Exam 2 - Cell/Mol Phys

Chapters 11 -

Plasma Membrane

Thin transparent fatty-film like layer that separate and protect cellular components from the outside environment

Dynamic structure that can change its constituent molecules upon needs

Cell membranes act as selective ______ barriers

permeability

Cholesterol content in the biological membranes

• 20% of plasma membrane

• tend to stiffen the membrane (but depends on the temperature)

Synthesis of phospholipids - the Endoplasmic Reticulum

Newly synthesized membranes get exported out via vesicles

The enzymes are bound to the cytosolic side of the ER, depositnig the cytosolic side of the membrane

Phospholipids and glycolipids are distributed ______ in the plasma membrane lipid bilayer

asymmetrically

Glycolipids

Mainly located in the plasma membrane (not other membrane bound organelles)

Glycolipid molecules acquire their sugar groups in the Golgi lumen where the glycosylating enzymes reside

The membrane spanning segment of the membrane protein tends to be _____

helical

Integral membrane proteins can be removed only by ______ treatment

detergent

A transmembrane hydrophilic pore can be formed by multiple ____ helices

a

Hydrophilic side containing amino acids are oriented internally, shielded by hydrophobic amino acids from the _____ _____

lipid bilayer

Detergents

Small, amphipathic, lipidlike molecules (usually with only single hydrophobic tail)

SDS

A strong ionic detergent that can also denature proteins

Triton X-100

A mild nonionic detergent

Studying the structure of membrane proteins

Extraction from the membrane is not easy because membrane proteins are not stable outside the membrane

Solubilizing membrane lipid disrupts the membrane composition and separate the membrane proteins from the lipid

Porin proteins form ____ _____ channels in the outer membrane of a bacterium

Water filled

_____ acts as a proton pump

Bacteriorhodopsin

• 7 alpha helices

• polar amino acids are involved in the H+ transfer process

• retinal in our eyes also bind to a protein with a structure similar to bacteriorhodopsin

The ____ blood cell membranes as a model structure for studying plasma membrane structure

red

Erythrocyte

mature red blood cell

Spectrin

Long, thin, flexible rod

Forms a meshwork that provides support for the plasma membrane and maintaining the cell shape

Anchored by attachment proteins that bind to transmembrane proteins

Spectrin mutation can result in

anemia (fewer red blood cell count due to fragility of the cell resulted from abnormal shape)

Human-mouse hybridoma experiment

A landmark experiment that demonstrated membrane fluidity and mobility of membrane proteins

Eukaryotic cells are coated with sugars (extracellularly)

Oligosaccharide chains - 3 to 50 units

Membrane proteins are restricted to a ____ ____of the plasma membrane of an epithelial cells in the gut

particular domain

Cell membrane selectivity allows the cell to maintain a chemically distinct

microenvironment

Membrane proteins can be classified as ____ or ____ proteins based on the relative placement with respect to the membrane

Integral or peripheral

Phosphatidylcholine

The most common phospholipid in cell membranes

Hydrophobic interactions

Exclusion from water

Different types of membrane lipids

Phosphatidylserine (phospholipid)

Cholesterol (sterol)

Galactocerebroside (glycolipid)

• the most abundant glycolipid component of myelin

Fat (Triacylglycerol) =

1 glycerol + up to 3 fatty acids

Fat molecules are ____ while phospholipids are ____

hydrophobic, amphipathic

Phospholipid bilayer in aqueous environment

Head - hydrophilic

Tail - hydrophobic

This configuration is thermodynamically most stable for the lipid molecules

The fluidity of membrane depends on

1. phospholipid composition

2. the nature of the hydrocarbon tails

3. the amount of cholesterol (animal cells)

Phospholipid bilayer is NOT a ____ structure

static

Shorter tail

less interactions between tails; increase in fluidity

More double bonds in the tail

Kinks interferes with packing closely; increase in fluidity

Some cells can change the composition of membrane lipids to adjust its ___ as an adaptation measure

fluidity

Why is maintaining membrane fluidity important for the cell?

Some proteins need to be mobile within the membrane

Allows lipids contents mixing when needed

Scramblase (ER)

Flippase (Golgi)

The lipid bilayer is ____

asymmetrical

Phosphatidylinositol molecules are concentrated on the ___ side of the plasma membrane, mediating signals from the outside to the inside of the cell - minor species

cytosolic

The amino acid backbone in a polypeptide is ___ and ____

polar and hydrophilic

Transporters

Na+ pump

Ion channels

K+ leak channel

Anchors

integrine

Receptors

platelet derived growth factor (PDGF) receptor

Enzymes

adenylyl cyclase

Detergents are

amphipathic

FRAP: Fluorescence Recovery After Photobleaching

A technique to study the dynamic behavior/movement of molecules

Requires GFP fusion to the protein of interest

Lectins

Sugar binding proteins

Mild ____ can be used to solubilize and reconstitute functional membrane proteins

detergents