All Guyton Chaps Nutrition/metabolism Flashcards
Where is phosphorylation of glucose in the cell reversible and why?
Liver, kidney, and intestinal cells — glucose phosphatase is present
How is glycogen formed?
G6P —> G1P —> uridine diphosphate glucose—> glycogen
Lactic acid, glycerol, pyruvic acid, and some deaminated amino acids can be converted to glucose then glycogen
What occurs during the process of glycolysis?
Splitting glucose to form 2 pyruvic acid molecules
Glucose —> g6P —> fructose 6P —> fructose 1,6, diphosphate —> 2 glyceraldehyde 3 phosphate —> 2 pyruvic acid molecules
Breakdown of fructose 1,6 diphosphate to pyruvate results in 4 ATP, but 2 ATP are needed to phosphorylation the original glucose before glycolysis can begin
Overall net products of glycolysis = 2 pyruvate, 2 ATP, and 4 hydrogen
Step one of the TCA cycle
2 pyruvate are converted to acetyl CoA
2 pyruvate + 2 CoA —> 2 acetyl CoA
Products per glucose molecule = 2 CO2, 4 H, no ATP
What is the process of oxidative phosphorylation?
Sequence of oxidative reactions that results in a large amount of ATP
Occurs in mitochondria by chemiosmotic mechanism (series of enzymatically catalyzed reactions)
Hydrogen ions produced by the earlier stages of cellular respiration are processed by dehydrogenase and produce reduced NADH and one hydrogen ion
The electrons are removed from the NADH and H as they enter the electron transport chain — a series of proteins (flavoprotein, iron sulfide proteins, ubiquinone, and cytochromes B, C1, C,A, and A3) found between the inner and outer chamber of the mitochondrion
Electrons are shuttled down the chain until they reach cytochrome oxidase (A3) which combines oxygen and hydrogen to form water
A large amount of potential energy is produced in the form of a hydrogen gradient between the inner and outer chamber of the mitochondrion
Hydrogen ions flow through ATPase converting ADP and ionic phosphate into ATP
ATP is transported out of the cell by facilitated diffusion and then simple diffusion
ADP is transported into the cell by simple diffusion and then facilitated diffusion
This results in 30 ATP by chemiosmotic mechanism and 4 H+ outside the chemiosmotic mechanism (these 4 H are produced during the succinct and fumaric acid stages of the TCA cycle)
Summarize total ATP formation during breakdown of glucose
Glycolysis: 2 ATP
TCA cycle 2 ATP
ETC: 30 ATP (by chemiosmotic mechanism) + 4 ATP (outside the chemiosmotic mechanism — H+ are produced during the succinct and fumaric acid stages of the TCA cycle)
Total = 38 ATP
Heat - unable to be used by cells
Which enzymes, regulated by concentrations of ADP and ATP help to regulate glycolysis and glucose oxidation?
Phosphofructokinase - early enzyme in glycolysis that is inhibited by ATP and promoted by ADP
Citrate ion (in the TCA cycle) — inhibits the function of phosphofructokinase, allows the TCA cycle to catch up
Finite amount of ADP - prevents unnecessary ATP formation
What occurs during anaerobic glycolysis?
Small amount of energy can be released from pyruvate without oxygen
Pyruvate + NADH+ H is converted to lactic acid, which can be shuttled into the extra cellular space or less vital cells
Anaerobic respiration can occur for minutes
When oxygen is available again, then lactic acid can be returned to pyruvic acid or glucose
What is the pentose phosphate pathway?
Another mechanism to degrade glucose to be used for energy
Can provide energy independent of all the enzymes of the TCA cycle
Glucose + 12 NADP + 6 H2O —> 6CO2+12H and 12NADPH
Unlike in glycolysis, H+ that is released does not combine with NAD+ but rather NADP+ to produce NADPH
NADPH is used to synthesize fats (this is a means of producing fat from carbohydrates )
What are the building blocks for triglycerides and phospholipids?
Fatty acids
What is the difference between triglycerides and cholesterol?
Cholesterol does not contain fatty acid, but rather a sterol from portions of fatty acid molecules
What is the basic chemical structure of triglyceride?
Made up of three long chain fatty acids with a glycerol backbone
How are triglycerides and other lipids absorbed from the GI tract?
Absorbed into intestinal lymph
- Triglycerides are split into monoglycerides and fatty acids during digestion
- Triglycerides are resynthesized from components in the intestinal epithelial cells and lymph into droplets call chylomicrons
- Cholesterol and phospholipids join triglycerides in chylomicrons
- Chylomicrons are then transported to the thoracic duct and emptied into venous blood (at junction of subclavian and jugular vein)
Chylomicrons have outer surface proteins to help prevent adherence to lymphatic vessel walls
How are chylomicrons removed from blood?
In capillaries, lipoprotein lipase, which is transported to the surface of capillary endothelium, hydrolysis triglycerides of chylomicrons as they contact the blood vessel wall. This releases fatty acid and glycerol
Fatty acids liberated by lipoprotein lipase diffuse into fat and muscle cells to make new triglyceride or be used as fuel
After removal of triglycerides, chylomicrons remnants are cholesterol rick and are rapidly cleared form plasma in liver sinusoids
How is stored fat broken down and transported to areas of the body that require energy?
Hydrolysis of triglyceride back into FFA and glycerol
FFA combine with albumin - aka FFA or nonesterified FA
Conditions such as starvation/ DKA may increase fat utilization and increased FFA concentration in blood
What are lipoproteins?
Predominant plasma lipid in fasting state that contain varying conmbinations of triglycerides, cholesterol, phospholipid and protein
Almost all are formed in liver
Primary function is to transport their lipid components in blood
Examples: VLDL, IDL,LDL, HDL
Name the different lipoproteins and what their main components are
VLDL: high concentration of triglycerides and moderate concentrations of cholesterol and phospholipid
IDL - similar to VLDL with some triglyceride removed, increased concentrations of cholesterol and phospholipid
LDL - almost all triglyceride removed, increased concentration of cholesterol and phospholipid
HDL - high concentration of protein (50%) and smaller concentration of cholesterol and phospholipid
What are important aspects about adipose tissue?
Store triglycerides as source for energy later
Provide heat and insulation
Secrete hormones lepton and adiponectin
Triglycerides inside fat cells are stored in liquid form
Tissue lipases permit exchange of fat between adipose tissue and blood
What role does the liver play in fat metabolism?
Degrades fatty acids into small compounds that can be used for energy Makes triglycerides (mainly from carbs, but also proteins) Makes other lipids from fatty acids (esp cholesterol and phospholipids)
How are triglycerides used for energy/ formed into ATP?
- Hydrolysis of triglycerides into FFA and glycerol —> glycerol enters cytosol and is converted to Glycerol 3 phosphate —> G3P can enter glycolysis and form pyruvate, fatty acids are processed in mitochondria
- Fatty acids bind with carnitine to enter mitochondria, then they split from carrier
- Beta oxidation of FFA occurs, meaning that there is progressive release of Acetyl CoA and hydrogen from FA —> acetyl CoA can directly enter the TCA cycle
What occurs in regards to fatty acid breakdown during starvation?
Fat is almost exclusively used for energy — starvation state: increased release of glucocorticoids, glucagon, and low insulin levels
Large amounts of ketone bodies are produces via fatty acid breakdown and release of acetyl CoA (acetoacetic acid —> beta hydroxybutyrate —> acetone)
This results in ketoacidosis (cells can’t use all Ketone bodies in the TCA cycle, as oxaloacetate is derived from carbohydrates
How are triglycerides synthesized from carbohydrates?
Triglyceride synthesis occurs in the liver, and then once made they are transported to tissues via VLDL
Carbohydrates are first converted to acetyl CoA and then into FFA via Malonyl-CoA and NADPH
1 acetyl CoA + malonyl CoA + 16 NADPH + 16H —> 1 stearic acid + 8 CO2 + 9 CoA +.16 NADPH + 7 H2O
Once FFA have grown to contain 14 to 18 carbon atoms, they are bound to glycerol and glycerol 3 phosphate to form triglycerides
How is fat utilization regulated?
Downregulation: high amounts of G3P —> act to form triglycerides, faster FFA synthesis than degradation, presence of acetyl CoA carboxylase (enzyme in lipogenesis) is upregulated due to high levels of intermediates of the TCA cycle
Hormonal regulation: absence of insulin, epinephrine and norepinephrine, glucocorticoids, thyroid hormone
What are phospholipids and why are they important?
Major types: lecithins, cephalons, sphingomyelin
Lipid soluble, contain one or more fatty acid, one phosphoric acid radical, and nitrogenous base
Made ion all cells of the body but liver produces the majority
Functions:
Components of blood lipoproteins, component of thromboplastin, component of nerve sheath, donors of phosphate radicals during different chemical processes, component of structural elements of cells (membranes)
