Membrane structure part 1

Plasma membrane does what?

Membrane transport which is the movement of ions or molecules across the membrane in and out.

cell signaling which is the ability to detect changes in the environment and arapt/react, ability to communicate between cells

Cell adhesion which is protein interactions in the plasma membrane promoting binding cells to each other to form essentail nutrients

Part of the fluid mosiac model

1. Leaflet: all sections of the phospholipid, extracellular and cytosolic leaflet

2. assymetrical lipid composition: not all lipids are inside the bilayer

Transmembrane protein

integral proteins, One or more regions physically embedded into the hydrophobic region of the bilayer

Lipid anchored proteins

integral proteins, uses it lipids to get itself stuck into the membrane

Peripheral membrane proteins

peripheral proteins

does not interact themself with the hydrophobic region and they are not bonded covalently to the membrane

What is Fluidity

Molecules remain in close association with one another but can move within the membrane

liquid type of movement

what is semifluid

movement is 2D within the membrane, partial flow and mobility

like thick pastes or gels

What are lipid rafts and what do they do

group of lipids that float together as a unit

they are used for cell signlaing, lipid rafts will go check to see if something is actually wrong within the environment

how does phospholipid tails affect membrane fluidity

1. Shorter tails are less likely to interact – increased fluidity

2. Longer tails form more van der Waals dispersion forces with each other - less fluidity

What does Cholesterol and optimal fluidity do?

1. Stabilizes the membrane…until temperature is introduced

   1. Higher temperatures = membrane less fluid

   2. Lower temperature = makes the membrane more fluid (ex. prevents freezing)

   3. Optimal fluidity is key for normal cell functions; it’s a balance

      between “leaky” and “solid’’

Mobility of the transmembrane protein (this is what physical embedds itself into the plasma membrane/integral protein)

These have similar movements to lipids in the membrane, however they are much bigger

but not all the proteins can move in the membrane

1. may be attached to cytoskeleton

2. may be attached tomolecules outside the cell

phospholipid building blocks

2 fatty acids

1 glycerol molecule

1 phosphate

1 polar head

these come from dietary sources and taken into our cells and proccessed by cytosol by enzymes

what is happening here?

1. Fatty acids are activated by attachment to coenzyme A (CoA). Promotes binding to glycerol-phosphate molecule.

2. Phosphatase removes the phosphate from glycerol, and a polar molecule linked to a phosphate group is attached to the glycerol, allowing for insertion to cytosolic leaflet of smooth ER membra

3. Choline phosphotransferase transfers a phosphate group to diacylglycerol now we have a phospholipid

What happens to the phospholipids now that they are in the smoor ER?

1. flippase in the ER membrane will transfer about half of the new phospholipids to the other leaflet in the ER, so each equal

2. the lipids remaning are then shuttled to other membranes

Lipid transfer involves what?

the extraction of 1 lipid from a membrane diffuse through the cell and then insert into the membrane of interest

Lipid exchange proteins can occur where

between any two membranes

1. Allows for the exchange of lipids between mitochondria and chloroplasts to other organelles

how do transmembrane proteins get to the ER membrane

most have ER signal directing them to the ER

they can also be shuttled out pf the ER via vesicle to other membranes throughout the cell

what is glycosylation

the process of covalently attaching a carbohydrate to a lipid or protein

glycosylation with a lipid is called

glycolipid

glycosylation with a protein is called

glycoprotein

functions of glycosylation

cell surface recognition

protective effect

forms 2 types of proteins glycosylation in eukareotes

1. N-linked: attachment of carbohydrate to the amino acid asparagine by the nitrogen of asparagine's side group

2. O-linked":ONLY IN GOLGI, addition of a string of sugars to the oxygen of serine or threonine side chain. Important for proteoglycans which help with extracellular matrix.

extracellular leaflet

your phopholipid layer facing the outside of the cell

cytosolic leaflet

faces toward the cytosol, aka inside the cell

integral proteins

Embedded into the bilayer and cannot be released from the membrane unless the membrane is dissolved, disturbing the membrane integrity.

Length and Double Bonds of Phospholipid Tails

14-24 carbon atoms, most commonly 16-18 carbon atoms

does flip flop occur in transmembrane proteins

NO, the protein contains a hydrophilic region protruding from the phospholipid head. Making it energetically unfavorable for a hydrophilic region to pass into a hydrophobic region

In Eukaryotic cells the cytosol and endomembrane system work to synthesize most lipids this occurs where?

cytosolic leaflet and smooth er membrane