Chapter 11 Summary

Chapter 11.1

• Energy balance involves the homeostatic regulation of energy intake and energy expenditure (energy demand).
• Energy balance is strongly influenced by the ability to synthesize ATP via metabolism of organic molecules with appropriate enzymes and other reagents like oxygen.
• Cells in energy balance, exhibiting acceptable concentrations of ATP and ROS, function normally.
• Prolonged periods in high or low energy states can cause energy stress, either due to energy excess (available energy > energy demand) and energy limitation (energy demand > available energy).
• High energy states are characterized by high ATP concentrations (relative to ADP and AMP) and high abundance of ROS (reactive oxygen species), while low energy states are characterized by high ADP and AMP concentrations (related to ATP) and low abundance of ROS.

Chapter 11.2

• AMP-dependent kinase (AMPK) is an enzyme (specifically a kinase) with a central role in cell signalling and detection of energy stress.
• When AMP/ADP concentration is high in the cell, AMPK is activated.
• When ATP concentration is high in the cell, AMPK is inhibited.
• AMPK activity can also be influenced by redox state (e.g., ROS).
• In its most active state, the three subunits (α, β, and γ) of AMPK are associated with each other, AMP is bound to the γ subunit, and Thr172 in the α subunit is phosphorylated.

Chapter 11.3

• Strategies to tolerate energy limitation include increasing available energy and decreasing energy demand.
• Strategies to tolerate energy excess include decreasing available energy and increasing energy demand.
• AMPK is active under energy limitation, and stimulates various cellular responses that increase available energy and decrease energy demand.
• Mechanisms affected by AMPK include increasing the activity of catabolic processes (e.g., glycolysis, fatty acid oxidation) that synthesize ATP, stimulating autophagy and glucose uptake to increase the availability of organic molecules available for ATP synthesis pathways, and preventing the use of ATP in anabolic processes (e.g., protein synthesis, fatty acid synthesis).

Chapter 11.4

• Autophagy (self-eating) involves selective or non-selective degradation of macromolecules and organelles using the lysosome (animal cells) or vacuole (plant and fungal cells). self-degradation process used to remove various organelles.
• Macroautophagy is a type of autophagy that involves the formation of autophagosomes to move the autophagic cargo to the lytic organelle (lysosome/vacuole).
• Mitophagy is an example of selective macroautophagy that removes and degrades damaged mitochondria.
• Microautophagy is a type of autophagy that involves direct uptake of material from the cytosol by invagination of the membrane of the lytic organelle.