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IB DP Biology- B1.2 Proteins- IB Style Questions For HL Paper 2 -FA 2025

IBDP Biology HL Paper 2 -FA 2025- All Chapters

Question

(a) Identify the products formed when two amino acids undergo a condensation reaction.
amino acid + amino acid →
(b) Explain how variations among amino acids contribute to the wide range of shapes seen in proteins.

Titin is the longest known human protein, made of a single chain containing more than \( 34{,}000 \) amino acids.

(c)
(i) Describe the type of secondary protein structures indicated by the arrows in the diagram.
(ii) Outline the function of titin within sarcomeres.

Most-appropriate topic codes (CED):

• TOPIC B1.2: Proteins — parts (a), (b), (c-i)
• TOPIC B3.3: Muscle and motility — part (c-ii)
▶️ Answer/Explanation
Detailed solution

(a)
amino acid + amino acid → a dipeptide and a molecule of water

(b)
Amino acids vary in their R-groups, which differ in chemical properties such as being polar, non-polar, acidic, basic, hydrophobic, or hydrophilic. These differences influence how amino acids interact within a polypeptide chain, determining how the protein folds into its unique three-dimensional conformation. As a result, proteins can take on an enormous variety of structures and functions.

(c)
(i) The arrows in the diagram point to beta-pleated sheets, a type of secondary structure formed through hydrogen bonding between backbone N–H and C=O groups in parallel or antiparallel regions of the polypeptide.

(ii) Titin functions as an elastic spring inside sarcomeres. It helps restore the sarcomere to its resting length after muscle contraction and also prevents excessive stretching, maintaining structural stability during muscle activity.

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