Chapter 7 Bio 1406

What does it mean that the plasma membrane is selectively permeable?

Only certain substances are allowed through the plasma membrane

How are plasma membrane selectively permeable?

Proteins are created to allow certain substances to travel through the hydrophobic component of the lipid bilayer

What are the most common lipids in plasma membrane?

Phosplipids

Basic structure of phospholipid (draw)

Phospholipid Bilayer (draw)

Phospholipids are amphipathic, this means that

they contain both hydrophobic and hydrophilic components

The fluid mosaic model:

fluid: explains movement in cell

Mosaic: Model that explains structure of cells

What membrane components can move across the bilayer & how?

Lipids, Proteins; Laterally (side-by-side)

Difference between saturated fatty acids and unsaturated fatty acids

Saturated (dense) fatty acid: no double bond between carbons/hydrogens in skeleton; therefore less movement/space

Unsaturated (non-dense) fatty acid: one carbon bond in carbon skeleton, resulting in “kink” tail; therefore more movement/space

As temperature cools, how does membrane fluidity change

More unsaturated fatty acids in phospholipid, to allow nutrients to come in

As temperature heats, how does membrane fluidity change

Due to excess nutrients in this temperature, phospholipid’s fatty acids become saturated to avoid excessive intake

How does cholesterol affect membrane fluidity?

Applies only to animal cell

Acts as a buffer for fluidity

At cold temps, it increases fluidity to prevent tight packing

At hotter temps, it decreases fluidity to prevent excessive intake

What determines most of a membranes specific functions?

Proteins

Peripheral Proteins

Proteins that are embedded in either the upper or lower phosphate head of the lipid bilayer

Integral Proteins

Proteins that are penetrate through the phosphate head and station themselves inside the hydrophobic tails of lipid bilayer

Transmembrane proteins

Integral proteins that penetrate lipid bilayer to the point they open and exit at the upper and lower phosphate heads

What are six functions of proteins in cell membranes.

1) Transportation of materials

2) Enzyme Activity

3) Receptor Proteins

4) Cell to Cell Identification

5) Joining with other cell membranes

6) Attach to extra cellular matrix and/or cytoskeleton

How do cell recognize each other?

By binding to carbohydrates on surface.

Glycoproteins are most common

Glycolipids are also possible

How do hydrophobic (non-polar) molecules move through lipid bilayer.

Dissolve in lipid bilayer and can move rapidly. E.g. oxygen or carbon dioxide

How do Hydrophilic (polar) molecules move through lipid bilayer.

Ions or polar molecules have a hard time moving through lipid bilayer

Diffusion

The tendency for any group of molecules to spread out evenly over time. Without energy

Passive Transport

Diffusion of substances through plasma membrane without any dedicated energy investment from cells

Equilibrium

As a result of diffusion, molecules are equally spread across both sides of membrane

Concentration Gradient

Solute’s moving from higher concentration to lower concentration

Osmosis

diffusion of water molecules, water will go from lower concertation to higher concentration in order for all substances to achieve equilibrium

Tonicity

The ability of a outside solute to cause a cell to gain/lose water

Hypertonic

The solute concentration OUTSIDE of the cell is higher than the solute concentration inside of the cell. Therefore, the water will leave to cell for the outside.

Hypotonic

The solute concentration OUTSIDE of the cell is higher than the solute concentration inside of the cell. Therefore, the water will leave to cell for the outside.

Isotonic

Solute concertation OUTSIDE of cell is same as inside cell. Therefore, there will be not water movement.

Lysed Meaning

(red cell) For hypotonic solution, water will rush inside cell. Caused the cell to rupture.

Shrivel/Crenation

(red cell) For hypertonic solution, water will try to exit blood cell, causing poles to form.

Osmoregulation

the maintenance of stable solute/water concentrations

Turgid

Hypotonic = Water In = Turgidity

Flaccid/Limp

Isotonic = equal water movement = flaccid

Plasmolysis

Hypertonic = Water Out = Shrinkage/Plasmolysis

Facilitated Diffusion

Transport proteins increase passive diffusion of molecules

Active Transport

Moving substances against their natural concentration gradient with the use of ATP

Active Transport Example

Substance A is unwanted in cell/ Substance B is wanted. A is attached to protein and ATP cell causes phosphate group to attach to protein. Protein shape changes and A is expelled. Substance B is inserted from outside, phosphate group detaches causing protein to restructure into original shape. Substance B is dumped inside cell.

Ion Pumps

Transport proteins that move certain ions AGAINT their concentration gradient with the use of energy (ATP)

Membrane Potential

difference in electrical charges of charged atoms inside membrane and outside membrane

Electrochemical gradient

Two forces that cause the diffusion of ions

The two forces in electrochemical gradient

As name implies:

Electrical: The charges of ions that cause attraction

Chemical: natural concentration gradient

Electrogenic Pump

transport protein that engages in active transport, uses ATP

e.g. sodium-potassium pump (animal) or proton pump (plant/fungi)

Cotransport

active transport indirectly causes another type of transport to happen in cell membrane

Bulk transport

Active transport of large solutes through vesicles (e.g. proteins/polysaccharides)

Exocytosis

Bulk Transport; transport vesicles leave cell membrane and dump contents outside

Endocytosis

Bulk Transport: outside foreign materials are converted by plasma membrane into vesicles that than enter cell

Endocytosis Three Examples

1) Phagocytosis: Food particle is converted into food vesicle by plasma membrane

2) Pinocytosis: Liquid particle is converted into transport vesicle by cell plasma membrane

3) Receptor-mediated endocytosis: the plasma membrane will use receptors to attract specific molecules (ligands) and create them into vesicles.