IBDP Biology 2025 SL&HL: B1.2 Proteins Study Notes

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B1.2.1—Generalized structure of an amino acid

Proteins: biomolecules comprised of amino acids  joined together by peptide bonds.

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

B1.2.3—Dietary requirements for amino acids
Essential amino acids: cannot be synthesized, must be taken through the diet
Conditionally essential:
  • Tyrosine can be synthesised from phenylalanine.
  • Arginine cannot be synthesised by infants

Diet sources of essential amino acids

Vegan diets require attention to ensure essential amino acids are consumed.
 

B1.2.4—Infinite variety of possible peptide chains

There are infinite possibilities of polypeptides because:

  • 20 different amino acids are coded by the genetic code
  • polypeptides can be of any length (up to thousands)
  • amino acids can be in any order

If a polypeptide contains just 7 amino acids , there can be \(20^7\) = 1,280,000,000 possible polypeptides generated.

B1.2.5—Effect of pH and temperature on protein structure

Protein structure determines function
Interactions between amino acid side chains determine the structure of the protein
 

B1.2.6—Chemical diversity in the R-groups of amino acids as a basis for the immense diversity in protein form and function

Interactions between amino acid side chains determine the structure of the protein

Protein structure determines function

B1.2.7—Impact of primary structure on the conformation of proteins

(a) Primary structure

(b) Secondary structure

(c) Tertiary structure

(d) Quaternary structure

Primary structure:

  • Sequence of amino acids linked through covalent bonds
  • Determines the subsequent conformation -> allows us to predict protein structures

B1.2.8—Pleating and coiling of secondary structure of proteins

Secondary structure is due to hydrogen bonding between the amine and carboxyl groups of non adjacent amino acids

B1.2.9—Dependence of tertiary structure on hydrogen bonds, ionic bonds, disulfide covalent bonds and hydrophobic interactions

 
Bonds between R groups of aminoacids in tertiary structure:
  • Hydrogen bonds
  • Ionic bonds: between positively or negatively charged amine and carboxyl group
  • Disulfide bonds: between cysteins
  • Hydrophobic interactions

 

B1.2.10—Effect of polar and non-polar amino acids on tertiary structure of proteins

B1.2.11—Quaternary structure of non-conjugated and conjugated proteins
Quaternary structure: bonds between R groups of different peptide chains
 
Insulin                                                                     
Collagen
 
Quaternary structure: bonds between R groups of different peptide chains
 
NOS: Technology allows imaging of structures that would be impossible to observe with the unaided senses. For example, cryogenic electron microscopy has allowed imaging of single-protein molecules and their interactions with other molecules.
 
 
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