Learning Objectives: Cell Physiology and Cell Membrane

Q: What are the major cellular organelles and their functions?

A:

• Nucleus: Stores DNA; controls cell activities.

• Ribosomes: Synthesize proteins.

• Rough ER: Protein synthesis and modification.

• Smooth ER: Lipid synthesis and detoxification.

• Golgi Apparatus: Modifies, sorts, and packages proteins/lipids.

• Mitochondria: Produce ATP via cellular respiration.

• Lysosomes: Digest cellular waste and pathogens.

• Peroxisomes: Break down fatty acids and detoxify.

• Cytoskeleton: Provides structure and aids movement.

• Centrioles: Organize cell division (in animal cells).

• Plasma Membrane: Regulates entry/exit of substances.

Q: What happens during glycolysis?

A: Glucose is broken into 2 pyruvate molecules in the cytoplasm, producing 2 ATP and 2 NADH.

Q: What happens during the citric acid cycle (Krebs cycle)?

A: In the mitochondrial matrix, acetyl-CoA is oxidized, producing 2 ATP, 6 NADH, and 2 FADH₂ per glucose.

Q: What happens during the electron transport chain (ETC)?

A: In the inner mitochondrial membrane, electrons from NADH and FADH₂ pass through protein complexes, pumping H⁺ ions to create a gradient.

Q: What is chemiosmosis?

A: H⁺ ions flow back into the matrix through ATP synthase, driving the production of ~28 ATP.

Q: Why is cellular respiration important?

A: It converts biochemical energy from nutrients into ATP, the cell’s usable energy currency.

Q: What are the key substrates, products, and net ATP yields of cellular respiration?

A:

• Glycolysis: Glucose → 2 Pyruvate + 2 ATP + 2 NADH

• Citric Acid Cycle: Acetyl-CoA → 2 ATP + 6 NADH + 2 FADH₂

• ETC & Chemiosmosis: NADH/FADH₂ + O₂ → ~28 ATP + H₂O

• Total Net Yield: ~32 ATP per glucose

Q: What happens during transcription?

A: DNA is used to synthesize mRNA in the nucleus using RNA polymerase.

Q: What happens during translation?

A: mRNA is decoded by ribosomes in the cytoplasm to assemble amino acids into a protein.

Q: How do RNA and DNA differ?

A:

• Sugar: RNA has ribose; DNA has deoxyribose.

• Strands: RNA is single-stranded; DNA is double-stranded.

• Bases: RNA has uracil (U); DNA has thymine (T).

• Function: RNA helps in protein synthesis; DNA stores genetic info.

Q: What is the structure and function of the plasma membrane?

A: A phospholipid bilayer with embedded proteins; it controls what enters and exits the cell and facilitates communication.

Q: How can a substance cross the cell membrane?

A: Based on size, polarity, and concentration gradient, substances use passive or active transport mechanisms.

Q: What is simple diffusion?

A: Passive movement of small, nonpolar molecules (e.g., O₂, CO₂) down their concentration gradient.

Q: What is facilitated diffusion?

A: Passive transport of larger or polar molecules via membrane proteins (e.g., glucose, ions).

Q: What is primary active transport?

A: Uses ATP to move substances against their gradient (e.g., Na⁺/K⁺ pump).

Q: What is secondary active transport?

A: Uses energy from another substance’s gradient (e.g., Na⁺/glucose symport).

Q: What is osmosis?

A: Passive diffusion of water across a semipermeable membrane toward higher solute concentration.

Q: What is endocytosis?

A: Active process where the cell engulfs materials into vesicles (e.g., phagocytosis, pinocytosis).

Q: What is exocytosis?

A: Active process where vesicles fuse with the membrane to release contents outside the cell.

Q: How do hypotonic, isotonic, and hypertonic solutions affect cells?

A:

• Hypotonic: Water enters cell → swelling or lysis.

• Isotonic: No net water movement → cell remains stable.

• Hypertonic: Water leaves cell → shrinkage (crenation).