Basics of Bacteriology

Question 1

What are the main differences between prokaryotic and eukaryotic cells

Answer 1

Prokaryotic cells: no membrane bound nucleus, no membrane bound organelles, possess pili, fimbriae (adhesion/attachment) and flagella (propulsion), cell wall is made up of peptidoglycan.

Eukaryotic cells: membrane bound nucleus, membrane bound organelles, possess cilia and flagella(movement), cell wall (if present) made up of cellulose

Question 2

Describe how viruses differ from cells

Answer 2

Viruses are non living infectious bundles of genes with a protective protein capsid, that depend on human hosts to reproduce.

Cells are basic units of life that can reproduce and survive on their own, but can also be part of a larger organism.

Question 3

Describe the structure and functions of the capsule

Answer 3

structure: hydrated polysaccharide structure, composed of monosaccharides linked via glycosidic bonds.
function: Adhesion, prevents phagocytosis, reservoir for polysaccharides.

Question 4

Describe the structure and function of cell wall

Answer 4

structure: consists of peptidoglycan, a rigid, highly conserved, complex polymeric of carbohydrates and amino acids.
function: provides structural support, protects against chemical and physical effects.

Question 5

Describe the structure and function of the plasma membrane

Answer 5

structure: phospholipid bilayer consisting of a hydrophilic head attached by an ester bond to two hydrophobic tails.
function: selective barrier that separates the inside of the cell, from outside of the cell, regulates transport in and out of the cell.

Question 6

Describe the structure and function of porins

Answer 6

structure: channels with wide, water filled pores composed of beta sheets, made up of beta strands, linked together by beta turns on the cytoplamic side, and long loops of amino acids on the other.
function: crosses the bacterial outer membrane, acts as a pore so molecules can diffuse through (concentration gradient is required)

Question 7

Describe the structure and function of cytoplasm

Answer 7

structure: gel like matrix
function: cell fluid that holds, DNA, water, ribosomes, enzymes and waste products

Question 8

Describe the structure and function of DNA

Answer 8

structure: single circular chromosome
function: replication, recombination/mutation, gene expression, encoding information.

Question 9

Describe the structure and function of plasmids

Answer 9

structure: circular double strands of DNA, each strand is linked by covalent bonds. Extrachromosomal DNA containing 5-100 genes.
function: encodes advantageous properties.

Question 10

Describe the structure and function of Ribosomes

Answer 10

structure: 21 nm particles consisting of a small (30S) subunit and large (50S) subunit
functions: synthesize proteins

Question 11

Describe the structure and function of flagellum

Answer 11

structure: hair like appendage composed of a filament, hook and basal body, the filament extends from the cell`s surface and is composed of the protein flagellin in helical chains so as to form a hollow core.
function: movement in an aquatic environment.

Question 12

Describe the structure and function of fimbriae and pili (f and p)

Answer 12

structure: consists of long and thin filamentous polymeric protein tubes.
function: fimbrae & p- fili for attachment/adhesion, f-pili transfers plasmids via conjugation

Question 13

What is the nucleoid?

Answer 13

An irregularly shaped region within the cell of a prokaryote that contains all or most of the genetic material

Question 14

What are plasmids?

Answer 14

Extrachromosomal circular DNA, independent of the genome.

Question 15

Describe in detail how a plasmid is moved from a donor to recipient cell

Answer 15

The donor cell usually contains a DNA sequence called the fertility (f) factor, this f factor enables the donor cell to produce a thin tubelike structure called pilus, the pilus then makes contact with the recipient and then the donor cell transfers the plasmid to the recipient cell.

Question 16

What is passive transport (diffusion) and how does this differ from facilitated diffusion?

Answer 16

Diffusion is the movement of substances along a concentration gradient (high to low) without the input of energy. It differs from facilitated diffusion due to the fact that facilitated diffusion involves transport proteins (carriers/channels) across a cell membrane.

Question 17

In which ways can transport across membranes occur?

Answer 17

passive transport & active transport

Question 18

What is osmosis and what happens to a cell found in isotonic, hypertonic and hypotonic environments, respectively?

Answer 18

Osmosis is the movement of water or other solvents, through a semi permeable membrane from a region of high concentration to a region of low concentration.
Isotonic - nothing, Hypertonic- the cell shrinks, Hypotonic- the cell swells

Question 19

What is active transport? Give some examples of active transport?

Answer 19

Active transport is the movement of molecules across a membrane with the input of energy. Examples are: sodium potassium pump.

Question 20

Describe in detail how the cell-wall of prokaryotes is organised? What are the differences between Gram-positive and Gram-negative cell-walls?

Answer 20

The cell wall is made up of peptidoglycan, peptidoglycan is further made up of chains of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
Gram positive cell walls are thick (35-40 layers of peptidoglycan) with large quantities of teichoic acid and gram negative cell walls are thin (1-2 layers) with cytoplasmic inner membrane and bacterial outer membrane.

Question 21

What is teichoic and lipoteichoic acid?

Answer 21

Teichoic acid is a unique sort of polysaccharide that maintains cell wall structure and attracts cations.
Lipoteichoic acid is teichoic acid with a liquid tail, anchored with the cell membrane.

Question 22

What is LPS? Describe the structure and function of LPS. If you are an animal, what is the problem with having LPS in the blood.

Answer 22

LPS is lipopolysaccharide, a toxin located inside the bacterial cell. Has a very complex lipid structure, and three structural domains namely: the core oligosaccharide, lipid A and the O antigen.
function: increases the negative charge of the cell membrane maintaining membrane stability.

LPS is dangerous in animals because it is strongly immunogenic and can induce inflammation, fever, septic shock and lead to death.

Question 23

What is the difference between slime and capsule?

Answer 23

A slime layer is loosely attached to bacteria and can easily be washed off, capsule is tightly attached to bacteria and has definite boundaries.

Question 24

What is a biofilm and describe in detail how a biofilm is formed and organized. What are the bacterial advantages with growing as a biofilm?

Answer 24

A biofilm is a group of microorganisms that stick to a surface by creating a slimy layer outside the cells. It contains bacterial cells, polysaccharides, proteins and DNA.

Formation: Biofilms form in stages, beginning with the attachment of cells to a surface. Attachment is often mediated by flagella, fimbriae, or pili. Colonization of the surface starts when microbes begin to grow and produce sticky extracellular polysaccharides (EPS). Microbial colonization and growth on the surface causes changes in the biofilm that lead to development. During development, cells in the biofilm begin to change their metabolism. These changes can cause biofilms to develop complex systems of mushroomlike columns and channels that trigger metabolic differentiation of microbes at the surface of the biofilm from those at its base. Finally, dispersal of cells from a mature biofilm allows microbes to colonize new sites
Advantages: provide survival sites for bacteria, adhesion capabilities, nutritional sources, resistance to drugs.

Question 25

How do you perform a Gram-stain and what is happening in each step?

Answer 25

1. Apply primary stain (crystal violet). All bacteria are stained purple by this basic dye.
2. Apply mordant (Gram’s iodine). The iodine combines with the crystal violet in the cell to form a crystal violet-iodine complex. (CV-1).
3. Apply decolorizing agent (ethyl alcohol or ethyl alcohol acetone).Decolorizers dissolve membranes. The primary stain is washed out (decolorized) of some bacteria, while others are unaffected.
4. Apply secondary stain or counterstain (safranin). This basic dye stains the decolorized bacteria red.

Question 26

Describe the morphologies of prokaryotes

Answer 26

coccus (spheres), coccobacillus (short rods/ovals), bacillus (rods), vibrion (slightly bent), spirillium (twisted spiral one or several turns), spirichaete (very long, thin twisted spiral), pleomorphic (change in shape), diplococcus (two and two), tetrad (four and four), sarcinae(eight and eight), staphylococcus (bunches), streptococcus (chains), singlebacillus(one and one), streptobacillus (chains), diplobacillus(two and two), palisades (picket fences)

Question 27

What are endospores?

Answer 27

differentiated cells formed within the cells of certain gram positive bacteria that is resistant to heat and other harmful agents.

Question 28

What is chemotaxis and phototaxis?

Answer 28

Chemotaxis is the movement of a cell in response to a chemical stimuli, Phototaxis is the movement of a cell in response to a light source.

Question 29

Describe endospore formation and germination

Answer 29

The chromosome is replicated
• Aligns alongside the cell
2. The cytoplasmic membrane invaginates
• A ”pre-spore” is formed
3. The cytoplasmic membrane grows and engulfs the ”pre-spore”
• The DNA of the vegetative cell is dissolved
4. A cortex of calcium and dipicolinic acid is formed between the membranes
• Most of the water is removed from the cell
5. A spore-coat is formed around the endospore
• Consists for instance of keratin that makes the endospore extremely rough
6. Finally an outer spore-coat is formed
• Increases its resistance to heat and different chemicals
7. The endospore is released
• The vegetative cells goes through lysis

Question 30

Describe flagellar movement and structure.

Answer 30

hair like appendage composed of a filament, hook and basal body, the filament extends from the cell`s surface and is composed of the protein flagellin in helical chains so as to form a hollow core. Moves in a clockwise or counterclockwise direction like a propeller.