Question

1. Describe the basic structure and components of a prokaryotic cell including the cell wall, membrane, nuclear area, ribosomes, types of inclusions and endospores.
2. How do the cell walls of Mycoplasma, the Archaea and Mycobacterium differ from the cell walls of most other bacteria?
3. What characteristics are used to group viruses into taxonomic families? What is a viral species? What are the suffixes that are used to represent genus, family and order names for viruses?

Answer 1

a)

Cellwall – The prokaryotic cell’s cell wall is present outside the plasma membrane. It provides rigidity to the cell shape and structure and protects the cell from its environment. Bacterial cell wall is primarily composed of peptidoglycan and on the basis of cell wall composition the bacteria classified into gram-positive and gram negative organisms.

Cytoplasmic Membrane– The cytoplasmic membrane is a membrane that provides a selective barrier between the environment and the cell’s internal structures.

Cytoplasm

Cytoplasm is thick.aqueous, semitransparent, and elasticsmifluid present inside the prokaryotic cell. It is about 80% water and contains primarily proteins (enzymes), carbohydrates, lipids, inorganic ions, and many low- molecular-weight compounds. Inorganic ions are present in much higher concentrations in cytoplasm than in most media.

Nucleoid/Genetic material – The cytoplasm also contains a region called the nucleoid, which is where the DNA of the cell is located. The prokaryotic cell consists of a chromosome that isn’t contained within a nuclear membrane or envelope. The nucleoid or bacterial chromosome comprises a closed circle of double stranded DNA, many times the length of the cell and is highly folded and compacted.

Ribosomes – Ribosomes are the principle structure in a prokaryotic cell after the nucleoid. They are composed of a complex of protein and RNA, and are the site of protein synthesis in the cell. The prokaryotic ribosomes are 70S, comprised of sub units 50S and 30S (S stands for the sydberg coefficient which is a function of their size and shape, and determined by their rate of sedimentation in a centrifuge)

Inclusion bodies – Many granular structures known as inclusion bodies are found in the cytoplasm of certain bacteria. These contain organic compounds such as starch, glycogen or lipid and act as food reserves. Some sulphur and polyphosphate containing bodies are also found and are known as volutin or metachromatic granules.

Endospore – A number of gram-positive bacteria can form a special resistant, dormant structure called an endospore. Endospores develop within vegetative bacterial cells and are extraordinarily resistant to environmental stresses such as heat,ultraviolet radiation,gamma radiation, chemical disinfectants, and desiccation.

b)The key difference between mycoplasma and mycobacterium is the presence of a cell wall. Mycobacterium is a genus of bacteria where all species possess a thick, protective and waxy cell wall. Mycoplasma is another unique bacterial genus in which all species do not contain a cell wall around their cell membrane

c)The formal endings for taxa of viroids are the word viroid for species, the suffix -viroid for genera, the suffix -viroinae for sub-families, should this taxon be needed, and -viroidae for families. Retrotransposons are considered to be viruses in classification and nomenclatur