BCHM 4115: Lectures 1-6

What effect do enzymes have on the activation energy (ΔG^± or ΔEa) and Gibbs Free Energy (ΔG) of a reaction?

Answer explanation

Enzymes function by lowering the activation energy of a reaction, which affects the kinetics—that is, how quickly the reaction proceeds. However, enzymes do not alter the Gibbs Free Energy (ΔG) of the reaction, meaning they do not change whether a reaction is thermodynamically favorable, only how fast it reaches equilibrium.

Given that the histidine side chain has a pka = 6, draw what this amino acid would look like if it was in a solution of a pH of 5.

Answer explanation

To determine the protonation state of histidine at a given pH, we use the rule that if the pH < pKa, that part of the molecule will be protonated; if the pH > pKa, it will be deprotonated. At pH 5, which is below the pKa of histidine’s side chain (around 6), the imidazole ring will be protonated at the nitrogen that does not already bear a hydrogen, giving it a positive charge. The amino terminus has a pKa of approximately 9.6, and since 5 is well below that, the amino group will also be protonated (as NH₃⁺) and carry a +1 charge. The carboxyl group, however, has a much lower pKa of about 2.5, and because 5 is above this value, the carboxyl group will be deprotonated (as COO⁻) and carry a –1 charge. Therefore, at pH 5, histidine will have a net charge of +1.

Tags

NGSS.HS-LS1-6

Peptide Bonds have a _ configuration.

In thermodynamics, a closed system usually means that...

• Energy exchange and/or matter exchange may occur

• There is no exchange of matter or energy

• Energy exchange may occur

Tags

NGSS.HS-PS3-4

A spontaneous reaction consists of...

• ΔG > 0 and the reaction is exergonic

• ΔG < 0 and the reaction is endergonic

• ΔG < 0 and the reaction is exergonic

• ΔG > 0 and the reaction is endergonic

Answer explanation

In the following peptide, identify the following amino acids by their full name, three letter name, and one letter abbreviation:

Answer explanation

Tags

NGSS.HS-LS1-1

NGSS.HS-LS1-6

Define a polyprotic acid.

Answer explanation

An acid that can donate more than one proton or hydrogen atom (H+) per molecule to an aqueous solution.

Which amino acid does not have a D stereochemistry according to the drawings?

• 
• 
• 

Tags

NGSS.HS-LS1-6

What is the third law of thermodynamics?

• The entropy of any crystalline perfectly ordered substance is exactly 0 at 0K temperature.

• The entropy of any crystalline perfectly ordered substance is less than 0 at 0K temperature.

• The entropy of any crystalline perfectly ordered substance greater than 0 at 0K temperature.

Phosphoric anhydride linkages connect phosphates together in ATP. What is the other name for this linkage?

Answer explanation

Pyrophosphoral Bonds.

Tags

NGSS.HS-LS1-7