Biochemistry Tutoring

Biochemistry sits between organic chemistry and biology, and it borrows the hard parts of both. You need the structures and charges from organic chemistry, the pathways and regulation from biology, and a little kinetics and thermodynamics to tie them together. Exams ask what happens when a pathway is blocked, when an enzyme is inhibited, or when a cell runs low on ATP. STEM Tutor 360's one-on-one biochemistry tutoring teaches the logic that connects the facts, so new questions feel familiar.

We follow your course, whether it is a one-semester survey or a full two-semester sequence. Topics include amino acids and protein structure, enzymes, carbohydrates, lipids and membranes, nucleic acids, metabolism, and regulation. Much of this material appears in the MCAT's Biological and Biochemical Foundations of Living Systems section, so sessions can double as MCAT review when you are heading in that direction.

A typical biochemistry problem, worked

An enzyme has $V_{\text{max}} = 120\ \mu\text{mol/min}$ and $K_m = 4.0\ \text{mM}$. Find the rate at $[S] = 2.0\ \text{mM}$ and at $[S] = 40\ \text{mM}$. Then find the rate at $[S] = 4.0\ \text{mM}$ when a competitive inhibitor is present at 2.0 mM ($K_i = 2.0\ \text{mM}$).

Use $v = \dfrac{V_{\text{max}}[S]}{K_m + [S]}$. At 2.0 mM: $v = \dfrac{120 \times 2.0}{4.0 + 2.0} = 40\ \mu\text{mol/min}$. At 40 mM: $v = \dfrac{120 \times 40}{4.0 + 40} = 109\ \mu\text{mol/min}$, about 91% of $V_{\text{max}}$. As a check, at $[S] = K_m$ the rate should be exactly half of $V_{\text{max}}$, and $\dfrac{120 \times 4.0}{8.0} = 60\ \mu\text{mol/min}$ is.

A competitive inhibitor multiplies the apparent $K_m$ by $1 + \dfrac{[I]}{K_i} = 1 + \dfrac{2.0}{2.0} = 2$, so the apparent $K_m$ is 8.0 mM. $V_{\text{max}}$ does not change. Now $v = \dfrac{120 \times 4.0}{8.0 + 4.0} = 40\ \mu\text{mol/min}$, down from 60. At 40 mM substrate the rate is back up to 100 µmol/min, because enough substrate outcompetes the inhibitor.

Where students usually get stuck

• Memorizing pathways as lists of names. Follow what changes at each step: the carbon skeleton, the electrons carried by $\ce{NADH}$ and $\ce{FADH2}$, and ATP.
• Mixing up $K_m$, $V_{\text{max}}$, and $k_{cat}$, and which of them each type of inhibitor changes.
• Confusing $\Delta G$ with $\Delta G^{\circ\prime}$, and not seeing how a reaction with a positive $\Delta G^{\circ\prime}$ can still run in the cell.
• Ionization states of amino acids at a given pH, and finding the pI of a peptide.
• ATP totals per glucose, which differ by textbook (older books say 36 to 38, newer ones 30 to 32). Use your instructor's number.
• Regulation: telling allosteric control, covalent modification, and feedback inhibition apart.