BIO 1141 Midterm Review: Cell Structure, Membrane Transport, Cytoskeleton and the Cell Cycle

Terms in this set (31)

1. Three tenets of cell theoryAll living things are made of one or more cells; the cell is the basic unit of life; and all cells arise from pre-existing cells.
2. What did the Miller-Urey experiment show?Passing electric sparks through a mixture of gases thought to resemble the early atmosphere (methane, ammonia, hydrogen, water vapour) produced amino acids, showing organic molecules can form from simple inorganic precursors.
3. RNA world hypothesisThe idea that early life used RNA both to store genetic information and to catalyze reactions (ribozymes), before DNA and proteins took over those roles.
4. Evidence for the endosymbiotic origin of mitochondria and chloroplastsThey have their own circular DNA, bacteria-like ribosomes, double membranes, and divide by a process like binary fission, consistent with descent from engulfed bacteria.
5. Prokaryotic vs eukaryotic cellsProkaryotes (bacteria and archaea) lack a nucleus and membrane-bound organelles and are usually smaller. Eukaryotes have a nucleus, membrane-bound organelles and an extensive cytoskeleton.
6. Rough ER vs smooth ERRough ER has ribosomes and makes secreted, membrane and lysosomal proteins. Smooth ER lacks ribosomes and synthesizes lipids, detoxifies drugs and stores calcium.
7. Function of the Golgi apparatusIt receives proteins and lipids from the ER, modifies them (for example by glycosylation), sorts them and packages them into vesicles for delivery to the membrane, lysosomes or secretion.
8. What do lysosomes do?They are acidic, membrane-bound compartments containing hydrolytic enzymes that digest macromolecules, worn-out organelles (autophagy) and material taken in by endocytosis.
9. Structure and roles of the nucleusA double-membrane nuclear envelope with nuclear pores encloses the DNA. The nucleolus makes ribosomal RNA and assembles ribosome subunits. Pores control traffic of RNA and proteins.
10. Fluid mosaic model of the plasma membraneThe membrane is a fluid phospholipid bilayer in which proteins, cholesterol and carbohydrates are embedded or attached and can move laterally.
11. How does cholesterol affect membrane fluidity?It buffers fluidity: at warm temperatures it restrains phospholipid movement, and at cool temperatures it prevents tight packing that would make the membrane rigid.
12. Simple diffusion vs facilitated diffusionBoth move substances down their concentration gradient without ATP. Simple diffusion goes directly through the bilayer (O2, CO2). Facilitated diffusion uses channel or carrier proteins (glucose, ions).
13. What does the Na+/K+ pump do?It uses one ATP to pump 3 Na+ out of the cell and 2 K+ in, against their gradients. This primary active transport maintains the gradients and contributes to the membrane potential.
14. Secondary active transportUses the energy of one ion moving down its gradient (often Na+, set up by the Na+/K+ pump) to move another substance against its gradient, as in the Na+/glucose symporter.
15. What happens to animal and plant cells in a hypotonic solution?Water enters by osmosis. Animal cells swell and may burst (lyse). Plant cells swell until the cell wall pushes back, becoming turgid, which is their healthy state.
16. Types of endocytosisPhagocytosis: engulfing large particles. Pinocytosis: taking in fluid. Receptor-mediated endocytosis: specific molecules bind receptors in clathrin-coated pits before uptake.
17. Three types of cytoskeletal filamentsMicrofilaments (actin, about 7 nm): cell shape, crawling, muscle contraction. Intermediate filaments (about 10 nm): mechanical strength. Microtubules (tubulin, about 25 nm): tracks for transport, spindle, cilia and flagella.
18. Kinesin vs dyneinBoth are motor proteins that walk along microtubules using ATP. Kinesin generally moves toward the plus end (outward), and dynein moves toward the minus end (inward). Myosin is the motor that moves along actin.
19. Structure of eukaryotic cilia and flagellaA 9 + 2 arrangement: nine outer microtubule doublets around two central microtubules. Dynein arms cause doublets to slide, bending the structure. They are anchored by a basal body.
20. Sliding filament model of muscle contractionCa2+ binds troponin, which moves tropomyosin and exposes binding sites on actin. Myosin heads bind actin, pull (power stroke) and release when ATP binds, so thin filaments slide past thick filaments.
21. Extracellular matrix and integrinsThe ECM is a network of proteins (such as collagen) and polysaccharides outside animal cells. Integrins are membrane proteins linking the ECM to the cytoskeleton and transmitting signals.
22. Tight junctions vs desmosomes vs gap junctionsTight junctions seal neighbouring cells to block leakage. Desmosomes anchor cells together for strength. Gap junctions form channels that let ions and small molecules pass between cells.
23. Phases of the eukaryotic cell cycleG1 (growth), S (DNA replication), G2 (preparation for division) and M phase (mitosis and cytokinesis). G1, S and G2 make up interphase. Non-dividing cells may exit to G0.
24. Stages of mitosisProphase: chromosomes condense, spindle forms. Prometaphase: envelope breaks down, kinetochores attach. Metaphase: chromosomes line up. Anaphase: sister chromatids separate. Telophase: nuclei re-form.
25. How do cyclins and CDKs control the cell cycle?Cyclin-dependent kinases are active only when bound to cyclins, whose levels rise and fall during the cycle. Active cyclin-CDK complexes phosphorylate targets that push the cell past checkpoints.
26. Role of p53A tumour suppressor protein that responds to DNA damage by halting the cell cycle for repair or triggering apoptosis if the damage is too great. Mutations in p53 are common in cancers.
27. Cytokinesis in animal vs plant cellsAnimal cells form a cleavage furrow by a contractile ring of actin and myosin. Plant cells build a cell plate from Golgi-derived vesicles that becomes the new cell wall.
28. Key enzymes of DNA replication and their jobsHelicase unwinds the helix, topoisomerase relieves supercoiling, primase lays RNA primers, DNA polymerase adds nucleotides and proofreads, and ligase seals gaps between fragments.
29. Where do transcription and translation occur in eukaryotic cells?Transcription and mRNA processing happen in the nucleus. The mature mRNA is exported and translated by ribosomes in the cytosol or on the rough ER.
30. Roles of the ribosome's A, P and E sitesA site: accepts the incoming aminoacyl-tRNA. P site: holds the tRNA carrying the growing polypeptide. E site: where the empty tRNA exits.
31. How are secreted proteins directed to the ER?An N-terminal signal sequence is recognized by the signal recognition particle (SRP), which brings the ribosome to the ER membrane. The protein is threaded into the ER lumen as it is made.