The approximately 20 basic building blocks of protein are called
a. amino acids.
b. lipids.
c. lipoproteins.
d. triglycerides.

AMINO ACIDS

Explanation:

When the amino acids are linked by dehydration process to form peptide bonds protein is formed.  

Amino acids are organic compounds which contain both the amine group (-NH2 ) and the acid group (-COOH ).  

Peptide bond:

Peptide bond is a link between amino acid through the acid group ( -COOH) of one amino acid to the amine group (-NH2 ) of other amino acid. This peptide bond is shows as follows:

-CO-NH-

Essential amino acids:

These amino acids are also known as indispensable amino acid. An essential amino acid is that cannot be synthesized by the living organism, means by biosynthesized. It must be supplied only by its diets. The following are essential amino acids with three letter and one letter abbreviations:

1.Histidine, His, H

2.Isoleucine, Ile, I

3.Leucine, Leu, L

4.Lysine, Lys,K

5.Methionine, Met, M

6.Phenylalanine, Phe, F

7.Threonine, Thr, T

8.Tryptophan, Trp, W

9.Valine; Val, V

Nonessential amino acids:

These amino acids are also known as conditionally essential amino acids. A nonessential amino acid is that can be synthesized by the living organism means by biosynthesized. The following are nonessential amino acids with three letter and one letter abbreviations:

1.Alanine; Ala, A

2.Arginine, Arg,R

3.Asparagines,Asb,N

4.Aspartic acid, Asp, D

5.Cysteine, Cys ,C

6.Glutamic acid, Glu, E

7.Glutamine,Gln,Q

8.Glycine; Gly, G

9.Proline, Pro, P

10.Serine, Ser, S

11.Tyrosine,Tyr,Y

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explanation: