Microbial Structure

Question 1

Describe the differences between Eukaryotes and prokaryotes with respects to genetic material

Answer 1

Eukaryotic:
Nucleus bound with double membrane, linear DNA, DNA organised into chromosomes and large complex ribosomes
Prokaryotic:
No nucleus, has a nucleoid which has no physical boundary, circular DNA which is present in plasmids and has 70S ribosomes.

Question 2

Describe the difference in structures between eukaryotes and prokaryotes

Answer 2

Eukaryotes:
Cytoplasm filled with large organelles, mitochondria with cristae are ‘energy centres’ and transcription requires formation of mRNA and then movement of mRNA to cytoplasm for translation.
Prokaryotes:
No membrane bound organelles, mesosomes are used in aerobic respiration and transcription and translation occur simultaneously.

Question 3

Name the structural components of bacteria

Answer 3

Capsule, Pili (fimbriae), flagella, spores, slime and a cell wall.

Question 4

Describe the basic structure of the capsule and how protects the bactrium

Answer 4

It is made of a loose polysaccharide and protects baterium from phagocytosis and desiccation (removal of moisture)

Question 5

Describe the structure and features of pili/fimbriae

Answer 5

KEY- NOT on all bacteria. Pilus and fimbria for singular. They are composed of oligomeric proteins, used for bacterial conjugation (transfer of plasmids between cells), highly antigenic (triggers a quick immune response), facilitates attachment. and contains lectins which are easily recognisable by the body.

Question 6

Describe the structure and features of flagella

Answer 6

Flagellum is singular term. They can be singular or a bacteria cell can have multiple. The are composed of flagellin protein and are thick helical hollow tubes. They facilitate movement and are driven by a rotary engine at the anchor point on the inner cell membrane.

Question 7

Give two examples of bacterium with flagellum

Answer 7

Vibrio cholerae and Escherichia coli

Question 8

Describe some of the features of spores

Answer 8

Metabolically inert, has a hard, multi-layered coats making them very resistant.

Question 9

Describe the features of slime

Answer 9

It’s made from a polysaccharide material and is secreted by bacteria growing in biofilms. It protects them against the immune system and antibiotics.

Question 10

What groups can bacterium be separated into due to staining?

Answer 10

Gram positive and Gram negative. These are based on the properties on the cell walls.

Question 11

What makes a cell wall Gram positive?

Answer 11

The thick peptidoglycan layer. Only 2 layers

Question 12

What makes a cell wall Gram negative?

Answer 12

The presence of lipopolysaccharides in the phospholipid layer. It contains 3 layers

Question 13

Describe the steps in Gram staining

Answer 13

Primary stain - use of a crystal violet dye that stains all cells purple.
Trapping agent - the use of Gram’s iodine which forms a CVI complex in the cell wall.
Decolourisation- use of alcohol or acetone which interacts with lipids. Gram negative loses the outer LPS layer exposing the inner PGN layer so the colour is washed away. Gram positive becomes dehydrated and traps the complexes in the thick PGN layer.
Counterstain - use of safranin which stains Gram negative pink and Gram positive purple.

Question 14

Name some of the bacteria cell wall components

Answer 14

Peptidoglycan (PGN)
Lipoteichoic acid (recognised by immune cells)
Lipopolysaccharide (LPS) in Gram negative, essental for function.
Outer membrane proteins (OMPs)

Question 15

Explain bacterial replication

Answer 15

They reproduce asexually (by binary fission) has circular DNA which is self replicating; it replicatees in two directions with replicating forks splitting from the origin and meeting at the bottom.

Question 16

what are the four growth phases of bacteria and explain them.

Answer 16

Lag phase - Cells grow in size
Log phase - Cells divide at maximum rate
Stationary phase - Exhaustion of nutrients, oxygen and accumulation of inhibitory end products. No. cells reproducing = No. dying
Death phase - Number of cells dying starts to exceed the number born.

Question 17

Name the three ways of bacterial recombination

Answer 17

Conjugation - Bacterium connect through pilus and genes are transferred.
Transformation - bacteria take up DNA from environment
Transduction - exchange of DNA through bacteriophages (virus that infects bacteria cells)

Question 18

What are the basic classifications of Bacteria?

Answer 18

Gram staining, cell shape, atmospheric preference, key enzymes and fastidiousness

Question 19

Name the three different shapes of bacteria

Answer 19

Cocci - spherical
Bacilli - rod shaped
Spiral - helical rod

Question 20

Name a Gram positive cocci

Answer 20

staphylococcus aureus

Question 21

Name a Gram negative Bacilli

Answer 21

Haemophilus influenzae

Question 22

Name the viral structural components

Answer 22

Nucleic acid, capsid, envelope and spikes

Question 23

Describe some of the features of a caspid coat

Answer 23

It is a protein shell composed of protein subunits called capsomeres. Can have a variety of different shapes; rod-like, polyhedral and complex.

Question 24

Name some of the features of the viral envelope

Answer 24

amorphous structure that surrounds SOME viruses. It’s composed of lipids, proteins and carbohydrates.

Question 25

Name some of the features of viral spikes

Answer 25

They are glycoprotein projections arising from the envelope, highly antigenic meaning they trigger a quick immune response and the may have an enzymatic, adsorption or haemagglutin (causing haemogglutination -the clumping of red blood cells) activity.

Question 26

Name the six steps of viral replication

Answer 26

Adsorption, penetration, replication, assembly, maturation and release.

Question 27

Describe absorption (step 1)

Answer 27

virus binds to host cell

Question 28

Describe penetration (step 2)

Answer 28

Virus injects its genome into host cell, occurs by fusion, binding and ingestion.

Question 29

Describe Replication (step 3)

Answer 29

Caspid digested by proteolytic enzymes and the viral genome replicates using host cell machinery

Question 30

Describe Assembly and maturation (step 4 & 5)

Answer 30

Viral components and enzymes are produced and begin to assemble.
In maturation the virus fully develops

Question 31

Describe release of naked viruses (step 6)

Answer 31

It occurs at the site of nucleic acid replication, the viral enzymes break down the cell wall.
RNA viruses are released as they are produced. DNA viruses are expelled from host cell as cell autolyse and in inclusion bodies.

Question 32

Describe the release of enveloped viruses (step 6)

Answer 32

Viruses migrate to either plasma or nuclear membrane. Envelopes formed around nucleocapsids by budding of cell membrane. Slow continuous release, no inclusion bodies.

Question 33

What are the classifications of protozoas?

Answer 33

Sporozoa - intracellular parasites
Flagellates - possess tail-like structures for movement
Aomeba - uses temporary cell-body projections
Ciliates - move by beating cilia.

Question 34

Name some common protozoal infections

Answer 34

Malaria, Giardiasis, Toxoplasmosis and cryptosporidiosis.

Question 35

Describe some of the features of fungi

Answer 35

Multinucleate or multicellular organisms. usually grow as thread-like filaments (hyphae), Reproduce asexually by budding and occasionally binary fission.

Question 36

What are fungal infection called?

Answer 36

Mycoses.

Question 37

Name some common fungal infections

Answer 37

Candidiasis, cryptococcosis, aspergillosis and ringworm.

Question 38

What are the three types of helminths found in humans?

Answer 38

Cestoda - tapeworms
Trematoda - flukes
Nematoda - roundworm

Question 39

Name some examples of helminths

Answer 39

Schistosomiasis, Trichuriasis, tapeworm