2.4 Membranes

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.

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”)

Lipids do NOT Mix With Water Oil on Water Calming Effect

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

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

How Diffusion Works

How Osmosis Works

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

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

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

NaCl Exchange Pump

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

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

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?