Which best describes the structure of the molecules that make up proteins?

Proteins are made up of monomer units connected together. These units are called amino acids. Each amino acid has a carbonyl group and an amine group. These two groups will link when the amino acids are added. Also, an amino acid has a specific R group that characterizes which type of amino acid it is.

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the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.