BFCP1 S13

S13: Biological Membranes

2 key functions of biological membranes

1. Compartmentation

2. Potential energy gradient: diff concentrations of solutes inside and outside the cell

Translocases

Transport proteins embedded in the membrane

When does PE spike in a membrane?

When a polar/charged molecule crosses, because it is unstable and unfavorable

Facilitated diffusion

No energy needed, molecule moves with gradient

Primary active vs secondary active diffusion

Primary: compound requires ATP to move against gradient

Secondary: compound moves against gradient powered by another compound moving with its gradient (no ATP required)

Channel proteins

Tunnels to allow molecules to move in

Carrier proteins

Molecules bind and change conformation of carrier proteins to allow movement

Transporters/transporter proteins allow for _______ diffusion.

Primary active diffusion

Integral vs peripheral membrane proteins

Which one can be removed with salt/base without dissolving the bilayer?

Integral: embedded in bilayer, can’t be removed without dissolving membrane

Peripheral: bound to membrane surface, can be removed with salt/base

What does it mean for a lipid to be hydrolyzable?

If you treat that lipid with an enzyme or strong base, the fatty acid will be released

What is the only membrane lipid that is not hydrolyzable?

Cholesterol

Glycerophospholipid

Ether glycerolipid/phospholipid

Sphingophospholipid/sphingomyelin

Glycolipid/glycosphingolipid

A lipid is a phospholipid if it contains _______

a phosphate group

A lipid is a glycerolipid if it contains ______

glycerol

A lipid is a sphingolipid if it contains _______

a sphingosine

Glycerophospholipid composition

Glycerol backbone, 2 FAs, 1 phosphate and a head group

Ether glycerolipid composition

Glycerol backbone, 1 ether, 1 FA, phosphate, and head group

Sphingomyelin composition

Sphingosine backbone, 1 FA, phosphate, and head group (choline)

Glycosphingolipid composition

Sphingosine backbone, 1 FA, and 1+ carbs/sugars

FAs are connected to the glycerol backbone via ____ bonds.

ester

Glycerophospholipids are named after their _____. Ex: phosphatidyl_____

head group

Phosphatidic acid

A glycerophospholipid with no head group

Also the precursor for glycerophospholipids

Where does synthesis of glycerophospholipids take place?

ER

Synthesis of _______ requires acyl transferase enzymes and CoA.

glycerophospholipids

Ceramide

Sphingosine + FA

Ceramide + head group =

sphingolipid

Sphingomyelins and glycosphingolipids are examples of _______.

sphingolipids

The head group of sphingomyelin is _____

phosphate + choline

The head group of glycerosphingolipid is ______

1+ sugars/carbs

Ceramides are synthesized in the ______.

Sphingolipids (ceramide + head group) is finished off in the ______.

ER

golgi

Lipid rafts for transportation

Transport of sphingolipids with clusters of cholesterol

A sphingosine is linked to a FA via a _____ bond.

amide

Sphingomyelin is found in which cells? Diseases affecting sphingomyelin will affect what?

Nervous tissue and immune clls

Will affect the brain

What happens if enzymes in the lysosome can’t break down sphingolipids?

Accumulation occurs, especially affecting the brain

Platelet activating factor and plasmalogens are examples of _______

ether phospholipids/glycerolipids

Platelet activating factor vs plasmalogen composition

PAF: glycerol backbone + 1 ester + 1 acetyl group + phosphate + head group

Plasmalogen: glycerol backbone + 1 ester + 1 FA + phosphate + head group

Plasmalogens are synthesized and broken down in ______

peroxisomes

Peroxisomal disorders can lead to (catabolism/anabolism) of _____ lipids and affect synthesis of ______

Peroxisomal disorders can lead to catabolism (aka buildup) of long-chain lipids and affect synthesis of plasmalogens

Zellweger spectrum disorders, RCDP disorders, and refsum disease are all examples of ____

peroxisomal disorders

We ned to have controlled hydrolysis of _______ lipids.

hydrolyzable

Cholesterol is the precursor to _____ and has a characteristic _____ structure.

steroids

4 ring structure

Functions of cholesterol

1. Regulates fluidity of bilayer

2. Regulates stability and permeability

3. Contributes to lipid raft formation

When is cholesterol ester created?

It is acylated: attached to a ____ via a ____ linkage

For storage or transport

Acylated: attached to FA via an ester linkage

ACAT and LCAT enzymes

ACAT: catalyzes the fatty acylation of cholesterol

LCAT: disposes of cholesterol

T/F: membrane lipids are randomly organized

F

In humans, most transmembrane proteins have a ______ shape. This shape requires _______.

alpha helical

a stretch of 20+ consecutive nonpolar AAs

Explain how these components affect fluidity:

1. Temperature

2. Lipid composition

3. Cholesterol

1. Higher temp = more fluid

2. More long or saturated FA = less fluid

3. Cholesterol: acts as a buffer to moderate changes in fluidity

How can fluidity of a membrane be measured?

Fluorescence recovery after photobleaching (FRAP)

Lipid rafts are (thinner/thicker) and (less/more) fluid domains of the lipid bilayer

Thicker, less fluid

T/F: lipid rafts are self-organizing

T

Function of lipid vesicles

Can deliver mRNA or other cargo into the body more stably

Ex: mRNA vaccine for COVID

Glycophorins

In which cells?

Link cytoskeleton to the lipid bilayer

RBCs, notably