Study Guide: Proteins, Energy, and Enzymes

Q4. Define the primary structure of a protein and identify and locate the peptide bonds that maintain primary structure.

Background

Topic: Protein Structure

This question tests your understanding of the primary structure of proteins, which is the sequence of amino acids in a polypeptide chain, and the peptide bonds that link them together.

Key Terms and Concepts:

• Primary Structure: The unique sequence of amino acids in a protein.

• Peptide Bond: A covalent bond formed between the carboxyl group of one amino acid and the amino group of another.

Step-by-Step Guidance

1. Recall that the primary structure of a protein is determined by the linear sequence of amino acids, which are linked together by peptide bonds.

2. Identify the peptide bond: It forms between the carboxyl group ($-COOH$) of one amino acid and the amino group ($-NH_2$) of the next, releasing a molecule of water ($H_2O$) in a condensation reaction.

3. Examine a polypeptide chain and locate the repeating pattern of $-N-C-C-$ backbone, where each peptide bond is between the carbon of the carboxyl group and the nitrogen of the amino group.

4. Look for the $C=O$ (carbonyl) and $N-H$ (amide) groups in the backbone, which are characteristic of peptide bonds.

Try solving on your own before revealing the answer!

Q15. Identify whether a reaction is endergonic or exergonic using a graph of the free energy change of a reaction.

Background

Topic: Bioenergetics

This question tests your ability to interpret graphs of Gibbs free energy to determine if a reaction releases or requires energy.

Key Terms and Concepts:

• Exergonic Reaction: A reaction that releases free energy ($\Delta G < 0$).

• Endergonic Reaction: A reaction that requires an input of free energy ($\Delta G > 0$).

• Gibbs Free Energy ($\Delta G$): The energy associated with a chemical reaction that can be used to do work.

Step-by-Step Guidance

1. Examine the y-axis of the graph, which represents Gibbs free energy.

2. Compare the energy level of the reactants and products. If the products are lower in energy than the reactants, $\Delta G$ is negative (exergonic). If the products are higher, $\Delta G$ is positive (endergonic).

3. Look for the direction of the arrow or the value of $\Delta G$ indicated on the graph.

4. Use the sign of $\Delta G$ to classify the reaction as exergonic or endergonic.

Try solving on your own before revealing the answer!