Glucose: Tolerance curves, Absorption, Transporters, Storage and Synthesis Flashcards
(110 cards)
1
Q
How much energy is there in one molecule of ATP?
A
30.5kJ/mol
2
Q
How much energy is there in one molecule of NADH?
A
220kJ/mol
3
Q
What does metabolism link?
A
Breakdown (catabolism) of food to the synthesis of proteins and other biomolecules (anabolism)
4
Q
What does anaerobic metabolism of glucose produce?
A
2ATP
5
Q
What does aerobic metabolism of glucose produce?
A
32ATP
6
Q
What is the fasting reserve of glucose?
A
Glycogen
7
Q
What are the 2 major families of sugar?
A
Aldose and ketose
8
Q
Which family do glucose and galactose belong to?
A
Aldose
9
Q
Which family does fructose belong to?
A
Ketose
10
Q
What are the 3 important GLUT transporters?
A
GLUT-1, GLUT-2 and GLUT-4
11
Q
Where is GLUT-1 found?
A
Ubiquitous
12
Q
Where is GLUT-2 found?
A
Liver and pancreas - important for responding to rising glucose
13
Q
Where is GLUT-4 found?
A
In muscle and adipose tissue - key to diabetic rise in glucose because it is insulin responsive
14
Q
What does anaerobic glycolysis produce?
A
Lactate
15
Q
Why are red blood cells obligated to follow anaerobic metabolism?
A
Because they don’t have mitochondria
16
Q
What does gluconeogenesis generate?
A
New glucose from glycerol or amino acids, never from fat
17
Q
Which sugar correlates with increased obesity?
A
High fructose in processed food
18
Q
What is ATP?
A
Adenosine triphosphate
19
Q
What are enzymes using ATP called?
A
ATPases
20
Q
What is the ∆G’˚ for ATP hydrolysis to ADP?
A
-30.5kJ/mol
21
Q
What is always the cellular substrate for ATP?
A
Mg-ATP
22
Q
What role does Mg2+ play in free ATP?
A
Removes charge propulsion between two O- atoms.
23
Q
What is ∆G’˚ for PEP+ADP→pyruvate+ATP?
A
-31.4kJ/mol
24
Q
What is ∆G’˚ for ADP+Pi→ATP+H2O?
A
+30.5kJ/mol
25
What is the ∆G’˚ for NADH oxidation to NAD-?
-220kJ/mol
26
What is the ∆E for NADH oxidation relative to the H-electrode?
-0.32V
27
What is the storage molecule for most of the electrons in metabolism?
NADH
28
What are the 3 stages to metabolism?
Stage 1: Acetyl-CoA production (Glycolysis)
Stage 2: Acetyl-CoA oxidation (Citric acid cycle)
Stage 3: Electron transfer and oxidative phosphorylation (Electron transfer chain)
29
What are glycosides?
Part sugar e.g. glycoprotein and cardiac glycosides
30
What do mono- and di-saccharides end in?
“‐ose”. e.g. glucose, maltose
31
How many carbons do monosaccharides have?
3‐7
32
Which configuration do Fischer projections of aldoses have?
D configuration
33
Which family do aldehyde sugars belong to?
Aldoses
34
What type of a sugar is glucose?
Aldehyde
35
What underlies circulatory problems leading to limb amputation and blindness in diabetes?
Glycation.
All amino groups, mostly in protein, are prone to this glycation.
Glycated blood vessels become brittle and prone to clots that stop the circulation.
Circulatory problems in diabetes can cause blindness, or gangrene with loss of feet.
36
What is the glycation reaction illustrated by?
Largely benign formation of haemoglobin‐A1C that acts as a diagnostic indicator of uncontrolled high glucose levels in blood.
The b‐subunits of Hb are particularly prone to glycation of the N‐termini.
A similar use is made of the fructosamine derivatives of serum albumin (half life 20 days).
37
Where are GLUT-4 transporters found?
Muscle
Fat
Heart
38
What does the insulin signal do?
Stimulates GLUT-4 to membrane
39
Where is Glucose-6-P found? What is its function?
Only liver and kidney.
Releases free glucose.
40
What is the intermediate between Glycogen and Glucose-6-P?
Glucose-1-P
41
Does glycolysis produce ATP aerobically or anaerobically?
Anaerobically
42
In which structures is glycolysis essential?
Red cells
Lens
Retina
43
What are the 2 phases to glycolysis?
Preparatory
Payoff
44
What is the reaction equation for glycolysis?
Glucose + 2NAD+ + 2ADP + 2Pi → 2pyruvate + 2NADH + 2ATP + 2H2O
45
What percentage of the 2.84MJ in a mole of glucose is captured as ATP?
2.1% (61kJ)
46
Why do anaerobes consume much more glucose than aerobes?
Because they only receive 2ATP per molecule of glucose during anaerobic glycolysis.
47
How many molecules of ATP per glucose do aerobes produce in glycolysis?
32
48
What are the net products of glycolysis?
2 pyruvate
2ATP
2NADH
49
Where in the cell does glycolysis occur?
In the cytosol
50
What happens to every glycolysis metabolite except pyruvate?
Phosphorylated
51
What prevents leakage of glycolysis metabolites through the cell membrane?
Negative charge
52
How many ATPs are consumed in the preparatory phase of glycoloysis?
2
53
What is created in the payoff phase of glycolysis?
4 Created in payoff phase
2 created in total
54
What is the first step of glycolysis?
Conversion of glucose to glucose-6-phosphate by hexokinase
55
What do the kinases do?
Transfer phosphate from ATP
56
What is the structure of hexokinase?
Hexokinase: two domain enzyme exhibiting induced fit
Glucose binds to one domain, ATP to other
57
What is the ∆G’˚ for conversion of glucose to glucose-6-phosphate?
-16.7kJ/mol
58
What is the end product of glycolysis?
2 pyruvate
59
Which two compounds have sufficiently high free energy of hydrolysis to be coupled to substrate level ATP synthesis?
1,3-BPG
PEP
60
Which enzyme catalyses the second step of glycolysis?
Phosphohexose isomerase
61
What happens in the second step of glycolysis?
Glucose-6-Phosphate converted to fructose-6-phosphate
62
How does formation of the G-6P isomer F-6P proceed?
Via the linear conformatin of glucose-6-P, i.e. glucose-6-P must be in its linear conformation to be converted to fructose-6-phosphate
63
Is step 2 of glycolysis regulated?
No
64
Is the second step of glycolysis (G-6P to F-6P) a regulated step?
No
65
What is the third step of glycolysis?
Conversion of fructose-6-phosphate to fructose-1,6-bisphosphate
66
What catalyses step 3 of glycolysis?
Phosphofructokinase-1
67
When is phosphofructokinase active?
When cells have low ATP concentration
68
Why is the third step of glycolysis an efficient step to regulate?
Because the high negative free energy change makes it functionally irreversible and commits metabolism to the glycolytic pathway.
69
Which enzyme catalyses the reverse of step 3 in gluconeogenesis?
Fructose-1,6-bisphosphatase
70
What does anaerobic metabolism in humans end in?
Lactate
71
What does anaerobic glycolysis depend on?
Regenerating NAD+
72
What converts pyruvate to lactate?
Lactate dehydrogenase
73
What is generated as a product of anaerobic metabolism?
Lactate (lactic acid)
74
Why is pyruvate reduced to lactate in anaerobic metabolism?
Because lactate is more energy rich than pyruvate
75
What effect does creatine have?
Increases muscle stores of phosphocreatine, increasing the muscle’s ability to resynthesize ATP from ADP.
Phosphocreatine becomes ATP + creatine.
76
What happens to blood lactate levels during vigorous exercise?
Increase
77
What does the retina rely mostly on for ATP production?
Anaerobic glycolysis
There are few blood vessels in the fovea
78
What do red blood cells rely on for ATP production? Why?
Anaerobic glycolysis.
Because mitochondria are lost during maturation
79
What contributes to the background level of lactate in the blood?
Anaerobic glycolysis in red blood cells
80
How many grams of glucose does the brain need per day?
120g
81
Which carbon sources can be used in gluconeogenesis?
Lactate
Amino acids
Glycerol
82
Where does lactate used in gluconeogenesis come from?
After exercise or anaerobic tissue (e.g. RBCs)
83
Where do the amino acids used in gluconeogenesis come from?
Protein breakdown
84
Where does glycerol used in gluconeogenesis come from?
Mobilisation of TAGs in adipose tissue
85
What is the major carbon source for gluconeogenesis when starvation continues for several days?
Glycerol from mobilisation of TAGs in adipose tissue
86
How does glycerol enter into gluconeogenesis if adipose issue lacks glycerol kinase?
It circulates to the liver to enter gluconeogenesis
87
Are fatty acids glucogenic?
No, they are ketogenic
88
What is the only difference between gluconeogenesis and glycolysis?
The 3 bypass reactions and the direction of the reaction.
89
What does aerobic metabolism produce?
CO2 + H2O and 32 ATP per glucose
90
What do fatty acids never make?
Glucose
91
What is galactose?
4-epimer of glucose
92
Where is galactose found?
Sphingolipid membrane strctures
Saccharide tags
Structural polymers
Lactose
93
What is lactose?
β1-4 linked disaccharide of glaactose and glucose
94
How is lactose created?
By an epimerase enzymes which needs energy supplied by UTP
95
What does utilisation of lactose require?
Epimerisation of the galactose back to glucose
96
What is galactosaemia?
Failure of epimerisation of galactose back to glucose
97
What breaks lactose into 4-epimer galactose and glucose?
Lactase in the inestinal villi
98
What happens if a galatosaemic infant is given milk?
Unmetabolised milk sugars build up and there's damage to the liver, eyes, kidneys and brain
99
What is galactosaemia a failure of?
Enzyme(s) in the galactose → glucose pathway
100
Which side of the Fischer projections to D-series ketoses have their OHs on?
Right hand side
101
When is a sugar a D-sugar?
When the highest number carbon with a chiral -OH is D-
102
What are ketose sugars?
Ketones
103
What is fructose?
The ketose form of glucose
104
What is the sweetest of the common sugars?
Fructose
105
What is fructose a breakdown product of?
Glycolysis
D-Glucose → a-D-fructofuranose
Catalysed by gluose isomerase
106
How is fructose metabolised?
Liver forms fructose‐1‐phosphate which then undergoes aldolase splitting
107
What is fructose half of?
Sucrose
108
How is fructose implicated in obesity?
Does not elicit insulin release from the pancreas.
Fructose fails to increase the production of leptin from fat cells.
Both insulin and leptin act as signals to the brain to turn down the appetite and control body weight.
fructose does not appear to suppress the production of ghrelin, a hormone that increases hunger and appetite
109
Which enzyme is used by industry to create fructose?
Isomerase
110
What is aspartame?
Aspartyl-phenylalanine methyl ester
200x sweeter than sucrose
