BT102 Midterm Current Solved Paper December 2019

BT102 – Microbiology

Current paper solved question mid term December 2019

Q1. Function of cell membrane factors of bacterial cell death. (5 marks)

cell membrane is composed of a phospholipid. molecules arranged tail to tail with heads facing away from each other. This makes lipid molecules to appear as a bilayer. So all membranes enclosing the organelle in the cell or the cell itself look as bilayer structures. This is the basic design of the plasma membrane. Protein and carbohydrates are also inserted into the plasma membrane.

There are some basic function of cell membrane in bacteria.

1. Selective permeable barrier
2. Passive and Active Transport
3. Respiration in microbes (bacteria)
4. Photosynthesis in microbes
5. Lipid synthesis
6. regulates the transport of substances in and out of the cell.
7. receives chemical messengers from other cell.
8. cell mobility, secretions, and absorptions of substances

• Cell wall parts are transported by a molecule called bactoprenol which is present in the plasma membrane.
• PM has many receptors in it with which various ligands can bind and initiate signals for gene expression etc.

Cell membrane lipids can be disrupted by alcohols, quaternary ammonium compounds and polymixins. So, these compounds are used as disinfectants or for controlling microbial growth.

Q2. Oxidative phosphorylation and mechanism of phosphorylation. (3 marks)

Oxidative Phosphorylation

a. Electrons captured from foods are transferred to co-enzymes such as NAD+ or FAD etc.

b. Then these electrons pass through a series of electron carriers and then ultimately to the last electron acceptor molecules such as O2 or other inorganic compounds (nitrate, sulphate, carbonate etc) through a series of these electron carriers in system called electron transport chains.

c. During these events, ATP is generated by chemiosmosis.

Photophosphorylation

a. This occurs in plants and chlorophyll containing microbes or photosynthetic cells. In these cells, light energy is finally converted into ATP. An electron transport chain is also involved here. This is summarized in the accompanying diagram above.

Q3. Dry heat method of sterilization. (3 marks)

Form of dry heat include:

1. Dry heat (hot-air oven),
2. Flaming (Platinum loop sterilization in the flame of Bunsen burner),
3. Incineration (burning to ashes).

Similarly, moist heat can also be grouped into autoclaving (15psi), boiling at 100oC, and Tyndallization (100oC for 3 consecutive days to sterilize sugar solution that can be degraded by autoclaving) and pasteurization (usually at low temperature than 100oC).

Q4. F+cell. (2 marks)

In E. coli, fertility factor (F factor) plasmid was the first plasmid observed to be transferred from one organism to the other, hence those bacteria that have this plasmid are called F+ cells to differentiate from those that do not have one (F-). However, once Fcells acquire F+ plasmid, they also become F+.

Q5. Western boltting. (5 marks)

Western Blotting: We can use this technique for the detection of antigen in the serum. Microbial proteins can be separated on SDS-PAGE by electrophoresis and the presence of these proteins can be detected by enzyme-tagged antibodies specific to those proteins. A color band will be seen where the specific protein (antigen) is present on the gel. Please remember that proteins in the gel are first transferred to a paper strip before they could be detected by specific antibodies as seen in the accompanying figure.

Q6. Function of cell wall in bacteria . (5 marks)

Cell wall is the most important layer in bacteria. It is rigid layer just outside the plasma membrane.

•  Most important structure in prokaryotes
•  It provides shape to the organism.
•  It provides protection from osmotic lysis.
•  It is involved in pathogenicity (ability of the organism to cause the disease).
•  Several antibiotics act on it.

Each bacterium is enclosed by a rigid cell wall composed of peptidoglycan, a protein-sugar (polysaccharide) molecule. The wall gives the cell its shape and surrounds the cytoplasmic membrane, protecting it from the environment. It also helps to anchor appendages like the pili and flagella, which originate in the cytoplasm membrane and protrude through the wall to the outside. The strength of the wall is responsible for keeping the cell from bursting when there are large differences in osmotic pressure between the cytoplasm and the environment.

Q7. What is vertical and horizontal gene transfer and also write type of lateral gene transfer. (3 marks)

Vertical Gene Transfer

This is a normal way of transferring genes from parents to offspring. This happens when a cell divides. Each daughter cell receives exactly what its parent cell has.

When genes are transferred from cells to cells within the same species, the process is called horizontal gene transfer. This can happen between cells of the same species, or across different species of organisms. Horizontal gene transfer involves a donor and a recipient cell. The recipient cell then incorporates received DNA into its own genome and this genome becomes a recombinant molecule or recombinant DNA. The cell that has this recombinant DNA in it is called a recombinant cell. Three processes are known by which genes can be transferred horizontally from one cell to the other, and they include:

1. Transformation
2. Conjugation
3. Transduction

Q8. Osmotic pressure.osmtic layer and plasmolysis . (3 marks)

Osmotic pressure is the force caused by a solution passing through a semi permeable surface by osmosis, which is equal to the force required to resist the solution from passing back through the surface. An example of osmotic pressure is the process to filter water.

plasmolysis

If cells are placed in hypertonic solutions, water leaves the cells shrinking the cells and damaging them. This process is called plasmolysis. Plasmolysis is the process in which cells lose water in a hypertonic solution

Q9. What is sporogenesis. (2 marks)

Formation of spores takes place within a vegetative cell and the process is called sporulation or sporogenesis. It is initiated when nutrients become unavailable.

Q10. Why 70% alcohol is more effective the 100% alcohol. (2 marks)

Ethanol, isopropanol are examples. Alcohols denature proteins, and dissolve lipids. Alcohols require water for being more effective. This is the reason that seventy percent alcohol is more effective than 100%. Please note that alcohols can effectively kill vegetative form of bacteria, and fungi but not spores. Alcohols are not very effective on wounds. Commonly used in hand sanitizers.

Q11. L-form bacteria. (2 marks)

Some cells, called L-form organisms, are naturally found without the cell wall. In other words, normally, they have cell wall but under certain conditions, they may lack a cell wall. These cells can be created when grown in the presence of penicillin which inhibits cell wall synthesis.

Q12. What is HRF and function. (2 marks)

13. If F factor gets integrated into the chromosome of the recipient cells, the bacterium becomes high frequency of recombination cell (Hfr). ➢ Conjugation can be used for gene mapping on the chromosomes. ➢ conjugation_mapping.html ➢ High frequency of recombination is also a kind of conjugation.

Can be used for mapping genes. high frequency of recombination In some cells that carry F+, F+ (Fertility factor) gets incorporated in the chromosomal DNA which converts F+ cells to high frequency of recombination cells (Hfr cells). When conjugation occurs between an Hfr cell and an Fcell, the Hfr cell’s chromosome (with its integrated F factor) replicates, and a parental strand of the chromosome is transferred to the recipient cell. Since this transfer starts from the middle of F factor gene, and most of the time, this transfer is not complete; the whole chromosome of Hfr cell is not transferred. However, some genes can be transferred during this process. When these genes become integrated into the genomic DNA of the recipient cells, the recipient cells acquires new versions of genes that were not part of its genome previously. It may be noted that Fcells remains Fnegative cell because F factor is not transferred completely. This whole process is illustrated in the accompanying diagram. Also remember that these newly acquired genes can be mapped easily with respect to the time they get transferred to Fcells. So, conjugation can be used to map the genes on the bacterial chromosome. Video clip in the lecture illustrates this mapping very well.

Q14. Pilli and its functions. (5 marks)

These are hair-like structure composed of pilin, usually one to ten in number.

a. Longer than fimbriae b. Used for attachment to:

• Host cells

Bacteria

1. Used for DNA transfer from on bacterium to another:

Conjugation (Sex pili) d. Also function in twitching Motility

Gliding Motility is also the function of the pili.

15. Process of fermentation.

Fermentation: Initial steps for glucose oxidation by fermentation are the same as they occur in glycolysis for respiration. However, when pyruvate is generated through glycolysis, electrons are also captured by NADH and this NADH needs to be regenerated into NAD+ for recycling. If the final electron acceptor is one of the end products such as ethanol, lactic acid, acetic acid etc, the process is called fermentation. Both anaerobic respiration and fermentation do not use oxygen during these processes, and during fermentation, there are no electron transport chain involved as you can see in the accompanying diagram. Examples of fermentation are given in the accompanying diagram:

16. Process of germination of spore.

Spore germinates when it finds a conducive environment for its growth. Germination has 3 phases or stages: Activation: It prepares the spore for germination. Heat can activate the spore when appropriate moisture and nutrients are present in the environment. Germination: Spore starts swelling and loosing its coats etc. It becomes metabolically active.