Chapter 8 - Intro to Cells

Can cells create or destroy energy?

No, but they can transform it

Potential Energy

Stored energy

Examples:

• chemical bonds

• concentration gradients

Kinetic Energy

Energy that does work

Examples:

• muscle contraction

Metabolism

The sum total of all chemical reactions in an organism

Anabolic

Building molecules → requires energy

Catabolic

breaking molecules → releases energy

Change in free energy

The symbol is ΔG

ΔG = G products - G reactants

ΔG negative → reactants have more energy than the products, energy was released (catabolic)

ΔG positive → products have more energy than reactants, energy required (anabolic)

Exergonic Reactions

Releases energy, ΔG negative, catabolic

Examples: cell respiration, catabolism

Endergonic Reactions

Uses energy, ΔG positive, anabolic

Examples: photosythesis, protein synthesis, DNA replication

PE and KE relationship

PE turns into KE

Reactions are coupled

Exergonic releases energy that Endergonic uses

ATP

Energy currency

Two jobs:

1) Store energy

2) Phosphorylation

Can be broken into ADP + Pi (releases energy)

Catalysts

Things that speed up the rate of reaction.

1) Used because reactions have an energy barrier (energy needed to start the reaction) → called ACTIVATION ENERGY

2) Activation energy needed to overcome energy barrier

What are biological catalysts?

Enzymes:

1) they reduce the energy barrier

2) they are proteins, fundamental for life

3) highly specific; specific shape that only bonds to one reactant

Reactants (substrate) → Products

Substrate and enzyme relationship:

Enzyme + substrate → enzyme substrate complex → product + enzyme

• Enzyme can do job again and again

• have a maximum rate (point of saturation)

• Enzyme has an active site with SPECIFIC SHAPE that only binds to ONE substrate

• The more substrate, the more reactions

• If not enough enzymes, they work at their maximum rate, and cannot go any faster

How are enzymes named?

1) function is the first part of the word

2) -ase is at the end

Example: enzyme that breaks down lactose is named lactase

Metabolic pathways

1) Each step is catalyzed by an enzyme

2) First step is called the commitment step: enzyme used to regulate that pathway

How are pathways regulated?

1) by cell signaling from interacting with the environment

2) regulate pathways by regulating enzymes (activating/deactivating)

3) Inhibitors:

• naturally occurring (reversible)

• artificial (BOTH)

Example: aspirin binds to pain and inflammation enzymes to deactivate them

• Cell is activating or inhibiting enzymes for pathways ALL THE TIME

Naturally Occurring Inhibitors

1) Competitive

• inhibitor binds to the active site

• dependent on concentration (whichever is more; substrate or inhibitor)

2) Non-competitive

• binds to another sit different from active site

• most common

• changes the shape of the enzyme so it goes from active to inactive → allosteric regulation → one big way this happens in PHOSPHORYLATION

• Not dependent on concentration or substrate

  Example: product can allosterically inhibit the key enzyme (commitment step). Product can also activate a different key enzyme to produce something else. For example, same ATP produced can bind to glucose (or enzymes) and inhibit it from breaking down → negative feedback loop.

• SAME INHIBITOR CAN BE AN ACTIVATOR

Every enzyme has an optimal temperature

• varies by organism

• for humans it is 37 degrees Celsius

• Fever is meant to stimulate enzymes in humans

• every enzyme has an optimal pH as well