Bell Work

• What is the difference between osmosis and diffusion?

• What is similar between osmosis and diffusion?

Biology – Lecture 45

Facilitated Diffusion and Active Transport

Facilitated diffusion

• Also called carrier-mediated diffusion• The movement of molecules across the cell

membrane via special transport proteins that are embedded within the cellular membrane.

Why Use Facilitated Diffusion?

• Many large molecules (glucose, etc) are insoluble in lipids and too large to fit through the membrane pores.

How Does Facilitated Diffusion Work?

• Large molecules will bind with its specific carrier proteins, and the complex will then be bonded to a receptor site and moved through the cellular membrane.

Why Doesn’t This Use Energy?

• Facilitated diffusion is a passive process: The solutes move down the concentration gradient and don't use energy to move.

What is inside a cell?

Active Transport

• Moves material from area of low concentration to area of higher concentration, and therefore referred to as moving the material "against the concentration gradient“.

Active Transport

• Active transport uses cellular energy, unlike passive transport, which does not use cellular energy.

• Active transport is a good example of a process for which cells require energy.

Why Would a Cell Do this?

• This is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose and amino acids.

Active Transport

• Metal ions, such as Na+, K+, Mg2+, or Ca2+, require ion pumps or ion channels to cross membranes and distribute through the body

How Can it Move against The Gradient?

• By Using ATP– Primary Active Transport

• By Using the Electrochemical Gradient– Secondary Active Transport

Primary Active Transport

• The proteins involved in it are used as pumps• Normally uses the chemical energy of ATP

Secondary Active Transport

• Use an electrochemical gradient• Involve pore-forming proteins that form

channels through the cell membrane

Secondary Active Transport

• Occasionally two substances are transported at the same time.

• One of the two substances are transported in the direction of their concentration gradient utilizing the energy derived from the transport of second substance down its concentration gradient.

Examples of Active Transport

• sodium-potassium pump – maintains cell potential

• electron transport chain - that uses the reduction energy of NADH to move protons across the inner mitochondrial membrane against their concentration gradient.

Example: Sodium-Potassium Pump