Ch 3 Notes Part 3 Cell Membrane Structure

Ch 3 Notes Part 3 – Cell Membrane Structure and Function • ALL cells have an outer membrane • Eukaryotes have an outer membrane and an inner membrane system • Prokaryotes only have an outer membrane

• Functions of the cell membrane : • Regulates what enters and leaves cell • Recognizes and interacts with external environment (other cells, pathogens, toxins, etc) • Carries out reactions based on signals received

Selective Permeability • The cell membrane exhibits selective permeability - It allows some substances to cross it more easily than others 3

Membrane Structure-Phospholipid • Main cell membrane piece is the phospholipid • Phospholipids are arranged so that the hydrophobic tails are away from the watery (aqueous) environment that cells are in 4

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Membrane Structure - Cholesterol • Cholesterol helps strengthen the cell membrane Cholesterol 6

Membrane Structure - Proteins • Proteins embedded in the cell membrane carry out specific jobs based on their structure 7

• Channel proteins – sites of facilitated diffusion 8

• Transport (or carrier) proteins – sites of active transport 9

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EXTRACELLULAR FLUID Channel protein Solute Carrier protein Solute CYTOPLASM 11

• Glycoproteins – used for recognition – carbohydrate chains attached to proteins help cells to “know” what is outside of the cell 12

• Cell Membrane forms vesicles or accepts fusion of vesicles during endocytosis or exocytosis – membrane is versatile, not fixed 13

Fluid Mosaic Model - a mosaic that is fluid – membrane is constantly shifting and changing Glycoprotein • In 1972, Extracellular fluid proposed the Fluid Mosaic S. Singer and G. Nicolson Model of membrane structure Glycolipid Carbohydrate Cholesterol Transmembrane proteins Peripheral protein Cytoplasm Filaments of cytoskeleton 14

Three General Ways Solutes Enter or Leave Cells • Passive Transport - does not require cell energy – Examples: Diffusion, Osmosis, and Facilitated diffusion • Active Transport Requires cell energy (ATP) – Example: movement through transport proteins • Bulk Movement – Endocytosis and Exocytosis

Methods of Passive Transport: • 1. Diffusion: the movement of particles of a solute from an area of higher concentration to an area of lower concentration. – Particles always move down a concentration gradient across a membrane if they can pass through it freely – A concentration “gradient” means there is MORE of a solute on one side of the membrane than there is on the other side of the membrane – Water, carbon dioxide, and oxygen can all move through membranes freely • They all move DOWN their gradient if there is a gradient

Diffusion through a Plasma Membrane -requires no special membrane parts (water moves through aquaporins, others can move directly through the membrane)

Methods of Passive Transport: • 2. Osmosis: the diffusion of water through a cell membrane. - Water molecules move from a higher concentration OF WATER to a lower concentration OF WATER. – Water will move to where there is a greater amount of solute because there is less water there – Cells may be in one of three types of solutions : • Isotonic • Hypotonic • hypertonic

Cell in Isotonic Solution • Isotonic solutions: the concentration of solute inside and outside of the cell is the same. • • • Isotonic: Water in = Water out No net movement of water. Molecules in equilibrium. Normal state for animal cells. Cell in homeostasis.

Cell in Hypotonic Solution • Hypotonic solutions: the concentration of solute is lower outside the cell than inside the cell. • Water enters cell. • Cell swells • Gives plant cells shape and support. • Animal cells burst (no wall)

Cell in Hypertonic Solution • Hypertonic solutions: the concentration of solute is higher outside the cell than inside the cell. • Water exits cell. • Animal cell shrinks and shrivels up • Plant cell wall stays intact but inside of cell shrinks

The effects of osmosis on animal cells – which of these cells is in isotonic, hypotonic, or hypertonic solution?

The effects of osmosis on animal cells – which of these cells is in isotonic, hypotonic, or hypertonic solution? isotonic hypertonic hypotonic

Hypo, Iso, Hyper – animal cells

Hypo, Hyper – plant cells

Elodea plant cells in hypotonic solution (under positive pressure)

Elodea plant cells in hypertonic solution (water left cell – heading toward higher solute concentration)

The effects of osmosis on plant cells – which of these cells is in isotonic, hypotonic, or hypertonic solution?

The effects of osmosis on plant cells – which of these cells is in isotonic, hypotonic, or hypertonic solution? isotonic hypertonic hypotonic

Methods of Passive Transport: • 3. Facilitated Diffusion • Particles always move with (down) a concentration gradient. • Uses channel proteins that span membrane • Usually for specific molecules such as glucose

Active transport • Active Transport: requires energy in the form of ATP. – Capable of moving solute particles against the conc. gradient (from low conc. to high conc. ) – Uses transport proteins in the cell membrane

Active Transport moves solutes against the concentration gradient through transport proteins

Bulk movement • Endocytosis: a process of taking material into the cell by means of pockets, of the cell membrane (usually putting them into a vesicle). – Phagocytosis -“Cell eating” • Intake of solids – Pinocytosis –”Cell Drinking” • Intake of small droplets of liquid • Exocytosis : the membrane of the vesicle surrounding the material fuses with the cell membrane, forcing the contents out of the cell.

EXO and ENDO

• What is happening in each of these diagrams? 35

• What is happening in each of these diagrams? Diffusion of molecule that can fit through phospholipid bilayer Facilitated diffusion through a channel protein Osmosis – both through the bilayer and through a channel protein Active transport of glucose 36