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what are essential amino acids? why are they essential?

An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized de novo by the organism, and thus must be supplied in its diet. The nine amino acids humans cannot synthesize are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine.

Essential amino acids cannot be made by the body. As a result, they must come from food. The 9 essential amino acids are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine

1. Mutations in protein-coding genes and regulatory DNA contribute to evolution if the organism carrying them survives and_c. reproduce. Mutations in a_a. gene lead to different effects. For example, a mutation may change the _h. function of the protein or the protein will no longer be produced.

2. Mutations within a_i. regulatory sequence may lead to major changes in_g. body form, for example, if a Hox gene is affected. Moreover, if a transposable element inserts here, it may lead to a decreased or increased_d. protein production. This may impact the organism and if passed on to the offspring, become_e. inherited. The result of these events may eventually lead to increased fitness and the formation of new species.

Explanation:

Mutations can be defined as genetic changes (nucleotide changes) in the genome sequence of an organism. Mutations can be beneficial, neutral or deleterious (depending on their effects on the adaptive fitness of the individual). Mutations that occur in the somatic (body cells) will not be inherited, whereas mutations in the germinal (gamete) cells can be passed on to the next generations. Moreover, Hox genes are major developmental regulators involved in a wide variety of aspects of animal development. In consequence, changes in the expression level of Hox genes caused, for example, through 1-mutations of their regulatory sequences, such as promoter sequences, or 2-the insertion of transposable elements, may lead to conspicuous phenotypic changes by affecting protein production. Eventually, these mutations may confer an adaptive advantage.