BIOSCI107 · Biology for Biomedical Science: Cellular Processes and Development
Cell Structure & Cellular Respiration
Topic 2 opens with the eukaryotic cell — the plasma membrane, the organelles and the three cytoskeletal filaments — then follows a glucose molecule through cellular respiration: glycolysis, pyruvate oxidation, the citric-acid cycle and oxidative phosphorylation, for a maximum of about 30–32 ATP. It nails the control point (phosphofructokinase: AMP stimulates, ATP and citrate inhibit) and the insulin/glucagon/diabetes link. Assessed in the 30% mid-semester test as Teleform multiple-choice, with recurring items on ATP yields, the largest producer of electron carriers, and poisons/uncouplers.
What this chapter covers
- 01The plasma membrane: phospholipid bilayer (polar heads out, tails in), fluid mosaic, integral vs peripheral proteins
- 02Organelles: nucleus/nucleolus, ribosomes (free vs RER-bound), rough & smooth ER, Golgi, mitochondria (not part of the endomembrane system)
- 03The cytoskeleton: microfilaments (actin), intermediate filaments (keratin), microtubules (tubulin — chromosome movement, cilia/flagella)
- 04Cellular respiration overview: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + energy
- 05The four stages, their locations and ATP yields: glycolysis (cytosol, +2), pyruvate oxidation (matrix, 0), citric-acid cycle (matrix, +2), oxidative phosphorylation (inner membrane, ~26–28)
- 06Substrate-level vs oxidative phosphorylation; O₂ as the final electron acceptor; chemiosmosis and ATP synthase
- 07Regulation by phosphofructokinase (PFK): stimulated by AMP, inhibited by ATP and citrate; cyanide and uncouplers
- 08Blood-glucose homeostasis: insulin (β-cells) lowers, glucagon (α-cells) raises; type 1 vs type 2 diabetes mellitus
Counting ATP per glucose through the four stages
- +1Glycolysis — in the cytosol, anaerobic. Glucose → 2 pyruvate, net +2 ATP (substrate-level phosphorylation) plus 2 NADH. [+1]
- +1Pyruvate oxidation — in the mitochondrial matrix. Each pyruvate → acetyl-CoA, giving 0 ATP directly but +1 NADH and 1 CO₂ per pyruvate (2 per glucose). [+1]
- +1Citric-acid (Krebs) cycle — in the matrix. +2 ATP (substrate-level) per glucose, plus the bulk of the NADH and FADH₂ electron carriers and CO₂. This cycle produces the largest number of electron carriers. [+1]
- +1Oxidative phosphorylation — at the inner mitochondrial membrane. NADH/FADH₂ feed electrons into the electron-transport chain; H⁺ is pumped out to build a gradient that drives ATP synthase; O₂ is the final electron acceptor (reduced to water). This yields ~26–28 ATP — the bulk. Total ≈ 30–32 ATP per glucose. [+1]
Key terms
- Oxidative phosphorylation
- ATP synthesis at the inner mitochondrial membrane driven by the electron-transport chain and chemiosmosis: electrons from NADH/FADH₂ pump H⁺ into the intermembrane space, and the H⁺ gradient turns ATP synthase. O₂ is the final electron acceptor, reduced to water. Produces the bulk of the ~30–32 ATP.
- Substrate-level phosphorylation
- Direct transfer of a phosphate to ADP by an enzyme, independent of the electron-transport chain. It occurs in glycolysis and the citric-acid cycle and accounts for only about 4 of the ~30–32 ATP per glucose.
- Phosphofructokinase (PFK)
- The rate-limiting, irreversible gate-keeper enzyme of glycolysis (step 3). It is stimulated by AMP (signalling low energy) and inhibited by ATP and citrate (signalling plenty of energy) — the main point of feedback control on respiration.
- Chemiosmosis
- The coupling of the proton gradient across the inner mitochondrial membrane to ATP synthesis. Electron transport pumps H⁺ out; the H⁺ flows back through ATP synthase, driving ADP + Pi → ATP. An uncoupler that leaks H⁺ dissipates the gradient and lowers ATP yield without stopping electron flow.
- Cytoskeleton
- The cell's protein scaffold: microfilaments (~7 nm actin, motility/tension), intermediate filaments (8–12 nm, e.g. keratin, structural), and microtubules (25 nm α/β-tubulin, organelle transport, chromosome movement in division, cilia/flagella).
- Insulin / glucagon
- The opposing pancreatic hormones of blood-glucose homeostasis: insulin (β-cells of the Islets of Langerhans) promotes glucose uptake and storage as glycogen, lowering blood glucose; glucagon (α-cells) breaks glycogen down, raising it. Diabetes mellitus = impaired insulin production (type 1) or response (type 2).
Cell Structure & Cellular Respiration FAQ
How many ATP does one glucose really make?
Use ~30–32 ATP per glucose — that is the figure BIOSCI 107 teaches. Older textbooks quote 36–38, but the course uses the lower, more accurate value that accounts for the cost of importing ADP/Pi and shuttling electrons. Break it down as glycolysis +2, citric-acid cycle +2 (substrate-level), and oxidative phosphorylation ~26–28 (the bulk). Pyruvate oxidation makes 0 ATP directly but feeds NADH into the chain.
Why does cyanide kill cells so fast?
Cyanide blocks the passage of electrons to O₂ at the end of the electron-transport chain. With no final electron acceptor, the chain backs up, the proton gradient collapses, and oxidative phosphorylation stops — cutting off ~90% of ATP production. An uncoupler is different: it lets electrons keep flowing but leaks H⁺ across the membrane, so the gradient dissipates and ATP yield per NADH falls, releasing the energy as heat instead.
What does phosphofructokinase have to do with the exam?
PFK is the recurring control question. It is the rate-limiting enzyme of glycolysis, stimulated by AMP (low energy → speed up) and inhibited by ATP and citrate (high energy → slow down). A typical item asks what happens if PFK stops responding to AMP: glycolysis fails to speed up even when the cell is short of ATP. Learn the direction of each modulator.
Can AI help me with cellular respiration in BIOSCI 107?
Yes, for learning. Sia can walk the four stages with locations and yields, drill the PFK control logic, and explain poison/uncoupler effects on ATP. Use it to prepare for the mid-semester test — it does not sit the test for you, and the test is an AI-free lane under the course's academic-integrity policy. Confirm the rules on Canvas.
Exam move
Make a single respiration table — stage, location, ATP contribution, key products — and be able to reproduce it from memory, because the test items sit right on it (total yield, largest electron-carrier producer, which stage is anaerobic). Lock in the ~30–32 ATP figure and the split between substrate-level (~4) and oxidative (~26–28). Learn the control point cold: PFK is stimulated by AMP, inhibited by ATP and citrate, and be ready for 'what if PFK ignores AMP' and 'what does an uncoupler do' items. Keep the insulin/glucagon/diabetes trio and the type 1 vs type 2 distinction on a flashcard. For cell structure, drill the three cytoskeletal filaments (size, protein, job) and the one that moves chromosomes (microtubules), plus which organelles are/aren't in the endomembrane system (mitochondria are not). This is test-only material (Topics 1–3); confirm the mid-semester test date and Teleform format on Canvas.
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