Cells, Membranes & Diffusion Thurs 9/5/13

Cells, Membranes & Diffusion Thurs 9/5/13 • finish up lecture on macromolecules…. • Prokaryotes vs. Eukaryotic cells • plants vs. animals cells • plasma membranes of cells • diffusion & facilitated diffusion • osmosis - movement of water • active transport - energy required • endocytosis & exocytosis - large molecules

Cell sizes • cells are typically • why aren’t cells larger? Figure 3.2 Figure 3.1

Cell Structure: Prokaryotes • Bacteria & Archaea • plasma membrane surrounded • sometimes a • movement via Figure 3.3

Cell Structure: Prokaryotes • DNA within a ‘ • many • ribosomes • important in • smaller and structurally different from Figure 3.3

Eukarya -- Plant vs. Animal Cells fig 3.4 fig 3.5 animal cell plant cell

Eukarya -- Plant vs. Animal Cells fig 3.4 fig 3.5 animal cell plant cell • cytoplasm: • nucleus: • ribosomes: • endoplasmic reticulum • smooth: • rough:

Membranes: • importance • examples:

Plasma Membrane:phospholipidbilayer • phosphate (phosphorus & oxygen) in place of one fatty acid • hydrophilic end - head • hydrophobic end - tails fig 2.21

Plasma membrane: lipid bilayer • non-polar regions • polar regions • repels

Cell’s plasma membrane: fig. 4.1 see fig 4.2 • proteins embedded in lipid bilayer

Plasma Membrane: • selective permeability: • some • non-polar molecules • water • via • ions

Solutes vary in their rates of penetration • membrane is selectively permeable • phospholipidbilayer • small molecules • larger molecules (macromolecules) fig 4.3

MEMBRANE TRANSPORT • Working cells must control the flow of materials Diffusion Across Membranes • Diffusion is one result of the movement of molecules fig 4.4

Diffusion Across Membranes movement of molecules DOWN concentration gradient • example: movement of oxygen from the lungs to the circulatory system and vice versa. • breathe in oxygen rich air (high concentration oxygen) and blood flowing passed alveolus is low in oxygen. fig 4.5

Selective Permeability -- • proteins embedded in membrane • Channel Proteins • “open channels” • “gated channels” • ex: • Carrier Proteins – fig 4.2a fig 4.2b

Facilitated Diffusion • use of a channel protein or a carrier protein • channel protein: • carrier protein: fig 4.8

Osmosis: Movement of Water Molecules hypertonic vs. hypotonic -- comparing solute concentrations

Osmosis: Movement of Water Molecules passive diffusion of water across selectively permeable membrane • water moves from • as solute concentration increases

Regulation of Water: • aquatic organisms have to pump out water wilted leaves - lacking water healthy leaves - turgor pressure

Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a salt solution become limp and soft. From this we can deduce that the inside of the cells of the celery stalks are _____. a. hypotonic to both fresh water and the salt solution b. hypertonic to both fresh water and the salt solution c. hypotonic to fresh water but hypertonic to the salt solution d. hypertonic to fresh water but hypotonic to the salt solution e. isotonic with fresh water but hypotonic to the salt solution

The total solute concentration in a red blood cell is about 2%. Sucrose cannot pass through a red blood cell’s plasma membrane, but water and urea can. Osmosis will cause such a cell to shrink the most when the cell is immersed in which of the following solutions? a. a hypertonic sucrose solution b. a hypertonic urea solution c. a hypotonic sucrose solution d. a hypotonic urea solution

Active Transport: Pumping of Molecules Across Membrane movement of molecules UP concentration gradient fig. 4.9 • uses ATP - energy molecule • Na+ / K+ pump

Exocytosis & Endocytosis: Moving Large Molecules into and out of cells Endocytosis • examples: • phagocytosis – • pincosytosis – Figure 4.11

Exocytosis & Endocytosis: Moving Large Molecules into and out of cells • Exocytosis • secretory vesicles • examples of substances released: • pancreas releasing digestive enzymes Figure 4.10

Cells, Membranes & Diffusion Thurs 9/5/13