Enzymes and Membrane Function Notes

Activation Energy

Spontaneous reactions need a bit of energy to start.
- Example: Pushing a pen or a ball.
Chemical Reaction Example:
- Gasoline + Oxygen → CO_2 + Water
- Gasoline doesn't spontaneously convert; it needs activation energy like a spark.
Activation energy is the energy required to start a reaction.
Reactions release energy to stimulate subsequent reactions.
All reactions have some activation energy; enzymes lower it.

Enzymes lower activation energy by:
- Orienting molecules together.
- Facilitating bond formation or breakage.
Enzymes are like assembly line workers that manipulate molecules and Activation energy is what initiates the reaction. Some of the energy required involves bringing molecules together in the right orientation.
Enzymes speed up reaction rates significantly (millions or billions of times).
Life requires coordinated chemical reactions at specific rates.
- Example: Oxygen conversion needs to be fast enough.
Enzymes control the speed and timing of reactions.

Enzymes are sensitive to environmental conditions:
- Temperature
- pH
- Ion concentrations (including pH which is specifically H+ and OH- ion concentration)

Heating increases molecular movement; cooling decreases it.
Enzymes have an optimal temperature range for the active site to accommodate the substrate.
Most human enzymes prefer around 37°C or 98.6°F.
Immune system enzymes function better at higher temperatures (fever).
Fever is the body's response to infection to enhance immune enzyme function, but excessively high fevers are dangerous.

Denaturation: Distorting a protein (enzyme) to the point where it cannot function.
- The active site loses its shape, so it cannot properly bind to the substrate.

Enzyme helpers:
- Cofactors: Typically metal ions (e.g., copper, magnesium, iron).
- Coenzymes: Small organic molecules like vitamins (e.g., Vitamin C, A, K).
These help maintain shape, attract/bind substrates, or facilitate the chemical reaction.

Vitamin C acts as a coenzyme in some immune system enzymes.
Vitamin C also is important in collagen, which holds your cells together.
Scurvy results from long-term vitamin C deficiency. Consequences may include skin issues, bone issues, and eye issues.

Enzymes must work when needed.
Inhibitors: Molecules that distort the enzyme or block the active site.
Activators: Improve or allow access to the active site.
Allosteric Site: A distant site where inhibitors can bind and distort the enzyme.

Metabolic pathways: Step-by-step approach to produce a final product, involving multiple enzymes.
- Initial enzyme and final enzyme.
- Initial substrate and final product.
- Intermediate substrates and products.
These pathways are under feedback control.

The reaction inhibits the stimulus.
The final product inhibits the reaction.
Negative feedback: The response to the stimulus decreases or counteracts the stimulus.
Most homeostatic control systems use negative feedback.

Positive feedback: The response to the stimulus increases the stimulus.
The mechanism step increases the stimulus.
Examples of positive feedback:
- Clotting proteins stimulating the production of more clotting proteins.
- Labor and Delivery: Uterine stretches cause pain, increasing oxytocin production, and further contractions.

Fluid Mosaic: A description of the cell membrane.
Phospholipids create a bilayer structure with polar heads and a nonpolar interior.
Cholesterol maintains flexibility.
Transmembrane proteins span the membrane.
Surface proteins reside on the surface.
The membrane is semiselectively permeable.

Does not require added energy (ATP).
Molecules move down the concentration gradient (from high to low concentration).

Diffusion: Movement from high to low concentration.
Simple diffusion: Molecules cross the membrane without assistance.
- Example: Oxygen, carbon dioxide, and water.
Facilitated diffusion: Requires a transport protein to help molecules cross.
Osmosis: Diffusion of water molecules across the membrane.