1. Chapter 6: The Biochemical Basis of Life

2. Organic Chemistry
Carbon Bonds
Cyclic Compounds
Biochemistry
Carbohydrates
Lipids
Proteins
Nucleic Acids

3. Introduction
A microorganism can be thought of as a “bag” of chemicals that interact with each other in a variety of ways; even the bag itself is composed of chemicals.
Everything a microorganism is and does is related to chemistry.
Organic chemistry is the study of compounds that contain carbon.
Inorganic chemistry involves all other chemical reactions.
Biochemistry is the chemistry of living cells

4. Organic Chemistry Organic compounds contain carbon.
Organic compounds are not necessarily related to living organisms
Organic chemistry involves fossil fuels, dyes, drugs, paper, ink, paints, plastics, gasoline, rubber tires, food, and clothing.

5. Organic Chemistry Carbon Bonds
Carbon atoms can bond to four other atoms.
There are three ways in which carbon atoms can bond to each other: single bond, double bond, and triple bond.
A covalent bond is one in which a pair of electrons is shared.
When atoms of other elements attach to available carbon bonds, compounds are formed.
A series of carbon atoms bonded together is referred to as a chain.
When carbon atoms link to other carbon atoms to close a chain, they form rings or cyclic compounds.

6. Organic Chemistry Carbon Bonds (cont.)
If only hydrogen atoms are bonded to the available carbon bonds, hydrocarbons are formed.
Therefore, a hydrocarbon is an organic molecule that contains only carbon and hydrogen atoms; some examples of simple hydrocarbons are shown here:

7. Biochemistry
Biochemistry is the study of biology at the molecular level; it is the chemistry of living organisms.
Biochemistry involves the study of biomolecules present within living organisms; biomolecules in living organisms are usually large molecules called macromolecules.
Macromolecules include carbohydrates, lipids, proteins, and nucleic acids.
Other examples: vitamins, enzymes, hormones, and energy-carrying molecules such as adenosine triphosphate (ATP).

8. Biochemistry Carbohydrates
Carbohydrates are biomolecules composed of carbon, hydrogen, and oxygen (in the ratio 1:2:1).
Examples include glucose, fructose, sucrose, lactose, maltose, starch, cellulose, and glycogen.
Categories of carbohydrates include monosaccharides, disaccharides, and polysaccharides.

9. Carbohydrates Monosaccharides
Monosaccharides are the smallest and simplest of the carbohydrates. Mono means one, referring to the number of rings in the structure.
Glucose (C6H12O6) is the most important monosaccharide in nature
The main source of energy for body cells is glucose.

10. Carbohydrates Disaccharides
“Di” means two; disaccharides are double-ringed sugars that result from the combination of two monosaccharides
Sucrose (table sugar), lactose, and maltose are examples of disaccharides.
Disaccharides react with water in a process called a hydrolysis reaction, which causes them to break down into two monosaccharides.

11. Carbohydrates Polysaccharides
polysaccharides are defined as carbohydrates that are composed of many monosaccharides. Most contain hundreds (e.g., starch and glycogen).
Polysaccharides serve two main functions:
Store of energy (e.g., glycogen in animal cells and starch in plant cells)
Provide a “tough” molecule for structural support and protection (e.g., bacterial capsules)
In the presence of the proper enzymes or acids, polysaccharides may be hydrolyzed or broken down into disaccharides, and then into monosaccharides.

12. Lipids An important class of biomolecules.
Lipids are essential constituents of most living cells.
Lipids can be classified into the following categories:
-Waxes -Glycolipids
-Fats and oils -Steroids
-Phospholipids -Prostaglandins and leukotrienes

13. Lipids Fatty Acids
Fatty acids are the building blocks of lipids; they are long-chain carboxylic acids that are insoluble in water.
Saturated fatty acids contain one single bond between carbon atoms; they are solid at room temperature.
Monounsaturated fatty acids have one double bond in the carbon chain and are found in butter, olives, and peanuts.
Polyunsaturated fatty acids contain two or more double bonds and are found in soybeans, safflowers, and corn.
Essential fatty acids cannot be synthesized in the human body and must be provided in the diet.

14. Lipids Waxes, Fats, and Oils
A wax consists of a saturated fatty acid and a long- chain alcohol.
Examples: the wax coating on fruits, leaves, skin, fur, and feathers of animals.
Fats and oils are the most common types of lipids. They are also known as triglycerides because they are composed of glycerol and three fatty acids.
Most fats come from animal sources (e.g., beef); most oils come from plant sources (e.g., olive oil).

15. Lipids Phospholipids
Phospholipids contain glycerol, fatty acids, a phosphate group, and an alcohol. There are two types:
Glycerophospholipids (also known as phosphoglycerides)
Sphingolipids
Glycerophospholipids are the most abundant lipids in cell membranes.
A cell membrane is a lipid bilayer, consisting of two rows of phospholipids, arranged tail-to-tail.

16. Proteins Proteins are the most essential chemicals in all living cells
Some proteins are the structural components of membranes, cells, and tissues; others are enzymes and hormones.
All proteins are polymers of amino acids.
All proteins contain carbon, hydrogen, oxygen, and nitrogen (and sometimes sulfur).

17. Proteins Amino Acids
Amino acids contain carbon, hydrogen, oxygen, and nitrogen; some also have sulfur in the molecule.
Humans can synthesize certain amino acids, but not others.
The thousands of different proteins in the human body are composed of a wide variety of amino acids in various quantities and arrangements.

18. Proteins Enzymes
Enzymes are specialized protein molecules produced by living cells. They are known as biological catalysts; that is, they catalyze (speed up) metabolic reactions.
Almost every chemical reaction in a cell requires a specific enzyme.

19. Nucleic Acids Function
DNA and RNA form the fourth major group of biomolecules in living cells.
DNA and RNA are critical to proper functioning of a cell.
DNA is the “hereditary molecule”the molecule that contains the genes and genetic code.
RNA molecules participate in the conversion of the genetic code into proteins and other gene products.
The five nitrogenous bases in nucleic acids are adenine (A), guanine (G), thymine (T), cytosine (C), and uracil (U). A and G are purines; T, C, and U are pyrimidines.
Thymine is found in DNA but not in RNA. Uracil is found in RNA, but not in DNA. The other three bases are found in both.

20. DNA Structure
For a double-stranded DNA molecule to form, the nitrogenous bases on the two separate strands must bond together.
A always bonds with T via two hydrogen bonds.
G always bonds with C via three hydrogen bonds.
A–T and G–C are known as “base pairs.”
The bonding forces of the double-stranded polymer cause it to assume the shape of a double -helix, similar to a right-handed spiral staircase.

21. DNA Replication
When a cell is preparing to divide, all DNA molecules in the chromosomes of the cell must duplicate, thereby ensuring that the same genetic information is passed on to both daughter cells. This is called DNA replication.

22. DNA Replication Gene Expression
A gene is a particular segment of a DNA molecule or chromosome.
It is the sequence of the four nitrogenous bases of DNA (i.e., A, G, C, and T) that spell out the instructions for a particular gene product.
The Central Dogma explains the flow of genetic information within a cell (proposed by Francis Crick in 1957).
DNA mRNA protein.
One gene of a DNA molecule is used to make one molecule of mRNA by a process known as transcription.
The genetic information in the mRNA is then used to make one or more protein by a process known as translation.

23. DNA Replication Gene Expression (cont.)
All genes on a chromosome are not being expressed at any given time. It would not be logical for a cell to produce a particular enzyme if it was not needed.
Genes that are only expressed when the gene products are needed are called inducible genes.
Genes that are expressed at all times are called constitutive genes.