General Biology I - Plasma Membrane Structure & Function

Boundary that seperates living cell from surroundings in and out of the cell

Plasma membrane

The plasma membrane is

composed of phospholipids and proteins

Phospholipids

Made of glycerol, 2 fatty acids & phosphate group

Glycerol

3 Carbon Chain that has hydroxyl groups on each carbon

Fatty acids are

long hydrocarbon chains with carboxyl groups

Fatty acids are

very hydrophobic

Phosphate group is

hydrophilic

The phospholipid bilayer

made of 2 layers of phospholipids

Both the inside and outside of cells

contain H20

Due to H2O presence, the phospholipids

self-assemble into the bilayer while the hydrophilic heads will orient to outside while tails orient to inside

Nothing in the plasma membrane is

static

The plasma membrane has a different concentration than the cell

Consistency is like salad oil

Hydrophobic interactions

Hold hydrophobic molecules together, Hold Fatty acid tails together in the bilayer

Proteins are normally clustered

with growth

Integral proteins

Proteins that are partially or formally imbedded into the membrane

Peripheral Proteins

Proteins that sit on the surface of the plasma membrane

Glyco-

is a short chain of carbohydrates

Glycoproteins and Glycolipids

Act as nametags for the cell

Glycoproteins

Sugar chains attached to proteins

Glycolipids

Sugar chains attached to fats

PM has a consistency of salad oil due to

hydrophobic interactions and Sat v. Unsat FA

Different species will have

different concentrations of Fatty Acid types

Cholesterol

type of lipid that is found in Animal Plasma Membranes acts as a fluidity buffer and maintains fluidity of Plasma Membranes

Cholesterol also

wedges itself in between Fatty Acids

Plasma membrane is

selectively permeable which allows certain molecules to cross easier than others

Difference in the amount of substance across a membrane

Concentration gradient

Passive transport is the movement of

High to low concentration

No additional energy is required to move

molecules in passive transport

Simple diffusion

movement of molecules from high to low conc until equilibrium is reached

Equilibrium

State where molecular concentration is equal throughout

Molecular motion still occurs but

no net movement in molecules (isotonic)

Osmosis

Movement of H20 from low solute to high solute concentration

Water can move but

sugar does not due to size

H20 forms hydration shells around solute and

H20 is not able to move because of the barrier

Tonicity

Ability of a cell to gain or lose water

Solutes cannot

cross the plasma membrane

Isotonic

Equal solute and no net movement

Animal Isotonic

Perfect

Plant isotonic

Flaccid, cells PM is not pushed against cell wall

Hypertonic

more solute on outside than on the inside

Hypertonic Animals

Crenation

Plasmolysis

Hypertonic Plants

Hypotonic Plants

Erect due to turgor pressure

Hypotonic Animals

Cell lysis

Facilitated diffusion

movement of molecules that are polar and ions fro m high to low concentraitons

Channel Proteins

Hydrophilic tunnel that moves molecules

Carrier Proteins

Protein shape changes when molecule binds & shape changes

Tunnels will be specific molecules

for specific molecules

Active transport

against the concentration gradient with the use of ATp

Sodium Potassium Pump

3 NA out of cell 2 K into cell

Sodium Potassium Pump Steps

1. 3 Na bind to the cytoplasm

2. Na binding causes phosphorylation of ATP into ADP and Pi

3. Protein changes shape and moves 3 Na outside

4. K will bind to protein & releases phosphate group

5. Protein shape will be intact

6. K enters the cell

Bulk Transport

Need to move in bulk if they are large

Exocytosis

Secretion of molecules outside of the cell

Endocytosis

MOvement of molecules into the cell

Exocytosis Steps

1. Materials are at the golgi

2. Vesicles move to plasma membrane

3. PM and vesicle will bind to each other

4. Vesicles become a part of plasma membrane

Endocytosis

Phagocytosis, Pinocytosis, Receptor-Mediated Endocytosis

Phagocytosis

Cell-eating non-specific substances

Pinocytosis

Cell drinking non-specific substances

Receptor-Mediated ENdocytosis

Specific substances by receptors