Download The Chemical Basis of Life

The Chemical Basis of
Life
Basic Chemistry
Matter: anything that has mass and takes up
space
Element: simple form of matter, a substance that
cannot be broken down into two or more
different substances
26 elements in the human body
11 major elements
15 trace elements
Compound: atoms of two or more elements joined
to form chemical combinations
96% of the human body is made up of
1. Carbon
2. Oxygen
3. Hydrogen
4. Nitrogen
ESSENTIAL ELEMENTS
Element
Symbol
% by Mass
Element
Symbol
% by Mass
Oxygen
O
65.0
Iron
Fe
Trace
Carbon
C
18.5
Zinc
Zn
Trace
Hydrogen
H
9.5
Copper
Cu
Trace
Nitrogen
N
3.3
Iodine
I
Trace
Calcium
Ca
1.5
Manganese
Mn
Trace
Phosphorus
P
1.0
Boron
B
Trace
Potassium
K
0.4
Chromium
Cr
Trace
Sulfur
S
0.3
Molybdenum
Mo
Trace
Sodium
Na
0.2
Cobalt
Co
Trace
Chlorine
Cl
0.2
Selenim
Se
Trace
Magnesium
Mg
0.1
Flourine
F
Trace
Atoms Structure
Protons: +
Electrons: –
Neutrons: no charge
Atomic Number =
proton number
Atomic Mass = protons
+ neutrons
Chemical Bonds
1.
2.
3.
Ionic or electrovalent bond: formed by a
transfer of electrons; electrostatic force
binds positively and negatively charged
ions together
Covalent bond: formed by sharing of
electron pairs between atoms
Hydrogen bond: weak bond; results from
unequal charge distribution on molecules
Chemical Bonds
Chemical Bonds
Ionic Bond
Chemical Bonds
Covalent Bond
Chemical Bonds
Chemical Reactions
There are 3 basic types of chemical reactions
involved in physiology:
1.
Synthesis reaction (dehydration synthesis):
combining of two or more substances to form
a more complex substance; A+B
AB
2.
Decomposition reaction (hydrolysis): breaking
down of a substance into two or more
substances;
AB
A+B
1.
Exchange reaction: decomposition of two
substances and, in exchange, synthesis of two
new compounds; AB+CD
AD+BC
Metabolism


Metabolism—all of the chemical reactions
that occur in body cells
Catabolism



Ultimately, the end products of catabolism are carbon
dioxide, water, and other waste products
More than half the energy released is transferred to
ATP, which is then used to do cellular work
Chemical reactions that break down complex
compounds into simpler ones and release energy;
hydrolysis (decomposition) is a common catabolic
reaction
Metabolism

Anabolism


Chemical reactions that join simple molecules
together to form more complex molecules
Chemical reaction responsible for anabolism is
dehydration synthesis
Inorganic Compounds
1.
2.
3.
4.
Water: Body’s most abundant compound
Oxygen and Carbon Dioxide
Electrolytes: acids, bases, and salts:
dissociate in solutions to form ions
Buffers: maintain the constancy of the
pH
Organic Compounds

Organic molecules


Have at least one carbon atom and at least
one C–C or C–H bond in each molecule
Often have functional groups attached to the
carbon-containing core of the molecule
Organic Compounds
Sugars, starches and cellulose are carbohydrates.
Sugars and starches serve as energy sources for cells; cellulose is the main
structural component of the walls that surround plant cells.
Carbohydrates contain carbon, hydrogen, and oxygen in a ratio of two
hydrogen and one oxygen to every carbon atom.
Typically contain 3 to 7 carbon atoms.
Large numbers of polar hydroxyl groups, plus a carbonyl
group, gives a monosaccharide hydrophilic properties.
Glucose (C6H12O6), the most abundant monosaccharide, is used as an
energy source in most organisms.
Glucose is so important in metabolism that its concentration is carefully
kept at a homeostatic level in the blood of humans and other complex
animals.
When dissolved in water, glucose undergoes a rearrangement of its atoms,
forming one of two possible ring structures.
When the hydroxyl group is on the plane of the ring as the –CH2OH side
group, the glucose is designated beta-glucose.
When its on the side opposite the -- CH2OH side group, the compound is
designated alpha-glucose.
A disaccharide contains two monosaccharide rings joined by a glycosidic
linkage, consisting of a central oxygen covalently bonded to two carbons,
one in each ring.
The most abundant carbohydrates are polysaccharides. A group that
includes starches, glycogen, and cellulose.
A polysaccharide is a macromolecule consisting of repeating units of simple
sugars, usually glucose. Thousands of units are typically present in a single
molecule.
Starch, the typical form of carbohydrate used for energy storage in plants,
is a polymer consisting of a-glucose subunits. When energy is needed for
cellular work, the plant can hydrolyze the starch, releasing the glucose
subunits.
Humans and other animals that eat plant foods have enzymes to hydrolyze
starch.
Glycogen (sometimes referred to as animal starch) is the form which glucose
is stored as energy sources in animal tissues.
It is more extensively branched and more water soluble.
Glycogen is stored mainly in the liver and muscle cells.
Cellulose is the most abundant carbohydrate; it accounts for 50% or
more of all the carbon in plants.
Cellulose is a structural carbohydrate.
Cellulose is an insoluble polysaccharide composed of many glucose
molecules joined together.
Humans do not have the enzymes needed to break down cellulose.
Carbohydrates may also be combined with proteins to form glycoproteins,
compounds present on the outer surface of cells other than bacteria.
Some of these carbohydrate chains allow cells to adhere to one another,
while others provide protection
Most proteins secreted by cells are glycoproteins. These include the
major components of mucus.
Carbohydrates can also combine with lipids to form glycolipids,
compounds present on the surface of animal cells that are thought to
allow cells to recognize and interact with one another.
The most abundant lipids in living organisms are triacyglycerols, also
known as triglycerides.
These compounds commonly known as fats, are an economical form
of reserve fuel storage because, when metabolized, they yield more
than twice as much energy per gram as do carbohydrates
Saturated fatty acids contain the maximum possible number of hydrogen
atoms.
Fats high in saturated fatty acids, such as animal fat and solid vegetable
shortening, tend to be solid at room temperature
Unsaturated fatty acids include one or more adjacent pairs of carbon
atoms joined by a double bond. They tend to be liquid at room
temperature.
Fatty acids with one double bond are called monounsaturated fatty
acids.
Those with more than one double bond are polyunsaturated fatty
acids.
At least two unsaturated fatty acids (linoleic acid and arachidonic
acid) are essential nutrients that must be obtained from food
because the human body cannot make them.
Phospholipids belong to a group of lipids, called amphipathic lipids,
in which one end of each molecule is hydrophobic and the other end is
hydrophilic.
The properties of these lipid molecules cause them to form lipid bilayers
in aqueous solution, making them uniquely suited to function as the
functional components of cell membranes.
linoleic acid

Name% LA†ref.Safflower oil78%Grape seed
oil73%Poppyseed oil70%Sunflower oil68%Hemp
oil60%Corn oil59%Wheat germ
oil55%Cottonseed oil54%Soybean
oil51%Walnut oil51%Sesame oil45%Rice bran
oil39%Pistachio oil32.7%Peanut
oil32%[17]Canola oil21%Chicken fat1823%[18]Egg yolk16%Linseed
oil15%Lard10%Olive oil10%Palm oil10%Cocoa
butter3%Macadamia oil2%Butter2%Coconut
oil2%
arachidonic acid
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
Meat, eggs and dairy
Synthesized from linoleic acid
Lipids are a group of compounds that are defined, not by their
structure, but rather by the fact that they are soluble in nonpolar
solvents (ether and chloroform) and are relatively insoluble in water
(hydrophobic).
They consists mainly of carbon and hydrogen, with few oxygencontaining functional groups.
Groups of lipids are fats, phospholipids, caratenoids, steroids, and
waxes.
The orange and yellow plant pigments called carotenoids are classified
with lipids because they are insoluble in water and have an oily
consistency.
Most animals can convert carotenoids to vitamin A, which can then be
converted to the visual pigment retinal.
A steriod consists of carbon atoms arranged in four attached rings; three
of the rings contain six carbon atoms, and the fourth contains five
The length and structure of the side chains that extend from these rings
distinguish one steroid from another.
Among the steroids of biological importance are cholesterol, bile salts,
reproductive hormones, and cortisol and other hormones secreted by the
adrenal cortex
Cholesterol is an essential structural component of animal cell
membranes, but when there is excess cholesterol in the blood it forms
plaques on artery walls. Leading to an increased risk of heart attack.
Plant cell membranes contain molecules similar to cholesterol. Some
of these plant steroids are able to block the absorption of cholesterol
by the intestines.
Bile salts emulsify fats in the intestine so that they can be
enzymatically hydrolyzed.
Steroid hormones regulate certain aspects of metabolism in a
variety of animals.
Most genetic information is used to specify the structure of proteins.
Proteins are involved in virtually all aspects of metabolism because most
enzymes (molecules that regulate the thousands of different chemical
reactions that take place in an organism) are proteins.
Proteins can be assembled into a variety of shapes, allowing them to
serve as major structural components of cells and tissues.
For this reason, growth and repair, as well as maintenance of the
organism, depend on these compounds.
The protein constituents of a cell are the clues to its lifestyle.
Each cell type contains characteristic forms, distributions, and amounts of
protein that largely determine what the cell looks like and how it functions.
Amino acids, the constituents of proteins, have an amino group (--NH2)
and a carboxyl group (--COOH) bonded to the same asymmetrical
carbon atom, know as the alpha carbon.
There are about 20 amino acids commonly found in proteins,
each uniquely identified by the variable side chain (R group) bonded to the
a-carbon
Amino acids classified as having nonpolar side chains tend to have
hydrophobic properties, whereas those classified as polar are more
hydrophilic.
With some exceptions, bacteria and plants can synthesize all their needed
amino acids from simpler substances.
If the proper raw materials are available, the cells of humans and
animals can manufacture some, but not all, of the biologically significant
amino acids.
Those that animals cannot synthesize and so must obtain from the diet are
known as essential amino acids.
Polar Amino Acids
Nonpolar Amino Acids
Electrically Charged Amino Acids
Acidic
Basic
Amino acids combine chemically with one another by a condensation
reaction that bonds the carboxyl carbon of one molecule with the amino
nitrogen of another.
The covalent carbon-to-nitrogen bond linking two amino acids together is
called a peptide bond.
When two amino acids combine, a dipeptide is formed; a long chain of
amino acids is a polypeptide.
An almost infinite variety of protein molecules is possible, differing from one
another in the number, types, and sequences of amino acids they contain.
The overall structure of a protein helps determine its biological activity.
The biological activity of a protein can be disrupted by a change in
conformation.
When a protein is heated, subjected to significant pH changes, or treated
with a number of chemicals, its structure can become disordered and the
coiled peptide chains can unfold to give a more random conformation.
Such changes in shape and the accompanying loss of biological activity are
termed denaturation of the protein.
Denaturation generally cannot be reversed (you can’t “unfry” an egg).
Nucleic acids transmit hereditary information and determine what proteins a
cell manufactures.
Ribonucleic acids (RNAs)
Deoxyribonucleic Acids (DNAs)
DNA comprises the genes, the hereditary material of the cell, and contains all
the instructions for making proteins, as well as all the RNA, needed by the
organism.
RNA is required as a direct participant in the complex process in which amino
acids are linked to form polypeptides.
Nucleic acids are polymers of nucleotides, molecular units that consist of:
1. A five carbon sugar, either ribose (in RNA) or deoxyribose (in
DNA)
2. One or more phosphate groups, which make the molecule
acidic
3. A nitrogenous base, a ring compound that contains nitrogen.
The base may either be a double-ringed purine or a single-ringed
pyrimidine
Adenosine triphosphate (ATP), composed of adenine, ribose, and three
phosphates , is a major importance as the primary energy currency of all
cells.
The two terminal phosphate groups are joined to the nucleotide by covalent
bonds.