is a “mosaic” in having diverse protein molecules embedded in its “fluid” framework – the phospholipid bilayer. 

Most components of the cell membranes move around – they are not stuck in one place!

Some proteins help maintain cell shape and coordinate changes inside and outside the cell through their attachment to the cytoskeleton & ECM.

Some proteins function as receptors for chemical messengers (signaling molecules) from other cells in a process called signal transduction.

Some membrane proteins function as enzymes.

Membrane proteins may participate in the intercellular junctions that attach adjacent cells to each other.

Some membrane glycoproteins are involved in cell-cell recognition.

Example: Attached sugar molecules act as ID tags that enable cells of your immune system to know if a cell is you or foreign!

Membranes may exhibit selective permeability, which means some substances can cross more easily than others.

Certain ions and glucose require help in the form of transport proteins to get in and out of the cell.

the key ingredient of biological membranes, spontaneously self-assemble into simple membranes.  This was a critical step in the origin of the first cells.

Below a test tube with phospholipids and water is shaken – the phospholipids naturally organize into bilayers.

When molecules diffuse across a membrane without any work by the cell (no output of energy required).

2) When molecules diffuse down their concentration gradient.  In other words molecules move from an area of higher concentration to an area of lower concentration.

Eventually, the molecules reach equilibrium where the concentration of molecules is the same throughout.

1)  Expend energy (Use the energy molecule, ATP).

2)  Move a substance against its concentration gradient (go from low to high concentration).

Active transport is critical in nerve cells (neurons) for them to generate a nerve impulse.

is the energy of motion.  Moving objects perform work by transferring motion to other matter.

Example: Pumping your legs to move bicycle pedals to get you and your bike to move forward

Energy is constant – it cannot be created or destroyed.

Energy can be changed or transformed from one form to another

Energy transformations or conversions increase the disorder (entropy) of the universe!

Every time energy is put to work or is converted from one form to another, some energy is lost as heat.

Heat is also a form of energy, but it is so chaotic, so unorganized, and so spread out that it cannot be put to work. 

Any energy converted to heat radiates out of the system and so can no longer be put to use by the system. 

All of the energy is conserved, but the energy that is converted to heat escapes the system and is no longer useful. 

ATP acts like a battery for storing and transporting energy. 

ATP is the molecule of energy transfer in living systems.

Every reaction in the body that requires energy uses ATP.

chemical, mechanical, and transport.

ATP drives all three of these types of work

The interaction between a substrate molecule and the active site of an enzyme, which changes shape slightly to embrace the substrate more snugly like a handshake.  

The substrate bonds are contorted or strained during the induced fit catalyzing the reaction

takes the place of a substrate in the active site.

Can be overcome by adding more substrate