Exam 3 Review – Cell Membranes, Transport, Energy & Enzymes

Question-and-answer flashcards covering membrane structure, fluidity, transport, thermodynamics, enzyme function, energy transformations, redox reactions, and ATP synthesis. Designed for Exam 3 preparation.

Which of the listed molecules will need a transport protein to cross a membrane: N2, Cl2, CH4, C6H6, or C2H6O?

C2H6O (ethanol) – it is polar enough to require help through the hydrophobic core.

If a membrane-impermeable ligand must bind its receptor, where is that receptor located?

On the cell surface (plasma-membrane receptor).

Leucine-rich proteins are most likely what class of membrane protein?

Transmembrane proteins (because leucine is non-polar and spans the bilayer).

How does a transmembrane protein differ from a general integral protein?

All transmembrane proteins are integral, spanning the entire bilayer, whereas some integral proteins penetrate only partway into the hydrophobic core.

Integral membrane protein – key features

Permanent, amphipathic, embedded in bilayer; often function in transport or signaling.

Peripheral membrane protein – key features

Loosely attached to membrane surface or to integral proteins; mostly hydrophilic; can detach; roles in signaling, recognition, and cytoskeleton anchoring.

Name two macromolecules NOT normally found inside the plasma-membrane bilayer.

Glycogen and ribosomes.

What does cholesterol do for a membrane at high and low temperatures?

Restrains movement at high temperatures and prevents tight packing (maintains fluidity) at low temperatures.

Define the Fluid Mosaic Model.

The membrane is a fluid combination of phospholipids with proteins and other molecules drifting laterally within it.

True/False: Membrane proteins are fixed in place within the phospholipid bilayer.

False – lateral movement makes the membrane fluid.

What property term describes the ability of lipids and proteins to move laterally in a membrane?

Membrane fluidity.

Desert organisms tend to incorporate more _ fatty acids into their membranes and why?

More saturated fatty acids to decrease fluidity and prevent membrane melting at high temperatures.

List four functions of membrane-bound proteins.

Transport, enzymatic activity, signal transduction, cell-cell recognition (also intercellular joining and attachment to cytoskeleton/ECM).

Na⁺ and an amino acid moving together through the same protein in the same direction illustrate what transport mechanism?

Co-transport (symport), a form of secondary active transport.

Which transport processes require a membrane protein?

Facilitated diffusion and active transport (simple diffusion does not).

The two types of facilitated diffusion proteins are and .

Channel proteins and carrier proteins.

Do channel or carrier proteins consume ATP during facilitated diffusion?

Neither; facilitated diffusion is passive.

Aquaporin is what type of protein and what does it transport?

A transmembrane channel protein that specifically facilitates water movement.

Define diffusion.

Net movement of molecules from high concentration to low concentration (down the concentration gradient).

Pure water relative to typical animal cells is a(n) solution.

Hypotonic solution.

Extreme halophiles placed in the human body would find the external environment to them.

Hypotonic (the cells themselves would be hypertonic relative to body fluids).

Soda, tea, and coffee are solutions and can lead to dehydration.

Hypertonic.

State the First Law of Thermodynamics.

Energy cannot be created or destroyed, only transformed.

State the Second Law of Thermodynamics.

Every energy transfer increases the entropy (disorder) of the universe, often as heat.

What term describes the disorder that increases in energy transformations?

Entropy.

What biological catalyst speeds up reactions?

An enzyme (protein catalyst).

Give two ways enzymes lower the activation energy (EA).

(1) Orient substrates properly for reaction; (2) Strain or bend bonds in the substrate, making them easier to break.

Kinetic vs. potential energy – give one biological example of each.

Kinetic: heat or molecular motion; Potential: energy stored in chemical bonds such as ATP.

Does an enzyme change the ΔG of a reaction?

No – enzymes lower EA but do not affect the overall free-energy change (ΔG).

Define exergonic reaction.

A reaction that releases free energy (ΔG < 0) and proceeds spontaneously.

Define endergonic reaction.

A reaction that requires an input of free energy (ΔG > 0) to proceed.

Protein losing its shape due to pH or temperature change is called .

Denaturation.

To determine if strychnine is a competitive or non-competitive inhibitor of the glycine receptor, what must you know?

Where strychnine binds relative to glycine’s binding site on the receptor.

Competitive inhibitor – defining characteristic

Mimics substrate shape and binds the active site, blocking substrate access.

Non-competitive inhibitor – defining characteristic

Binds to an allosteric site, changes enzyme shape, making the active site non-functional.

What does an allosteric activator do to an enzyme?

Stabilizes the enzyme’s active form, making the active site the correct shape for substrate binding.

How could you test whether an inhibitor is competitive?

Add more substrate; if inhibition is relieved, it is competitive.

What causes an enzyme to become saturated?

All active sites are occupied by substrate; adding more substrate no longer increases reaction rate.

Hydrolyzing ATP is an reaction involving _ bonds.

Exergonic hydrolysis of phosphoanhydride bonds (a hydrolysis reaction).

Oxidative phosphorylation uses NADH in its form to power ATP synthesis.

Reduced form (NADH).

Define phosphorylation and state whether building ATP by oxidative phosphorylation is catabolic or anabolic.

Addition of a phosphate group; oxidative phosphorylation synthesizes ATP and is anabolic.

Proton-motive force converts energy to energy via ATP synthase.

Potential energy of the proton gradient to kinetic (rotational) energy that drives ATP synthesis.

Identify the oxidizing agent in the reaction 2Mg + O₂ → 2MgO.

O₂ is the oxidizing agent (it gains electrons).

In redox shorthand, oxidation is often seen as loss of , and reduction as gain of .

Loss of hydrogen (or electrons); gain of hydrogen (or electrons).

What reaction does ATP synthase catalyze?

ADP + Pi → ATP (phosphorylation of ADP).

Name the two main ways cells synthesize ATP.

Substrate-level phosphorylation and oxidative phosphorylation (chemiosmosis).

Describe substrate-level phosphorylation.

Energy released by removing a phosphate from a substrate directly drives addition of the phosphate to ADP to make ATP.

Describe chemiosmosis in ATP production.

H⁺ ions flow down their gradient through ATP synthase, providing energy to phosphorylate ADP to ATP.

In metabolic pathways, how are successive steps linked?

The product of one enzyme-catalyzed step serves as the substrate for the next step.

Enzymes are polymers of which monomer?

Amino acids (proteins).

List three factors that can affect enzyme activity.

Temperature, pH, substrate or inhibitor concentration (also salinity, cofactors, etc.).

What graphical change indicates competitive inhibition when substrate concentration is increased?

Reaction rate eventually reaches the uninhibited maximum as substrate outcompetes the inhibitor.

What is ΔG a measure of?

Change in free energy between products and reactants (Gproducts – Greactants).

In a biological context, what is considered the ‘system’?

The specific matter under study – e.g., a cell, an organism, or a reaction mixture.

Moving molecules from low to high concentration through a protein using energy depicts what transport?

Active transport.

What bond in ATP is broken during hydrolysis to release energy?

A phosphoanhydride bond between the terminal phosphate groups.

During oxidative phosphorylation, NADH is to NAD⁺.

Oxidized (loses electrons).

Give the equation for Gibbs free-energy change.

ΔG = Gend – Gstart.