The Function of ATP, Enzymes, and Protein Pathways in Biology

The structure of the ATP molecule consists of five main components. They are three phosphate groups, a five carbon base sugar ribose, and the N base adenine. Most of the energy is stored in the high-energy bond of the last phosphate group. ATP is referred to as the "energy currency" of the cell because it is earned in exergonic reactions and spent in endergonic reactions. At certain steps of many metabolic processes, an unbound phosphate atom that an enzyme cleaves from some substance becomes attached to ADP.

The result is an ATP molecule. When ATP transfers a phosphate group somewhere else, it reverts to ADP. Energy is input through aerobic respiration and the product is energy output for diverse cellular reactions and activities. Energy necessary to make usable ATP comes from aerobic respiration. Energy released as ATP goes to ADP is used for in cellular activities and cellular reactions.

Enzymes are the organic molecule protein. The effect that enzymes have on the chemical reactions that they catalyze are that they speed up them up. The enzyme produces this effect by lowering the activation energy required.

The theory of enzyme action is also known as the induced fit theory. Enzymes must complex with the substrates they catalyze. Enzymes are very specific with the shapes that enter the active site, so the shape must fit precisely, known as enzyme specificity. When the substrates are complexed, it's called the transition state. The products are released and the enzyme can be used again.

Heating an enzyme beyond its optimum temperature alters the shape of the enzyme and its active site will decrease the enzyme activity because weak bonds holding the enzyme in its three-dimensional shape.

Diffusion is the net movement of like molecules or ions down a concentration gradient. Osmosis is the diffusion of water molecules in response to a water concentration gradient between two regions that are separated by a selectively permeable membrane.

A plant cell placed in an isotonic solution would not change. In a hypertonic solution, they lose water by osmosis and shrivel as the cytoplasm and central vacuole shrink and the internal fluid pressure drops. In a hypotonic solution, the cell wall protects them from bursting.

This differs from what will happen to a red blood cell because red blood cells don't have built-in mechanisms that adjust to shifts in tonicity. In isotonic solutions, they remain the same. In hypertonic, they shrink, and in hypotonic they swell up and burst.

Passive transport is the flow of solutes through the interior of transport proteins down their concentration gradients, with no additional energy cost. Active transport is the net diffusion of a solute against its concentration gradient. The transporting protein must be activated, as by ATP. Proteins are the gateways that make the plasma membrane selectively permeable.

By exocytosis, a cytoplasmic vesicle fuses with the plasma membrane, so that its contents are released outside the cell. By endocytosis, a small patch of the plasma membrane sinks inward and seals back on itself, forming a vesicle inside the cytoplasm. Membrane receptors often mediate this process.

Phagocytosis is an active form of endocytosis by which a cell engulfs microorganisms, large edible particles, and cellular debris. Human cells that engage in phagocytosis as they carry out their function are macrophages and some other white blood cells. Their function is to defend the body against harmful viruses, bacteria, and other threats to health.

Sources:
Glencoe Science, Biology: The Dynamics of Life.