Consider statements about human anatomy: 1. The skeletal system provides support and protection. 2. The muscular system enables movement. 3. The endocrine system produces hormones. Which are correct? MCQ with Answer and Explanation

Explanation:
Down syndrome (trisomy 21) is an autosomal aneuploidy caused by nondisjunction resulting in three copies of chromosome 21. It is characterized by intellectual disability, flat facial profile, protruding tongue, and simian crease. Turner's syndrome is monosomy X (45, X). Klinefelter's is 47, XXY. Phenylketonuria is an inborn error of metabolism (autosomal recessive) due to deficiency of phenylalanine hydroxylase.

Explanation:
Pellagra, characterized by dermatitis, diarrhea, and dementia (3 Ds), is due to deficiency of niacin (vitamin B₃) or its precursor tryptophan. Niacin is part of NAD and NADP coenzymes.

Explanation:
Insulin is a peptide hormone produced by the beta cells of the Islets of Langerhans in the pancreas. It is initially synthesized as a single, inactive polypeptide precursor called proinsulin. During processing, a connecting peptide (C-peptide) is removed, leaving two polypeptide chains: the A chain (21 amino acids) and the B chain (30 amino acids). These two chains are held together by two interchain disulfide bridges (covalent bonds between sulfur atoms of cysteine residues), and there is also one intrachain disulfide bridge within the A chain.