BIO 311C Exam Review: Cell Structure, Membranes, Photosynthesis, Cell Signaling and the Cell Cycle

Terms in this set (31)

1. Prokaryotic vs eukaryotic cellsProkaryotes (bacteria, archaea) lack a nucleus and membrane-bound organelles; their DNA sits in a nucleoid region. Eukaryotes have a nucleus and organelles such as mitochondria, ER and Golgi, and are usually much larger.
2. What evidence supports the endosymbiotic theory?Mitochondria and chloroplasts have double membranes, their own circular DNA, bacteria-like ribosomes, and divide by a process like binary fission, consistent with descent from engulfed prokaryotes.
3. Rough ER vs smooth ERRough ER has ribosomes and makes secreted and membrane proteins. Smooth ER lacks ribosomes and makes lipids, detoxifies drugs, and stores calcium.
4. What does the Golgi apparatus do?It receives proteins from the ER at its cis face, modifies them (for example, adding or trimming sugars), sorts them, and ships them from the trans face in vesicles to their destinations.
5. What are lysosomes?Membrane-bound sacs with acidic interiors and hydrolytic enzymes that digest macromolecules, worn-out organelles (autophagy), and material taken in by phagocytosis.
6. Trace the path of a secreted protein from synthesis to export.Ribosome on rough ER, into the ER lumen, transport vesicle, Golgi (cis to trans), secretory vesicle, then fusion with the plasma membrane to release the protein (exocytosis).
7. Three types of cytoskeletal fibers and their rolesMicrotubules (tubulin): tracks for transport, mitotic spindle, cilia and flagella. Microfilaments (actin): cell shape, muscle contraction, cytokinesis. Intermediate filaments: tension-bearing strength, such as anchoring the nucleus.
8. Why are cells small?As a cell grows, volume rises faster than surface area. A high surface area-to-volume ratio is needed so the membrane can exchange enough nutrients and wastes for the cell's volume.
9. Describe the fluid mosaic model.The membrane is a phospholipid bilayer with hydrophobic tails inward and hydrophilic heads outward, with proteins embedded in or attached to it, and lipids and many proteins able to move laterally.
10. How does cholesterol affect membrane fluidity?It acts as a fluidity buffer: at high temperatures it restrains phospholipid movement, and at low temperatures it prevents tight packing that would make the membrane solidify.
11. Which molecules cross a lipid bilayer easily, and which need help?Small nonpolar molecules (O2, CO2) and lipid-soluble molecules diffuse through easily. Ions and large polar molecules (glucose) need channel or carrier proteins.
12. Simple diffusion vs facilitated diffusion vs active transportSimple diffusion: down a gradient directly through the bilayer. Facilitated diffusion: down a gradient through a protein, no energy needed. Active transport: against a gradient through a protein, requiring energy such as ATP.
13. What happens to animal and plant cells in a hypotonic solution?Water moves in by osmosis. An animal cell swells and may burst (lyse). A plant cell becomes turgid, which is its healthy state, because the cell wall resists bursting.
14. What does the sodium-potassium pump do?Using one ATP per cycle, it pumps 3 Na+ out of the cell and 2 K+ in, maintaining concentration gradients and contributing to the membrane potential.
15. What is cotransport (secondary active transport)?A protein uses the energy of one solute moving down its gradient (often Na+ or H+, set up by an ATP-driven pump) to move another solute against its gradient, as in the sodium-glucose symporter.
16. Phagocytosis vs pinocytosis vs receptor-mediated endocytosisPhagocytosis: engulfing large particles or cells. Pinocytosis: taking in droplets of extracellular fluid. Receptor-mediated endocytosis: specific molecules bind receptors in coated pits, as with LDL cholesterol uptake.
17. Overall equation for photosynthesis6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2.
18. Light reactions: where do they happen and what do they produce?In the thylakoid membranes. Light energy splits water (releasing O2) and drives electron flow through photosystems II and I, producing ATP and NADPH for the Calvin cycle.
19. Calvin cycle: where does it happen and what does it do?In the stroma. Rubisco fixes CO2 onto RuBP; ATP and NADPH from the light reactions reduce the products to G3P, a 3-carbon sugar used to build glucose and other molecules.
20. Where does the O2 released in photosynthesis come from?From water, split by photosystem II, not from CO2. Experiments with heavy-oxygen isotopes confirmed this.
21. What is photorespiration, and how do C4 and CAM plants reduce it?When CO2 is low (stomata closed on hot, dry days), rubisco binds O2 instead, wasting energy and releasing CO2. C4 plants fix CO2 in separate cells; CAM plants fix CO2 at night and open stomata only then.
22. Compare chemiosmosis in mitochondria and chloroplasts.Both use an electron transport chain to pump H+ and ATP synthase to make ATP. Mitochondria pump H+ into the intermembrane space; chloroplasts pump H+ into the thylakoid space. The electrons come from food vs from water.
23. Three stages of cell signalingReception: a signal molecule binds a receptor. Transduction: a relay of molecules (often phosphorylation cascades and second messengers) carries the signal. Response: a cellular activity changes, such as gene expression or enzyme activity.
24. Outline a G protein-coupled receptor pathway using cAMP.Ligand binds the GPCR, which activates a G protein by swapping GDP for GTP. The G protein activates adenylyl cyclase, which makes cAMP from ATP. cAMP activates protein kinase A, which phosphorylates target proteins.
25. How do receptor tyrosine kinases work?Ligand binding causes two receptors to pair up and phosphorylate each other's tyrosines. Relay proteins bind the phosphorylated sites, activating pathways such as Ras. Overactive RTKs or Ras contribute to many cancers.
26. How do steroid hormones signal differently from most protein hormones?Steroids are lipid-soluble, cross the plasma membrane, and bind intracellular receptors; the hormone-receptor complex acts as a transcription factor to change gene expression.
27. Why do signal transduction cascades amplify signals?Each activated enzyme in a cascade can activate many molecules of the next component, so one signal molecule can lead to thousands or millions of product molecules.
28. Phases of the cell cycle and the stages of mitosisInterphase: G1 (growth), S (DNA replication), G2 (preparation). M phase: prophase, prometaphase, metaphase, anaphase, telophase, then cytokinesis.
29. How are cell cycle checkpoints controlled?Cyclins bind and activate cyclin-dependent kinases (CDKs), which phosphorylate targets to push the cell into the next phase. Proteins such as p53 can halt the cycle at checkpoints if DNA is damaged.
30. Proto-oncogene vs tumor suppressor geneProto-oncogenes promote cell division; gain-of-function mutations turn them into oncogenes (like Ras). Tumor suppressors inhibit division; loss-of-function mutations in both copies remove the brakes (like p53).
31. Catabolic vs anabolic pathwaysCatabolic pathways break down complex molecules and release energy (cellular respiration). Anabolic pathways build complex molecules and consume energy (protein synthesis, photosynthesis).