Chemical Basis of Life

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Chemical Basis of Life

• Chapter 2
• Bio 160

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Atoms

• Atoms smallest complete unit of an element

Protons ()
Neutrons (neutral)
Electrons (-)
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Atoms

• Nucleus of an atom is comprised of neutrons and
  protons and therefore has a charge electrons
  (-) are attracted to the nucleus and move around
  the nucleus in specific areas of space called
  shells

1st shell holds 2 e-
2nd shell holds 8 e-
3rd shell holds 8 e-
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Elements

• Elements consist of only one kind of atom

arranged in periodic table by symbols, along with
atomic number and weight

• Atomic number number of protons number of
  electrons (in a neutral atom)

atomic number determines which element is in
question
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Elements

• Atomic weight number of protons number of
  neutrons

(mass (weight) of protons or neutrons is 1840 x
larger than that of e-)

• Isotopes - elements with the same of protons
  but a varying of neutrons, ie, element with the
  same atomic number but a different atomic weight

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Elements
atomic weights are not whole numbers, but merely
an average of all isotopes of an element
unstable isotopes emit energetic particles and
are known as radioisotopes

• All elements with atomic number gt 84 are
  radioactive but these elements are not normally
  present in biological material

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Molecules Compounds

• Molecules - chemical combination of 2 or more
  atoms of one or more elements bonded together by
  chemical bonds (atoms don't have to be different)
  (H2 is a molecule as is H2O)

• Compounds - 2 or more different elements joined
  together

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Chemical Bonding

• Electrons are the part of an atom that actively
  participates in a chemical reaction (never the
  nucleus)

• Chemical behavior of atoms can be explained by
  behavior of electrons

• Octet rule atoms react with one another to
  achieve 8 e- in outer shell (except 1st shell)

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Chemical Bonding

• Atoms with fewer than 8 electrons in outer shell
  may transfer or share electrons to complete outer
  shell

• When atoms react with one another they are
  attracted to each other by chemical bonds

• Ions - atoms that are electrically charged either
  by gaining or losing electrons

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Types of Chemical Bonding

• Ionic bond formed when electrons are
  transferred from one atom to another the bond is
  therefore the electrical attraction between 2
  oppositely charged ions

compounds containing ionic bonds readily separate
(dissociate) into ions in water and are called
electrolytes because as charged particles they
can conduct an electric current
examples of electrolytes are acids, bases, and
salts
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Types of Chemical Bonding

• if outer shell has 1,2, or 3 e-, the atoms tend
  to lose the electron and become ions cations

if outer shell has 6 or 7 e-, the atoms tend to
gain electrons and become - ions anions
if outer shell has 4 or 5 e-, they don't tend to
form ions they tend to share electrons and form
covalent bonds
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Types of Chemical Bonding

• Covalent bond results from sharing electrons
  atoms with 4 or 5 electrons in outer shell tend
  to share electrons and will not form ions
  therefore covalent compounds tend to be
  nonelectrolytes

Carbon has 4 electrons in outer shell and needs 4
more electrons
More compounds of carbon than any other element
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Types of Chemical Bonding

• Nonpolar covalent - equal sharing of electrons
  no charged regions

• Polar Covalent - electrons are not equally
  shared results in charged regions

water is a good example of a polar covalent
compound
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Types of Chemical Bonding

• Hydrogen bonds - weak attraction between a
  slightly hydrogen and a slightly -oxygen or
  nitrogen

H bonds can be between molecules (intermolecular
as in water) or within molecules (intramolecular
as in DNA and protein)
H bonds are significantly weaker than covalent or
ionic bonds
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Chemical Reactions

• Chemical Reactions the making and breaking of
  chemical bonds

• Reactants starting materials in a reaction

• Products ending materials in a reaction

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Types of Chemical Reactions

• Synthesis - reactions that consume energy to
  build complicated molecules from simpler ones

• Decomposition - reactions that break down complex
  molecules into simpler compounds

• Exchange reactions

• Reversible reactions

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Acids and Bases

• Acids - substances that release H in water

• Bases - release OH- or accept H

• pH - measure of H concentration

• Salts - strong acid strong base? salt and H2O

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Organic Compounds

• Organic compounds - any substance that contains
  both carbon and hydrogen

• Polymer - long chain of a repeating molecular unit

monomer monomer ? polymer H2O (dehydration
synthesis condensation)
polymer H2O ? monomer monomer (digestion
reaction hydrolysis)
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Carbohydrates

• Carbohydrates (contain C, H, O) sugars and
  starches

most abundant group of organic compounds
provides most readily available source of energy
short term storage of energy
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Carbohydrates

• Monosaccharides

• Pentose - 5 carbon sugar - ribose/deoxyribose of
  RNA/DNA

• Hexose - 6 carbon sugar

• glucose - most abundant hexose
• galactose
• fructose

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Carbohydrates

• Disaccharides - Monomer Monomer disaccharide

Sucrose Table sugar
Lactose - Milk
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Carbohydrates

• Polysaccharides

• Starches - principal storage polysaccharide in
  plants ex) potatoes, rice, grain

• Glycogen - principal storage polysaccharide in
  animals

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Lipids - all tend to be insoluble in water
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Lipids

• Triglycerides (fats) - largest of class of lipids

• glycerol (monomer) 3 fatty acids(monomers)?trigl
  yceride

• saturated fats all bonding sites of the fatty
  acid are filled with hydrogen

• unsaturated fats - some double bonds present so
  not all bonding sites are filled with hydrogen
  and the fatty acid has a kink in its shape,
  preventing solidification

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Lipids

• Phospholipids - in cell membranes and membranes
  of organelles

• consists of glycerol 2 fatty acids phosphate
  group (- charge)

fatty acid tail - hydrophobic insoluble in water
phosphate head - hydrophilic soluble in water

• phospholipids are arranged as a bilayer with
  phosphate heads toward water (outside of bilayer
  in contact with aqueous solutions inside and
  outside the cell) and the fatty acid tails toward
  the interior of the membrane

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Lipids

• Steroids

cholesterol (precursor from which most other
steroids are synthesized)
sex hormones - estrogen, progesterone,
testosterone
cortisol and aldosterone
Vitamin D and bile salts
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Proteins

• Protein - most abundant organic molecule in
  organism (makes up 50 of dry weight)

Monomer amino acid polymer protein
(polypeptide chain)
Amino acids are linked by peptide bonds (covalent
bonds)
Proteins - contain C, H, O, N and some S
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Proteins

• Proteins have four levels of structure which
  contribute to their unique three-dimensional
  shape, or conformation

• Denaturation - Proteins lose their conformation,
  hence their function, due to exposure to heat,
  radiation, electricity, pH changes, or various
  chemicals

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Nucleic Acids

• DNA and RNA

monomer nucleotide

• pentose sugar (5-carbon monosaccharide)
  ribose/deoxyribose

• phosphate group

• nitrogenous base