Question

Glycine, alanine, and valine are classified as nonpolar amino acids. Compare their codons. What similarities do you find? What differences do you find?

Short answer

Answer: The similarities between the codons for glycine, alanine, and valine include starting with the nucleotide "G" (guanine) and having four possible codons for each amino acid. The differences between the codons involve the second nucleotide (glycine has "G," alanine has "C," and valine has "U") and the varying third nucleotide within each amino acid group, following a certain pattern (_ _ U/C, _ _ G, _ _ A).

Step-by-step solution

List the codons for each amino acid

: First, let's list the codons for each of the three nonpolar amino acids - glycine, alanine, and valine. Glycine: GGU, GGC, GGA, GGG Alanine: GCU, GCC, GCA, GCG Valine: GUU, GUC, GUA, GUG Now that we have the codons for each amino acid, we can compare them.

Identify similarities

: Upon comparing the codons for glycine, alanine, and valine, we can see several similarities: 1. All codons for these amino acids start with the nucleotide "G" (guanine). 2. There are four possible codons for each amino acid. These similarities indicate that the nonpolar amino acids are part of the same family of amino acids that share a common structure.

Identify differences

: There are also a few differences between the codons for glycine, alanine, and valine: 1. The second nucleotide of each codon is different for each amino acid: glycine has "G," alanine has "C," and valine has "U." 2. The third nucleotide of each codon varies within each amino acid group, but still follows a certain pattern (_ _ U/C, _ _ G, _ _ A). These differences help distinguish the three nonpolar amino acids from one another and ensure that the ribosomes can properly identify which amino acid is specified by each codon during protein synthesis.

Key concepts

Understanding the Genetic Code

The genetic code is the set of rules used by living cells to translate information encoded within genetic material (DNA or mRNA sequences) into proteins. It is essentially the language that cells use to interpret the 64 different codon sequences to synthesize amino acids, which are the building blocks of proteins. Each codon consists of three nucleotides, also known as a triplet.

The genetic code is universal; with few exceptions, nearly all species use this same language. For instance, the codons listed for nonpolar amino acids glycine (GGU, GGC, GGA, GGG), alanine (GCU, GCC, GCA, GCG), and valine (GUU, GUC, GUA, GUG) will code for the same amino acids in almost every organism you can study. This consistent language allows for the transfer of genetic information between species, which is how the genetic code plays a vital role in evolutionary biology.

Understanding the genetic code also involves recognizing redundancy, which is the concept that multiple codons can code for the same amino acid, as seen with the nonpolar amino acids discussed. This redundancy helps protect against mutations; if a nucleotide changes, it may not necessarily change the encoded amino acid.

Amino Acid Classification

Amino acids, the building blocks of proteins, can be grouped into different classes based on their properties and where they are found within the protein structure. The classification of amino acids includes categories such as nonpolar, polar, acidic, and basic.

In the context of nonpolar amino acids, such as glycine, alanine, and valine, their side chains are characterized by hydrophobic (water-repellent) properties. They typically reside within the interior of proteins, away from the aqueous cellular environment. These side chains do not form hydrogen bonds and therefore are not attracted to water molecules or the environment.

Within the codons for these nonpolar amino acids, there are similarities, such as all codons starting with 'G' and each having four codons. However, differences like the varying second nucleotide distinguish them. This classification helps in predicting the behavior of amino acids in proteins and supports the understanding of protein structure and function.

Protein Synthesis

Protein synthesis is a complex cellular process involving two main stages: transcription and translation. During transcription, the DNA sequence of a gene is copied into messenger RNA (mRNA), which is a mobile genetic format that can exit the nucleus and enter the cytoplasm in eukaryotic cells. The mRNA sequence is a mirror image of the gene's DNA, rewritten in the nucleotide alphabet of RNA.

During translation, which occurs in the cytoplasm, ribosomes read the sequence of the mRNA in triplets or codons. Each mRNA triplet matches to a specific transfer RNA (tRNA) that carries the corresponding amino acid. For instance, the nonpolar amino acid codons for glycine (GGU, GGC, GGA, GGG) will be recognized by tRNA molecules that are specific to glycine.

The ribosome helps to facilitate the bonding between the amino acids to form a polypeptide chain, which will fold into a functional protein. Each tRNA anticodon pairs with its complementary mRNA codon, ensuring that the correct amino acid is added to the growing polypeptide chain. This intricate process is central to the flow of genetic information within a cell and results in the expression of traits encoded within DNA.