Chemical Aspects of Physiology

Unit Overview: Chemical Composition of the Body. A basic review of chemistry at the atomic and molecular level.
What makes up Atoms, Molecules, Carbohydrates, Lipids, Proteins, and Nucleic Acid.


1. Atoms, Ions, and Chemical Bonds

Atoms - the smallest units of the chemical elements. They are too small to be seen individually, even with the most powerful
electron microscope.
Atoms are composed of protons, neutrons, and electrons. The nucleus contains protons (+ charge) and neutrons (no charge.) Electrons (- charge) occupy the orbitals or shells outside the nucleus.

external image A4atom.jpg Atomic mass is the sum of protons and neutrons in an atom.

Atomic number is a number of protons in an atom.

Electron shells or orbitals, are in layers around the nucleus. The number of shells depends on the atomic number.
-The first shell can contain only 2 electrons.
-The second shell can contain up to 8 electrons.

Valence electrons are those in outermost shell. These can participate in chemical reactions and form bonds.

Isotopes are different forms of the same atom.
The atomic number is the same, but the atomic mass is different because it contains different numbers of neutrons.

Ions - an atom or group of atoms that has a net positive or a net negative charge because of a loss or gain of electrons.

Chemical bonds - an attraction between atoms that allows the formation of chemical substances that contain two or more atoms.

Covalent bonds occur when atoms share valence electrons.
-Nonpolar covalent bonds electrons are shared equally.
-Polar bonds electrons are shared unequally because they are pulled more toward one atom.

Ionic bonds occur when valence electrons are transferred from one atom to another. They are formed by attraction of + and - charges.
Hydrophilic molecules are soluble in water because they readily form hydration spheres.
Hydrophobic molecule are nonpolar. They cannot form hydration spheres.

Hydrogen bonds - when hydrogen forms a polar bond with another atom, it takes on a slight + charge making it attracted to any nearby negatively charged atoms.

2. Carbohydrates and Lipids

Carbohydrates are organic molecules that are made up from oxygen, carbon, and hydrogen. Simple sugars are a form of carbohydrates that are also called monosaccharides. If you have two monosaccharides that come together you have a disaccharide and if you have many monosaccharides together you formed a polysaccharide. Disaccharides are mostly know because it consists of our table sugar, lactose, and maltose. If you have enough polysaccharides joining together they can form starch and cellulose. In your body, a lot of your cells store carbohydrates as a use for energy.


This video explains how Molecules make Carbohydrates.
It also breaks the process down on why certain molecules need more then one or more bonds.

Dehydration Synthesis and Hydrolysis

Lipids are also organic molecules, but are hydrophobic so they are water fearing, yet, they can be disolved in nonpolar solvents. Carbohydrates consist of Triglycerides, Phospholipids, and Steroids. Triglycerides have both saturated and unsaturated fats. It is saturated if it has two hydrogen atoms, but if it only has one hydrogen atom it is known as an unsaturated fat. One way phospholipids are important is that with the surface tension forces on the lungs they prevent the lungs from collapsing. Cholesterol is considered to be under steroids. It is very important to cell membranes, and being precursor for bile salts, vitamin D, and for the steroid hormones.

This video explains how Molecules make Lipids.
It continues breaking the process down on how to create fatty acids.

Lipid Bilayer

Lipid Molecule

If you want a better understanding of Carbohydrates click on the molecule you want to know more about.

Carbohydrates- Monosaccharides: Disaccharides: Polysaccharides

Lipids- Phospholipids, Waxes, and Steroids

3. Proteins- are large, complex molecules that perform specific functions in the body.

Structure of a Protein

There are 20 different types of amino acids that can be combined to make a protein. The sequence of amino acids determines a protein’s unique 3D shape and its specific function.

Each amino acid contains an amino group (NH2) at one end of a molecule and a carboxyl group (COOH) at the other end. The difference between amino acids are because of differences in their functional groups (R).


Amino Acids are linked together by peptide bonds which connect one carbon and nitrogen bond together by dropping one oxygen and two hydrogen which creates water. This process is called a dehydration reaction.


Protein is formed by amino acids which are linked by dehydration synthesis. The chain of amino acids is also known as a polypeptide. Some proteins contain only one polypeptide chain which is made up of 100 or less amino acids bonded by peptide bonds. If a chain of amino acids makes up more then 100 it is called a protein.

There are 4 types of Protein structures:

Primary Structure- describes the sequence of amino acids in a certain protein.
Secondary Structures- created by hydrogen bonds that connect different amino acids together, the polypeptide chain bends into a certain shape. There are two way it can form the alpha helix (twisted) or the beta pleated sheet. Shown below.
Tertiary Structure- is one of the most common forms for a protein. Polypeptide chains bend and fold to produce complex 3D shapes. They are formed and stabilized by weak bonds. They aren't very stable and can be denautured by heat or acid.
Quaternary Structure- are composed of 2 or more polypeptide chains covalently (one or more chemical bonds formed by sharing electron pairs between atoms) bonded together.


Polypeptide Chart

This video explains how amino acids are formed and how amino acids form proteins through dehydration synthesis

Protein Function

All Proteins have a function. One way is by acting as a receptor receiving information from other proteins; here is a list of a few of their other functions.

Examples of protein functions
Antibodies bind to specific foreign particles, such as viruses and bacteria, to help protect the body.
Immunoglobulin G (IgG) (illustration)
What is an enzyme
Enzymes carry out almost all of the thousands of chemical reactions that take place in cells. They also assist with the formation of new molecules by reading the genetic information stored in DNA.
Phenylalanine hydroxylase (illustration)
Messenger proteins, such as some types of hormones, transmit signals to coordinate biological processes between different cells, tissues, and organs.
Growth hormone (illustration)
Structural component
These proteins provide structure and support for cells. On a larger scale, they also allow the body to move.
Actin (illustration)
These proteins bind and carry atoms and small molecules within cells and throughout the body.
Ferritin (illustration)

Click here for more detailed information on Proteins

4. Nucleic Acid are molecules that are essential for life, that includes DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Which are macromolecules made from nucleotides.

Nucleotides are subunits of nucleic acids bonded together during dehydration reactions to form long polynucleotide chains. One nucleotide contains a pentose (5 carbon) sugar, a phosphate group, and a nitrogenous base. Bases can contain either pyrimidines (1 ring) or purines (2 rings).


DNA (deoxyribonucleic acid) this structure serves as the basis for our genetic code. It is the largest molecule in the cell, and is simpler then the structure of most proteins. There are four sugar molecules in the nucleotides of DNA which are called deoxyribose.

Each deoxyribose is covalently bonded to 1 of 4 bases:

(Purines) Guanine or Adenine

(Pyrimidines) Cyotsine or Thymine

If you remember Purine has 2 rings and Pyrimidine has only 1 ring. Which means a Purine can only bond with a Pyrimidine. Guanine can only bond with Cytosine, Adenine can only bond with Thymine. However these molecules can be laid out in any order depending on our genetic code.

The DNA Chain is formed by a sugar of one nucleotide bonding to the phosphate of another nucleotide. Each base can form hydrogen bonds with other bases. This bond is what holds the DNA together.


The two strands of DNA then twist to form a double helix because of the number of purines= pyrimidines.

RNA (ribonucleic acid) this structure helps DNA to direct the activities of the cell. RNA consists of long chains of nucleotides joined together by sugar-phosphates just like DNA. However RNA differs from DNA in 3 ways: 1) deoxyribose is replaced with a ribonucleotide which contains the sugar ribose. 2) The base thymine is replaced with the base uracil which is similar to thymine. 3) RNA is comprised of a single polynucleotide strand not a double helix like in DNA.

There are 3 types of RNA. These are synthesized from DNA to allow it to direct activities of a cell.

Messenger RNA- mRNA
Transfer RNA- tRNA
Ribosomal RNA- rRNA

RNA reads and decodes the DNA code to make copies which are then used to build what ever is needed to keep the cell alive.

Purine-containing nucleotides are used for other purposes besides helping RNA in genetic regulations. They include carrying energy as ATP and GTP; regulation of cellular events as cyclic AMP (cAMP); being coenzymes as nicotinamide, adenine dinucleotide (NAD); and flavin adenine dinucleotide (FAD). Purines ATP and adenosine can also be used as neurotransmitters by some neurons.

Essential Questions:

-Describe buffers, their importance, and the buffering system used in the blood to regulate the narrow range of pH in the blood. What is the difference between acidosis and alkalosis?

Buffers are molecules that slow changes in pH by either combining with or releasing H+s to stabilize the pH of a solution.5.

Acidosis is when the blood pH is to low and falls below 7.35, and alkalosis is when the blood pH is to high and above 7.45.

-What are enzymes? What role do they play in human physiology?

Enzymes cause an increased chemical reaction within a protein by decreasing the energy needed during the activation . Enzymes make the reaction happen, but don't react or make a chemical change themselves during the process and can be used over and over again.

Enzymes are important because they are responsible for most of the chemical reactions in our body, and life couldn't exist without them.

How it pertains to PTA:

By knowing how the body works at a molecular level can really help a PTA know how certain medicines or pathologies can affect the body. For example PTA's work with all types of people with many different types of problems, may it be a fracture, or someone just out of surgery, or working with someone who has Down-syndrome. We know what the body does in all of these cases. We know that with a fracture or surgery the cells will sense the damage in the area and will replicate and build what the body needs to heal and repair what was broke or torn. With Down-syndrome we know at the DNA level that during Meiosis there was an extra chromosome made which caused a genetic defect.

Knowing the chemical aspects of how the body works helps us help our patients because we know what is going on inside their body. We will be able to explain to them what is exactly happening in their body. For example, for a post surgery patient, we will be able to explain to them why their incision itches. This is because of the cells building new tissue to close the wound, which may irritate the pain receptors, which then in turn causes the area to itch.

5. Ch. 3 notes
6.Fox, Stuart I. "Human Physiology." New York: McGraw-Hill, 2011. Print.