Final answer:
Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy needed for those reactions to occur. The correct statement about enzymes is D) They speed up chemical reactions.
Step-by-step explanation:
The correct statement about enzymes is D) They speed up chemical reactions. Enzymes are biological catalysts that play a crucial role in facilitating biochemical reactions within living organisms. Without enzymes, most chemical reactions would occur at a rate far too slow to sustain life. Enzymes accomplish the speed-up of these reactions by lowering the activation energy required for the reaction to proceed, which increases the rate at which the products are formed.
Enzymes are typically composed of proteins, made up of long chains of amino acids that fold into unique three-dimensional structures. This structure determines the enzyme's specificity, allowing it to recognize, bind, and transform particular substrates. The area of the enzyme where the substrate binds is known as the active site, and it is this site that provides the ideal conditions for the chemical reaction to occur. The induced fit model suggests that enzymes undergo a slight change in shape to achieve a more precise fit with the substrate upon binding.
It is also critical to understand what enzymes do not do. They do not increase the activation energy of a reaction (A), are not consumed during the reaction (B), and do not alter the equilibrium of the reaction (C), as the reactions will reach the same equilibrium point at a faster rate thanks to the presence of the enzyme. These properties highlight the remarkable efficiency and specificity of enzymes in biological systems.