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Biological Sciences
Aarti Ashok

Macromolecules in Cells The Atom  basic unit of matter  Protons and neutrons in the ‘nucleus’  Electrons in the outer ‘shells’ Electrons of Atoms  # of outer shell electrons determines the chemical properties of an element Biological Molecules  molecules: 2 or more atoms in a definite arrangement held together by chemical bonds  biochemicals  molecules made by living organisms  centered around Carbon  Carbon binds up to 4 other atoms – 4 electrons in outer shell o Able to bond with other Carbon atoms o size + electronic structure of Carbon is ideally suited to generate large biological molecules Types of Molecular Bonds in Biochemicals (Covalent + Noncovalent Bonds) 1. Covalent Bonds (very strong bonds)  Electron pairs are shared b/w atoms to form molecules  Atoms are most stable when their outermost electron shells are full  # of covalent bonds formed by an atom depends on the number of electrons needed to fill its outermost shell  atoms can share more than one pair of electrons  covalent bonds can lead to: o Polar Molecules  unequal sharing of electrons (when atoms are different)  the more positively charged nucleus of one atom will attract the electrons more strongly than the other atom’s nucleus  one atom has a partial –ve charge and the other atom has a partial +ve charge  asymmetric charge distribution  atom w/ the greater attractive force is called the electronegative atom  in water: o [O] partially –ve o [H] partially +ve  biologically important polar molecules have electronegative atoms: O, N, S and/or P o Nonpolar Molecules  Equal sharing of electrons (when atoms are different)  Lack electronegative atoms  Ie. molecul
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