ELEBC Unit 2

7 membrane functions

Compartmentalization
Scaffold for Biochemical activites
Selective permeable barrier
Transports solutes
External signal detection
Intercellular interaction
Energy transduction

Charles Overton

Observed that lipophilic substances easily penetrate to plant root hair cells, proposing they are made from fatty oil

Irving Langmuir

Observed that lipids spontaneously form monolayers in water

Gorter & Grendel

DIscovered that when comparing surface area of RBC and its lipid monolayer, the monolayer area is twice the RBC

Danielli & Davson Model

Proposed that membranes are composed of lipid bilayers and is coated with continous layer of proteins

Improved Davson & Danielli model

Proposed that there are hydrophilic proteins penetrating the bilayer that provides a polar pore

J. David Robertson

States that the membrane is continuous sheet of lipid bilayers occasionally coated with functional proteins on its polar surface

Fluid mosaic model

States that membrane has embedded protein which exists in discontinuous regions and is said to be fluid in nature

Who proposed fluid mosaic model

J. Singer & Nicholson

Fix the error. Fluid mosaic model proposes that membranes are gel-like in nature

False

Fix the error. Fluid mosaic model states that membrane is incapable of movement

False

3 compositions of the membrane

Membrane protein
Membrane lipid
Membrane carbohydrate

Fix the error. Lipid membrane allows diffusion of polar solutes

False

How many carbons required to form a stable bilayer

Between 16 to 22

What are 3 types of membrane lipids

Cholesterol
Phosphoglyceride
Spingholipid

What are 3 membrane proteins

Intrinsic protein
Extrinsic protein
Lipid-anchored protein

What are 2 membrane carbohydrates

Glycoproteins
Glycolipid

True or false. Membrane ratio varies depending on function

True

_____ are _____ featuring small functional head groups attached to glycerol backbone via phosphate ester bonds

Phosphoglycerides, diacylglycerides

Give 6 phosphoglyceride

Phosphatidylcholine (lecithin)
Phosphatidylserine
Phosphatidylethanolamine (cephalin)
Phosphatidylinositol
Phosphatidic acid
Diphosphatidylglycerol (cardiolipin)

_____ are ceramides formed by attaching a _____ chain to a _____ backbone

Sphingolipids, fatty acid, sphingosine

Give 3 sphingolipid

Sphingomyelin
Cereboside
Ganglioside

True or false. Prokaryotic cells possess cholesterol

False

True or false. Cholesterol is a steroid component in the membrane

True

Fix the error. Cholesterol makes up 75% of animal membrane lipids

50%

What are 2 fundamental function of cholesterol

“Mortar” that makes cell membrane impermeable to polar solutes
Regulates membrane fluidity

Fix the error. The lipid bilayer is a continuous unbroken construct with a hydrophilic core

Hydrophobic core

What is liposome

Spontaneous structure formed by lipid bilayers in aq. solution

Lipids give membranes the ability to _____, _____, and _____.

fuse, form network, separate charge

True or false. Membrane lipid composition depends on function

True

True or false. Liposome formation can be used to entrap aqueous fluids

True

Membrane proteins function

Transport
Enzymatic activity
Structural
Signal reception
Energy transduction
Cell identifcation

Give 3 membrane proteins for structure

Spectrin
Actin
Clathrin

Give 3 membrane proteins for transport

Carrier protein
Channels
Active transport proteins

Give 3 membrane proteins for light transduction

Rhodpsin
Bacteriorhodopsin
Reaction center protein

Fix the error. Integral proteins are synonymous with extrinsic proteins

Intrinsic proteins

Fix the error. Membrane proteins are distributed symmetrically across the cell membrane

distrbuted asymmetrically

_____ proteins make up 20-30% of all encoded proteins

Integral

True or false. Integral proteins penetrate through the lipid bilayer

True

Integral proteins are _____ in nature, with _____ domains anchoring them inside the bilayer while also having a _____ regions that forms functional domains outside the bilayer

ampipathic, hydrophobic, hydrophilic

Fix the error. Cell membrane is held together by covalent bonds

Noncovalent interactions, specifically hydrophobic interactions

Channel proteins have _____ cores that form _____ channels in the membrane-spanning region

hydrophilic, aqueous

_____ proteins lack transmembrane segments and located on the cell surface

Peripheral

Fix the error. Peripheral proteins are attached covalently to the membrane and is easily solubilized

attached non-covalently

True or false. The amphipathic nature of membrane lipids allow them to aggregate spontaneously in aqueous environments

True

Peripheral vs Integral in terms of dissociation requirements

Peripheral: Mild conditions are sufficient eg. high ionic strength metal ion chelating agents
Integral: Hydrophobic bond-breaking agents required

Peripheral vs Integral in terms of lipid attachment when solubulized

Peripheral: Soluble, free of lipid attachment
Integral: Has lipids attached when solubulized

Peripheral vs Integral in terms of solubility after dissociation from membrane

Peripheral: Soluble, easily dispersed in neutral aqueous buffers
Integer: Insoluble, often aggregates in neutral aqueous buffers

Give 2 example of peripheral protein

Cytochrome C
Spectrin of erythrocytes

Give 2 example of integral protein

Histocompatibility antigen
Drug & hormone receptors

What is lipid-anchored proteins

Located outside the lipid bilayer, but covalently attached to a lipid molecule embedded to the bilayer

Only small proportion of membrane carbohydrate is present as _____, but mostly in the form of _____

glycolipid, glycoprotein

Glycolipid are _____ and _____ carbohydrates

short, branched

Glycoproteins are _____ and _____ carbohydrate chains

Larger, longer

Fix the error. Membrane carbohydrates can only be found on both the internal and the external surface of the cell

Found only on the external surface of cell

Fix the error. Membrane carbohydrate play no key role in cellular recognition

Play key role, acts as binding site for cell recognition

3 common features of membrane components

Membrane fluidity
Asymmetric ratio distribution
Made of lipid, proteins, carbohydrates

_____ refers to freedom of motion of membrane components

Fluidity

Why is membrane fluidity important?

Make it possible for proteins to move and allows the membranes to assemble and grow

What are 3 dynamic properties of plasma membranes

Movement
Division
Fusion

What are 3 types of movements available in the ell

Lateral diffusion
Transverse diffusion
Rotational motion

True or false. Cell fusion can be induced by viruses

True

_____ is an event where two different types of cell can be fused to produce an organism with a common cytoplasm and a single continuous plasma membrane

Cell fusion

What is the most important environmental factor that affects membrane fluidity

Temperature

Regulation of membrane fluidity can be done by altering? (2)

Changing length of fatty acid present
Changing degree of unsaturation present

_____ is a minor phospolipid found in the mitochondrial membrane and activates cytochrome

Cardiolipid

Fix the error. Phosphatidylethanolamine is found in the mitochondrial membrane and activates cytochrome

Diphospatidylglycerol (Cardiolipin)

_____ is a minor phospholipid present in most membranes and is a source of inositol triphosphate

Phospatidylinositol

Distinguish Peripheral proteins from Integral proteins

Integral Proteins is insoluble/aggregates in neutral buffer solution while peripheral proteins are easily solubillized and easily dispersed

Integral proteins when dissociated often has lipid attachments while peripheral has no lipid attached when dissociated

Integral proteins require strong reagents (eg. detergents) to be denatured while peripheral proteins only need mild conditions (eg. high ionic strength and metal ion chelating agents)

Why is temperature an important factor in membrane fluidity

Because it drives the kinetic thermal energy present in the lipid molecules in the membrane which competes with the noncovalent interaction keeping it together

What is the role of cholesterol in fluidity

Fluidity buffer

_____ is a sterol whose rigid structure _____ fluidity at _____ temperatures and _____ fluidity at _____ temperatures by preventing the membrane from compressing to close at low temperatures

Cholesterol, decreases, high, increases, low

_____ are highly ordered, more fluid and disordered membrane filled regions with _____ and _____ and are often more dense and thicker than surroundings, its job is to create a ideal environment for receptor molecules to bind on to like _____ proteins

Lipid rafts, sphingolipids, cholesterol, GPI-anchored

Selective permeability enables…..

Enables the controlled separation and exchange of materials between the intracellular cytoplasm and the extracellular environment.

Movement across membranes is evaluated by net flux, which represents the difference between the _____ and _____ of materials.

influx, efflux

Diffusion is the spontaneous movement of materials down a concentration gradient from an area of _____ to an area of _____

high concentration, low concentration

What is diffusion

It is the spontaneous movement of materials from a region of high concentration to an area of low concentration

Electrolyte vs non-electrolyte in terms of free energy change

Electrolyte: free energy change is fueled by an electrochemical gradient
Non-electrolyte: free energy change is fueled by concentration gradient

Factors that affect diffusion rate (3)

Polarity
Molecular Size
Ionic strength

True or false. Small uncharged molecules have a hard time diffusing into the lipid bilayer

False

True or false. Small uncharged molecules like O2 N2 exhibit high permeability but requires specialized protein transports

False

True or false. Charged ions exhibit low permeability requiring protein transport to cross

True

What is osmosis

It is the diffusion of water across a semi permeable membrane from a region of low solute concentration to high solute concentration

_____ is the diffusion of water across a semi-permeable membrane from a region of _____ concentration to a region of _____ concentration.

Osmosis, low solute, high solute

What is flux

Movement of nutrients

What are 2 mechanism for cellular transport

Passive diffusion
Active transport

What are aquaporins

Specialized protein channels that allow passive moment of water

True or false. Plants do not have aquaporins

False

In a _____ there is net water gain, leading the cell to _____

Hypotonic solution, swell

In a _____ there is net water loss, leading the cell to _____

Hypertonic solution, shrink

What is uniport

Moving one specific solute in one direction

What is symport

Different solutes in one direction

What is anitport

Different solutes in two directions

Plant cells in hypotonic solution develop _____

Turgor pressure

Plant cells in hypertonic solution develop _____

Plasmolysis

What is facilitated diffusion

It is the movement of solutes mediated by proteins down a gradient

Fix the error. Facilitated diffusion is an endergonic process

Exergonic process

2 main classes of transport proteins

Carrier proteins
Channel proteins

Carrier proteins are also called _____

Permease

What are carrier proteins

Functions by binding specific solutes on one side of the membrane, undergoes conformational change and releases the solute on the opposite side