Carbohydrate Metabolism Flashcards
1
Q
Osmotic pressure equation
A
II=iMRT
M=molarity R=ideal gas constant T=absolute temperature in kelvin i=van''t Hoff factor =number of particles obtained from the molecule from a molecule in solution ex. glucose= 1, NaCl=2
2
Q
Where is sodium needed to uptake glucose
A
In digestive tract
3
Q
What is normal glucose concentration in peripheral blood?
A
5.6 mM
4
Q
GLUT 2
A
Low affinity transporter in hepatocytes and pancreatic cells
Has a high Km value and it will pick up glucose from the liver in proportion to glucose concentration in blood (when blood glucose is high)
5
Q
What serves as a sensor for glucose release in pancreatic B islets?
A
GLUT 2 and glucokinase enzyme
6
Q
What does a high Km mean?
A
Low affinity for substrate
7
Q
GLUT 4
A
In adipose tissue and muscle and responds to glucose concentration in peripheral blood
Low Km
8
Q
Effect of insulin
A
Stimulates more GLUT 4 transporters to membrane by exocytosis
9
Q
What order of kinetics are GLUT 4 transporters?
A
Zero order, saturated transporters still permit only a constant rate of glucose influx
10
Q
How can glucose uptake be increased in muscle and adipose tissue?
A
More GLUT 4 transporters
11
Q
What happens in liver when blood glucose drops below high Km?
A
Rest enters peripheral circulation
12
Q
What energy pathway can red blood cells use?
A
Glycolysis
13
Q
Glycolysis
A
Cytoplasm
Converts glucose into pyruvate releasing energy in 2 phosphorylation and 1 oxidation
14
Q
Can glycolysis be done anaerobically?
A
Yes
15
Q
What does hexokinase do?
A
Phosphorylate transported in glucose to make glucose 6-phosphate
16
Q
What does glucokinase do?
A
Hexokinase in the liver & pancreatic B-islets along with GLUT 2
17
Q
What inhibits hexokinase?
A
Glucose 6-Phosphate
18
Q
What inhibits glucokinase?
A
Insulin
19
Q
Phosphofructokinase-1
A
Rate limiting step
Converts Fructose 6-phosphate to fructose 1,6-bisphosphate use ATP
20
Q
What inhibits Phosphofructokinase-1
A
ATP (don’t need pyruvate during high energy)
Citrate
Glucagon
21
Q
What stimulates PFK-1?
A
Insulin
22
Q
PFK-2
A
Converts an amount of fructose 6-phosphate to fructose 2,6 bisphosphate
23
Q
What is the effect of fructose 2,6 bisphosphate?
A
Activates PFK-1
24
Q
What is the effect of glucagon?
A
Inhibits PFK-2 and lowers F2 2,6-BP to inhibit PFK-1
25
Where is PFK-2 mostly found?
Liver
26
Glyceraldehyde 3-phosphate dehydrogenase
Catalyzes oxidation and addition of inorganic phosophate to Glyceraldehyde 3-phosphate
G3P-->to 1,3-bisphosphoglycerate & creation of NADH
27
3-Phosphoglycerate Kinase
1,3 bisphophoglycerate --> 3-phosphoglycerate and ATP
28
What enzyme uses substrate-level phosphorylation?
3-phosphoglycerate kinase
| Pyruvate kinase
29
Pyruvate kinase
In presence in O2 only
| Phosphoenolpyruvate (PEP) -->Pyruvate
30
What activates pyruvate kinase?
Fructose 1,6 bisphosphate from PFK-1 in feed forward reaction
31
Lactate dehydrogenase
Key fermentation enzyme
| Oxidizes NADH to NAD+ so that it can be used by G3P
32
What is pyruvate turned into in yeast cells?
ethanol and carbon dioxide
33
Dihydroxyacteone phosphate (DHAP)
Use in hepatic and adipose tissue for TAG synthesis
Formed from fructose 1,6-bisphosphate
Isomerized to glycerol 3-P -->glycerol
34
What is used to generate ATP by substrate level phosphorylation?
1,3-bisphosphoglycerate (1,3-BPG) and phosphoenolpyruvate (PEP)
35
Irreversible reactions in glycolysis?
Glucokinase/hexokinase
PFK-1
Pyruvate kinase
36
How much ATP is made in anaerobic glycolysis in erythrocytes?
2 ATP
37
Biphosphoglycerate mutase
Produces 2,3-bisphosphoglycerate (2,3-BPG) from 1,3-BPG in glycolysis in erythrocytes
Binds to B-chains of hemoglobin A and decreases affinity for oxygen
38
What has a higher affinity for oxygen, fetal or maternal hemoglobin?
Fetal hemoglobin
39
Lactase
Hydrolylzes lactose to galactose and glucose
40
Galactoskinase
Phosphorylates galactose inside the cell from the liver
41
What transfers galactose 1-phosphate to glucose 1-phosphate
Galactose 1-phosphate uridyltransferase and epimerase
42
Sucrose
Fructose and glucose
43
What phosphorylates fructose?
Fructokinase
44
What cleaves fructose 1-phosphate into DHAP and glyceraldehyde?
aldolase B
45
Is pyruvate dehyrogenase reversible?
No
46
What is pyruvate dehydrogenase activated by in the liver?
Insulin (Burn glucose when there is food & store it)
47
What pathways can acetyl-CoA take?
Fatty acid synthesis if enough ATP is present
| Ctiric acid cycle if not enough ATP
48
Glycogen
A branched polymer of glucose that stores glucose primarily in liver and muscle
49
What is liver glycogen used for?
Used in between meals to prevent low blood glucose
50
What happens during glycogenesis?
Glycogenin core protein adds G6P to it and its converted to G1P
51
What does glycogen synthase use to integrate into the glycogen chain?
Glycogen 1-phosphate activated by coupling to uridine triphosphate to make UDP phosphate & pyrophosphate
52
Glycogen synthase
Rate-limiting enzyme of glycogen synthesis and forms a-1,4 glycosidic bonds in a linear fashion
53
What stimulates glycogen synthase?
Glucose 6-phosphate
| Insulin
54
What inhibits glycogen synthase?
Epinephrine
| Glucagon
55
Branching enzyme
Introduces a-1,6 linkages into the granule as it grows by hydrolyzing a-1,4-glycosidic linkages and moves them
56
What breaks down glycogen?
Glycogen phosphorylase into glucose 1-P
57
What bonds can glycogen phosphorylase not break?
a-1.6 bonds
58
What stimulates glucagon?
AMP
Epinephrine
Glucagon
59
What inhibits glycogen phosphorylase?
ATP
60
Debranching enzyme ( a1,4;a-1,6 transferase)
Deconstructs branches in glycogen that have been exposed by glycogen phosphorylase
Moves terminal end of branch point to the core chain
61
Debranching enzyme (a-1,6 Glucosidase)
Removes glucose monomer present at the branch point (the a-1,6 linkage
62
Glycogenolysis produces how many free glucose?
1
63
Order of formation of glucose?
G6P -->G1P -->Glucose
64
Isoform
Slightl different versions of the same protein
65
Gluconeogenesis
Formation of glucose by the liver
66
What is the effect on blood sugar by glucagon and epinephrine and cortisol and growth hormone?
Increase blood sugar
67
What is the effect on blood sugar by insulin?
Decrease blood sugar
68
What are sources for gluconeogenesis?
Glycerol 3-Phosphate (from fats), Lactate (from anaerobic glycolysis), Glucogenic amino acids *from muscle proteins)
69
Glucogenic amino acids
Can be converted into intermediates of gluconeogenesis
| All except leucine and lysine
70
Ketogenic amino acids
Can be converted into ketone bodies that can be used as alternative fuel during prolonged starvation
71
What kind of fatty acids can yield glucose?
Odd-chained
72
What do odd-chained fatty acids yield?
Propionyl-CoA that can be turned into glucose
73
Can acetyl CoA be turned back into glucose?
No
74
4 Enzymes in gluconeogenesis that circumvent irreversible steps of glycolysis in liver?
Pyruvate carboxylase
Phophoenolpyruvate Carboxykinase (PEPCK)
Fructose 1,6 Bisphosphate
Glucose 6-phosphatase
75
Pyruvate Carboxylase
Mitochondrial enzyme that is activated by acetyl-CoA
| Creates OAA in the mitochondria which is reduced to malate and leaves mitochondria in the malate-aspartate shuttle
76
What signals pyruvate carboxylase to work?
Acetyl-CoA from B-oxidation of fatty acids
77
What turns of pyruvate dehydrogenase?
A high level of Acetyl-CoA, the cell should stop burning glucose because it has enough
78
What must be used to produce glucose during gluconeogenesis?
Fatty acids must be used in the liver because pyruvate dehydrogenase is turned off by acetyl CoA
79
Phosphoenolpyruvate Carboxykinase (PEPCK)
In cytoplasm induced by glucagon and cortisol to raise blood sugar
Converts OAA to PEP requires GTP
Circumvents pyruvate kinase
PEP becomes F 1,6 BP
80
Fructose 1,6 Bisphosphatase
Reverses action of phosphofructokinase-1 (rate limiting step)
Fructose 1,6 bisphosphate -->Fructose 6-phosphate
Activated by ATP and inhibited by AMP
81
What is the effect of F2,6-BP on gluconeogenesis?
Glucagon will lower F2,6-BP and stimulate gluconeogenesis
| Insulin will increase F2,6-BP and repress gluconeogenesis
82
What does high AMP mean to gluconeogenesis?
Energy is low and can't make enough to make glucose for the rest of the body
83
What does high ATP mean to gluconeogenesis?
Enough energy to make glucose for the rest of the body
84
Glucose 6-Phosphatase
In lumen of ER in liver
| Glucose 6-Phosphate in ER -->Glucose out of cell
85
Where is there no glucose-6- phosphatase?
In skeletal muscle, can't provide blood glucose
| Circumvents glucokinase and hexokinase
86
Why does gluconeogenesis require acetyl-CoA?
Inhibit pyruvate dehydrogenase and stimulate pyruvate carboxylase
Links to fatty acid oxidation
87
What gluconeogenic intermediate can glycerol be converted into?
DHAP
88
What can acetyl-CoA be converted into as alternative fuel?
Ketone bodies
89
Is gluconeogenesis an energy source for the liver?
No, requires expenditure of ATP from B-oxidation
90
Pentose phosphate pathway/Hexose monophosphate shunt
Produces NADPH
| Serves as a source of ribose 5-phosphate for nucleotide synthesis
91
First step of pentose phosphate pathway
Glucose 6-phosphate -->Ribulose 5-phosphate and NADPH
BY glucose-6-phosphate dehydrogenase (G6PD)
92
What affect does insulin have on the pentose phosphate pathway?
Stimulate G6PD to go through pentose phosphate pathway
93
What is created from ribulose 5-P in the pentose phosphate pathway?
Ribose 5-P for nucleotide synthesis and other sugars
94
What can glyceraldehyde 3-P and Fructose 3-P be converted into ?
Glycolytic intermediates by transketolases and transaldolases
95
NADH acts primarily as ?
A elecron acceptor and oxidizing agent
96
NADPH acts primarily as?
A electron donor and reducing agent
97
When is NADPH needed?
Biosynthesis (FA and cholesterol)
Immune system
Prevent oxidative damage using glutathione
98
Where does gluconeogenesis take place?
In the cytoplasm and mitochondria
99
Which reactions in glycolysis are irreversible?
Glucokinase/hexokinase
PFK-1
Pyruvate kinase
100
Is glucokinase/hexokinase a rate-limiting step?
No
