Chapter 3:
Part II Biochemistry
• Water makes up between 60 and 70% of
organisms’ bodies
• Polarity
• Molecules with partial charges on
opposite ends are polar
• Oxygen atoms are larger than hydrogen, so
electrons spend more time near oxygen,
giving it a slight negative charge, and
hydrogen a slight positive charge.
Why is polarity important?
•“Like dissolves like” – polar substances are
good at dissolving other polar substances and
substances that are ionic – hydrophilic
•Ex: sugar and salt
•Polar substances DO NOT dissolve
substances that are nonpolar (without
charged ends) – hydrophobic
•Ex: oil, grease, wax
•Polarity helps chemical reactions to take
place.
Negative ends of water are attracted to Na+
Positive ends of water are attracted to Cl-
• Hydrogen bonds form when a
covalently-bonded H+ is attracted to a
negatively-charged atom in a
neighboring molecule (such as oxygen in
neighboring water molecule, or chlorine
in NaCl).
• Hydrogen bonds are relatively weak
bonds.
Properties of water
•Ice floats
•Water absorbs and retains heat
•Water molecules stick to each other
•Water molecules stick to other polar
substances
•Ice floats:
•When water freezes, hydrogen bonds
lock water molecules into a structure
that has empty spaces, making it less
dense than liquid water
Liquid water
Ice
Water absorbs and retains heat
•Because of hydrogen bonds, water can
absorb large amounts of energy
•Absorbs lot of heat before it boils
•Helps keep cells at an even temperature
despite changes in the environment –
homeostasis again!!
•Allows large bodies of water to maintain
a relatively constant temperature.
Water molecules stick to each other
•Cohesion – the attraction of water molecules
to each other
•Cohesive forces are strong enough to cause
water to act as though it has a thin “skin” on
its surface – surface tension.
Jesus lizards walking on surface tension
Water molecules stick to other polar
substances
•Adhesion - the attraction between
particles of different substances.
•Ex: Water sticks to the surface of
your car after it rains, sticks to your
skin after a shower
•Capillarity - adhesion and cohesion
enable water molecules to move
upward through narrow tubes
•Ex: water moving through a stem
of a plant, helps blood flow in
blood vessels
Organic Molecules
• Examples: carbohydrates, lipids, proteins,
nucleic acids
• Always contain carbon
• Why carbon? Carbon has 4 electrons in
outer shell – can form covalent bonds with
up to 4 other atoms.
•Carbon can share electrons with other
carbon atoms to form a chain
•Hydrocarbon chain can
turn back on itself to
form a ring
Carbohydrates
Importance:
• Quick energy and short-term energy
storage
• Make up cell wall in plants
• Make up shells of crabs, lobsters and
insects
• Help cells to recognize one another
•Monosaccharides (single sugar):
•glucose – blood sugar
•fructose – found in fruit
•galactose – found in milk
•Glucose, fructose, and galactose all have
the same molecular formula, C6H12O6,
but different structural formulas
Fructose
Galactose
Glucose
•Below are 3 ways to represent glucose:
• Disaccharide - made from linking two
monosaccharides together.
• Examples of disaccharides:
• Maltose = glucose + glucose
• Sucrose = glucose + fructose
• Lactose = glucose + galactose
Sucrose
•Polysaccharides – contain many glucose
units
•Ex: starch, glycogen, & cellulose
•Starch can be up
to 4000
glucose units
•Ex: Glycogen
– after eating
starchy foods,
the body
converts
glucose in the
blood into
glycogen –
stored in liver
and released as
needed
•Ex: Cellulose –
found in plant
cell walls.
•Glucose units
joined in such a
way that we can’t
digest it – passes
through as
roughage – may
help prevent
colon cancer
•Foods they can be found in:
•Simple sugars –Fruit, milk, sweets,
sodas, juices
•Starches –
Breads, pasta,
rice, corn,
wheat, cereal,
leafy vegetables,
carrots
Lipids
• Examples:
• Fats - solid at room temp. – animal
origin
• Oils - liquid at room temp. – plant
origin
• Waxes – protective covering on plants
& animals
• Phospholipids and steroids
• Lipids do not dissolve in water - nonpolar
Importance:
•Long-term energy reserves
•Form membranes in cells
•Hormones such as testosterone
and estrogen
•Insulation, nerve impulses
•Repel water – duck feathers
•Structure – 1 glycerol plus 3 fatty acid
molecules
• Saturated vs. unsaturated fatty acids:
• Saturated – no double covalent bonds
between carbon atoms – makes butter
and lard solids
• Monounsaturated – has 1 double bond
between carbon atoms
• Polyunsaturated – 2 or more double
bonds – makes cooking oil liquid
• Unsaturated and polyunsaturated
are better for you than saturated fats
•Foods they can be found in:
•Butter, foods fried in oil, bacon,
red meat, cheese
Proteins
Importance:
• Build living tissue – hair, nails, tendons,
ligaments, muscle, bone, etc.
• Act as enzymes to speed reactions
• Act as antibodies to fight disease
Proteins are made of amino acids
•
•
•
•
•
Central carbon atom
Hydrogen atom
Amino group (-NH2)
Carboxyl group (-COOH)
“R” group – which differs between amino
acids
Amino acids are joined by peptide bonds
to form polypeptides.
•Foods they can be found in:
•Meat, eggs, cheese, beans, nuts, soy
Levels of organization:
• Shape of protein is related to its function.
• When exposed to extremes in heat or pH,
proteins change their shape – undergo
denaturation – normal bonding between
R groups is disturbed.
• Change cannot be reversed – protein no
longer works.
Nucleic Acids
• Examples: DNA (deoxyribonucleic
acid) and RNA (ribonucleic acid)
• Importance: molecules of inheritance
– needed for cell reproduction and
making proteins
•Structure –
made of
nucleotides.
DNA is double-stranded, with complementary
base pairing – A and T, C and G always pair.