Biochem Lecture 14- Biological Membranes

What does every cell have?

A (plasma) membrane

What do Eukaryotic cells have?

Membrane-enclosed organelles which include a nuclei and mitochondria

What composes a membrane?

Lipid and protein components

What do membranes do?

Separates and transfers substances in and out of the cell

Formation of lipid bilayers

Are hydrophobic interactions that contain proteins and lipids

Lipid Bilayer

Major force driving the formation of lipid bilayers in hydrophobic interactions

What does the hydrocarbon interior of the lipid bilayer contain?

It consists of saturated/unsaturated fatty acid chains and the fused-ring systems of cholesterol

What is the lipid bilayers held together by?

Held together by noncovalent interactions which includes van der waals and hydrophobic interactions

Bulkier molecules

Outer layer of the lipid bilayer

Smaller molecules

In the inner layer of the lipid bilayer

What isn’t found in biological membranes?

Triacyglycerols

Membrane fluidity

Arrangement of hydrocarbon interior of the bilayer can be ordered and rigid or disordered and fluid

How are saturated fatty acids composed?

Linearly and are rigid

How are unsaturated fatty acids composed?

Disorderly and are fluid

What can cholesterol do?

It can enhance order and rigidity in membranes

What is the purpose of the fused-ring structure of cholesterol?

It is rigid and stabilizes saturated fatty acids by van der waals interactions

What makes animal membranes different from from plant membranes?

Animal membranes are less fluid and more rigid than plant membranes because plant membranes have a higher percentage of unsaturated fatty acids

How are membranes of prokaryotes different?

They are the most fluid and contain no appreciable amounts of steroids

Phase transition of the lipid bilayer

Ordered bilayers become LESS ordered in the presence of heat which increases the mobility of the lipid chains

Structural role of membranes

They separate cellular contents from an external environment

Transportation role of membranes

They transport cells across membranes and can be active or passive

Enzyme action role of membranes

For the membrane; associated proteins to activate enzymes

Receptor proteins role in membranes

They detect extracellular signals and trigger intercellular signaling pathways

Peripheral proteins

Loosely bound by polar or electrostatic interactions (or both) to the outside of a membrane

Integral proteins

Embedded in a membrane and can be removed by signification which could lead to the denaturation of proteins

Anchoring proteins

They span across membranes in an alpha helix or a beta sheet and can be anchored to lipids via covalent bonds

Fluid-Mosaic Model

Proteins and lipid bilayer can co-exist through only noncovalent bonds. “The lateral motion of proteins with patchwork of lipids”

Lipid “rafts”

Local assemblages of lipids and proteins (high concentration of glycolipids and cholesterol)

Passive transport

When a substance enters the cell WITHOUT expenditure of cell energy which is driven by the concentration gradient

Simple diffusion

When an ion moves through membrane without requirement for a carrier

Facilitated diffusion

Substances enter a cell by binding to a carrier protein which no energy is required to do so

Active transport

Moving substances AGAINST a concentration gradient which involves a carrier protein and requires an energy source to move solutes against a gradient

Primary active transport

Uses a sodium potassium ion pump

Secondary active transport

Proton pumps are used with a H+ gradient

What role does ATP play in active transport?

ATP is hydrolyzed to provide “work” needed to pump ions, which is a multi-subunit enzyme

membrane receptors

Large oilgometric proteins with molecular weights by binding an active ligand to a receptor which initiates an action within the cell

Low-density Lipoprotein (LDL’s)

Principle carrier of cholesterol in the bloodstream which contains various lipids and proteins

Phosphorylation of electron transport

Coupling of electron transport to oxidative phosphorylation and requires the complex protein Oligomer (ATP synthase)