Metabolism Flashcards
What is homeostatic eating?
What is non-homeostatic eating?
Homeostatic: Eating when energy fuels are depleted, and non eating when energy fuels are sufficient.
Non-homeostatic: Eating in the absence of hunger, and eating despite large fat reserves.
Which type of eating is also considered metabolically-driven eating?
Homeostatic eating.
Which type of eating is also known as “hedonic” eating?
Non-homeostatic eating.
How many centers in the hypothalamus are responsible for homeostatic eating?
- The “hunger/feeding” center, and the “satiety” center.
What is the glucostatic theory?
- Intake regulated by glucose levels, monitored by centers in the hypothalamus.
- Plasma glucose low -> Satiety center suppressed -> Feeding center dominant.
What is the lipostatic theory?
Signal from fat stores to brain modulates eating behaviour.
What does leptos mean?
Thin.
What is the relationship between leptin and the “ob” and “db” genes?
In the 1950’s, a spontaneous mutation arose in a mouse colony that made the mice more obese, voracious eaters.
In the 1990’s, the mutation was identified to be in the “ob” gene, and mice who were “ob/ob” or “db/db” had dysfunctional leptin receptors.
What is the purpose of leptin?
Inhibit hunger.
What happens to the stomach during increased appetite?
Increase in ghrelin, secreted by cells of an empty stomach.
What happens to the stomach during decreased appetite?
Increase in stretch, causing an increase in acid from the acid-sensing ion channels).
What happens to the upper small intestine during decreased appetite?
- Increase in CCK (in response to fat/protein in lumen).
- Increase in glucose in lumen.
What happens to the lower small intestine/colon during decreased appetite?
- Increased peptide YY (PYY), inhibits release of neuropeptide Y.
- Increased GLP-1
What are PYY and GLP-1 triggered by?
Macronutrients in lumen and also neural reflex from upper small intestine.
What is neuropeptide Y a key neurotransmitter in the stimulation of?
Appetite.
What interacts to influence appetite?
Many hormones, neuropeptides, and products of adipocytes.
What is metabolic rate?
Glucose + Oxygen + ADP + Pi -> Carbon Dioxide + Water + ATP + Heat
True or False: The rate of CO2 produced to O2 consumed is the same for all macronutrients.
False.
What are some factors that affect metabolic rate?
- Age/sex
- Lean muscle mass
- Activity level
- Diet
- Hormones, gut peptides
- Genetics
What are the 3 possible fates of ingested biomolecules?
1) Metabolized to provide energy to fuel mechanical work.
2) Used in synthesis reactions for growth and maintenance of tissues.
3) Stored as glycogen (liver, skeletal muscles) or fat.
What are the 2 states of metabolism?
1) Fed/absorptive state
2) Fasted/postabsorptive state
What is the fed/absorptive state?
Anabolic. Products of digestion being absorbed and used for synthesis or stored.
What is the fasted/postabsorptive state?
Catabolic. Body taps into stores.
What are the 3 nutrient pools available for immediate use?
1) Free fatty acid pool
2) Glucose pool
3) Amino acid pool
What is lipogenesis?
The formation of fat.
What happens to the direction of metabolism if there is no regulation of enzymatic activity?
No net synthesis of A or B.
The pathway will simply cycle back and forth.
What happens to the direction of metabolism during a fed-state?
Net glycogen synthesis.
Under the influence of insulin, enzyme activity for the forward reaction increases. Enzymes for glycogen breakdown are inhibited.
What happens to the direction of metabolism during a fasted-state?
Net glucose synthesis.
Under influence of glucagon, enzymes that break down glucose are more active, and enzymes for glycogen synthesis synthesis are inhibited.
Where does glycolysis occur? Where does the citric acid cycle occur?
Glycolysis occurs in the cytoplasm, whereas the CAC occurs in the mitochondria.
What is the destination(s) of carbohydrates (glucose)?
Travels to the liver, where 70% passes through to the brain, muscles, and other tissues. The other 30% moves into hepatic cells.
What is the purpose of glycogen?
Provides ready energy source in skeletal muscles.
It is the main source of glucose in the postabsorptive state.
How much glycogen does the liver keep on supply?
~ 4 hour supply.
What is the destination(s) of amino acids?
Travels through the liver to:
- Pass through and used for synthesis of structural proteins, enzymes, hormones, amines…
- Some move out of sinusoids into hepatic cells, for the synthesis of liver enzymes, plasma proteins, lipoproteins…
If not used for protein synthesis, what can amino acids be used for?
They can be deaminated and their carbon skeletons re-deployed:
- Converted to key metabolites that lead to pathways that generate glucose.
- Converted to acetoacetate but can’t enter CAC. Instead, use to make fatty acids.
What are gluconeogenic AA’s?
Converting key metabolites that lead to pathways that generate glucose.
I.e. Acetoacetate, pyruvate, CAC intermediates.
What are ketogenic AA’s?
Those used to make fatty acids (reverse of beta-oxidation).
Produce ketone bodies.
What is the process of fat synthesis?
1) Glycerol can be made from glucose through glycolysis.
2) Fatty acids made when 2-carbon acyl units from acetyl CoA linked together.
3) One glycerol + 3 fatty acids -> triglycerides. Occurs in smooth ER.
4) Even with zero dietary cholesterol, cholesterol can and will be synthesized from acetyl CoA.
What is the transport of fats from the intestine to the blood?
Fats (triglycerides) exit the intestine via the lymph as chylomicrons (formed in enterocytes) and eventually reach systemic circulation.
What are chylomicrons?
Particles consisting of a fatty core (triglycerides, cholesterol esters) and an outer coating of amphipathic and hydrophilic molecules (free cholesterol, phospholipids, apoproteins).
What are apoproteins involved in?
Delivery to certain cell types.
What happens to fats as it passes through capillaries in key organs?
They’re “harvested”, mostly through the action of lipoprotein lipase (lpl), expressed by endothelial cells lining capillaries.
True or False: Free fatty acids travel in the blood unbound.
False. Bound to serum albumin.
What happens to fat as it’s being removed?
The remaining particle becomes smaller and more dense (less fatty).
What is the density of fat particles from lowest to highest?
- Chylomicron
- Chylomicron remnant
- VLDL
- IDL
- LDL
- HDL
What are the 3 possible fates of a fat particle taken up by liver?
1) Havested/metabolized
2) Store (triglycerides)
3) Export (release into circulation)
Which type of fat particle can only be taken into cells by receptor-mediated endocytosis?
LDL
What is the process of fasted-state metabolism?
1) Liver glycogen -> glucose
2) TG’s in adipose -> FFA’s and glycerol -> Enter blood.
3) Glycogen used for energy. Muscles also use fatty acids and break down their proteins to AA’s that enter blood.
4) Brain can use only glucose and ketones for energy.
What are the 2 options for the formation of glucose 6-PO4 from glycogen?
1) Splitting off glucose by addition of Pi.
2) Splitting off glucose then spending an ATP to phosphorylate.
True/False: Only the liver has the enzymes to generate free glucose for export to plasma.
True
How can muscle contribute to plasma glucose?
Only indirectly by exporting pyruvate or lactate.
What is the process of AA catabolism?
1) AA’ s are deaminated, giving rise to intermediates.
2) Intermediates can either directly enter glycolysis or CAC, OR
3) Be sent to the liver to be converted to glucose (gluconeogenesis).
What is proteolysis?
Breakdown of muscle protein.
What is the process of lipolysis?
1) Lipase digests TG’s into glycerol and fatty acids.
2) Glycerol becomes a glycolysis substrate.
3) Beta-oxidation chops 2-carbon acyl units off of free fatty acids.
4) Acyl units become acetyl CoA and can be used in CAC.
What happens if lipolysis proceeds faster than acetyl CoA can be used in TCA Cycle?
Ketone bodies are formed.
What are ketone bodies typically used for?
What kind of diet generates ketone bodies?
Can enter blood and serve as energy substrates for brain during times of starvation.
Typically generated by low carb, high fat/protein diets.