Chapter 14 Flashcards
Many organisms use glucose to generate what things?
- amino acids (by breaking glucose down into pyruvate then use pyruvate)
- membrane lipids
- nucleotides in DNA and RNA
- cofactors necessary for metabolism
Gluconeogenesis is the synthesis of glucose from simpler precursors like ______ and ______
pyruvate and lactate
What pathway is an alternative pathway for glucose oxidation?
the pentose phosphate pathway
Glucose can be efficiently stored in what form?
Polymeric (starch, glycogen)
What two things can happen to pyruvate after glycolysis?
- pyruvate can be further aerobically oxidized
- pyruvate can be used as a precursor in biosynthesis
How many ATP molecules are consumed in the preparatory phase of Glycolysis (steps 1-5)
2 molecules of ATP
In the payoff phase of glycolysis, how many pyruvate molecules are created for each molecule of glucose
2 pyruvate per 1 glucose
What are the reactants for glycolysis?
Glucose + 2(NAD+) + 2ADP + 2Pi
What are the products of glycolysis?
2 pyruvate + 2NADH + 2H +2ATP + 2H20
The conversion of glucose to pyruvate is (endergonic or exergonic) ?
exergonic = favorable
delta G = -146jk/mol
Under standard cellular conditions, glycolysis is (reversible or irreversible) ?
irreversible
energy stored in pyruvate can be extracted in which two processes?
aerobic and anaerobic processes
Aerobic: oxidative reactions in Krebs, oxidative phosphorylation
Anaerobic: reduction to lactate, reduction to ethanol
What is the purpose of the first step in glycolysis?
To trap glucose inside the cell & to lower intracellular glucose levels so that further glucose uptake can occur
Which steps in glycolysis require ATP?
steps 1 and 3
Which steps in glycolysis PRODUCT ATP?
steps 7 and 10 (substrate level phosphorylations)
Which steps in glycolysis are carried out by isomerases?
steps 2 and 5
What are the functions of phosphoryl groups in glycolysis?
- to prevent glycolytic intermediates from leaving the cell
- to serve as essential components in the enzymatic conservation of metabolic energy
- to lower the activation energy and to increase the specificity of the enzymatic reactions
In what step of glycolysis does an aldose isomerize into a ketose via an enediol intermediate?
Step 2- Isomerization of glucose (an aldose) to fructose (a ketose) via enzyme phosphohexose isomerase
What is the mechanism of the phosphohexose isomerase mechanism in the isomerization of glucose to fructose?
General acid-base catalysis
What is the first committed step of glycolysis?
Step 3 - The Second Phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate
**fructose 1,6-bisphosphate is committed to becoming pyruvate
**irreversible reaction
What is the least energetically favorable step of the preparatory phase?
Step 4 - Aldol cleavage
In step 6, DHAP must be oxidized to _____ via triose phosphate isomerase
DHAP OXIDIZED TO GAP
What step completes the preparatory phase of glycolysis?
step 5- triose phosphate isomerization
Enzymes that transfer phosphate groups between ATP and various substrates
Kinases
Define substrate-level phosphorylation
The formation of ATP by phosphoryl group transfer from a substrate
Why does glycolysis need to be regulated?
To ensure proper use of nutrients and to ensure ATP is only produced when it is needed
What two molecules is glucose cleaved from?
Glycogen and Starch
In step 6 of glycolysis, each molecule of glyceraldehyde-3-phosphate is oxidized and phosphorylated by ________ to form 1,3 Bisphosphoglycerate
Inorganic Phosphate (Pi)
What is the purpose of step 2 in glycolysis?
makes the next steps in the reaction require less energy - the isomerization of glucose-6-phosphate to fructose-6-phosphate moves the carbonyl to C-2 : a prerequisite for steps 3 and 4
–C1 of fructose is easier tot phosphorylate by PFK , allows for symmetrical cleavage by aldolase
What is the purpose of step 3 in glycolysis?
the 2nd phosphorylation converts fructose-6-phosphate to fructose-1,6-bisphosphate
– this is the first committed step of glycolysis…b/c fructose 1,6 bisphosphate is committed to becoming pyruvate
What is the purpose of step 4 in glycolysis?
Step 4 is the aldol cleavage of a 6-carbon sugar into two 3-carbon sugars GAP and DAP
What is the purpose of step 5 in glycolysis?
This step completes the preparatory phase of glycolysis - allows glycolysis to proceed to the payoff phase by a single chemical pathway
conversion of dihydroxyacetone phosphate to GAP (glyceraldehyde-3-phosphate)
What is the purpose of step 6 in glycolysis?
The oxidation of GAP produces a high-energy acyl phosphate compound
– incorporates inorganic phosphate
– the first energy-yielding step in glycolysis, produced NADH
What is the purpose of step 7 in glycolysis?
Substrate level phosphorylation to make ATP
Purpose of step 8 in glycolysis?
The migration of a phosphate group from C-3 to C-2, sets up for the final steps of the pathway
Purpose of step 9 in glycolysis?
Dehydration activates the phosphoryl for transfer to ADP in the last step
Purpose of step 10 in glycolysis?
Production of the 2nd ATP
For both phosphorylations in the preparatory phase of glycolysis, what is the phosphoryl group donor?
ATP serves as the phosphoryl group donor
Which process in glycolysis is endergonic?
The formation of ATP from ADP and Pi
What is anaerobic glycolysis called
Fermentation
What is lactic acid fermentation?
the reduction of pyruvate to lactate
What is ethanol fermentation?
the two-step reduction of pyruvate to ethanol
What is the CO2 produced in the first step of ethanol fermentation used for?
carbonation in beer and dough rising
Gluconeogenesis
Pathway that converts pyruvate (and its related 3 and 4 carbon compounds) to glucose
Is any ATP produced during gluconeogenesis?
No
What molecules in gluconeogenesis are permeable to the mitochondrial membrane…which are impermeable
Permeable molecules = Malate, PEP, pyruvate
IMpermeable = oxaloacetate
What is oxaloacetate converted to in order to allow for transport to the cytosol for gluconeogenesis?
oxaloacetate can be converted to PEP or malate
A reason why gluconeogenesis is physiologically necessary
The brain, NS, and red blood cells can only generate ATP from glucose
What can animals produce glucose from, what can they not produce glucose from?
Animals CAN produce glucose from certain sugars (pyruvate, lactate, oxaloacetate) and from the amino acids capable of being converted to Kreb’s cycle intermediates (al but Leucine and Lycine)
Animals CANNOT produce glucose from fatty acids b/c the product off fatty acid degradation is acetyl-coA
What are hexokinase I,II and III all inhibited by?
Their product, glucose-6-phosphate
What is hexokinase IV inhibited by?
Hexokinase IV is inhibited by Fructose-6-phosphate which is an allosteric effector
When is pyruvate converted to PEP?
when fatty acids are available
What are the molecular costs of gluconeogenesis?
4 ATP, 2 GTP, 2 NADH
During fermentation (anaerobic glycolysis). ATP is generated without consuming ______ or ______
generation of ATP without consuming oxygen or NAD+
In mammals, where is the main site of gluconeogenesis
liver
What are the three bypass points (steps) in gluconeogenesis?
Pyruvate –> phosphoenolpyruvate (PEP)
Fructose 1,6 bisphosphate —> fructose 6-phosphate
Glucose 6-phosphate –> glucose
How is phosphofructokinase-1 (PFK-1) regulated?
PFK-1 is regulated by the binding of ATP to an allosteric site - this occurs when there is an excess in ATP
Citrate inhibits PFK-1 by increasing the inhibitory effects of ATP – causes a smaller concentration of ATP to seem like more
How is (FBPase) fructose 1,6 bisphosphate ALLOSTERICALY regulated (inhibited)
high concentrations of AMP (which corresponds to low concentrations of ATP) inhibit FBPase –> thus slowing glucose synthesis
high ATP concentrations slows glycolysis and speeds up gluconeogenesis
What molecule mediates the rapid hormonal regulation of glycolysis and gluconeogenesis?
FRUCTOSE 2,6-BISPHOSPHATE
How does fructose 2,6-bisphospate regulate PFK-1 (phosphofructokinase-1)
Binds to PFK-1 and increases its affinity for fructose-6-phosphate
How does fructose 2,6-bisphospate regulate FBPase-1 (fructose 1,6-bisphosphate)
binds to FBPase-1 and reduces its affinity for its substrate
What molecule catalyzes the formation of FBPase-1 ?
PFK-2 (phosphofructokinase-2)
What molecules catalyze the BREAKDOWN of FBPase-1?
FBPase-2
What are the main products of the Pentose Phosphate Pathway?
NADPH and ribose-5-phosphate
A process by which cells continue using glycolysis to extract energy in anaerobic conditions
Fermentation
Pentose phosphates can be regenerated into _______ which requires no ATP
glucose-6-phosphate
A process by which cells can generate pentose phosphates & NADPH
pentose phosphate patway
Ribose-5-phosphate is a biosynthetic precursor of _______?
nucelotides
Under aerobic conditions what does pyruvate become?
pyruvate gets oxidized to acetyl-coA
In the reduction of pyruvate to ethanol, pyruvate decarboxylase requires what two cofactors?
Mg2+ and thiamine pyrophosphate (TPP)
Tumor cells cause an increased expression of what?
LDH (lactate dehydrogenase)
