82 Questions
What is the primary function of gluconeogenesis in animals?
To maintain adequate glucose levels in the blood
Which organs are responsible for gluconeogenesis in animals?
Liver and kidney
What is the biggest consumer of glucose in the body?
Brain
During which periods is gluconeogenesis particularly important?
Periods of fasting or starvation
Which organ can use ketone bodies as an alternative fuel source?
Brain
What is the role of oxaloacetate in gluconeogenesis?
Serves as an intermediate to synthesize phosphoenolpyruvate
Which compound is synthesized from fructose-1,6-bisphosphate during gluconeogenesis?
Fructose-6-phosphate
What is the final product of gluconeogenesis?
Glucose
Why is the reciprocal regulation between glycolysis and gluconeogenesis emphasized?
To maintain appropriate glucose levels based on metabolic needs
What is the fate of glycerol released from adipose tissue?
It is taken up by the liver
Which molecule is glycerol converted to in the liver?
Dihydroxyacetone phosphate
What is the role of pyruvate kinase in glycolysis?
Generates ATP as a product
Why is the conversion of pyruvate to phosphoenolpyruvate considered a strongly exergonic reaction?
It releases energy
Where does the process of converting pyruvate to phosphoenolpyruvate start?
Mitochondria
Which of the following statements about gluconeogenesis is correct?
It involves the breakdown of ATP
What provides the energy necessary for driving the carboxylation of pyruvate to oxaloacetate?
ATP hydrolysis
What is the prosthetic group required by pyruvate carboxylase for carrying CO2 in a reactive manner?
Biotin
Why is acetyl CoA referred to as an obligate allosteric activator of pyruvate carboxylase?
It is required for the carboxylation reaction to occur
Why does oxaloacetate need to be converted to malate for transport out of the mitochondria?
There is no transporter for oxaloacetate
Which enzyme converts oxaloacetate to malate in order to facilitate its transport out of the mitochondria?
Malate dehydrogenase
What happens to malate once it reaches the cytosol?
It is converted back to oxaloacetate
Why does pyruvate carboxylase require acetyl CoA in addition to biotin?
To ensure the carboxylation reaction takes place
What happens if there is no bound acetyl CoA to pyruvate carboxylase?
Carboxylation does not occur
Which vitamin is biotin derived from?
'Vitamin B7
Why does oxaloacetate need to be transported out of the mitochondria into the cytosol?
To continue its involvement in metabolic pathways outside the mitochondria
What was surprising about the two enzymes, PFK-2 and FBPase-2?
They were present in the same protein.
What became evident upon determining the structure of the bifunctional enzyme?
It had two distinct domains: one for kinase activity and another for phosphatase domain.
What triggers the phosphorylation of the single serine residue in the regulatory domain of the bifunctional enzyme?
A rise in glucagon levels due to low blood sugar.
What effect does phosphorylation of the serine residue have on the bifunctional enzyme's activities?
Activates the phosphatase activity domain and inhibits the kinase domain activity.
Why is the phosphorylation of the single serine residue important for the regulation of the bifunctional enzyme?
It allows fine-tuning of the enzyme's activities based on blood sugar levels.
Which hormone is responsible for signaling phosphorylation of the serine residue in response to low blood sugar?
Glucagon
What cell signaling cascade leads to the phosphorylation of the serine residue in the regulatory domain?
$cAMP$ signal cascade
What is a central role of the pentose phosphate pathway (PPP)?
To generate ribose 5-phosphate for nucleotide synthesis
Which molecule serves as the currency of reducing power for most reductive biosynthetic reactions?
NADPH
What does ribose 5-phosphate, generated by the PPP, provide the sugar component for?
Nucleotide synthesis
In what tissues is the pentose phosphate pathway (PPP) particularly active?
Tissues where biomolecule synthesis is high
Which key molecule does the PPP share with glycolysis, leading to coordinated regulation?
Glucose 6-phosphate
What is the primary function of NADPH in the pentose phosphate pathway?
Serve as a reducing agent in biosynthetic reactions
How does ribose 5-phosphate contribute to the production of DNA and RNA?
By providing the sugar component necessary for nucleotide synthesis
Why is it important that the regulation of the pentose phosphate pathway (PPP) and glycolysis are coordinated?
To maintain balance in energy and reducing power needs
Which molecule is considered the currency of reducing power for most reductive biosynthetic reactions?
NADPH
In the Pentose Phosphate Pathway, what is the primary function of the oxidative phase?
To oxidize glucose-6-P and produce NADPH
What is the main outcome of the non-oxidative phase of the Pentose Phosphate Pathway?
Conversion of ribulose-5-P to ribose-5-P
Why is it important for the Pentose Phosphate Pathway to divert excess ribose-5-P to glycolysis?
To ensure a balance between NADPH and ribose-5-P levels
Which molecule serves as a significant product of the Pentose Phosphate Pathway?
Ribose-5-P
What is the main role of the Pentose Phosphate Pathway in relation to glycolysis?
Interconvert excess 5-carbon sugars to glycolysis intermediates
Which phase of the Pentose Phosphate Pathway involves the conversion of ribulose-5-P to ribose-5-P?
Non-oxidative phase
Why does the Pentose Phosphate Pathway need a mechanism to divert excess ribose-5-P to glycolysis?
Because NADPH demand is greater than ribose-5-P requirement
Which process is facilitated by the interconversion of 3-, 4-, 5-, 6-, and 7-carbon sugars in the Pentose Phosphate Pathway?
Glycolysis
What is the main purpose of the Pentose Phosphate Pathway (PPP) as discussed in the text?
To generate NADPH and ribose 5-phosphate
What is the significance of the PPP in relation to glycolysis?
It shares key intermediates with glycolysis and is coordinately regulated
Which molecule is primarily used as the reducing power currency in most reductive biosynthetic reactions?
NADPH
What is the sugar component provided by ribose 5-phosphate synthesized in the PPP for nucleotide production?
DNA and RNA
Why is it crucial for the PPP to generate ribose 5-phosphate?
To act as a precursor for nucleotide synthesis
What is the relationship between the PPP and NADPH production?
The PPP generates NADPH, acting as a source of reducing power
How does the Pentose Phosphate Pathway (PPP) contribute to nucleotide synthesis?
By producing ribose 5-phosphate, a sugar component for nucleotides
How does the regulation of the Pentose Phosphate Pathway (PPP) relate to glycolysis?
PPP and glycolysis share intermediates and are coordinately regulated.
What is the rate-limiting step in the Pentose Phosphate Pathway (PPP)?
Catalysis of glucose-6-P dehydrogenase
What is the primary role of NADP+ in the Pentose Phosphate Pathway?
To act as a substrate for glucose-6-P dehydrogenase
Why does a high concentration of NADPH result in a low rate through the PPP?
The reaction catalyzed by glucose-6-P dehydrogenase is rate-limited by NADP+ availability
What factor primarily determines which pathway glucose-6-P will be funneled into?
Cytosolic concentration of NADP+
Why is glucose-6-P considered a key molecule in the regulation of the Pentose Phosphate Pathway?
It is a limiting factor for NADPH production
What would be the consequence of a high concentration of NADPH in terms of PPP activity?
Decreased PPP activity due to inhibition by NADPH
How does the cytosolic concentration of NADP+ impact the Pentose Phosphate Pathway?
It determines the rate of glucose-6-P conversion in PPP
What is the primary function of the oxidative phase in the Pentose Phosphate Pathway?
Oxidize glucose-6-P
What is the second major product of the Pentose Phosphate Pathway?
Ribose-5-P
Why is it important for the PPP to interconvert sugars of different carbon lengths?
To provide a way to convert excess 5-carbon sugars to glycolysis intermediates
What is the fate of excess ribose-5-P that needs to be diverted from the PPP?
Metabolized into useful components in glycolysis
Which phase of the PPP involves converting ribulose-5-P to ribose-5-P?
Non-Oxidative Phase
What is the purpose of producing NADPH in the Pentose Phosphate Pathway?
Provide reducing power for biosynthetic reactions
Why does the PPP produce more NADPH than ribose-5-P?
NADPH is needed more than ribose-5-P in cellular processes
What is the significance of interconverting 3-, 4-, 5-, 6-, and 7-carbon sugars in the PPP?
To facilitate conversion of excess 5-carbon sugars to glycolysis intermediates
In Mode 3, where is the scenario with the need for greater NADPH than ribose-5-P, what is the fate of the ribulose-5-P produced by the oxidative portion of the PPP?
Converted to ribose-5-P
In Mode 4, which statement best explains how glucose-6-P can produce ATP despite ATP not being directly produced by the PPP?
Fructose-6-P is produced by the PPP and then enters glycolysis.
Which metabolite produced in Mode 4 can directly contribute to ATP production?
Glyceraldehyde-3-P
What is the end result of every glucose-6-P being oxidized in Mode 3?
$6 CO_2$ with $12$ NADPH produced
Which phase of the Pentose Phosphate Pathway produces NADPH and includes the conversion of glucose-6-P to ribulose-5-P?
Oxidative phase
What is the primary purpose of converting ribulose-5-P to ribose-5-P in Mode 3?
To replenish NADPH
Which metabolite from the PPP can be utilized for gluconeogenesis to produce glucose-6P in Mode 3?
Fructose-6-P
What is the significance of every glucose-6-P being oxidized to 6CO2 in Mode 3?
$CO_2$ reflects complete oxidation of glucose-$6P$
Which metabolite conversion occurs first after glucose-6P is oxidized in Mode 4?
$Ribulose-$5P
'Both NADPH and ATP are required' refers to Mode 4 in which glucose-$6P$ oxidation requires both molecules. Which pathway is essential for NADPH production in this mode?
$PPP$ (Pentose Phosphate Pathway)
Test your knowledge on the role of pyruvate carboxylase and the essential covalently bound prosthetic group, biotin, in biochemical reactions. Explore the relationship between acetyl CoA binding and enzyme catalysis based on the information from Tymoczko, Berg, and Stryer's Biochemistry: A Short Course (3rd ed.).
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