B1.2 Proteins

First Exams 2025 B1.2 Proteins

  • Theme: Form and Function

  • Level of Organisation: Molecules

  • Power of Science

SL and HL Combined Content

  • Focus on understanding the power of science relating to proteins.

IB Guiding Questions

  • What is the relationship between amino acid sequence and the diversity in form and function of proteins?

  • How are protein molecules affected by their chemical and physical environments?

Content Overview

B1.2 Proteins

  • B1.2.1: Generalized structure of an amino acid

  • B1.2.2: Condensation reactions forming dipeptides and longer chains of amino acids

  • B1.2.3: Dietary requirements for amino acids

  • B1.2.4: Infinite variety of possible peptide chains

  • B1.2.5: Effect of pH and temperature on protein structure

Key Terms

  • Amino Acid

  • Amine Group

  • Carboxylic Acid Group

  • Side Chain (R Group)

  • Condensation Reaction

  • Dipeptide

  • Peptide Bond

  • Polypeptide

  • Essential Amino Acids

  • Non-Essential Amino Acids

  • Genetic Code

  • Denaturation

Generalized Structure of Amino Acids

  • Components include:

    • Amine Group (-NH2)

    • Hydrogen atom

    • Central alpha carbon

    • Carboxyl group (-COOH)

    • Side chain (R Group)

Twenty Amino Acids

  • All organisms utilize the same twenty amino acids for protein synthesis.

  • Each amino acid has unique R groups which determine their properties.

Formation of Dipeptides

  • Condensation reaction:

    • Amino Acid + Amino Acid → Dipeptide + Water

  • A peptide bond forms between the carbon of the carboxylic acid and the amine group of another amino acid.

Amino Acid Models

  • To understand structures, diagrams and molecular models can be used (e.g., Molview).

Polypeptides

  • A long chain of amino acids formed through multiple condensation reactions during translation.

Dietary Requirements

Essential vs. Non-Essential Amino Acids

  • Essential amino acids must be obtained from food, while non-essential amino acids can be synthesized by the body.

  • Vegan diets need to ensure the intake of all essential amino acids through diverse plant sources.

Proteins and the Genetic Code

  • DNA codes for polypeptides; sequences can vary significantly leading to diverse proteins.

Protein Denaturation

  • Defined as a conformational change that results in loss of function, influenced by extreme pH and temperature changes.

Quaternary Structure

  • Exists in proteins with more than one polypeptide chain held together by various interactions (hydrogen, ionic, etc.).

Protein Examples

Non-Conjugated Proteins

  • Insulin: Hormonal regulation of glucose, composed of two polypeptide chains linked by disulfide bridges.

  • Collagen: Structural protein found in connective tissues, consisting of three polypeptide chains forming a triple helix.

Conjugated Proteins

  • Haemoglobin: Composed of multiple polypeptide chains and non-polypeptide groups (heme), it has a crucial role in oxygen transport.

Form and Function

  • Distinctions in globular and fibrous proteins influence their specific roles within living organisms (e.g., insulin vs. collagen).

Additional Notes

  • Students should recognize that the R-group variations affect protein structure and function, impacting interactions and protein folding.