Question

2. (a)

(b) Define viruses and virion

(c) Name three main importance of fungi

(d) Explain briefly nucleocapsid

Name 3 advantages and 3 disadvantages of normal flora

Examiner: Prof. K. K. Addo

e) Explain bacteriophages

(f) What are lentiviruses

Answer 1

2b) Virus is a submicroscopic organism who are parasitic in natures. They are capable of replicating only in a living vells.

Virion - its a complete viral particle consisting of an RNA and DNA surrounded by a protein shell. It is the infective form of the virus.

2c)The importance of fungii are as follows:

1. Fungi help to recycle the dead plants and animals. This helps to enrich the soil with nutrients and make it fertile.
2. Certain fungi help to produce antibiotics. These antibiotics save milions of lives everyday. Example - Drug penicillin is produced by a fungi penicillium
3. Certain type of fungi are used as food by humans and animals.

2d) Nucleocaspid- Nucleocaspid is the genetic material of the virus (DNA / RNA) and the protein coat that encloses the genetic material ( caspid )

Advantages of normal flora:

1. Prevents colonization of pathogenic organism
2. They synthesis certain micronutrients that are useful to the body. Example Vit -K and B-12
3. Oral flora contributes to immunity by secreting antibodies that may cross react with pathogenic organisms

Disavantages of normal flora:

1. If the normal flora gains access to certain body parts (which are normally sterile like brain, lower respiratory tract) they can establish infection and disease
2. When the immunity of the person reduces ( sa in case of HIV infection ) the commensal organism can turn pathogenic to the body.
3. Due to the presence of normal flora, when ever a person needs to undergo operation, the operative site needs to clean in order to disinfect it. This requires usage of multiple chemical and solutions. this can be time consuming and costly also.

e) Bacteriophages are virus that infect and live on bacteria

• The bacteriophage consists of nucleic acid which is the genetic material of the bacteriophage
• This is enclosed inside a protein coat called the caspid
• It has a tail which contains the contractile elements
• It also has tail fibre and base plate
• The process of invasion of a host by the bacteriophage involves
  • landing - the bacteriophase attaches itself to the bacteria with help of tail fibres
  • Pinning - in this phase the base plate attaches to the bacteria
  • Tail contraction and penetration - in this phase the tail of the virus contracts and penetrates the bacteria
  • DNA injection - in this phase the genetic material of the bacteriophage is released into the bacteria
• Importance of bacteriophage;
  • Inserting foreign genetic material into the bacteria to give it new properties
  • for typing bacteria
  • As vehicles for vaccine production
  • They can make a bacteria resistant to antibiotics

f) lentivirus

• Lentivirus is a genus of the retroviruses
• The virion is enveloped and spherical
• the genetic material of the virus is RNA
• They are able to incorporate into the host DNA.
• They can infect dividing and non-dividing cells.
• This property makes these viruses excellent vector of genetic material