3 - Fate of major nutrient groups Flashcards
Where are the major nutrient groups absorbed and where are they transported to?
GI tract - small intestine
Dietary carbs and proteins - liver via hepatic portal vain
Dietary fats - packaged into chylomicrons and distributed via lymphatic system
What are the 3 principle fates?
Energy production
Storage
Conversion
How are carbs found (3 types)?
Simple monosaccharides
Di- and oligosaccharides
Complex carbohydrates
In what form are carbs absorbed?
Glucose, fructose, galactose
What are the 3 fates of carbs?
Storage - glycogen (in liver and skeletal muscles)
Energy - ATP
Conversion - fat storage, nucleotide precursor
What is the main source of energy for the liver?
fat and amino acid oxidation
What happens to most carbs in the liver?
Stored or converted
Explain the importance of the GLUT2 transporter in the liver.
high Km -> low affinity and uptake
available for other tissues
high uptake in high glucose levels -> storage
Bonus question - why is GLUT2 important in pancreatic B cells?
Why is glucose readily phosphorylated in the liver?
Can’t escape cell so no glucose equilibrium
How does insulin and glucagon affect carbs in the liver?
Insulin: storage (glycogen) and conversion/storage (FFA synthesis)
Glucagon: breakdown (glycogen) and glucose release
Define reciprocal control
one pathway/process is activated and other is inhibited
Which glucose transporter do muscle cells have and what is its significance?
GLUT4
What is allosteric regulation and how is this achieved with carbs in muscle cells?
Regulation of an enzyme by binding an effector molecule at a site other than the enzyme’s active site
ATP:AMP ratio, effect on phosphfructokinase
What are the 3 fates of dietary fats?
Energy production - in liver and muscle
Storage - adipose tissues
Conversion - cholesterol, bile acids, steroids
How long does it take for each dietary group to enter blood circulation and why does it take longer for fatty acids?
2-4 hours normal, fats 2-4 hours extra
Effect of insulin on adipose tissue more complex
Describe the basic structure of triglycerides
Glycerol backbone
3 fatty acid chains
How are fatty acids transported around the body?
Free fatty acids (FFA) are esterified into triglycerides (TAG)
transported around the body in lipoproteins
(some FFA transported boudnd to albumin)
What are Chylomicrons and describe their structure
produced in intestines for dietary fat transport
phospholipid monolayer, surface proteins, what does it pack…
Name 3 lipoproteins
Chylomicrons
LDL
HDL
What are the principle roles of the liver in processing fats?
fatty acid synthesis (for storage in adipose)
oxidation (for energy)
ketogenesis (conversion) to provide ketones for the brain during ‘starved’ conditions
Define allosteric regulation
allosteric regulation is the regulation of an enzyme by binding an effector molecule at a site other than the enzyme’s active site
Which surface protein do chylomicrons acquire in circulation and why?
ApoCII (by transfer from HDL)
necessary cofactor for subsequent lipoprotein lipase activity, allowing delivering of contained TAG to tissues.
chylomicrons become smaller as a result, forming depleted remnant particles, where the ApoCII and ApoB48 are important in the activation of uptake of the particle by receptors, mainly in the liver.
How is metabolism of fats in the liver regulated? +explain
Compartmentation (Acyl CoA and carnitine)
Insulin:glucagon
Allosteric regulation
Why and how are fatty acids transported to the mitochondria?
For fatty acid oxidation
activated by attachment to coenzyme A
mitochondrial membrane is impermeable to CoA
switching the CoA for the alcohol carnitine
fatty acyl-carnitine is then transported to the mitochondria where is reattached to CoA
How does Malonyl coA regulate fat metabolism in the liver?
regulates transport across mitochondrial membrane
blocks movement of acyl-CoA into mitochondria and therefore from oxidation
When do skeletal muscles produce Malonyl coA and why?
produce malonyl coA (from glucose-derived acetyl CoA) when glucose is abundant
muscle fatty acid oxidation is slowed when glucose is plentiful -> fatty acid stores are more efficient
Which pathway provides energy for the liver during lipogenesis?
amino acid oxidation
How does insulin affect malonyl coA and how does this effect other pathways
Insulin promotes malonyl coA
without insulin the negative effect of malonyl- CoA on transport of acyl-CoA into mitochondria is lost and so is control of ketone body synthesis. This is the metabolic explanation for the high risk of ketoacidosis in uncontrolled diabetes due to absence of insulin (Type 1 Diabetes).
How does insulin effect fat in adipose tissues (2 ways)?
Insulin activates/elevates an enzyme on the endothelial cell layer around adipose tissue involved in fat uptake -Lipoprotein Lipase (LPL)
- hydrolyses…
- GLUT?
- stored as…
Insulin suppresses an enzyme within adipose tissue involved in fat breakdown - Hormone-Sensitive Lipase (HSL)
- hydrolyses…
- Adrenaline…
What are the fate of amino acids?
NO STORAGE
Conversion to substrate for fat synthesis or glycogen (indirect storage)
Energy in liver (especially during lipogenesis)
What can amino acids be converted to?
- Protein synthesis/turnover
- Hormones, nucleotides, etc.
- Carbon ‘skeletons’ enter pathways of glucose and fat metabolism
- NH3 excreted
