Microbiology - The Chemical Basis of Microbiology - Quick Guides

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Study GuideMicrobiology–The Chemical Basis of Microbiology1. Chemical PrinciplesLiving organisms may look very different from one another, but at a chemical level they aresurprisingly similar. In the 1700s, scientists discovered thatall living things share the same basicchemical and physical foundation. Microorganisms are no exception. Their structure, growth, andmetabolism are all based on chemical principles.Understanding these chemical basics helps us understand how microorganisms live and function.1.1Elements and AtomsAll living things on Earth, including microorganisms, are made ofelements.More than 100 elements are known, although only some are common in living systems.Anelementis a pure substance thatcannot be broken down into simpler substances bychemical means. Examples of important elements in biology include:•Oxygen•Hydrogen•Carbon•Nitrogen•Calcium•Iron•SodiumEach element is made up of onlyone kind of atom.Anatomis the smallest unit of an element that can take part in chemical reactions.1.2Structure of an AtomAtoms are made of three main particles:

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Study Guide•Protons–positively charged•Electrons–negatively charged•Neutrons–no electrical chargeProtons and neutrons are packed tightly together in the center of the atom, forming thenucleus.Electrons move around the nucleus in paths calledshells.The number and arrangement of electrons—especially in the outer shell—determine how an atombehaves chemically.1.3Electron Arrangement and StabilityAtoms are most stable when theirouter electron shell is full.A full shell usually contains:•2 electrons, or•8 electronsIf an atom’s outer shell is not full, the atom may:•Gain electrons, or•Lose electronsThis gain or loss of electrons allows atoms to react with other atoms, forming chemical bonds. Thesereactions are the basis of all biological processes.1.4Molecules and CompoundsMost substances in microorganisms are made ofmolecules.•Amoleculeis a specific arrangement of atoms bonded together.•Acompoundis a substance made of many identical molecules.Theproperties of a compounddepend on how its atoms are arranged.Each molecule also has amolecular weight, which is the sum of the atomic weights of all its atoms.For example:•Water (H₂O) has a molecular weight of18.

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Study Guide1.5Chemical Bonds in MoleculesAtoms in molecules are held together bychemical bonds. Two important types of bonds areionicbondsandcovalent bonds.1.6Ionic BondsAnionic bondforms when one atomtransfers electronsto another atom.•The atom that loses electrons becomes apositively charged ion.•The atom that gains electrons becomes anegatively charged ion.•Opposite charges attract, holding the ions together.Example:Sodium chloride (NaCl) forms when sodium transfers an electron to chlorine.

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Study Guide1.7Covalent BondsAcovalent bondforms when two atomsshare electrons.•Sharingone pairof electrons forms asingle bond.•Sharingtwo pairsof electrons forms adouble bond.Covalent bonds are very common in living organisms.Examples:•Methane (CH₄): carbon shares electrons with four hydrogen atoms•Water (H₂O): oxygen shares electrons with hydrogen atomsCovalent bonds are found in important biological molecules such as:•Proteins•Lipids•Carbohydrates1.8Synthesis of Organic MoleculesLarge biological molecules are formed by joining smaller molecules together.Fat Formation•Fatty acids bond to glycerol•Water is released during the process•This is calleddehydration synthesisProtein Formation•Amino acids join together•Apeptide bondforms between them•Water is released

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