AP BIOLOGY

Detailed explanation-1: -Arrayed along the DNA strand are the genes, specific regions whose sequences carry the genetic code for making specific proteins. The genes of bacteria are tightly packed together; virtually all the DNA encodes proteins.

Detailed explanation-2: -Human genes typically contain several “exons, ” or DNA sequences that code for amino acids, the building blocks of proteins. A single gene can produce multiple protein sequences, depending on which exons are included in the mRNA transcript, which carries instructions to the cell’s protein-building machinery.

Detailed explanation-3: -Yes. In fact, this is common, and very important for evolution. It occurs when a mutation duplicates a gene, chromosome or whole genome. The amount of times a particular gene (or different genes coding the same protein, if you wish) occurs in the genome is called its copy number.

Detailed explanation-4: -The number of genes in an organism that encode proteins may be far fewer than the number of proteins they actually make. Current estimates suggest that it takes just 25, 000 genes make and operate a human and all its proteins (check out Pertea and Salzberg at Estimating the number of genes in the human genome).

Detailed explanation-5: -Each gene’s code uses the four nucleotide bases of DNA: adenine (A), cytosine (C), guanine (G) and thymine (T)-in various ways to spell out three-letter “codons” that specify which amino acid is needed at each position within a protein.