Straighterline Microbiology Lab Module
BIO250L Lab 4 Selective Media & Agar
Worksheet (New Version Updated)
2024/2025
What is microbiology?
As the name suggests, it is the study of biological process at the micro (microscopic) level.
These microorganisms usually consist of a single cell and as such, are too small to study with
just your eyes. Examples would include bacteria, archaeons, fungi, protozoa and algae.
Although they are also microscopic, viruses are not living and as such are not considered
microorganisms—a point that will be expanded later in this course. Viruses can, however,
be classified as microbes, a more general term that includes microorganisms and viruses.
Taken together, microbiology is the study of microbes.
Despite being invisible to the naked eye, microbes play a complex role in our world. For
instance, microbes can be beneficial in a variety of ways ranging from aiding in food
digestion to protecting us when we are exposed to potentially harmful foreign invaders to
helping crops grow. However, microbes can also be detrimental as harmful strains of
bacteria, fungi, protozoa and viruses kill millions of people each year and sicken even more.
Indeed, microbes can be just as harmful as they can be advantageous.
Biomolecules
carbohydrates,( monosaccharide -glucose one sugar
disaccharide- sucrose
polysaccharide - found in cell walls
lipids - non polar dont dissolve in water , simple lipids triglycerides
phospholipids - complex
sterol - highly non- polar
,proteins-
building block are amino acids 20 different acids
are put together by peptide bonds
polypeptide - strain of amino acid
ribonuclease ( found in viruses and bacteria)
nucleic acids-
RNA and DNA
DNA- deoxyribonucleic acid
found in the nucleus and the longest molecule in the cell . highly coiled.
Nucleotide -
1. Nitrogen base
2. Deoxynbase ( sugar)
3 Phosphate
Purine
A- ademine
G-guamine
Pyrimedine
C - cytosine
T - thymine
complementary base pairs
A-T
G-C
Double stranded helix- in human.
one stranded in some organisms.
RNA -ribonucleic acid
,bases
A-U (urecile
G-C
building blocks larger unit
1 Sugars -----------Polysaccharides
2. Fatty acids -------Fats , Lipids
3. Amino acids ---- Proteins
4. Nucleotides------Nucleic Acid( DNA, RNA)
cell
basic unit of life
macromolecules found in cell
Proteins
Nucleic acids
Lipids
Polysaccharides
Proteins
are polymers (a large molecule comprised of many smaller subunits) of amino acids and are
the most abundant form of macromolecule. Proteins have a variety of functions in the life of
a cell. Proteins may facilitate the movement of materials in or out of a cell. Some can act as
enzymes that catalyze, or speed up, biochemical processes. Others play a structural role
while other proteins, such as filaments, enable movement. Due to the very nature of how
proteins are formed from varying combinations of amino acids yields a remarkable diversity
within the cell. Note: there are 20 different amino acids and the order and length in which
they are assembled give rise to different protein sizes, structures and functions. Each
protein has its own unique sequence of amino acids, which is known as the primary
structure of the protein. The largest known protein, titin is made up of ~ 33,000 amino
acids! Of the twenty amino acids it should also be noted that 9 are considered essential
, amino acids, as the human body cannot produce them—they must instead be taken in from
the environment through other sources (i.e.) the food you eat.
nucleic acids
re chemical molecules that carry genetic information within the cell. There are two major
types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). DNA contains
a vast amount of hereditary information and is responsible for the inheritable characteristics
of living organisms. RNA is responsible for deciphering the hereditary information in DNA
and using it to synthesize proteins. While both DNA and RNA can be found in the nucleus
(center of the cell), only RNA is capable of leaving the nucleus. DNA molecules are coiled
and twisted into a highly compact form to fit in the nucleus of the cell. Deoxyribonucleic
acid (DNA) is made from building-block molecules called nucleotides. Each nucleotide has
three parts, a nitrogenous (nitrogen-containing) base, a sugar called deoxyribose, and a
phosphate group. There are four kinds of nitrogenous bases that can occur in DNA
nucleotides: adenine or guanine (purine bases) and cytosine or thymine (pyrimidine bases).
The bases can be abbreviated, A, G, C and T, respectively. Structurally, the sugar and
phosphate portions form the backbone of a DNA strand while the nitrogenous base
protrudes outward from the deoxyribose sugar. Strands of DNA form a double helix,
meaning there are two strands held together by hydrogen bonding. As shown in Figure 1.1
below, the top strand complements and pairs with the corresponding bottom strand.
Hydrogen bonds are formed between adenine (A) on one strand and the thymine (T) on the
complementary strand while guanine (G) on one strand pairs with cytosine (C) on the other
strand, and vice versa. For this reason [adenine and thymine] or [guanine and cytosine] are
called complementary base pairs. Further, base pairings between A-T results in two
hydrogen bonds being formed, while G-C pairings results in the formation of three hydrogen
bonds.
Lipids
are mainly composed of hydrophobic (water fearing) hydrocarbons (hydrogen + carbon
atoms). The primary role of lipids in cells is forming the foundation of the plasma
membrane. In its most basic form, the plasma membrane serves the cell as a surrounding
barrier that separates the inside of the cell from the outside surrounding environment. The
