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AP Biology Ch 2 Cheat Sheet (DRAFT) by

AP Bio Chapter 2: Cell Structure and Function

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Defini­tions and Processes

Eukary­otes: most of the DNA is stored in the nucleus (bounded by a double membrane)
Prokar­yotes: the DNA is concen­trated in the nucleoid (not membrane enclosed)
- Larger organisms do not necess­arily have larger cells, just more of them
- Lipids and proteins are the staple ingred­ients of membranes, though carboh­ydrates are also important
- Phosph­olipids are the most abundant lipids in cell membranes
Amphip­athic: has both a hydrop­hyllic and a hydrop­hobic region
- The phosph­olipid bilayer can exist as a stable boundary between two aqueous compar­tments
Fluid mosaic model: proposes that the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phosph­olipids
- Membranes are held together primarily by hydrop­hobic intera­ctions which are weaker than covalent bonds, allowing for flexib­ility
- The temper­ature at which a membrane solidifies depends on its comprising lipids
- Kinks in the tails where double bonds are located prevent unsatu­rated tails from packing as closely together as saturated tails, making the membrane more fluid
Choles­trol: helps membranes resist changes in fluidity when the temper­ature changes
Steroid lipids: resist temper­ature changes in plant cells
- Cells recognize other cells by binding to molecules on the extrac­ellular surface of the plasma membrane
- The diversity of molecules and their location on the cell's surface enable membrane carboh­ydrates to function as markers distin­gui­shing cells apart
Selective permea­bility: substances do not cross the cell membrane indisc­rim­inately
- Nonpolar hydrop­hobic molecules can dissolve in the lipid bilayer and can cross it easily without the aid of membrane proteins
- The hydrop­hobic interior of the membrane impedes the direct passage of ions and polar (hydro­phy­llic) molecules through the membrane
Transport (channel) proteins: span the membrane and have hydrop­hyllic channels which certain molecules and atomic ions ise as tunnels through the membrane
Carrier proteins: hold onto their "­pas­sen­ger­s" and change shape in a way which shuttles them across the membrane
- Diffusion occurs from a region of higher concen­tration to a region of lower concen­tration
- Molecules diffuse randomly, but popula­tions may diffuse direct­ionally
- Each substance diffuses along its own concen­tration gradient, unaffected by those of other substances
- The behavior of a cell in a solution relies on both solute concen­tration and membrane permea­bility
Tonicity: the ability of a surrou­nding solution to cause a cell to gain or lose water
- Higher concen­tration of non-pe­net­rating solutes: water leaves the cell
- Lower concen­tration of non-pe­net­rating solutes: water enters the cell
Isotonic: no net movement of water (equil­lib­rium)
Hypert­onic: more NPS; the cell loses water, shrivels, and dies
Hypotonic: less NPS; the cell swells and lyses
Turgor pressure: the pressure exacted back on a cell which opposes further water intake (in plant cells due to their cell walls)
Plasmo­lysis: occurs when a plant is submerged in a hypertonic enviro­nment; the cell membrane pulls away from the cell wall at multiple locations
Sodium­-Po­tassium pump: exchanges sodium for potassium across the cell membranes of animal cells
- Ions diffuse down their electr­och­emical gradients
3 stages of cell signaling: reception, transd­uction, and response
Reception: the target cell's detection of a signaling molecule outside the cell
Transd­uction: converts the signal to a form which can bring about a specific cellular response
Response: the transduced signal triggers a specific cellular response
- Proteins relay signals from receptor to response
- A signaling pathway may regulate the activity of proteins rather than causing their synthesis by activating gene expression
Nuclear envelope: encloses the nucleus and seperated its contents from the cytoplasm


Vesicles: transport membrane sacs
Smooth ER: carries out lipid synthesis, carboh­ydrate metabo­lism, detoxi­fic­ation, and storage of calcium ions
Rough ER: produce proteins which are secreted by cells
Golgi apparatus: modifies stores and ships products of the ER
Lysosomes: digest (hydro­lyze) macrom­ole­cules
Vacuoles: large vesicles from the ER
Food vacuoles: formed by phagoc­ytosis (engulfing of smaller organisms or food particles)
Contra­ctile vacuoles: pump excess water from the cell and maintain a suitable intrac­ellular concen­tration of ions and molecules
Central vacuole: allows plant cells to become larger with minimal investment in new cytoplasm
Mitoch­ondria: sites of cellular respir­ation (the use of oxygen to drive the generation of ATP from sugar fuels)
Chloro­plasts: sites of photos­ynt­hesis (the conversion of solar energy into chemical energy)
Thylak­oids: membranous system of flattened interc­onn­ected sacs inside the chloro­plast
Granum: a stack of thylakoids
Stroma: the fluid outside the thylakoids which contains chloro­plast DNA, ribosomes, and many enzymes
Cytosk­eleton: network of fibres extending throughout the cytoplasm which organize the structures and activities of a cell; made up of microt­ubules, microf­ila­ments, and interm­ediate filaments
Microt­ubules: hollow rods constr­ucted of tubulin
Microf­ila­ments: thin solid rods made up of actin (globular protein)
Myocin: causes the contra­ction of muscle cells
Interm­ediate filaments: specia­lized for bearing tension
Cell wall: protects and shapes plant cells; prevents an excessive uptake of water
Integrins: cell surface receptor proteins which span the plasma membrane and bind on their cytopl­asmic side to associated proteins attached to microf­ila­ments of the cytosk­eleton
Cell junctions: three types; tight junctions, desmos­omes, and gap junctions
Tight junctions: the plasma membranes of neighb­oring cells are very tightly pressed together (bound by specific proteins)
Desmos­omes: fasten cells together into strong sheets
Gap junctions: provide cytopl­asmic channels from one cell to an adjacent cell
Cytosol: semifluid inside all cells in which sub-ce­llular components are suspended
Nucleus: control center
Ribosomes: sites of protein synthesis
Nuclear envelope: encloses the nucleus and seperates its contents from the cytoplasm
Chromo­somes: structures which carry genetic inform­ation (the units into which DNA is organized in the nucleus)
rRNA: ribosomal RNA; synthe­sized from genes in the DNA of the nucleolus
Endome­mbrane system: all orgenelles in a eukaryotic cell
Endopl­asmic reticulum: network of membranes
Fimbriae: attachment structures on the surface of some prokar­yotes
Nucleoid: region where the cell's DNA is located (not membrane enclosed)
Glycoc­alyx: outer coating of many prokar­yotes consisting of a capsule (slime layer)
Flagella: locomotive organelles of some prokar­yotes
Bacterial chromo­some: carriers of genetic inform­ation (DNA)
Microv­illi: long, thin projec­tions in the surface of cells