cell structure & transport. cell structure cytoplasm fluid material in which the cell contents...
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Cell Structure & TRANSPORT
Cell Structure
Cell Structure Cytoplasm• Fluid material in which the cell contents are suspended• 75% - 90% water Cytoskeleton• framework of protein fibres
Microtubules: hollow rods which keep organelles in place + move them around cell
Microfilaments: (smaller) move materials around cell or move whole cell
Cell Structure Organelles
Nucleus- Surrounded by a nuclear membrane (double membrane) with nuclear poresContains genetic material (DNA)- DNA determines which enzymes (proteins) will be made by cell therefore controlling the functioning of the cell- Nucleolus contains RNA (protein synthesis)- Filled with nucleoplasm Ribosomessmall spherical structures which assist in protein production (amino acids polypeptides / proteins)
Cell Structure Endoplasmic reticulum- Network of channels formed by pairs of parallel membranes which connect with cell and nuclear membranes- Provide surface for chem.. reactions and channels allow molecule storage and transport
Rough / Granular ER: Ribosomes attachedSmooth / Agranular ER: No ribosomes Golgi Apparatus- series of flattened membranous bags which function to modify proteins and package them for secretion- addition of sugar, sulphate, phosphate, fatty acids- Ends of golgi apparatus pinch off to form vesicles with proteins inside
Cell Structure Lysosomes- small spheres bonded by a membrane from the golgi apparatus- contain digestive enzymes (breaks down proteins, lipids, nucleic acids and some carbs)
Mitochondria- spherical or sausage shaped structures with a double membrane (the inner one is folded)- contains enzymes which are involved in chem. reactions which release energy Centrioles- pair of cylindrical structures (which are at right angles) made up of a ring of very fine tubes- involved in cellular reproduction Cilia / FlagellaCilia: fine hair like projections which assist in movement along the cell membraneFlagella: one or two longer tail like projections
Cell MembraneCell membrane• Arranged in bilayer: • Semi-permeable membrane / differentially permeable /
selectively permeable: allow some materials to pass but not all.
• Composed of lipids (phospholipids) with tails pointing inward & proteins throughout
• Fig 3.2
• Transport may be• Passive: doesn’t require energy or;• Active: requiring energy
Cell MembraneTransport may occur in three main ways:• 1. Net Diffusion — (passive) the random movement of ions and
molecules until they are evenly distributed, and osmosis (passive), a special case of diffusion specifically involving water movement.
• 2. Carrier-mediated transport — (passive or active) Special proteins that bind to an ion/molecule to help it move through membrane.
• 3. Vesicular transport — (active) process where materials are moved in membrane-bound sacs.
Cell MembraneNet Diffusion• The movement of particles from a high concentration to a low concentration
until at equilibrium as a result of straight and random movements/collisions.
• Particles moving away from high conc are in fewer collisions than particles moving towards and therefore continue in a straight line.
• Diffusion gradient / Concentration gradient: difference in conc which brings about diffusion. (If conc gradient is larger, diffusion occurs faster.)
• Fig 3.4
• Fat soluble substances (e.g alcohol, steroids) and gases (CO2, O2) can diffuse directly through phospholipid layer
• Water, ions and small molecules can diffuse through protein membrane channels
• Fig 3.5
Cell MembraneOsmosis• Special case of diffusion
• Diffusion of the SOLVENT (often water) through a semi permeable membrane (differentially permeable membrane)
• Semi permeable membrane: membrane which allows some substances to pass through but not all.
• Often movement of solvent creates two different fluid levels on either side of the membrane creating osmotic pressure
• Fig 3.6
Cell MembraneCarrier-Mediated Transport• Proteins which bind to one particular ion/molecule and assist it in
moving across a membrane.
• Facilitated Diffusion: Passive process allowing larger molecules to diffuse, through a process of binding and being released from special proteins.
• Speed is limited by the number of binding proteins.• E.g glucose
• Active Transport: Movement of substances across the membrane, requiring energy, against the conc gradient.
• E.g amino acids.
• Fig 3.7
Cell MembraneVesicular Transport (Bulk Transport)An active process where materials move into/out of cell enclosed in vesiclesVesicles: Bubble surrounded by a membrane. Endocytosis: Movement of a substance from the outside of the cell to the inside by the folding of the cell membrane around the substance forming a vesicle (fluid filled sac)
Phagocytosis: solid particles (specialised cells only)Pinocytosis: liquid particles
Fig 3.8 Exocytosis: Movement of a substance from the inside of the cell to the outside by the migration of the vesicle. (may be waste or a substance needed elsewhere) Fig 3.9 Surface AreaAs objects get smaller their surface area to volume ratio increases.