Feast And Famine Flashcards
To list the major nutrient stores
To list the major tissues involved
To describe what occurs during feast period
To describe what happens during fasting
To describe the general function of the liver,
adrenal gland and pancreas
To explain the significance of the key hormonal controllers
D
What are the major nutrients storage for
- Carbohydrates
- Fats
- Proteins
- Glycogen in liver and muscle
- Triacylglycerol in adipose tissue and liver (packaged into lipoproteins for export)
- Proteins in skeletal muscle and liver
Glycogen supply glucose continuously to which organ and cell? Why?
Brain - Only can use ketone body and glucose due to blood-brain barrier (Lipid cannot pass)
RBC - Only can use glucose due to absent of mitochondria( Kreb’s cycle and oxidative phosphorylation in ETC) as glycolysis takes place in cytosol only
Glycogen occupies how many percent of the total weight of the following organ?
- Liver
- Skeletal muscle
- 6-8% in a well-fed adult liver
- To maintain blood glucose levels at 5mM - 1-2% in a fresh weight of muscle
- Energy for muscle contraction
How to identify a well-fed or fasted/famine hepatocyte (liver cell) using an electron micrograph?
Well-fed hepatocyte has black spot on it while fasting hepatocyte only has minimal black dot
What is the process of glycogenesis in term of the involvement of molecules?
State the enzyme involved and in which state does it occur
Addition of glucose unit
Step 1:
UTP (Uridine Triphosphate) + Glucose-1-P ——> UDP-glucose + PPi
Step 2: (Enzyme involved - glycogen synthase)
UDP-glucose + [Glucose]n-1 ——> [Glucose]n + UDP
Occur in well-fed stage when excess glucose not used for energy generation are channeled to glycogenesis
What is the process of glycogenolysis in term of the involvement of molecules?
State the enzyme involved and in which state does it occur
Glucose units released from glycogen to maintain blood glucose level
Step 1: (Enzyme involved - Glycogen phosphorylase)
[Glucose]n ——> [Glucose]n-1 + Glucose-1-phosphate
Occurs in the fasting state
Describe the process involved in glycogen metabolism
Glucose—> Glucose-6-phosphate —>Glucose-1-phosphate—>Glycogen
Forward movement (From Glucose to Glycogen)
- Hexokinase
- Phosphoglucomutase
- Glycogen synthase
Backward movement ( From Glycogen to Glucose)
- Glycogen phosphorylase
- No enzyme
- Glucose-6-phosphatase
Synthesis and degradation occur in separate pathway and cannot occur simultaneously
What are the method of regulation of glycogen metabolism?
- Allosteric regulation
2. Covalent modification
What is allosteric regulation in glycogen metabolism?
Positive or negative allosteric effector
Positive will induce while negative will inhibit enzyme activity
What are the positive and negative allosteric effectors involved in glycogen metabolism?
Positive allosteric effectors
Glucose-6-phosphate, induce activity of Glycogen synthase to synthesise more glycogen from Glucose-1-phosphate
Negative allosteric effectors
Glucose-6-phosphate, ATP, Glucose, inhibit activity of Glycogen phosphorylase to reduce synthesis of glucose-1-phosphate from glycogen
What happens in covalent modification in glycogen metabolism?
Enzyme is phosphorylated or dephosphorylated to activate or deactivate which is regulated by insulin, glucagon and epinephrine
Hormones involved can be divided into glycogen synthesis promoters and glycogen breakdown promoters
What are the glycogen synthesis promoters and glycogen breakdown promoters?
Glycogen synthesis promoters
Insulin - stimulate glycogen phosphorylase to convert Glucose-1-phosphate to glycogen
Glycogen breakdown promoters (counter-regulatory to insulin, induce glycogen phosphorylase)
Glucagon
Adrenaline
Cortisol (in starvation, stress)
How does glucagon control glycogen phosphorylase activity?
Glucagon (liver) or epinephrine (muscle) bind to G-protein coupled receptor, which induce release of cAMP (2nd messenger.
PkA is phosphorylated and activated, which phosphorylate and activates phosphorylase kinase to form phosphorylase kinase-P
Next phosphorylase beta (glycogen phosphorylase) is phosphorylated and activated to form phosphorylase alpha (glycogen phosphorylase-P)
Glycogen is phosphorylated and inactivated
How does insulin control glycogen synthase activity?
Insulin bind to insulin receptor to induce a series of signalling pathway to activate protein kinase B (PkB)
Activated PkB phosphorylate and deactivate glycogen phosphorylase which forms glycogen phosphorylase-P
Glycogen synthase is then dephosphorylated and activated
What are the promoter for protein synthesis and proteolysis?
Protein synthesis
- Amino acid
- Growth factors, eg IGF-1 (insulin like growth factor-1, insulin
- Exercise
Proteolysis
- Low amino acid
- Low energy intake
- Reduced growth factors, eg insulin
- Reduced exercise
- Stress response: glucocorticoids, eg cortisol
What happen to the muscle during first few days of fasting?
- Rapid muscle proteolysis
- Liver uptake of amino acid
- Gluconeogenesis, amino acid conversion to glucose
Initiated by low insulin
What happen to the muscle after prolonged fasting/ starvation?
Rate of muscle proteolysis decreases, parallel with the decline in glucose requirement by the brain
What is gluconeogenesis? Describe in term of Importance Location Substrate Enzymes
- Maintain blood glucose levels during fasting (for brain and RBC)
- Liver and kidney
- -Amino acids (converted to intermediates of TCA cycle)
-Glycerol
-Lactate
4.
i Pyruvate carboxylase
ii PEP carboxykinase
iii Fructose-1,6-bisphosphatase
iv Glucose-6-phosphatase
Gluconeogenesis is production of glucose from non-carbohydrate source
Describe triglyceride synthesis during well-fed state
Glucose is converted to pyruvate through glycolysis and then to Acetyl CoA, which is the substrate for fatty acid synthesis, which eventually form triglyceride
Acetyl-CoA carboxylase converts Acetyl-CoA to Malonyl-CoA, which is the precursor for fatty acid synthesis
State the pathway of gluconeogenesis starting from pyruvate
Pyruvate is converted to oxaloacetate by pyruvate carboxylase
Oxaloacetate is converted to phosphoenolpyruvate by PEP carboxlase
Phosphoenolpyruvate is converted to 2-phosphoglycerol by Enolase
2-phosphoglycerol is converted to 3-phosphoglycerol by phosphopyruvate mutase
3-phosphoglycerol is converted to 1,3 bisphosphoglycerate by phosphoglycerate kinase
1,3-bisphosphoglycerate is converted to glyceraldehyde 3-phosphate by glyceraldehyde 3-phosphate dehydrogenase
Glyceraldehyde 3-phosphate is converted to Fructose 1,6-bisphosphate by fructose bisphosphate aldolase
Fructose 1,6-bisphosphate is converted to fructose 6-phosphate by fructose 1,6-bisphosphatase
Fructose 6-phosphate is converted to Glucose 6-phosphate by phosphoglucose isomerase
Glucose 6-phosphate is converted to glucose by glucose 6-phosphatase
Where can amino acid enters the Kreb cycle for gluconeogenesis?
a-ketoglutarate
Succinyl CoA
Fumarate
When is lipolysis promoted?
- Low energy intake
- Low plasma glucose
- Low insulin
- High epinephrine
How is triglyceride broken down to fatty acid?
Hormone-sensitive lipase is inhibited by insulin but activated by epinephrine, which converts triglyceride to glycerol and fatty acid
What happens to fatty acid released by adipose tissue?
- Released into blood
- Used as energy source by muscle
- Oxidised to acetyl CoA in Liver to be converted to ketone bodies
What are the examples of ketone bodies?
Acetoacetone
Acetone
D-3-hydroxybutyrate
B-hydroxybutyrate
Where and when does ketogenesis take place?
Where: Liver, to be exported
When: During fasting to be used as energy sources of peripheral tissue
It uses excess Acetyl CoA from fatty acid oxidation
Can brain use ketone bodies?
Yes, little
What does alpha, beta and delta cells of islets of Langerhans in pancreas produce?
a: Glucagon
B: Insulin
D: Somatostatin (no need to know)
When is insulin produced?
- Well-fed state
- High glucose level
- High level of amino acid and fatty acid
- Release of gut peptide (GLP-1, GIP)
What are the metabolic effect of insulin?
Synthesis of glycogen, fatty acid and triglyceride, protein
When is glucagon produced?
- Fasting and starvation
- Low blood glucose
- Low amino acid and catecholamines
What are the metabolic effect of glucagon?
Breakdown of glycogen, protein and triglyceride
Describe cortisol in term of
- Location of synthesis
- Function
- Zona Fasciculata of Adrenal Cortex
2. Promote glycogen backdown and proteolysis
