6. biological membranes✅

What makes fatty acids hydrocarbon carboxylic acids?

they have a large hydrocarbon tail and a polar carboxylic acid head group

Why are fatty acids classified as amphipathic?

they have a polar head group, but are more hydrophobic than hydrophilic

What is a saturated fatty acid?

no double bonds

What is a monounsaturated fatty acid?

has one double bond

What is a polyunsaturated fatty acid?

multiple double bonds

What is a cis double bond?

H atoms are on same side of the bond

What is a trans double bond?

H atoms are on opposite sides of the bond

What conformation are most naturally occurring double bonds in?

cis

How do we name fatty acids?

-alpha carbon is second carbon
-beta carbon is third carbon
-omega carbon is last carbon (methyl)
-first number indicates # of carbons
-second number indicates # of double bonds
-superscript indicates location of double bonds
-must indicate if the double bonds are trans

What is the general formula of fatty acids?

CH3(CH2)nCOOH

What changes a fatty acid from being amphipathic to amphiphilic?

reducing the number of hydrocarbons

What effect do cis double bonds have on fatty acid shape?

produces a kink/bend in the molecule

Which fatty acids have maximal van Der Waals interactions?

saturated, because they can align closely

Why is a mixture of saturated and unsaturated fatty acids liquid at room temp?

double bonds create bent shapes, cannot pack as tightly, less van Der Waals interactions

What two factors affect fatty acid melting points?

length and unsaturation

How does fatty acid length affect melting point?

longer = melt at higher temps
shorter = melt at lower temps

What does melting point reflect?

amount of energy required to separate individual molecules in a solid from one another

Saturated fatty acids melt at temps.

higher

Unsaturated fatty acids melt at temps.

lower

Are cis or trans fatty acids harder to break?

trans

Do cis or trans bonds create a larger bend in the molecule?

cis

What do fatty acids form in water and why?

micelle; because they have a cone shape

What is an ester bond?

a bond formed by a condensation reaction between glycerol and a fatty acid

How are fatty acids stored?

as triacylglycerides

Are TAGs amphipathic?

no, non polar

What is an acyl group?

formed by the removal of one or more hydroxyl groups from a carboxylic acid. contains a double bonded oxygen atom and an alkyl group

What is the general formula for an acyl group?

CnH2n+1O

What are the most common type of TAGs?

ones with variable fatty acids. one fatty acid may be saturated, or have some or many double bonds

What do glycerophospholipids form?

leaflets, not micelles

What is the structure of sphingolipids?

have a very large polar head group

What are sphingolipids involved in?

cell cell communication

Does cholesterol form leaflets?

no, but is part of both inner and outer leaflet

What parts of glycerophpospholipiids can vary?

head group and tails

What part of glycerophospholipids does not vary?

glycerol backbone

What bond links the phosphate and glycerol in glycerophospholipids?

phosphoester bond

What is the structure of cholesterol?

-four carbon rings
-sterol head group (OH)
-weakly amphipathic

Is cholesterol found in bacteria?

no

Is cholesterol found in plants?

yes in relatively low levels

How can excess cholesterol be stored?

modified with a fatty acid forming an ester bond with OH, eliminating amphipathicity

What is the role of cholesterol?

membrane lipid which maintains fluidity and rigidity

Why do glycerophospholipids form bilayers?

they are cylindrical

Does cholesterol form membranes alone?

no. its head group is too small and its fatty acid chain is too short

What allows the membrane to be fluid but stable?

non covalent assembly

How is cholesterol found in the bilayer?

almost entirely buried

What is the melting temperature of a bilayer?

the temperature of its transition from an ordered gel phase to a more fluid (liquid) crystalline phase

What it the fluidity of a membrane the function of?

temperature and lipid composition

Membranes with longer saturated chains have _ transition temperatures.

higher

Membranes with shorter _ chains have lower transition temperatures.

unsaturated

What effect does cholesterol have at high temperatures?

because it it rigid and planar, cholesterol limits the rotational movement of neighbouring acyl tails, thereby increased van Der Waals interactions

What effect does cholesterol have at lower temperatures?

inserts between the phospholipids and prevents them from clustering together and stiffening

What blurs the distinction between the gel and fluid state?

cholesterol

The transition temperature is _ for an artificial membrane.

sharp

The transition temperature is not sharp for ___ membranes.

biological

How do membranes adapt to decreasing temperatures?

more unsaturated fatty acids and shorter fatty acids are incorporated into membrane lipids

How do membranes adapt to increasing temperatures?

more saturated fatty acid and longer fatty acids are incorporated into membrane lipids

In what direction do lipids move freely in the bilayer?

laterally

Why do lipids not flip flop?

there is a significant energy barrier associated with desolvating a polar head group to move it through a hydrophobic barrier

What increases the rate of transverse diffusion?

flippases and floppases

What is an integral membrane protein?

Transmembrane, spans entire width of membrane and has both hydrophilic and hydrophobic portions

What is a peripheral membrane protein?

A protein held close to the membrane through H bonds and ion pairs

What is a lipid linked membrane protein?

a protein where the protein is not actually in the membrane, but rather is attached to a lipid which is attached to the membrane

Why do integral membrane proteins have hydrophobic amino acids on their surface?

to interact with the acyl tails of the bilayer

How can integral membrane proteins be separated from the membrane?

detergents which disrupt the membrane

What are the amino acids that form a transmembrane alpha helix?

hydrophobic

What do beta barrels do in the membrane?

create a hole in the outer mitochondrial membrane

What is the movement of proteins in the membrane limited by?

cytoskeleton

How can smaller membranes pass the lipid bilayer?

simple diffusion

What does the rate of simple unmediated diffusion depend on?

concentration gradient, lipid solubility, size of molecule

What does membrane transport require?

proteins

What energy do ion gradients harness?

potential

What do porins and ion channels enable?

passive transport via membrane spanning pores

What are porins?

-relatively non specific, water filled pores in the centre of a beta barrel
-most are trimers
-each subunit contains a pore

What are ion channels?

-channel is formed between subunits
-highly selective

Is a K+ ion channel simple diffusion?

no

What does selectivity of channels depend on?

size of the pore and the properties of the side chains placed there

How do transporter proteins work?

change conformation, as they do not have membrane spanning pores. extremely selective

Are transporter/carrier proteins passive or active transport?

have both a passive and active component

What are the three classifications of carrier proteins?

uniport, symport, antiport

What are primary active transporters?

uses ATP as the source of free energy (can also use energy of oxidation)

What are secondary active transporters?

uses an ion gradient as the source of free energy

Can you have a secondary active uniporter?

no

Can you have a primary active uniporter?

yes

What is the Na+ K+ ATPase?

primary active transporter

How many concentration gradients are formed with the sodium potassium pump?

2. high [Na+] outside, high [K+] inside

What type of transporter is the sodium potassium pump?

electrogenic antiporter

What is the purpose of sodium potassium pump?

-maintain resting membrane potential
-effect transport
-regulate cellular volume

What are the steps of the sodium potassium pump?

1) bind 3 Na+ on the inside
2) phosphorylate
3) undergo conformational change
4) Release 3 Na+ to the outside
5) Bind 2 K+ on the outside
6) Dephosphorylate
7) undergo conformational change
8) release 2 K+ to the inside

What is the activity of the sodium potassium pump determined by?

size of the concentration gradient

What is the Na+ glucose transporter?

-secondary symporter that moves sodium and glucose into cell
-uses energy from sodium moving down its concentration gradient to move glucose up its concentration gradient

What is the glucose uniporter?

allows downhill, passive movement of glucose from epithelial cell to blood