Study Guide for Exam 3
Chapter 7: Integration & Regulation of Metabolism: Fed versus Fasted State
1.What can be used to make fat?
Carbs can be converted to fat, however lipogenesis from glucose is less effective oWeight gain from CHO thought to be caused by sparing lipolysis rather than direct CHO lipogenesis oPDH Complex main link of glucose metabolism to FA synthesis (pyruvate acetyl CoA) Most AAs can serve as precursors for fat synthesis
2.What can Acetyl CoA be used for?
Acetyl CoA must be used for energy, lipgenesis, cholesterogenesis, or ketogenesis oNot Glucogenic
3.What do amino acids and fatty acids produce during gluconeogenesis?
Amino acids and fatty acids are oxidized to generate NADH & ATP needed for gluconeogenesis (b/c when liver is producing glucose, it cannot synthesize lipids and proteins at the same time)
4.What is produced during hepatic lipogenesis?
Glucose must be used to produce NADPH and ATP necessary for the conversion of acetyl CoA to fatty acids
5.What are the two intermediates that the TCA cycle provides that cross-link CHO, proteins, and lipids?
Oxaloacetate (OAA) and a-ketoglutarate
6.What is the purpose of citrate?
Citrate moves from mitochondria to cytoplasm, where it is broken down to OAA and acetyl CoA (initiator of FA synthesis)
7.What is the purpose of malate?
Malate may provide a portion of the NADPH required for reductive stages of FA synthesis
8.Know what is happening to the body/organs during a fed state. What pathways are being used? What hormones are secreted? What products are being produced? What enzymes are involved in covalent modification?
Fed state lasts 3 hours after a meal
RBC & Central Nervous System
oRBC have no mitochondria and can only burn glucose anaerobically (glycolysis & gluconeogenesis) and CNS has no metabolic mechanism to convert energy stores Glucose available immediately oxidized to produce energy
oGlucose can be converted directly to glycogen
However, most liver glycogen made directly from gluconeogenic precursors rather than directly from glucose •Pyruvate, alanine, and lactate
oLiver is the 1st tissue to have opportunity to use dietary glucose When glucose or Glucogenic precursors exceed glycogen storage in liver, excess glucose can be: •Converted to FAs and stored as TG in adipose
Some exogenous glucose (dietary) bypasses the liver and circulates to other tissues
Converts glucose to lactate or uses as a source of NADPH via PPP
Can use glucose as a precursor for both glycerol & FA components of TG
Makes glycogen or uses glucose for energy
9. Know what is happening to the body/organs during a fasted state. What metabolic shifts occur? What hormones are secreted? What substrates become important to produce energy? What enzymes are involved in covalent modification?
Postabsorptive State (3-18 hours following a meal)
oTissues no longer deriving energy directly from ingested nutrients and must rely on other sources of fuel
oHepatic Glycogenolysis (in between meals)
Major provider of glucose to blood, which is delivered to other tissues (occurs for short period of time; a few hrs after eating)
When this is occurring, glycogen & TG synthesis in liver diminish and gluconeogenesis begins to help maintain blood glucose •Lactate becomes important carbon source for gluconeogenesis •Glucose-Alanine cycle also becomes important
oCarbon in form of alanine returns to liver from muscle
Alanine Pyruvate Glucose
oGlucose provided to muscle from liver comes primarily from recycling lactate & alanine and a lesser extent from hepatic Glycogenolysis oThe brain & CNS tissues are extravagant consumers of glucose Oxidize glucose for energy & release no gluconeogenic precursors in return The rate of glucose use is greater...