Transcript The Chemical Basis of Life

The Chemical Basis of Life
BASIC CHEMISTRY
• ATOMIC STRUCTURE
– NUCLEUS
• PROTONS – ATOMIC MASS = 1
• NEUTRONS – ATOMIC MASS = 1
– ELECTRONS
• NOT ENOUGH MASS FOR US TO
CONSIDER.
Atomic Structure
(-)
(+)
Chemical Elements
• All matter on Earth is composed of
combinations of chemical elements.
• Elements cannot be broken down by
chemical processes into simpler
substances.
• There are over 90 naturally-occurring
chemical elements.
• The most common chemical
elements in living things are:
– S, P, O, N, C, H
Periodic Table
MOLECULES and COMPOUNDS
• MADE OF MORE THAN ONE
KIND OF ATOM HELD TOGETHER
BY A CHEMICAL BOND.
• FAMILIAR ONES INCLUDE
WATER, SUGAR, FAT, PROTEIN,
CARBOHYDRATE, SALT.
WHY DO SOME ATOMS COMBINE
TO FORM COMPOUNDS AND
MOLECULES?
• An Atom’s ability to combine with
other atoms relies on its number of
electrons in its outer shell (energy
level): the outer shell needs to be full
for the atom to become stable
(stable atoms do not combine with
other atoms).
• For our purposes, the first shell
contains 2 electrons, and each
successive shell contains up to 8
electrons.
Electron Energy Levels:
First energy level holds up to 2
electrons
Second energy level holds up to
8 electrons
Third energy level holds up to 8
electrons
Stable atoms:
• Some atoms already have a full
outer energy level.
• These atoms do not react with
other atoms to form molecules.
• These include the inert or noble
gases: helium, argon, neon,
krypton, xenon, and radon.
If an atom is not stable:
• It will combine with other atoms
• Some will give up or gain electrons.
– These form ionic bonds
– Each member is an ion
– The opposite electrical charges attract
each other
• Some will share electrons between
them.
– The force holding them together is called
a covalent bond.
Ionic Bonds
NaCl = salt
POLAR MOLECULES
• BECAUSE OF THE WAY SOME
MOLECULES COMBINE, THEY
CONTAIN DIFFERENT
ELECTRICAL CHARGES AT
OPPOSITE ENDS.
• THIS CREATES ATTRACTION TO
OPPOSITE CHARGES ON OTHER
MOLECULES
Polar Molecules
Positive end
HYDROGEN BONDS
• HOLD TOGETHER MOLECULES
THAT CONTAIN HYDROGEN.
• IMPORTANT IN WATER
MOLECULES AND MANY
MOLECULES IN LIVING
ORGANISMS.
• WEAKER THAN IONIC OR
COVALENT BONDS.
• THESE HOLD DNA TOGETHER
CHEMICAL REACTION
• ONE OR MORE SUBSTANCES IS
CHANGED INTO NEW
SUBSTANCES BY BREAKING OR
FORMING CHEMICAL BONDS.
• EX:
– 6CO2 + 6H20  C6H12O6 + 6O2
– WHAT IS THE ABOVE EQUATION
AND WHAT DOES IT MEAN?
ALL CHEMICAL REACTIONS
INVOLVE ENERGY
• WHEN BONDS
FORM,
ENERGY IS
STORED
• WHEN BONDS
BREAK,
ENERGY IS
RELEASED
ATP = energy carrier of a cell
ORGANIC COMPOUNDS
• COMPOUNDS THAT CONTAIN
CARBON, HYDROGEN AND
OXYGEN IN DEFINITE
PROPORTIONS.
• USUALLY ASSOCIATED WITH
LIVING THINGS
CARBOHYDRATES
• BUILDING BLOCKS = SIMPLE
SUGARS (MONOSACCHARIDES).
• MONOSACCHARIDES INCLUDE
– GLUCOSE
– FRUCTOSE
ISOMERS
– GALACTOSE
ALL THREE HAVE THE SAME MOLECULAR
FORMULA, BUT DIFFERENT STRUCTURE:
C6H1206
THESE MOLECULES ARE THE MOST
COMMON SOURCE OF ENERGY FOR
LIVING THINGS.
Isomers – can you tell
the difference?
glucose
C6H12O6
MORE COMPLEX CARBS
• DISACCHARIDES
– MADE UP OF TWO MONOSACCHARIDES
CHEMICALLY COMBINED.
– GLUCOSE + GLUCOSE = MALTOSE
– GLUCOSE + GALACTOSE = LACTOSE
• THIS IS MILK SUGAR
– GLUCOSE + FRUCTOSE = SUCROSE
• THIS IS TABLE SUGAR
• These molecules store energy for later
use
THE MOST COMPLEX
CARBS
• STARCH – MADE UP OF MANY GLUCOSE
UNITS COMBINED.
– PLANT LONG-TERM FOOD STORAGE
• GLYCOGEN – MADE OF MANY GLUCOSE
UNITS COMBINED
– ANIMAL STORAGE IN LIVER AND
MUSCLES
• CELLULOSE – MADE OF MANY GLUCOSE
UNITS COMBINED.
– PLANT CELL WALLS; FIBER
• CHITIN – PROTECTIVE COVERINGS IN
INSECTS AND OTHER ARTHROPODS; ALSO
IN FUNGUS CELL WALLS
DEHYDRATION SYNTHESIS
• In order for two molecules to join
together, each molecule must break
off atoms to provide a bonding place.
• Most organic molecules do this by
losing a hydrogen atom from one
molecule and a hydroxyl group from
the other.
• These two join to form water, and
allow the molecules to make a bond.
Dehydration Synthesis
C6H12O6 + C6H12O6  C12H22O11 + H2O
disaccharide
Hydrolysis
• In order to break down a large
molecule to make smaller
molecules, a molecule of water
has to be added.
• This fills in the spots where the
bond broke – one molecule gets
a hydrogen atom, the other gets
the hydroxyl group.
Hydrolysis
ADD WATER
TO A
POLYSACCHARIDE
AND
FORM
MANY
MONOSACCHARIDES
Dehydration Synthesis and
Hydrolysis store and release
energy
• Dehydration synthesis stores
energy by forming bonds.
– As in the formation of
polysaccharides from
monosacharides
• Hydrolysis releases energy by
breaking bonds.
Lipids:
fats, oils, waxes,
phospholipids, steroids
• Used for longer-term storage of
energy
• Fats – in animals
• Oils – in plants
• Waxes – water repellent (In your ears,
beeswax, coat plant leaves),
waterproof bird feathers.
• Steroids – in animal cell membranes
and some hormones.
• Phospholipids – make up parts of cell
A common fat = Triglyceride
• Composed of one glycerol and
three fatty acids, joined together
by dehydration synthesis:
3
G
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C
F
A
T
T
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A
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C
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L
D
S
Saturated and unsaturated
fats:
• Saturated fats have no C=C bonds
within the fatty acids
– These are considered unhealthy – they
clog up the coronary (heart) arteries.
– These are solid at room temperature.
– From animals.
• Unsaturated fats have at least one
C=C bond in one of its fatty acids
– These are considered healthier.
– Plant oils are usually unsaturated.
– Liquid at room temperature.
PROTEINS
• Important for movement, structure,
regulation, transport, nutrition, and
defense.
• Composed of building blocks called
amino acids
• Humans cannot make these from
scratch – we must eat foods with
proteins, then use the amino acids to
make our own proteins.
Amino Acids
• There are 20 different aa’s
• They are combined in various numbers and
orders to produce a great number of
different proteins.
• Each aa has an amino group, an acid group
(carboxyl), and a variable group (there are
20 different variable groups).
• Amino acids attach to each other by
dehydration synthesis forming a peptide
bond between the amino group of one aa
and the acid group of the other aa.
• Change the number or arrangement of the
aa’s and the protein is changed.
Amino acids
Acid group
Amino group
Three
different R
groups:
Dipeptide – two aa’s joined by a
peptide bond.
Polypeptide
Enzymes – Special Proteins
• Change the rate of chemical
reactions without being used up
themselves (biological catalyst).
• Can be used over and over.
• Action is very specific –
each enzyme will only
work on one particular
substance (the substrate).
HOW DOES AN ENZYME
WORK?
• LOCK AND KEY
MODEL
• INDUCED FIT
MODEL
Nucleic Acids
• Molecules of heredity.
• DNA – deoxyribonucleic acid
– makes up chromosomes (GENES)
– Contains the genetic code
• Determines the organism’s traits
• Contains the code for making proteins
Which control the cell’s activities
• RNA – ribonucleic acid
– Helps DNA make proteins
Metabolism
• All the chemical reactions that
take place in the organism
• These reactions need to be
balanced to keep the organism
alive
– The balance is called homeostasis
Water and Solutions
• H2O
• Forms solutions easily – all life’s
chemical reactions take place in
solutions.
• Solution – two or more substances
are mixed together that they cannot
be distinguished.
– Ex- sugar + water or salt + water
solute
• Water is the solvent
• Sugar or salt is the
Salt + Water Solution:
Acids and Bases
• Form when an ionic compound
is mixed with water to form a
solution.
• Acid – releases H+ (hydrogen)
ions (like HCl = hydrochloric acid)
• Base – releases OH- (hydroxide)
ions (like NaOH = sodium hydroxide)
pH scale
• Standard measurement of the
H+ ions in a solution
• Ranges from 0 – 14
• 7 is neutral
– Water has an equal number of H+
and OH- ions, so there is no excess
of either ion.
pH scale
• Acids are less than 7
• Bases are more than 7
• The further away from 7, the
stronger the acid or base
• Most chemical reactions in
humans take place between 6+8
– However, stomach acid is 2-3
– Enzymes are pH specific