Water and its Properties
Water is a polar molecule. This means that water is partially negative (around the oxygen) and partially
positive (around the hydrogens).
Polarity is the property responsible for allowing water to dissolve (break apart) ionic compounds like
NaCl (salt).
Cohesion is a property of water where water molecules stick to each other. Adhesion, on the other
hand, is a property of water where water molecules stick to other substances (such as glass or plastic).
When a water strider walks on the pond water, the tension in the water, caused by cohesion, prevents
the water strider from sinking.
The U-shape water curve seen in a graduated cylinder is a result of water sticking to the plastic. This is
an example of adhesion.
Cohesion and adhesion properties of water are seen in plants during the process of transpiration.
Transpiration is the evaporation of water from plants into the atmosphere. Both, cohesion and adhesion
properties in plants, are referred to as capillary action.
Water has high specific heat capacity. In other words, the temperature of water is very stable; it has to
be extremely hot or cold for water to change its temperature.
Usually substances become denser when they are in their solid forms; however, water becomes LESS
DENSE when it is in its solid form (ice). This is extremely important for the survival of organisms. If ice
would sink (instead of floating) then all animals in the lakes, ponds, and oceans would die because the
whole habitat would freeze.
The human body is mostly water. Water helps regulate temperature due to its high specific heat
capacity, and all chemical reactions in the human body (include fertilization – making babies) happen in
water.
Hydrogen bonding is a special type of bond seen when a hydrogen atom shows a partial attraction to an
oxygen, nitrogen, or fluorine atom. Hydrogen bonding is seen in water and is a result of water’s polar
nature.
Macromolecules
Nucleic Acids
Deoxyribonucleic acid (DNA) is a double stranded macromolecule made up of monomers called
nucleotides. DNA codes the genetic information for all life and is composed of four nitrogenous bases:
adenine-thymine and guanine-cytosine
The nitrogenous base adenine always pairs with thymine in DNA. Guanine and cytosine always pair
together in both DNA and RNA.
Ribonucleic acid (RNA) is a single stranded macromolecule made up of monomers called nucleotides
(just like DNA). RNA contains four bases: adenine-uracil and guanine-cytosine.
Notice that the base thymine is only seen in DNA, while the base uracil is only seen in RNA. The other
bases (adenine, guanine, and cytosine are found in both DNA and RNA).
A nucleotide is a monomer that forms both DNA and RNA. Nucleotides are composed of a sugar, a
phosphate, and a nitrogenous base. In DNA the sugar is deoxyribose, and in RNA the sugar is ribose.
DNA and RNA are both nucleic acids. Nucleic acids are polymers formed by monomers called
nucleotides.
The nucleic acid DNA is transformed into RNA, which is then transformed into a protein on a ribosome.
The central dogma of molecular biology states that DNA RNA  Protein. This form of RNA is referred
to as mRNA (messenger RNA) because it carries the message to be translated to a protein.
Nucleic acids are composed of the atoms carbon, hydrogen, oxygen, nitrogen, and phosphorus.
Macromolecules
Carbohydrates
Carbohydrates are composed of carbon, hydrogen, and oxygen atoms in a 1:2:1 ratio in that order. This
means that there will always be the same amount of carbons and oxygen atoms, but there will be twice
as many hydrogen atoms. For example, the molecular formula for the sugar glucose is C6H12O6. Notice
that glucose has the same amount of carbon and oxygen atoms, but twice as many hydrogen atoms.
One sugar is called a monosaccharide. Glucose is an example of a simple one sugar molecule.
Two sugars that combine together are called disaccharides. Maltose is an example of a disaccharide
formed by two glucose molecules. Lactose is another disaccharide formed by two sugars, glucose and
galactose.
When many sugars combine they form polysaccharides. Cellulose, a carbohydrate in plant cell walls is
one example of a polysaccharide.
Starch is another example of a polysaccharide in plants. Starch is used by plants to store energy.
Glycogen is a polysaccharide in animals found in muscle cells and in the liver. Glycogen stores energy in
animals.
Carbohydrates provide the body with the quickest source of energy. It is easier for the body to break
down carbohydrate than fat or protein.
Foods that contain carbohydrates include bread, pasta, vegetables and fruits, candy, milk, and other
products
You may be able to recognize a sugar by its name. Sugars tend to end with the suffix –ose. For example,
glucose, fructose, lactose, sucrose, and maltose. Pay attention to this little detail.
Macromolecules
Lipids
Lipids (Fats) are similar to carbohydrates because they are made up of the same atoms: carbon,
hydrogen, and oxygen. However, fats do not have the 1:2:1 ratio seen in carbohydrate.
Lipids have very little oxygen atoms and many hydrogen atoms.
If a Lipid has all carbons in its tail surrounded by hydrogen atoms, then the fat is said to be saturated
(filled with hydrogen. If some carbons are missing hydrogen atoms, then the fat is said to be
unsaturated (not saturated with hydrogen atoms). Unsaturated fats have double bonds, while saturated
fats have single bonds.
Saturated fats tend to be solid and are unhealthy (e.g. butter), while unsaturated fats tend to be liquid
and are healthy (e.g. olive oil).
Lipids carry a lot of energy and are stored in the body as an energy reservoir.
Lipids offer water proof protection. For example, plants have a waxy cuticle on their leaves to prevent
excess water from evaporating and causing dehydration.
Examples of lipids include fats, phospholipids, triglycerides, cholesterol, sterols, some vitamins, and
more.
Macromolecules
Proteins
Proteins are polymers formed by monomers called amino acids.
Amino acids (and thus proteins) are composed of the atoms carbon, hydrogen, oxygen, and nitrogen.
Two amino acids come together by the removal of a water molecule. This is called dehydration
synthesis.
The addition of water tends to break the bonds of molecules, which release energy. The addition of
water is called hydrolysis.
Proteins are so important for life that almost all of a living thing is protein. Your whole body is protein
with some exceptions that include water, teeth, and bones.
Examples of proteins include enzymes, antibodies, hormones, and foods (steak, chicken, and fish).
Hemoglobin is another example of a protein. It carries oxygen throughout the body in red blood cells.
Proteins have various shapes. These shapes are primary, secondary, tertiary, and quaternary.
Hemoglobin has a quaternary shape because it is made up of 4 separate tertiary-shaped proteins. The
primary structure of a protein is a straight chain of amino acids.
pH
The term pH refers to the “power of hydrogen ions.”
A pH meter can be used to determine whether a solution is acidic, basic (alkaline), or neutral.
The more hydrogen ions (H+) that are in solution, the smaller the pH and the more acidic the solution is.
The less hydrogen ions (H+) that are in solution, and the greater the hydroxide (OH-) ions in solution, the
greater the pH and the more basic (alkaline) the solution is.
A pH less than 7 indicates an acidic solution, while a pH greater than 7 indicates a basic (alkaline)
solution.
A pH of exactly 7 is a neutral pH. Pure water has a pH of 7.
Enzymes
The majority of enzymes are classified as proteins, but some enzymes are made from RNA (these are
called ribozymes).
However, for the test (and high school Biology) you need to know that enzymes are proteins.
Enzymes work best at certain temperatures, pH, and salt concentrations. Therefore, every enzyme has
its own optimum temperature and pH.
In the human body, the enzymes optimal temperature is 37 degrees Celsius or 98.6 degrees Fahrenheit.
In the human stomach the enzyme pepsin has a low pH between 0 through 2.
You can tell that a substance is an enzyme by its name. Most enzymes end in –ase. Examples of enzymes
include amylase, luciferase, catalase, and reverse transcriptase.
There are some exceptions to the naming rule. The enzyme pepsin, for example, does not end in –ase.
Trypsin is another enzyme that does not end in –ase.
When the temperature is too high or too low, the shape of the enzyme may change. If the enzyme’s
protein shape changes, the enzyme may stop working properly. This condition is referred to as
denatured.
Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy of
that reaction. Enzymes are also reaction-specific. This means that there is one enzyme for every type of
reaction.
Enzymes attach to their substrate at an active site. This analogy is similar to a lock (enzyme) and key
(substrate).
If enzymes can be denatured, and enzymes are proteins, then proteins can also be denatured. Girls
denature the protein that makes up their hair when they iron it. The excess heat of the iron causes the
3-dimensional curly hair shape to become straight.
Basic Chemistry
Atoms are small indivisible particles known as the building blocks of matter.
Atoms are composed of protons and neutrons in the center, and electrons circulating around.
Protons are positive, electrons are negative, and neutrons are neutral.
Electrons can be lost or gained, but protons and neutrons stay in the nucleus.
When an electron is lost, the atom becomes more positive because it has less negative charges.
When an electron is gained, the atom becomes more negative because it has more negative charges.