unit 2 membrane structures and function

The ______ _______ is semipermeable

and selectively permeable

plasma membrane

_________ most abundant lipids in

plasma membrane

Phospholipids

amphipathic

hydrophobic and hydrophilic regions

1972 Singer and Nicolson -

fluid mosaic model

Proteins ______ in lipid bilayer

embedded

Phospholipids in membrane move laterally

~10^7 time per second

Some lipids, proteins move flip-flop

~once a month

Plasma membranes are _____

dynamic

phospholipid fluid

unsaturated hydrocarbon tails with kinks

phospholipid viscous

saturated hydrocarbon

Temperature

cool → gel

Tightly packed tails

warm → fluid

Cholesterol

Stabilizes membrane fluidity with changing temperature

Can make up to 50% of membrane!

Can make up to ___ of membrane!

50%

Membrane fluidity affected by:

1. Type of phospholipid

2.Temperature

3. Cholesterol (lipid)

Membrane Proteins and Their Functions

Mosaic of proteins embedded in lipid bilayer

Proteins determine membrane’s functions

Proteins

1. Peripheral or

2. Integral (Transmembrane)

3. Integral (monotopic)

1. Receptor proteins for signal transduction

Insulin receptor bind

insulin → sends

signal into cell →

(many signals) →

glucose enters cell

2. Channel proteins for passage of water or ions through a hydrophilic core

Millions of ions (Cl-)can pass through at a time

Aquaporin

a channel for water

3. Transport proteins

Glucose transporter shuttles glucose across membrane into cell

4. Cell-cell recognition

Blood groups = carbohydrate attached to protein

5. Intercellular joining proteins

Gap junctions allow passage of small molecules between cells

6. Extracellular ______ proteins

matrix

7. Membrane _____

enzymes

Lipid Bilayer-

selectively permeable

Lipid Bilayer-selectively permeable

Hydrophobic molecules dissolve in lipid bilayer and pass through membrane rapidly

Passive transport =

no energy used

Molecules have kinetic energy and move randomly

t/f

t, kinetic energy and move randomly

Diffusion

Molecules diffuse down their concentration gradient from high to lower concentration until equilibrium

Diffusion ____ a membrane

across

Osmosis

Water diffuses across membrane from region of higher water concentration to the region of lower water concentration until equilibrium

Osmosis=

water!

Tonicity

ability of solution to cause cell to gain/lose water

Isotonic solution

same as in cell no net water movement across membrane

Hypotonic solution:

less in the solution than inside cell

Lysis

burst

Hypertonic

concentration greater outside than inside cell

cell loses water

Crenation

shriveled

flaccid

limp

Hypotonic solution →

cell (vacuole) swells

Cell wall opposes uptake →

turgid (firm)

ATP

required to move solutes against their gradients

what is this?

Sodium-potassium pump

Sodium-potassium pump on the outside

Na+ high

K+ low

Sodium-potassium pump on the inside

Na+ low

K+ high

step to Sodium-potassium pump

1. Cytoplasmic 3 Na+ bind to pump

2. ATP needed

3. Na+→ out of cell

4. Extracellular 2 K+ bind to pump

5.K+ → inside cell

WHICH ONE REPRESENTS THE CHANNEL PROTEIN?

Facilitated diffusion

Why do cells need pumps?

Maintain membrane potential = voltage difference across membrane

Inside of cell less electronegative than out

t/f

f, more

chemical =

concentration gradient

electrical =

membrane potential

Passive transport has NO ____ think diffusion and facilitated diffusion

ATP

Active has ATP is need or being used

t/f

True, atp is active transport

Bulk transport=

Active transport

Exocytosis (active transport)

-Secrete products from cell

-Vesicles

Endocytosis

cell takes in large items by forming vesicles from membrane

Phagocytosis

for large particles

Pinocytosis

for fluids/small molecules

example of Endocytosis

White Blood Cells Engulfing Bacteria

Exocytosis an example

Saliva Secretion from Salivary Glands