3. Transport across membranes

What is the fluid mosaic model of membranes?

Fluid- phospholipid bilayer in which idividualphospholipids can move

Mosaic- extrinsic & intrinsic proteins of different sizes and shapes embedded

What is the role of cholestorol in membranes?

Sterioid molecule in some plasma membranes

connects phopholipids and reduces fluidity to make bilayer more stable

What is the role of glycolipids in membranes?

Cell signalling and cell recognision

What are the functions of extrinsic proteins in membranes?

• Binding sites/ receptors

• Antigens

• bind cells together

• involved in cell signaling

What are the functions of intrinsic proteins in membranes?

• Electron carriers

• channel proteins

• carier proteins

What is the functions of membranes within cells?

• Provide internal transport system

• Selectively permiable to regulate passage of molecules in/ out of organelles

• Provide reaction surface

• Isolate organelles from cytoplasm for specific metabolic reactions

What is the fuction of the cell surface membrane?

• Isolates cytoplasm from extracellular environment

• Selectively permiable to regulate transport of substances

• involved in cell signalling/ recognision

What factors can affect permiability?

• Temperature

• PH

• Use of solvent

What is osmosis?

Water diffuses across semi-permiable membranes from an area of high water potential to an area of lower water potential until equalibrium is reached

What is water potential?

Pressure created by water molecules measured in kPa

What is simple diffusion?

Passive process thatrequires no energy from ATP. Net movment of small molecules directly through a bilayer froman area of high oncentration to an area of lower concentration.

What is faccilitated diffusion?

A passive process where specific channel or carrier proteins with complimentary binding sites transport large ions down the concentraton gradient.

How do channel proteins work?

Hydrophobic chanels bind to specific ions = one side of the protein closes the other opens

How do carrier proteins work?

Bind to complimentary molecule = conformationsal change releases molecule of other side of membrane

What factors affect the rate of diffusion?

• Temperature

• Diffusion distance

• Surface area

• Size of molecule

• Difference in concentration

What is Ficks law?

Surface are x distance in concentration / diffusion distance

How are cells adapted to maximise the rate of transport acress their membranes?

• Many carrier/ channel proteins

• Folded membranes increase surface area

What is active transport?

Active process. ATP elease phosphate group that binds to carrier protein causing it to change shape

Transports molecules from area of low concentration to higher conc

What is co-transport?

Movement of a substance againstthe concentration gradient couples with the movement of another substance down the concentration gradient.