The Krebs Cycle

MCAT Basics (from MedSchoolCoach)

One of the most fundamental biochemical processes is the Krebs cycle. This metabolic pathway plays a critical role in both the Chem Phys and Bio/Biochem sections of the MCAT, so understanding it is key.

In this episode, our guest host, Alex Starks, walks us through the transformation of pyruvate into acetyl CoA via the Pyruvate Dehydrogenase Complex (PDC). We’ll explore how thioester bonds help transfer energy within the cycle, how acetyl CoA combines with oxaloacetate to form citrate, the difference between enzymes like synthetases and synthases, and how GTP is produced. We’ll also make connections to the electron transport chain and discuss how the TCA cycle influences blood pH through CO2 production.

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Jump into the conversation:

(00:00) Intro

(01:05) Recap of glycolysis and pyruvate

(02:45) Pyruvate dehydrogenase complex (PDC)

(03:40) Role of acetyl CoA in the Krebs cycle

(05:37) How citrate is formed

(07:17) How isocitrate is formed

(10:00) How alpha-ketoglutarate is formed

(13:42) How succinate and GTP are formed

(16:28) How succinate, fumarate and oxaloacetate are formed

(18:23) Fumarate converted to malate

(21:53) Recap of the Krebs cycle and ATP yield

(25:00) Regulation of the Krebs cycle

(26:16) Quiz