Glycolysis Flashcards
What is the principle pathway through which ATP is generated in the body?
glycolysis
Is glycolysis present in every cell type?
Yes
Where in the cell does glycolysis occur?
cytosol
Is glycolysis high in RBCs? Why or why not?
Yes. They don’t have mitochondria so their only source of ATP is glycolysis
What are the two phases of glycolysis?
1) Preparative phase
2) ATP-generating phase
What happens in the preparative phase of glycolysis?
take glucose, consumes 2 ATPs, and generates 2 triose phosphates
What happens in the ATP generating phase of glycolysis?
2 gylcerol triphoshphates (the triose phosphates from the preparative phase) are converted to 2 pyruvates, generating 4 ATP and 2 NADH
What are the NET products of aerobic glycolysis?
2 NADH, 2 ATP, and 2 pyruvates
What is the first regulated step of glycolysis?
Is this step an ATP consuming step?
glucose is phosphoylated into glc-6-p by hexokinase (glucokinase in the liver)
Yes. An ATP is needed
What happens after glc is phosphorylated into glc-6-p?
glc-6-p is converted to fructose-6-p by phosphoglucose isomerase
What happens after glc-6-p becomes fructose-6-p?
fructose-6-p is acted upon (in an ATP dependent fashion) by phosphofructokinase-1 making fructose-1,6- biphosphate
subject to negative feedback inhibition by ATP and citrate
What is the rate limiting enzyme in glycolysis?
phosphofructokinase-1 (PFK-1)
Why is phosphofructokinase-1 the rate limiting enzyme in glycolysis?
It has four allosteric enzymes on its structure (the most of all) that regulate its activity
What happens to fructose-1,6-biphosphate?
it undergoes a cleavage via an aldolase to generate the two triose phosphates, glyceraldhyde-3-phosphate and dihydroxyacetone phosphate (the two end products of the preparatory phase of glycolysis)
NOTE: these two can be interconverted via an isomerase
What are the intermediates of the preparative stage of glycolysis?
1) glucose
2) glc-6-p
3) fructose-6-p
4) fructose-1-,6-biphosphate
5) glyceraldhyde-3-phosphate and dihydroxyacetone phosphate
What is the committed step of glycolysis?
conversion of fructose-6-phosphate to fructose-1,6-biphosphate via phosphofructokinase-1
What is the major difference between hexokinase and glucokinase other than their location?
hexokinase is regulated through a feedback system. So if glucose is made into glc-6-p and not used, it will inhibit further kexokinase action.
Glucokinase will not be feedback inhibited
What is the first step of the ATP generating phase of glycolysis?
a de-hydrognase step
glyceraldeyhde-3-phosphate is converted to a high energy intermediate (1,3- bisphosphoglycerate). This step consumes NAD+ and produces NADH+
What enzyme produces 1,3-bisphosphoglycerate from glyceraldehyde-3-phosphate?
glyceraldehyde-3- phoshphate dehydrogenase
What happens to 1,3-bisphosphoglycerate?
phosphoglycerate kinase converts it (using ADP and creating ATP!!) to 3-phosphogylcerate in a process called substarte-level phosphorylation
What is substrate level phosphorylation?
substrate gives a phosphate to ADP generating ATP
What happens to 3-phosphogylcerate?
it is interconverted to 2-phosphogylcerate by phosphoglycero-mutase (not ATP requiring)
What happens to 2-phosphoglycerate?
it is made into phosphoglenol-pyruvate by annuals (giving off H20 in the process).
a high energy phosphate group is created here
What happens to phosphoglenol-pyruvate?
It is transformed into pyruvate by pyruvate kinase (making ATP from ADP-i.e. substrate level phosphorylation- in the process)
What are the net products of the ATP-generating phase of glycolysis?
from each triose phosphate -2 ATPs, 1 NADH, and 1 pyruvate
so 4 ATP, 2 NADH, and 2 pyruvate total
Can glycolysis occur with or without O2?
yes. The availability of O2 determines how the products are metabolized
Under anaerobic conditions, what does glycolysis result in?
results in NADH, ATP, and pyruvate.
The NADH must be re-converted back to NAD (b/c cellular NAD levels are too low to continue glycolysis without it) in the cytosol by lactate dehydrogenase. This is accomplished by converting pyruvate to lactate using NADH, which produces NAD as a bi-product
So the end yield is 2 ATP (no NADH b/c it is reconverted)
Under aerobic conditions, what does glycolysis result in?
results in NADH, ATP, and pyruvate.
Pyruvate is then fully oxidized to C02 in mitochondria, forming more ATP via oxidative-phosphorylation
What happens to lactate in anaerobic glycolysis?
(seen especially in RBC which can only do anaerobic glycolysis due to lack of mitochondria)
it is taken out into circulation, taken up by the LIVER, and reconverted to pyruvate (which can be used a pre-cursor for gluconeogenesis)
Regeneration of pyruvate (and subsequently glucose) from lactose is called what?
The Cori cycle
In aerobic glycolysis, how is cytosolic NADH reconverted back to NAD+?
occurs in mitochondria via the ETC
In aerobic glycolysis, how does cytosolic NADH enter mitochondria?
the inner mitochondrial membrane is impermeable to hydrophilic or charged molecules, so NADH cannot simply diffuse into the mitochondrial matrix. There are also no transporters in the mito. to transport NADH in.
So, shuttle systems are used.
What are the names of the two shuttle systems used to move NADH into the mitochondrial matrix?
1) glycerol-3-phosphate shuttle (prevalent in skeletal muscle)
2) Malate-Asparate shuttle (prevalent in liver)
How does the glycerol-3-phosphate shuttle work?
dihydroxyacetone-phosphate (the end product of the preparative phase of glycolysis) is converted to glycerol-3-p (now has H) by cytosolic glycerol 3-p dehydrogenase by using NADH (which makes NAD+ in the process)
Glycerol-3-p diffuses across the outer mitochondrial membrane (but it can’t diffuse across the inner mito. membrane) and is re-converted to dihydroxyacetone-phosphate by mitochondrial glycerol 3-p dehydrogenase, using FAD and making FAD(2H)
What are the steps of the Malate-Asparate shuttle?
1) reduction of oxaloacetate to malate (causing a transfer of H+ from NADH to malate, and creating NAD+)
2) malate is exchanged into the mito. matrix in an antiproton system in exchange for a-ketogluterate (a-KG) (aka malate in and a-KG out)
3) once inside, malate is re-oxidized to oxaloacetate, in the process donating H+ to NAD+ in the matrix to make NADH (then NADH cycles through the ETC to re-generate NAD+)
These next steps are just re-maming substrates:
4) oxaloacetate undergoes transamination (TA) to make asparate, which uses glutamate and makes a-KG as a bi-product
5) Asparate undergoes antiporter with glutamate (asp going out, glut going in)
6) Outside the cell, aspirate undergoes TA to remake oxaloacetate, using a-KG which makes glutamate as a byproduct
How can 1,3-bis-phosphoglycerate impact oxygen movement in the body?
1,3-bis-phosphogylcerate can make 2,3-bis-phosphoglycerate, which when bound to hemoglobin it facilitates the release the oxygen from hemo under low O2 conc.
Pyruvate can be altered to make which AA?
alanine
3-phosphoglycerate can be altered to make which AA?
serine
Acetyl CoA is a precursor of what in adipose cells?
FA synthesis (along with glycerol-3-phosphate)
What regulated the action of pyruvate kinase?
high ATP levels will cause negative feedback
high fructose-1,6-bisphosphate will cause positive feedback
What regulates the action of phosphofructokinase-1?
high ATP and citrate levels will cause negative feedback
high AMP and fructo-2,6,-bis-phosphate will cause positive feedback
What enzyme converted pyruvate to acetyl CoA?
pyruvate dehydrogenase (makes NADH from NAD+)
What regulates the action of phosphofructokinase-1?
high levels of NADH or Acetyl CoA will cause negative feedback
high levels of ADP or Ca2+ will cause positive feedback
How does regulation of phosphofructokinase-1 by ATP work?
ATP is both a substrate and an inhibitor. If ATP levels are low, ATP will bind to the substrate binding sites, if high ATP will bind to inhibitory sites
How does citrate regulate PFK-1?
Citrate is a bi-product of the TCA. If there is lots of citrate, no more glycolysis is needed
How does F-2,6-bisphosphate regulate PFK-1?
PFK2 also acts on f-6-p (in addition to PFK1), making F-2,6,-bisphosphate.
Thus, high fructose-6-p results in high F-2,6-bispohpsphate, which binds to PFK-1 and overrides the inhibitory effect of ATP. So then PFK-1 will act on f-6-p more to make more f-1,6- bispohosphate
allosteric regulation of pyruvate kinase only occurs where?
in the liver (NOT in muscle)
