Sugar metabolism review notes

1. What is the use of sugar in addition to energy supply?

Sugar is not only a source of energy, it is also an important component of tissue cells, such as nucleic acids, proteoglycans, glycoproteins, glycolipids and so on.

2. How does glucose change to lactic acid under anoxic conditions? What is the point?

The reducing equivalent (NADH+H+) produced by glucose in the glycolysis pathway is reoxidized to NAD+ and the glycolysis can continue. Because the amount of NAD+ in the cells is very small. Therefore, under hypoxic conditions, pyruvic acid can act as a hydrogen acceptor, accepting hydrogen and then converting to lactic acid to regenerate NAD+. In this way, glycolysis can continue.

In vigorous exercise, muscle oxygen supply is insufficient, glycolysis is an important means of productivity, and lactic acid accumulated in the muscle can be transported from the blood to the liver to become glucose. Atomic glycolysis uses only a small fraction of the energy stored by glucose. However, this method of release is very rapid and is important for muscle contraction. In addition, cell tissues such as the retina, red blood cells and brain produce some lactic acid even under aerobic conditions. Red blood cells are more dependent on glycolysis due to wireless granules. Energy Supply.

3. Describe the composition and catalysis of the pyruvate dehydrogenase complex and what factors are regulated? P129

The pyruvate dehydrogenase complex is composed of three different enzymes (pyruvate dehydrogenase, dihydrolipoamide transacetylase, dihydrolipoamide dehydrogenase). There are TPP, FAD, lipoic acid and NAD+ and CoA. This enzyme catalyzes an irreversible reaction. It is also a regulatory enzyme that is regulated by allosteric effects and chemical modifications.

4. There are several regulatory enzymes in TAC? What substances are they regulated by each? What reactions do they catalyze?

There are four regulatory enzymes in the TAC, the pyruvate dehydrogenase complex (not part of TAC, a step in the conversion of pyruvate to acetyl CoA), citrate synthase, isocitrate dehydrogenase and alpha ketone The acid dehydrogenase complex is a key regulatory enzyme.

The pyruvate dehydrogenase complex (catalyzing the conversion of pyruvate to acetyl CoA) is strongly inhibited by its catalytic products ATP, acetyl CoA and NADH, fatty acids; activated by AMP, NAD+, CoA, Ca2+.

Citrate synthase (catalyzing the conversion of acetyl CoA to citric acid): Inhibited by NADH, succinyl-CoA, citric acid and ATP, activated by ADP.

Isocitrate dehydrogenase (catalyzes the conversion of isocitrate to alpha ketoglutarate): inhibited by ATP, NADH, activated by Ca2+ and ADP. Alpha ketoglutarate (catalyzes the conversion of alpha ketoglutarate to succinyl CoA): by succinyl-CoA, NADH; by Ca2+ activation.

5. What is the pentose phosphate pathway? How does it react? What is the physiological significance?

The main metabolic pathway for glucose is glycolysis, and there are other metabolic modalities, such as the pentose phosphate pathway, which produces pentose phosphate and NADPH.

6-phosphate glucose + NADP+ ====6-phosphogluconolactone + NADPH+H+

6-phosphogluconolactone + H2O ====6-phosphogluconate

6-phosphogluconate + NADP+ ====5-nucleoside ribulose + CO2+NADPH+H+

5-nucleoside ribulose----5-phosphate ribose

In some tissues, the pentose phosphate pathway ends here, and the overall result is:

Glucose 6-phosphate +2 NADP++H2O ====5-phosphate ribose +CO2+2 NADPH+ 2H+

Physiological significance: The pentose phosphate nucleus and NADPH produced by the pentose pathway can be used for the synthesis of nucleic acids and other substances.

6. How does the liver synthesize glycogen and how to break down glycogen? What factors are regulated?

Glycogen is a form of animal storage of sugar. Liver and muscle are the main places for storing glycogen. Liver storage glycogen is mainly used to maintain blood sugar concentration and supply systemic utilization. Muscle glycogen is used to give muscles to produce ATP for contraction. .

Decomposition of glycogen:

Glycogen + Pi2- ====1-phosphoglucose + glycogen (degraded a G) Glycogen phosphorylase catalyzes the phospholysis of α[1-4] glycosidic bonds.

1-phosphate glucose ====6-phosphate glucose

6-phosphate glucose + H2O ====glucose + Pi2-

Synthesis of glycogen:

Glucose + ATP ====6-phosphate glucose + ADP

Glucose 6-phosphate ====1-glucose phosphate

1-phosphate glucose + UTP====UDP-G + PPi

UDP-G+ glucose n====(glucose)n+1 + UDP

Branching chain formation: When the glycogen synthase extends with α1====4 glycosidic bonds until the length of 11 glucose groups, the branching enzyme can transfer a strand of about 7 glucose residues to the adjacent sugar chain to α1 ====6 glycosidic linkages.

Regulation of the synthesis and metabolism of glycogen:

Both the glycogen phosphorylase of the glycogen catabolic pathway and the glycogen synthase in the glycogen synthesis pathway are catalytically unbalanced reactions. These two enzymes are regulatory enzymes of the respective metabolic pathways.

1. Glycogen phosphorylase is regulated by allosteric effectors and covalent modifications.

2, glycogen synthase allosteric regulation and covalent modification regulation.

cAMP, which is catalyzed by adenylate cyclase, is an important intracellular signal that regulates glycogen phosphorylase and glycogen synthase. Increased intracellular cAMP activates glycogen phosphorylase by two different mechanisms, and also inhibits glycogen synthase by both mechanisms.

7. How do non-sugar substances turn into sugar? Which enzymes are most noteworthy?

The formation of glucose from non-sugar substances becomes a gluconeogenesis effect. The non-sugar materials utilized include various amino acids/lactic acid, pyruvic acid, propionic acid, and glycerin. The carbon of these substances becomes the carbon of glucose. For those cells and tissues that first use glucose as a metabolic energy source, such as brain, red blood cells, renal medulla, and lens of the eye, the maintenance of blood glucose levels depends on gluconeogenesis during fasting. The liver is an important organ of gluconeogenesis and plays an important role in maintaining blood sugar concentration. (Saccharin is a different enzyme used to bypass the irreversible reaction pathway in glycolysis.) The gluconeogenesis from lactic acid is as follows: In mitochondria:

Lactic acid (dehydrogenation) + lactate dehydrogenase ====pyruvate + NADH (lactate dehydrogenase, in cytosol)

Pyruvate + ATP4-+HCO3-==== oxaloacetate + ADP3-+Pi2-+H+ (pyruvate carboxylase)

Oxaloacetate + GTP4-==== phosphoenolpyruvate (PEP) (phosphoenolpyruvate carboxylase)

Transfer of phosphoenolpyruvate to cytosol (gluconeogenesis in cytosol)

The following are in the cytosol:

PEP==2-phosphoglycerate==3-phosphoglycerate====1,3 diphosphoglycerate====3-glycerophosphate ====1,6-diphosphate fructose

Fructose 1,6-diphosphate+H2O====6-phosphate fructose+Pi2-

6-phosphate fructose ====6-phosphate glucose

Glucose 6-phosphate + H2O====glucose + Pi2-

There are several regulatory positions for gluconeogenesis, namely the regulation of four enzymes involved in irreversible reactions: pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructose diphosphatase and glucose phosphatase (dephosphorylation).

8. How do you influence ATP, AMP, NAD+, how to affect the metabolism of sugar?

Glucose metabolism produces ATP, NADH, which is produced by inhibition of glycolysis.

In general, allosteric effectors that activate the gluconeogenesis pathway regulating enzyme are inhibitory to the regulatory enzymes of the glycolysis pathway.

ATP increase accompanied by AMP decline is beneficial to gluconeogenesis; hypoxia, lack of fatty acid oxidation and oxidative phosphorylation are inhibited or uncoupled, ATP concentration decreases, AMP activity increases, gluconeogenesis closes, and glycolysis opens. The increase of NAD+ is beneficial to the progress of glycolysis, and conversely, it is beneficial to gluconeogenesis.

Hormone regulation of gluconeogenesis is important to maintain the body's stable state. The regulation of gluconeogenesis by hormones is actually a regulating enzyme that regulates both the heterogeneous and glycolysis pathways and regulates the fatty acids supplied to the liver. Glucagon promotes the breakdown of fat in fat tissue, increases plasma fatty acids, and promotes gluconeogenesis; the role of insulin is just the opposite. Glucagon and insulin both regulate gluconeogenesis by affecting the phosphorylation state of the enzyme in the liver. Glucagon promotes phosphorylation of dual-enzymes (6-phosphate fructokinase 2 and fructose-2,6-bisphosphatase) by cAMP.

9. What are the sources of blood sugar and which ones are there? What hormones have an important effect on maintaining blood sugar levels? How do they regulate blood sugar levels?

Blood sugar (normally 700 ~ 1100mg / l) Source:

1, after the meal, more glucose is absorbed from the small intestine, and the blood sugar concentration is increased;

2. Hepatic glycogen decomposition;

3, non-sugar substances gluconeogenesis.

Blood sugar goes:

1. Glycogen synthesis: After eating, the body stores excess glucose in the blood in the form of glycogen;

2, glucose for the body (brain and other tissues) for energy consumption, oxidation to CO2 and water;

3. The glucose in the pentose phosphate pathway is converted to 5-phosphate ribose and NADPH;

4. Acetyl CoA produced by glucose glycolysis can be converted into fat and amino acids and stored in the body.

There are some hormones in the maintenance of blood sugar levels: insulin, glucagon, adrenaline, and adrenal cortisol. Here's how these hormones regulate blood sugar levels.

A insulin pancreatic beta cell secretion. Its secretion is controlled by blood sugar. The increase in blood sugar immediately causes its secretion, and as the blood sugar is lowered, the insulin is also lowered. Insulin is the only hormone in the body that lowers blood sugar. 1, promote muscle, fat cell carrier transport glucose into, 2, glycogen phosphorylase activity decreased (by inhibition of protein kinase A); glycogen synthase activity increased (activate glycogen synthase dephosphatase), Accelerate the synthesis of liver and muscle glycogen, 3. Indirectly activate pyruvate dehydrogenase (the reaction of pyruvate from cytosol to acetyl CoA, the part is mitochondria) through the second messenger, accelerate the oxidative decarboxylation of pyruvate to acetyl CoA, 4, Inhibition of phosphoenolpyruvate carboxykinase activity, promotes the entry of amino acids into muscle synthesis proteins, thereby reducing gluconeogenesis. Lower blood sugar. 5, reduce fat tissue mobilizes fatty acids and promotes aerobic oxidation of sugar.

B glucagon secreted by pancreatic alpha cells. Elevating blood sugar, in contrast to insulin, insulin and glucagon are the opposite.

C Adrenaline is a potent and potent hormone that raises blood sugar. It activates phosphorylase by binding to liver and muscle cell membrane receptors, produces a cascade effect, accelerates glycogen breakdown, releases glucose from the liver, and muscle exports lactic acid to the liver. This works when stressed.

D Adrenal cortisol promotes muscle protein breakdown, transports it to the liver for gluconeogenesis (when starved), and inhibits extracellular tissue uptake of glucose, thereby raising blood sugar.

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