Chapter 15 Flashcards
Lipid asymmetry is maintained by
enzymes
Two classes of vitamins
lipid-soluble
water-soluble
Function of Vitamin A
site of the primary photochemical reaction in vision
Function of Vitamin D
regulates calcium metabolism
Function of Vitamin E
serves as an antioxidant; necessary for reproduction in rats and may be necessary for reproduction in humans
Function of Vitamin K
regulatory function in blood clotting
Two modes of passage across the membrane
passive and active
Passive transport
does not require energy input
diffuse according to the concentration gradient
Active transport
always requires the input of energy
always requires a transporter protein
Two types of passive transport
simple diffusion
facilitated diffusion
Simple diffusion
solute diffuses through the bilayer or through a static protein channel
Facilitated Diffusion
works kind of like an enzyme
1. solute binds to transporter
2. conformational change brings the solute across the membrane
3. Reverse protein conformational change resets the transporter for another round of transport
water specific porin
Aquaporin
How does water-specificity of an aquaporin work
each subunit contains a small pore
lined with hydrophobic residues except for two asparagine side chains
these asparagine side chains attract water and disrupt hydrogen-bonded chain of water molecules
prevents proton transport across the membrane
Ion channels
proteins that provide a hydrophilic route through the greasy bilayer
K+ channel selectivity filter
pore narrows and four polypeptide backbones fold so their carbonyl groups project into the pore
carbonyl oxygen atoms arranged with geometry suitable for coordinating desolvated K+ ions
desolvate Na+ is too big
facilitated diffusion
passive transport
solute binds to a membrane protein changes shape so that the transported molecule is released on the other side of the membrane
Glucose transporters are what type of diffusion
facilitated diffusion
Transporter proteins act like
enzymes
- accelerate the rate at which a substance crosses the membrane
- can be saturated by high concentrations of their substrate
- susceptible to competitive and other types of inhibition
GLUT transporter has a
glucose binding site that alternately faces the cell exterior and interior
Conformations of GLUT proteins
12 membrane-spanning alpha helices arranged in two domains
two conformational states are in equilibrium- can move glucose in either direction
Uniporter
transports one substance
Symporter
two substances moved in the same direction
Antiporter
two substances moved in the opposite direction
what is essential to keep the concentrations of some solutes be different inside and outside cells
active transportM
more than or equal to 25% of the cell’s energy is spent to
maintain the ionic gradient
The inside of the cell is
negative
The outside of the cell is
positive
The charge difference in the cell is essential for
conduction of action potentials in neurons
Reaction cycle of Na, K-ATPase
- 3 intracellular Na+ ions bind
- ATP binds
- phosphoryl group transferred from ATP to Asp side chain of the pump. ADP is released
- protein conformation changes, exposing the Na+ binding sites to the cell exterior
5.two extracellular K+ ions bind
6.aspartyl phosphate group is hydrolyzed - protein conformation changes, exposing K+ binding sites to the cell interior.
Secondary active transport
the transporter takes advantage of a gradient already established by another pump
endocytosis
cells absorb external material by engulfing it with the cell membrane
Na can be found in greater quantities in the
outside of the cell
K+ ions can be found in greater value in
the inside of the cell
Action potential
depolarization of the membrane potential
Myelin sheath do what
propagate action potentials rapidly
Electron transport is highly _______ and coupled to _______
exergonic
phosphorylation of ATP which is highly endergonic
Oxidative phosphorylation is the process by which
ATP is formed as a result of electrons being transferred from NADH or FADH2 to O2 by a series of electron carriers
Electron transport drives
the pumping of protons across the inner membrane to the intermembrane space of the mitochondria
Electron transport is the result of a
proton gradient
proton gradient provides
the energy for phosphorylating ADP to ATP
Electron Transport Chain equation
ADP+Pi -> ATP + H2O
Goals of the electron transport chain
transport protons from the matrix across the inner membrane of the mitochondria
creates a higher concentration of protons outside the matrix and in the intermembrane space
Active transport of H+, driven by electron transfer steps from NADH to O2 forms
a proton gradient
The flow of electrons in the electron transport chain is ______ and involves a series of oxidation-reduction reactions
directional
How does this directional flow of electrons from one protein complex to the next occur?
What determines the direction of electron flow?
Reduction potentials
Reference point for reduction potentials is the
hydrogen electrode
overview of mitochondrial electron transport
NADH -> NAD+
complex 1
Q
Complex III
Cytochrome c
Complex IV
O2 and H2O
Complex I transfers electrons from
NADH to ubiquinone
four protons from the matrix to the intermembrane space via a proton wire
Flavin mononucleotide (FMN) does waht
picks up the first two electrons donated by NADH near the far end of the complex I arm
then they are transferred one at a time to an iron-sulfur cluster
Iron in the iron-sulfur clusters is ____ when it gins an electron
reduced to Fe2+
Iron in the iron-sulfur clusters is _____ when it loses an electron
oxidized to Fe3+
Iron-sulfur clusters carry how many electrons
one at a time
Electrons are passed from iron-sulfur complex to
coenzyme Q
Overall net reaction for complex I
NADH + H+ + CoQ -> NAD+ + CoQH2
extremely exergonic
Complex II is
succinate dehydrogenase
Complex III passes electrons from the
ubiquinol pool to cytochrome c and pumps protons across the membrane
The Q cycle- ubiquinol to cytochrome c
- QH2 donates one electron to the iron-sulfur protein- electron travels to cytochrome C1 and then cytochrome c
- QH2 donates other electron to cytochrome b- two protons are released
- oxidized ubiquinone diffuses to another quinone binding site- accepts electron from cytochrome b- half reduced semiquinone
SECOND ROUND - second QH2 surrenders its two electrons to complex III and two protons to the intermediate space- one electron goes to cytochrome c
- other electron goes to cytochrome b and then to the waiting semiquinone produced in the first part of the cycle- regenerates QH2
Net result of the Q cycle
two electrons from QH2 reduced two molecules of cytochrome c
four protons are translocated to intermembrane space- two from QH2 in the first round of the Q cycle and two from QH2 in the second round
Cytochrome oxidase- Complex IV contains
two copper atoms which are involved in electron transport
Complex IV does what
transfers electrons from cytochrome c to oxygen
The last step of Complex I involves electrons being
passed to coenzyme Q
also called ubiquinone when oxidized and ubiquinol when reduced
How is the proton gradient used to make ATP?
energizes the membrane with two forms of potential energy- electrical and chemical
Chemiosmotic coupling
coupling of oxidation and phosphorylation that converts the electrochemical potential to the chemical energy of ATP
ATP synthase is known as the
F0-F1 complex
ATP is functionally
separate from the electron transport complexes (I-IV)
F0 part of the ATP synthase functions as
a transmembrane channel that permits H+ to flow back into the matrix following its gradient
F1 part of ATP synthase does what
catalyzes the reaction
ADP+Pi -> ATP+H2O
Proton transport through ATP synthase requires
rotation of the c ring past the stationary a subunit
ATP Synthase uses what to form what chemical bond
mechanical energy (rotation)
the attachment of a phosphoryl group to ADP
Three possible conformations for the sites for substrate on ATP synthase
Open
Loose binding
tight binding
Open
a low affinity for substrate
loose binding
loosely binds ADP and Pi
Tight binding
catalytically active, binds ATP
Proton flux converts Loose to _____, which ____
tight
produces ATP
Proton flux converts Tight to ____, which ____
open
releases ATP
NADH is oxidized to produce a P/O ratio of
2.5
FADH2 is oxidized to form a P/O ratio of
1.5
Why does NADH produce a higher ratio than FADH2
oxidation of NADH exports more protons from the matrix than FADH2 and a bigger contribution to the proton gradient
Yield of ATP per glucose oxidation
Glucose + 6O2 -> 6H2O + 6CO2 + 30 (32) ATP
