Biochemistry Lecture


     The chemicals important for life fall into two categories:
Inorganic Compounds
     With some exceptions, such as CO2, these are compounds that lack C. They are small, simple molecules. Inorganic molecules include:
     Water is vital for life and accounts for about two-thirds of the chemicals in the body. The properties that make water important for life include:
  High Heat Capacity
     Water can absorb or release a large amount of heat before changing temperature. This helps to stabilize the temperature for the various chemical reactions that occur in the body.
  Polarity/Solvent Properties 
     Water is called the “universal solvent” because of its ability to dissolve a large variety of solutes. The chemical reactions that occur in our body depend upon the solvent properties of water. The solvent properties of water enable it to transport materials around the body and serve as the medium of exchange between cells.
     Water with its various solutes also serves as a lubricant in various places in the body.
  Chemical Reactivity 
     Water is an important reactant in many reactions. Water is involved in hydrolysis (decomposition) reactions that break down larger molecules and condensation (synthesis) reactions that build up larger molecules from smaller ones.
  Cushioning Jesus Lizard
     Water mechanically cushions organs against mechanical shock. For example, cerebrospinal fluid (CSF) cushions the brain and spinal cord.
     Salts are ionic compounds that involve metal and nonmetal elements. Important elements that form salts in the body include, calcium (Ca), phosphorus (P), sodium (Na), potassium (K) and chlorine (Cl). All salts are electrolytes because they conduct electrical currents in solution.
Organic Compounds
These are all carbon-containing compounds. Organic molecules are larger and more complex. Organic compounds can be divided into the following groups:
     Carbohydrates are organic molecules that contain C, H and O in the proportions of CnH2nOn. The proportion of H to O of 2 to 1 as in H2O has given rise to the name carbohydrate as the hydrate part of this word refers to the water molecule.
     Carbohydrates can be grouped into the following categories:
  Monosaccharide means “one sugar” and serves as the building block for more complex carbohydrates that include disaccharides (two sugars) and polysaccharides (many sugars). A monosaccharide may contain from 3 to 7 carbon atoms.
  The most important monosaccharides are:
  Glucose – Also called blood sugar. Glucose is the preferred fuel for the nervous system.
  Fructose – This sugar is found in sucrose.
  Galactose – This sugar is found in milk.
  Ribose and deoxyribose – These 5-carbon sugars contribute to the structure of nucleic acids and other organic molecules.
  Disaccharides form when monosaccharides become covalently bonded by a condensation reaction which is also known as a dehydration-synthesis.
  Important disaccharides in our diet include:
  Sucrose – Glucose bonded to fructose.
  Lactose – Glucose bonded to galactose.
  Maltose – Glucose bonded to glucose.
  Polysaccharides are large branching macromolecules made up of sugars linked by covalent bonds. They form large storage molecules that include:
  Starch – The storage molecule found in plants.
  Glycogen – The storage molecules found in animals including ourselves. Glycogen is found in liver and muscle cells.

Polymer of glucose subunits. Storage form of carbohydrates in animal cells.


Polymer of glucose subunits. Storage form of carbohydrates found in plants.


Polymer of glucose subunits  Indigestible polysaccharide that forms dietary fiber..

     Lipids contain C, H and O but C and H outnumber the number of O atoms. They are insoluble in water but dissolve in other lipids. Lipids are a diverse group of molecules and include:
  Triglycerides are composed of 3 fatty acids and one glycerol molecule. The resulting molecule can vary depending on the length of the fatty acids and the presence of double bonds between the carbon atoms.
  Saturated Fats – are fats where the carbon atoms are bonded to as many H atoms as possible and there are none or very few double bonds between carbon atoms. These form the animal fats.
  Unsaturated Fats – have fatty acids that have double bonds between the carbon atoms. Vegetable oils are unsaturated fats.
  Triglycerides are the body's most abundant and concentrated source of usable energy. Triglycerides are also useful for insulation and padding.
  Phospholipids are similar to triglycerides except that one of the fatty acids is replaced by a phosphate group that is covalently bonded to another polar molecule. Phospholipids have a charged and an uncharged end that enable them to form cell membranes.
  Steroids consist of a lipid molecule formed from four interlocking rings. Cholesterol is the most important steroid molecule. Cholesterol is found in the cell membrane and is modified to form Vitamin D, the various steroid hormones and bile salts.
  Proteins YouTube Video: Proteins
     Proteins are the most versatile of large molecules in the body. They form the structural components of cells and regulate almost all the reactions that occur in the body in the form of enzymes.
     Amino acids form the building blocks of proteins. Amino acids consist of a C atom attached to an amino group – NH2, a carboxy group – COOH, a H atom and a R-group. The R-group can be any one of a number of possible combinations of atoms. There are 20 different R-groups forming 20 different amino acids from which all the proteins in our body are produced.
     Amino acids are linked together by peptide bonds (a special type of covalent bond) and the sequence of amino acids thus linked determines the properties of the protein. The sequence of amino acids also determines the overall shape of the molecule and there are two basic shapes:
  Fibrous proteins
  These proteins form fibers and are structural proteins. They include collagen found in bones, tendons and cartilage, and keratin found in skin and nails.
  Globular proteins
  These proteins have a more compact shape and are functional proteins. Some of the functions performed by globular proteins include serving as catalysts, hormones, transport molecules and antibodies.
  Proteins as Enzymes
     Enzymes are proteins that act as catalysts. A catalyst is a substance that increases the rate of a chemical reaction without changing itself. The activity of an enzyme depends upon its shape which can change if the temperature or pH changes. An enzyme which loses its shape is said to be denatured. Enzymes are capable of catalyzing millions of reactions each minute.
  Nucleic Acids
     Nucleic acids form the genes that provide the blueprint for life. Nucleic acids determine all activities of the cell by directing protein synthesis. The basic building block of a nucleic acid is the nucleotide.
     A nucleotide is made up of a:
  1. Nitrogen containing base which include adenine, guanine, cytosine, thymine and uracil.

2. Five-carbon sugar (pentose) which is either ribose or deoxyribose.

  3. Phosphate group.
     There are two kinds of nucleic acids:
  DNA (deoxyribonucleic acid)
  The nucleotides of DNA have deoxyribose as the 5-carbon sugar and the nitrogen containing base is adenine, guanine, cytosine or thymine. DNA encodes the genetic information of the nucleus. In other words, it contains the instructions for synthesizing proteins.
  RNA (ribonucleic acid)
  The nucleotides of RNA have ribose as the 5-carbon sugar and the nitrogen containing base is adenine, guanine, cytosine or uracil. RNA carries out the instructions contained in the DNA molecule by being directly involved in protein synthesis.
  There are three kinds of RNA molecules:
  Ribosomal RNA – Contributes to the structure of ribosomes that are the protein assembly “factories”.

Messenger RNA – Transfers the instructions for protein assembly from DNA to the ribosomes.

  Transfer RNA – Brings the amino acids to the ribosomes and enables the formation of peptide bonds between them.
  Adenosine Triphosphate (ATP)
     ATP is a nucleotide that plays an additional and important role in the cell. It is the “energy currency” of the cell.


Acids and Bases  
     Acids are molecules that have a sour taste, dissolve metals and are compounds that give a proton (H+) to another molecule. Acids dissolve in water to release protons and an anion. Strong acids such as HCl disassociate completely while weak acids such as carbonic acid disassociate only partially.
     Bases are molecules that have a bitter taste, feel slippery and are proton receptors. Hydroxides (OH-) are common inorganic bases. Hydroxides are strong bases because OH- is an avid proton receptor. Weaker bases include the bicarbonate ion that is a weaker proton receptor.
     When acids and bases are mixed an exchange reaction occurs that forms water and salt.
  pH (quantification of acid-base concentration) Animation
     The acidity or alkalinity (base-ness) of a solution is measured according to the pH scale. A pH of 7 represents a solution that is neither acidic nor basic; it is neutral. Every digit interval below or above 7 represents a 10 fold increase or decrease in the concentration of H+, respectively.
     For example:
  pH = 6 means that there are 10 times as many H+ in solution compared to a pH of 7.
  pH = 8 means that there 1/10 as many H+ in solution compared to a pH of 7.
Living cells need to control pH within acceptable limits.