Textbook Notes (368,794)
Canada (162,165)
Biology (653)
BIO206H5 (60)
Chapter 2


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George S Espie

CELL BIOLOGY CHAPTER 2  The chemistry of life is based o carbon compounds  It depends on chemical reactions that take place in watery or aqueous solutions and in the relatively narrow range of temperatures experienced on Earth  It is enormously complex and is dominated and coordinated by a collection of enormous polymeric molecules whose unique properties enable organisms to grow and reproduce  The polymeric molecules form from chains of chemical subunits linked end- to-end  It is tightly regulated; cells deploy a variety of mechanisms to make sure that all their chemical reactions occur at the proper place and time CHEMICAL BONDS  Matter is made of combinations of elements  Elements are substances that cannot be broken down or converted into other substances by chemical means.  The smallest particle of an element that still retains its distinctive properties is an atom  The characteristic of substances other than pure elements depends on the atoms they contain and the way these atoms are linked together in groups to form molecules  Living cells are made up of a limited number of elements , four of which H, C, N, O make uo 96.5% of their mass CELLS ARE MADE OF RELATIVELY FEW TYPES OF ATOMS  Each atoms has at its center a dense, positively charged nucleus which is surrounds at some distance by a cloud of negatively charged electrons held in an orbit by electrostatic attraction to the nucleus  The nucleus consists of two kinds of subatomic particles: 1) Protons; which are positively charged 2) Neutrons; which are electrically neutral  The number of protons present in an atomic nucleus determines its atomic number  The electrical charge carried by each proton is exactly equal and opposite to the charge carried by a single electron.  Number of protons = number of electrons  All atoms of a given element have the same atomic number  Neutrons are uncharged subatomic particles with essentially the same mass as the protons  Neutrons contribute to the structural stability of the nucleus; if there are too many or two few the nucleus may disintegrate by radioactive decay  Neutrons do not alter the chemical properties of the atom  An element can exist in several physically distinguishable but chemically identical forms called isotopes, each having a different number of neutrons but the same number of protons  The atomic weight of an atom or the molecular weight of a molecule is its mass relative to that of a hydrogen atom, this is essentially equal to the number of protons plus the number of neutrons that the atom or the molecule contains  The mass of an atom or a molecule is generally specified in Daltons  6 x 10 is called Avogadro’s number, it is the key scale factor describing the relationship between everyday quantities and
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