If a gene encoding a protein whose third amino acid is tyrosine is affected by a single nucleotide substitution in that tyrosine codon, how many of the other 19 amino acids could possibly end up replacing tyrosine as the third amino acid?

6 different amino acids (no including Stop codons)

Explanation:

First of all, it is necessary to know that tyrosine is an amino acid coded by two different codons: UAU and UAC.

If there's a single nucleotide substitution, we need to redefine the new possible codons:

For UAU:

- Substitution in the first nucleotide:

* CAU: His

* GAU: Asp

* AAU: Asn

- Substitution in the second nucleotide:

* UCU: Ser

* UGU: Cys

* UUU: Phe

- Substitution in the third nucleotide:

* UAG: Stop

* UAC: Tyr

* UAA: Stop

For UAC:

- Substitution in the first nucleotide:

* CAC: His

* GAC: Asp

* AAC: Asn

- Substitution in the second nucleotide:

* UUC: Phe

* UGC: Cys

* UCC: Ser

- Substitution in the third nucleotide:

* UAG: Stop

* UAA: Stop

* UAC: Tyr

Possible amino acids replacing tyrosine (His, Asp, Asn, Phe, Cys, Ser)

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.