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50 Cards in this Set
- Front
- Back
Why is glucose an important metabolic fuel? |
1. A source of energy 2. A source of NADPH needed for synthetic reactions (fatty acids, steroids) 3. A source of pentose sugars for synthetic reactions (nucleotides, DNA) 4. A source of carbon for other sugars and glycoconjugates |
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What properties of glucose make it a good fuel? |
Water soluble so does NOT require a carrier in the circulation Can cross the blood brain barrier Can be oxidised anaerobically |
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All tissues use glucose. What does the liver do in terms of glucose? |
The liver can provide glucose for other tissues |
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What pathways is glucose involved in in skeletal muscle? |
Glycolysis Glycogen synthesis and degradation |
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What pathways is glucose involved in in the heart and brain? |
Glycolysis |
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What pathways is glucose involved in in in adipose tissue? |
Glycolysis |
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What pathways is glucose involved in in erythrocytes? |
Glycolysis Pentose phosphate pathway |
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What pathways is glucose involved in in the liver? |
Glycolysis Pentose phosphate pathway shunt Glycogen synthesis and degradation Gluconeogenesis |
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What is the function of glucose in the heart and brain? |
A source of energy |
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What is the function of glucose in skeletal muscle? |
A source of energy Anaerobic muscle contraction (converted to glycogen) an energy store for muscle contraction |
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What is the function of glucose in adipose tissue? |
Production of glycerol-3-phosphate for TAG's |
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What is the function of glucose in erythrocytes? (red blood cells) |
A source of energy (pentose phosphate pathway) produces NADPH for synthesis of fat, cholesterol and steroids |
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What is the function of glucose in the liver? |
Produces acetyl CoA so excess glucose is converted into fatty acids (pentose phosphate pathway) produces NADPH for synthesis of fat, cholesterol and steroids store of glucose for other tissues |
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What are the sources of glucose that are available to the body? |
Diet Liver glycogen Liver gluconeogenesis * |
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In conditions of carbohydrate deprivation, glucose is synthesised from non-carbohydrate sources in the liver (gluconeogenesis). What are these sources? |
Lactate Glycerol Glucogenic amino acids Other monosaccharides |
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Can glucose be synthesised from fatty acids? |
NO!!!!! |
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Which amino acids are glucogenic? |
All except leucine and lysine. |
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After ingestion of 100g of glucose, what forms of glucose are used and in what order? |
Injested glucose Glycogen Gluconeogensis |
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What kind of hormone is insulin and what does it promote? |
Anabolic hormone promotes synthesis and storage |
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What kind of hormone is glucagon and what does it promote? |
Catabolic hormone promotes degradation of stored fuel |
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Where are the Islets of Langerhans found? What kind of cells make up the Islets of Langerhans? |
Pancreas Beta cells (secrete insulin) and alpha cells (secrete glucagon) |
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Insulin, glucagon (as well as adrenaline) and glucose, signal and coordinate the activities of which tissues? |
The liver Adipose tissue Muscle tissue |
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What are some metabolic effects of insulin on the liver? |
Inhibition of gluconeogenesis Activation of glycogen synthesis (glycogen synthase activated) Increased fatty acid synthesis and lipid assembly Increased amino acid uptake and protein synthesis |
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What are the metabolic effects of insulin on muscle? |
Increased glucose uptake by increasing glucose transporters (GLUT 4) Increased amino acid uptake and protein synthesis Activation of glycogen synthesis ( glycogen synthase activated) |
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What are the metabolic effects of glucagon? |
Increase in blood glucose by increasing glycogenolysis and gluconeogenesis (liver) Increase in circulating fatty acids and ketone bodies Decrease in plasma amino acids |
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Why does glucagon cause a decrease in plasma amino acids? |
Increased uptake by the liver for gluconeogenesis |
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Why does glucagon cause an increase in circulating fatty acids and ketone bodies? |
Increase in lipolysis in adipose tissue Increase in fatty acid oxidation |
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Why is gluconeogenis not simply the reversal of glycolysis? |
Because there are 3 irreversible reactions in glycolysis |
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What are the 3 irreversible reactions in glycolysis? |
D-glucose ---> glucose-6-phosphate Fructose-6-phosphate ---> fructose-1,6-bisphosphate Phosphoenol pyruavte ---> pyruvate |
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How is pyruvate converted to glucose? |
Pyruvate is first converted to oxaloacetate and then it is converted to phosphoenol pyruvate . The PEP is then converted to glucose via many stages. |
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How is gluconeogenesis regulated? |
1. Mobilisation of substrate (glycerol from fat breakdown, amino acids from muscle protein breakdown) 2. Activation of enzymes ( including pyruvate carboxylase) |
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What activates pyruvate carboxylase? |
Acetyl CoA |
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Which enzyme converts pyruvate to oxaloacetate? |
Pyruvate carboxylase |
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Which enzymes converts oxaloacetate to PEP? |
PEP carboxykinase |
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Following a meal, how are blood glucose and insulin levels related? |
They follow a similar pattern |
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Following a meal, how are blood glucose and glucagon levels related? |
Glucagon pattern is opposite to glucose pattern |
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What is the physiological circulating concentration of glucose? |
3.9-6.2 mM |
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What are some disadvantages of glucose as a metabolic fuel? |
Relatively low yield of ATP/mole compared to fatty acids Osmotically active In high concentrations can directly damage cells or lead to accumulation of toxic by-products |
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In the FED state, what is glucose converted to in the liver? |
Majority of glucose converted to glycogen XS glucose converted to fat |
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In the FED state, what is glucose converted to in the muscle? |
Glycogen |
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In an aerobically respiring muscle, what is glucose converted to? |
Glucose AND glycogen are converted to pyruvate, which is then converted to acetyl CoA which ends the TCA cycle and then oxidative phosphorlyayion to produce ATP |
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In erythrocytes, in the FED or fasting state, what is glucose converted to? |
Lactate |
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When the liver is in the fasting state, what is converted to what? |
Lactate and glycogen are converted back to glucose |
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When the brain is into the FED or fasting state, what is glucose converted to? |
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These are the glucose tolerance curves of normal and diabetic subjects. Which curve is for a normal person, one with type I diabetes and a person with type II diabetes? |
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What is the molecular basis for the observation that liver glycogen is used for maintaining blood glucose concentration but muscle glycogen is not? |
Muscle lacks the enzyme, glucose-6-phosphatase that catalyses the dephospho rylation of glucose-6-phosphate to glucose, whereas the liver has this enzyme. In muscle glucose-6-phosphate is thus directed to glycolysis for ATP production within the muscle fibres, which makes sense as muscles require ATP for contraction |
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What is the cofactor for pyruvate carboxylase? |
Biotin |
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Where does carboxylation of pyruvate take place? |
Carboxylation of pyruvate occurs in themitochondria while other reactions of gluconeogenesis occur in the cytosol. |
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One role of glucose in to provide NADPH in the hexose monophosphate shunt in which two places? |
Liver Erythrocytes |
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In which two places is the role of glycolysis not for energy? |
Adipose tissue ( to produce glycerol P' for TAGS) Liver ( XS glucose converted to acetyl CoA) |