24.3 Amino Acids and their polymers

As three letters are read at a time, the Transfer RNA delivers the corresponding amino acid to be added to a growing chain of amino acids. How are amino acids held together?

By Peptide Bonds

Review from Biology

From DNA to protein - 3D

Our bodies can produce some of the amino acids that our cells use to make proteins. Where do the other amino acids our bodies need come from?

Other amino acids must be obtained by eating foods rich in proteins. Beans and brown rice are good sources of amino acids.

Describe the pleated sheet 3D shape of a protein

Peptide chains arranged side by side form a pleated sheet.

Describe the helix 3D shape of a protein

Sections of a peptide chain may coil into a regular spiral, known as a helix. The peptide chains of most myoglobin (protein found in the muscle tissue that stores oxygen) are twisted into a helix.

Differentiate between substrate & active site.

Substrates are the molecules on which an enzyme acts. The place on an enzyme where a substrate binds is called the active site.

Proteins fold into complicated 3D shapes. The 3D structure is very important; if the shape is changed, the protein may act very differently. What determines the three-dimensional shape of a protein?

The 3D shape of a protein is determined by interactions among the amino acids in its peptide chains. Protein shape is maintained partly by hydrogen bonds between adjacent folded chains.

Describe a peptide bond.

The amide NH2 bond between the carboxyl COOH group of one amino acid and the nitrogen in the amino group of the next amino acid in the peptide chain is called a peptide bond. The side chains are not involved in the bonding. Each peptide bond is a condensation reaction because a water molecule is produced.

More amino acids may be added to the peptide in the same fashion to form long chains by condensation polymerization. The order in which the amino acids of a peptide are linked is called the amino acid sequence of that molecule. How is the amino acid sequence of a peptide conveniently expressed?

The amino acid sequence of a peptide is conveniently expressed using the three-letter abbreviations for the amino acids. For example, Asp—Glu—Gly represents a peptide containing three amino acids.

Each amino acid has different properties. What causes the differences?

The chemical nature of the side-chain group accounts for the differences in properties of the 20 amino acids. In some amino acids, the side chains are nonpolar aliphatic or aromatic hydrocarbons. In other amino acids, the side chains are neutral but polar. In still others, the side chains are acidic or basic.

What is the correct way to write the peptide formula?

The convention is to write the peptide formula so that the free amino group is at the left end. There is also a free carboxyl group, which appears at the right end of the molecule.

What is a catalyst?

a substance that increases the rate of a chemical reaction by lowering the activation energy ; the catalyst is not used up in the reaction.

What are some of the most important nitrogen-containing molecules in organisms?

amino acids For chemists and biochemists, the term is usually reserved for the 20 common amino acids that are formed and used by living organisms.

Enzymes are proteins that act as biological catalysts. Explain.

"biological" - The study of life. Reactions occur inside living cells. Enzymes increase the rates of chemical reactions in living things. Most chemical reactions that occur in a cell involve enzymes.

What is the general structure of an amino acid?

Amino acids consist of a carboxyl group, an amino group, a hydrogen, and an R-group side chain that are all covalently bonded to a central carbon atom.

What is a peptide called with more than 100 amino acids?

A peptide with more than 100 amino acids is a protein. Proteins are an important class of biomolecules. For example, your skin, hair, nails, and muscles are all made of proteins.

The process of adding amino acids to a peptide chain can continue indefinitely. What is a peptide called with more than ten amino acids?

A peptide with more than ten amino acids is a polypeptide.