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.

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 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

• 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

Sensory neuron

depolarization

Ca++

Na+

Complex stimuliSugarsBitter

Ionic stimuliSalt (Na+)Sour (H+)

Second messenger

Intracellular Ca++

Taste Receptor

Olfaction

Press Release: The 2004 Nobel Prize in Physiology or Medicine4 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"

ATP cAMP

Odourant molecule

G-proteinreceptor

Na+

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

MuscleNext Class: BGYB30 Pose-Off

Winner 2002

Winner 2003

Muscle

Striated Smooth

Skeletal•movement

Cardiac•heart

Blood vesselslungs

intestine

•Mechanisms of muscle contraction essentially the same

•Differences in how muscle cells are organized and how contractions initiated

MuscleTendon

Bone

Muscle Fibers

nucleus

Myofibril

Skeletal muscle

Z Z ZM

Sarcomere (2-3 m)

Aband

I

H

Myofibril

band

zone

Banding patterns due to overlapping protein filaments

H

A I

Z disk

Actinfilament

Myosinfilament

Actinfilament

‘cross bridges’

• When muscle contracts the sarcomere length is reduced

REST

CONTRACTION

STRETCH

• Length of filaments doesn’t change

• but the degree of overlap doessliding filament hypothesis

The degree of overlap is important for generating tensionSpecifically the number of cross-bridges

Stimulator

Sarcomere length (m)

Rel

ativ

e te

nsio

n

1.25 1.65 2 2.25 3.65

1.0

0.5

Control musclelength

Length – Tension relationship for single sarcomere

Measuretension

Sarcomere length (m)

Rel

ativ

e te

nsio

n

1.25 1.65 2 2.25 3.65

1.0

0.5

5

4

3 2

1

1

2

3

4

5

• 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

Next ClassBGYB30 Pose-Off

Winner 2002

Winner 2003

Myosin

Tail• assembles into filaments

Head • binds Actin• ATPase

Myosin Light ChainsS2 Link

protein filaments of the sarcomere

Actinfilament

Myosinfilament

Actinfilament

‘cross bridges’

Myosin filament

~150 cross-bridges at each end of the myosin filament

Myosin self-assembles into filaments

Actin filaments

• F-Actin (flimanetous) assembles from G-actin (globular)• Actin has myosin binding sites

Myofilament chemistry

Actin + myosin Actomyosin complex

Actin + myosin Actomyosin complexATP

Myosin-ATP Myosin-ADP-Pi Myosin +ADP +Pi

Myosin-ADP-Pi + Actin Actomyosin + ADP + Pi

Very slow!

Very fast!

Releases energy

Actin rate of ATP hydrolysis by myosin

Myosin-ADP-Pi binds Actin weakly

Myosin-ADP Head rotates

ADP is released and ATP binds Myosin

Myosin-ATP released from Actin

Myosin hydrolyzes ATPADP+Pi

Myosin-ADP binds Actin strongly

Pi

Myosin-ATP

Actin-Myosin Cycle

• Transition between weakly bound and strongly bound complex generates tension

Myosin filament

Myosin head group

S2 link

Actin filament Binding sites

Stretching of the link generates tension

Weakbinding

Strongbinding

Equal and opposite forceon thick filament

Why do thin filaments move?

Net forceNet force

Actin + myosin Actomyosin complexATP

What if we don’t have this?

X

Rigor mortis

Role of calcium• Intracellular Calcium is required for muscle

contraction

• Used ‘skinned’ muscle fibers

• Membranes chemically removed

• just protein components left

Calcium concentration (mM)

Rel

ativ

e fo

rce

1.0

0.01 0.1 1.0

Role of calcium

Troponin complex

Tropomyosin

•Troponin and Tropomyosin bind to actinblock 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

CaCa

Summary

• Myosin binds to Actin in ADP/ATP-dependent manner

• Transition from weak to strong bond rotates myosin head group

• Lengthening of the link generates tension

• Calcium is required to remove Troponin-Tropomyosin 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 10-21Myofibril

Sarcoplasmic Reticulum

Transverse tubules

Transverse tubules