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Cell Biology!
Shouldn’t this be review… ;( Transport Across the Membrane: Transport Type Passive Transport/Diffusion Active Transport Simple Diffusion Facilitated Diffusion Osmosis Types of Molcules Small & Nonpolar (like gases) Smaller than a protein Water anything Concentration Gradient High > low High > low Low >High (in terms of solute) Low > High Through protein?
Specific to the molecule, (usually) unidirectional, can be closed off
Aquaporin: rapidly transport a LOT both ways
Use Energy? ❌ ❌ ❌ ❌ Direct Transportation (avoiding membrane): for LARGE(r than a protein) molecules ● Endocytosis: into the cell ○ Most flexible cells create pseudopods (branches like of an amoeba) and surround the molecule with the cell membrane ■ Contained within a vesicle inside the cell ○ Phagocytosis: “eating” ○ Pinocytosis: “drinking” (Hint: پینے) ● Exocytosis: OUT of the cell ○ Vesicle joins with cell membrane to essentially dump out the molecule(s) ■ The cell membrane manages to rearrange itself
Water Transportation: Osmosis ● Tonicity: to describe concentration (the ratio of solute to solvent) ○ “Relative concentration” > how do the concentrations compare with each other ■ Hypertonic: more concentrated ■ Hypotonic: less concentrated ● Hypo to Hyper (if all else is equal) due to there being more free energy of water on the hypo side ○ Less water is occupied in the hypotonic solution ● Plants prefer this so they can stay swelled up ○ The cell wall is their osmosis defence mechanism ■ Isotonic: equally concentrated ● No net movement of water if all else is equal ● Plasmocylosis: cell shriveling because a lot of water osmosed OUT ○ A cell placed into a hypertonic solution ○ Cells avoid this by constantly pumping out water ● Cytolysis: cell expanding (or bursting = lysed) because a lot of water osmosed IN ○ A cell placed into a hypotonic solution ○ Cells avoid this by constantly pumping out salt ● In uneven conditions, water will osmose from the solution with lower water potential to the one with the higher water potential ○ Ψs is affected by temperature, ionization constant, and molarity ■ I = 2 for salt and 1 for sugars ○ Ex. A higher temperature can cause a lower potential, so water can osmose towards there Key Cell Organelles ● Endomembrane System: ○ Internal membranes facilitate cellular processes by minimizing competing interactions and by increasing surface areas where reactions can occur. ● Plants Only (and some Prokaryotes) ○ Cell Wall: ■ Structural boundary ■ Permeability barrier for some substances to the internal environments. ○ Chloroplast:
Fluid Mosaic Model! ● Cell Membrane can easily rearrange itself and recover from msot disturbances ● Varying Fat Composition: ○ Unsaturated to be more liquidy ■ Cold adapted organisms increase unsaturated fats in membrane to avoid freezing ○ Saturated to more solid ○ Cholesterol controls fluidity of membranes and minimizes the effects of temperature ● Membrane Carbohydrates ○ Cell-Cell recognition ■ Important in organ & tissue development ■ Basis for rejection of foreign cells ○ “Antigens”: the identifiers (but could be proteins) ● Membrane Proteins ○ Peripheral: loosely bounded to surface ■ Enzymes (usually of this shape) ○ Integral: Penetrate bilayer ■ Protein Channels and Pumps ■ Receptors: cell communication ○ Antigens and Fusion (to attach to other cells) ○ Embedded proteins can be hydrophilic, with charged and polar side groups, or hydrophobic, with nonpolar side groups. Endosymbiosis ● Mitochondria and Chloroplasts evolved from once free-living prokaryotic cells ○ Contain their own DNA ○ Have an inner membrane ○ Can self-replicate Surface Area: Volume ● Larger cells have a smaller ratio, which makes them less efficient ○ Larger transport needs but with more cost in transportation
■ More complex cellular structures (e.g., membrane folds) are necessary to adequately exchange materials with the environment. ○ So cells tend to be smaller! Variation ● At the molecular level provides organisms with the ability to respond to a variety of environmental stimuli. ● Variation in the number and types of molecules within cells provides organisms a greater ability to survive and/or reproduce in different environments.
