✅ BIOCHEM - Metabolic Pathways Flashcards
Example of an amphibolic pathway
Krebs
Where does glycolysis occur?
Cytoplasm
Substrate of glycolysis
Glucose
End product of glycolysis
Pyruvate or lactate
Rate limiting step of glycolysis
Fructose 6 phosphate -> fructose 1,6 bisphosphate
Enzyme: PFK-1
What type of glycolysis happens in cells with mitochondria and adequate O2?
Aerobic glycolysis
2 stages of glycolysis
Energy investment and energy generation
3 important steps in glycolysis
Step 1
Step 3
Step 10
NADH generating step in glycolysis
Glyceraldehyde 3 phosphate –> 1,3 bisphosphoglycerate
Enzyme: glyceraldehyde phosphate dehydrogenase
Which has a lower km and comsequently higher affinity?
Hexokinase or glucokinase?
Hexokinase
Glucokinase is present only in what type of tissues
Liver
Islet cells of pancreas
Hexokinase has a higher Vmax than glucokinase. True or false.
False
Glucokinase has a higher Vmax
Hexokinase is inhibited by
Glucose 6 phosphate
Glucokinase is inhibited by
Fructose 6 phosphate
Glucokinase liver activity is induced by
Insulin
Action of PFK-2
Converts fructose 6 phosphate to fructose 2,6 BP
Inhibitor of PFK-1
ATP and Citrate
Inhibitor of PFK 2
Starved state
Decrease insulin and inc glucagon
2 steps in glycolysis that produce ATP via substrate level phosphorylation
1,3 BPG to 3 PG
Enzyme: phosphoglycerate kinase
PEP to pyruvate
Enzyme: pyruvate kinase
2 outcomes of pyruvate in glycolysis
Can enter the citric acid cycle in aerobic glycolysis
Can be reduced to lactate in anerobic glycolysis
NADH produced in glycolysis cannot pass through thr mitochondrial membrane so it needs what?
Malate aspartate shuttle
Glycerol phosphate shuttle
Malate aspartate shuttle is used in what organs?
Liver kidney heart
Glycerol phosphate shuttle is used in which organs?
Skeletal muscle
Brain
Kinds of metabolic pathways
Anabolic
Catabolic
Amphibolic
NADH in the malate aspartate shuttle will yield how many ATP?
3
NADH in the glycerol phosphate shuttle will yield how many atp?
2
In what part of the cell can u find the ETC?
Inner mitochondrial membrane
What happens to pyruvate in anaerobic glycolysis?
Lactate dehydrogenase uses up NADH and converts pyruvate to lactate.
Anaerobic glycolysis strictly happens in which organs?
Cornea Lens Kidney medulla Wbc Rbc Testes
Enzyme responsible for conversion of 1,3 BPG to 2,3 BPG
Bisphosphoglycerate mutase
The Luebering-Rapoport pathway bypasses what enzyme
Phosphoglycerate kinase
Most common enzyme defect in glycolysis
Pyruvate kinase deficiency
Characteristic peripheral smear of G6PD deficiency
Heinz bodies
Most common precipitating history of G6PD
Infection
Pyruvate is converted to ethanol by
Pyruvate carboxylase (yeasts)
Pyruvate is converted to oxaloacetate by
Pyruvate carboxylase (gluconeogenesis)
What is the mechanism in arsenic poisoning?
Arsenic inhibits pyruvate dehydrogenase by binding to LIPOIC ACID
Pyruvate is converted to acetyl Coa by
Pyruvate dehydrogenase complex
Coenzymes of pyruvate dehydrogenase
Thiamine pyrophosphate FAD NAD+ Coenzyme A (Pantothenic Acid) Lipoic Acid
Pyruvate kinase deficiency usually manifests clinically as
Chronic hemolytic anemia
Products of conversion of pyruvate to acetyl coa
Acetyl coa
NADH
CO2
Most common cause of congenital lactic acidosis
Pyruvate dehydrogenase deficiency
Pattern of inheritance of pyruvate kinase deficiency
X-linked DOMINANT
Treatment for pyruvate dehydrogenase deficiency
Ketogenic diet
Rationale for ketogenic diet in pyruvate dehydrogenase deficiency
Increase lysine and leucine to bypass glycolysis
Mechanism of pyruvate dehydrogenase deficiency in chronic alcoholism.
Thiamine deficiency (acquired)
Where does the Kreb’s cycle occur?
Mitochondrial matrix
TCA occurs in the mitochondrial matrix except for which process?
Succinate to fumarate
Enzyme: succinate dehydrogenase
Rate limiting step in krebs
Isocitrate to alpha ketoglutarate
Enzyme: isocitrate dehydrogenase
Inhibitor of aconitase
Fluoroacetate (rat poison)
Inhibitor of alpha ketoglutarate dehydrogenase
Arsenite
Process in the TCA that produces GTP
Succinyl Coa to succinate
Enzyme: succinate thiokinase
Citrate delivers acetyl Coa to the cytoplasm for ______ via the _______
Fatty acid synthesis via the citrate shuttle
Succinyl coa in TCA is also involved in _______
Heme synthesis
Activation of ketone bodies in extrahepatic tissues
Malate in TCA is also use for
Gluconeogenesis
What is the main function of gluconeogenesis
Prevent hypoglycemia
What is the main function of the Cori cycle?
Conversion of lactate to glucose
Gluconeogenesis occurs in which organs
Liver 60% and kidney 10%
Prolonged fasting: kidney up to 40%
Gluconeogenesis occur in the
Cytoplasm and mitochondria
Rate limiting step in gluconeogenesis
Fructose 1,6 bisphosphate to fructose 6 phosphate
Enzyme: fructose 1,6 bisphosphatase
Energy expense in the cori cycle
4 ATPs
In glucogeonesis pyruvate is converted back to PEP through which of the following steps?
Pyruvate to OAA
Enzyme: Pyruvate carboxylase
OAA to PEP
Enzyme: PEP Carboxykinase
All carboxylases require _____ as a cofactor
Biotin
PEP carboxykinase require ____
GTP
Inhibitor of fructose 1,6 BP to fructose 6-P in gluconeogenesis
Fructose 2,6 BP and AMP
Energy expenditure in gluconeogenesis
4Atps
2 gtps
2 NADH to NAD+
Glucosuria occurs when venous blood glucose concentration exceeds
9.5-10 mmol/L (renal threshold)
180 g/dl
Redness when drinking is due to which enzyme
Acetaldehyde dehydrogenase
High amounts of NADH favors the ff reactions
Pyruvate to lactate
OAA to malate
DHAP to glycerol 3 phosphate
Insulin resistance in pregnancy is due to
Human placental lactogen
Hyperinsulinemia in pregnancy is due to
Increased estrogen levels
Major carbohydrate storage in animals
Glycogen
Processes that happen in the cytoplasm and mitochondria
Gluconeogenesis
Urea synthesis
Heme synthesis
Glycogen stores are used up after
12-18 hours
Glycogen is stored in which 2 organs?
Liver and muscle
Activated form of glucose
UDP-glucose
Synthesis of new glycogen molecules from alpha-d-glucose
Glycogenesis
Rate limiting step in glycogenesis
Elongation of glycogen chains
Enzyme: glycogen synthase
Enzyme involved in conversion of glucose 6 phosphate to glucose 1 phosphate
Phosphoglucomutase
Enzyme involved in the synthesis of UDP glucose
UDP glucose phosphorylase
Formation of branches in glycogen is mediated by what enzyme
Branching enzyme (amylo and transglucosidase)
Glycogen synthase is to glycogenesis
_____ is to glycogenolysis
Glycogen phosphorylase
Glycogen phosphorylase requires what coenzyme
Pyridoxal phosphate
Glycogen phosphorylase cannot cleave a 4 glucose residue before a branch called the
Limit dextrin
Rate limiting step in glycogenolysis
Removal of glucose using glycogen phosphorylase
Lysosomal degradation of glycogen happens with what enzyme
Alpha 1,4 glucosidase
Other name of alpha 1,4 glucosidase
Acid maltase
In glycogen phosphorylase, the active form is the phosphorylated or dephosphorylated?
Phosphorylated
Deficiency in acid maltase
Pompe disease
Deficiency in glucose 6 phosphatase
Von gierke disease
Deficiency in skeletal muscle glycogen phosphorylase
McArdle’s disease
Deficient in Andersen’s disease
Branching enzyme
Cori’s disease deficiency
Debranching enzyme
Deficient PFK
Tarui’s disease
Major dietary source of galactose
Lactose
Activated form of galactose
UDP galactose
Glucose 1 phosphate + UDP glucose forms _____ through which enzyme
UDP galactose and glucose 1 phosphate
Enzyme: galactose 1 P uridyl transferase
UDP galactose –> UDP galactose
Enzyme?
UPD hexose 4 epimerase
Main products of the pentose phosphate pathway
NADPH
Ribose 5 phosphate
Substrate of the pentose phosphate pathway
Gucose 6 phosphate
The pentose phosphate pathway is divided into the
Oxidative and non oxidative phase
Main product of the oxidative phase of the PPP
NADPH
Ribulose 5 P
Phase 1 of PPP is
Oxidative and irreversible
Key enzyme in oxidative phase of pentose phosphate pathway
G6PD
Key enzymes in non-oxidative phase of the pentose phosphate pathway
Transketolases
Transketolases require
Thiamine
Rate limiting step in the pentose phosphate pathway
Glucose 6 P to 6 phosphogluconate
Enzyme: G6PD
Reduced glutathione is recreated using
NADPH
Enzyme: glutathione REDUCTASE
Reduced glutathione sequestere harmful H2O2 using
Glutathione peroxidase
Drugs that precipitate G6PD deficiency
AAA
Antibiotics (sulfonamides, chloramphenicol)
Antimalarials (primaquine)
Antipyretics (except ASA and Paracetamol)
Chronic granulomatous disease is secondary to to deficiency in
NADPH OXIDASE
Chronic granulomatous disease is caused by what type of bacteria
Catalase positive
Sorbitol dehydrogenase is found in
The seminal vesicles only
Catalyzes sorbitol to fructose (main sperm energy source)
Glucose to sorbitol
What enzyme?
Aldose reductase
Mannise is an important component in
Glycoproteins
How is mannose 6 P used?
Mannose 6 P is converted to fructose 6 P by
Phosphomannose isomerase
Fructose 1 P to dihydroxyacetone phosphate
What enzyme?
Aldolase B
Fructose to fructose 1 P
Fructokinase or hexokinase