Presentation is loading. Please wait.

Presentation is loading. Please wait.

Membranes and Transport Unit 4

Similar presentations


Presentation on theme: "Membranes and Transport Unit 4"— Presentation transcript:

1 Membranes and Transport Unit 4

2 What does the Membrane Do?
Support keeps cell shape Transport moves material in and out of the cell Recognition receives info on material around the cell Communication send info to outside of cell Adherence stick cell to other materials; hold it in place

3 Membrane Structure What are the parts?
1) Phospholipids hydrophilic and hydrophobic ends; 2 layers 2) Sterols non-polar rings and polar alcohol groups; cholesterol 3) Embedded proteins Transport proteins and enzymes 4) Glycolipids and glycoproteins protective coat or communication (act like receptors)

4 Fluid Mosaic Model Membrane and it proteins are in a semi-fluid state which allows proteins to move freely in all directions How do cells maintain fluidity at low temps? More unsaturated fatty acid chains Raise cholesterol levels How do cells maintain stability at high temps? Cholesterol reduces fluidity of the membrane; nonpolar region keep nonpolar tails close together

5 How do we know it is fluid?
Frye and Edidin; 1970 Created antibodies for human (glow red) and mice (glow green) proteins Mixed human and cell membranes and watched the red and green lights over time After 40 mins the lights went from half an half to completely diffused around the membrane Found membrane fluidity is similar to machine oil

6 Membrane Proteins 4 Types of proteins:
Transport move H2O, ions, and molecules Recognition cell recognize each other in a system; communication Receptor bind to signal molecules from the environment Adhesion bind cells to each other or other materials

7 Two Structures Integral cross through both layers of the membrane; all 4 types Peripheral bind to one side of the membrane, mostly the inside, through non-covalent bonds; cytoskeleton parts, glycolipids, and glycoproteins

8 How do we know these types exist?
Freeze faction experiments: Cool cell down and cut apart membrane layer Under an electron microscope, holes and dents in the membranes match like puzzle pieces

9 Why Are Cells SOOO Small?
Cell Size Limitations: Diffusion limits cell size too big and it will take too long for things for move around the cell DNA limits cell size Too big and it will take too long to make the proteins needed Surface area-to-volume ratio Too big and the ratio between the surface area and cell size takes too long to take nutrients and release waste 6:1 3:1 96:64 1.5:1

10 Transportation through the Membrane
Transport of material is the most activity role of the membrane Always must be: Directional in or out Specific only one type of cargo 2 Ways to Go: 1) Passive requires no energy by the cell 2) Active requires energy for at least one step

11 Passive Transport All movement “requires” energy
Where does the energy come from for passive transport? Kinetic energy Diffusion the net movement of molecules from a region of high conc. to a region of low conc. down a conc. gradient Is it directional? Yes, though molecules move in all directions, the over movement is from high to low What happens when the gradient levels out? Dynamic equilibrium

12 Simple Diffusion What can diffuse through the membrane?
Non-polar molecules can pass through hydrophobic barrier in the middle Steroid hormones Inorganic gases O2, N2, and CO2 H2O? If water is polar why does it diffuse? It is small enough to pass though the phospholipids but very slowly Water needs a little help

13 Facilitated Diffusion
1) Aquaporins water channels Billion/sec 2) Ion channels Na+, Ca2+, and K+ 2 types: Gated Channels have to be opened by a stimulus that changes proteins shape Carrier Proteins doors that allow one solute at a time (uniport) What is the rate limiter for facilitated diffusion? saturation all the doors are full; can only go so fast

14 Osmosis The movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane Movement controlled by water potential difference 3 solution types: Hypotonic high water potential outside the cell; water flows into the cell (turgor pressure) Hypertonic low water potential outside the cell; water flows out of the cell (plasmolysis) Isotonic equal water potentials; water flows in and out at same rate

15 Active Transport The energy-consuming transport of molecules or ions across a membrane against a conc. gradient made possible by transferring energy from respiration 3 main functions: Brining important nutrients into the cell Removing waster from the cell Maintaining concentrations of ions across the membrane What ions are most important? H+, Na+, K+, and Ca2+ Ions create membrane potential electrical potential difference between sides of membranes

16 Active Transport Na+/K+ Pumps:
Essential for all animal cells and the nerve system of complex organisms 1 ATP 3 Na+ out and 2 K+ in Generates membrane potentials from -20mV to – 200mV Electrochemical gradient concentration gradient produces both a movement of chemicals and an electrical charge

17 Bulk Transport Exocytosis: What limits exocytosis rates? Endocytosis:
Remove waste material and release secretions Vesicle fuses with plasma membrane What limits exocytosis rates? Cell size; plasma membrane can only grow to a certain point Endocytosis: Bulk-phase (pinocytosis) Cell pulls in part of ECF through the vesicle; non-specific What might trigger this? Cytosol is too thick; lack of general nutrition; reduce plasma membrane

18 Bulk Transport Receptor mediated Endocytosis
Receptor protein in membrane binds to specific substrate Receptors form coated pit after activation and pull in molecule Bind to lysosome to breakdown contents Phagocytosis “cell eating” Cell consumes whole other bacteria cell for energy or defense (white blood cells) Pinocytosis “cell drinking” Cell consumes fluid from ECF


Download ppt "Membranes and Transport Unit 4"

Similar presentations


Ads by Google