Biology 105 – Anatomy and Physiology  - Introduction

 

Anatomy – The study of the structure of the body and the physical relationships between organs and tissues.

 

Physiology – The study of the functions of the body, its organ systems, organs, tissues and cells.

 

I.  Basic Principles Derived from Studies of Organisms

A.      Complementarity of Structure and Function  - Structure facilitates function.

Examples:

1.        Femur

a.        Support

b.       Articular surfaces

c.        Attachment for muscles

d.       Blood formation

    

2.        Heart – The chambers and valves permit only one way traffic of blood.

 

B.       Homeostasis – The maintenance of a steady, relatively unchanging internal environment within the body in spit of wide ranging changes in the external environment.

 

Examples:

 

1.        Maintenance of Body Temperature

2.        Blood Pressure Regulation

3.        Blood Sugar Regulation

4.        Regulating Blood Oxygen Levels.

 

Feedback Mechanisms:

 

1.        Negative Feedback – The product of this mechanism relieves the stress and shuts down its own production.  Most homeostatic mechanisms use this feedback for control.

2.        Positive Feedback – The product of this mechanism enhances the stress.  These mechanisms are useful in a situation where a process is time limited, e.g., labor contractions and milk letdown from mammary tissue.

 

C.       Levels of Organization  - A common denominator of any organism would be that they are composed of several interdependent levels of organization.

 

Example:                        Atomic Level

                                                Molecular Level

                                                        Organelle Level

                                                                Cellular Level

                                                                      Tissue Level

                                                                      Organ Level

                                                                                     Organ System Level

                                                                                                Organism Level

 

     It is important to note that each level affects the operation of every other level in a complex, interactive manner.

 

D.      Continuity and Diversity – From one generation to the next, humans produce other humans (continuity).  The understanding of this phenomenon requires a study of the reproductive systems and processes.  At the same time we see differences between humans.  The science and principles of modern genetics have led to our understanding of diversity.

 

II.  Chemical Level of Organization

 

All life activities depend on chemical substances and the activities of these substances.  The term Metabolism refers to all of the chemical activities taking place in an organism.

 

Element –  A substance which cannot be broken down into simpler substances by ordinary chemical processes.  There are 92 naturally occurring elements on the earth.

 

Atom –  Smallest portion of an element that shows the chemical characteristics of that element.

 

A.  Basic Building blocks of an atom

 

1.        Proton

a.        positively charged

b.       weighs 1 atomic mass unit (amu)

c.        located in the nucleus of the atom

d.       number of protons in an atom is the atomic number

e.        all atoms of an element have the same atomic number.

 

2.        Electrons

a.        negatively charged

b.       Orbit around the nucleus at different distances (shells).

c.        Very light ( 1/1836 th the weight of a proton).

d.       In all atoms, the number of electrons equals the number of protons.

e.        The electrons in the outer shell determine the chemical properties of the element.

 

3.        Neutron

a.        Electrically neutral (no charge)

b.       Same mass as a proton.

c.        Isotopes are atoms of the same element that have different atomic weights due to different numbers of neutrons.

d.       Located in the nucleus, neutrons plus protons account for atomic weight.

 

B.  Chemical Reactions

 

     The reactions of an atom with other atoms depends on the number of electrons in its outermost shell.  There are certain numbers of electrons that stabilize (satisfy) the outer shell.  In order to achieve those numbers, atoms may give up, take or share electrons with other atoms.

 

1.        Ionic Bond

  1. Forms Between oppositely charged ions.
  2. During the formation of this bond, one atom loses and electron (is oxidized) and the other atom takes an electron (is reduced).

 

For example:           Na+                                      Cl-

                               cation                                    anion

 

 

2.  Covalent Bond

  1. result of sharing electrons
  2. very strong bonds
  3. two atoms may share more than one pair of electrons

For example:       single covalent bond      double covalent bone      triple covalent bond

                                                                                                                             

                       H - H             O = C = O           C = C

 

3.        Polar Covalent Bonds

a.        due to unequal sharing of electrons

b.       elements vary in their ability to attract electrons.  For example, in the water molecule, shared electrons spend more time around oxygen.  The result:

                                    -

                                   O           The oxygen end of the molecule takes on

                                                 a negative charge while the hydrogen end  

                           H     +      H   becomes slightly positive.

 

c.        As a result of the unequal sharing of electrons, this type of covalent bond is weaker.

 

4.        Hydrogen Bonds

  1. are relatively weak attractive forces between hydrogen, oxygen and nitrogen on different molecules or between different regions of the same molecule.
  2. Participating molecules must be polar.

 

 

Water

 

     Water is the single most important chemical in the body.  It makes of 2/3 of the body by weight.  Water has many characteristics which make it uniquely important for life processes.

 

Properties of Water

 

1.        Universal solvent – water dissolves most chemical substances except non-polar hydrocarbons and lipids.

 

2.        High Heat Capacity – the hydrogen bonds between water molecules retards the ability of water

       molecules to increase their movements.  Since increased molecular movement causes an increase in

       temperature, it takes a lot of heat to raise the temperature of water. 

a.         In the body this helps to stabilize body temperature.

b.       Heat travels with the blood in the body.  The water in our blood helps to distribute heat throughout the body.

 

3.        The hydrogen  bonds between water molecules helps blood return to the heart and also assists in the expansion of the lungs during inspiration.

 

4.        Water acts as an effective lubricant in the peritoneal cavity, within synovial (free moving) joints and in the pericardial cavity.

 

5.        Water participates in important metabolic activities in the body, e.g., dehydration synthesis and hydrolysis.

 

6.        Water molecules ionize slightly.  In pure water only 0.0000001 mole/liter of water molecules ionize.  A mole is a unit used to measure the concentration of a solution.

 

 

       HOH                                        H+             +            OH-

                                                                                                                       

      10-7  mole/liter                      10-7  mole/liter                10-7  mole/liter

 

From this equation we can see that the concentration of hydrogen ions is equal to the concentration of hydroxide ions in pure water.

 

pH Scale – is a shorthand method of describing the concentration of hydrogen ions in any solution. 

a.        The pH scale uses numbers from 0 to 14.

b.       The pH scale is logarithmic, i.e., each unit change in pH is a 10 fold change in hydrogen ion concentration.

c.        A solution with a pH number below 7 is referred to as an acid.  If the number is greater than 7, the solution is called basic or alkaline.

 

III.  Organic Chemistry

 

    All life activities depend on interactions between compounds containing carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur (CHONPS).  These molecules are large, complex and composed of subunits called monomeres.

 

A.  Carbohydrates

 

1.        Contain carbon, hydrogen and oxygen with the ratio of hydrogen to oxygen  2:1.

 

2.        The subunits of carbohydrates are called monosaccharides.

  1. Glyceraldehyde (3C)
  2. Pentose sugars (5C) – Ribose and Deoxyribose
  3. Hexose sugars (6C) – Glucose, Galactose and Fructose

 

3.        Disaccharides are combinations of two hexose sugars

a.  glucose + glucose           maltose            

                                                                 Each of these reactions involves the loss of water

b.  glucose + fructose            sucrose                            (dehydration synthesis).

 

c.  glucose + galactose              lactose

 

4.        Polysaccharides – are multiple polymers of monosaccharides.

 

  1. Starch – Consists of 100’s or 1000’s of glucose molecules joined in a linear fashion.  Starch can be readily digested in the digestive tract with the enzyme amylase.

 

  1. Glycogen – is a highly branched polymer of glucose.  It is stored in liver and skeletal muscle cells.

 

  1. Cellulose – Consists of sheet-like polymers of monosaccharides.  It is found in plant cell wall and is essentially indigestible by humans.

 

5.        Carbohydrates function in the body as

  1. as an energy source.
  2. Stored food
  3. Component molecules of cell membranes.

 

 

B.  Proteins

 

1.      Form the basic chemical structure of the body.

 

2.         They contain CHONPS and trace amounts of cobalt, zinc, iron, magnesium and other elements.

 

3.         The subunits of proteins are amino acids.  There are 20 kinds of amino acids.  The illustrations below show the amino acids glycine and alanine.  The groups in black are referred to as the R groups. The R  group is responsible for most of the differences between the  amino acids.  The NH2 is referred to as the amine group.  The COOH group is called carboxyl.





       Glycine                                Alanine

4.  There are four categories of amino acids

  1. Amino acids with polar side chains

i.                     Form hydrogen bonds

ii.                    Don’t ionize

iii.                  Attract water

 

  1. Amino acids with non-polar side chains

i.                     Don’t form hydrogen bonds

ii.                    Don’t ionize

 

  1. Amino acids  which combine with hydrogen ions at their nitrogen end.

i.                     Reduce the acidity of the fluid

ii.                    Form hydrogen bonds

iii.                  Attract water molecules

 

  1. Amino acids whose carboxyl groups donate hydrogen ions to a solution

i.                     Increase the acidity of a solution

ii.                    Form hydrogen bonds

iii.                  Attract water molecules

 

4.        Cysteine contains sulfur in its side group.   Cysteine molecules on adjacent polypeptide molecules

       can react with each other forming disulfide bonds which will hold the two polypeptides together with a

       strong covalent bond.

 

5.        A peptide bond holds two amino acids together.  This bond forms between the carboxyl group of one amino acid and the amine group of another.  The formation of this bond involves the loss of water (dehydration synthesis).

 

6.        A polypeptide consists of a chain of  3 or more amino acids.  When the molecule reaches the size of 100 or more amino acids, it is called a protein.

 

 

Protein Structure

 

1.        Primary Structure – A simple linear arrangement of amino acids.  The most important factor distinguishing a primary structure protein would be the sequence of amino acids in the strand.

 

2.        Secondary Structure –  A spiral or pleated formation within a single polypeptide strand.  These formations depend on hydrogen bonds forming between areas on the strand.  Amino acid sequence will determine whether a spiral or a pleated arrangement develops

 

3.        Tertiary Structure – A complex folding and coiling of a helical strand results from interactions with surrounding water molecules and disulfide bond formation.  Most tertiary proteins are called globular.  An example of this level of structure can be seen in the protein myoglobin.

 

4.        Quaternary Structure – results from the chemical joining of individual polypeptide chains.  Each of the polypeptide chains has its  own secondary and tertiary structure.  Hemoglobin contains four globular subunits held together as one complex molecule.  Keratin and collagen molecules are formed by the winding of three helical polypeptides like the strands of a rope.

 

 

C.  Lipids

  

     Organic compounds containing carbon, hydrogen and oxygen.  Lipids are essential  structural components of all cells especially membranous structures.  Lipids also represent an important energy reserve molecule.  Gram for gram, lipids provide twice as much energy as carbohydrates.

     There are five types or classes of lipids:

 

1.        Fatty acids

  1. long hydrocarbon chains
  2. one end of the chain bears a carboxyl group which can be represented as:

                                                                                                OH

                    COOH            or structurally as              C 

                                                                                                                  O

  1. at the other end of the molecule only hydrogen is bound to carbon.
  2. The carboxyl end of the molecule is hydrophilic while the hydrocarbon end is hydrophobic.
  3. Fatty acids may be saturated (only single bonds between the carbons) or unsaturated (unoccupied bonds are found between the carbon atoms.

 

2.        Eicosanoids are lipids derived from arachidonic acid.  There are two major eicosanoids found in the body:

  1. Prostaglandins – are short chain fatty acids with five carbons forming a ring.  They are local mediators of cellular activity (they are released by cells and have their effects on nearby tissues.  Prostaglandins are released as a result of damage to tissue (induce pain) and during child birth (trigger uterine contractions).
  2. Leukotrienes – are released by leukocytes during inflammation and immune activities.  They help to coordinate the body’s defenses against infection and cancer.

 

3.        Glycerides – are compounds formed by the combination of glycerol with up to three fatty acids.

 

                                 Monoglyceride   -    glycerol   +   1 fatty acid           In each of these reactions

                                                                                                                    water is removed as the glycerol

                                 Diglyceride        -    glycerol    +   2 fatty acids         and fatty acids combine.

                                                                                                                               (hydrolysis)

                                Triglyceride       -     glycerol     +   3 fatty acids

 

4.    Triglyceride fats serve a number of important functions in the body: 

 

a.        Triglycerides represent a reserve of energy for the body.  Most of these molecules are stored in the

        adipose tissue that is located below the skin (subcutaneous fat).

 

b.       Subcutaneous fat serves as an  insulation preventing heat loss through the skin.  However, in a warm climate or following strenuous exercise, the elimination of excess heart from the body is retarded.

 

c.        Fat deposits in the skin or around vital organs like the kidney provide a cushion against impact or

       blows.

 

5.        Steroids  - are large lipid molecules that share a common

       structure, viz., the hydrocarbon chain has been rearranged

       to form four rings.  The different steroids will vary in the

       nature of side chains attached to the rings.  Cholesterol is

       the most abundant steroid in the body.

  1. All animal cell membranes contain cholesterol as a basic structural ingredient.
  2. Steroid hormones are essential for the regulation of sexual function (testosterone, estrogens), metabolism (cortisol) and mineral balance (aldosterone).
  3. Bile salts are steroid derivatives needed for the proper digestion of fat.  Bile salts are manufactured in the liver.

 

6.  Phospholipids and glycolipids are diglycerides which have been modified by the addition of phosphate to the former and a carbohydrate to the latter.  Both types of molecules contain two fatty acids attached to glycerol.  The fatty acid “legs” are hydrophobic.  The end of the molecule bearing either the phosphate or sugar is hydrophilic.  In water, large numbers of these molecules form lipid bilayer droplets or micelles.

 

 Notice that the molecules line up in a double row so that the

 hydrophilic ends of the molecules are facing water outside

 and inside the micelle.  Cell membranes are primarily composed of      

 phospholipids, glycolipids and cholesterol arranged in a Lipid  bilayer.
This separates and to some extent isolates the  interior of the cell from the
environment outside.

 

 


IV.  Chemical Reactions and Energy

 

 A.   Energy is defined as the ability to do work.  There are two major forms of energy:

 

1.        Kinetic energy – the energy of motion.  In the cell, this would correspond to the energy released during a chemical reaction, e.g., the breakdown of a glucose molecule within a cell.  Some of this energy is used for life activities such as muscle contraction or secretion of important substances.

2.        Potential Energy is stored energy that has the potential to do work.  When glycogen is synthesized in a liver cell the some of  the  energy stored in the glucose subunits is being stored for future cell functions.

 

B.  Metabolism is the total of all chemical reactions occurring in the body.  There are two types of metabolic reactions:

 

1.        Anabolic Reactions – result in the build up of complex molecules from simpler reactions.  Since it takes energy to create chemical bonds, anabolic reactions will store chemical energy.  Examples include the synthesis of glycogen from monosaccharides and the synthesis of triglyceride fats from fatty acids and glycerol.

2.        Catabolic Reactions – result in the breakdown or decomposition of molecules.  Since chemical bonds are being broken during these reactions, energy is being released.  For example, the breakdown of glucose in the cell releases energy for life activities.

 

 

 

 

C.  Activation Energy

 

     The chemical reactions of metabolism are not spontaneous.  Before they can occur, energy must be provided to “activate the reactants”.   The energy needed to do this is called activation energy (A.E.).  The amount of activation energy required to breakdown starch in a non-living system is very great.  This level of energy in heat would be destructive to living cells.  Special proteins called enzymes permit the essential chemical activities  of metabolism to occur in living systems without these destructive effects.

 

Enzymes – promote a chemical reaction by lowering the activation energy required for that reaction.  This, in turn, will cause the overall speed of the reaction to increase.  During this process the enzyme is not altered or consumed.   As a result, the enzyme molecule may be used many times.

 

                   

                                                               

                                                

                                                           

D.  Characteristics of an Enzyme

 

1.        Enzymes are globular proteins typically exhibiting a quaternary level of structure.

 

2.        In order for an enzyme to function as a catalyst:

  1. The substrate or reactants must bind with a special region of the enzyme molecule called the active site.
  2. At the active site, the chemical change occurs.
  3. The finished product(s) detaches from the active site.
  4. The freed enzyme molecule is now ready to carry out this reaction on another substrate molecule(s).

 

3.        Each enzyme catalyzes only one type of reaction on a specific substrate.  This specificity is based on the ability of the substrate to bind to the active site.  The analogy of a “lock and key” is often used to illustrate this characteristic.

 

4.        The speed or rate of an enzymatic reaction is directly proportional to the concentrations of substrate and enzyme molecules.

  1. Increases in enzyme concentration will cause an increase in the number of collisions between enzyme and substrate molecules.
  2. Increases in collision rate increase the reaction rate and cause an increase in product formation.

 

5.         A variety of factors both chemical and physical will affect the capacity of an enzyme to function:

  1. Cofactors are most often ions that must bind to the enzyme before it can bind to the substrate.  Examples are calcium, magnesium and zinc.  Calcium is an essential cofactor for many of the enzymes involved in blood clotting.
  2. Coenzymes are organic molecules that function as cofactors.  For example, vitamins are essential coenzymes in cellular respiration.  These are the reactions that lead to the breakdown of glucose.
  3. Each enzyme works best at an optimal temperature.  As temperatures rise above the optimal, proteins change shape or denature.  If this shape change alters the shape or accessibility of the active site, the enzyme ceases to function.  For example, most of the body’s enzymes work best at 37 degrees Celsius (body temperature).  At a body temperature of 43 degrees (110  F) these
  4. enzymes denature to the point where most life activities cease.
  5. Enzymes are also sensitive to pH changes.  Pepsin is an enzyme  which functions in the stomach  at a pH of 2.  In the small intestine the pH is about 7.8.  Pepsin will not work in the small intestine
  6. due to the denaturing of the molecule.  Certain heavy metals have a catastrophic effect on enzyme activity.   Lead, arsenic and mercury will bind to and denature enzymes irreversibly.  These substances have been associated with severe damage to the body especially the central nervous system.
  7. Certain inhibitors of enzyme activity produce an alteration in the shape of the binding site when they attach to the enzyme.  Cyanide acts as a poison by denaturing the configuration of the enzyme’s binding site.  Many antibiotics inhibit enzyme activity even more specifically by competing with the substrate for active site binding.  For example sulfanilamide has a molecular shape that resembles the substrate para- amino benzoic acid (PABA).  The antibiotic competes with PABA for binding with the enzyme which converts PABA to folic acid.  Folic acid is a necessary material for a wide range of metabolic activities.