Lecture 1: Membranes & Lipids

The Structure of Lipids 

Head

• changeable group

• phosphate

• glycerol

• hydrophilic 

Tails

• made up of carbons and hydrogens 

• hydrophobic 

Lipids & Membranes function & definition

Membranes are made of lipids & proteins, they act as a separation of the cell and the outside.

Definition of saturation and it’s implications

Saturation means that a carbon has the maximum number of hydrogens (3), making the bilayer more stiff

Definition of unsaturation and it’s implications

Unsaturation means that the carbon is NOT bonded to the highest number carbons possible (3), creating kinks in the bilayer and making it more fluid.

Amphipathic Definition

Lipids that have components that are hydrophilic (heads) and hydrophobic (tails)

How are lipids differentiated

the combinations of heads and tails and they way they individually differ, serving many diverse functions & lipids.

Sterols

a type of lipid where the head is an OH & it is amphipathic 

Glycolipids

a kind of lipid where the head is a sugar and it is amphipathic 

Cholesterol’s effect on the bilayer 

cholesterol stiffens tha bilayer

Symmetrical & Asymmetrical Bilayers

whether or not the bilayer is the same on both sides,

Things Asymmetrical Bilayers Assist With

1. Cell signaling

2. cell recognition

3. organelle recognition

4. membrane function

Two types of proteins in cell membranes

1. Integral Proteins 

2. Peripheral Proteins 

Intergal Proteins 

Proteins that integrate and interconnect themselves with the bilayer in 3 ways 

• monolayer 

• transmembrane 

• lipid link: protein is covalently attached to the lipid

Also hydrophobic amino acids interact with he hydrophobic tails 

Peripheral Proteins 

Proteins that interact with the bilayer through electrostatic interactions in 2 ways

• a protein integrated with the membrane

• through interaction with the amphipathic parts of the membrane

FRAP: Fluorescence Recovery After PhotoBleaching 

a technique used to test the fluidity of a membrane

FRAP Step by Step

1. Tag a membrane associated protein with GFP

2. Shoot the intense laser at a part of the membrane, bleaching it

3. The membrane will “recover” with non bleached lipids and proteins replacing the bleached 

How quickly it recovers gives us insight on how stiff the membrane is, fast  is fluid and slow is stiff. 

Membrane Proteins

proteins that are associated with the membrane 

Types of membrane proteins 

1. Transporters & Channels 

2. Anchors 

3. Receptors 

4. Enzymes 

Importance & Function of Transporters & Channels

• facilitate transport of molecules that wouldn’t be able to pass through  between the membrane 

• speed up rate of diffusion 

Remember

k 

Channels definition & function 

• protein allow molecules with the correct charge & size pass through the membrane 

• can exist in open confirmation or closed confirmation

• aqueous on the inside 

Transporters deifntion & funciton 

• protein that binds to molecules, changes, the releases molecules on the other side of the membrane 

Concentration Gradient

The idea that molecules will move from areas fo high concentration to low concentration

Going with the grain

• when molecules go from an area of high concentration to an area of low concentration, using passive transport.

• energetically favorable 

Passive transport

• type of transport that occurs when molecules got with the grain

• energetically favorable 

• can happen with channels & transporters 

Going against the grain

• when a molecule goes against the gradient & goes from an area of low concentration to an area of high concentration. 

• energetically unfavorable so energy has to come from somewhere 

• only happens with transporters 

Where the energy for Active Transport comes from

• Light

• ATP becoming ADP

• Gradient Driven Pumps 

Active Transport

• transport that happens for energetically unfavorable movements (ATG) 

• can only happen with Transporters NOT Channels 

• has the 3 ways (name them) 

Symports 

during Active Transport when the molecule hitching a ride and the molecule driving are going in the same direction

Gradient Driven Transport

a way that Active Transport is facilitated where the reaction is coupled with an energetically favorable one

Antiports 

during Active Transport when the molecule hitching a ride and the molecule driving are going in opposite directions