Chapter 10: Membrane Structure

Lipid Droplets

-Excess lipids stored by cell -Energy/food source/membrane synthesis -Neutral lipids (triacylglycerides and cholesterols) -Form rapidly when cell is exposed to high concentrations of fatty acids -Formed from discrete regions of the ER

micelles

-formed by soaps/detergents -contain one tail -usually "traps" dirt on the inside -round in structure -- NOT made by phospholipids

Majority of lipids that make up the phospholipid bilayer are

...

How do cells restrict the movement of proteins to localized membrane domains

1. Either corralled and tethered to the underlying cello cortex or to molecules of extracellular matrix 2. In the epithelial cells in the gut, transport proteins are confide to the apical domain by a TIGHT JUNCTION, limiting nutrient uptake to the apical surface

types of mobility a phospholipid has in the bilayer

1. lateral diffusion 2. flexion 3. rotation NO flip flopping

What type of distribution do molecules of the plasma membrane exhibit?

ASYMMETRICAL 1. Lipid composition of the monolayer differs; more bulky groups in outer layers, more negative charged groups in inside 2. All carbohydrate residues on glycolipids and glycoproteins are on the exterior surface of the plasma membrane.

pH of a solution will cause COOH (carboxyl) of a hydrophilic head to become ____

COO-

Neutral lipids

Do not contain hydrophilic head groups --Exclusively hydrophobic

When a cell is suddenly exposed to a high concentration of fatty acids...

Lipid droplet is formed

Action groups

Organic functional groups/side chains Methyl, hydroxyl, carboxyl, amino etc.. Action groups are where discrete changes take place on proteins

What are the most abundant membrane lipids?

Phospholipids /phosphoglycerides

Third asymmetrical property

Proteins are embedded in the bi-layer in a specific orientation

what is the cell surface (of the membrane) coated with?

THE GLYCOCALYX -a carbohydrate layer of oligosaccharides attached to glycolipids and glycoproteins and longer polysaccharides and longer polysaccharide chains attached to proteoglycans

In vivo

Within a living organism

Tight Junctions

a belt of proteins that form a SEAL to the adjacent cell, creating a diffusion barrier to protein movement

Aquaporin

a channel proteins that passively transport water molecules through a narrow passageway created by a group of alpha helices

the plasma membrane

a selective barrier surrounding all cells. Semi permeable due to proteins and lipids

The Cell Cortex

a supporting network of fibrous proteins on the cytosolic face of the plasma membrane. -Part of the cytoskeleton -It's function is support and protection -restricts protein movement in the lipid bilayer

asymmetrical property

all types of membrane proteins are associated with a membrane in a specific orientation

Why are RBCs used to study the plasma membrane?

because they contain only a plasma membrane, having lost all internal membranes during development. During experiment--lyse to break the membrane form the hemoglobin

Temoerature and fluidity of the membrane

cells grown at higher temperature will have longer chains and fewer unsaturated fatty acids

lipid domains/lipid rafts are rich in _____

cholesterol --this causes the migration of proteins **add more**

Phospholipids

contain a hydrophilic head attached at 3rd position and fatty acids (hydrophobic tail) attached to the first 2 positions of glycerol

The organelle membranes of eukaryotic cells contain

different proteins + different lipids that contribute to organelle's function

In all membrane proteins what type of bonds are found on the extracellular surface only?

disulfide bonds

Triglycerides

fatty acid with 3 glycerols attached

how is the lipid component arranged in biological membranes

in a 2-sheet layer of molecules called a lipid bilayer

cytosolic

inside

bacteriorhodopsin

is an archaebacterial protein that uses light energy to drive the transport go H+ across the plasma membrane -Polar side chains on the interior bind and actively transport H+ across the plasma membrane -uses a molecule of retinal to absorb light -contains 7 transmembrane alpha helices -CALLED A PUMP! a multipass transport pump

Cholesterol's effect on the membrane

it intercalates between phospholipids with the hydroxyl group of cholesterol oriented toward the exterior of the bilayer to tighten packing and decrease (enhances) permeability of the membrane

Cis double bonds ___

kink the phospholipid tail to keep fluidity at low temperatures

Fluidity depends on...

lipid composition and temperature. Membranes are less fluid at lower temps.

glycolipids

lipid substances with covalently linked sugar groups (monosaccharides, oligosaccharides, polysaccharide [longest] ) that are key structural elements in cell membranes. No phosphates Instead have sugar which increase hydrophilic nature of the head Abundant in nerve cells

fluidity of the membrane

membranes exhibit fluidity lipids and proteins are free to diffuse and rotate in 2 dimensions within each layer. The tails = WILD & CRAZY! not prized and the membrane is moving all the time. It can spin and flex but hard to flip flop.

Cytostolic face has what?

more negatively charged head groups than outer face

cis

natural fatty acids

trans

not natural fatty acids

unsaturated fatty acid

one or more doubled bonds usually produces 'kinks' or bends in tail takes up more space

In vitro

outside of the living organism (test tube, plate, petri dish)

phospholipid bilayer

phospholipids form a n=bilayer with hydrophilic head groups facing water on each surface while hydrophobic tails are excluded from water in the interior of the bilayer sealed compartment with no free edges (unlike fatty acids) Driving force = hydrophobic forces (exclusion of water)

Explain how the cortical skeleton/cortex "corrals" proteins

proteins are usually drifting around like big ice bergs in membrane but sometimes their movement is limited due to corral-like structure of the cortex.

transmembrane proteins

proteins that penetrate through the membrane...contained in the eukaryotic and prokaryotic phospholipid bilayers

what is the eukaryotic version of bacteriorhodopsin?

rhodopsin involved in vision and a family of more than 150 seven-span transmembrane proteins

what decreases fluidity of the membrane?

saturated and longer chains

Hydrophobic R groups

side chains of proteins contact the interior of the lipid bilayer. Exposed on outside of helix. Hydrophilic groups of the peptide bonds on the interior=forms hydrogen bonds parallel to the axis of the helix.

saturated fatty acid

straight no double bonds or bends in tail

The glycocalyx only occurs on which side. What is it's function?

the noncytosolic side. -It protects and lubricates the cell (increase solubility) -Play role in cell-cell recognition and adhesion

How far do proteins span compared to the plasma membrane

they span the membrane or associate with one surface

Membrane protein functions

transport molecules act as receptors catalyze biosynthetic processes

Porins

transport proteins that use a beta-barrel to form a pore across the bilayer abundant in gram-negative bacteria

what increases fluidity of the membrane?

unsaturated and shorter chain fatty acids