Ch. 25: Metabolism and Nutrition Flashcards
Metabolism.
All the chemical reactions that occur in the body. An energy-balancing act between catabolic reactions and anabolic reactions.
Catabolism.
Chemical reactions that break down complex organic molecules into simpler ones. Exergonic. Produce more energy than they consume. Release chemical energy stored in organic molecules.
Anabolism.
Chemical reactions that combine simpler molecules to form complex ones. Endergonic. Consume more energy than they produce.
A molecule synthesized in an anabolic reaction has…
A limited lifetime. It will eventually be broken down and its component atoms will be recycled into other molecules or excreted from the body.
How much energy released in catabolism is used for cellular functions, and how much is conserved for heat?
Cellular functions: 40%
Heat: 60%
Oxidation.
Removal of electrons. Decreases the potential energy. Dehydrogenation. Usually exergonic.
Reduction.
Addition of electrons. Increases the potential energy.
NAD.
Derivative of B-vitamin niacin.
When NAD+ is reduced to NADH + H+, the NAD+ gains a H- ion, neutralizing its charge, and H+ is released into the surrounding solution.
When NADH is oxidized to NAD+, the loss of the H- ion results in one less H atom and an additional positive charge.
FAD.
Derivative of vitamin B2 riboflavin.
FAD is reduced to FADH2 when it gains a H+ and a H- ion.
FADH2 is oxidized to FAD when it loses a H+ and a H-.
Phosphorylation.
Addition of a P group to a molecule. Increases potential energy.
Organisms use 3 mechanisms of phosphorylation to generate ATP.
1) Substrate-level phosphorylation.
2) Oxidative phosphorylation.
3) Photophosphorylation.
Substrate-level phosphorylation.
Generates ATP by transferring a high-energy P group from an intermediate phosphorylated metabolic compound directly to ADP. Occurs in the cytosol.
Oxidative phosphorylation.
Removes electrons from organic compounds and passes them through a series of electron receptors to molecules of O2. Occurs in inner mitochondrial membrane.
Photophosphorylation.
Occurs only in chlorophyll-containing plant cells or in certain bacteria that contain other light-absorbing pigments.
Blood glucose is maintained at…
90 mg / 100 mL of plasma
____ of glucose normally circulates in the blood.
2-3 g
What are the 4 fates of glucose?
1) ATP production: Glucose is oxidized to produce ATP in cells that require immediate energy.
2) Amino acid synthesis: Amino acids can then be used to produce proteins.
3) Glycogen synthesis: Hepatocytes and muscle fibres can perform glycogenesis, where hundreds of glucose monomers are combined to form glycogen. Total storage capacity is 125g in liver and 375g in skeletal muscles.
4) Triglyceride synthesis: When the glycogen storages are filled, hepatocytes can transform glucose to glycerol and FAs that can be used for lipogenesis to make triglycerides. These are deposited into adipose tissue which has unlimited storage capacity.
How is glucose absorbed in the GI tract?
Secondary active transport via Na+ glucose symporters.
How is glucose absorbed in other body cells?
Facilitated diffusion via GluT transporter molecules. A high level of insulin increases the insertion of GluT4 into the PMs of body cells, increasing the rate of facilitated diffusion of glucose into cells. On entering a cell, glucose becomes phosphorylated. Because GluT cannot transport phosphorylated glucose, this reaction traps glucose within the cell.
Cellular respiration.
Oxidation of glucose to produce ATP.
Glucose catabolism.
1) Glycolysis.
2) Formation of acetyl coenzyme A.
3) Krebs cycle.
4) ETC.
Anaerobic respiration.
Glycolysis –> pyruvic acid –> lactic acid.
Aerobic respiration.
Glycolysis –> acetyl coenzyme A –> Krebs cycle –> ECT.
Glycolysis.
A set of reactions split a 6-carbon molecule of glucose into two 3-carbon molecules of pyruvic acid. Also produces 2 ATP and 2 NADH + H+.
The fate of pyruvic acid depends on…
Availability of oxygen.
Anaerobic: 1 pyruvic acid + 2 NADH + 2 H+ –> 2 lactic acid + 2 NAD+ (the lactic acid is converted back to pyruvic acid by hepatocytes)
Aerobic: 1 pyruvic acid –> 1 acetyl coenzyme A
RBCs only produce ATP via…
Glycolysis.
Acetyl coenzyme A formation.
CoA is derived from pantothenic acid (B vitamin).
Pyruvate dehydrogenase located in mitochondrial matrix converts pyruvic acid into a 2-carbon acetyl group by removing 1 CO2 (decarboxylation). Pyruvic acid is also oxidized. Each pyruvic acid loses 1 H+ and 1 H-. NAD+ is reduced as it picks up the H-, and the H+ is released into mitochondrial matrix.
So this reaction produces NADH + H+ + CO2 and acetyl coenzyme A.
Krebs cycle.
In mitochondrial matrix. Oxidation-reduction reactions transfer chemical energy in the form of electrons to NAD+ and FAD. Pyruvic acid derivatives are oxidized, and NAD+ and FAD are reduced.
Produces 3 NADH, 3 H+, 1 FADH2, 1 ATP, 6 CO2 (each turn).
Because each glucose provides 2 acetyl CoA, how many turns of the Krebs cycle are there per glucose catabolized?
2, resulting in 6 NADH, 6 H+, 2 FADH2, 2 ATP, 12 CO2.
Describe CO2 in Krebs cycle.
It is released as pyruvic acid is converted to acetyl CoA during the two decarboxylation reactions in Krebs cycle. They diffuses out of mitochondria, through cytosol and PM, into blood, into lungs, and exhaled.
ETC.
The inner mitochondrial membrane is folded into cristae that increases its SA, accommodating thousands of copies of the ETC in each mitochondrion. As electrons pass through the chain via carriers, a series of exergonic reactions release small amounts of energy which is used to form ATP.
Electron carriers of ETC.
FMN, cytochromes, Fe-S enters, Cu atoms, coenzyme Q.
Glycogenesis.
Glucose storage. If glucose is not currently needed, it combines with other glucoses to form glycogen. Glucose is phosphorylated to glucose 6-phosphate by hexokinase –> glucose 1-phosphate –> uridine diphosphate glucose –> glycogen.
What hormone stimulates hepatocytes and skeletal muscle cells to carry out glycogenesis?
Insulin.
How much glucose can the body store?
500g. 75% in skeletal muscle fibres. 25% in liver cells.
Glycogenolysis.
Glucose release.
Liver: Begins by splitting off glucose from glycogen via phosphorylation –> glucose 1-phosphate –> phosphorylase is activated by glucagon from pancreatic alpha cells and EP from adrenal medullae –> glucose 1-phosphate is converted to glucose 6-phosphate –> glucose –> leaves hepatocytes via GluT in PM. Phosphatase is absent in skeletal muscle cells, so only hepatocytes can release glucose from glycogen into the blood.
Skeletal muscle: Glycogen is broken down into glucose 1-phosphate –> catabolized for ATP production via glycolysis and Krebs. Lactic acid produced in muscle cells can be converted to glucose in the liver, so muscle glycogen can be an indirect source of blood glucose.
Gluconeogenesis.
Formation of glucose from proteins and fats. Stimulated by cortisol and glucagon. Cortisol stimulates the breakdown of proteins into amino acids to expand the pool of amino acids available for gluconeogenesis.
How are thyroid hormones involved in gluconeogenesis?
They mobilize proteins and triglycerides from adipose tissue to make glycerol more available for gluconeogenesis.
Lipoproteins.
Transportation method of lipids. Lipid and protein combinations. Spherical particles with an outer shell of proteins, phospholipids and cholesterol molecules surrounding an inner core of triglycerides and lipids.
Apoproteins.
Proteins in the outer shell of lipoproteins. Designated by the letters A, B, C, D, E plus a number.
4 major classes of lipoproteins (from largest and lightest to smallest and heaviest).
Chylomicrons, VLDLs, LDLs, HDLs.
Chylomicrons.
Form in mucosal epithelial cells of small intestine. Transport dietary lipids to adipose tissue for storage. Contain 1-2% proteins, 85% triglycerides, 7% phospholipids, 6-7% cholesterol, small amount of fat-soluble vitamins. Enter lacteals of intestinal villi and are carried by lymph into venous blood and then into systemic circulation.
Which substance gives blood plasma a milky appearance?
Chylomicrons.
Apo C-2 of chylomicrons.
As chylomicrons circulate through the capillaries of adipose tissue, apo C-2 activates endothelial lipoprotein lipase which removes FAs from chylomicron triglycerides. The free FAs are taken up by adipocytes for synthesis and storage as triglycerides, and by muscle cells for ATP production.
How are chylomicrons removed from the blood?
By hepatocytes via receptor-mediated endocytosis. The docking protein for this process is apo E.
Very low density lipoproteins.
Form in hepatocytes. Contain endogenous lipids, 10% proteins, 50% triglycerides, 20% phospholipids, 20% cholesterol. Transport triglycerides synthesized in hepatocytes to adipocytes for storage. Lose triglycerides as their apo C-2 activates endothelial lipoprotein lipase. Resulting FAs are taken up by adipocytes for storage and by muscle cells for ATP production.
What happens to VLDLs as they deposit some of their triglycerides in adipose cells?
They are converted to LDLs.
Low density lipoproteins.
Contain 25% protein, 5% triglycerides, 20% phospholipids, 50% cholesterol. Contain a single apoprotein of apo B100, which is the docking protein that binds to LDL receptors on the PM of body cells so that the LDL can enter the cell via receptor-mediated endocytosis. Within the cell, LDL is broken down and the cholesterol is released to serve the cell’s needs. Then, a negative feedback inhibits the cell’s synthesis of new LDL receptors.
____ carry 75% of the total cholesterol in blood and deliver it to body cells for repair of cell membranes and synthesis of steroid hormones and bile salts.
LDLs.
What happens when there are an abundance of LDLs?
They deposit cholesterol in and around smooth muscle fibres in arteries, forming fatty plaques that increase CAD risk.
If you have not many LDL receptors…
Your body cells remove LDL from the blood less efficiently, so your plasma LDL level will be abnormally high, producing fatty plaques.
Eating a high fat diet increases…
Production of VLDLs –> LDLs –> fatty plaques.
High density lipoproteins.
Contain 45% protein, 10% triglycerides, 30% phospholipids, 20% cholesterol. Remove excess cholesterol from body cells and blood, and transport it to liver for elimination.
A high level of HDLs is associated with…
Decreased CAD risk. HDLs prevent accumulation of cholesterol in the body.
What are the 2 sources of cholesterol in the body?
Food, hepatocytes (most).
How can fatty foods that do not contain cholesterol still increase blood cholesterol?
A high intake of dietary fats stimulates reabsorption of cholesterol-containing bile back into the blood, so less cholesterol is eliminated from the body. And when saturated fats are broken down, hepatocytes use some of the products to make cholesterol.
Lipid profile test.
Measures total cholesterol (TC), HDL-cholesterol, and triglycerides (VLDLs).
LDL-cholesterol = TC - HDL-cholesterol - (triglycerides / 5)
Desirable levels of blood cholesterol in adults.
TC < 200 mg/dL, LDL-cholesterol < 130 mg/dL, HDL-cholesterol > 40 mg/dL, VLDLs 10-190 mg/dL.
When TC > ___ mg/dL, the risk of a heart attack doubles with every ___ mg/dL increases in TC.
200, 50.
Borderline high cholesterol.
TC 200-239 mg/dL
LDL 130-159 mg/dL
Borderline high cholesterol.
TC 200-239 mg/dL
LDL 130-159 mg/dL
High blood cholesterol.
TC > 239 mg/dL
LDL > 150 mg/dL
