
A
only myosin
19
Q
Each myofibril =
A
plenty of sarcomeres repeating horizontally
20
Q
Each sarcomere is bound by
A
Z lines which anchor the actin
21
Q
A band
A
in the middle of the sarcomere
• all the myosin filaments
22
Q
H zone
A
non overlapping part of actin
23
Q
I band
A
non overlapping part of myosin
24
Q
H zone and I band
A
non overlapping part of actin and myosin
25
Titin
holds the myosin to the Z
| • "bungee cord" = resistance to stretch in a relaxed muscle
26
Sliding filaments cause the muscle to contract
actin slides past myosin = contraction
27
When a muscle contracts
* sarcomeres shorten and band pattern changes
| * non overlapping parts - H and I - diminish because there is more overlapping between actin and myosin filaments
28
2 main actors of the muscle contraction
myosin and actin
29
Myosin
2 polypeptide chains coiled together, ending in a globular head
• a myosin filament is made of many molecules in parallel with heads projecting sideways
30
Actin filament
actin monomers in a long twisted molecule
31
Tropomyosin is twisted around
actin
| • troponin binds to tropomyosin, which binds to actin
32
Troponin has 3 subunits and each of them binds to
* tropomyosin
* actin
* Ca2+
33
Calcium binds to
```
troponin
• 1 site changes conformation and
changes conformation of tropomyosin and
twist tropomyosin around actin
--> reveals hidden site
--> binds to myosin
```
34
Actin and myosin can interact
there is a binding site on actin for myosin
| BUT ONLY WHEN THERE IS CA2+
35
By default, the actin sites for myosin
are hidden,
but when there is Ca2+ in the sarcoplasm,
it binds to troponin,
troponin changes conformation,
which twists the tropomyosin around the actin to
expose actin sites for myosin
• myosin head binds -->
changes conformation, head bends
= actin moves relative to myosin
(5-10nm)
36
The role of the Ca2+
* when actin sites are exposed, the myosin head can bind the specific sites on actin to form cross-bridges between myosin and actin
* when myosin head binds the actin, the head conformation changes, the head bends and causes a tiny force that causes the actin filament to move 5-10 nm relative to the myosin filament
37
The role of ATP
* when a myosin head is bound to actin, it can bind a hydrolyze ATP
* the energy released when it binds ATP changes the conformation of the head again and causes it to release the actin and return to its extended position
* the head is now ready to start a new binding with actin (new cycle)
* ATP contributes to myosin and actin dissociation
myosin head bound, binds and hydrolyzes ATP, changes head conformation --> releases actin
38
Rigor mortis (right after death)
* ATP production stops, and so myosin can't release actin filaments and muscles stay contracted
* eventually the proteins lose their integrity and the muscles soften
* timing of these events help medical examiners examine the time of death
39
Repetition of a cycle
* contraction of the sarcomere involves many consecutive cycles of interaction between actin and myosin molecules
* when a cycle is over, a single myosin head breaks its contact with actin
* the actin filaments do not slip backward because there are many other myosin heads attached to the actin filament
* as long as Ca2+ and ATP are available, the cycle of actin and myosin interactions continues and the filaments slide past each other
1 binds, another releases
• actin doesn't slip back bc myosin is still grabbing
40
End of the contraction
* when Ca2+ pumps (active pumps requiring ATP) remove Ca2+ from sarcoplasm, contraction stops...
* when absence of Ca2+, tropomyosin twists back to its original conformation and is hiding the actin site for myosin
- Ca2+ always pumped inside
- need Ca2+
(usually low concentration in sarcoplasm bc of Ca pump)
41
The sliding of actin and myosin is regulated by
the sarcoplasmic concentration of calcium ions
42
Muscle cells are
excitable - the plasma membrane can conduct action potentials
43
Contraction is initiated by
action potentials from a motor neuron at the neuromuscular junction
44
Motor unit
one motor neuron and all the muscle fibers it synapses with (3-1,000)
45
The neuromuscular junction
the fibers in a motor unit contract simultaneously when the neuron fires
46
Chemical synaptic transmission begins with
the arrival of an action potential
47
The action potentials in muscle fiber travel
deep within the cell
48
The plasma membrane is continuous with
T tubules that run through the sarcoplasm
49
T tubules run close to the
sarcoplasmic reticulum (muscle fiber ER) that surrounds every myofibril
50
T tubule
fold (in) of sarcolema around myofibril
• action potential through membrane, depolarize through T tubule
• meets sarcoplasmic reticulum that's full of Ca2+
51
The sarcoplasmic reticulum is full of
Ca2+
52
The T tubule is connected to the sarcoplasmic reticulum by
receptor proteins
53
Channel opens in sarcoplasmic reticulum with action potential -->
Ca2+ into sarcoplasm and available for myofibrin
54
Ca2+ binds to
tropomyosin
55
In the resting muscle, the Ca2+ is highly concentrated in
the sarcoplasmic reticulum
56
Ca2+ has a low concentration in the sarcoplasm thanks to
the active pumps of Ca2+ in the sarcoplasmic reticulum membrane that pumps it back from the cytoplasm to the sarcoplasmic reticulum
57
An action potential spreads through the T tubules...
when it reaches the receptor proteins, they change conformation
• this opens Ca2+ channels and
Ca2+ flows out of the sarcoplasmic reticulum
58
Summary of contraction
1. release of Ca2+ from the sarcoplasmic reticulum triggers muscle contraction
2. when Ca2+ binds to troponin, troponin changes conformation which causes the tropomyosin attached to troponin to rotate and expose the binding sites for myosin -->
exposes myosin-binding sites of the actin
3. Myosin heads can bind to actin
4. when myosin head binds the actin, the head changes conformation.
The head bends and and causes a tiny force that causes the actin filament to move 5-10 nm relative to the myosin filament
5. when a myosin head is bound to actin, it can bind and hydrolyze ATP. The energy released when it binds changes the conformation of the head again and causes it to release the actin and return to its extended position. The head is now ready to a bind with a new actin. ATP helps myosin and actin to dissociate.
6. as long as Ca2+ and ATP are available, the cycle of actin and myosin interactions continues and the filaments slide past each other. A Ca2+ active pump (ATP) helps the Ca2+ reuptake in the sarcoplamsic
59
Contraction steps
1. Ca2+ is released from the sarcoplasmic reticulum
2. Ca2+ in the sarcoplasm binds troponin and exposes myosin-binding sites on the actin filaments
3. myosin heads bind to actin - release of Pi initiates a power stroke
4. In the power stroke, the myosin head changes conformation. filaments slide past each other
5. ADP is released - ATP binds to myosin, causing it to release actin
6. ATP is hydrolyzed. the myosin head returns to its extended conformation
7. if Ca2+ is returned to the sarcoplasmic reticulum, the muscle relaxes
8. if Ca2+ remains available, the cycle repeats and muscle contraction continues
60
Ca2+ is released from the
sarcoplasmic reticulum
61
Ca2+ in the sarcoplasm binds
troponin and exposes myosin-binding sites on the actin filaments
62
Myosin heads bind to
actin - release of Pi initiates a power stroke
63
In the power stroke, themyosin head
changes conformation - filaments slide past each other
64
ADP is release - ATP binds to
myosin, causing it to release actin
65
If Ca2+ is returned to the
sarcoplasmic reticulum, the muscle relaxes
66
If Ca2+ remains available
the cycle repeats and muscle contraction continues
