Chapter 6.3-6.4 Flashcards
what are the 3 types of membrane proteins?
- membrane-bound receptors
- membrane-bound metabolic enzymes
- membrane transport proteins
what do membrane transport proteins do?
move polar molecules across the hydrophobic membrane
list and describe the 2 ways that membrane transport molecules move molecules across hydrophobic membranes and the energy dependence of each
- passive: down concentration gradient; energy independent
- active: up concentration gradient; energy dependent
give 2 example of passive membrane transporters
- gramicidin A; an antibiotic polypeptide
- porins; ion channels made of beta barrel proteins
describe the structure of porin passive transport proteins
alternating hydrophobic and hydrophilic residues
describe how the structure of membrane transport enables their function and give an example
helices form substrate-selective channels; like the K+ channel protein,which allows for passive transport of K+ and excludes other ions like Na+
what do aquaporins allow for?
passive transport of water
what are the 3 types of active transporters? and what are the 2 main categories of the 3 types?
either primary or secondary
1. primary active transporter
2. secondary active antiporter
3. secondary active symporter
describe how primary active transporters work
ATP turnover drives the movement of molecules up their concentration gradient
describe how secondary active antiporters work
molecules moving down their concentration gradients drive other molecules up their concentration gradients (opposite directions)
describe how secondary active symporters work
molecules moving down their concentration gradient drive other molecules moving up their concentration gradients (in same direction)
what does the Na+/K+ ATPase membrane protein do? generally and specifically
creates membrane potential important for neurons by pumping 3 Na+ out of the cell and bringing 2 K+ into the cell (both against concentration gradients)
what drives the conformational shift of the Na+/K+ ATPase membrane protein?
ATP hydrolysis
what is the Na+/I- secondary symporter essential for? generally then specific ion movement
essential for thyroid hormone biosynthesis by bring one I- and 2 Na+ into the cell
what is the Na+/I- secondary symporter coupled to?
coupled to the Na+/Kt ATPase transporter
what does SERCA stand for?
sarco/endoplasmic reticulum Ca2+ ATPase
what is SERCA responsible for?
uptake of Ca2+ from cytosol into sarcoplasmic reticulum lumen
where is SERCA abundant and as what?
abundant in animal muscle cells as a Ca2+ transporter
what kind of transporter is SERCA?
a primary active transporter
what does SERCA promote?
muscle relaxation
what is phospholamban?
a protein that attaches to SERCA when dephosphorylated, preventing SERCA from working
what deactivates phospholamban and what is the result?
phosporylation deactivates phospholamban, causing it to dissociate from SERCA and allow muscle contraction to begin
what 2 things phosphorylate phospholamban and where?
- adrenaline phosohorylates Ser16 by protein kinase A
- high Ca2+ phosphorylates Thr17 by Ca2+/calmodulin kinase II
give the 4 steps of the SERCA mechanism
- ATP hydrolysis and phosphorylation of Asp351 releases H+ and binds Ca2+ in the transmembrane helices, causing a conromfationa change
- ADP dissociated, casuing M2 to open toward the luminal side and release Ca2+
- ATP binding repositions M2 to trap H+
- Asp351 dephosphorylates
draw a muscle fiber, label all 4 parts
parts are
1. actin filament
2. myosin filament
3. titin
4. z disk
go draw this!!
what does titin function as?
a spring
give an analogy for contraction as ,yosin heads pull actin
actin is like a rope; it does not change length when pulled but moves relative to myosin
what changes length during muscle contraction?
titin only! is like a spring that can compress and decompress
what are myoblasts?
large fused muscle cells/super cells
what do myoblasts contain? (3)
- many nuc;ei
- share sarcolemma (plama membrane)
- share bundle of small fibers (myofibrils)
what are myofibrils composed of and what are they organized into?
composed of nyosin and actin; organized into thin and thick filaments
describe myosin (3)
- make up thick filaments
- arranged so fibrous tails are in the middle and
- gloubular heads are at the ends and grab the thin filament
describe actin (2)
- make up thin filaments
- bound to troponin and tropomyosin
what are the 2 kinds of bands in the sliding filament muscle model? describe
- A band: stretches from myosinhead to myosin head; does NOT change in length during contraction
- 2 I bands shorten as muscles contract as titin tightens
what is troponin? describe the 3 binding sites
a complex of 3 domains
1. TnT: binds troponin
2. TnI: inhibits myosin from binding to actin
3. TnC: binds Ca2+
describe the mechanism of muscle contraction (3)
- in relaxed muscle, myosin binding sites on actin are blocked by tropomyosin
- Ca2+ binding to TnC inudces a conformational change in troponin and tropomyosin that unvocers the myosin binding site on actin
- myosin heads bind to actin and initiate muscle contraction
describe calcium control of muscle contraction and relaxation (5)
- Ca2+ binding to troponin (TnC) uncovers myosin binding sites on actin thin filaments
- Pi release induces the power stroke, which pulls the actin filament toward the center
- ADP release empties the nucleotide binding site in myosin
- ATP binding causes myosin to dissociate from actin
- ATP hydrolysis induces the recovery conformation
what causes muscle contraction?
the relative movement of filaments
how does the power stroke occur?
ADP and Pi are both negatively charged, the release of Pi releases energy = power stroke
what is need to initiate and continue muscle contraction and why?
- Ca2+ needed to start contraction
- ATP needed to provide energy to continue contraction
what does SERCA do? generally
pumps Ca2_ out of sarcoplasm into sarcoplasmic reticulum lumen to keep Ca2+ away from troponin to prevent contraction and allow for relaxation
