Chapter 5

"Diffusion"

Chapter 5: Passive Transport is diffusion across a memmbrne with no energy investment

Concentration Gradient

 "a gradual change in the concentration of solutes in a solution as a function of distance through a solution."

Chapter 5: Membrane Strucutre and Function

Passive Transport is Diffusion

Passive Transport

Diffusion of a a substance across a biological membrane

• because cells do not perform work when moelcules diffuse across a biological membrane.

Osmosis

Pertaining to a solution that has the same tonicity as some other solution with which it is compared. For example, blood serum is isotonic to a physiologic salt solution. Solutions that have same tonicity will result in no net flow of water across the cell membrane.

The control of water ballance

• For an aniaml to survice in a hypotonic or hypertonic enviroemnt it must have a way to prevent excessuve uptake or excessive loss of water. 

Transport Proteins faciltate diffusion across membranes

Facilitated Diffusion

a cell must expend energy to move a solute against its concentration gradientthat is, across a membrane toward the side where the solute is more concentrated. 

• Allows a cell to maintain concentrations of small molecules that are different from conentrations in its surroundings. 

A cell uses this to export buliky materials

• Proteins or polysaccharides

a transport process that is the opposite of exocytosis

• cell takes in substances, a depression in the plasma membrane pinches in and forms a vesicle enclosing material that had been outside the cell. 

*high specific compared to pinocytosis.

• Receptor proteins for specific molecules are embedded in regios of the membrane that are lined by a layer of coat proteins. 

1st Law of Thermodynamics

2nd Law of Thermodynamics

• 1st law-known as the law of energy conservation, the enrgy of the universe is constant, it can not be created or destroyed just transformed.
• 2nd law-Energy conversions increate the entropy (disorder) of the universe. 

Celluar Respiration

Similarties

• Both are exogonic

Differences

• Burning is a one step process that releases energy all at once
• CP-involves many steps, each a seperate chemcial reaction; can be thought of as a "slow burn."

The other type of chemcial reaction, requires a net input of energy. 

• Yields products that are rich in potentional energy
• Endergonic-means "energy inward."

• Metabolism-
• Metabolic Pathway-
• Energy Coupling-

• Metabolism- total of an organisms chemical reactions.
• MP-a series of chemical reactions that either builds a complex molecule or breaks down a complex molecule into simpler compounds. 
• EC-the use of energy released from exergonic reactions to drive essential endergonic reaction, is a crucial ability of all cells. 

ATP

• what kind of reaction is its hydrolysis?

key to energy coupling and powers nearly all cellular work

• Exergonic Reaction-it releases energy

• Phosophorylation- Usually does this by transferring the thir phosphate group from ATP to some other molecule

• Most cellular word depends on ATP energizing molecules by phosphorylating them. 

1. Chemical-the phosphorlation of reactants provides energy to drive the endergonic synthesis of products.
2. Mechanical-the transfer of phosphate groups to sepcial motor proteins in muscle cells causes the proteins to change shape and pull on actin filaments, causing the cells to contract. 
3. Transport-ATP drives the active transport of solutes across a membrane against their concentration gradient tby phosphorylating centain membrane proteins. 

Energy of Activation

(E

   A)

Energy must be absorbed to contort or waken bonds in reactant molecules so that they can break and new bonds can form.

• Can be thought of as the amount of energy needed to to push the reactants over an energy barrier , or "hill," so that the "downhill" part of the reaction can begin. 

1. One way is heat, but too much would kill the cell.

• Enzymes-the solution, proteins that function as biological catalyists, increasing the reaction rate without being consumed by the reaction. 

• By lowering the Ea barrier

1. Enzyme's
2. Substrate relationship to Active site
3. Active Site

1. Substrate- a spsecific reactant that an enxyme acts on
2. Substrate relation to AS-substrate fits into the "active site."
3.  Active Site- typially a pocket or groove on the surface of the enzyme formed by only a few of the Enzymes amino acids. 

1. Cofactors
2. Coenzyme

1. Cofactsor-nonprotein helpers, some are inorganic (ions of zinc iron, and copper.)
2. Coenzyme-organic Cofactor such as vitamins. 

1. Competitive Inhibitor
2. Noncompetitve Inhibitor
3. Feedback Inhibitor

1. CI-reduces an enxymes productivity by blocking substrates from entering the active site.
2. NCI-does not enter the active site, instead it binds to the enzyme somewhere else, adn its binding changes the shape of the enzyme so that the active site no longer fits the substrate
3. FI-if a cell is producing more of that product than it needs, the product may act as an inhibitor or one of the enzymes early in the pathway. Feedback Inhibitors is where metabolic reaction is blocked by its own products.