Biochemistry
It can be divided into three fields:
It deals with the structures, functions, and interactions of biological
macromolecules such as proteins, nucleic acids, carbohydrates, and
lipids. They provide the structure of cells and perform many of the
functions associated with life. The chemistry of the cell also depends
upon the reactions of small molecules and ions. These can be inorganic
(for example, water and metal ions) or organic (for example, the amino
acids, which are used to synthesize proteins). The mechanisms used by
cells to harness energy from their environment via chemical reactions
are known as metabolism. The findings of biochemistry are applied
primarily in medicine, nutrition and agriculture.
Structural biology
It studies structural analysis of living material (formed, composed of, and/or maintained and refined by living cells) at every level of organization. The most prominent techniques are X-ray crystallography, nuclear magnetic resonance, and electron microscopy. Through the discovery of X-rays and its applications to protein crystals, structural biology was revolutionized, as now scientists could obtain the three-dimensional structures of biological molecules in atomic detail, like the one demonstred below, for the Myoglobin. Likewise, NMR spectroscopy allowed information about protein structure and dynamics to be obtained.
Image 1. Structure and refinement of oxymyoglobin at 1.6 angstroms resolution. PDB DOI
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Enzymes are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life.Metabolic pathways depend upon enzymes to catalyze individual steps. Enzymes are known to catalyze more than 5,000 biochemical reaction types.
Image 2. Here we can see that the enzyme glucosidase converts the sugar maltose into two glucose sugars. Active site residues in red, maltose substrate in black, and NAD cofactor in yellow.
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Metabolism
Metabolism is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the conversion of food to building blocks of proteins, lipids, nucleic acids, and some carbohydrates; and the elimination of metabolic wastes. These enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. The word metabolism can also refer to the sum of all chemical reactions that occur in living organisms, including digestion and the transportation of substances into and between different cells, in which case the above described set of reactions within the cells is called intermediary (or intermediate) metabolism.
Image 3. A diagram of cellular respiration including glycolysis, Krebs cycle (AKA citric acid cycle), and the electron transport chain.
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