Biological and Biochemical Foundations of Living Systems: Content Category 1D

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Principles of bioenergetics and fuel molecule metabolism

Living things harness energy from fuel molecules in a controlled manner in order to sustain all of the processes responsible for maintaining life. Cell maintenance and growth is energetically costly. Cells harness the energy stored in fuel molecules, such as carbohydrates and fatty acids, and convert it into smaller units of chemical potential known as adenosine triphosphate (ATP).

The hydrolysis of ATP provides a ready source of energy for cells that can be coupled to other chemical processes in order to make them thermodynamically favorable. Fuel molecule mobilization, transport, and storage are regulated according to the needs of the organism.

The content in this category covers the principles of bioenergetics and fuel molecule catabolism. Details of oxidative phosphorylation including the role of chemiosmotic coupling and biological electron transfer reactions are covered, as are the general features of fatty acid and glucose metabolism. Additionally, regulation of these metabolic pathways, fuel molecule mobilization, transport, and storage are covered.

Topic Level Key

The abbreviations found in parentheses indicate the course(s) in which undergraduate students at many colleges and universities learn about the topics and associated subtopics. The course abbreviations are:

BC = first-semester biochemistry
BIO = two-semester sequence of introductory biology
GC = two-semester sequence of general chemistry
OC = two-semester sequence of organic chemistry

Please note topics that appear on multiple content lists will be treated differently. Questions will focus on the topics as they are described in the narrative for the content category.

Principles of Bioenergetics (BC, GC)

  • Bioenergetics/thermodynamics

    • Free energy/Keq

      • Equilibrium constant

      • Relationship of the equilibrium constant and ΔG°

    • Concentration

      • Le Châtelier’s Principle

    • Endothermic/exothermic reactions

    • Free energy: G

    • Spontaneous reactions and ΔG°

  • Phosphoryl group transfers and ATP

    • ATP hydrolysis ΔG << 0

    • ATP group transfers

  • Biological oxidation-reduction

    • Half-reactions

    • Soluble electron carriers

    • Flavoproteins

Carbohydrates (BC, OC)

  • Description

    • Nomenclature and classification, common names

    • Absolute configuration

    • Cyclic structure and conformations of hexoses

    • Epimers and anomers

  • Hydrolysis of the glycoside linkage

  • Monosaccharides

  • Disaccharides

  • Polysaccharides

Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway (BIO, BC)

  • Glycolysis (aerobic), substrates and products

    • Feeder pathways: glycogen, starch metabolism

  • Fermentation (anaerobic glycolysis)

  • Gluconeogenesis (BC)

  • Pentose phosphate pathway (BC)

  • Net (maximum) molecular and energetic results of respiration processes

Principles of Metabolic Regulation (BC)

  • Regulation of metabolic pathways (BIO, BC)

    • Maintenance of a dynamic steady state

  • Regulation of glycolysis and gluconeogenesis

  • Metabolism of glycogen

  • Regulation of glycogen synthesis and breakdown

    • Allosteric and hormonal control

  • Analysis of metabolic control

Citric Acid Cycle (BIO, BC)

  • Acetyl-CoA production (BC)

  • Reactions of the cycle, substrates and products

  • Regulation of the cycle

  • Net (maximum) molecular and energetic results of respiration processes

Metabolism of Fatty Acids and Proteins (BIO, BC)

  • Description of fatty acids (BC)

  • Digestion, mobilization, and transport of fats

  • Oxidation of fatty acids

    • Saturated fats

    • Unsaturated fats

  • Ketone bodies (BC)

  • Anabolism of fats (BIO)

  • Non-template synthesis: biosynthesis of lipids and polysaccharides (BIO)

  • Metabolism of proteins (BIO)

Oxidative Phosphorylation (BIO, BC)

  • Electron transport chain and oxidative phosphorylation, substrates and products, general features of the pathway

  • Electron transfer in mitochondria


    • Flavoproteins

    • Cytochromes

  • ATP synthase, chemiosmotic coupling

    • Proton motive force

  • Net (maximum) molecular and energetic results of respiration processes

  • Regulation of oxidative phosphorylation

  • Mitochondria, apoptosis, oxidative stress (BC)

Hormonal Regulation and Integration of Metabolism (BC)

  • Higher level integration of hormone structure and function

  • Tissue specific metabolism

  • Hormonal regulation of fuel metabolism

  • Obesity and regulation of body mass

Additional Review: Khan Academy MCAT Collection Tutorials

To support your studies, see the following video tutorials below from the Khan Academy MCAT Collection. The videos and associated questions were created by the Khan Academy in collaboration with the AAMC and the Robert Wood Johnson Foundation.

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