Membrane Function, composition, and transport

What are the functions of cell membranes

Regulate the passage of substances in and out of cell and between organelles and cytosol

detect chemical messengers arriving at the cell surface

link adjacent cells together by membrane junction

anchor cells to the extracellular matrix

anchor the cell to its cytoskeleton

What is the plasma membrane?

It is an outer boundary of the cell. It exhibits characteristic trilaminar (outer, inner, innermost) appearance in electron micrographs

What does a more lipid soluble solution do and what did it contribute

It enters the root hair cells more rapidly, it found that the outer boundary of lipid bilayers matched a fatty oil

What is the fluid mosaic model

The core lipid bilayer exists in a fluid state, capable of movement membrane proteins form a mosaic of particles penetrating the lipids

What is diffusion of cell membrane proteins and what did it contribute

It is induced by certain viruses or with polyethylene glycol. Labeled proteins showed that membrane proteins can move

The faces of cellular membranes

all membranes have a cytosolic face and an exoplasmic face

What is bulk membrane (vesicular) transport

The movement of macromolecules such as proteins or polysaccharides into or out of the cell. It requires the expenditure of ATP

What are the two types of vesicular transport

exocytosis and endocytosis

What is exocytosis

it is used to release signals (receptors) into the extracellular environment and to insert newly made proteins and lipids into the plasma membrane. Removes junk too.

What is endocytosis

It is used to allow things to move across the membrane. Debris can be taken in

What are common membrane lipids?

Phosphoglycerides and sphingolipids; they both have long tails (less fluid)

How does temperature affect lipid mobility

It allows them to rotate freely around their long axes and diffuse laterally.

A typical molecule exchanges place 107 times/sec

Can switch to a gel like consistency at lower temperatures

Lipid mobility in the plasma membrane

Phospholipid diffusion is restricted in the bilayer

lipids are confined for brief periods in certain areas and move

feces restricting motion are constructed of rows of integral proteins bound to the membrane skeleton by their cytoplasmic domains

What are membrane proteins and what do they do?

They are proteins that attach to the bilayer asymmetrically (giving it a distinct sidedness

They are responsible for most of the differences between cells in their activities

What are the 3 distinct membrane protein classes

integral, peripheral, GPI-anchored

What is an integral membrane protein

a type of membrane protein that is permanently attached/embedded into the cell membrane

What is a peripheral membrane protein

a type of membrane protein that is attached to either the inner or outer surface of the lipid bilayer

What is a GPI-anchored membrane protein

a type of membrane protein that is located on the cell surface and is anchored to GPI (a glycolipid anchor attached to the cell membrane)

What was FRAP and what did it test

Proteins containing a fluorescent substituent are used to monitor protein movement, a section is bleached, and measures movement of proteins in that area

Why is diffusion limited at 0.5 microns in FRAP

It is limited because of the net effect causing everything to go to equilibrium

What is diffusion

the movement of molecules from one location to another as a result of their random thermal motion. It is limited by distance.

What is osmosis

water tends to flow from a solution of low solute concentration to one of higher concentration

What is a hypotonic solution

a solution where the solute is less concentrated on the outside so the cell swells

What is a hypertonic solution

a solution that is more concentrated on the outside so the cell shrinks

What is an isotonic solution?

no net loss or gain (solution and solute are equal)

How do non-permeable molecules enter the cell

The enter through the assistance of transmembrane proteins

What is passive transport (facilitated diffusion)

a mechanism that likes diffusion, uses no energy, and goes along with the concentration gradient

What is active transport

a mechanism that requires energy to get done, has one or two go against their concentration gradients

Which transmembrane proteins are passive

channels and uniporters

What is facilitated transport (diffusion)

A passive process, doesnt require ATP, in which molecules are transported from high to low concentration

What do channels do

They transport ions, water, and small hydrophilic molecules via facilitated transport

Uniporters (carrier)

The molecule to be transported binds to carrier

upon binding, the carrier changes its conformation (x→ Y)

transported molecule detaches from carrier

• the binding site has a fixed affinity for the molecule being transported

• energy binding triggers the conformational rearrangement that exposes the binding site to the opposite side of the membrane

Which transmembrane proteins are active

Symporters, antiporters, and pumps

(symporters and antiporters are cotransporters (2 reactions))

What do symporters do