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Biochemistry > Glyocgen Metabolism And Gluconeogenesis > Flashcards

Glyocgen Metabolism And Gluconeogenesis Flashcards

1
Q

Roles of carbs in body

A

. Structural: proteoglycans important in CT
. Energy: source of ATP
. Storage of energy: glycogen storage in liver and muscle
. Cell-cell recognition: cell surface carbs

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2
Q

Monosaccharides

A 
. Simple sugars (glucose and fructose) 
. Sweet
. Glucose is from starches 
. Galactose is from milk
. Fructose is from table sugar, fruit, honey
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3
Q

Disaccharide

A

. 2 monosaccharides joined together
. Lactose: composed of galactose and glucose (found in milk)
. Sucrose: glucose and fructose (common table sugar), major source of dietary fructose

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4
Q

Oligosaccharides

A

. Short chains of monosaccharides

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5
Q

Polysaccharides

A

. Long chains w/ no defined molecular weight
. No template used in synthesis
. Structural roles (ground substance, cellulose)
. Fuel storage: glycogen and plant starches form compact dense granules well-suited for cellular storage

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6
Q

Blood glucose level normal

A

5mM (100 mg/dL)

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7
Q

Hypoglycemia

A

. Blood glucose drops too low

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8
Q

Hypoglycemia adrenergic symptoms

A

. epinephrine release
. Occurs when glucose level falls off abruptly
. Anxiety, palpitation, tremor, sweating

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9
Q

Hypoglycemia neuroglycopenic symptoms

A

. From insufficiency delivery of glucose to brain
. Result of gradual decline in glucose (<40 mg/dL)
. Headache, confusion, slurred speech, seizures, coma, death

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10
Q

Hyperglycemia

A

. No symptoms

. If remains elevated diabetes mellitus may be the cause

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11
Q

Blood glucose maintained by ____

A

. Dietary intake of carbs: transport glucose from GI to blood
. Glycogen catabolism in liver: transport glucose from hepatocytes to blood
. Gluconeogenesis in liver: transport glucose from hepatocytes

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12
Q

Percentage glucose brain uses per day

A

25%

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13
Q

Why is glucose important for rbcs

A

Lack organelles, can’t make ATP other than glycolysis

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14
Q

When is glucose important for muscle cells?

A

. Prolonged and/or intense muscle activity

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15
Q

Role of mouth in dietary absorption of carbs

A

. Saliva contains alpha-amylase (ptyalin)
. Breaks bonds btw sugars in carbs
. Some glucose absorbed directly across mucous membrane

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16
Q

Role of stomach in dietary carb absorption

A

. Acidic environment (pH: 1-3)
. Inactivates alpha-amylase
. Acid cleaves bonds btw monosaccharide units of polysaccharides

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17
Q

Small intestine role in dietary carb absorption

A

. Neutral/slightly basic environment (pH: 6-8)
. Low pH from food triggers secretion of secretin
. Stimulates pancreas to secrete bicarbonate into small intestine to neutralize gastric acid and bring pH up

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18
Q

Pancreatic amylase

A

. Hydrolyzes starches and glycogen

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19
Q

Disaccharidases

A

. Sucrase: sucrose+H2O -> D-fructose and D-glucose
. Lactase: lactose+H2O -> D-galactose and D-glucose
. Resulting glucose foes to intensional cells, then blood, then tissues
. Galactose and fructose made are taken up in GI tract then moved to liver where they are converted into glucose by enzymes

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20
Q

Lack of dissaccharidase

A

. Diarrhea and gas when excess carbs consumed
. Water follows non-digested nutrients into GT causing diarrhea and gas is produced by bacteria in lower intestine that metabolize non-digested nutrients
. Relatively common in people

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21
Q

Large intestine role in dietary carb absorption

A

. escherichia coli: digest substances that we can’t digest making gas an end product
. Some nutrients absorbed (H2O, electrolytes, and anything left over)
. Carbs not digested are excreted (fiber)

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22
Q

Glycemic index

A

. Classifies food based on their ability to raise blood glucose after consumption

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23
Q

Goods with high glycemic index

A

. White bread
. Bagel
. White rise

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24
Q

Medium glycemic index foods

A

. Whole grain bread, oats, brown rice

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25
Q

Low glycemic index foods

A

. Lentils, fruits, non-starchy veggies

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26
Q

What lowers glycemic index of food?

A

Fat and fiber (putting butter on bread lowers glycemic index)

27
Q

Why does glycemic index matter

A

. People w/ diabetes try to maintain blood glucose

. People w/ high GI diets have inc. risk of developing type 2 diabetes

28
Q

Glycogen

A

. Readily accessible storage form of glucose
. Large branched polymer of alpha-D-glucose residues
. 90% of glucose molecules in glycogen are linear, 10% are branch points
. Makes glucose available btw meals
. Synthesis and degradation are different pathways regulated by hormones

29
Q

Cellular location of glycogen

A

. Granules in the cytosol

30
Q

Tissue location of glycogen

A

. Present in many by predominant in liver (10% weight is glycogen) for fuel reserve for blood and muscle (1-2% weight glycogen) for fuel reserve for own use
. More glycogen in muscle tissue than liver tissue because there is 2 fold more glycogen in total muscle than in liver

31
Q

Glycogenin

A

. Protein at core of every glycogen molecule
. Has oligosaccharide chain of glucose from post-translational modification
. Auto-catalyzes addition of 8 more glucose resides onto chain

32
Q

Glycogen synthase

A

. Takes over from glycogenin

. Using UDP-glucose as donor to add more glucose molecules one by one to the chain

33
Q

What occurs in glycogen synthesis after glycogen synthase starts?

A

. Branching enzyme moves 5-8 glucose molecules from end and reattached it to interior site creating branch point

34
Q

Why is glycogen branching important?

A

Creates large number of terminal glucose molecules

. Rate of synthesis/degradation can be faster

35
Q

What enzyme is key step in glycogen synthesis?

A

Glycogen synthase

36
Q

Glycogenolysis (glycogen breakdown)

A

. Glycogen phosphorylates uses inorganic phosphate to cleave individual glucose molecules from end of glycogen molecule making glucose-6P
. Continues cleaving until 4 glucose from branch point
. Transferase activity of bifunctional protein moves black of 3 glucoses from outer branch to another
. Debranching activity from Same protein uses H2O to cleave branch-point glucose

37
Q

Glucose 6-phosphatase

A

. In liver but not muscle

. Cleaves phosphate from glucose-6P so liver generates glucose for body

38
Q

Key regulated step in glycogenolysis

A

Glycogen phosphorylase

39
Q

Glycogen metabolism regulation

A

. Substrate availability
. Allosteric regulation of key steps
. Hormones (tissue dependent) by altering covalent modification of key proteins

40
Q

Why does liver has glucose 6-phosphatase and muscle doesn’t?

A

. Liver has to transport glucose from liver cells to blood stream for entire body
. Muscle only makes glucose for itself and it does not have to enter bloodstream

41
Q

Glycogen phosphorylase inhibitors and activators

A

. Inhibitors: ATP, glucose-6P, glucose (liver)

. Activators: Ca and AMP in muscle

42
Q

Glycogen synthase activators

A

Glucose-6P

43
Q

Hormones involved in liver glycogen metabolism

A

. Insulin and glucagon

. Epinephrine

44
Q

Hormones important in muscle glycogen metabolism

A

Insulin and epinephrine

45
Q

What occurs to liver glycogen when epinephrine is present?

A

. Goes through G-protein Adenylate cyclase activation pathway to activate PKA
. PKA phosphorylates glycogen synthase to turn it odd
. Phosphorylates glycogen phosphorylase which activates it and glycogen is broken down
. Same thing occurs in muscle cells

46
Q

What happens to liver glycogen when insulin is present?

A

. Insulin binds to RTK
. Protein phosphatase dephosphorylates glycogen synthase turning it on
. Glycogen phosphorylase is dephosphorylated and is turned off
. Glycogen is synthesized from glucose

47
Q

Gluconeogenesis

A

. Pathway in cytosol in liver (and somewhat in cortex of kidney)
. non-carb precursors are used to synthesize glucose

48
Q

How much glycogen in body is stored to last w/o gluconeogenesis?

A

1 day

49
Q

Gluconeogenesis start and end products

A

2 pyruvate+4ATP+2GTP+2NADH+6H2O -> glucose+4ADP+2GDP+6P+2NAD+2H

50
Q

Gluconeogensis enzyme for pyruvate to oxaloacetate and qualities

A 
. Pyruvate carboxylase 
. Activated by acetyl CoA 
. Inhibited by ADP
. Need biotin to function 
. Uses ATP and bicarbonate 
. Occurs in mitochondria 
. Replenishes oxaloacetate when TCA intermediates are drawn off for biosynthetic purposes
51
Q

Gluconeogenesis enzyme from oxaloacetate to phosphoenol pyruvate

A

Phosphoenol pyruvate carboxykinase

. Inhibited by ADP

52
Q

Number of pyruvate and oxaloacetate in gluconeogenesis

A

2 of each

53
Q

Gluconeogenesis enzyme for fructose 1,6-BP to fructose-6P

A

Fructose 1,6-bisphosphatase
. Activated by citrate
. Inhibited by fructose 2,6-BP

54
Q

Gluconeogenesis enzyme for glucose-6P to glucose and qualities

A

Glucose 6-phosphatase
. Important to enable liver to export glucose to blood
. Also found in glycogen catabolism in liver

55
Q

Similarities btw glycolysis and gluconeogenesis

A

. Both primarily in cytosol
. Share enzymes
. Regulated allosterically and via hormones

56
Q

Differences btw glycolysis and gluconeogenesis

A

. Glycolysis in all tissues, gluconeogenesis in liver and kidney
. Regulation is opposite
. Enzymes shared are used in opposite directions

57
Q

Short term regulation of gluconeogenesis

A

. Opposite glycolysis

. Activities of enzymes controlled by availability of substrates

58
Q

Long term regulation of gluconeogenesis

A

. Synthesis fo enzymes regulated by pattern of nutritional state
. Eating well inc. synthesis of liver glycolytic enzymes and dec. synthesis of gluconeogensis enzymes
. Starvation inc. liver gluconeogenesis enzymes and dec. glycolytic

59
Q

Subcellular compartmentation w/ pyruvate carboxylase

A

. Oxaloacetate generated in mitochondria for gluconeogenesis is transported into cytoplasm via shuttle

60
Q

When glucagon present in liver what occurs W/ gluconeogenesis?

A

. Gluconeogenesis stimulated

61
Q

Cori cycle

A

. Lactate from muscle is carried into liver
. Converted to pyruvae via lactate dehydrogenase
. Pyruvate used in gluconeogenesis to make glucose
. Glucose brought back to muscle to start glycolysis

62
Q

What does epinephrine stimulate in liver?

A

Gluconeogenesis

63
Q

What occurs when glucagon present with liver glycogen?

A

Glycogen breakdown stimulated

Does not occur in muscle bc there are no glucagon receptors

64
Q

Von Gierkes disease

A

Glucose 6-phosphatase deficiency

Causes hypoglycemia during fasting, hepatomegaly

Biochemistry (64 decks)

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