Cell Bio Exam 2 - Main Set

Saturation (enzymes)

Inability to increase reaction velocity beyond a finite maximum despite increasing substrate

Vmax

Maximum reaction velocity when enzyme is saturated

Km (Michaelis constant)

Substrate concentration at 1/2 Vmax

Low Km meaning

High substrate affinity

High Km meaning

Low substrate affinity

Turnover number (kcat)

Number of substrate molecules converted per enzyme per second

Initial velocity

Reaction rate measured early before substrate depletion or product buildup

Michaelis-Menten equation

v = (Vmax[S])/(Km + [S])

Effect of low substrate concentration on rate

Rate is highly sensitive to changes in [S]

Effect of high substrate concentration on rate

Rate approaches Vmax and plateaus

What Km indicates

Affinity of enzyme for substrate

What determines Vmax

Enzyme concentration and catalytic efficiency

Multi-substrate enzyme analysis

Hold one substrate constant while varying the other

Lineweaver-Burk plot

Double reciprocal plot that linearizes Michaelis-Menten equation

Slope (Lineweaver-Burk)

Km/Vmax

Y-intercept (Lineweaver-Burk)

1/Vmax

X-intercept (Lineweaver-Burk)

-1/Km

Advantage of Lineweaver-Burk

Easy determination of Km and Vmax

Disadvantage of Lineweaver-Burk

Distorts data at low substrate concentrations

Ribozyme

Catalytic RNA molecule

Examples of ribozymes

rRNA peptidyl transferase RNase P self-splicing introns

RNA world hypothesis

RNA served as both genetic material and catalyst early in evolution

Importance of ribozymes

Demonstrates RNA can catalyze biochemical reactions

Competitive inhibition

Inhibitor competes with substrate for active site

Effect of competitive inhibition on Vmax

No change

Effect of competitive inhibition on Km

Increases

Noncompetitive inhibition

Inhibitor binds allosteric site

Effect of noncompetitive inhibition on Vmax

Decreases

Effect of noncompetitive inhibition on Km

No change

Allosteric regulation

Binding at regulatory site changes enzyme conformation

Allosteric activator

Stabilizes active enzyme form

Allosteric inhibitor

Stabilizes inactive enzyme form

Feedback inhibition

End product inhibits an earlier step in pathway

Phospholipid bilayer

Membrane structure composed of amphipathic lipids

Amphipathic molecule

Contains both hydrophilic and hydrophobic regions

Membrane protein functions

Transport signaling structure

Membrane carbohydrates

Cell recognition and signaling

Membrane asymmetry

Different lipid composition on each leaflet

Flippase

Transfers specific phospholipids between layers

Scramblase

Randomly redistributes phospholipids

Cholesterol function in membrane

Regulates fluidity and stability

Effect of temperature on membrane fluidity

Higher temperature increases fluidity

Effect of unsaturated fatty acids

Increase membrane fluidity

Effect of fatty acid chain length

Shorter = increase fluidity

Long = decrease fluidity

Cholesterol role in fluidity

Stabilizes membrane at extreme temperatures

Homeoviscous adaptation

Adjustment of membrane composition to maintain fluidity

FRAP technique

Measures lateral movement of membrane proteins

Freeze fracture technique

Splits membrane to observe protein distribution

Simple diffusion

Movement of small nonpolar molecules down gradient without protein

Facilitated diffusion

Transport down gradient using membrane proteins

Active transport

Movement against gradient requiring energy

Osmosis

Movement of water across membrane

Aquaporins

Water channel proteins

Hypotonic solution

Cell swells

Hypertonic solution

Cell shrinks

Isotonic solution

No net movement of water

Primary active transport

Uses ATP directly

Secondary active transport

Uses ion gradient

Na+/K+ pump

Transports 3 Na+ out and 2 K+ in

Effect of Na+/K+ pump

Makes inside of cell more negative

Symporter

Transports substances in same direction

Antiporter

Transports substances in opposite directions

Membrane potential

Voltage difference across membrane

Resting membrane potential

Negative inside relative to outside

Depolarization

Membrane becomes more positive

Repolarization

Return to negative potential

Hyperpolarization

Membrane becomes more negative than resting

Role of Na+ channels in depolarization

Na+ influx

Role of K+ channels in repolarization

K+ efflux

Excitatory neurotransmitter

Increases likelihood of action potential

Inhibitory neurotransmitter

Decreases likelihood of action potential

ΔG (uncharged solute)

ΔG = RT ln([in]/[out])

ΔG (charged solute)

ΔG = RT ln([in]/[out]) + zFVm

Exergonic transport

Movement down gradient

Endergonic transport

Movement against gradient

Overall glycolysis reaction

Glucose → 2 pyruvate + 2 ATP + 2 NADH

Glycolysis phases

Energy investment cleavage payoff

ATP used in glycolysis

2 ATP

ATP produced in glycolysis

4 ATP gross 2 net

NADH produced in glycolysis

2 NADH

Hexokinase function

Phosphorylates glucose

PFK-1 function

Rate-limiting step of glycolysis

Pyruvate kinase function

Produces ATP in final step

Purpose of fermentation

Regenerate NAD+ for glycolysis

Lactic acid fermentation

Pyruvate → lactate

Alcohol fermentation

Pyruvate → ethanol + CO2

Fermentation ATP yield

No additional ATP beyond glycolysis

Fermentation NADH usage

NADH converted back to NAD+

Gluconeogenesis

Synthesis of glucose from non-carbohydrate sources

Relationship glycolysis vs gluconeogenesis

Opposite pathways with different enzymes

Regulation of glycolysis vs gluconeogenesis

Energy status determines pathway activity