Organization of Life and Enzymes: An Overview

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Organization of Life

Atoms: smallest unit of an element that still retains the element's properties.

Molecules: two or more joined atoms of the same or different elements.

Cell: smallest unit of life that can live and reproduce on its own or as part of a multicellular organism.

Multicellular organisms: made of specialized, interdependent cells that are often organized into:

Population: consists of individuals of the same species in a specified area.

Community: consists of all populations occupying the same area.

Ecosystem: a community interacting with its physical and chemical environment.

Biosphere: includes all regions of Earth's atmosphere, waters, and land where we find living organisms.

DNA is inherited.

Inheritance: an acquisition of traits after parents transmit their DNA to offspring.

Each organism's DNA holds the specific instructions for its development and is unique.

Reproduction: refers to the actual mechanisms by which parents transmit DNA to offspring.


Enzymes: a type of protein (or, rarely, RNA) that accelerates a chemical reaction.

Enzymes speed up specific metabolic reactions by these mechanisms:

  • Functional-group transfer: one molecule gives up a functional group, which another molecule accepts.
  • Electron transfer: one or more electrons stripped from one molecule are donated to another molecule.
  • Rearrangement: a juggling of internal bonds converts one type of organic compound into another.
  • Condensation: through covalent bonding, two molecules combine to form a larger molecule.
  • Cleavage: a molecule splits into two smaller ones.

Condensation reaction: Covalent bonding of two molecules into a larger molecule, often with the formation of water as a by-product.

Hydrolysis: An enzymatic cleavage reaction in which a molecule is split, and the components of water become attached to each of the fragments.

Proteins have four levels of structure.

  • Primary structure: defined as the chain (polypeptide) of amino acids each linked together in a definite sequence. (Not a protein yet)
  • Secondary structure: the helical coil or sheetlike array into which the polypeptide chain is formed by the interaction of hydrogen bonds.
  • Tertiary structure: the result of interactions among R (functional) groups that produce a complex three-dimensional shape.
  • Quaternary structure: describes the complexing of two or more polypeptide chains.

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