Glycolysis Flashcards
Exam 2
What does glycolysis mean?
Sweet lysis
Lyse sugars to get energy
Is glucose or fat a better fuel?
Fat
What is the starting sugar for glycolysis?
Glucose
What happens when glucose is oxidized?
It yields energy
What is the storage form of glucose?
Glycogen in animals
T/F: Many organisms and tissues can meet their energy needs on glucose only.
True
What can glucose be used to generate other than energy?
Membrane lipids
Nucleotides in DNA and RNA
Glycoproteins
Is forming glycogen from glucose anabolic or catabolic?
anabolic (building up)
Is glucose oxidation via the pentose phosphate pathway anabolic or catabolic?
Anabolic
Makes Ribose 5-phosphate
Is glycolysis catabolic or anabolic?
Catabolic
Makes pyruvate
What does glycolysis do overall?
It is the sequence of 10 steps that are catalyzed by enzymes by which glucose is converted into pyruvate
How does glycolysis keep the reactions pushing forward even when they are endothermic?
The products of one reaction is the substrate of another which decreases the product and pushes the reaction to the product side
Where does glycolysis take place in the cell?
Cytoplasm
How do we activate glucose in glycolysis?
Phosphorylate it so it is anionic and is stuck inside of the cell
This also changes the concentration of glucose inside the cell when it is converted so glucose continues to flow in
Where does the energy from glycolysis come from?
High energy metabolites (“BASICALLY ATP” -SARAH)
What is made in one round of glycolysis?
2NADH, 2ATP, 2H2O, 2H+ and two pyruvates
How many carbons are in glucose?
6
How many carbons are in one pyruvate molecule?
3
when we use one glucose we make 2 pyruvate and 3x2=6 which is how many sugars are in glucose
What does the preparatory phase of glycolysis do?
Uses energy (2ATP) to activate sugars Makes glucose into 2 trioses
What phase of glycolysis makes ATP?
The Payoff phase
Where is hexokinase found?
in the muscles
Where is glucokinase found?
in the liver
What does hexokinase and glucokinase do?
Converts Glucose to Glucose 6-phosphate by using ATP and Mg+ (cofactor)
Phosphorylates the glucose on the C6
What does Mg2+ do for phosphorylation?
Stabilizes the close negative charges of phosphate groups
It is a cofactor
Is converting glucose to glucose 6-phosphate exo or endo thermic?
Exothermic
-16.7 kJ/mol
What does phosphorylating glucose do?
Traps glucose inside of the cell and lowers intracellular glucose concentration to allow further uptake (remember when you phosphorylate a glucose it is no longer glucose)
Where does the energy for phosphorylation come from in glycolysis?
Hydrolysis of ATP
How are hexokinases and glucokinases isoenzymes?
They both phosphorylate but in different areas of the body
Hexo in the muscles
Gluco in the liver
Is phosphorylation of glucose irreversible?
Yes
How is hexokinase inhibited?
Allostericly inhibited by glucose 6-phosphate (feedback)
How is glucokinase activated?
Allostericly activated by glucose and inhibited by fructose 6-phosphate
What is a molecular sensor of high glucose levels?
Glucokinase
It has a low affinity for glucose (higher Km)
Can glucokinase be inhibited by a product?
no
What does the liver do when blood glucose levels are high?
It pulls in extra glucose and traps it by phosphorylation
Acts as a glucose sensor and stimulates insulin release
What can hexokinase phosphoryate?
Mannose, fructose, glucose
In most tissues of body
T/F Hexokinase has a high affinity for glucose. What is its Km relative to glucokinase?
True
Much smaller Km than glucokinase
What does phosphohexose isomerase do?
Converts glucose 6-phosphate to fructose 6-phosphate
Makes an isomer
Glucose 6-phosphate is an aldose
Fructose 6-phosphate is a ketose
What is the cofactor used for phosphohexose isomerase?
Mg++
TF: Converting glucose 6-phosphate into the isomer fructose 6-phosphate is Irreversible and unfavorable
FALSE
It is unfavorable (endothermic) but has a low free energy near equilibrium so it is reversible
Since converting glucose 6-phosphate to fructose 6-phosphate is reversible, how does glycolysis keep moving forward and not back?
Keeping the product concentration low by pairing it with favorable next step to drive the reaction forward
What does phosphofructokinase 1 do?
Phosphorylates Carbon 1 on fructose 6-phosphate to make it fructose 1,6-bisphosphate by using ATP and Mg++
What is the first committed step of glycolysis?
Step 3 using PFK-1
Fructose 1-6 bisphosphate is committed to become pyruvate and yield energy
What is the favorability of step 3 with PFK-1?
Highly thermodynamically favorable and hence it is IRreversible
How is PFK-1 regulated?
Allosterically inhibited by ATP and citrate (high energy state)
Allosterically activated by AMP and ADP (low energy state)
Why does glycolysis phosphorylate the sugar yet again in step 3?
To make it more symmetrical and to further activate glucose
What does aldolase do to fructose 1-6 bisphosphate?
The six carbon sugar is cleaved into two three carbon sugars to make high energy phosphate trioses (a ketone and an aldehyde)
Does glyceraldehyde 3-phosphate or dihydroxyacetone phosphate feed into step 5 of glycolysis?
Dihydroxyaceton phosphate (ketone) to be made into another glyceraldehyde 3-phosphate by triose phosphate isomerase (unfavorable)
Is step 4 favorable?
No it is endergonic and reversible
What kind of reaction does glyceraldehyde 3-phosphate dehydrogenase perform in step 6?
Redox reaction
What must be used in redox reactions?
NAD+
coenzyme that will be reduced
What does step 6 allow for?
Net production of ATP via glycolysis
What does step 6 generate?
1,3-bisphosphoglycerate which is a high energy phosphate compound
Where does the phosphate for step 6 come from?
An inorganic phosphate
How is NAD+ regenerated after being reduced to NADH?
Aerobically by ETC
Anaerobically by lactate dehydrogenase
Is step six reversible?
Yes it is endergonic
What happens in step 7?
The 1st production of ATP by phosphoglycerate kinase (phosphorylation of ADP from a substrate 1,3-bisphosphoglycerate)
Is step 7 favorable?
Yes because you are breaking off a high energy bond from 1,3 bisphosphoglycerate (phosphate) and adding it onto ADP to make ATP and 3-phosphoglycerate
Is step 7 irreversible since its favorable?
No it is reversible (net ATP is now zero)
What does a mutase do?
Moves functional groups in same molecule
What does phoshoglycerate mutase do?
Moves the phosphate from on 3-phosphoglycerate to carbon 2 to make 2-phosphoglycerate
What is used for phosphoglycerate mutase?
Mg++ cofactor to stabilize the negative charges
Is step 8 favorable?
No it is endergonic and reversible
What does enolase do in step 9?
Removes an OH group from C3 and an H group from C2 on 2-phosphoglycerate through dehydration and makes a double bond between C3 and C2 to make phosphoenolpyruvate
Creates an enol through dehydration
Why does 2-PG need to be convertedinto phosphoenolpyruvate?
Because 2-PG is not a good enough phosphate donor to generate ATP but Enol phosphate is since it is a higher energy compound with a double bond
PEP has a much better phosphoryl transfer potential
Is step 9 favorable?
No and it is reversible
What does step 10 do?
Creates pyruvate form PEP and creates an ATP from ADP and the phosphate on C2 of PEP
What cofactors does pyruvate kinase need?
K+ and Mg++
Is step 10 reversible?
NO
It is very highly favorable exergonic
What is tautomerization?
Lowers the concentration of the reaction product and drives the reaction towards ATP formation
Makes pyruvate a keto form from enol form which the keto form predominates and drives ATP production
What regulates pyruvate kinase?
ATP, divalent metals, and other metabolites
Activated by feed forward regulation by fructose 1,6- bisphosphate
What is used in glycolysis/
1 glucose, 2 ATP and 2 NAD+
What is made in glycolysis?
2 pyruvate, 4 ATP, 2 NADH
net 2 ATP
WHY is glycolysis regulated?
Ensure proper use of nutrients
ensure production of ATP only when needed
What cleaves glucose from glycogen?
Glycogen phosphorylase
What is made when glucose is cleaved from glycogen
Glucose 1-phosphate
What does lactose hydrolyze into?
Glucose and galactose
WHat does sucrose hydrolyze into?
Glucose and fructose
What other sugars can enter glycolysis besides glucose?
Fructose
Galactose
Mannose
What are the 2 fates of pyruvate?
Anaerobic it is converted into lactate
Aerobic it is converted into Acetyl-CoA for the krebs cycle
What is fermentation?
Generation of ATP without consuming oxygen
Pyruvate to Lactate and this regenerates NAD+ for further glycolysis under anaerobic conditions
What converts pyruvate into lactate?
Lactate dehydrogenase and NADH and H+
Where is lactate converted into glucose?
The liver
How can tumor cells increase expression of LDH ?
By induction
What is the warburg effect?
When rapidly growing tumors obtain ATP by metabolizing glucose to lactate even in the presence of oxygen
