Carbohydrate metabolism I Flashcards

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1
Q

This glucose transporter:
-Found in hepatic and pancreatic cells
-Has a low affinity for glucose
-Appears when glucose levels are high (Km~15 mM)
-Acts as sensor for insulin release by interacting with pancreatic B-cells
-Has a low affinity for glucose

A

GLUT 2

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2
Q

This glucose transporter:
-Found in adipose tissue and skeletal muscles
-Responds to glucose levels in peripheral blood
-Is saturated when glucose levels are only slightly elevated (Km~5 mM)
-Is modulated by insulin, where insulin increases the amount of transporters brought to the cell membrane

A

GLUT 4

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3
Q

The end products of glycolysis are: __ ATP, __ pyruvate and __ NADH

A

2, 2, 2

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4
Q

This glycolysis enzyme:
-Prevents glucose from leaving the cell by phosphorylating it
-Is irreversible
-Is widely distributed in tissue and has a high affinity for glucose
-Is inhibited by it’s product glucose-6-phosphate

A

Hexokinase

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5
Q

This glycolysis enzyme:
-Prevents glucose from leaving the cell by phosphorylating it
-Is irreversible
-Is found only in liver and pancreatic B-cells, and has a low affinity for glucose
-Is induced by insulin (in the liver)

A

Glucokinase

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6
Q

Compare and contrast hexokinase and glucokinase?

A

Both are involved in the phosphorylation of glucose so that it cannot leave once it enters the cell

Hexokinase is found in every cell because it helps with normal glycolysis and is inhibited by glucose-6-phosphate, its product. Associate it with GLUT 4, in that it’s saturated at normal glucose levels and has a high affinity for glucose

Glucokinase is found only in liver and pancreatic B-cells. It only helps with glycolysis in the liver and is stimulated by the presence of insulin (which indicates the levels of glucose are increased). Think of it like GLUT 2, where it isn’t saturated at normal glucose levels and has a low affinity for glucose

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7
Q

This phosphofructokinase:
-Is a rate limiting enzyme
-Is irreversible
-Turns fructose-6-phosphate into fructose-1,6-biphosphate
-Is inhibited by ATP and citrate
-Is activated by AMP

A

PFK 1

Essentially determines whether or not glycolysis needs to proceed or if the cell has enough energy for the time being

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8
Q

Why is PFK-1 activated by AMP but inhibited by citrate and ATP?

A

PFK-1 is involved in an energy making process, so if the cell already has enough energy (indicated by levels of ATP and citrate) there’s no need for glycolysis to continue. Similarly, if the cell only has AMP, it’s lacking in energy and glycolysis is necessary

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9
Q

This phosphofrutokinase:
-Activates PFK-1
-Allows PFK-1 to override the presence of ATP and citrate and keep glycolysis active

A

PFK-2

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10
Q

This dehydrogenase:
-Adds phosphate to glyceraldehyde-3-phosphate to form 1,3-biphosphoglycerate
-Forms NADH from NAD+, which is then brought into the electron transport chain

(Has a name based on the molecule it’s adding to)

A

Glyceraldehyde-3-phosphate dehydrogenase

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11
Q

This kinase:
-Forms ATP from ADP and 1,3-biphosphoglycerate
-Is the only means of ATP generation in anaerobic tissue
-Is irreversible

A

3-Phosphoglycerate kinase

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12
Q

This kinase:
-Creates ATP from ADP and phosphoenolpyruvate
-Is activated by PFK-1
-Is irreversible

A

Pyruvate kinase

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13
Q

_____ occurs when ADP is directly phosphorylated to ATP via a high energy intermediate

A

Substrate-level phosphorylation

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14
Q

What are the four irreversible enzymes of glycolysis?

A

The glucokinases (hexo and gluco)
PFK-1
3-phosphoglycerate kinase
Pyruvate kinase

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15
Q

This pathway occurs anaerobically to replenish NAD+ that can then be used to continue glycolysis

A

Fermentation

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16
Q

This glycolysis intermediate:
-Is nicknamed DHAP
-Is found in hepatic and adipose tissue
-Forms the backbone of triacylglycerol

A

Dihydroxyacetone

17
Q

These two glycolysis intermediates:
-Form ATP from substrate level phosphorylation
-Are the only anaerobic source of ATP

A

1,3-biphosphoglycerate (1,3-BPG) and phosphoenolpyruvate

18
Q

In the galactose metabolism, galactose is transformed into ____

A

Glucose-1-phosphate

19
Q

In the fructose metabolism, fructose is transformed into ____

A

DHAP and glyceraldehyde

20
Q

This complex of enzymes:
-Can enter the citric acid cycle as either acetyl-CoA if ATP is needed, or become fatty acids if there’s already enough ATP
-Is activated by insulin (when it’s in the liver)
-Is inhibited by acetyl CoA

A

Pyruvate dehydrogenase

21
Q

Glycogen is synthesized and degraded in ____ and ___ muscle, and is stored in the ____ as granules

A

Liver and skeletal muscle

Cytoplasm

22
Q

This pathway creates new glycogen

A

Glycogenesis

23
Q

This glycogenesis enzyme:
-Forms the linear alpha 1,4 bond in glycogen
-Is the rate limiting enzyme
-Is stimulated by insulin and glucose-6-phosphate
-Is inhibited by ephinephrine and glucagon

A

Glycogen synthase

24
Q

This glycogenesis enzyme:
-Creates the alpha 1,6 branches in glycogen by hydrolyzing areas of the linear 1,4 chain and moving them into the branched position at carbon 6

A

Branching enzyme

25
Q

This pathway breaks down glycogen

A

Glycogenolysis

26
Q

This glycogenolysis enzyme:
-Breaks alpha 1,4 bonds but cannot break 1,6 branches
-Is the rate limiting step
-Is activated by glucagon in the liver and by AMP and epinephrine in the skeletal muscle
-Is inhibited by ATP

A

Glycogen phosphorylase

27
Q

This glycogenolysis enzyme breaks the 1,6 branching in two steps: first by breaking the 1,4 bond closest to the branch and placing it back on the linear chain and second by hydrolyzing the 1,6 bond to release the single free glucose left from the branch

A

Debranching enzyme

28
Q

This pathway:
-Forms new glucose
-Is inhibited by insulin
-Is activated by glucagon and epinephrine
-Activates or increases during the the first 12 hours of fasting

A

Gluconeogenesis

29
Q

____ amino acids can turn into intermediates for gluconeogenesis, except for lysine and leucine

A

Glucogenic AA’s

30
Q

____ amino acids can turn into ketone bodies and serve as alternative fuel during starvation

A

Ketogenic AA’s

31
Q

This important gluconeogenesis enzyme:
-Is mitochondrial
-Forms Oxaloacetate as a product
-Is activated by the beta oxidation of acetyl-CoA

A

Pyruvate carboxylase

32
Q

This important gluconeogenesis enzyme:
-Is in the cytoplasm
-Is induced by glucagon and cortisol
-Circumvents pyruvate kinase by converting pyruvate into phosphoenolpyruvate

A

Phosphoenolpyruvate carboxykinase

33
Q

This important gluconeogenesis enzyme:
-Is the rate limiting step
-Circumvents PFK-1 by creating fructose-6-phosphate

A

Fructose-1,6-biphosphatase

34
Q

This important gluconeogenesis enzyme:
-Is only found in the lumen of the rough ER
-Circumvents hexo and glucokinase by tranposting glucose-6-phosphate to the ER and releasing it as glucose

A

Glucose-6-phosphatase

35
Q

This pathway:
-Occurs in the cytoplasm of all cells
-Has two major functions: to act as a source of NADPH and ribose-5-phosphate for nucleotide synthesis

A

Pentose phosphate pathway

(Also called the hexose monophosphate shunt)

36
Q

This enzyme of the pentose phosphate pathway:
-Is the rate limiting enzyme
-Is induced by insulin
-Is activated by NADP+
-Is inhibited by NADPH

A

Glucose-6-phosphate dehydrogenase

37
Q

What is the difference between NADH and NADPH?

A

NADH indirectly produces ATP by feeding into the electron transport chain. As NAD+, it’s a powerful oxidizing agent and electron acceptor

NADPH acts an electron donor and reducing agent, and is required for fatty acid and cholesterol synthesis, bleach production in some white blood cells, and maintaining glutathione to prevent free radicals