# Anatomy and Physiology of Animals/Chemicals

!original image by
jurvetson
CC-BY{width="400"}

## Objectives

After completing this section, you should know the:

-   symbols used to represent elements;
-   names of molecules commonly found in animal cells;
-   characteristics of ions and electrolytes;
-   basic structure of carbohydrates with examples;
-   carbohydrates can be divided into mono- di- and poly-saccharides;
-   basic structure of fats or lipids with examples;
-   basic structure of proteins with examples;
-   function of carbohydrates, lipids and proteins in the cell and
    animals\' bodies;
-   foods which supply carbohydrates, lipids and proteins in animal
    diets.

## Elements And Atoms

The elements (simplest chemical substances) found in an animal's body
are all made of basic building blocks or atoms. The most common elements
found in cells are given in the table below with the symbol that is used
to represent them.

  Element       Symbol
  ------------- --------
  Calcium       Ca
  Carbon        C
  Chlorine      Cl
  Copper        Cu
  Iodine        I
  Hydrogen      H
  Iron          Fe
  Magnesium     Mg
  Nitrogen      N
  Oxygen        O
  Phosphorous   P
  Potassium     K
  Sodium        Na
  Sulphur       S
  Zinc          Zn

## Compounds And Molecules

A **molecule** is formed when two or more **atoms** join together. A
compound is formed when two or more different elements combine in a
fixed ratio by mass. Note that some atoms are never found alone. For
example **oxygen** is always found as molecules of 2 oxygen atoms
(represented as O~2~).

The table below gives some common compounds.

  Compound                           Symbol
  ---------------------------------- ---------------
  Calcium carbonate                  CaCO~3~
  Carbon dioxide                     CO~2~
  Copper sulphate                    CuSO~4~
  Glucose                            C~6~H~12~O~6~
  Hydrochloric acid                  HCl
  Sodium bicarbonate (baking soda)   NaHCO~3~
  Sodium chloride (table salt)       NaCl
  Sodium hydroxide                   NaOH
  Water                              H~2~O

## Chemical Reactions

Reactions occur when atoms combine or separate from other atoms. In the
process new products with different chemical properties are formed.

Chemical reactions can be represented by **chemical equations**. The
starting atoms or compounds are usually put on the left-hand side of the
equation and the products on the right-hand side.

For example

-   H~2~O + CO~2~ gives H~2~CO~3~
-   or H~2~O + CO~2~ = H~2~CO~3~
-   Water + Carbon dioxide gives Carbonic acid

## Ionization

When some atoms dissolve in water they become charged particles called
**ions**. Some become positively charged ions and others negatively
charged. Ions may have one, two or sometimes three charges.

The table below shows examples of positively and negatively charged ions
with the number of their charges.

  Positive Ions   Negative Ions
  --------------- ----------------
  H+              Hydrogen
  Ca^2^+          Calcium
  Na+             Sodium
  K+              Potassium
  Mg^2^+          Magnesium
  Fe^2^+          Iron (ferrous)
  Fe^3^+          Iron (ferric)

Positive and negative ions attract one another to hold compounds
together.

Ions are important in cells because they conduct electricity when
dissolved in water. Substances that ionise in this way are known as
**electrolytes**.

The molecules in an animal's body fall into two groups: **inorganic
compounds** and **organic compounds**. The difference between these is
that the first type does not contain **carbon** and the second type
does.

## Organic And Inorganic Compounds

Inorganic compounds include water, sodium chloride, potassium hydroxide
and calcium phosphate.

**Water** is the most abundant inorganic compound, making up over 60% of
the volume of cells and over 90% of body fluids like blood. Many
substances dissolve in water and all the chemical reactions that take
place in the body do so when dissolved in water. Other inorganic
molecules help keep the **acid/base balance (pH)** and concentration of
the blood and other body fluids stable (see Chapter 8).

Organic compounds include **carbohydrates, proteins** and **fats** or
**lipids**. All organic molecules contain carbon atoms and they tend to
be larger and more complex molecules than inorganic ones. This is
largely because each carbon atom can link with four other atoms. Organic
compounds can therefore consist of from one to many thousands of carbon
atoms joined to form chains, branched chains and rings (see diagram
below). All organic compounds also contain hydrogen and they may also
contain other elements.

![](Anatomy_and_physiology_of_animals-organic_compounds.jpg "Anatomy_and_physiology_of_animals-organic_compounds.jpg")

## Carbohydrates

The name "carbohydrate" tells you something about the composition of
these "hydrated carbon" compounds. They contain carbon, hydrogen and
oxygen and like water (H~2~O), there are always twice as many hydrogen
atoms as oxygen atoms in each molecule. Carbohydrates are a large and
diverse group that includes sugars, starches, glycogen and cellulose.
Carbohydrates in the diet supply an animal with much of its energy and
in the animal's body, they transport and store energy.

Carbohydrates are divided into three major groups based on size:
**monosaccharides** (single sugars), **disaccharides** (double sugars)
and **polysaccharides** (multi sugars).

**Monosaccharides** are the smallest carbohydrate molecules. The most
important monosaccharide is glucose which supplies much of the energy in
the cell. It consists of a ring of 6 carbon atoms with oxygen and
hydrogen atoms attached.

**Disaccharides** are formed when 2 monosaccharides join together.
Sucrose (table sugar), maltose, and lactose (milk sugar), are three
important disaccharides. They are broken down to monosaccharides by
digestive enzymes in the gut.

**Polysaccharides** like starch, glycogen and cellulose are formed by
tens or hundreds of monosaccharides linking together. Unlike mono- and
di-saccharides, polysaccharides are not sweet to taste and most do not
dissolve in water.

:\* **Starch** is the main molecule in which plants store the energy
gained from the sun. It is found in grains like barley and roots like
potatoes.

:\* **Glycogen**, the polysaccharide used by animals to store energy, is
found in the liver and the muscles that move the skeleton.

:\* **Cellulose** forms the rigid cell walls of plants. Its structure is
similar to glycogen, but it can't be digested by mammals. Cows and
horses can eat cellulose with the help of bacteria which live in
specialised parts of their gut.

![](Anatomy_and_physiology_of_animals-Polysaccharides.jpg "Anatomy_and_physiology_of_animals-Polysaccharides.jpg")

## Fats

**Fats** or **lipids** are important in the plasma membrane around cells
and form the insulating fat layer under the skin. They are also a highly
concentrated source of energy, and when eaten in the diet provide more
than twice as much energy per gram as either carbohydrates or proteins.

Like carbohydrates, fats contain carbon, hydrogen and oxygen, but unlike
them, there is no particular relationship between the number of hydrogen
and oxygen atoms.

The fats and oils animals eat in their diets are called
**triglycerides** or **neutral fats**. The building blocks of
triglycerides are 3 **fatty acids** attached to a backbone of
**glycerol** (**glycerine**). When fats are eaten the digestive enzymes
break down the molecules into separate fatty acids and glycerol again.

**Fatty acids** are divided into two kinds: **saturated** and
**unsaturated fatty acids** depending on if they contain much
(saturation) or little (unsaturation) hydrogen in their composition, and
whether any there is at least one double bond (saturation) between
carbons or not (unsaturation). The fat found in animals bodies and in
dairy products contains mainly saturated fatty acids and tends to be
solid at room temperature. Fish and poultry fats and plant oils contain
mostly unsaturated fatty acids and are more liquid at room temperature.

**Phospholipids** are lipids that contain a phosphate group. They are
important in the plasma membrane of the cell.

![](Triglyceride.JPG "Triglyceride.JPG")
![](Chain_of_amino_acids.jpg "Chain_of_amino_acids.jpg")

## Proteins

**Proteins** are the third main group of organic compounds in the cell -
in fact, if you dried out a cell, you would find that about 2/3 of the
dry dust you were left with would consist of protein. Like carbohydrates
and fats, proteins contain C, H and O, but all also **nitrogen**. Many
also contain **sulphur** and **phosphorus**.

In the cell, proteins are an important part of the plasma membrane of
the cell, but their most essential role is as **enzymes**. These are
molecules that act as biological catalysts and are necessary for
biochemical reactions to proceed. Protein is also found as **keratin**
in the skin, feathers and hair, in muscles, as well as in antibodies and
some hormones.

Proteins are built up of long chains of smaller molecules called **amino
acids**. There are 20 common types of amino acid and different numbers
of these arranged in different orders create the multitude of individual
proteins that exist in an animal's body.

Long chains of amino acids often link with other amino acid chains and
the resulting protein molecule may twist, spiral and fold up to make a
complex 3-dimensional shape. As an example, see the diagram of the
protein lysozyme below. Believe it or not, this is a small and
relatively simple protein.

![](Protein_conformation.jpg "Protein_conformation.jpg")

It is this shape that determines how proteins behave in cells,
particularly when they are acting as enzymes. If for any reason this
shape is altered, the protein stops working. This is what happens if
proteins are heated or put in a solution that is too acidic or alkaline.
Think what happens to the "white'" of an egg when it is cooked. The
"white" contains the protein albumin, which is changed or
"**denatured**" permanently by cooking. The catastrophic effect that
heat has on enzymes is one of the reasons animals die if exposed to high
temperatures.

In the animal's diet, proteins are found in meat (muscle), dairy
products, seeds, nuts and legumes like soya. When the enzymes in the gut
digest proteins they break them down into the separate amino acids,
which are small enough to be absorbed into the blood.

## Summary

-   **Ions** are charged particles, and **electrolytes** are solutions
    of ions in water.
-   **Carbohydrates** are made of carbon with hydrogen and oxygen (in
    the same ratio as water) linked together. The cell mainly uses
    carbohydrates for energy.
-   **Fats** are also made of carbon, hydrogen and oxygen. They are a
    powerful energy source, and are also used for insulation.
-   **Proteins** are the building materials of the body, and as
    **enzymes** make cell reactions happen. They contain nitrogen as
    well as carbon, hydrogen and oxygen.
-   Many also contain sulphur and phosphorous.

## Worksheet

Worksheet on Chemicals in the
Cell

## Test Yourself

1\. What is the difference between an atom and a molecule?

2\. What is the chemical name for baking soda?

:   And its formula?

3\. Write the equation for carbonic acid splitting into water and carbon
dioxide.

4\. A solution of table salt in water is an example of an electrolyte.

:   What ions are present in this solution?

5\. What element is always present in proteins but not usually in fats
or carbohydrates?

6\. List three differences between glucose and glycogen.

:   1\.
:   2\.
:   3\.

7\. Which will provide you with the most energy -- one gram of sugar or
one gram of butter?

8\. Why do organic compounds tend to be more complex and larger than
inorganic compounds ?

/Test Yourself Answers/

## Website

-   Survey of the living world organic
    molecules

A good summary of carbohydrates, fats and proteins.

## Glossary

-   Link to
    Glossary

