Bacterial Cell Structure and Function

Question 1

What are the types of microorganisms?

Answer 1

Bacteria (prokaryotes)
Viruses
Protozoa and Fungi (eukaryotes)

Question 2

What is the average size of the bacterial cell?

Answer 2

0.2 - 5 micrometers. The smallest bacteria (mycoplasma) is equal to the size of the largest virus (0.1 to 0.2 micrometre)

Question 3

What cellular structures are missing in bacterial cells?

Answer 3

Bacterial cells have no mitochondria, no endoplasmic reticulum, no Golgi apparatus and no lysosomes

Question 4

What are some characteristics of bacterial cells?

Answer 4

Bacterial cells have a rigid cell wall containing peptidoglycan, they have both DNA and RNA, they replicate via binary fission and some of them can move.

Question 5

What are the differences between the characteristics of the different microorganisms?

Answer 5

Viruses are not cells; whereas, bacteria, fungi and Protozoa are cells.

The approximate diameter of viruses are 0.02-0.2 micrometers, bacteria are 1-5 micrometers, fungi are 3-10 micrometers and protozoa are 15-25 micrometers.

Viruses have either DNA or RNA; whereas, bacteria, fungi and Protozoa have both DNA and RNA.

Viruses have no nucleus, bacteria have a prokaryotic nucleus and both fungi and protozoa have an eukaryotic nucleus.

Viruses have no ribosomes, bacteria have 70S, fungi have 80S and protozoa have 80S.

Mitochondria are absent in both bacteria and viruses, but present in fungi and protozoa.

Viruses have an outer layer of protein capsid and lipoprotein envelope, bacteria have an outer layer of rigid wall containing peptidoglycan, fungi have an outer layer of rigid wall containing chitin, and protozoa have an outer layer of flexible membrane.

Viruses and fungi cannot move, some bacterias can move and most protozoa can move.

Viruses do not replicate by binary fission, bacteria replicated by binary fission, fungi replicate by budding or mitosis and protozoa replicate by mitosis.

Question 6

What is the morphology of bacterial cells?

Answer 6

Bacterial cells can be:

• cocci (round)
• bacilli (rods)
• spirochetes (coils)

They can also be straight rods e.g. escherichia, branching rods e.g. actinomyces or comma/s/c/ curvy shape e.g. vibrio.

Question 7

What are the different arrangements of the cocci cells?

Answer 7

Diplococci e.g. neisseria
Chain e.g. streptococcus
Tetrad e.g. sarcina
Cluster e.g. staphylococcus

Question 8

What are the cellular components of bacterial cells?

Answer 8

Capsule, cell wall, cell membrane, cytoplasm, ribosomes, flagella, pilli and nucleoid DNA

Question 9

What are the types of prokaryotic cells?

Answer 9

Gram-positive and Gram-negative

Question 10

What are the differences between Gram-positive and Gram-negative bacteria?

Answer 10

• The peptidoglycan in the cell walls of gram-positive bacteria is much thicker than in gram-negative bacteria.
• Only gram-negative bacteria have an outer membrane containing endotoxin and have a periplasmic space where lactamases are found.
• Gram-positive bacteria have a cell membrane, cell wall, flagella, pili and nucleiod DNA; whereas, gram-negative bacteria have a capsule, cell membrane, cell wall, outer membrane, ribosomes, pili and granules.

Question 11

What are the functions and medical importance of the bacterial cell wall?

Answer 11

• It protects the cell from osmotic pressure (lysis)
• It is rigid and strong and therefore, gives shape and support.

Medical importance:

• the cell wall carries virulence factors (molecules that allow a bacterium to cause disease)
• it is a site of action for many antibiotics such as penicillins
• it is a site of action for body defense molecules (lysozyme- target site is peptidoglycan layer of cell wall)

Question 12

What is the outer membrane of the Gram-positive bacteria made of?

Answer 12

Lipoteichoic acid (LTA) which assist in the attachment of the bacteria to the host cell, contains antigenic determinants and contain endotoxins (structural component acting as a toxic substance) which cause toxic shock (high fever, low blood pressure and multi organ dysfunction)

Question 13

What is the outer membrane of the Gram-negative bacteria made of?

Answer 13

The outer membrane of gram-negative bacteria is composed of a phospholipid layer, proteins and lipopolysaccharides. The lipopolysaccharides are core, O-antigen and Lipid A which contain endotoxins that cause toxic shock.

Question 14

What type of bacteria causes the worst type of toxic shock?

Answer 14

In gram-positive bacteria, the symptoms of toxic shock are very mild; however, in gram-negative bacteria the symptoms are severe.

Question 15

What colors do the bacteria appear as after gram staining?

Answer 15

Gram-positive appears blue and gram-negative appears red

Question 16

What staining procedures are used for non-gram staining bacteria?

Answer 16

• Mycobacteria uses acid-fast stain because there is too much lipid in the cell wall for the dye to penetrate
• Treponema pallidium uses dark-field microscopy or fluorescent antibody because it is too thin to see
• Mycoplasma pneumoniae doesn’t use any other staining procedure because it has no cell wall and is very small.
• Legionella pneumoniae uses a prolonged time of countertsain because of poor uptake of red counterstain.
• Chlamydiae uses inclusion bodies in the cytoplasm because they are intra cellular and very small.
• Rickettsiae uses giemsa or other tissue stains because they are intracellular and very small

Question 17

What are the differences in the results in Acid-fast staining?

Answer 17

If the bacteria is pink, then it is acid-fast.

If the bacteria is purple, then it is non acid-fast

Question 18

Does the phospholipid bilayer contain sterols?

Answer 18

The phospholipid bilayer in prokaryotes do not contain sterols EXCEPT mycoplasma, it does contain sterols.

Question 19

What are the functions of the cytoplasmic membrane?

Answer 19

• It transports compounds in and out of the cell by both passive transport and active transport.
• It is the site for metabolic pathways such as electronic transport and oxidative phosphorylation- energy generation, cytochromes, respiratory chain enzymes
• It is the site for biosynthetic function.

Question 20

Why does oxidative phosphorylation take place at the cell membrane?

Answer 20

Because there are no mitochondria

Question 21

What bacterial components are not essential for survival but give an additional advantage, not present in all bacterial cells and is important for contact between bacteria and the immune system?

Answer 21

Flagella, pili and capsule

Question 22

Where is the flagella located, what is it composed of and what are the functions?

Answer 22

The flagella is anchored on the cell envelope, cell membrane and cell wall.

It is composed of a protein known as flagellin.

It functions as a movement organelle and it may enhance invasion in pathogenic bacteria e.g. most pathogens of the UTI are flagellated

Question 23

What is chemotaxis?

Answer 23

Chemotaxis is the movement of a microorganism e.g. bacteria in response to a chemical stimuli (attraction to sugars and amino acids and repulsion towards bacterial waste products)

Question 24

Where are pili located, what is it composed of and what are the functions?

Answer 24

Pili are hair like filaments found mostly among gram-negative bacteria.

It is composed of protein called pilin.

There are two types.

• Attachment pili is involved in the initiation of infection by adhering to epithelial cells and the removal of pili results in loss of pathogenicity
• Sex pili are responsible for conjugation (temporary union of two bacteria for exchange if genetic material) and is involved in genetic transfer between bacterial cells.

Question 25

What is the capsule composed of and what are the functions?

Answer 25

The capsule is a gelatinous material that covers the cell wall. It is composed of polysaccharides except in bacillus species (polymers of D-glutamic acid).

Functions: it enhances virulence (ability to cause disease), it is anti-phagocytosis (prevents phagocytosis from occurring), it facilitates the adherence to host cells which initiates colonization, it is antigenic therefore is used for serologic typing and vaccine

Question 26

What are mesosomes?

Answer 26

Mesosomes are inward foldings of the membrane involved in cell division

Question 27

What is the function of bacterial granules?

Answer 27

Bacterial granules function as a food storage area. They are not present in all bacteria and are not always in a particular cell. They also stain differently than the rest of the cytoplasm.

Question 28

What is the function of the nucleoid?

Answer 28

The nucleoid is the area of the cytoplasm in which DNA is located

Question 29

What are the functions of plasmids?

Answer 29

There are two types:

• transmissible plasmids which can be transferred from cell to cell by conjugation
• non transmissible plasmids which are frequently present in many copies per cell

Functions:

• antibiotic resistance which is meditated by a variety of enzymes
• resistance to heavy metals such as mercury and silver which is mediated by a reductase enzyme
• resistance to ultraviolet light, which is mediated by DNA repair enzymes
• pili (fimbriae) which mediates the adherence of bacteria to epithelial cells
• exotoxins (secretion of toxic substances) including several enterotoxins

Question 30

What is a bacterial spore (endospore)?

Answer 30

An endospore is a form of bacteria and a highly resistant structure found in adverse conditions such as when nutrition is depleted.

It is found in the two gram-positive genera: genus bacillus and clostridium

It has no measurable metabolic activity and can survive for many years in the environment. Contaminated soils may contain spores such as tetanus and gas gangrene.

It is highly resistant to dehydration, heat, chemicals radiation. It is not killed by boiling but is killed at 121° C