Chapter II Flashcards by Riley Hrasky

What allows the lipid bilayer to be stable in water?

Hydrophobic interactions
hydrophobic molecules stack together (aggregate) in order to have the least amount of surface area exposed to water

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What are the three major structures of lipid aggregates?

micelles
bilayers
liposomes (spherical bilayer)

what forms depends on the type of lipid and concentration of lipid

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Micelles

wedge shaped individual units, the polar head group is larger than the tail

no water inside the center

*monolayers

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Lipid Bilayer

composed mainly of phospholipids and sphingolipids

smaller bilayers are unstable

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Vesicles (liposomes)

-small bilayers sealed into spherical vesicles
-central aqueous cavity
- responsible for relaying signals
- vesicles have the ability to fuse with cell membranes or another vesicles

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Functions of the cellular membrane?

Define boundaries of the cell
allow for import and export
retain metabolites and ions
sense external signals and transmit info into the cell
provide compartmentalization within the cell
produces nad transmits nerve signals
stores energy as a proton gradient
supports synthesis of ATP

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Characteristics of the Membrane

flexible
composed of two leaflets
forms spontaneously
stabilized by noncovalent forces (hydrophobic effect)
asymmetric

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What does it mean to say the bilayer has asymmetry?

The two leaflets have different compositions

outer leaflet is more positively charged

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What do LTPs (lipid transfer proteins) do?

soluble proteins that have a hydrophobic lipid-binding pocket that carries lipids fro one membrane to another

*can be bispecific - can carry two different types of lipids

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Peripheral membrane proteins

non GPI linked

-either noncovalently attached or linked to membrane lipids
- can be removed from the membrane easily through changes in ionic strength (change pH or increase salt)

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Integral membrane proteins

span entire membrane
can be reversibly removed by strong detergent

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Amphitropic Membrane proteins

attached to membrane through covalent interactions with lipids or carbohydrates attached to lipids

linked to the membrane during specific regulatory events

-biologically regulated
- reversibly removed

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Properties of the Membrane

dynamic and flexible
can exist in various phases and change phases
not permeable to large polar solutes / ions
permeable to small polar solutes and polar compounds
permeability can be increased artificially by chemical treatment

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What types of molecules are permeable to the membrane?

small polar solutes and non-polar compounds

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What types of molecules are NOT permeable to the membrane?

large polar solutes / ions

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What two phases can the membrane exist?

Fluid or gel
- liquid ordered state (gel) = individual molecules don’t move around
- liquid disordered state (fluid) = individual molecules can move around

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Under physiological conditions, what phase is the membrane in?

More fluid-like

Heating causes phase transition from gel to fluid

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Molecules in the membrane that favor the fluid state of the membrane?

Kinked unsaturated fatty acids (interfere with packing)

Short-chained fatty acyl groups

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Molecules in the membrane that favor the GEL state of the membrane?

Long-chain saturated fatty acids (no kinks, can pack well)

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Affect of sterols (steroids) on the bilayer?

sterols interact with phospholipids that contain unsaturated fatty acyl chains, compacting them and restricting motion

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Affect of sterols (steroids) on the bilayer?

sterols interact with phospholipids that contain unsaturated fatty acyl chains, compacting them and restricting motion

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What type of membrane proteins can be removed by changes in ionic strength like pH change?

peripheral

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What type of membrane proteins can be removed reversibly

Amphitrophic

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What type of membrane protein can be removed by detergents?

Integral

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Type of membrane protein that once purified, no longer is associated with lipids

Peripheral

Type of membrane protein that once purified remains associated with phospholipids

integral

What is glycosylation?

attachment of oligosaccharides to proteins - attaching 1+ lipids serves as a hydrophobic anchor or targeting tags occurs mainly on the outer leaflet

Purpose of hydropathy plots

tell what regions of the protein are inside or outside. of the membrane

3 Types of Integral Proteins?

1. Integrins 2. Cadherins 3. Selectins

Name the protein : surface adhesion proteins that mediate a cell's interaction with the extracellular matrix and with other cells

Integrins - carry signals across the pm - heterodimeric, composed of alpha and beta subunits

Name the protein: interact with other of these proteins in adjacent cells, involved in surface adhesion

cadherins

Name the protein: require calcium, part of the blood-clotting process... have extracellular domains that bind specific polysaccharides on the surface of an adjacent cell

selectins

Lipoproteins

- Proteins that contain covalently linked lipid molecules - some are found only on the outer face of the PM (GPI-linked) others only found on the inner face, and some found on both the lipid can become part of the membrane anchoring the protein

What enzymes facilitate flip‑flop diffusion?

lipid translocators

What are the three lipid translocators?

Flippases, Floppases, Scramablases

What lipid translocators use ATP to catalyze the movement of phospholipids across the membrane?

Flippases and Floppases

How are integral membrane proteins firmly embedded into the membrane?

as a result of the hydrophobic interactions b/w the NP core of the bilayer and the NP side chains of the proteins

Type of membrane protein that can be found both in the membrane and cytosol due to its reversibly atttachment

Amphitrophic

Which protein catalyzes the translocation of aminophospholipids phosphatidylethanolamine (PE) and phosphatidylserine (SE) from the extracellular matrix to the cytoplasmic leaflet

Flippases

which protein moves plasma membrane phospholipids and sterols from the cytoplasmic leaflet to the extracellular leaflet

Floppases

which protein can move any membrane phospholipid across the bilayer via the concentration gradient

Scramblases

How are peripheral (non-GPI) linked proteins associated with the membrane?

Through H-bonding and electrostatic interactions

What kinds of interactions allow integral proteins to be firmly embedded in the bilayer?

Hydrophobic interactions b/w the non-polar core of the bilayer and the non-polar side chains of the protein

What is the positive charge rule

Positively charged Lys and Arg residues occur more commonly on the cytoplasmic face

What are lipid rafts composed of ?

clusters of glycosphingolipids and cholesterol (thicken the bilayer) as well as doubly/triply acylated proteins leads to segregation of proteins in the membrane so they can carry out signaling. cascade

Where can caveolin be found?

lipid rafts

These integral proteins form dimers and associate with cholesterol rich regions in the membrane They cause an inward curving of the membrane

Caveolin which form caveola

What makes membranes able to undergo fusion with other membranes without losing their continuity?

Changes in CURVATURE

Why does passive diffusion of molecules across the membrane have a high activation barrier?

b/c passive diffusion involves desolvation, which is energetically costly

What types of molecules can freely diffuse through the membrane ?

Small nonpolar molecules

This type of transport utilizes movement down a concentration gradient, increasing transport rate

Passive transport aka facilitated diffusion

This type of transport moves substrates against a concentration gradient or electrical potential.

Active transport

This type of active transport uses energy provided by a chemical reaction (ATP hydrolysis)

Primary active transport

This type of active transport couples the uphill transport of one substrate with the downhill transport of another

Secondary active transport

Ways in which solutes can cross the membrane

Passive diffusion, active transport (primary/secondary) or ion channels / pores

How does a ligand-gated channel work ?

Binding of a ligand causes allosteric conformational change causing the pore to open

How do voltage-gated channels work?

A membrane potential causes charged protein domain to move --> pore opens

Aquaporins

Allow for water molecules only to flow freely across membrane

What is membrane fluidity affected by?

temp, fatty acid composition & sterol content

Integral proteins that associate with the inner leaflet of the plasma membrane, forcing it to curve inward to form caveolae, which are involved in membrane transport, signaling, and the expansion of plasma membranes.

Caveolins

What does it mean that the lipid bilayer is ampiphatic?

Amphiphatic they contain hydrophilic and hydrophobic regions.

where does glycosylation typically occur?

on the OUTER face of the plasma membrane

Beta barrel characteristics?

- 7-9 residues needed to span a membrane - stabilized by intra-chain H-bonds - every second residue in the membrane spanning segment is hydrophobic and interacts with the lipid bilayer

What are proteins that allow certain polar solutes to cross the outer membrane of gram - bacteria?

porins

This type of lipoprotein is only found on the outer face of the PM

GPI linked proteins

The two types of SNARE proteins involved in NT release?

t-SNARE assemble on the Target protein v-SNARE assemble on the Vesicle membrane

What are the two conformations of glucose transport ?

T1 form: glucose-binding site is exposed to the outer surface membrane T2: glucose-binding site exposed on the inner surface

GLUT 1 transporter

An integral membrane protein with 12 hydrophobic segments, forms 12 membrane-spanning helices --- the helices are amphipathic (residues all NP on one side, all polar on the other)

Type I vs Type II diabetes

Type 1: inability to release insulin Type 2: not enough insulin, reduced ability to recognize inslun

Family of cation transporters that are reversibly phosphorylated by ATP as part of the transport cycle (flippases are in this family)

P-type

Family of transporters that use ATP hydrolysis to drive transport of substrates against a concentration gradient, ATP-binding cassette transporters (floppases are in this amily)

ABC transporters A mutation in the human CFTR (an ABC) results in cystic fibrosis

This type of gated channel is composed of multiple subunits (oligomeric) and the binding of a small molecule ligand causes an allosteric conformational change so that the pore opens

LIGAND GATED

This type of gated channel relies on a membrane potential which causes the protein domain to move and the pore to open

VOLTAGE GATED

Chapter II Flashcards

(73 cards)