Plasma Membrane & Movement of Materials in Cells

Plasma Membrane & Movement of Materials in Cells

Why do cells need to control what enters and exits? Plasma membrane boundary between the cell and its environment Homeostasis maintaining the cells environment Cells need to bring in nutrients, get rid of wastes, and keep harmful molecules out

Selective Permeability The plasma membrane allows some molecules into the cell while keeping others out. A window screen is also selectively permeable.

Selective Permeability cont. Water freely enters and exits cells. Glucose, sodium, and calcium ions are only allowed to enter in certain amounts at certain times.

Membrane Models Fluid-Mosaic Model Membrane -fluid phospholipid bilayer - protein molecules partially/fully embedded. p. 84

Plasma Membrane Structure/Function Hydrophilic polar heads face out Hydrophobic nonpolar tails face each other. P. 85

Phospholipid Bilayer

Plasma Membrane Structure/Function Proteins - peripheral or integral. Peripheral proteins -inner membrane surface. Integral proteins - embedded in the membrane. p. 86

Protein Functions Channel Proteins Help pass molecules through membrane. Carrier Proteins Bind to substancehelp in passage through membrane. Cell Recognition Proteins - Help body recognize foreign substances.

Protein Functions (cont.) Receptor Proteins Bind moleculesprotein changes shape -causes cellular change. Enzymatic Proteins cause and speed metabolic (chemical) reactions

Plasma Membrane Permeability Plasma membrane- differentially permeable. Passive Transport - No ATP (energy) requirement. Molecules follow concentration gradient. Active Transport - Requires carrier protein and ATP.

p. 88 Crossing Plasma Membrane

Diffusion Particles of matter are in constant motion. Moving particles will collide with each other. Diffusion the net movement of particles from an area of high concentration to an area of low concentration.

Osmosis Osmosis - Diffusion of water across a selectively permeable membrane caused by concentration differences. (HIGH Low) Osmotic pressure- due to osmosis. Greater the pressure, stronger the water diffusion toward low concetration.

p. 90 Osmosis

Osmosis Isotonic Solution - Solute and water concentrations same (equal) inside and outside membrane. Hypotonic Solution - Lower concentration of solute on one side of membrane. Cells in hypotonic solution. Lysis (burst)

Osmosis Hypertonic Solution - Higher concentration of solute on one side of the membrane. Cells placed in a hypertonic solution will Plasmolysis

Transport by Carrier Proteins Carrier proteins- bind certain molecules p. 92 Transport them through membrane. Facilitated Transport Small molecules follow concentration gradient by combining with carrier proteins. (No Energy Required)

Transport by Carrier Proteins Active Transport Small molecules move against concentration gradient by combining with carrier proteins. (Requires Energy- ATP)

Membrane-Assisted Transport Large macromolecules- transported into/out of the cell by vesicle. Exocytosis - Vesicles fuse with plasma membrane as secretion occurs. p. 94

Membrane-Assisted Transport Endocytosis - Cells take in substances by vesicle formation. Phagocytosis - Large, solid material. (eat) Pinocytosis - Liquid or small, solid particles. (drink) Receptor-Mediated - pinocytosis of specific molecules by receptor binding.

p. 95

Cell Surface Modifications Junctions between Animal Cells Adhesion Junctions Intercellular filaments between cells. Tight Junctions Form impermeable barriers. Gap Junctions Plasma membrane channels are joined (allows communication).

Cell Surface Modifications Extracellular Matrix Mesh of polysaccharides and proteins outside cells that produced them. Plant Cell Walls Permeable cell wall of cellulose Plasmodesmata cytoplasm strands between cells- allow material passage between cells.