Week 11: Pathogenic Fungi

Question 1

What are fungi?

Answer 1

Eukaryotes that contain a cell wall and produce spores

Fungi are very diverse and inhabit a wide variety of habitats, with at least 100,000 named species.

Question 2

What is the estimated total number of fungal species?

Answer 2

Over 500,000

Only ~500 can cause mycosis in humans or animals.

Question 3

What are unicellular fungi commonly known as?

Answer 3

Yeasts

Example: Saccharomyces cerevisiae – budding yeast or baker’s yeast.

Question 4

What is tinea corporis and what causes it?

Answer 4

A skin disease caused by Microsporum canis

Lesions vary in size and location, commonly affecting scalp, face, and body.

Question 5

What is superficial candidiasis usually caused by?

Answer 5

Candida albicans

Infections are normally relatively harmless.

Question 6

What is invasive candidiasis and its impact?

Answer 6

A severe infection caused by Candida species with a very high mortality rate

It can occur in certain cases.

Question 7

What are some species of Aspergillus and their effects?

Answer 7

Aspergillus flavus and Aspergillus fumigatus

Aspergillus flavus grows on important agricultural crops; Aspergillus fumigatus can cause allergic reactions or aspergillosis.

Question 8

What are aflatoxins and their significance?

Answer 8

Strong carcinogens produced by many Aspergillus species

Example: aflatoxin B1.

Question 9

Who first characterized penicillin?

Answer 9

Alexander Fleming

He discovered it was produced by Penicillium notatum.

Question 10

What is the structure of Penicillin G?

Answer 10

Core structure specific for Gram-positive bacteria

Sensitive to β-lactamase produced by penicillin-resistant bacteria.

Question 11

What is the role of sulfanilamide in antibiotic treatment?

Answer 11

It inhibits growth of certain bacteria by blocking folic acid biosynthesis

It is a competitive inhibitor of dihydropteroate synthetase (DHPS).

Question 12

What is the mutation rate in E. coli?

Answer 12

1 × 10–9 to 1 × 10–10 per nucleotide

This leads to an average of 1 resistant cell per 500 bacteria.

Question 13

How can bacteria acquire antibiotic resistance?

Answer 13

Through point mutations, plasmids, transposons, or horizontal gene transfer

Some resistance genes existed before the antibiotic era.

Question 14

What are azole compounds used for?

Answer 14

To inhibit fungal growth by targeting cytochrome P450 enzyme 14α-demethylase

Example drugs include Clotrimazole and Fluconazole.

Question 15

What is the mechanism of action for echinocandins?

Answer 15

Inhibit β-(1,3)-D-glucan synthase for cell wall synthesis

Important in treating fungal infections.

Question 16

What is the target of antiviral treatments?

Answer 16

Specific viral processes without damaging host cells

Examples include fusion inhibitors and inhibitors of viral replication.

Question 17

What is the function of restriction endonucleases in bacteria?

Answer 17

They cut double-stranded DNA at specific recognition sequences

This mechanism helps bacteria discriminate between foreign and their own DNA.

Question 18

What is the significance of the ‘silver bullet’ concept?

Answer 18

Substances that specifically target vital metabolic functions of bacteria

It aims to minimize damage to host cells.

Question 19

What happens when cell wall synthesis is inhibited in bacteria?

Answer 19

It can lead to bacterial death

Example: Penicillin inhibits cell wall synthesis.

Question 20

What is the role of quorum sensing in new antibiotics?

Answer 20

Blocks communication in pathogens without affecting growth

This reduces the likelihood of developing resistance.

Question 21

What is the primary mechanism of action for acyclovir?

Answer 21

Inhibits viral DNA polymerase

It is effective for HSV and varicella-zoster virus.

Question 22

What are restriction endonucleases?

Answer 22

Enzymes that cut double-stranded DNA

They play a critical role in bacterial defense mechanisms.

Question 23

What is the primary function of restriction endonucleases?

Answer 23

To cut DNA at or near specific recognition sequences

This allows bacteria to distinguish between foreign and their own DNA.

Question 24

What does EcoRI stand for?

Answer 24

Escherichia coli, R class of endonuclease, 1st enzyme discovered

It is one of the most commonly used restriction enzymes in molecular biology.

Question 25

What is the recognition sequence for EcoRI?

Answer 25

GAATTC

EcoRI cuts at this specific sequence.

Question 26

What is the role of EcoRI methylase?

Answer 26

To methylate the recognition sequence GAATTC

Methylation protects the bacterial DNA from being cut by EcoRI.

Question 27

Fill in the blank: EcoRV is a type of _______.

Answer 27

[restriction endonuclease]

Question 28

What is the recognition sequence for EcoRV?

Answer 28

GATATC

This sequence is specifically cut by EcoRV.

Question 29

What is the function of modification methylase EcoRV?

Answer 29

To methylate the recognition sequence GATATC

This modification helps in distinguishing between foreign and self DNA.

Question 30

True or False: Restriction endonucleases can only cut DNA from foreign sources.

Answer 30

False

They can also cut their own DNA unless it is methylated.

Question 31

What is one method bacteria use to discriminate between ‘foreign’ and ‘own’ DNA?

Answer 31

Methylation of specific recognition sequences

This prevents the restriction endonucleases from cutting the bacterial DNA.

Question 32

What does the term ‘CRISPR-Cas’ refer to?

Answer 32

A system used by bacteria for adaptive immunity

It allows bacteria to remember and fight off past infections.