Cell Bio Exam 2

Simple diffusion

Unassisted net movement down a concentration gradient; passive and toward equilibrium.

Facilitated diffusion

Protein-mediated movement down a gradient; passive but can saturate.

Active transport

Moves solutes against a gradient using energy directly or indirectly.

Osmosis

Diffusion of water across a selectively permeable membrane.

Hypertonic solution

Higher solute concentration outside the cell; water tends to leave the cell.

Hypotonic solution

Lower solute concentration outside the cell; water tends to enter the cell.

Channel protein

Forms a hydrophilic passage through the membrane.

Carrier protein

Binds a solute, changes conformation, and releases it on the other side.

Aquaporin pore

Hydrophilic and selective for water.

Saturation kinetics

Transport rate levels off when available transport proteins are occupied.

Uniport

Moves one solute.

Symport

Moves two solutes in the same direction.

Antiport

Moves two solutes in opposite directions.

Voltage-gated channel

Opens or closes in response to membrane potential changes.

Ligand-gated channel

Opens or closes when a ligand binds.

Mechanosensitive channel

Responds to mechanical forces on the membrane.

GLUT1

Reversible glucose carrier; net direction depends on glucose concentrations.

Hexokinase's effect on glucose

Phosphorylates glucose to glucose-6-phosphate, lowering free intracellular glucose.

Electrochemical gradient

Combined chemical concentration gradient and electrical potential difference.

Na+/K+ ATPase

Uses ATP to maintain Na+ and K+ gradients across the membrane.

Glycolysis location

Cytoplasm.

Net glycolysis yield

Per glucose: 2 pyruvate, net 2 ATP, and 2 NADH.

Glycolysis ATP accounting

4 ATP formed minus 2 ATP invested = net 2 ATP.

NAD+ role

Electron carrier that accepts electrons and is reduced to NADH.

Oxidation

Loss of electrons; often loss of hydrogen atoms.

Reduction

Gain of electrons; often gain of hydrogen atoms.

Dehydrogenase

Enzyme that catalyzes a redox reaction by transferring hydrogen/electrons.

Substrate-level phosphorylation

Direct phosphate transfer from a high-energy substrate to ADP.

Fermentation purpose

Regenerates NAD+ so glycolysis can continue without relying on the ETC.

Lactate dehydrogenase

Reduces pyruvate to lactate while oxidizing NADH to NAD+.

Cori cycle

Lactate from muscle can be taken up by liver and used for gluconeogenesis.

Pyruvate oxidation location

Mitochondrial matrix.

Pyruvate oxidation products per glucose

2 acetyl-CoA, 2 CO2, and 2 NADH.

Citric acid cycle location

Mitochondrial matrix; succinate dehydrogenase is in the inner membrane/Complex II.

TCA yield per acetyl-CoA

3 NADH, 1 FADH2, 2 CO2, and 1 ATP/GTP equivalent.

TCA yield per glucose

6 NADH, 2 FADH2, 4 CO2, and 2 ATP/GTP equivalents.

Oxidative phosphorylation

ETC builds a proton gradient; ATP synthase uses proton flow to make ATP.

ETC final electron acceptor

Oxygen, which is reduced to water.

Cristae

Infoldings of the inner mitochondrial membrane that increase surface area.

Mitochondrial matrix

Location of pyruvate oxidation and most citric acid cycle reactions.

Intermembrane space

Compartment where protons accumulate during mitochondrial electron transport.

ATP synthase energy source

Exergonic movement of H+ down its electrochemical gradient.

Why FADH2 yields less ATP

It enters at Complex II, bypassing Complex I and supporting less proton pumping.

Maximum theoretical ATP range

36–38 ATP per glucose in the model because cytosolic NADH shuttles differ.

Conservative ATP yield

Slides estimate about 30–32 ATP per glucose in actual cells.

Glycerol phosphate shuttle

Transfers cytosolic NADH electrons to mitochondrial FAD, yielding FADH2-like ATP output.

Uncoupler

Separates ETC/proton-gradient activity from ATP synthesis by allowing H+ to bypass ATP synthase.

DNP effect on proton gradient

Dissipates the gradient; proton distribution moves closer to equilibrium.

DNP effect on ATP

Decreases ATP synthesis and increases energy lost as heat.

DNP and oxygen consumption

Can increase oxygen consumption because ETC electron flow continues while the gradient is dissipated.

AMP in regulation

Low-energy signal; activates glycolysis and inhibits gluconeogenesis.

ATP in regulation

High-energy signal; inhibits glycolysis.

Gluconeogenesis

Energy-consuming synthesis of glucose from precursors such as pyruvate.

Gluconeogenesis energy cost

From 2 pyruvate: 4 ATP + 2 GTP (ATP equivalents) and 2 NADH are used.

Gluconeogenesis bypass reactions

Three highly exergonic glycolysis steps are bypassed using four unique enzymes.

Futile cycle prevention

Reciprocal regulation of glycolysis and gluconeogenesis, especially at bypass steps.

Fructose-2,6-bisphosphate

Major reciprocal regulator: promotes glycolysis and suppresses gluconeogenesis.

Insulin signal

Fed state; favors F-2,6-BP and glycolysis.

Glucagon signal

Fasting state; favors gluconeogenesis and reduces glycolysis.

Acetyl-CoA and citrate

Citric acid cycle-related signals that can inhibit glycolysis and reduce pyruvate formation.

Warburg effect

Cancer cells use glycolysis and lactate fermentation even when oxygen is available.

Chloroplast stroma

Compartment where the Calvin cycle occurs.

Thylakoid membrane

Contains photosystems, electron carriers, and ATP synthase.

Thylakoid lumen

Compartment where protons accumulate during light reactions.

Grana

Stacks of thylakoids.

Light reactions inputs

Photons and water.

Light reactions outputs

ATP, NADPH, and O2.

Carbon assimilation inputs

CO2, ATP, NADPH, and water.

Carbon assimilation output

Triose phosphate/G3P.

Photosystem II reaction center

P680.

Photosystem I reaction center

P700.

Antenna pigments

Absorb photons and pass excitation energy to reaction-center chlorophyll.

PSII role

Uses light energy and oxidizes water, producing O2 and H+ while supplying electrons.

PSI role

Re-excites electrons so they can reduce NADP+ to NADPH.

Photosynthetic final electron acceptor

NADP+, reduced to NADPH.

Rubisco

Catalyzes CO2 attachment to RuBP during Calvin-cycle carboxylation.

RuBP

Five-carbon CO2 acceptor in the Calvin cycle.

Calvin cycle stages

Carboxylation, reduction to G3P, and regeneration of RuBP.

CO2 for one G3P output

Three CO2 enter for one G3P to leave the cycle.

Calvin cycle inputs per one G3P

3 CO2, 3 H2O, 9 ATP, and 6 NADPH.

G3P regeneration role

Five of six G3P molecules regenerate three RuBP molecules; one is available for biosynthesis.

Photosynthesis vs respiration

Both use electron transport, proton gradients, and ATP synthase; electron sources, acceptors, and energy inputs differ.

Carbon fixation vs oxygen production

Reduced CO2 directly limits carbon assimilation; do not assume O2 output changes by the same percentage.