CH1010 (19) Cellular Membrane

What are the two types of membrane proteins?

Peripheral = found loosely attached on the membrane surface Integral (transmembrane) = bound within the membrane

Facilitated Diffusion

Protein channels (Na+) and carrier proteins (GLUT-1) control diffusion of ions which can't diffuse through the membrane (passive)

Describe the fluid mosaic model.

Proteins are embedded in the lipid bilayer in an orientated fashion. The membrane structure is dynamic, proteins often have lateral motion (they float along the plane of the membrane like icebergs)

What makes a hydrocarbon interior rigid? Fluid?

Rigid = rich in saturated fatty acids Fluid = rich in unsaturated fatty acids

What two things allow passive transport to occur?

i) small, neutral molecules (O2 and CO2) can simply diffuse through the membrane ii) gap junctions (transmembrane protein channels) present a pore through which small molecules under 1 kDa can pass - eg. osteocytes, connexin 43, PGE2

What releases energy, transfers ATP to ADP?

Hydrolysis

What is the major force in the formation of a lipid bilayer

Hydrophobic interaction

What are the three types of active transport mechanisms?

- uniport - symport - antiport

What are the 3 types of functional proteins?

1) Receptor proteins: transmit extracellular signals into the cell (signal transduction) 2) Transport proteins: move substances in and out of the cell 3) Enzymes

What are the 4 functions of a membrane>

1) Structural boundaries for cells and containers for organelles 2) Semi permeable barriers that allow the flow of substances in and out of cells and organelles 3) Membrane proteins may act as enzymes whose reactions occur on the membrane surface 4) receptor proteins bind specifically to biologically important substances that trigger biochemical responses in the cell.

What are the two mechanisms of transport in and out of a cell?

1) passive transport 2) active transport

How much do proteins move laterally in one second?

2 micrometres per second

What is the percent composition of phospholipids and proteins?

40-50% phospholipids 50-60% proteins

ATP/ADP translocase

A dimer with 2 30kDa subunits that moves the substrate in and product out using the proton gradient AFTER atp synthase creates ATP from ADP

What is active transport?

A process involving the movement against their concentration gradient from low to high. Energy is expended as the transmembrane proteins change conformations to pump materials cross the membrane

What occurs in passive transport?

A process that involves the diffusion of chemicals down their concentration gradient from high to low. No energy is expended.

Lactose permease

A symporter that pushes lactose against a concentration gradient while H+ travels downhill (both moving in the same direction). This is considered secondary active transport because it does not directly use ATP.

What is a proton (H+) pump?

Active transport mechanism. - ATP is consumed - pumping of lactose is driven by H+ ion gradient and flow (secondary active transport)

What happens after fusion? Where is it strongest and why?

After fusion is diffusion to become one full cell. Diffusion is strongest laterally due to the oriented nature of the bi-layer. Transverse diffusion is VERY slow.

ATP/ADP Antiporter

An antiporter that operates alongside oxidative phosphorylation in the inner mitochondral membrane (ATP/ADP translocase)

What lipid is found nearly always in animal membranes?

Cholesterol

Why are membranes more complicated than a simple lipid bilayer?

Due to its composition of proteins.

Describe the structure of a membrane.

Due to the polar and non polar nature of glycerophospholipds, they are considered amphipathic. Polar heads (hydrophilic) - in contact with the aqueous environment Non polar tails (hydrophobic) - buried within the bilayer

What is a complex lipid?

Encompass glycolipids and phospholipids. They typically have amphipathic character and due to their polar/non polar characteristics, they are often a key component in membranes. Lipids containing parts other than or including fatty acids and glycerol. Found in cell membranes, brain/ nervous tissues, myelin sheaths of nerves and blood platelets

What is the interior of a vacuole membrane and why?

Fluid to store H2O, nutrients and waste.

What indicates the fluidity of the structure?

Fusion of unrelated cells

Which molecules are not evenly distributed throughout the membrane?

Lipids (outer and interior) and proteins.

What is an example of an antiporter?

Na+/K+ ATPase - consumes ATP to transport ions in opposite directions

Secondary active transport

Secondary active transport is a form of active transport across a biological membrane in which a transporter protein couples the movement of an ion (typically Na+ or H+) down its electrochemical gradient to the uphill movement of another molecule or ion against a concentration/electrochemical gradient

What happens to phospholipids when they are placed in an aqueous solution?

They self assemble into "micelle-like" structures called vesicles, or a monolayer.

What do complex lipids do in aqueous solutions?

They spontaneously form a lipid bilayer with a back to back arrangement of lipid monolayers with no energy required. Often makeup the membranes around cells and organelles.

Gap Junctions

Transmembrane protein channels that present a pore through which small molecules can pass.