Glucose, Fatty Acids, and Metabolism Flashcards
How does ATP store energy?
High-energy phosphate bonds
ATP powers most reactions that require a driving force in the cells including muscle contraction and the activity of the Na+/K+ pump
How does NADH store energy?
High-energy electrons of the hydride ion
Primarily produced during glycolysis and citric acid cycle
Where are carbohydrates primarily stored in the body?
In the muscle and the liver as glycogen
Storage process is called glycogenesis
Glucose -> glycogen
Breakdown process is called glycogenolysis
Glycogen -> glucose
Breakdown of glucose is called glycolysis
Glucose -> ATP
Where are lipids primarily stored in the body?
Primarily stored in adipocytes (fat cells) in form of triglycerides
Breakdown of fatty acids is called beta-oxidation
Fatty acid -> energy, Acetyl-CoA
Glycolysis
Series of reactions that converts 6-C glucose molecule into two 3-C molecules of pyruvate
Most common chemical pathway for this process
Can occur with or without presence of oxygen
Occurs in cytosol of cells
First half adds two phosphate groups from 2 ATP to glucose and split in half, second half converts two 3-C molecules into pyruvate
Describes the steps of glycolysis in the energy input half.
- Glucose converted to Glucose 6-phosphate with addition of ATP
- Converted to Fructose 6-phosphate
- Converted to Fructose 1,6-bisphosphate with addition of ATP
- Split to two Glyceraldehyde 3-phosphates
How does insulin affect glycolysis?
Increases the rate of glycolysis
Insulin is released when there is an excess of glucose in the blood
How does glucagon affect glycolysis?
Glucagon inhibits glycolysis and will slow it down
Glucagon is released when there is a scarcity of glucose in the blood
Describe the steps of glycolysis in the energy output half.
- Each Glyceraldehyde 3-phosphate is converted to 1,3-Bisphosphoglycerate w/ production of 1 NADH from NAD+
- Converted to 3-Phosphoglycerate w/ production of 1 ATP
- Converted to 2-Phosphoglycerate
- Converted to Phosphoenolpyruvate
- Converted to pyruvate w/ production of 1 ATP
What is the net energy product of glycolysis?
2 ATP and 2 NADH
2 ATP are used, 4 ATP are produced and 2 NADH are produced
Called substrate-level phosphorylation for ATP production here
Substrate-level phosphorylation
Phosphate group being donated to ADP is initially attached to another molecule and is transferred to ADP by a kinase enzyme
What monosaccharides feed into glycolysis in addition to glucose?
Fructose and galactose can enter glycolysis as an intermediate of the 6-C phase
Fermentation
Metabolism in the absence of Oxygen
Includes glycolysis as well as the reduction of pyruvate to ethanol or lactic acid and the oxidation of NADH back to NAD+ (for use in glycolysis)
Lactic acid, ethanol, or CO2 dispelled from cell as waste product
Cori Cycle
Lactic acid expelled from cells is transported through the blood to the liver
In liver, lactic acid is oxidized back to pyruvate
Pyruvate is converted to glucose and can be sent back to other tissues to help produce ATP
Pentose Phosphate Pathway (PPP)
Alternative pathway to glycolysis
Diverges from glycolysis after glucose is phosphorylated and rejoins at glyceraldehyde-3-phosphate (PGAL or G3P)
Main purpose is to create NADPH and 5-C sugars (ribose) to build DNA and RNA
Ensures the oxidative state of all cells remains in balance, greatest levels of PPP in liver & fat cells
How is the PPP regulated?
By levels of NADPH
High levels of NADPH inhibit first step in oxidative half of PPP
Gluconeogenesis
Synthesis of glucose from non-carbohydrate products, such as proteins and lactic acid
Only liver cells can perform this process
Glucose is released for use by other cells
Glycogen
Polymer of glucose molecules linked by alpha-1,4’ glycosidic bonds
Glycogenesis
Production of glycogen from glucose
Primary substrate: glucose 6-phosphate, product of first step of glycolysis
Glycogenolysis
Breakdown of glycogen to glucose
Uses UTP, equiv. To ATP
Adds inorganic phosphate to each alpha-1,4’ bound glucose
What processes help to maintain blood-glucose levels many hours after a meal?
Gluconeogenesis and Glycogenolysis
Gluconeogenesis
Similar to glycolysis run in reverse (enzymes catalyze forward and reverse reactions, except when deltaG is very large)
Substrates: molecule must have a 3-C backbone
Glycerol, lactic acid, some amino acids
Glucagon increases gluconeogenesis
Which processes will increase when blood-glucose is low?
As blood-glucose drops, glucagon will be released, which will stimulate processes that increase free glucose
These processes include gluconeogenesis and glycogenolysis
Considered more catabolic processes, because breaks down molecules and uses to power ATP synthesis
Do saturated or unsaturated fats have a higher reducing potential? How about higher energy storage?
Saturated fats have a higher reducing potential, as they have more electrons to reduce other compounds. Unsaturated fats have two less electrons for every double bond present, and therefore they also store less energy.
How can fatty acids be used in the body?
They can be broken down into acetyl-CoA in beta-oxidation
In liver, hey can be converted into a ketone body for ketogenesis- prolonged fast after body cannot synthesize enough glucose from gluconeogenesis
Describe what happens to fatty acids in the initial fasting state
Fatty acids are freed from adipocytes as triglycerides by enzyme lipase into bloodstream via lipoproteins
Fatty acids diffuse through cell membrane into mitochondria for beta-oxidation where they are oxidized two carbons at a time
Beta-Oxidation
Fatty acids are first converted into acyl-CoA with 1 ATP in outer membrane of mitochondria
Acyl-CoA cleaved two carbons at a time to acetyl-CoA in mitochondrial matrix
- produces FADH2 and NADH for every acetyl-CoA
Acetyl-CoA -> Citric Acid Cycle
What are the Four steps of Beta-Oxidation?
- Oxidation
- Hydration
- Oxidation
- Thiolysis
OHOT
What is the yield of Beta-Oxidation?
108 ATP / 16-C fatty acid
For odd fatty acids, last 3-C molecule can be used as substrate for gluconeogenesis
Ketone Bodies
Produced by ketogenesis from fatty acids when in prolonged fast
Three primary in humans: acetone, acetoacetic acid, beta-hydroxybutyrate
- carbonyl allows dissolution in blood stream
Spare glucose for the brain and RBCs with alternative source of energy
Ketogenesis
Fatty acid eneters liver and is processed into ketone body that can be sent to other organs
Ketone bodies are not substrates for gluconeogenesis
Ketone bodies can be converted back into acetyl-CoA and fed into Citric acid cycle for synthesis of ATP
Where are lipoproteins primarily produced?
Liver, intestines, and adipocytes- expelled via exocytosis
How do intestine cells transport lipids to the liver?
Intestines produce chylomicrons (higher lipid to protein ratio) which carry lipids to liver
Liver repackages chylomicrons as VLDL and HDL
What do Very low density lipoproteins carry (VLDL)?
Triglycerides, phospholipids, cholesterol from liver to other parts of the body such as muscle and adipocytes
What do high density lipoproteins (HDL) carry?
Pick up stray fatty acids and triglycerides from periphery and bring them to the liver
How can the liver generate fatty acids out of non-lipids?
Excess of sugar and carbohydrates after a meal can produce an excess of acetyl-CoA
With insulin, acetyl-CoA can be converted into fatty acids in cytosol
Lipase (Hormone sensitive and intestinal)
HS: Enzyme that hydrolyzes triglycerides and releases free fatty acids into the bloodstream
Intestinal: Also an enzyme in intestine that breaks down triglycerides in intestines
Fatty acids are then taken around body to various tissues to use for beta-oxidation
Is there a storage form of amino acids analogous to glycogen or triglycerides?
Amino acids have no storage form and are either present in proteins or as a pool of amino acids
How does protein breakdown begin in the small intestine?
Trypsin, chymotrypsin, and carboxypeptidase cleave proteins into mono-, di-, or tri-amino acids by hydrolysis
Small amino acid chains are cleaved by enzymes of the brush border and then absorbed and released into circulation by intestinal epithelial cells
How does amino acid breakdown begin?
Removal of nitrogen group, producing ammonia and a carbon chain
Ammonia -> urea cycle to become urea (excreted in urine)
Carbon chain -> substrate for various stages of CAC
What are uses of amino acids besides synthesis of proteins?
Substrates for gluconeogenesis, ketogenesis
Form neurotransmitters, hormones, heme, and other amino acids
11/20 amino acids can be formed from other amino acids, 9 are essential and must be obtained from diet
What processes occur when your intestine is your main store of glucose?
Blood-glucose levels are high so insulin is released from pancreas
Glycolysis occurs in all tissues
Glycogenesis occurs in liver and muscle cells to store glycogen
Extra glucose converted to fatty acids and stored as triglycerides in adipocytes (fatty acid synthesis)
What processes occur when your liver is your main store of glucose (a few hours after eating)?
Blood-glucose levels start to drop and the pancreas releases glucagon
Glucagon stimulates glycogenolysis in liver and muscle cells, gluconeogenesis in liver, fatty acid release in adipocytes, and beta-oxidation in all cells
In late starvation, what processes occur?
Ketogenesis begins in the liver, which is the production of ketone bodies which can be produced by any molecule that can be converted to acetyl-CoA. Beta-ox, glycogenolysis also occur
Ketone bodies can be used by all organs and tissues except for RBCs.
Gluconeogenesis produces glucose primarily for RBCs at this point.
How do stress responses affect metabolism?
Epinephrine and Cortisol are both released by stress response
Epinephrine has a quick response and promotes glycogenolysis
Cortisol is later and more sustained and promotes gluconeogenesis
Where do the hormones insulin, epinephrine, glucagon, and cortisol have receptors in the cell?
Insulin, epinephrine, and glucagon are hydrophilic hormones and therefore have receptors on outside of membrane
Cortisol is a glucocorticoid, is hydrophobic and therefore has receptors in the nucleus
Through what enzymatic mechanisms do insulin and glucagon exert their effects?
Usually via reversible phosphorylation, but can use regulation of synthesis of enzymes, or use of control enzymes
What is an example of a Control Enzyme and how does it work?
Phosphofructokinase-2 is activated by insulin and catalyzes the creation of a molecule that is a potent activator of glycolysis.
Therefore insulin activates phosphofructokinase-2, phosphofructokinase-2 catalyzes creation of a molecule, the molecule then activates glycolysis
What is an example of regulating the synthesis of enzymes?
Cortisol and glucagon regulate glucose 6-phosphatease, the last enzyme of gluconeogenesis, by increasing its synthesis
What are four ways hormones control metabolic enzymes?
- Phosphorylation
- Regulation of the synthesis of enzymes
- Use of control enzymes
- Local metabolic effects
Name the anabolic processes that occur during a fed state:
Glycolysis
Glycogenesis
Fatty acid synthesis
Name the catabolic processes that occur a few hours after eating:
Gluconeogenesis
Glycogenolysis
Beta-Oxidation
Prolonged hunger- then ketogenesis
Which processes will increase when blood-glucose is high?
As blood-glucose levels raise, insulin is released to use the glucose and processes that reduce free glucose are stimulated.
These processes include glycolysis and glycogenesis
These processes are more anabolic (uses molecules to synthesize glycogen, fatty acids, nucleic acids, steroids)
NADPH
Used in various synthetic or anabolic functions of the body (making cholesterol and fatty acids)
Acts as antioxidant
