Learning Exercise - Microorganisms

Question 1

With regards to prokaryotes, briefly describe each:

Nuclear membrane
Chromosomes
Cell replication
Energy production
Specialized organelles

Answer 1

Nuclear membrane: absent
Chromosomes: one, circular
Cell replication: binary fission
Energy production: on the cytoplasmic membrane
Specialized organelles few (e.g. ribosomes)

Question 2

With regard to eukaryotes, briefly describe each:

Nuclear membrane
Chromosomes
Cell replication
Energy production
Specialized organelles

Answer 2

Nuclear membrane: present
Chromosomes: multiple, linear
Cell replication: mitosis
Energy production: in mitochondria
Specialized organelles: several

Question 3

What is meant by “antigenic group”, and how are groups often designated?

Answer 3

organisms possessing a major antigen that may be common to more than one species of the genus; usually designated by capital letters.

Question 4

Describe the major shapes and arrangements of bacteria cells.

Answer 4

coccus: spherical
bacillus: rod or cylindrical
coccobacillus: short, plump bacillus which resembles a coccus
coryneform or diphtheroid: club shaped or chinese letter shape
pleomorphic: an organism that commonly has various distinct forms
spirochete or spirillum: spiral or corkscrew shape
(not usually visible by the Gram stain method)

arrangement:

Single - no particular arrangement

Pairs - division on one plane; daughter cells remain paired

Chains - division on one plane, perpendicular to the long axis of the chain; cells remain attached “end-to-end”

Clusters - division on three planes

Palisades - “picket fence”, division on one plane perpendicular to the short axis of the chain (bacilli only)

Question 5

What is meant by “antigenic type”, and how are types often designated?

Answer 5

organisms possessing a specific antigen that is common to only very limited, closely related organisms (such as members of an antigenic group); usually designated by numbers.

Question 6

What are the major components of the bacterial cytoplasm and what is the overall function of those components?

Answer 6

Cytoplasm:
Composition – thick, aqueous, elastic
(a) Cell sap (e.g. water, nutrients, storage granules, etc.)
(b) Genetic material and mechanisms (DNA, RNA, ribosomes)
(2) Function: Metabolism and replication

Question 7

What are the major components of the bacterial cytoplasmic membrane and what are the overall functions of those components?

Answer 7

Cytoplasmic membrane:

Components:

(a) Phospholipid bilayer – Hydrophilic “heads” and hydrophobic “tails” affect movement of aqueous materials through the membrane
(b) Proteins – some function as porins (proteins that form channels through which large molecules can pass) and others as enzymes

Functions:

(a) Selective permeability – Controls transport of most compounds entering and leaving the cell
(b) Site of energy production
(c) Site of synthesis and transport of peptidoglycan, teichoic acids, and outer membrane components
(d) Site of secretion of extracellular hydrolytic enzymes

Question 8

What are the major overall functions of the bacterial cell wall?

Answer 8

Function

(a) Shape and rigidity
(b) Provides protection from the environment and from some antimicrobic agents
(c) Certain molecules are used in the attachment to tissue cells
(d) Site of antibody attachment to major cell antigens

Question 9

What is the metabolically dormant, heat resistant structure within the cytoplasm of certain gram-positive bacteria, and what is its function?

Answer 9

An endospore

Survival of adverse environmental conditions (resists heat, chemicals, and irradiation). Spore may be viable for years.

Question 10

What is the mucoid (slimy) material surrounding certain bacterial cells and what is its function?

Answer 10

Capsule

(1) Composition: Polysaccharides
(2) Function
(a) Resistant to phagocytosis
(b) May “hide” surface antigens
(c) Sometimes assists in attachment (dental plaque)

Question 11

What are the thread-like structures on the exterior of bacteria cells and what is their composition?

What are the functions of these structures?

Answer 11

Flagellum

(1) Composition: protein
(2) Function:

(a) Motility – propel the bacterium; provide locomotion
(b) Moves toward a favorable environment and away from adverse ones: Types: Chemotaxis; Phototaxis
(3) Spirochetes move by means of axial filaments, bundles of fibrils arising at ends of cell beneath outer sheath and spiral around the cell – causes corkscrew motion

Question 12

Describe the components and structure of the gram-positive cell wall, including details of peptidoglycan.

Answer 12

In a gram-positive cell wall, the concentration of peptidoglycan is higher than in gram-negative.

(a) Peptidoglycan (60 - 80%): Alternating units of N-acetylglucosamine and N-acetylmuramic acid cross-linked by short peptide (amino acid) chains
(b) Teichoic acid strands connect to cytoplasmic membrane (Usually long chain glycerol or ribitol connected with phospholipid bridges)
(c) Protein inclusions are less frequent than in gram-negatives

Question 13

Describe the components and structure of the gram-negative cell wall, including details of the “outer membrane” and their significant roles/functions.

Answer 13

(a) Peptidoglycan (10 - 20%)
(b) Lipoprotein layer creates a periplasmic space between peptidoglycan and the “outer membrane”. Site of certain enzymatic processes
(c) “Outer Membrane”
i. Phospholipid bilayer
ii. Pore proteins

iii. Lipopolysaccharides – Lipid with repeating units of various combinations of carbohydrates
♦ The “O” antigen (i.e. “cell wall antigen”) in antigenic tests of gram-negatives

♦ Site of Lipid A, the endotoxin molecule

Question 14

A clump of a few million identical bacteria originating from the same bacterium is called a __________.

Answer 14

a colony

Question 15

Most medically significant bacteria will reproduce about every __________ minutes under optimal conditions.

Answer 15

30 to 60 minutes; some 15-30 hours

Question 16

Describe the types of oxygen utilization.

Answer 16

(a) Aerobic – requires atmospheric oxygen (~21%)
(b) Microaerophilic – requires reduced oxygen concentration (5-10%)
(c) Anaerobic – requires absence of oxygen
(d) Facultative – can grow in presence or absence of oxygen

Question 17

What are the optimal temperature, pH, CO2, and humidity for growth of typical medically significant bacteria?

Answer 17

Temperature: 35°C (optimal)

pH: 6.8 to 7.4 (optimal)

Humidity: 60-80% (Water comprises about 70% of cell volume)

CO2 – Most medically significant bacteria do not require increased CO2, but some bacteria need 5 to 7% CO2

Question 18

When compared to “typical bacteria,” what are the major characteristics that are different for those designated in class as “Atypical” bacteria? Why might this be significant to laboratory diagnosis of disease?

Answer 18

1. Cell sizes: very small (0.1 to 0.3 um)

Cell characteristics

a. Metabolically limited - Some are obligate, intracellular parasites
b. Modified cell wall structures, if present (Mycoplasma has no cell wall)
c. Complicated or modified reproductive method

Laboratory cultivation requires living host (e.g. tissue culture, embryonated egg, etc.) or special highly enriched media

Question 19

Mold cells that are multicellular long filaments are called ____________. When these cells/structures grow in a mass, they are referred to as _____________.

Answer 19

Hyphae

Mycelium

Question 20

Reproductive forms of molds typically grow on ___________. (what structure)

Answer 20

Reproduce by forming spores on reproductive hyphae.

Question 21

True/False.

Molds typically grow on artificial media similar to that used for bacteria, except that the media usually contains antibiotics to inhibit viruses. [If false, what is needed to make it true?]

Answer 21

False

Fungus can be grown on artificial media similar to that used for bacteria however the antibiotics are to inhibit bacteria growth during longer growth periods.

Question 22

Describe a virus?

(type of organism, size, reproduction, etc.)

Answer 22

Viruses are not considered to be living organisms; however, taxonomic organization is similar to other microbes as if it were “Kingdom Virus”

Virus description:

a. Obligate, intracellular parasite
(1) Takes control of the host cell
(2) Requires metabolic processes of living cell to reproduce virus
b. Contains only one type of nucleic acid (RNA or DNA), not both
c. Unaffected by most antibiotics which are effective against bacteria (due to differences in bacterial cell morphology and structure vs virus)

Virus size: 18 to 300 nm (0.018 to .3 um) [some up to 14,000 nm in length]

Question 23

What is the inner-most structure of the virus, what is it composed of, and what is its function?

Answer 23

Core

(a) Composition: nucleic acid (DNA or RNA, but not both)
(b) Function: genetic information

Question 24

What is the structure found on the exterior of only certain viruses; what is its structural composition, and what are its primary functions?

Answer 24

Envelope

(a) Composition:
i. Lipid bilayer acquired from host cell or nuclear membrane
ii. Glycoproteins (“spikes”) – site for attachment and serve as antigens
(b) Function:
i. Lipid bilayer provides general protection from the environment
ii. Proteins are primary site of attachment to host cell surface
iii. Proteins serve as antigens during infection and as site for antibody attachment

Question 25

Bacterial viruses are structurally similar to animal viruses, but with an additional structure known as the ____________. One significant role of this additional structure is ________________________.

Answer 25

Tail

(a) Sheath
i. Column of protein which connects the head to the base
ii. Reconfigures into a tube when the virus attaches to a bacterium
(b) Tail fibers – protein fibers with polysaccharide tips which help in determining the attachment site on bacterial cells
(c) Base with enzymatic pins – punch a hole in the bacterial cell wall through which the viral nucleic acid can enter

Question 26

Describe the major steps of the virus infection.

Answer 26

a. Attachment – adsorption of virus to receptor sites on the cell membrane (cell wall of bacteria); due to random collision and proper “match” of attachment determinants
b. Penetration and Uncoating of Nucleic Acid
(1) Entrance of the virus into the cell
(a) Method similar to ingestion in phagocytosis or
(b) Fusion of envelope with host cell’s cytoplasmic membrane
(2) Uncoating of the nucleic acid – the process of opening the capsid and thus releasing the viral nucleic acid into the cell’s cytoplasm
(3) ALTERNATE: virion remains on cell surface and only the nucleic acid enters the cell
c. Eclipse or Synthesis Phase
(1) Viral nucleic acid is transcribed into mRNA if needed
(2) Viral mRNA is translated into viral proteins
(3) New viral proteins inhibits the host’s synthetic mechanisms and normal host activity
(4) New viral nucleic acid copies are produced
(5) New viral capsids are produced
d. Maturation – new viral nucleic acid copies are packaged into new viral capsids
e. Release
(1) Enveloped viruses – bud through the cell membrane
(a) Viral proteins are inserted into the host’s membrane
(b) Viruses retain some of the host cell’s membrane as they bud through it
(2) Non-enveloped viruses – Lysis of the host cell
(a) Mature viruses accumulate in large groups in the cytoplasm awaiting release
(b) A viral enzyme ruptures the cell membrane, thus releasing the viruses

Question 27

Describe the characteristics of latency of viral infection.

Answer 27

Latency – the DNA of certain viruses can incorporate into the host DNA and lie hidden (latent or dormant). During this time the viral genes may be replicated as if they were normal host DNA. Upon certain stimuli, the viral DNA is removed from the host DNA and new viruses are produced. In bacteria this is referred to as lysogeny (lysogenic cycle)

Question 28

What growth conditions are required for virus replication?

Answer 28

a. Requires living cell for viral replication (e.g. cell culture, embryonated egg)
b. Isolation and identification time: 2 days to 4 weeks, depending on the virus

Question 29

State the means of locomotion for the different types of protozoa.

Answer 29

(1) Amoebae – move by pseudopodia (false feet)
(2) Flagellates – move by flagella (long whip-like structures)
(3) Ciliates – move by cilia (many short hair-like structures)
(4) Apicomplexans (Sporozoans) – non-motile in their mature forms

Question 30

What are the characteristics of the major morphologic stages of protozoa?

Answer 30

a. Trophozoite stage
(1) Active, vegetative, motile, feeding stage
(2) Responsible for major pathological conditions in host
b. Cystic stage
(1) Dormant, nonmotile, nonfeeding stage
(2) Protected by formation of cyst wall; able to survive certain adverse environments

Question 31

Describe the major characteristics of Trematodes (size, shape/appearance, reproduction, etc.).

Answer 31

Under Platyhelminthes (flatworms)

a. Trematodes (the flukes)
(1) One body part, non-segmented; leaf shaped (most trematodes)
(2) Size: 500um to 60mm (microscopic to over 2 ½ inches)
(3) Partial alimentary tract - mouth, esophagus, caeca, but no anus
(4) Reproduction - most are monoecious – male and female reproductive structures in one organism (internal fertilization)

Question 32

Describe the major characteristics of Cestodes (size, shape/appearance, reproduction, etc.)

Answer 32

Under Platyhelminthes

b. Cestodes (the tapeworms)
(1) Multiple body parts, segmented
(2) Size: elongated 2mm to over 12 meters (1/16 inches to 50 feet)
(3) No alimentary tract
(4) Reproduction: Monoecious

Question 33

Describe the major characteristics of Nematodes (size, shape/appearance, reproduction, etc.).

Answer 33

Nematodes (the true roundworms)

a. Unsegmented and cylindrical – body surface may be wrinkled
b. Size: elongated 300um to over 1 meter (microscopic to 3 feet)
c. Complete alimentary tract
d. Reproduction: Dioecious – sexes separated into male and female worms (fertilization by sexual copulation)

Question 34

Cells which are about 1.2 µm in diameter, grow on routine culture media, and reproduce by binary fission are known as ________________.

Answer 34

Bacillus cells

Question 35

A microbe which consists of segmented body parts and is about 50 mm in length is most likely ____________.

Answer 35

cestodes (tapeworm)

Question 36

A microbe which reproduces only when it is inside a living “host” cell is most likely __________________.

Answer 36

virus