Xeroderma pigmentosum is characterized by:

# Xeroderma pigmentosum is characterized by:
A. Autosomal dominant inheritance
B. Inability to repair sunlight induced damage to DNA
C. Irregular accumulation of melanin in the basal cell layer
D. Acanthosis of epithelium with elongation of rete pegs

The correct answer is B. Inability to repair sunlight induced damage to DNA

Xeroderma Pigmentosum
- Inherited disorder involving defective DNA repair genes.
- Increased risk for the development of cancers of the skin when exposed to the UV rays.
- UV light causes crosslinking of pyrimidine residues, thus preventing normal DNA replication.
- Such DNA damage is repaired by the nucleotide excision repair (NER) pathway. Several proteins and genes are involved in NER, and an inherited loss of any one can give rise to xeroderma pigmentosum.

Most common form of reversible cell injury is:

# The earliest and most common form of reversible cell injury is:
A. Cloudy swelling
B. Fatty degeneration
C. Hydropic changes
D. Necrosis

The correct answer is A. Cloudy swelling.

- Reversible cellular changes, cellular swelling, or fatty degeneration (cloudy) are the forms of reversible cell injury.

- Necrosis and apoptosis represent irreversible cell injury. 

Most reactive free radical is:

# Out of the various free radical species, the following radical is most reactive:
A. Superoxide (O2-)
B. Hydrogen peroxide (H2O2)
C. Hydroxyl (OH-)
D. Nitric oxide (NO)

The correct answer is C. Hydroxyl Ion (OH-)
Important mechanisms of cell injury are by damage to DNA, proteins, lipid membranes, and circulating lipids (LDL) by peroxidation caused by oxygen-derived free radicals- superoxide anion (O2-), hydroxyl radical (OH-) and hydrogen peroxide (H2O2). Hydroxyl ion is the most reactive.

Koch postulates were modified for periodontitis by:

# Koch postulates were modified for periodontitis by
(A). Socransky
(B). Glickman
(C). Carranza
(D). Orban

The correct answer is: A. Socransky