Biology  5/e   Raven/Johnson
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Nature of chemical bond: Chemical bonds hold atoms together to form molecules. In ionic bonds electrons are transferred between atoms, and the resulting ions are attracted to each other. In covalent bonds pairs of electrons are shared between atoms. Chemical bonds represent stored energy – potential energy. When a chemical bond is broken, energy is released. If the bond being broken is within an organism, the organism may use the released energy to help carry out its life processes.

Protein structure: A protein consists of one or more polypeptide chains. Each polypeptide chain consists of a particular sequence of amino acids. This sequence is referred to as the primary structure, and it determines the chemical properties and further structures of the protein. The pleated folding or helical coiling of the chain is called the secondary structure of the protein. The tertiary structure refers to the complex, three-dimensional globular structure assumed by some proteins as their polypeptide chains bend and ball up. Finally, a protein is said to have a quaternary structure if it has more than one polypeptide chain; quaternary structure refers to how these chains are shaped and associated with each other. The structure of a protein is responsible for the way it functions. The enzymes that control the chemistry of living organisms are proteins.

Nucleotides: Nucleotides are the building-block units of nucleic acids. Each nucleotide consists of a five-carbon sugar, a phosphate group, and a nitrogenous base. Nucleotides are also components of other biologically important compounds such as ATP and the coenzyme NAD⁺.

Proton pump: The proton pump establishes a proton gradient across a cell or organelle membrane and uses that gradient to produce ATP, the universal energy currency. Protons are actively pumped across the membrane, and their diffusion back through special channels is coupled with the production of ATP. The cell (and organism) can then use the ATP to perform work. The energy needed to pump the protons is supplied by photosynthesis or the breakdown of energy-rich molecules.

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