7-3 Cell Membrane
pinocytosis
" to drink" - the cell takes in only fluid
phagocytosis
"to eat" - the cell takes in particulate matter then fuse with lysosome for digestion
Cell survival depends on
balancing water uptake & loss
Active Transport
cell does use energy; 3 types: Protein Pumps; Endocytosis; Exocytosis
Passive Transport
cell doesn't use energy; 3 types: Diffusion; Facilitated Diffusion; Osmosis
active transport
• cell uses energy • actively moves molecules to where they are needed • Movement can be opposite from Passive Transport •Can go from an area of low concentration to an area of high concentration (Low to High)
cell membrane
thin, flexible barrier around a cell; regulates what enters and leaves the cell
hypertonic
when comparing two solutions, the solution with the greater concentration of solutes
hypotonic
when comparing two solutions, the solution with the lesser concentration of solutes
equilibrium
when the concentration of a solute is the same throughout a solution
isotonic
when the concentration of two solutions is the same
Membrane carbohydrates
§ Play a key role in cell-cell recognition: the ability of a cell to distinguish one cell from another; basis for rejection of foreign cells by immune system
lipid bilayer
2 layers of phospholipids Phosphate head is polar (water loving - hydrophilic) b. Fatty acid tails non-polar (water fearing - hydrophobic) c. Proteins are embedded in membrane
How protists Deal with Osmotic Pressure
A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from over-expanding.
net movement of water
ALWAYS from Hypo to Hyper
How animal cells Deal with Osmotic Pressure
Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.
How bacteria and plants Deal with Osmotic Pressure
Bacteria and plants have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall is called tugor pressure.
cell membranes
Cell membrane separates the living cell from nonliving surroundings; thin barrier = 8nm thick; Controls traffic in & out of the cell; selectively permeable; allows some substances to cross more easily than others; Made of phospholipids, proteins & other macromolecules
Protein Pumps
Cells may need to move molecules against concentration gradient; Proteins changes shape to transport solute from one side of membrane to other; called a protein "pump" "costs" energy = ATP
Diffusion
DIFFUSION ALWAYS OCCURS DOWN A CONCENTRATION GRADIENT, FROM THE AREA OF GREATER or HIGHER CONCENTRATION TO THE AREA OF LESS OR LOWER CONCENTRATION. • When the concentration of the molecules of a substance is the same throughout a space, a state of EQUILIBRIUM EXISTS.
Diffusion
Diffusion is driven by the KINETIC ENERGY the molecules possess. Because of their kinetic energy, molecules are in constant motion. • Diffusion occurs when molecules move randomly in a liquid or gas.
Endocytosis
Endocytosis occurs when the plasma membrane envelops "bulk" food particles (or bacteria) and liquids and "pinches off" inside the cell. It "costs" energy = ATP
Exocytosis
Exocytosis occurs when "bulk" material is discharged from the cell. It"costs" energy =ATP
phospholipids
Fatty acid tails: hydrophobic; Phosphate group head: hydrophilic; Arranged as a bilayer
Channels through cell membrane
Membrane becomes semi-permeable with protein channels; specific channels allow specific material across cell membrane
Membrane Proteins
Membrane proteins have various functions: 1. transporters 2. enzymes 3. cell surface receptors 4. cell surface identity markers 5. cell-to-cell adhesion proteins 6. attachments to the cytoplasm
Osmosis:
Movement of water across the cell membrane; Diffusion of water from high concentration of water to low concentration of water across a semi-permeable membrane; Direction of osmosis is determined by comparing total solute concentrations (hypotonic, hypertonic, isotonic)
cell walls
Outside cell membrane (does NOT replace membrane!!!); Plants, algae, fungi, prokaryotes; Have pores to allow things in; Function: SUPPORT and PROTECT
Membrane Proteins
Proteins determine membrane's specific functions; cell membrane & organelle membranes each have unique collections of proteins; Membrane proteins: § peripheral proteins: loosely bound to surface of membrane; often act as cell surface identity markers (antigens) § integral proteins: penetrate lipid bilayer, usually across whole membrane; act as transport proteins with Channels and pumps
How salt water fish deal with osmotic pressure
Salt water fish pump salt out of their specialized gills so they do not dehydrate.
Diffusion
The Rate (speed) of Diffusion depends on the TEMPERATURE and the SIZE of the molecules that are DIFFUSING; • Molecules diffuse FASTER at HIGHER temperatures than at lower temperatures. • SMALLER molecules diffuse FASTER than large Molecules.
Isotonic
The concentration of solutes in the solution is equal to the concentration of solutes inside the cell; Water moves equally in both directions and the cell remains same size!
concentration gradient
The difference in the concentration of molecules across a space
Hypertonic
The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water); Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis or Crenation)
Hypotonic
The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water); Result: Water moves from the solution to inside the cell): Animal Cell Swells and bursts open (cytolysis)!
Facilitated Diffusion
diffusion of specific particles through integral channel proteins found in the membrane; Channel Proteins are specific - they "select" only certain molecules to cross the membrane; Specific for larger or charged molecules that can't simply diffuse across the lipid bilayer. (ex. Glucose)
osmosis
diffusion of water through a selectively permeable membrane
Osmosis
diffusion of water through a selectively permeable membrane; Water moves from high to low concentrations; Water moves freely through proteins
lipid bilayer
double-layered sheet that forms the core of nearly all cell membranes
active transport
energy-requiring process that moves material across a cell membrane against a concentration difference
Isotonic
equal solute, equal water; Cell is placed in isotonic solution; animal cell immersed in mild salt solution; example: blood cells in blood plasma; problem: none; no net movement of water; flows across membrane equally, in both directions; volume of cell is stable;
What molecules can get through phospholipid bilayer directly?
fats & other lipids
Vesicles in the cytoplasm
fuse with the cell membrane and release their contents to the exterior of the cell -used in plants to export cell wall material -used in animals to secrete hormones, neurotransmitters, digestive enzymes
Hypotonic
less solute, more water; Cell is placed in Hypotonic solution (therefore cell is hypertonic); a cell in fresh water example: problem: cell gains water,swells & can burst water continually enters; solution: contractile vacuole pumps water out of cell ATP; plant cells become turgid because of cell wall; in a hypotonic solution, water enters the cell, which may burst (lysis); in a hypotonic solution vacuoles fill with water, tug or pressure develops, and chloroplasts are seen next to the cel wall
Hypertonic
more solute, less water; Cell is placed in Hypertonic solution (therefore cell is hypotonic); a cell in salt water example: shellfish problem: lose water & die plant cells; plasmolysis = wilt animal cells crenation = shrivel; solution: take up water or pump out salt; In a hypertonic solution, water leaves the cell, which shrivels (crenation); In a hypertonic solution, vacuoles lose water, the cytoplasm shrinks (plasmolysis), and chloroplasts are seen in the center of the cell
facilitated diffusion
movement of specific molecules across cell membranes through protein channels
What molecules can NOT get through directly?
polar molecules: H2O ions: salts, ammonia large molecules: starches, proteins
exocytosis
process by which a cell releases large amounts of material
pinocytosis
process by which a cell takes in liquid from the surrounding environment
diffusion
process by which molecules tend to move from an area where they are more concentrated to an area where they are less concentrated
phagocytosis
process in which extensions of cytoplasm surround and engulf large particles and take them into the cell
Diffusion
random movement of particles from an area of high concentration to an area of low concentration. (High to Low) Diffusion continues until all molecules are evenly spaced (equilibrium is reached)-Note: molecules will still move around but stay spread out.
receptor-mediated endocytosis
specific molecules are taken in after they bind to a receptor; triggered by molecular signal
cell wall
strong supporting layer around the cell membrane in plants, algae, and some bacteria
concentration
the mass of solute in a given volume of solution, or mass/volume
