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20 Cards in this Set

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  • Back
What do inherited gentic defects in metabolic enzymes give rise to?
They can give rise to human diseases that are caused by decreased levels of enzyme or altered enzyme activities
What does complete loss of an enzyme usually cause?
Embryonic lethality
Two metabolic diseases are those caused by enzyme deficiencies of what?
Lactate dehydrogenase and fructose-1P aldolase
What are irreversible reactions in metabolic pathways called?
They are called rate-limiting steps
Why are irreversible reactions called rate-limiting steps?
They are called rate-limiting steps because the level of enzyme activity can be low even when substrate levels are high.
What do rate-limiting enzymes in nmetabolic pathways serve as?
They serve as regulated "valves" that are opened or closed n response to cellular conditions.
What is glucokinase a molecular sensor of?
It is a molecular sensor of high glucose levels
Give a description of hexokinase 1
It has a high affinity for substrate. It is expressed in all tissues. It phosphorylates a variety of hexose sugars. It is inhibited by Glucose-6-P
Give a description of hexokinase IV
It is also known as glucokinase. It has a low affinity for substrate. It is highly specific for glucose. It is expressed primarily in liver and pancreatic cells and is not inhibited by glucose-6-P
What is the role of glucokinase in liver cells?
The role of glucokinase in liver cells is to trap the extra glucose that is available from the diet so that it can be stored as glycogen for an energy source later
What does phosphofructokinase-1 (PFK-1) do?
It catalyzes reaction 3 in glycolysis
What does phosphofructokinase-2 (PFK-2) do?
It is a bifunctional enzyme that catalyzes the synthesis of fructose-2,6-bisophosphate (F-2,6-BP), a potent allosteric regulator of PFK-1 activity
What happens first under aerobic conditions to pyruvate?
The majority of pyruvate is metabolized in te mitochondria to acetyl CoA, and ultimately to CO2 and H2O
What occurs under anaerobic conditions to pyruvate?
Pyruvate is converted to lactate (the ionized form of lactic acid) by the enzyme lactate dehydrogenase
What happens in microorganisms such as yeast to pyruvate?
They utilize alcoholic fermentation to convert pyruvate to CO2 and ethanol using the enzymes pyruvate decarboxylase and alcohol dehydrogenase
What occurs to patients with lactate dehydrogenase deficiency (LDHA)?
They cannot maintain moderate levels of exercise due to an inability to utilize glycolysis to produce ATP needed for muscle contraction under anaerobic conditions.
What occurs when lactate dehydrogenase is not fully functional?
NADH oxidation does not occur at a high enough rate to sustain glycolysis
What does this ultimately cause?
This causes muscle cells to quickly run out of ATP leading to fatigue and even muscle damage if anaerobic conditions persist
How does substrate availability and enzyme activity levels control glycolytic flux?
Substrate availability and enzyme activity levels control glycolytic flux by regulating reaction rates
Why is muscle lactate dehydrogenase activity required for short bursts of intense exercise?
Cytosolic NAD+ is required to maintain glycolytic flux through the glyceraldehyde-3-P dehydrogenase reaction