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Biochemistry > Carbohydrates Metabolism (Part 1) > Flashcards

Carbohydrates Metabolism (Part 1) Flashcards

1
Q

Carbohydrates …. of food

A

2/3 - (65-70%)

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2
Q

Monosaccharide

A

Glucose
Ribose
Fructose

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3
Q

Disaccharide

A

Lactose (Milk)
Sucrose (White sugar)
Maltose (Barley)

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4
Q

Polysaccharide

A

Starch (Bread - Rice)
Glycogen (Liver - meat)
Cellulose

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5
Q

Metabolism

A

All the chemical reactions that occur to the food stuff inside living cells

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6
Q

These substances is not metabolized

A

Vitamins , Minerals

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7
Q

Metabolism divide to

A

Anabolism :
- Required energy provided by cleavage of ATP into ADP or AMP
- For synthesis of PTN , CHO , lipids or their derivatives

Catabolism :
Involve oxidative processes that release energy (ATP)

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8
Q

CHO must be converted into …. to be absorbed

A

Monosaccharide

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9
Q

….. are chief CHO in our food

A

Starch, glycogen, sucrose, lactose, and cellulose

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10
Q

CHO hydrolyzed to ….. in GIT before they are absorbed

A

hexose sugar (glucose, fructose, and galactose)

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11
Q

Mouth enzymes

A

Salivary α – amylase (Ptylin)

pH : 6.7
Activation : Cl-

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12
Q

Stomach pH

A

2

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13
Q

Digestion action in mouth

A

Amylase hydrolyzes α-(1,4) glycosidic linkage

Starch , Glycogen , dextrin → Maltose , Glucose

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14
Q

Small intestine enzymes

A

Pancreatic α-amylase

pH : 7.1
Activation : Cl-

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15
Q

Digestion action in stomach

A

Stop due to its acidity inactivate salivary α – amylase

HCL → Hydrolyze dietary sucrose to glucose and
Fructose

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16
Q

Digestion action in small intestine

A
  • Pancreatic α-amylase
    hydrolyzes α-(1,4) glycosidic linkage
  • Intestinal enzymes (Disaccharidases)
    Lactase : Lactose → Glucose + Galactose
    Maltase : Maltose → Glucose + Glucose
    Sucrase : Sucrose → Glucose + Fructose
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17
Q

Intestinal enzymes

A

Disaccharidases

Lactase : Lactose → Glucose + Galactose
Maltase : Maltose → Glucose + Glucose
Sucrase : Sucrose → Glucose + Fructose

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18
Q

Lactose Intolerance

A

Inability to digest lactose due to deficiency of lactase enzyme which remain in intestines and get fermented by bacteria (Treated by milk lactose free)

May be congenital (Rare – Birthed with) or acquired (Common – Adult)

Symptoms:
1. Bloating , Abdominal cramps and pain due to ↑ CO2 produced by bacterial fermentation
2. Diarrhea due to increasing osmotic pressure

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19
Q

Cellulose digestion in human

A

There is no β (1-4) glucosidase in human that can digest β (1-4) glycosidic bond between glucose molecules in cellulose

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20
Q

Congenital Lactose Intolerance

A

Complete absence or deficiency of enzyme

The child develop intolerance to lactose immediately after birth

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21
Q

Passive diffusion

A

Concentration gradient : Down the concentration gradient from high to low
Energy required : None
Protein carrier : Not required
Speed : Slowest

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22
Q

Active transport

A

Concentration gradient : Against concentration
gradient from low to high
Energy required : Required ATP
Protein carrier : Required
Speed : Fastest
E.g. : Glucose

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23
Q

Glucose transporter

A

Na+ dependent transporter
Na+ independent transporter

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24
Q

Fate of the absorbed sugar

A
  1. Glucose is delivered to liver
  2. All other monosaccharides are converted to glucose in the liver
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25
Utilization by tissues
1. Oxidation 2. Storage 3. Conversion to substances
26
Complete oxidation of glucose
CO2 + H2O + Energy
27
Oxidation Major pathways
Glycolysis , Krebs’ cycle and oxidative decarboxylation
28
Oxidation Minor pathways
Hexose monophosphate shunt and Uronic acid pathway
29
Sugar Storage
* Glycogen in the liver and muscle (Limited) * Triacylglycerol in the adipose tissue
30
Conversion to substances
Galactose → Lactose , glycolipids & mucopolysaccharides synthesis Fructose → Sperm sugar Others : Amino sugar - Ripose - Fatty acid - Non essential a.a
31
Excretion of glucose in urine
Normally urine contains no glucose because the kidneys can reabsorb all the filtered glucose from the tubular fluid back into the bloodstream When glucose blood level exceeds a certain limit (180 mg/dl) , it will pass to urine causing glucosuria Normal range = 60 – 110 mg/dl
32
Glycolysis
Oxidation of glucose or glycogen to give 1. Pyruvate (in O2 presence) 2. Lactate (in O2 absence)
33
Glycolysis site
Cytoplasm of all tissue cells (Cytosol)
34
Glycolysis has a physiological importance in ...
RBCS and Muscles during exercise
35
Uptake of Glucose by Cells
- Glucose is freely permeable to Liver cells - Intestinal mucosa and kidney tubules, glucose is taken up by active transport - Skeletal muscle, cardiac muscle, insulin facilitates the uptake of glucose
36
Glucose is freely permeable to ...
Liver cells
37
Glucose is actively absorbed in ....
Intestinal mucosa and kidney tubules
38
The conversion of : Glucose → Glucose 6 Phosphate Needs ... enzyme
Glucokinase or Hexokinase
39
The conversion of : Glucose 6 Phosphate → Fructose 6 Phosphate Needs ... enzyme
Phosphoglucose isomerase
40
The conversion of : Fructose 6 Phosphate → Fructose 1,6 Bisphosphate Needs ... enzyme
Phosphofructokinase "PFK-1"
41
The conversion of : Fructose 1,6 Bisphosphate → DHA-P , G3P Needs ... enzyme
Aldolase
42
The conversion of : DHA-P → G3P Needs ... enzyme
Triose phoshateisomerase
43
The conversion of : G3P → 1,3 Bisphosphoglycerate Needs ... enzyme
G3P Dehydrogenase
44
The conversion of : 1,3 Bisphosphoglycerate → 3 Phosphoglycerate Needs ... enzyme
Kinase
45
The conversion of : 3 Phosphoglycerate → 2 Phosphoglycerate Needs ... enzyme
Mutase
46
The conversion of : 2 Phosphoglycerate → Phosphoenolpyruvate Needs ... enzyme
Enolase
47
The conversion of : Phosphoenolpyruvate → Pyruvate " Pyruvic acid" Needs ... enzyme
Pyruvates
48
Pyruvate " Pyruvic acid" in aerobic conditions
Oxidation of 2NADH+H in mitochondria
49
Pyruvate " Pyruvic acid" in anaerobic conditions or RBCs
Remains within the cytoplasm and converts to lactate by the action of lactate dehydrogenase
50
Fate of Blood lactate
1. Conversion to pyruvate by LDH 2. Lactate in liver can be converted to glucose or glycogen 3. Lactate may be accumulated in muscle causing muscle fatigue 4. Excretion in urine or sweat
51
Hyperlactatemia
↑ blood lactate above normal level (5mg/dl) Causes : physiological (severe muscular exercise) or pathological (anoxia) Symptoms : Lacticacidosis , Coma
52
Glycolysis Importance
Energy production 1. Under aerobic condition; glycolysis produces 8 ATP 2. Under anaerobic condition; glycolysis produces 2 ATP Synthetic function DHA-P can be converted to glycerol-3-phosphate for synthesis of Triacylglycerol and phospholipids Importance of glycolysis in RBCs 1. Energy production: the only pathway that provide RBCs with ATP 2. Provides NADH for reduction of metHb (Hb + Fe+3) → Hb 3. 1,3 Bisphosphoglycerate is converted to 2,3 Bisphosphoglycerate which help release of 02 from Hb at tissues level
53
.... can be converted to glycerol-3-phosphate for synthesis of Triacylglycerol and phospholipids
DHA-P
54
DHA-P can be converted to .... for synthesis of Triacylglycerol and phospholipids
glycerol-3-phosphate
55
DHA-P can be converted to glycerol-3-phosphate for synthesis of ....
Triacylglycerol and phospholipids
56
Triacylglycerol and phospholipids synthesis needs .. enzyme
Triosephoshate isomerase
57
Glycolysis regulation
Regulated by 3 irreversible enzymes : 1. Glucokinase or Hexokinase 2. Pyruvate kinase 3. PKF1 (main)
58
PFK-1 (Main)
Activated by → AMP / ADP / F-6-P Inhibited by → ATP
59
Glucokinase
Site : Liver only Substrate : Glucose only Affinity : Few (High Glucose Conc.) Act : After meal Activators : Glucose Inhibition : Fructose – 6 - p Insulin : Increase activity Glucagon : Decrease activity
60
Hexokinase
Site : All tissues include liver Substrate : Hexose but glucose mainly Affinity : High (Low Glucose Conc.) Act : Between meals Activators : Glucose and other sugars Inhibition : Glucose – 6 - p Insulin : No effect Glucagon : No effect
61
Primary Acquired lactase deficiency
occur in adults due to defect in translation of RNA into enzyme
62
Secondary Acquired lactase deficiency
occur at any age due to GIT disease or medication Gastroenteritis due to rotavirus Intestinal parasite as giardia Chemotherapy
63
CHO Site of absorption
- Duodenum, upper jejunum (Mainly) - Very small amount is absorbed in the stomach or large intestine
64
Facilitated diffusion
Concentration gradient :Down the concentration gradient from high to low Energy required : No Protein carrier : Required Speed : Fast E.g. : Fructose
65
Na+ dependent transporter
SGLT Apical / Brush border
66
Na+ independent transporter
GLUT Base Border to transport to blood
67
SGLUT 1
intestine and kidney
68
SGLUT 2
Kidney to reabsorb
69
SGLUT has 2 binding site
* One for glucose and the other for Na * Na binding is important because after binding conformational changes occur in transporter so that glucose can bind * Na is transported & down the concentration gradient while glucose transported & against concentration gradient * ATP is required by Na-K ATPase pump to expel Na out
70
... are down the concentration gradient from high to low
Na and glucose
71
Why Expulsion of sodium is important ?
1. Na is osmotically active causing osmotic flow to the cells leading to osmolysis 2. Na concentration must be kept low to maintain downward gradient 3. Na is inhibitory to many enzyme action
72
GLUT 1
All cells with predominant in RBCs Greatly affinity to glucose
73
GLUT 2
In intestine , liver and pancreas Transport glucose and fructose
74
GLUT 3
All body mainly brain cells independent
75
GLUT 4
Adipose tissue , Sk Muscle , Cardiac Muscle Only transporter that under the effect of Insulin (High glucose level)
76
GLUT 5
Luminal surface of intestine , Testicals , seminal vesicle Greatly affinity to Fructose And low to glucose
77
GLUT 6
Has no role uptake of glucose
78
GLUT 7
Surface of Endoplasmic reticulum
79
Factors affecting rate or monosaccharide absorption
* The absorption is faster through intact mucosa * The absorption is decreased if there are inflammatory or injurious conditions in mucosa * Thyroid and mineralocorticoid increase glucose absorption * Vitamins B6, B12, B5 , folic acid required for glucose absorption * With advanced age, glucose absorption declines * Insulin has no role in absorption of glucose
80
Cancer cells express high levels of .....
GLUT 1 to initialize more glucose which used as source of energy for highly divided cells
81
Normal blood glucose level is ....
70-110 mg/dl

Biochemistry (6 decks)

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