Important enzymes Flashcards
What is the name of the molecule that acts as as small free energy store in muscle and which enzyme catalyses the reaction (forward and backward) of energy storage/release?
Store: creatine phosphate
Enzyme: creatine kinase
creatine + ATP –> creatine phosphate + ADP
What are the group of enzymes called that hydrolyse dietary polysaccharides into glucose, maltose and smaller polysaccharides (dextrins)?
glycosidase enzymes
What type of glycosidase enzyme is secreted in the mouth?
Salivary amylase
starch&glycogen –> glucose, maltose and smaller polysaccharides (dextrins)
What type of glycosidase enzyme is secreted into the duodenum?
Pancreatic amylase
starch&glycogen –> glucose, maltose and smaller polysaccharides (dextrins)
What are the names of the gyocosidase enzymes which break down dietary disaccharides (maltose and sucrose), maltose and dextrins in the duodenum and jejunum, releasing the monosaccharides glucose, fructose and galactose?
Lactase
Glycoamylase
sucrase/isomaltase
Where are the glycosidase enzymes lactase, glycoamylase and sucrase/isomaltase found in the gut?
They are large glycoprotein complexes that are attached to the brush border membranes of the epithelial cells of the duodenum and jejunum
What is the function of hexokinase?
Converts glucose + ATP –> glucose-6-phosphate + ADP in all tissues
What is the function of glucokinase
Converts glucose + ATP –> glucose-6-phosphate + ADP
in the liver
What is the role of glycerol kinase?
It is an enzyme found in the liver (not in adipose) which can catalyse:
glycerol + ATP –> glycerol phoshate + ADP
Which can then be used to synthesise triacylglycerol and be stored as be stored as fat
What is the role of myokinase in muscle?
It enables the high energy of hydrolysis phosphate bond in ADP to drive ATP synthesis under emergency conditions:
2ADP ATP + AMP
What is the role of phoshofructokinase (PFK)?
It is the most important rate-limiting step of glycolysis and catalyses:
fructose-6-phosphate + ADP –> fructose 1,6-bisphosphate + ADP
This commits glucose to glycolysis
What is the role of glucose 6-phosphate dehydrogenase?
It is the first enzyme (and key regulated enzyme) in the pentose phosphate pathway
Deficiency in which enzymes can cause galactosaemia?
galactokinase, galactose-1-P uridyl transferase or UDP-galactose 4’-epimerase
What is the name of the enzyme that is involved in the conversion of galactose to galacitol in galactosaemia?
Aldose reductase
What is the role of pyruvate dehydrogenase (PDH)?
Enzyme complex which irreversibly converts:
pyruvate + CoA + NAD+ –> acetyl-CoA + CO2 + NADH + H+
What is the role of isocitrate dehydrogenase?
It catalyses an early irreversible step of the citric acid cycle:
isocitrate + NAD+ –> alpha-ketoglutarate + NADH + CO2
What is the role of pyruvate carboxylase?
It catalyses the reaction of pyruvate into oxaloacetate to:
- Replace intermediates lost to biosynthesis from the TCA cycle
- A means of avoiding the irreversible step 10 of glycolysis in gluconeogenesis
What is the role of aldehyde dehydrogenase?
Catalyses the reaction:
acetaldehyde + NAD+ –> acetate + NADH
In alcohol metabolism
What is the role of fatty acyl CoA synthase?
It activates fatty acids by linking them to coenzyme A (creates a high energy bond):
fatty acid + CoA + ATP -> fatty acyl CoA + ADP + 2Pi
Glycerol from adipose tissue or from enterocytes (dietary TAGs) can be transported to the liver in the blood. In the liver it is activated by what enzyme into glycerol phosphate?
Glycerol kinase
What is the function of the enzyme HMG-CoA synthase?
Synthesises HMG-CoA from acetyl coA (and acetoacetyl CoA)
What is the function of the enzyme HMG-CoA lyase?
Converts HMG-CoA into acetoacetate which can then be converted into the other two ketone bodies (acetone and beta-hydroxybutyrate)
What is the function of the enzyme HMG-CoA reducatase?
Converts HMG-CoA into Mevalonate (the first step in the synthesis of cholesterol and therefore also steroid hormones)
What is the name of the enzyme that statins inhibit?
HMG-CoA reductase
