IB Biology SL Topic B1.2

How many amino acids are coded for in DNA?

There are 20 standard amino acids encoded directly by the genetic code in DNA.

Draw a generic amino acid.

Every amino acid features a central carbon ($\text{C}$) bonded to an amine group, a carboxyl group, a hydrogen atom, and a variable R-group.

What is similar and different between amino acids?

• Similarities: All amino acids share the same central alpha carbon, an amine group NH, a carboxyl group COOH, and a hydrogen atom H.

• Differences: They differ solely by their variable R-group (side chain), which determines distinct chemical properties (polar, non-polar, acidic, basic).

Name the reactions that link two amino acids and separate them. State the role of water in both.

• Linking reaction: Condensation reaction (anabolic). Water is produced/released as a byproduct.

• Separating reaction: Hydrolysis reaction (catabolic). Water is consumed/added to split the covalent bond.

Explain why condensation reactions have that name.

It is called a condensation reaction because small molecules combine to form a larger molecule while "condensing" out a small water molecule H2O as a product.

Explain why hydrolysis reactions have that name.

The name breaks down into hydro- (water) and -lysis (splitting or loosening)—meaning the breakdown of a chemical bond using water.

Draw a condensation reaction between two generic amino acids.

Below is the reaction process where an OH group from one carboxyl group combines with an H from another amino group:

What is the bond called between two amino acids?

The covalent bond connecting two amino acids is a peptide bond (specifically formed between C=O and N-H)

What is the name for two bonded amino acids, and the name for many bonded amino acids?

• Two bonded amino acids: Dipeptide

• Many bonded amino acids: Polypeptide

What is the name for a fully folded and functioning molecule made from many bonded amino acids?

A fully folded, 3D functional unit made of one or more polypeptide chains is a protein.

State the difference between essential and non-essential amino acids.

• Essential amino acids: Cannot be synthesized by the human body at a sufficient rate and must be obtained through diet.

• Non-essential amino acids: Can be synthesized internally by the body from other compounds.

State two conditions that can affect the overall shape of a protein.

• Temperature (excessive heat disrupts weak intramolecular interactions like hydrogen bonds).

• pH level (deviations from optimal pH alter ionization state and disrupt ionic/hydrogen bonds).

What happens in protein denaturation?

Denaturation is a structural change in a protein where it loses its specific 3D tertiary/quaternary structure due to broken intramolecular bonds (like hydrogen or ionic bonds). This causes the polypeptide to unfold and renders the protein biologically non-functional. Denaturation is typically irreversible.