Chapter 5 Membrane Structure and Function

Active Transport

move molecules from high to low concentration gradient need ATP (energy) Protein tunnel -substance move against their concentration protein

Fluid Mosaic Model

"Fluid" because the phospholipids move around "mosaic" because there are many other structures embedded in the bilayer Shown by freeze-fracture electron microscopy

Facilitated Transport

-Movement of molecules that cannot pass directly through the membrane lipids -These molecules must combine with carrier proteins to move across the membrane -Follow concentration gradient, moving from high concentration to low concentration

plant cell

1) A plant cell in a hypotonic solution 2)Central vacuole will fill up and push all the other organelles against the cell wall 3) Resulting pressure against the cell wall is called turgor pressure

Functions of Membrane Proteins

1) Channel protein- or carrier protein -transport proteins inside and out the cell membrane 2)Cell Recognition protein- signature (Glycoproteins) 3) Enzymatic protein - speeds up chemical reaction 4) Receptor Proteins-Allow a cell to respond to signals from other cells 5)Junction Proteins-Attach adjacent cells

3 types of Osmotic Solutions:

1) Isotonic Solution- the concentration of the solute is the same inside the cell and outside the cell 2) Hypotonic Solution -( below levels) solutes inside the cell 3) Hypertonic Solution -(to much) tons of solutes (turgor pressure in plants, may cause animal cells to lyse (rupture) -Crenation in animal cells (hypertonic solution) -Plasmolysis in plant cells (hypertonic solution)

2 types of Passive Transport

1) Simple transport/diffusion (ex. gases, ethanol, water) 2) Facilitative transport/diffusion (ex. proteins, salts, sugars)

3 types of Endocytosis

1) phagocytosis - single cells engulfing other cells -Scanning Electron Micrograph of a Macrophage Phagocytosis of E. coli - Trichomonas vaginalis phagocytizing yeast cells 2) pinocytosis solutes are not specific 3)receptor mediated endocytosis solutes are specific -Viruses take advantage of receptor mediated endocytosis to get "taken in"

Passive Transport Across a Membrane

A solution consists of both Solvent (liquid), and Solute (dissolved solid)

I. Four main parts to biologically membranes 1)The Phospholipid Bilayer

Membranes are elements of 2 layers of phospholipids -- The Phospholipid Bilayer hydrophilic - polar "water-lover" hydrophobic- non polar "water-fearing"

Facilitated transport / diffusion

Molecules move across their concentration gradient thru a protein tunnel (carrier protein or channel protein)

Diffusion

Movement of substances from an area of high concentration to low concentration Another definition: movement of substances across their concentration gradient Gas Exchange in Lungs: Diffusion Across Lung

III. How substance move across membranes two different ways?

Passive transport (no ATP) vs. Active transport (needs ATP) -across concentration gradient -against concentration gradient high to low concentration low to high concentration

Plant Cell Walls

Plants have a freely permeable cell wall, with cellulose as the main component Plasmodesmata- penetrate the cell wall Each contains a strand of cytoplasm Allow passage of material between cells

3) Cholesterol

Polar head groups Cholesterol -stiffened region more fluid region Cholesterol is found in animal membranes function: to stabilize and strengthen the membrane Cholesterol fits between phospholipids

What do you do if you are an aquatic single-celled organism?

cell wall live in water need away to get rid of it a freshwater pond is a hypotonic environment contractile vacuoles pumps the extra water out

4) Carbohydrates

flags or ID tags that identify the cell glycolipid - phospholipid bilayer glycoprotein - polar and non polar **These carbohydrate chains exist only on the outside of the membrane** (the membrane asymmetrical)

II. Why substances move in and out of a cell

membranes are differentially permeable or selectively permeable some substances can pass thru the membrane and some cannot

Animal vs. Plant Cells

Animal cell that are made up of us are happy in isotonic Red blood cells in a hypertonic cells blown up in lysis Crenation -cells shrinks because the water exist in the cell Plants are happy when they are fat Plant cell don't like hypertonic

Phospholipid bilayer

External surface lined with hydrophilic polar heads Cytoplasmic surface lined with hydrophilic polar heads Nonpolar, hydrophobic, fatty-acid tails sandwiched in between

IV. Modifications of Cell Surfaces

Extracellular Matrix (ECM): Meshwork of proteins and polysaccharides in close connection with the cell that produced them Collagen - resists stretching Elastin - provides resilience to the ECM Integrin - play role in cell signaling Proteoglycans - regulate passage of material through the ECM to the plasma membrane

Cell Surfaces in Animals

Junctions Between Cells Adhesion Junctions - Intercellular filaments between cells Desmosomes - internal cytoplasmic plaques Tight Junctions - form impermeable barriers Gap Junctions Plasma membrane channels are joined (allows communication)

Three components of the plasma membrane?

Lipids- Phospholipid bilayer Protein molecules- (integral and peripheral protein) Cholesterol-affects the fluidity of the membrane

2) Proteins

Protein -2 types in the fluid mosaic model (membrane) 1 transmembrane protein (integral protein)- the protein travel to one direction to the other in the transmembrane there's hydrophobic regions and hydrophilic regions 2 Peripheral protein -are found on the inner membrane surface

Glycoprotein

Red blood cells have glycoprotein that identify cells as type A, B or O

Permeability of the Plasma Membrane

Selectively permeable - Allows some substances to move across the membrane Inhibits passage of other molecules Concentration gradient- move from an area of high concentration to an area of low concentration. Aquaporins- speed up water transport across the membrane

How Cells Talk to One Another

Signaling molecules serve as chemical messengers allowing cells to communicate with one another Cell receptors bind to specific signaling molecules Once the signaling molecule and the cell receptor bind a cascade of events occurs that elicits a cellular response Signal transduction pathway

Types of Active Transport

Sodium-potassium Pumps pump - a transport protein that moves ions against their concentration gradients slight positive charge on the extracellular side and a slight negative charge on the intracellular side membrane potential Exocytosis- moving a large item out of the cell -Vesicle fuses with the plasma membrane -Neurotransmitters are released by exocytosis Endocytosis-moving bulk or large items into the cell -Vesicle fuses with the plasma membrane

Additional Membrane Structure

cytoskeletal filaments - on intracellular side and aid in shape and strength Extracellular Matrix (ECM)- Proteins that provide structural support and communication for the cell

What is a plasma membrane?

is common to all cells, that separates the Internal cytoplasm from the external environment of the cell

Osmosis

the movement of water from an area of high concentration to low concentration thru a selectively permeable membrane Point: to get the solutes into equilibrium Osmotic pressure- is the pressure that develops due to osmosis