1. 2.4 Membranes

2. 2.4.1 Draw and label a diagram to show the structure of membranes.
phospholipid bilayer,
cholesterol,
glycoproteins,
integral AND peripheral proteins.
Integral embedded in phospholipids
Peripheral attached to surface
“plasma membrane “
not cell surface membrane for the membrane surrounding the cytoplasm
Variations in composition related to the type of membrane are not required.

7. 2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.
Hydrophobic Tails
nonpolar, not water soluble
Hydrophilic Heads
polar (phosphorylated alcohol region; water soluble)
Always align as bilayer if water present
Tails don’t strongly attract each other, so membrane flexible (“fluid”)

9. Lipids do NOT Mix With Water
Oil on Water Calming Effect

10. 2.4.3 List the functions of membrane proteins. Include the following:
hormone binding sites
Specificity; binds & changes shape of ptn  message into cell
Membrane enzymes
Catalyze rxns inside or out; often grouped for metabolic pathways
cell adhesion
Proteins hook together (gap or tight junctions)
cell-to-cell communication
Attached carb molecules (ID label for cell)
channels for passive transport
(high to low); facilitated diffusion channels
pumps for active transport
ATP used, no conc gradient needed

14. 2.4.4 Define diffusion & osmosis.
passive movement of particles from a region of high conc to a region of low conc.
“along” the conc gradient
Oxygen, carbon dioxide in/out cells
Osmosis
passive movement of water molecules, across a partially permeable membrane, from a region of lower solute conc to a region of higher solute conc
Hyper/hypo/iso -osmotic or –tonic solutions
equilibrium

15. How Diffusion Works

16. How Osmosis Works

22. Facilitated diffusion:
2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion.
Simple diffusion:
substances other than water move between phospholipids or through channel proteins
Facilitated diffusion:
non-channel protein carriers change shape to allow movemt of substances other than water
Specificity; no energy; ptn changes shape
Rate levels off when total saturation of available carriers occurs

23. Ability to cross membrane
Small, non-polar = easily
Oxygen, carbon dioxide, nitrogen, water, glycerol
Large, polar = difficult
Ions, glucose, sucrose
How Facilitated Diffusion Works

24. 2.4.6 Explain the role of protein pumps and ATP in active transport across membranes.
Chemiosmosis in respiration
Chemiosmosis in photosynthesis
nerve transmission
kidney function
root hairs
Liver cells pump glucose from plasma
Na/K pump (1 example)
3 Na+ bind, ATP phosphorylates protein, protein changes shape, Na OUT of cell
2 K+ bind (different regions), releases P group, restores original ptn shape, K+ INTO cell

27. NaCl Exchange Pump

29. Protein produced by ribosomes (& enter rER)
2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.
Protein produced by ribosomes (& enter rER)
Exits ER, enters cis side of Golgi (vesicle)
Moves through Golgi, modified, exits on trans side (vesicle)
Vesicle moves to and fuses with plasma memb, modified protein is secreted from cell

33. 2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.
Fluid membrane—phospholipids not closely packed b/c loose connections b/w fatty tails
Stable b/c bilayer due to hydrophilic/phobic regions
Vesicles fuse or pinch off from: phospholipids match up
Endocytosis (out)
Phagocytosis (lg particulate matter)
Pinocytosis (extracellular fluids)
Exocytosis (in)
Pancreatic cells secrete insulin
Neurotransmitters released at synapse

36. Review
Why is the term equilibrium used with passive but not active transport?
What type of amino acids are present where integral proteins attach to cell membranes?
Why are exo- and endocytosis known as examples of active transport?