Fireflies and Bioluminescence: How do they produce light?
I. Energy and the Underlying Organization of Life
1. Potential energy is the capacity to do work; in molecules it is called chemical energy.
3. Energy transfers release heat.
B. What Can Cells Do With Energy?
2. Cells use energy for work: chemical, mechanical, and electrochemical.
C. How Much Energy Is Available?
2. Energy cannot be produced by a cell; it can only be borrowed from someplace else.
D. The One-Way Flow of Energy
2. Second law of thermodynamics states that the spontaneous direction of energy flow is from high- to low-quality forms.
b. As systems lose energy, they become more disorganized; the measure of this disorder is called entropy.
3. The world of life (plant and animal) maintains a high degree of organization only because it is being resupplied with energy from the sun.
II. Doing Cellular Work
2. Exergonic (energy out) reactions result in products with less energy than the reactants had.
B. ATP, The Cells Energy Currency
b. ATP transfers energy to many different chemical reactions; almost all metabolic pathways directly or indirectly run on energy supplied by ATP.
2. Energy input links phosphate to ADP to produce ATP.
b. ADP can be recycled to ATP very rapidly.
C. Electron Transfers
b. The receptor molecule gains an electron and is reduced.
2. Certain electron transfers proceed in an orderly, stepwise fashion to control the release of energy.
D. Metabolic Pathways
b. In degradative pathways, large molecules such as carbohydrates, lipids, and proteins are broken down to form products of lower energy. Released energy can be used for cellular work.
2. Terms used in describing metabolic pathways include:
b. Intermediates are substances that form between the start and conclusion of metabolic pathway.
c. End products are the substances present at the conclusion of a reaction or pathway.
d. Energy carriers donate energy to substances by transferring functional groups to them; ATP is the main type.
e. Enzymes are proteins that catalyze (speed up) specific reactions.
f. Cofactors are organic molecules or metal ions that assist enzymes or transport electrons/atoms.
g. Transport proteins adjust the concentration gradients at cell membranes in way that influence the direction of metabolic reactions.
III. Enzyme Structure and Function
B. Four Features of Enzymes
2. Enzymes can be reused.
3. Enzyme actions are reversible.
4. Enzymes are selective and act upon specific substrates.
C. Enzyme-Substrate Interactions
2. Enzymes increase the rate of a reaction by lowering the activation energy through extensive bonding of substrate at the active site.
b. In order to proceed reactants must reach a "transition" state.
IV. Factors Influencing Enzyme Activity
2. Most enzymes function best at a pH near 7.
Higher or lower pH values disrupt enzyme shape and keep them from functioning.
B. How Is Enzyme Action Controlled?
2. Feedback inhibition operates when a substance triggers a cellular change that shuts down production of that substance.
3. Allosteric enzymes have (in addition to active sites) regulatory sites where control substances can bind to alter enzyme activity; if this control substance is the end product in the enzymes metabolic pathway, feedback inhibition occurs.
4. Hormones are the signaling molecules in enzyme control.
V. Reactants, Products, and Cell Membranes
B. Gases, nonpolar molecules, and water can move through the lipid bilayer by Diffusion.
C. Glucose and other large polar molecules must cross the membrane through transport proteins, in some cases via diffusion and in other cases by Active Transport.
VI. Working With and Against Concentration Gradients
2. The net movement of like molecules down a concentration gradient (high to low) is simple diffusion.
3. Gradients in temperature, electric charge, and pressure, can influence movements.
B. Passive Transport
2. Transport proteins change shape to move substances into and out of the cell.
C. Active Transport
2. The sodium-potassium pump is a major cotransport system in that it can set up concentration gradients that can in turn drive other transport activities.
VII. Movement of Water Across Membranes
2. Osmosis is the passive movement of water across a differentially permeable membrane in response to solute concentration gradients, pressure gradients, or both.
B. Effects of Tonicity
2. Three conditions can occur:
b. A hypertonic fluid has a greater concentration of solutes than does the fluid in the cell; cells in it may shrivel.
c. An isotonic fluid has the same concentration of solutes as the fluid in the cell; immersion in it causes no net movement of water.
C. Effects of Fluid Pressure
2. Osmotic pressure is the amount of force that prevents any further increase in the volume of solution inside a cell.
VIII. Exocytosis and Endocytosis
2. Exocytosis moves substances from cytoplasm to plasma membrane during secretion.
2. Phagocytic cells (amoebas and white blood cells) digest the contents of the endocytic vesicles by means of enzymes within lysosomes which fuse with the vesicles.