Question

Draw the structures of the tripeptides gly-ala-ser and ser-alagly. How many other tripeptides are possible using these three amino acids?

Short answer

The structures of the tripeptides gly-ala-ser and ser-ala-gly are as follows: Gly-Ala-Ser: \[H_2N-CH_2-C(=O)-NH-CH(CH_3)-C(=O)-NH-CH(OH)CH_2-COOH\] Ser-Ala-Gly: \[H_2N-CH(OH)CH_2-C(=O)-NH-CH(CH_3)-C(=O)-NH-CH_2-COOH\] There are a total of \(3^3 = 27\) possible tripeptides using the three given amino acids (glycine, alanine, and serine).

Step-by-step solution

Identify the Structures of the Amino Acids

The three amino acids we're working with are: 1. Glycine (gly) - Its structure is H2N-CH2-COOH. 2. Alanine (ala) - Its structure is H2N-CH(CH3)-COOH. 3. Serine (ser) - Its structure is H2N-CH(OH)CH2-COOH.

Draw the Structure of the Tripeptide Gly-Ala-Ser

To draw the structure of the tripeptide gly-ala-ser, connect the amino acids in the following order: glycine -> alanine -> serine. The peptide bond is formed between the amino group (NH2) of one amino acid and the carboxyl group (COOH) of the next amino acid, releasing a molecule of water in the process. The structure of gly-ala-ser is: \[H_2N-CH_2-C(=O)-NH-CH(CH_3)-C(=O)-NH-CH(OH)CH_2-COOH\]

Draw the Structure of the Tripeptide Ser-Ala-Gly

To draw the structure of the tripeptide ser-ala-gly, connect the amino acids in the following order: serine -> alanine -> glycine. The peptide bond is formed as described in Step 2. The structure of ser-ala-gly is: \[H_2N-CH(OH)CH_2-C(=O)-NH-CH(CH_3)-C(=O)-NH-CH_2-COOH\]

Determine the Total Number of Possible Tripeptides Using the Given Amino Acids

To calculate the number of possible tripeptides using the three amino acids, we utilize combinatorial mathematics. Since there are three positions in a tripeptide and each position can be occupied by any one of the three amino acids, we can simply multiply the number of choices available at each position. Number of tripeptides = (number of choices for first position) x (number of choices for second position) x (number of choices for third position) Number of tripeptides = (3 choices) x (3 choices) x (3 choices) = \(3^3\) = 27 possible tripeptides

Key concepts

Amino Acids

Amino acids are the building blocks of proteins, making them essential for life.
They are organic compounds composed of an amino group ( H_2N ), a carboxyl group ( COOH ), and a unique side chain attached to the same carbon atom.
This central carbon is known as the alpha carbon.

Each amino acid has a distinct side chain that determines its properties and functions.

• Amino acids link together through peptide bonds, forming chains called peptides.
• Proteins are usually formed from one or more long polypeptide chains.

Amino acids play critical roles in metabolism, signaling, and maintaining structural integrity of cells.

Glycine

Glycine is the simplest amino acid, known for its minimalistic side chain.
Its structure is represented as H_2N-CH_2-COOH .
Unlike other amino acids, glycine's side chain is just a hydrogen atom, which makes it achiral, meaning it does not have distinct left or right-handedness.

Despite its simplicity, glycine serves several important functions:

• It acts as a neurotransmitter in the central nervous system.
• It participates in the synthesis of various biomolecules like heme and creatine.
• In proteins, glycine provides flexibility, often found in regions that give proteins their ability to fold or bend.

Its lack of complexity allows it to fit into tight spaces within a protein structure.

Alanine

Alanine is one of the most common amino acids found in proteins.
Its structure is H_2N-CH(CH_3)-COOH , featuring a methyl group as its side chain.
This simple alkyl side chain gives alanine its hydrophobic character, making it important in protein structure.

Here are some key aspects of alanine:

• It is known for its role in glucose-alanine cycle, which moves nitrogen from the muscle to the liver.
• Alanine can be converted into glucose, contributing to energy production when needed.
• Its presence in proteins helps stabilize the structure due to its nonpolar nature.

Alanine's versatility and abundance make it an essential component in biological systems.

Serine

Serine is a polar amino acid with the structure H_2N-CH(OH)CH_2-COOH .
It contains a hydroxyl group in its side chain, making it unique and reactive.
This property allows serine to play several crucial roles within the body.

Some important functions of serine include:

• Its involvement in the synthesis of purines and pyrimidines, necessary for DNA and RNA.
• Contribution to the creation of phospholipids, which are vital for cell membrane structure.
• It serves as a site for phosphorylation, a regulatory mechanism in proteins.

Serine's reactivity and involvement in critical biochemical pathways highlight its importance in cellular function.