Carbohydrate Metabolism Flashcards
GLucose carrier protein in intestine and kidney
intestine - SGluT-1
kidney - SGluT-2
ORS
- treatment for diarrhea
- contains glucose and sodium
- allows absorption of sodium to replenish body sodium chloride levels and glucose to provide energy.
GluT1
- RBC, brain, kidney, colon, retina, placenta
- Glucose uptake in most of cells
GluT2
- Serosal surface of intestinal cells, liver, beta cells of pancreas
- Low affinity
GluT3
- Neurons, brain
- High affinity
GluT4
- Skeletal, heart muscle, adipose tissue
- Insulin-mediated
Glut5
- Small intestine, testis, sperms, kidney
- Fructose transporter
GluT7
- Liver endoplasmic reticulum
- Glucose from ER to cytoplasm
Glycolysis mnemonic
Goodness Gracious Friendly Fred Did Go By Picking Pumpkins to Prepare Pie
Enzymes of glycolysis mnemonic
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Significance of glycolysis
- takes place in all cells
- only source for erythrocytes
- anaerobic glycolysis useful in times of stress
- preliminary step to complete oxidation
- provides C skeletons for non essential AA and glycerol
- can be used for gluconeogenesis
Inhibitors of glycolysis
Arsenate, iodoacetate - inhibit G3PDH
Flouride - inhibits enolase by removing Mg+2 - used when collecting blood fro sugar estimation
Energy yield of glycolysis
Anaerobic - 2
Aerobic - 7
Complete oxidation of glucose - 32
Regulatory enzymes of glycolysis
Hexokinase
Phosphofructokinase (-) by ATP and citrate (+) by AMP
Pyruvate Kinase
Pasteur effect
Under aerobic conditions, glycolysis is inhibited. This inhibitory effect of oxygen on glycolysis is known as Pasteur effect.
Warburg hypothesis
- cancer cells utilize energy from glycolysis and they require less oxygen
- growing tumor cells produce lactic acid which is taken to liver for gluconeogenesis - uses ATP - loss of weight (cancer cachexia)
- inhibition of glycolysis depletes cancer cells of ATP leading to their death
- works for colon cancers and lymphoma
- useful in case of multi drug resistance
Significance of BPG
- 2,3 BPG binds to Hb and reduces affinity to O2 - easy unloading
- When pO2 is low, 2,3 BPG inc., favouring more unloading
- no ATP generated
Pyruvate Dehydrogenase Complex
(TLC? Fuck No) TPP Lipolic acid CoA FAD+ NAD+ - Pyruvate dehydrogenase - Dihydrolipoyl transacetylase - Dihydrolipoyl dehydrogenase
Importance of Pyruvate Dehydrogenase
- Completely irreversible
- Cannot synthesize glucose from fat
- 2.5 ATP
Precursors of gluconeogenesis
- Pyruvate/Lactate
- Glucogenic AA (Cori’s, Cahill’s cycle)
- Glycerol
- Propionate
Site of gluconeogenesis
Mainly liver, renal cortex
Partly cytoplasmic, partly mitochondrial
AA for oxaloacetate
- Aspartic acid
- Asparagine
AA for Pyruvate
- Alanine
- Cysteine
- Glycine
- Tryptophan
- Serine
AA for alpha KGA
- Arginine
- Glutamine
- Glutamate
- Histidine
- Proline
AA for succinyl CoA
- Valine
- Isoleucine
- Threonine
- Methionine
AA for fumarate
- Tyrosine
- Phenylalanine
Significance of gluconeogenesis
- Only by liver as G6Pase is only in liver
- Maintains blood sugar level during starvation
- Uses 6 ATP
GLycerol to glucose
TAG-
Glycerol -
Glycerol 3 phosphate -
DHAP
Propionate to glucose
Odd chain fatty acids -
Propionyl CoA -
Methylmalonyl CoA -
Succinyl CoA
Regulation of gluconeogenesis
Pyruvate carboxylase (+) Acetyl CoA F 1,6 Bisphosphotase (+) Citrate (-) AMP
Glycogenolysis enzymes Mnemonic
Powerful Thor Gave Powerful Pennies Proudly Phosphorylase Transferase Glucosidase Phosphorylase Phosphoglyceromutase Phosphotase
Energetics of glycogenolysis
3 ATP released for 1 glucose residue
Glycogenesis enzymes mnemonic
Grey Psychopaths Predated Sluts Tactfully Glucokinase Phosphoglyceromutase UDP glucose Pyrophosphorylase Synthase Transglycosylase
Regulation of glycogenesis
- Reciprocal regulation of syn. and degradation
- Covalent modification of glycogen phosphorylase(+ phosphorylation) and glycogen synthase (+ dephosphorylation)
- Act through cAMP
Liver glycogen phosphorylase
- active on phosphorylation
- inhibited by ATP and glucose-6-phosphate
Types of glycogen storage diseases
Viagra Pills Cause A Major Hardon, Ted 1- Von Gierke's 2- Pompe's 3- Cori's 4- Anderson's 5- McArdle's 6- Her's 7- Tarui
HMP shunt intermediates mnemonic
Graceful and Gorgeous Gabriel Refused Refined Xylophones So Gideon Enslaved Frozen geese Forcibly Glucose 6 P 6 phosphoGulunolactone 6 phosphoGluconate Ribulose 5 ph Ribose 5 ph Xylulose 5 ph Sedoheptulose 7 ph Glyceraldehyde 3 ph Erythrose 4 ph Fructose 6 ph Glyceraldehyde 3 ph Fructose 6 ph
Regulation of HMP shunt
- mainly regulated by level of NADP+
- G6PDH is rate limiting, inhibited by NADPH
- non oxidative phase controlled by level of pentoses
(+) Insulin
Importance of HMP shunt
- To produce NADPH and pentose phosphates for
i. Reductive biosynthesis- fatty acids, cholesterol, steroid hormones
ii. Free radical scavenging
iii. Maintain RBC membrane integrity by keeping GSH in reduced state
iv. Prevention of met-hemoglobin formation
v. Detoxification by hydroxylation
vi. Maintain the transparency of lens
vii. Bactericidal activity of macrophages - Ribose-5-phosphate is required for nucleic acid synthesis
HMP shunt operates in
- Liver
- Adipose tissue
- Adrenal cortex
- Mammary glands
- Testes and ovaries
- RBCs
- Lens of eye
Free radical scavenging
- free radicals damage DNA, protein etc
- removed by enzyme systems containing superoxide dimutase, peroxidase, glutathione reductase
- reduced glutathione generated with help of NADPH
Functions of UDP glucuronic acid
It is active form of glucuronic acid
- conjugation of bilirubin
- conjugation of steroids
- conjugation of drugs to make them water soluble and easily excretable
- detoxification of environmental toxins and carcinogens
- precursor for glycosaminoglycan synthesis
Where is aldose reductase present and absent?
What does it do?
Absent - liver
Present -
Retina, Eye lens, Kidney, Placenta, Peripheral nerve cells
It converts glucose to sorbitol producing 1 NADP+
Where is sorbitol dehydrogenase found? What does it do?
Seminal vesicles, ovaries, spleen
Converts sorbitol to fructose using 1 NAD+
Why can and why cannot fructose be used to treat Diabetes Mellitus
- More easily absorbed than glucose as it is not controlled by insulin
- leads to inc. in fatty acid synthesis, raised serum triglycerides, high LDL
- atherogenic
- phosphorylation of fructose also uses ATP leading to low Pi
- this removes inhibition on adenosine deaminase
- more uric acid produced
