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Biochemistry > Glyocgen Metabolism And Gluconeogenesis > Flashcards

Glyocgen Metabolism And Gluconeogenesis Flashcards

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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
Low glycemic index foods
. Lentils, fruits, non-starchy veggies
26
What lowers glycemic index of food?
Fat and fiber (putting butter on bread lowers glycemic index)
27
Why does glycemic index matter
. People w/ diabetes try to maintain blood glucose | . People w/ high GI diets have inc. risk of developing type 2 diabetes
28
Glycogen
. 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
Cellular location of glycogen
. Granules in the cytosol
30
Tissue location of glycogen
. 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
Glycogenin
. 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
Glycogen synthase
. Takes over from glycogenin | . Using UDP-glucose as donor to add more glucose molecules one by one to the chain
33
What occurs in glycogen synthesis after glycogen synthase starts?
. Branching enzyme moves 5-8 glucose molecules from end and reattached it to interior site creating branch point
34
Why is glycogen branching important?
Creates large number of terminal glucose molecules | . Rate of synthesis/degradation can be faster
35
What enzyme is key step in glycogen synthesis?
Glycogen synthase
36
Glycogenolysis (glycogen breakdown)
. 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
Glucose 6-phosphatase
. In liver but not muscle | . Cleaves phosphate from glucose-6P so liver generates glucose for body
38
Key regulated step in glycogenolysis
Glycogen phosphorylase
39
Glycogen metabolism regulation
. Substrate availability . Allosteric regulation of key steps . Hormones (tissue dependent) by altering covalent modification of key proteins
40
Why does liver has glucose 6-phosphatase and muscle doesn’t?
. 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
Glycogen phosphorylase inhibitors and activators
. Inhibitors: ATP, glucose-6P, glucose (liver) | . Activators: Ca and AMP in muscle
42
Glycogen synthase activators
Glucose-6P
43
Hormones involved in liver glycogen metabolism
. Insulin and glucagon | . Epinephrine
44
Hormones important in muscle glycogen metabolism
Insulin and epinephrine
45
What occurs to liver glycogen when epinephrine is present?
. 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
What happens to liver glycogen when insulin is present?
. 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
Gluconeogenesis
. Pathway in cytosol in liver (and somewhat in cortex of kidney) . non-carb precursors are used to synthesize glucose
48
How much glycogen in body is stored to last w/o gluconeogenesis?
1 day
49
Gluconeogenesis start and end products
2 pyruvate+4ATP+2GTP+2NADH+6H2O -> glucose+4ADP+2GDP+6P+2NAD+2H
50
Gluconeogensis enzyme for pyruvate to oxaloacetate and qualities
``` . 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
Gluconeogenesis enzyme from oxaloacetate to phosphoenol pyruvate
Phosphoenol pyruvate carboxykinase | . Inhibited by ADP
52
Number of pyruvate and oxaloacetate in gluconeogenesis
2 of each
53
Gluconeogenesis enzyme for fructose 1,6-BP to fructose-6P
Fructose 1,6-bisphosphatase . Activated by citrate . Inhibited by fructose 2,6-BP
54
Gluconeogenesis enzyme for glucose-6P to glucose and qualities
Glucose 6-phosphatase . Important to enable liver to export glucose to blood . Also found in glycogen catabolism in liver
55
Similarities btw glycolysis and gluconeogenesis
. Both primarily in cytosol . Share enzymes . Regulated allosterically and via hormones
56
Differences btw glycolysis and gluconeogenesis
. Glycolysis in all tissues, gluconeogenesis in liver and kidney . Regulation is opposite . Enzymes shared are used in opposite directions
57
Short term regulation of gluconeogenesis
. Opposite glycolysis | . Activities of enzymes controlled by availability of substrates
58
Long term regulation of gluconeogenesis
. 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
Subcellular compartmentation w/ pyruvate carboxylase
. Oxaloacetate generated in mitochondria for gluconeogenesis is transported into cytoplasm via shuttle
60
When glucagon present in liver what occurs W/ gluconeogenesis?
. Gluconeogenesis stimulated
61
Cori cycle
. 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
What does epinephrine stimulate in liver?
Gluconeogenesis
63
What occurs when glucagon present with liver glycogen?
Glycogen breakdown stimulated | Does not occur in muscle bc there are no glucagon receptors
64
Von Gierkes disease
Glucose 6-phosphatase deficiency | Causes hypoglycemia during fasting, hepatomegaly

Biochemistry (64 decks)

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