Chapter 9- Carbohydrate Metabolism I Flashcards Preview

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Flashcards in Chapter 9- Carbohydrate Metabolism I Deck (65)
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1

what drives glucose entry into most cells

concentration (in peripheral blood its supposed to be 5.6mM-- between 4 and 6mM)

2

glucose transporters

GLUT 1
GLUT 2****
GLUT 3
GLUT 4****
****Most important b/c located in specific cells and are highly regulated

3

GLUT 2

low affinity transporter in hepatocyes (liver cells) and pancreatic cells.
in the hepatic portal vein (from spleen to liver) and captures excess glucose for storage, unless blood needs it... then it continues to the liver and goes into peripheral circulation.

4

GLUT 2 and glucokinase

serve as glucose sensor for insulin release

5

GLUT 4

in adipose tissue and muscle and responds to glucose concentration in peripheral blood. insulin stimulates movement of additional GLUT 4 transporters to the membrane by a mechanism involving exocytosis. these transporters will be saturated when blood glucose levels are a bit higher than normal.

6

type 1 and type 2 diabetes mellitus

1: insulin is absent and cannot stimulate the insulin receptor.
2: receport becomes insensitive to insulin and fails to bring GLUT 4 transporters to the cell surface
*glucose rises in both cases*

7

compare/contrast GLUT 2 and GLUT 4

GLUT 2 (liver/pancreas, Km = 15, not responsive to insulin but it acts as a glucose sensor to cause release of insulin in pancreatic B-cells)
GLUT 4 (adipose/muscle, Km = 5, responsive to insulin)

8

how does insulin promote glucose entry into cells?

GLUT 4 is saturated when glucose levels are only slightly above 5mM, so glucose entry can only be increased by increasing the number of transporters. Insulin promotes the fusion of vesicles containing preformed GLUT 4 with the cell membrane.

9

which cells are capable of performing glycolysis?

every cell. even red blood cells because no mitochondria are required.

10

glycolysis

cytoplasmic pathway that converts glucose into 2 pyruvates. (releases a bit on energy through 1 phosphorylation and 1 redox reaction).

*in the liver glycolysis is part of the process by which excess glucose is converted to fatty acids for storage.

11

5 important enzymes in glycolysis

1. hexokinase and glucokinase
2. phosphofructokinases (PFK-1 and PFK-2)
3. glyceraldehyde-3-phosphate dehydrogenase
4. 3-phosphoglycerate kinase
5. pyruvate kinase

12

rate-limiting enzyme for glycolysis

PFK-1

13

rate-limiting enzyme for fermentation

lactate dehydrogenase

14

rate-limiting enzyme for glycogenesis

glycogen synthase

15

rate-limiting enzyme for glycogenolysis

glycogen phosphorylase

16

rate-limiting enzyme for gluconeogenesis

fructose-1,6-bisphosphatase

17

rate-limiting enzyme for pentose phosphate pathway

glucose-6-phosphate dehydrogenase

18

first step in glucose metabolism for any cell

transport glucose across cell membrane and phosphorylate it by kinase enzymes to "trap" it in the cell

19

hexokinase

phosphorylates glucose to form glucose-6-phophate "trapping" it in the cell. low Km. inhibited by its own product. irreversible process.

20

glucokinase

phosphorylates and "traps" glucose in liver and pancreas cells, and works with GLUT 2 as part of the glucose sensor in B-islet cells. high Km. in liver cells its induced by insulin. irreversible process.

21

PFK-1

phosphorylates fructose 6-phosphate to fructose 1,6-bisphosphate using ATP. inhibited by ATP, citrate, and glucagon. activated by AMP, product, and insulin. irreversible process.

22

PFK-2

mainly in liver. activates PFK-1 and allows cells to override inhibition caused by ATP so glycolysis can continue even when cell is energetically satisfied.

23

glyceraldehyde-3-phosphate dehydrogenase

generates NADH while phosphorylating glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate. reversible process.

24

3-phosphoglycerate kinase

performs a substrate-level phosphorylation, transferring a phosphate from 1,3-bisphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate. reversible process.

25

pyruvate kinase

performs another substrate-level phosphorylation, transferring a phosphate from phosphoenolpyruvate (PEP) to ADP, forming ATP and pyruvate. activated by fructose 1,6-bisphosphate. irreversible process.

26

feed-forward activation

product of an earlier reaction of glycolysis stimulates a later reaction in glycolysis

27

Lactate dehydrogenase

Oxidizes NADH to NAD+, replenishing oxidized coenzymes for glyceraldehyde-3-phosphate dehydrogenase and reduces pyruvate to lactate

28

main result of fermentation

replenishing NAD+

29

3 intermediates of glycolysis used for other purposes

1. dihydroxyacetone phosphate (DHAP) used in hepatic and adipose tissue for triacylglycerol synthesis.

2/3. 1,3-bisphosphoglycerate (1,3-BPG) and phosphoenolpyruvate (PEP) are high energy intermediates used to generate ATP by substrate level phosphorylation. only ATP gained in anaerobic respiration

30

3 irreversible processes of glycolysis

How Glycolysis Pushes Forward the Process: Kinases
Hexokinase, Glucokinase, PFK-1, Pyruvate Kinases