Transcript Notes Chemical Basis for Life BIO.A.2

The Chemical Basis for Life
(Bio.A.2)
Properties Of Water
• Polarity – uneven distribution of
electrons between the hydrogen and
oxygen atoms
– Oxygen is bigger and attracts the
electrons more than hydrogen
• Hydrogen bonds – slightly positive H
atoms are attracted to slightly
negative atoms like O
• Cohesion – H bonds allow water
molecules to stick together
– Surface tension
• Adhesion – H bonds allow water
molecules to stick to other, polar
molecules
– Capillary action (ex. straws)
• High specific heat - water can
absorb lots of heat energy without
drastically changing its temperature
• Water stays in a liquid phase over
much of the planet and therefore
supports life
• Density of ice – allows ice to float
• Most biological reactions require
water.
• More about water….
Carbon as a backbone
• Covalent bond – electrons are
shared between atoms
– Example H2O and CO2
• Carbon has the unique ability to
make four covalent bonds
• Carbon is part of many biological
molecules
COVALENT BOND #’S
• Atoms want to fill their
electron shells. An atom
wants to make just enough
bonds to fill its shells.
• H makes one bond
• O makes two bonds
• C makes four bonds
Compounds
• Chemical Formulas - show how many and
which atoms are in a compound
– Ex. H2O
• Structural Formulas - show the
arrangement of the atoms in a compound
– Ex. H-O-H
• Isomers - molecules with the same
chemical formula, but different structure
(ex. propanol and isopropanol)
Isomers
MACROMOLECULES
• Macromolecules – giant molecules
• Monomers (smaller units) join to
make polymers (macromolecules)
• The four major biological
macromolecules
– Carbohydrates
– Lipids
– Proteins
– Nucleic acids
Carbohydrates
• Structure
– Composed of C, H, and O with
approximately twice as many H’s as
O’s
– Building blocks (monomers) are
sugars
• Function
– Main source of energy
• Types of Carbohydrates
– Monosaccharide – one sugar
• Example: glucose (C6H12O6)
– Disaccharide – two sugars joined
• Example: lactose (C12H22O11)
– Polysaccharide – many sugars
joined
• Example: starch and fiber
Building and breaking down molecules
• Dehydration synthesis - two molecules
joined together by losing a molecule of
water
• Hydrolysis - larger molecules broken down
into smaller molecules by the addition of
water (ex. digestion)
Dehydration Synthesis
Hydrolysis
Lipids
• Structure
– Composed of C, H, and O, but the # of
H’s is much greater than the # of O’s
– Building blocks – no monomers
• Functions:
– Energy storage, basic structure of plasma
membranes, protection, insulation, and
waterproof coverings
• Type of lipids
– Fats and Oils
• Example: Fatty Acids (a long carbon
chain with a –COOH at one end)
– Steroids
• Examples: cholesterol, testosterone,
estrogen, Vitamin A, and cortisone
– Waxes
• Example: ear wax
• Different types of fatty acids:
– Saturated - all single, covalent
bonds in between carbons in chain
– Unsaturated - one double bond
between carbons in chain
– Polyunsaturated - many double
bonds between carbons in chain
Steroids
Protein
• Structure
– Composed of C, H, & O as well as
nitrogen, N, and possibly sulfur
– Building blocks (monomers) are amino
acids
• Functions
– Proteins are building materials (like
muscle and hair), act as enzymes,
antibodies, transporters, and
markers
Amino Acid Structure
General structure
Alanine
Serine
Amino Acids
• There are 20 main amino acids.
• Each has same basic structure
with the only difference being
the “R” group
• Amino acids are linked by peptide
bonds (formed by dehydration
synthesis)
Nucleic Acids
• Structure
– Composed of C, H, O, N, and P
– Building blocks (monomers) are
nucleotides
• Nucleotides consist of a sugar, a
nitrogenous base, and a
phosphate
• Functions
– Genetics and energy transfer
• Types of Nucleic Acids
– DNA, RNA, and ATP
Chemical Reactions
• Chemical reactions always involve
breaking bonds in reactants and
making bonds in products
• Some reactions release energy and
therefore usually occur
spontaneously
• Other reactions need energy to
happen
• Activation energy – the minimum
amount of energy needed to start any
reaction
• Enzymes are catalysts which speed up
chemical reactions
• Enzymes are proteins that lower
activation energy and allow reactions to
occur at normal temperatures
• Without enzymes, too much energy
would be needed to start all of the
thousands of reactions your body
performs all of the time!
Reaction pathway Activation energy
without enzyme without enzyme
Activation energy
with enzyme
Reaction pathway
with enzyme
• Each enzyme is specific and has a
specific shape
• Enzymes are not permanently
changed and are not used up in
the reaction
• Enzyme activity is affected by
pH, temperature, and
concentration levels
– Most of your enzymes work
best at 98.6°F
• Most enzyme names end in -ase
• Reactants are called substrates.
• Enzymes work on substrates (either
breaking them down or adding
something to them.
• Example: Lactase (enzyme) breaks
down lactose (substrate), which is
the sugar in milk.
Enzyme Activity