CHAPTER 3
description
Transcript of CHAPTER 3
CHAPTER 3
A TOUR OF THE CELL
Concept 3.3: CELL MEMBRANE
MEMBRANE STRUCTURE
Membranes keep eukaryotic cells organized
Partition the cell Control the movement of substances into
and out of the cell Help maintain chemical environment for
the cell
MEMBRANE STRUCTURE
Membranes are mainly composed of 2 layers of phospholipid molecules with protein molecules embedded in them
Also contain small amounts of cholesterol and carbohydrate molecules
PHOSPHOLIPIDS Similar to lipid molecules, but have only
two fatty acids instead of three
Two fatty acids at one end of molecule—tails—are hydrophobic
Other end—head—is hydrophilic; has phosphate group attached
Membrane Phospholipids
PHOSPHOLIPID STRUCTURE ALLOWS MEMBRANES TO FORM
BOUNDARIES Plasma membrane separates watery inside
of cell from watery environment outside the cell
Phospholipids form a two layer “sandwich” of molecules—phospholipid bilayer—at boundaries that surround the cell or organelle
MEMBRANE PROTEINS Two main types —Fig. 3.4; p. 80:
1. Intracellular Receptors- Inside the Cell
2. Membrane Receptors – Located in the cell membrane.
MEMBRANE PROTEINS Perform most specific membrane
functions 1. Enzyme activity 2. Cell-to-cell recognition 3. Cell signaling 4. Transport of materials
Concept 3.4:Diffusion and Osmosis
DIFFUSION Diffusion: net movement of particles from
an area of greater concentration to an area of lesser concentration
Permeable membranes: membranes that particles to freely pass through them until the concentration of particles is equal on both sides of the membrane—balance or equilibrium
Example of Diffusion
PASSIVE TRANSPORT Selectively permeable membranes:
allow some substances to cross more easily than others; block some completely
Cell membranes are selectively permeable; O2 and CO2 pass freely; H2O must pass through protein channels; other molecules pass only under specific conditions
PASSIVE TRANSPORT Passive transport: diffusion of a
substance across a membrane with no energy expenditure by the cell
Simple Diffusion
TYPES OF PASSIVE TRANSPORT
Simple diffusion: passage of substance directly through the membrane—O2, CO2
Facilitated diffusion: substances pass through a channel in a transport protein in the membrane—sugars, H2O, some ions
Passive Transport
TYPES OF PASSIVE TRANSPORT
OSMOSIS Passive transport of water is so
common that it is given a special name
Osmosis: passive transport of H2O across a selectively permeable membrane
Aqueous (water is the solvent) solutions are classified into 3 categories called osmotic solutions
Movement of Water
TYPES OF OSMOTIC SOLUTIONS
Hypertonic Solution: a solution whose solute concentration is higher than the solute concentration inside the cell
- Animal cells will lose water and shrivel when placed in a hypertonic solution— water moves out of the cell
Cells placed in a hypertonic solution
TYPES OF OSMOTIC SOLUTIONS
Hypotonic Solution: a solution whose solute concentration is lower than the solute concentration inside the cell
- Animal cells will swell and possibly burst when placed in a hypotonic solution—water moves into the cell
Cell placed in a hypotonic solution
TYPES OF OSMOTIC SOLUTIONS
Isotonic Solution: a solution whose solute concentration is equal to the solute concentration inside the cell
- Animal cells retain their shape when placed in isotonic solutions—no net gain or loss of water inside the cell
Isotonic solution
Water molecules move in and out of the cell at the same rate, and the cell retains it’s normal shape.
BEHAVIOR OF RED BLOOD CELLS IN DIFFERENT OSMOTIC
SOLUTIONS
OSMOSIS & PLANT CELLS
Hypotonic environment: plant cells are firmest and healthiest
- Cell wall prevents cell membrane from bursting Isotonic environment: non-woody plants
wilt Hypertonic environment: membrane
pulls away from cell wall—kills the cell
PLANT & ANIMAL CELLS IN DIFFERENT OSMOTIC
SOLUTIONS
Concept 3.5:Active Transport, Endocytosis, and
Exocytosis
ACTIVE TRANSPORT Substance is moved from area of lower
concentration to an area of higher concentration
Requires the cell to expend energy
ACTIVE TRANSPORT Plays major role in maintaining cell’s
chemical environment
Two major types: 1) solute pumping 2) large molecule transport
SOLUTE PUMPING Specific membrane transport protein
pumps a solute across the membrane
Energy is used to move solute from area of lower concentration to area of higher concentration
Solutes moved into cells and out of cells
SOLUTE PUMPING
LARGE MOLECULE TRANSPORT
Some particles are too large to move through the membrane
Must be packaged in membrane sacs called vesicles
Particle fuses with plasma membrane and is moved either into (endocytosis) or out of (exocytosis) the cell
Both processes require energy
TYPES OF ENDOCYTOSIS
Phagocytosis: cell membrane engulfs and takes in particle of solid material;
“cell eating” Pinocytosis: cell membranes engulfs and
takes in small droplet of liquid; “cell drinking”
EXOCYTOSIS Product of cell is exported Requires energy
ENDOCYTOSIS Material is brought into the cell Requires energy
ENDOCYTOSIS & EXOCYTOSIS
PASSIVE vs. ACTIVE TRANSPORT