Biology 5A – Topics 5-8 Review (Membranes, Cell Structure, Metabolism & Respiration)

These Question-and-Answer flashcards cover key concepts, definitions, mechanisms, and examples from Biology 5A lecture Topics 5-8, including membrane structure/function, cellular organelles, metabolism, enzyme kinetics, and cellular respiration.

What is the basic structural framework of all biological membranes?

A phospholipid bilayer with hydrophilic heads facing water and hydrophobic tails facing inward.

Which model describes membranes as fluid structures with proteins embedded in or attached to a phospholipid sea?

The fluid-mosaic model (Singer & Nicolson, 1972).

Which technique first revealed proteins inside the membrane interior, contradicting the Davson-Danielli model?

Freeze-fracture electron microscopy (Branton, 1966).

What did the Frye-Edidin cell-fusion experiment demonstrate about membrane proteins?

That many integral proteins can move laterally within the lipid bilayer, showing membrane fluidity.

How does cholesterol affect membrane fluidity at human body temperature (37 °C)?

It restricts phospholipid movement, making the membrane less fluid.

How does cholesterol affect membrane fluidity at low temperatures?

It prevents tight packing of phospholipids, thus maintaining fluidity.

How do unsaturated fatty acid tails influence membrane viscosity?

Cis double bonds create kinks that keep phospholipids apart, increasing fluidity.

What are peripheral membrane proteins?

Proteins loosely bound to the membrane surface and not embedded in the hydrophobic core.

What defines an integral membrane protein?

A protein with one or more segments that penetrate the hydrophobic interior of the bilayer.

When is an integral protein classified as transmembrane?

When it spans the entire membrane from one side to the other.

Give an example of a disease-relevant transmembrane protein.

CFTR (cystic fibrosis transmembrane conductance regulator).

What is the most common CFTR mutation and its effect?

Deletion of three base pairs removing one amino acid, disrupting ATP-dependent Cl⁻ transport and causing cystic fibrosis.

How is cystic fibrosis inherited?

As an autosomal recessive disorder.

Why are membranes selectively permeable?

Because their hydrophobic core blocks ions and polar molecules while allowing small non-polar molecules to pass.

Define passive transport.

Movement of a substance across a membrane down its concentration gradient without energy input.

What is facilitated diffusion?

Passive transport aided by channel or carrier proteins.

Name the water channel that speeds osmosis in many cells.

Aquaporin.

What distinguishes a carrier protein from a channel protein?

Carrier proteins bind and change shape; channels form hydrophilic tunnels.

Define osmosis.

Net diffusion of water across a semipermeable membrane from lower solute concentration to higher solute concentration.

What is osmotic pressure?

The pressure needed to stop osmosis; proportional to solute concentration difference.

Describe an isotonic environment for an animal cell.

Solute concentrations inside and outside are equal; no net water movement.

What happens to an animal cell in a hypotonic solution?

Water enters, the cell swells and may lyse.

What is plasmolysis in plants?

Shrinking of the plasma membrane away from the cell wall in a hypertonic environment.

How many Na⁺ and K⁺ ions are moved per cycle of the Na⁺/K⁺ pump?

3 Na⁺ out, 2 K⁺ in.

Why is the Na⁺/K⁺ pump electrogenic?

It creates a net positive charge outside, contributing to membrane potential.

What is a proton pump inhibitor and its clinical use?

A drug (e.g., omeprazole) that irreversibly blocks the H⁺/K⁺ ATPase in stomach lining to reduce acid reflux.

Define cotransporter.

Carrier that couples downhill ion movement to uphill transport of another molecule (e.g., sucrose-H⁺ symporter).

Differentiate exocytosis and endocytosis.

Exocytosis releases materials by vesicle fusion; endocytosis imports materials by vesicle budding.

Name three forms of endocytosis.

Phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Which genetic disorder is caused by defective LDL receptor-mediated endocytosis?

Familial hypercholesterolemia.

Give two main differences between prokaryotic and eukaryotic cells.

Eukaryotes have a nucleus and membrane-bound organelles; prokaryotes do not and are smaller (≈1-5 µm).

Why do larger organisms need to be multicellular?

Many small cells provide a higher surface-area-to-volume ratio for efficient exchange with the environment.

List the four key components of the nucleus.

Double nuclear envelope, nuclear pores, nuclear lamina, and nucleolus.

Where are ribosomal subunits assembled?

In the nucleolus.

What are the two locations of ribosomes and their destination rules?

Free ribosomes synthesize cytosolic, nuclear, mitochondrial proteins; bound ribosomes on rough ER synthesize secreted, membrane, and lysosomal proteins.

What is the signal peptide?

N-terminal amino acid sequence that directs a ribosome to the rough ER.

State two major functions of smooth ER.

Lipid synthesis and detoxification of drugs/poisons; also Ca²⁺ storage.

What happens to proteins in the Golgi apparatus?

They are modified, sorted, and packaged into vesicles; cis side receives, trans side ships.

Which organelle contains hydrolytic enzymes active at low pH?

Lysosome.

What causes Tay-Sachs disease at the cellular level?

A defective lysosomal enzyme (hexosaminidase A) leading to lipid accumulation in neurons.

What is autophagy?

Lysosomal recycling of a cell’s own damaged organelles or macromolecules.

Describe the primary role of plant central vacuoles.

Store ions/compounds and absorb water to help regulate cell size and turgor.

What do peroxisomes generate and break down during detoxification?

They produce hydrogen peroxide (H₂O₂) and then convert it to water.

Identify the two membranes and two spaces of a mitochondrion.

Outer membrane, inner membrane; intermembrane space and matrix.

What are cristae?

Folds of the inner mitochondrial membrane that increase surface area for respiration enzymes.

Name the three internal regions of a chloroplast.

Thylakoids, grana (stacks), and stroma.

Give two pieces of evidence supporting the endosymbiont theory.

Mitochondria/chloroplasts have circular DNA and their own ribosomes; divide independently of the nucleus.

List the three cytoskeletal filaments with diameters.

Microtubules (25 nm), microfilaments/actin (7 nm), intermediate filaments (8-12 nm).

Which cytoskeletal element forms the mitotic spindle and cilia/flagella?

Microtubules.

Which cytoskeletal component forms the cleavage furrow during cytokinesis?

Microfilaments (actin).

What proteins anchor animal cells to the extracellular matrix?

Integrins connected to fibronectin and collagen fibers.

Define metabolism.

The sum of all chemical reactions in a cell.

Differentiate catabolic and anabolic pathways.

Catabolic pathways break molecules and release energy; anabolic pathways build molecules and consume energy.

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 of the universe.

What is ∆G for a spontaneous reaction?

Negative (∆G < 0); reaction is exergonic.

How does ATP power endergonic reactions?

By energy coupling: hydrolysis of ATP (exergonic) drives an endergonic process, often via a phosphorylated intermediate.

Give the ∆G sign and definition of an endergonic reaction.

Positive ∆G; requires input of free energy.

In the glutamic acid → glutamine reaction, why is ATP hydrolysis required?

The conversion is endergonic (+3.4 kcal/mol); ATP hydrolysis supplies energy making the overall ∆G negative.

What effect do enzymes have on ΔG and activation energy (Eₐ)?

They lower Eₐ but do not change ΔG.

What is the ‘induced fit’ model?

Enzyme active site changes shape slightly to fit the substrate better upon binding.

Why do extreme pH or temperature inhibit enzymes?

They denature the protein, disrupting its three-dimensional structure essential for activity.

Explain feedback inhibition using isoleucine synthesis.

Isoleucine binds allosterically to the first enzyme in its pathway, inhibiting it when product levels are high.

Distinguish competitive vs noncompetitive enzyme inhibition.

Competitive inhibitors bind the active site; noncompetitive inhibitors bind elsewhere causing allosteric change.

Write the overall balanced equation for cellular respiration.

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O (ΔG ≈ –686 kcal/mol).

In redox terms, what happens to glucose and oxygen during respiration?

Glucose is oxidized (loses electrons); oxygen is reduced (gains electrons to form water).

What are NAD+ and FAD?

Electron carriers that become NADH and FADH₂ when reduced, storing high-energy electrons.

Where does glycolysis occur and does it require O₂?

In the cytosol; it is anaerobic (does not require oxygen).

How many net ATP and NADH are produced per glucose in glycolysis?

2 ATP (net) and 2 NADH.

What three changes convert pyruvate to acetyl-CoA?

Carboxyl removal (CO₂ released), oxidation reducing NAD⁺, and attachment to Coenzyme A.

What are the main outputs (per acetyl-CoA) of the citric acid cycle?

3 NADH, 1 FADH₂, 1 ATP (or GTP), and 2 CO₂.

Where are the electron transport chain (ETC) components located?

In the inner mitochondrial membrane.

What is the terminal electron acceptor in aerobic respiration?

Molecular oxygen (O₂), forming water.

Define chemiosmosis.

Use of a proton gradient across a membrane to drive ATP synthesis via ATP synthase.

Approximately how many ATP molecules are generated per glucose under aerobic conditions?

About 30-32 ATP.

Why does fermentation regenerate NAD⁺?

So glycolysis can continue in the absence of oxygen.

What are the end products of alcohol fermentation?

Ethanol, CO₂, and NAD⁺.

What are the end products of lactic acid fermentation?

Lactate and NAD⁺.

What metabolic process breaks fatty acids into acetyl-CoA units?

Beta oxidation.

Why do fats yield more energy per gram than carbohydrates?

They have more C-H bonds (more reduced), storing more chemical energy.

How does high ATP inhibit glycolysis?

ATP allosterically inhibits phosphofructokinase, decreasing glycolytic flux (feedback inhibition).