MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 1d Fatty Acid Protein Metabolism

What this deck covers

This deck focuses on 1d Fatty Acid Protein Metabolism, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: State the number of acetyl-CoA molecules produced from a saturated even-chain fatty acid with $n$ carbons.

Answer: $\frac{n}{2}$ acetyl-CoA. Beta-oxidation of even-chain fatty acids produces acetyl-CoA molecules equal to half the original carbon count through sequential two-carbon cleavages.

Flashcard 2: What are the two nitrogen sources that enter the urea cycle to form urea?

Answer: Free NH$_3$ (carbamoyl phosphate) and aspartate. The urea cycle incorporates ammonia into carbamoyl phosphate and nitrogen from aspartate to eliminate excess nitrogen as urea.

Flashcard 3: What is the final cleavage step of $\beta$-oxidation called, and what cofactor is required?

Answer: Thiolysis by thiolase; requires CoA-SH. Thiolase performs CoA-dependent thiolysis to cleave beta-ketoacyl-CoA into acetyl-CoA and a shortened acyl-CoA in the final beta-oxidation step.

Flashcard 4: Which enzyme introduces a double bond during the first oxidation step of $\beta$-oxidation?

Answer: Acyl-CoA dehydrogenase. Acyl-CoA dehydrogenase catalyzes the initial dehydrogenation in beta-oxidation, forming a trans double bond and reducing FAD to FADH$_2$.

Flashcard 5: Identify the net ATP yield commonly used on MCAT for complete oxidation of palmitate ($C_{16}$).

Answer: 106 ATP (using $2.5$ per NADH and $1.5$ per FADH$_2$). Palmitate oxidation yields 106 ATP accounting for reduced cofactors at 2.5 ATP per NADH and 1.5 per FADH$_2$, minus activation cost.

Flashcard 6: State the number of $\beta$-oxidation cycles required for a saturated even-chain fatty acid with $n$ carbons.

Answer: $\frac{n}{2} - 1$ cycles. Complete beta-oxidation of an even-chain fatty acid requires cycles equal to half the carbon number minus one to yield acetyl-CoA units.

Flashcard 7: What are the direct products of one $\beta$-oxidation cycle of a saturated fatty acyl-CoA?

Answer: Acetyl-CoA + FADH$_2$ + NADH + shortened acyl-CoA. Each beta-oxidation cycle cleaves two carbons as acetyl-CoA while generating reduced cofactors and a fatty acyl-CoA shortened by two carbons.

Flashcard 8: What are the four recurring reaction types in one cycle of mitochondrial $\beta$-oxidation?

Answer: Oxidation (FAD), hydration, oxidation (NAD$^+$), thiolysis. Beta-oxidation cycles sequentially remove two-carbon units through FAD-dependent oxidation, water addition, NAD$^+$-dependent oxidation, and CoA-mediated cleavage.

Flashcard 9: What molecule inhibits CPT I to prevent mitochondrial fatty acid entry during fatty acid synthesis?

Answer: Malonyl-CoA. Malonyl-CoA, produced during fatty acid synthesis, allosterically inhibits CPT I to avoid simultaneous synthesis and degradation in mitochondria.

Flashcard 10: Which shuttle transports long-chain fatty acyl groups into the mitochondrial matrix for $\beta$-oxidation?

Answer: Carnitine shuttle (CPT I, translocase, CPT II). The carnitine shuttle facilitates transport of long-chain acyl groups across the mitochondrial membrane via CPT I conjugation, translocase movement, and CPT II reformation.

Flashcard 11: What is the immediate product formed when a fatty acyl-CoA is activated by acyl-CoA synthetase?

Answer: Fatty acyl-CoA (ATP is converted to AMP + PPi). Acyl-CoA synthetase activates fatty acids by forming thioester bonds with CoA, hydrolyzing ATP to AMP and PPi for energy.

Flashcard 12: Which ketone body is not a true ketone, and what is its name?

Answer: Beta-hydroxybutyrate (a hydroxy acid, not a ketone). Beta-hydroxybutyrate arises from NADH reduction of acetoacetate, classifying it as a hydroxy acid rather than a true ketone structure.

Flashcard 13: Which ketone body is spontaneously formed from acetoacetate and is exhaled in ketoacidosis?

Answer: Acetone. Acetone forms via non-enzymatic decarboxylation of acetoacetate, contributing to the fruity breath odor in uncontrolled diabetic ketoacidosis.

Flashcard 14: Which liver enzyme is rate-limiting for ketogenesis and what molecule does it produce first?

Answer: HMG-CoA synthase; forms HMG-CoA. HMG-CoA synthase condenses acetoacetyl-CoA with acetyl-CoA to form HMG-CoA, controlling the rate of ketogenesis in liver mitochondria.

Flashcard 15: Which tissue cannot use ketone bodies because it lacks thiophorase (succinyl-CoA:acetoacetate CoA transferase)?

Answer: Liver. The liver produces ketone bodies but lacks the transferase enzyme needed to convert them back to acetyl-CoA for energy use.

Flashcard 16: What is the nitrogen carrier that transports ammonia safely from most tissues to the liver?

Answer: Glutamine. Glutamine safely transports ammonia by incorporating it into its amide group, preventing toxicity during delivery to the liver for urea synthesis.

Flashcard 17: Which molecule carries amino nitrogen from muscle to liver in the glucose-alanine cycle?

Answer: Alanine. Alanine transfers amino groups from muscle amino acid breakdown to the liver, where transamination regenerates pyruvate for gluconeogenesis.

Flashcard 18: What is the key cofactor required by aminotransferases (transaminases) in amino acid catabolism?

Answer: Pyridoxal phosphate (PLP, vitamin B$_6$). Pyridoxal phosphate acts as a cofactor in transamination reactions, facilitating amino group transfer between amino acids and alpha-keto acids.

Flashcard 19: Which enzyme releases free ammonia from glutamate during oxidative deamination in the liver mitochondria?

Answer: Glutamate dehydrogenase. Glutamate dehydrogenase catalyzes NAD(P)$^+$-dependent oxidative deamination of glutamate, liberating ammonia for urea cycle entry in liver mitochondria.

Flashcard 20: What is the defining feature of ketone bodies regarding carbon content and typical tissues that use them?

Answer: Water-soluble $4$-carbon fuels; used by brain (fasting) and muscle. Ketone bodies serve as soluble four-carbon energy sources derived from acetyl-CoA, primarily utilized by brain during fasting and by muscle.

Flashcard 21: Which pathway uses fatty acids in peroxisomes and produces $H_2O_2$ instead of FADH$_2$ for the ETC?

Answer: Peroxisomal $\beta$-oxidation (acyl-CoA oxidase forms $H_2O_2$). Peroxisomal beta-oxidation shortens very long chains, with acyl-CoA oxidase directly producing H$_2$O$_2$ instead of FADH$_2$ for energy conservation.

Flashcard 22: What cofactor-dependent sequence converts propionyl-CoA to succinyl-CoA in odd-chain FA metabolism?

Answer: Biotin then B$_{12}$ (methylmalonyl-CoA mutase step). Propionyl-CoA carboxylase (biotin) forms methylmalonyl-CoA, which methylmalonyl-CoA mutase (B$_{12}$) rearranges to succinyl-CoA for TCA cycle entry.

Flashcard 23: What are the final products of odd-chain fatty acid $\beta$-oxidation after the last cycle?

Answer: Propionyl-CoA + acetyl-CoA (from the final cleavage). Odd-chain fatty acids undergo beta-oxidation until the final thiolysis yields propionyl-CoA and acetyl-CoA from the remaining five-carbon chain.

Flashcard 24: What is the key additional enzyme needed for polyunsaturated fatty acid oxidation beyond isomerase?

Answer: 2,4-Dienoyl-CoA reductase (uses NADPH). 2,4-Dienoyl-CoA reductase reduces conjugated double bonds using NADPH, enabling isomerase and hydratase to process polyunsaturated chains in beta-oxidation.

Flashcard 25: Which enzyme is required to continue $\beta$-oxidation past a cis double bond in an unsaturated fatty acid?

Answer: Enoyl-CoA isomerase. Enoyl-CoA isomerase repositions cis double bonds to trans configuration, allowing subsequent hydration and continuation of the beta-oxidation pathway.