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Biochemistry 2 > Glucose > Flashcards

Glucose Flashcards

1
Q

Glucose has four major fates

A

Synthesis of structural polymers; storage; glycolysis; penthose phosphate pathway

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2
Q

Glucose can undergo three pathway

A

Penthose phosphate; glycolysis; gluconeogenesis

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3
Q

Who discover glycolysis amoung yeast?

A

Hans Von Euler-Chelpin

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4
Q

Who discover glycolysis among muscles?

A

Gustav Embden and Otto Mereyhof

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5
Q

There are two phases in glycolysis

A

Preparatory + payoff

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6
Q

What is the fate of the preparatory phase?

A

Phosphorylation (2) of glu + conversion to G3P

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7
Q

There are five enzymes in the preparatory phase

A

Hexokinase; phosphohexone isomerase; phosphofructokinase-1; aldolase; triose phosphate isomerase

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8
Q

How many ATP broken down in the preparatory phase?

A

2

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9
Q

When are the ATP broken down?

A

First: glu to G6P via hexokinase;
Second: F6P to G1,6P via phosphofructokinase-1

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10
Q

What is the lysis step in glycolysis?

A

In preparatory phase via aldolase (step 4)

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11
Q

What is the end product of preparatory phase?

A

G3P (2)

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12
Q

What is the fate of the pay-off phase? (3)

A

NADH, ATP and G3P to pyruvate

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13
Q

What are the 5 enzymes of pay-off?

A

G3P dehydrogenase; phosphoglycerate kinase; phosphoglycerate mutase; enolase; pyruvate kinase

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14
Q

What is the substrate for pay-off?

A

G3P (2)

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15
Q

What is the end product of glycolysis?

A

2 pyruvate

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16
Q

What is the fate of first step in pay-off?

A

Phosphorylation to 1,3-biphosphoglycerate + NAD reduction via G3PDH

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17
Q

Once G3P is phosphorylated twice, it leads to… two dephosphorylations

A

ATP formation via phosphoglycerate kinase + ATP formation via pyruvate kinase

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18
Q

In preparatory phase, what is the first carbon phosphorylated?

A

C-6

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19
Q

In preparatory phase, what is the second carbon phosphorylated and why?

A

C-1, because it has been isomerized via phosphohexose isomerase

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20
Q

Which kind of phosphorylation are the ones in the preparatory phase?

A

Substrate level

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21
Q

How many phosphorylations in the pay-off phase?

A

1

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22
Q

What type of phosphorylation in the pay-off, why?

A

Oxidative, NAD is reduced via G3PDH

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23
Q

What is the role of dehydration in pay-off?

A

Activating the possible transfer of P to ADP (favorizing)

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24
Q

Where does the lysis occur?

A

C-3 and C-4

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25
Q

What are the three fates of pyruvate?

A

Alcoholic fermentation (ethanol + CO2); TCA cycle (2 Acetyl-CoA = 4 CO2 + 4 H2O); lactic fermentation (2 lactate)

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26
Q

What is the benefit of lactic fermentation?

A

No need for extra NAD reducer (NADH produced in glycolysis is reducing pyruvate, leading to lactate)

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27
Q

What is glycogenolysis?

A

Breakdown of glycogen into glucose monomers

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28
Q

How are the glycogen polysaccharides cut down into glucose?

A

Via phosphorylation of the C-1 of the non-reducing end

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29
Q

What is gluconeogenesis?

A

Anabolism of glucose via precursors

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30
Q

There are four precursors of glucose for gluconeogenesis

A

Lactate (into pyruvate); Glucogenic amino acids (alanine, aspartate); glycerol (from triacylglycerol); G3P from CO2 fixation

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31
Q

What is the glucose precursor that doesn’t come from a CHO origin?

A

G3P from CO2 fixation

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32
Q

Glycolysis and gluconeogenesis: there are 3 differentiations within enzymes, why?

A

Some reactions of glycolysis are too exergonic to be reversible, gluconeogenesis has its own exergonic enzymes.

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33
Q

What are the three differentiated enzymes of gluconeogenesis?

A

Hexokinase (from Glu to G6P) become G6Phosphatase (from G6P to glu)
F6P — F-1,6-P : phosphofructosekinase-1 becomes fructose-1,6-biphosphatase-1
Phosphoenol pyruvate — pyruvate: pyruvate kinase becomes a 2 step reaction of pyruvate carboxylase (via ATP breakdown) and PEP carboxylase (via GTP breakdown)

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34
Q

What is the end product of the reaction catalyzed by pyruvate carboxylase?

A

Oxaloacetate

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35
Q

What is the end product of the reaction catalyzed by PEP carboxylase?

A

Phosphoenolpyruvate

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36
Q

What are the by-product of PEP carboxylase?

A

CO2 and GDP

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37
Q

All intermediate of glycolysis can enter…

A

Gluconeogenesis!

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38
Q

What is the fate of pentose phosphate pathway?

A

Form Ribulose-5-phosphate + reducing power (NADP to NADPH)

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39
Q

Ribulose-5-phosphate can be converted into two products?

A

Via transketo/aldolase into G6P (substrate of the PPPathway) or ribose-5-phosphate

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40
Q

What are the roles of ribose-5-phosphate?

A

Precursor of DNA, nucleotides, RNA, coenzymes

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41
Q

NADPH of PPPathway can be oxidized to form…

A

Fatty acids, sterols, GSH

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42
Q

What is the fate of GSH?

A

Take out hydrogen peroxide to prevent oxidative damage on lipids, protein or DNA

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43
Q

How is GSH formed?

A

Oxidation of NADPH

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44
Q

Regulation of PPPathway by NADPH (which is a formed during the pathway)

A

NADPH inhibits G6PDH, so more G6P is available for glycolysis

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45
Q

Where does gluconeogenesis occur in mammals?

A

Liver

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46
Q

What is hexokinase isosyme?

A

The enzyme that catalyzes the entry of glu into glycolysis (into G6P)

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47
Q

How many hexokinase isosymes?

A

4

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48
Q

G6P (product of the hexokinase catalyzed reaction) is an inhibitor of…

A

Hexokinase isosymes I to III

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49
Q

Hexokinase IV is special: 2 reasons?

A

It can handle a much more bigger Glu concentration before being saturated + it is not inhibited by G6P

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50
Q

Why isn’t hexokinase IV inhibited by G6P?

A

It is inhibited by F6P (a further step)

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51
Q

Where can we find hexokinase IV?

A

Liver

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52
Q

How does the inhibition of hexokinase IV occur?

A

F6P competes with glu to bind to it and make it enter the nucleus, where its intrinsic regulatory protein inhibits it. When glucose concentration is high, it is released in the cytosol by porins

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53
Q

What is the associated enzyme of gluconeogenesis of the enzyme phosphofructokinase-1 in glycolysis (F6P to F-1,6-P)?

A

Fructobiphosphatase-1

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54
Q

What are the inhibitors of glycolysis among PKF-1 (2)?

A

ATP (no need for energy) + citrate (no need for TCA cycle)

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55
Q

What are the effectors of glycolysis among PKF-1 (2)?

A

ADP and AMP (need for energy)

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56
Q

What does inhibate FBPase-1 activity (2)?

A

AMP (no need for anabolism) + F-2,6-P

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57
Q

PFK-1 and FBPase-1 in the liver are originally regulated by?

A

F-2,6-P, which are regulated by PKK-2 and FBPase-2, which are regulated by insulin/glucagon

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58
Q

What does activate PKB-2 or FBPase-2?

A

Phosphorylation by ATP

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59
Q

Pyruvate kinase (last enzyme of glycolysis) is inactivated once…

A

Phosphorylated by ATP via PKA

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60
Q

What does activate pyruvate kinase?

A

Hydrolysis via PP

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61
Q

What is the role of pyruvate kinase?

A

From PEP to pyruvate

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62
Q

Pyruvate kinase is inhibited by all signs of abundant energy like… (3)

A

ATP, acetyl-CoA, fatty acids

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63
Q

What is an effector of pyruvate kinase?

A

F-1,6-P (presence of a lot of precursors)

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64
Q

Fate of pyruvate in the liver (2)

A

Converted to acetyl-CoA (for energy at the end) or converted to oxaloacetate (go to gluconeogenesis)

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65
Q

What does inhibits conversion of acetyl-CoA of pyruvate in the liver?

A

Acetyl-CoA, by inhibiting pyruvate dehydrogenase

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66
Q

Why does acetyl-CoA inhibits pyruvate dehydrogenase complex?

A

It means that liver has plenty of fatty acid to convert into it, so no spoiling of pyruvate for acetyl-CoA

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67
Q

Acetyl-CoA also activates which conversion of pyruvate in the liver?

A

Into oxaloacetate for gluconeogenesis

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68
Q

All we know about regulation of glucose metabolism are from 3 types of regulation

A

Allosteric effectors; covalent alterations (phosphorylation) or binding to regulatory protiens (hexokinase IV)

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69
Q

What extra type of regulation do we observe in glucose metabolism?

A

Transcriptional regulation of enzyme (regulation of number of enzymes in the cell, in opposite of activity regulation)

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70
Q

Transcriptional regulation is processed via…

A

Hormones

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71
Q

Transcriptional regulation can undergo via two activities

A

Dephosphorylation, which increases transcription of particular genes or phosphorylation, which reduces the transcription of some genes (phosphorylated substances are targeted by lysosymes)

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72
Q

Glycolysis occurs at ___ rates in tumor cells

A

Elevated

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73
Q

Why do tumor cells undergo extreme glycolysis (2)?

A

Anaerobic mechanism: less ATP/Glu = more Glu consumed

Glu transporters/enzymes are overproduced

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74
Q

What is the solution for tumor cells?

A

Enzymes can inhibit production of ATP via glycolysis (the cell die, and so do the tumor)

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75
Q

Why do phosphorylation/dephosphorylation affects transcription?

A

Phosphorylated substances cannot enter the nucleus

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76
Q

What is glycogen?

A

Glucose storage in large polymers

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77
Q

Where is glycogen primarly found?

A

In the liver (10% of its weight) + muscles (1-2% of their weight

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78
Q

How is the glycogen stock?

A

Into granules: a-rosettes

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79
Q

Why a-rosettes?

A

Less osmotic influence

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80
Q

What does contain an a-rosette?

A

20-40 B-particles

81
Q

What are B-particules?

A

55 000 glu into polymers with 2000 non-reducing ends

82
Q

How long does it take to deplete glycogen storage?

A

1 hour of intense physical activity for muscles + 12-24h of fasting in the liver

83
Q

What does an a-rosette granule contain except for glu?

A

Enzymes + machinery for glycogenolysis or glycogenesis

84
Q

To breakdown a glycogen molecule, what is the pathway?

A

Phosphorylation of a non-reducing end to obtain G1P + glycogen (n-1)

85
Q

What is the glycosidic bond?

A

a-(1-4)

86
Q

What is the formal name of G1P, once separated from its glycogen origin?

A

a-D-glucose-1-phosphate

87
Q

Why is the glycogenolysis not like a dietary hydrolysis?

A

Some energy remains in the C-1-Phosphate link

88
Q

Characterize the phosphorylation through glycogenolysis?

A

Substrate-level

89
Q

What is the enzyme of phosphorylation of glycogen?

A

Glycogen phosphorylase

90
Q

What is the essential cofactor of glycogen phosphorylase?

A

Pyridoxal phosphate

91
Q

What is the link of a branching?

A

a(1-6)

92
Q

Where does the glycogen phosphatase stop?

A

4 glucose away from an a(1-6) link

93
Q

How to breakdown a branch in 2 steps (enzymes as well)

A

1- transfer of three glucose to the nearby non-reducing end (transferase activity)
2- Release the 4th glu (the actual C-1 of the 1-6 link) (glucosidase activity)
Enzyme: debranching enzyme

94
Q

Once G1P is formed via glycogenolysis, what happens?

A

G1P is transformed into G6P to enter liver or muscles for Glu pahtways

95
Q

Formation of G6P: the enzyme

A

Phosphoglucomutase, which serine residue is phosphorylated

96
Q

Formation of G6P: the actual mechanism (2 steps)

A

G1P enters the enzyme and the serine residue phosphorylates its C-6 (G-1,6-P);
The C-6 phosphate binds to Ser, leading to G6P

97
Q

Why there is no G6Pase in other cells than liver?

A

Because the other cells would contribute to BG

98
Q

Where do we find G6Pase?

A

Embated in the ER membrane of hepatocytes

99
Q

Why is the G6Pase in the ER?

A

Because if not, it would stop glycolysis by turning G6P to glucose, which would inhibit glycolysis.. But if we do glycogenolysis, it is because we need energy from glucose

100
Q

What type of membrane protein is the G6Pase?

A

Integral

101
Q

How many helices does the G6Pase contain?

A

9

102
Q

How do glucose and Pi leave the ER after being dephosphorylated?

A

Transporters: T2 and T3

103
Q

Which transporter leads glucose to the bloodstream?

A

GLUT2

104
Q

What is glycogenesis?

A

Formation of glycogen from glu derivatives

105
Q

What is the glycogenesis formula?

A

G6P - G1P - UDP-glu - glycogen

106
Q

Who discovered sugar-nucleotide role?

A

Luis Leloir, 1953

107
Q

There are 4 benefits derivated from the formation of sugar-nucleotides

A

1- Their formation isn’t reversible
2- Nucleotide atoms do non-covalent links with enzymes (favorable)
3- Nucleotidyl groups are excellent leavers
4- Nucleotidyl tag is a recognition for cells that it isn’t part of the other sugars

108
Q

What is a sugar-nucleotide?

A

Glu-1,1-phosphate which is linked to C-6 of a ribose linked to a nucleotide

109
Q

How is the G6P transformed into G1P ?

A

Via phosphoglucomutase, which is reversible (with a G-1,6-P interstate)

110
Q

How is G1P transformed into UDP-Glu?

A

G1P (sugar-Pi) + nucleic acid (P-P-P-ribose-base) = Sugar-P-P-ribose-base + PPi (via NDP-sugar pyrophosphorylase

111
Q

What happens of PPi?

A

It is hydrolized via inorganic pyrophosphatase into 2 Pi

112
Q

Why is the conversion of G1P to UDP-Glu exergonic?

A

Favorable for polymerization

113
Q

Glycogenesis has two pathways

A

One for the initial short chains, one for the elongation

114
Q

How to generate initial short chain of glycogen? (2 steps and one enzyme)

A

1- UDP-Glu binds to Tyr residue of glycogenin (release of UDP) on its C-1 (glucosyltransferase intrinsic activity of glycogenin)
2- C-4 attacks the C-1 of another UDP-Glu via chain extending intrinsic activity of glycogenin (release of its UDP)

115
Q

How many glucose monomers does the glycogenin link together before glycogen synthase takes the relay?

A

8

116
Q

What is the glycogen synthase role?

A

Elongate glycogen chains of more than 8 glu by the non-reducing end

117
Q

What is the minimal number of glu in a glyco chain before branching?

A

11 (6 to 7 + 3 near a glycogen core, which will be the C-6 of the 1-6 branch)

118
Q

Branching pathway

A

6 to 7 glu chain is branched in C-1 to the C-6 of the glycogen core by the glycogen-branching enzyme

119
Q

What is the formal name of the glycogen-branching enzyme?

A

glycosyl-(4-6)-transferase

120
Q

What is a tier regarding glycogen?

A

A layer

121
Q

How many glycogen tiers in a B-particule?

A

12

122
Q

How many times is a glycogen chain branched?

A

2 times

123
Q

We know that stored glycogen cut down into glu via ___ is regulated by ___?

A

Glycogen phosphorylase; isosymes

124
Q

There are two types of glycogen phosphorylase

A

A for active (phosphorylated) and b (inactive and dephosphorylated)

125
Q

One inhibitor of glycogenolysis?

A

Glucose (no need for breaking down new ones)

126
Q

How do glucose inhibits glycogenolysis?

A

It binds allosterically to PP1, which dephosphorylate glycogen phosphorylase (inactive form)

127
Q

What is the name of the enzyme which catalyzes the activation of phosphorylase b into a?

A

Phosphorylase b kinase

128
Q

What does activates phosphorylase b kinase (2)?

A

Glucagon and epinephrine (Ca2+, AMP)

129
Q

What is the residue phosphorylated once phosphorylase a is activated?

A

Ser residues

130
Q

Insulin induces an ___ glycogenesis?

A

Increasing

131
Q

So insulin inhibits ___ ?

A

Glycogenolysis

132
Q

What is the enzyme that elongates glycogen chains?

A

Glycogen synthase

133
Q

Glycogen synthase can e found in two phases

A

Inactive (b - 3 phosphoserines near carboxyl terminus) or active (a - 3 -OH near carboxyl terminus)

134
Q

GSK3 stands for…

A

Glycogen synthase kinase III (inactivates it)

135
Q

Before GSK3 inactivates glycogen synthase, a primer reaction occur

A

Phosphorylation of glycogen synthase by ATP via casein kinase II

136
Q

PP1 stands for…

A

Phosphorylase a phosphatase

137
Q

PP1 role is to…

A

Dephosphorylate glycogen synthase (activating it)

138
Q

3 activators of PP1

A

Insulin; G6P; Glu

139
Q

An inhibitor of PP1

A

Glucagon or epinephrine (no time for storage)

140
Q

PP1 acts in…

A

The liver

141
Q

PP1 in the muscles?

A

No, but similar enzyme

142
Q

High blood glucose leads to…

A

No glycogen breakdown, more glycogen synthesis and more glycolysis

143
Q

Low blood glucose leads to…

A

More glycogen breakdown, less glycogen synthesis, less glycolysis

144
Q

Why glucagon leads to less glycolysis in the liver?

A

Because the glu is kept for the need of the other cells, like muscles’

145
Q

Three major stages of TCA cycle

A

1- Acetyl-CoA production
2- Acetyl-CoA oxidation into CO2
3- Reducing electron carriers

146
Q

NADH produces ___ ATP per pair of electrons

A

2,5

147
Q

What does oxidative decarboxylation stands for…

A

Release of CO2 via transfer of electrons

148
Q

Pyruvate is transformed into aceyl-CoA + CO2 via

A

Pyruvate dehydrogenase complex

149
Q

Pyruvate dehydrogenase complex has 5 coenzymes

A

CoA-SH, NAD, TPP, lipoate, FAD

150
Q

What is the role of coenzymes in PDH?

A

Electrons/acyl carriers

151
Q

CoA=?

A

Panthotenate

152
Q

NAD=?

A

Niacin

153
Q

TPP=?

A

Thiamine

154
Q

FAD=?

A

Riboflavin

155
Q

What is Acetyl-CoA?

A

An acetate + -S-CoA

156
Q

Describe acetyl-CoA

A

HS-B-mercaptoethylamine-(amide linkage)-panthotenic acid-3’-phosphoadenosine diphosphate

157
Q

PDH has 3 different enzymes present in several copies

A

1- pyruvate dehydrogenase (needs TPP)
2- Dihydrolipoyl transacetylase (needs lipoate)
3- Dihydrolipoyl dehydrogenase (FAD and NAD)

158
Q

What is so special with PDH E2?

A

It binds E1 to E3 + posses a lipoyl domain + acyltransferase activity

159
Q

From pyruvate to acetyl-CoA : 5 steps

From pyruvate to acetyl-CoA step 1

A

Substrate (pyruvate) binds to E1, release of CO2

160
Q

What is particular with From pyruvate to acetyl-CoA step 1?

A

Slowest step due to specificity

161
Q

From pyruvate to acetyl-CoA step 2

A

Lipoyl added to oxidized acetate

162
Q

From pyruvate to acetyl-CoA step 3

A

Transesterification (thioester bond to form Acetyl-CoA)

163
Q

From pyruvate to acetyl-CoA step 4

A

Oxidation of reduced lipoyllysine (FADH2)

164
Q

From pyruvate to acetyl-CoA step 5

A

FADH2 to NADH

165
Q

How many steps in TCA cycle?

A

8

166
Q

TCA cycle step 1

A

Condensation: Acetyl-CoA + oxaloacetate = citrate by release of CoA-SH via citrate synthase

167
Q

Is the TCA cycle step 1 favorable?

A

Yes, -32,2kJ/mol

168
Q

TCA cycle step 2

A

Hydration/dehydration: formation of isocitrate by removing and then adding water (formation of a double bond interstate) via aconitase

169
Q

Is TCA cycle step 2 favorable?

A

Nope, 13,3 kJ/mol

170
Q

TCA cycle step 3 (3 internal steps)

A

Oxidative decarboxylation: 3 internal steps
1- Reduction of NAD (oxidation = loose of water and creation of a double bond)
2-Decarboxylation via Mn2+
3- Rearrangement into a-ketoglutarate

171
Q

Enzyme in TCA cycle step 3

A

Isocitrate dehydrogenase

172
Q

TCA cycle step 4

A

Oxidative decarboxylation: a-ketoglutarate becomes succinyl-CoA , loose its carboxylic end, add a CoA, loose a CO2 and reduce NAD via a-ketoglutarate complex (like PDH)

173
Q

Is TCA cycle step 4 favorable?

A

Yes, -33,5kJ/mol

174
Q

Where is the energy in succinyl-CoA?

A

Thioester bond

175
Q

TCA cycle step 5

A

Substrate-level phosphorylation: removal of CoA + phosphorylation (by ADP/GDP) via succinyl-CoA synthetase, so now succinate

176
Q

Is transfering GTP into ATP favorable?

A

Neutral, 0 kJ/mol

177
Q

TCA cycle step 6

A

Dehydrogenation (oxidation): Succinate is oxidized to form fumarate (reduction of FAD) via succinate dehydrogenase

178
Q

How many ATP from FADH2?

A

1,5

179
Q

Dehydrogenation (step 6 of TCA) is inhibited by…

A

Malonate

180
Q

Where is the flavoprotein of succinate dehydrogenase in euk and pros?

A

Euk: mitochondrial membrane
Pros: plasma membrane

181
Q

Succinate dehydrogenase is formed of…

A

3 iron-sulfur clusters

182
Q

TCA cycle step 7

A

Hydration: Addition of water so fumarate becomes L-Malate via fumarase and a carbanion transition state

183
Q

Is TCA cycle step 7 favorable?

A

Yes, -3,8 kJ/mol

184
Q

What is so special about fumarase?

A

Highly specific about L, D, cis and trans

185
Q

TCA cycle step 8

A

Dehydrogenation: L-Malate is transformed into oxaloacetate by malate dehydrogenase, reduction of NAD

186
Q

Is dehydrogenation of L-malate favorable?

A

No, 29,7 kJ/mol, but more favorable as oxaloacetate is always taken off for citrate reaction

187
Q

Each turn of the TCA cycle produces…

A

3 NADH, 1 FADH2, 1 GTP/ATP, 2 CO2

188
Q

When is the NADH formed?

A

3 (oxidative decarboxylation), 4 (oxidative decarboxylation) and 8 (dehydrogenation of L-malate into oxaloacetate)

189
Q

When is FADH2 formed?

A

Dehydrogenation of succinate (step 6)

190
Q

When is GTP/ATP formed?

A

Substrate-level phosphorylation (when succinyl-CoA becomes succinate), step 5

191
Q

When is CO2 formed?

A

During the 2 oxidative decarboxylations (3 and 4) as isocitrate becomes a-ketoglutarate and when itself become succinyl-CoA

192
Q

What does amphibolic mean?

A

Can be catabolic or anabolic

193
Q

Why does TCA cycle is amphibolic?

A

Its by-products are precursors of biosynthetic pathways + it catabolizes acteyl-CoA

194
Q

Regulation of TCA cycle: what are the limiting steps?

A

3 NAD dependent steps (need for replenished NAD+), acetyl-CoA and oxaloacetate concentration as well

195
Q

What is a general activator of TCA cycle?

A

Ca2+

196
Q

Other general activators of TCA

A

AMP/ADP, CoA, NAD

197
Q

General inhibitors of TCA

A

ATP, acetyl-CoA, NADH, fatty acids, succinyl-CoA, citrate

198
Q

Where does the TCA cycle occur?

A

Euk: mitochondria
Pros: cytosol

199
Q

Where is the energy kept in TCA cycle?

A

Into electron transporters

Biochemistry 2 (3 decks)

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