Week 3 Sem 2 Med1022 Flashcards
Variation- 2 types of genetic mutation producing polymorphism
Single base mutation Variable length insertion/deletion
Pharmacogenetics
Study of how genetic differences influence the patient-drug interaction
Beta-2 adrenoreceptors
Receptor for salbutamol to cause bronchodilation n vasodilation Receptors may be mutated so become hyperresponsive (= initially great response but then becomes desensitised wit long term treatment ) Have to stop takin beta-2 agonists in long term
Metabolism of drugs
Metabolised by liver enzymes eg those part of CYP450 family Biotransformation Then leave the body
Gene for CYP450 r very polymorphic, thus can get these variations:
Deleted gene -no enzyme, no metabolism of drugs SNP-eg unstable enzyme (reduced metabolism) Normal enzyme Duplicated genes (higher enzyme levels, faster metabolism)
Some patients r CYP2D6 deficient
Slow metabolism Drug levels too high No prodrug activation
Some patients r CYP2D6 duplicants
Metabolism too fast
HER2
Human epidermal growth factor receptor 2 Tyrosine kinase receptor overexpressed in breast cancer Herceptin (monoclonal antibody) effective for this form of cancer, but not forms caused by other genetic mutations
Pharmacogenomics
Use of genetic info to guide drug therapy-dif in responses can be predicted if genetic makeup is known
Prospective efficacy
Using pharmacogenetics to select patients who r predicted to b responders/non-responders/hyper-responders to particular drug
Skeletal muscle
Regeneration: limited Voluntary movement Many nuclei peripherally Striated (due to sarcomeres)
structure of skeletal muscle
whole muscle (surrounded by epimysium) fascicles=bunches of muscle fibres (sur. by perimyiusm) each muscle fibre (sur. by endomysium) each muscle fibre has many myofibrils each myofibril has many myofilments myofilaments arranged into sarcomeres
sarcomere
segment bw 2 neighbouring Z-lines
I band
actin only
A band
entire length of myosin
H zone
myosin only
M line
proteins that form attachment site for myosin, half way through A band
Thin filaments
actin (+ tropomysin + TROPONIN)
tropomysin
long strand thingy that covers the active site on actin
troponin
has Ca2+ binding site
Thick filaments
myosin
myosin
globular heads are cross bridge projections each head has actin binding site n ATPase site
cross bridge cycle
- ATP splitting- BASICALLY ATP STUCK TO MYOSIN HEAD N IS CHOPPED IN HALF TO ADP AND PI 2. Attachment- BASICALLY CA2+ STICKS TO TROPONIN, CAUSING TROPOMYSIN TO EXPOSE ACTIVE SITES ON ACTIN 3. Power stroke- BASICALLY HEAD OF MYOSIN BINDS TO ACTIN, PULLING IT IN, using ENERGY FROM CHOPPING UP ATP BEFORE 4. Detachment- BASICALLY ADP AND Pi ARE RELEASED FROM MYOSIN HEAD. ANOTHER ATP ATTACHES TO MYOSIN HEAD. MYOSIN HEAD DETACHES FROM ACTIN. (THEN ATP IS SPLIT –CYCLE STARTS AGAIN)
notes for cross bridge cycle
ATP splitting occurs before any attachment to actin -to get myosin head ready to go. Need ATP to bind to myosin head before myosin head can let go off actin (STEP 4) otherwise, myosin head would get stuck on actin= cycle locks after step 3 hence Rigor Mortis (body becomes stiff after death)
other notes for cross bridge cycle
the faster u split the ATP the faster the cycle can keep going/repeat (i.e. faster rate of cycle) the faster the muscle can contract/shorten ie myosin ATPase activity is a determinant of muscle speed
isometric contraction
muscle stays same length tension mite be fluctuating, e.g. holding weights still the invisible chair
isotonic concentric contraction
u overcome the force n the muscle shortens muscle contracts against a load that it is able to move eg lifting up dumbell
isotonic contraction
tension stays the same length of muscle changes energy required by muscle changes
eccentric contraction
the opposing force is greater than the force created by the muscle and the muscle lengthens e.g. putting down dumbbells walking down steep hill if u keep doing this u get DOMS (Delayed Onset Muscle Soreness)
antagonist muscles
muscles with opposing actions one muscle is flexing and one is extending the joint eg bicep n tricep
agonist muscles
muscles doing same action two muscles which work in conjunction with one another to perform the same movement across a joint
Passive Force
when a resting muscle is stretched Reflects passive elastic property of the muscle nothing to do wit contraction
Active Force
force generated by the crossbridges during a contraction depends on the length of the muscle
ryanodine receptors
channels that release Ca2+ on Lateral sac of sarcoplasmic reticulum
Length - Force Relation of Muscle ??
at optimal muscle length: all cross bridges attached
= max force is produced
??? at longer lengths less force less overlap bw thin n thick filaments less cross bridges ??? at shorter lengths less force but reason is complex Z-lines hit ends of thick filaments causing them to buckle
dihydropyridine receptors
‘voltage sensors’ on T-tubule
muscle wen contracts does WORK (moves a load through a distance)
work done= load x distance
______% chemical energy is converted to work, the rest is dissipated as heat (muscles produce heat when they contract)
20 - 25%
2 important features of isotonic contractions
1.amount by which the muscle shortens: lighter the load the further the muscle can shorten?? 2. velocity, or speed, at which it shortens lighter the load the faster the muscle can shorten
velocity
Distance Shortened/ time
Force – Velocity Relation
relationship between load and the velocity of muscle shortening fastest velocity of shortening (Vmax) occurs with zero load (determined by its myosin ATPase activity bc this determines how quickly the crossbridges can cycle) lowest velocity of shortening = zero wen muscle cant move the load (i.e. isometric contraction)
Power def
rate at which work is done
formulas for power
Power= work done/time power= load x distance/time load=force, distance/time=velocity => power= force x velocity
power
determined by the force muscle is generating and the velocity at which it is shortening
max power
wen muscle is contracting wit 1/3 max force and 1/3 max velocity
Twitch contraction
Response to a single action potential contraction lasts much longer than the AP that triggered it also a latent period bw AP and contraction (cos takes time for EC-coupling (excitation-coupling) to occur)
SUMMATION of the contractions
wen a second contraction builds on the first, producing an overall higher force occurs wen a 2nd AP produced while muscle still contracting to 1st AP.
TETANIC CONTRACTIONS/tetanus
Response to repetitive stimulation if stimulation not very frequent, get unfused tetanic contractions if stimulation very frequent, get fused tetanic contractions