Cell Membrane

Function & Importance:

  • Separate internal environment of cell from external

  • Is the gateway into cell ←aren’t smart only detect anything if recognizable shape

  • Nutrients (need) goes in easily but harder to escape

  • Wastes can leave easily (opposite of nutrients)

  • Wide variety of molecules & substances must pass cell membrane → large, small hydrophobic / hydrophilic

  • Same size of molecule required to sort out 

  • Cells able to get large amount of molecules in & out anytime

↳ base on its structure & ratio of membrane to cytoplasm

  • recognizing cells (help immune system identify cell belong body & those that is invaders)

  • Tell the difference between different molecules & those with same size, “Selectively Permeable” → (what’s inside) 

  • Surface Area to Volume Ratio:

    • Small object (cell), has large surface area than volume

    • Diffusion, use to transport materials (gases) into cell (particle moving around from high concentration to low)

    • Object (surface area) become larger, volume become smaller 

    ↳ diffusion not effective = physical limit for a cell’s size (the middle area can’t get / do anything)

    • SMALLER IS BETTER FOR DIFFUSION

    • Cell aren’t cube-shape

    • Fluid Mosaic Model:

      • 2x layer of phospholipid

      ↳ light marchin oil (fluid)

      • Proteins in phospholipid bilayer form mosaic pattern

      • Carbohydrate chains connect to proteins, “glycoproteins” / lipids, “glycolipids” of membrane

Plant Cell Wall:

  • Cell wall & cell membrane in plants

↳ cell wall lies outside the cell membrane

  • Bacteria have cell walls → not the same as plants

  • Thickness of cell wall depends on cell function

  • Primary cell wall → outermost layer, made up cellulose microfibrils (threadlike)

  • “Middle Lamella” →sticky substances glueing cells together

  • Woody plant have secondary cell wall forming inside the primary wall (layers of cellulose  microfibrils with lignin(strengthen))

↳wood compose of largely on secondary cell wall

Human usage on cellulose of cell walls: cotton, rayon, flex, hemp, wood, paper (has lignin to prevent yellow) → Lignin (waterproof materials) use for rubber, plastics, pigments, adhesives

  • Small things that fit in cellulose microfibrils can go in plant cell wall, “Freely Permeable”

  • Plant cells relies on cell membrane (in & out materials)

Diffusion

  • Physical process with any type of particle

  • Particles move from high concentration to lower concentration (equally distributed) {ex. Opening perfume =the smell immediately move to the room}

  • slow process, doesn’t require energy (though adding energy speed up the process)

  • Lipid-soluble molecule (Steroids & Alcohol) diffuse easily across as itself made of lipids

  • Wate (not lipid- soluble) able to diffuse across membrane through the charge

↳ pores in membrane can’t go through other than water

      -   Gases (O2 & CO2) can pass by diffusion (important for cell respiration)

Rate of diffusion affect by: 

↳ Concentration Gradient (difference in concentration of diffusing molecule between 2 areas) 

↳ Size & Shape of molecules 

↳ Temperature (kinetic molecular theory)


3 Ways to Increase the rate of Diffusion:

  • Increase Temperature

  • Increase Concentration

  • Decrease the size of diffusing molecules

Osmosis 

  • A special case of diffusion

  •  the movement of water from greater concentration area to lesser concentration across a selectively-permeable membrane

  • Solute: particles dissolving in water

  • Solvent: liquid dissolving the solute (water)

  • Solution: combination of solute & solvent

  • Osmotic Pressure: the pressure due to flow of water from greater area of concentration to lesser area of concentration

↳ greater concentration difference = greater osmotic pressure

  • Cellular system, water can move easily across membranes (follow diffusion) other molecule can’t

  • More concentrated (solution having less solute, particles), Less concentrated (solution having more solute in) ← important on living system

  • Isotonic Solution- cell place solution contain same # of solute molecules per volume (no net movement), neither gain or loss water (ex. 0.9% of NaCl to red blood cell)

↳ remain same

  • Hypertonic Solution- greater # of solute molecule per volume than cell (lesser water), cell place in it = water leave the cell & shrinking it still keeping its shape, “Crenation”← Animal Cell, (ex. 10% solution of NaCL to RBC)

↳ “Plasmolysis” (osmosis), cell membrane shrinks & pulls from cell wall

  • Hypotonic Solution- lesser # of solute molecules per volume than cell, cell place in it = water enter & cause swell / possibly burst (ex. Salt solution less than 0.9% to red blood cell)

↳ greater water pressure inside cell against cell wall, “Turgor Pressure” ← Plant cells, hydrostatic pressure = osmotic pressure = turgor pressure

Transport By Carriers

Facilitated Transport

  • Effective use of protein carries in cell membrane to movement of cell (in & out)

  • Highly specific- each carrier pass only 1 type molecule

  • Molecule only pass concentration gradient

  • No energy needed like diffusion

  • Lipid-insoluble molecule (glucose & amino acid) across cell membrane 

    Active Transport

    • By protein carrier

    • Require energy (ATP)

    • Move molecule against the concentration gradient (opposite direction of diffusion)

    • Molecule more lower concentration area to higher concentration area

    • Active transport important to organisms: ex. Iodine & Thyroid Gland 

    ↳[ I ] low in blood, high in Thyroid Gland, active transport move I from blood to thyroid

    ↳Na always transport out urine by kidney tubule cells

  • ↳ Sodium / Potassium pump in nerve or muscle cells, move Na from inside to outside cell, K from outside to Inside

    ↳ Na, CI & Cystic Fibrosis- genetic disease, usually fatal cause by blockage of CI transport (affect the lung)

  • Endocytosis & Exocytosis

    • Way to get molecules, large particles in & out of cell

    • Endocytosis: cell membrane forms a vesicle (small hollow circle made by membrane & fill with water) around substance to be taken in

    ↳ Phagocytosis: (cell eating) larger particle taken in (ex. Human macrophages)- be seen with light microscope

    ↳ Pinocytosis: (cell drinking) same ideas as phagocytosis, though smaller particles taken in (need electron microscope to see)

    •  Exocytosis: (reverse of endocytosis) vacuole within cell combine to cell membrane & vacuole inside content are dispose to outside (important for secretion & excretion in cells)