Transcript BGYB30 Midterm 2004

BGYB30 Midterm 2004
• Total number of Marks available= 56
• I will record all of the grades out of 54 total
marks.
• Small adjustment of +0.5 for different
markers
• Average mark = 36.4
• Class average after adjustments = 36.4 /
54 = 67.4%
BGYB30 Midterm 2004
• Short Answers
• Available for pickup next week during TA
office hours (Mon 10-12, Wed 12-1)
• If you want your test remarked
– Compare your grade to posted marking scheme
– Tests will be entirely remarked /56
– Your test must NOT leave the office
– All requests submitted by 1pm Nov 18
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Taste
Smell
Taste
• Contact
• 4 basic tastes
– Salt, bitter, sweet, sour
– Complex mixing for taste
perception
• All modify synaptic
transmission between
taste receptor and a
sensory neuron
• Individual receptor cells
respond best to one type
of taste and less well to
others
Smell
• Long distance
• Many receptors
– 1000s mouse
– 100-200 human
• All receptors are G-protein
coupled receptors
• Depolarize olfactory cells,
leading to APs
• Each receptor cell has only
one or two types of receptor
molecules
Complex stimuli
Sugars
Bitter
Ionic stimuli
Salt (Na+)
Sour (H+)
Taste Receptor
Second
messenger
depolarization
Na+
Intracellular Ca++
Ca++
Sensory neuron
Olfaction
Press Release: The 2004 Nobel Prize in Physiology or Medicine
4 October 2004
The Nobel Assembly at Karolinska Institutet has today decided to award
The Nobel Prize in Physiology or Medicine for 2004
jointly to
Richard Axel and Linda B. Buck
for their discoveries of
"odorant receptors and the organization of the olfactory system"
Na+
Odourant molecule
receptor
G-protein
ATP
cAMP
glomerulus
Olfactory receptor cells with different receptor molecules
Taste & Smell
• Summary
– Both are receive and process external
chemical stimuli
– Taste receptors modify synaptic transmission
– Olfactory receptors generate APs
– Many types of olfactory receptors, only a few
types of taste receptors
Muscle
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Muscle
Striated
Skeletal
•movement
Cardiac
•heart
Smooth
Blood vessels
lungs
intestine
•Mechanisms of muscle contraction essentially the same
•Differences in how muscle cells are organized and how
contractions initiated
Skeletal muscle
Tendon
Muscle
Bone
Muscle Fibers
nucleus
Myofibril
Myofibril
Sarcomere (2-3 m)
Z
M
Z
H
zone
A
band
I
band
Z
Banding patterns due to
overlapping protein filaments
A
I
H
Z disk
Actin
filament
Myosin
filament
‘cross bridges’
Actin
filament
• When muscle contracts the sarcomere
length is reduced
REST
CONTRACTION
STRETCH
• Length of filaments doesn’t change
• but the degree of overlap does
sliding filament hypothesis
The degree of overlap is important for
generating tension
Specifically the number of cross-bridges
Relative tension
Length – Tension relationship for single sarcomere
Stimulator
1.0
0.5
1.25
Control muscle
length
Measure
tension
1.65
2
2.25
Sarcomere length (m)
3.65
1
3
4
Relative tension
2
1.0
3
2
4
0.5
1
5
5
1.25
1.65
2
2.25
Sarcomere length (m)
3.65
• At maximum stretch  no overlap
• At peak tension  optimal overlap
• As sarcomere shortens  filaments
interfere
Summary
• Muscles made of myofibrils
• Myofibrils have sarcomeres
Functional unit of muscle contraction
• Thick and thin filaments give a banding
pattern (myosin and actin)
• With contraction sarcomere length
changes
• Maximum tension produced with optimal
overlap of filaments
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Myosin
Tail
• assembles
into filaments
Head
• binds Actin
• ATPase
S2 Link
Myosin Light Chains
protein filaments of the sarcomere
Actin
filament
Myosin
filament
‘cross bridges’
Actin
filament
Myosin filament
Myosin self-assembles into filaments
~150 cross-bridges at each end of the myosin filament
Actin filaments
• F-Actin (flimanetous) assembles from G-actin (globular)
• Actin has myosin binding sites
Myofilament chemistry
Actin + myosin  Actomyosin complex
ATP
Actin + myosin

Actomyosin complex
Very slow!
Myosin-ATP  Myosin-ADP-Pi  Myosin +ADP +Pi
Releases energy
Myosin-ADP-Pi + Actin  Actomyosin + ADP + Pi
Very fast!
 Actin  rate of ATP hydrolysis by myosin
Actin-Myosin Cycle
Myosin-ADP-Pi binds Actin weakly
Pi
Myosin-ADP binds Actin strongly
Myosin-ADP Head rotates
ADP is released and ATP binds Myosin
Myosin-ATP released from Actin
Myosin hydrolyzes ATPADP+Pi
Myosin-ATP
• Transition between weakly bound and
strongly bound complex generates tension
Actin filament
Binding sites
Strong
binding
Weak
binding
Myosin head group
S2 link
Stretching of the link generates tension
Myosin filament
Why do thin filaments move?
Net force
Net force
Equal and opposite force
on thick filament
What if we don’t have this?
X
ATP
Actin + myosin

Actomyosin complex
Rigor mortis
Role of calcium
• Intracellular Calcium is required for muscle
contraction
• Used ‘skinned’ muscle
fibers
• Membranes chemically
removed
• just protein components
left
Relative force
1.0
0.01
0.1
1.0
Calcium concentration (mM)
Role of calcium
Tropomyosin
Troponin complex
•Troponin and Tropomyosin bind to actin
block the actin – myosin binding sites
•Troponin is a calcium binding protein
• When Troponin binds calcium it moves
Tropomyosin away from the actin-myosin
binding site
Ca
Ca
Summary
• Myosin binds to Actin in ADP/ATPdependent manner
• Transition from weak to strong bond
rotates myosin head group
• Lengthening of the link generates tension
• Calcium is required to remove TroponinTropomyosin from the binding sites
Where does Calcium come from?
• Intracellular storage called Sarcoplasmic
Reticulum
• Surround each myofibril of the whole muscle
• Contains high concentration of calcium
• Transverse Tubules connects plasma membrane
to deep inside muscle
Text Fig 10-21
Myofibril
Transverse tubules
Sarcoplasmic Reticulum
Transverse tubules