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.
Crossing Plasma Membrane
p. 88
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.
Osmosis
p. 90
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
p. 92
Transport by Carrier Proteins
• Carrier proteins- bind certain molecules – • 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.
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.
Crossing Plasma Membrane
p. 88
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.
Osmosis
p. 90
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
p. 92
Transport by Carrier Proteins
• Carrier proteins- bind certain molecules – • 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.
