15. glycolysis Flashcards
define metabolism
the highly organized/regulated collection of chemical transformations carried out by living cells. Carried out by metabolic pathways
what are metabolic pathways
a series of sequential reactions. The product of one becomes the substrate for the next
what are metabolites
small molecules that are intermediates in the degradation or biosynthesis reactions of biopolymers
what is intermediary metabolism
the study of metabolites throughout metabolic pathways
T or F; metabolic pathways can be highly connected and share intermediates
true
what is anabolism
synthesis of small molecules into large molecules
what is catabolism
breakdown of large molecules into smaller molecules
which type of metabolism requires an input of energy
anabolic pathways
what type of energy does anabolism require an input of
ATP (phosphoryl group transfer) and NADH/NADPH/FADH2 (reduced electron carriers)
which type of metabolism releases energy
catabolic pathways
describe the release of energy in catabolism
regenerates ATP from ADP and Pi, and regenerates the reduced electron carriers from their oxidized forms (NAD+, NADP+, FAD)
what are amphibolic pathways
pathways that are either catabolic or anabolic depending on the energy conditions of the cell
T or F: most metabolic reactions in cells are at steady state
true
define steady state
the amount of each intermediate is not changing
define flux
the rate of flow through the pathway
T or F: most cells have the enzymes to carry out both the degradation and synthesis of important biomolecules
true
T or F: feedback can activate or inhibit a metabolic pathway
true
explain how glucose plays a central role in the metabolism of animals and plants
- rich in potential energy (G’o = -2840kj/mol)
- large amounts can be stored
- quick release from storage when needed
where does glycolysis occur
in the cytosol
how many steps is glycolysis
10
what is the first 5 steps of glycolysis called
the preparatory phase
what does the preparatory phase produce
glyceraldehyde-3-phosphate
what is the cost of the preparatory phase
2 ATP
what is the last 5 steps of glycolysis called
the payoff phase
what does the payoff phase produce
pyruvate
what is the benefit of the payoff phase (ie what’s the payoff)
4 ATP
what happens to pyruvate after glycolysis
- complete oxidation to CO2 to produce reduced electron carriers for the ETC
- lactic acid fermentation to regenerate NAD+
- ethanol fermentation
step 1: what is the reagent and product
glucose –> glucose-6-phosphate
step 1: how does it happen
phosphorylation at C6 turns glucose into G6P
step 1: what phosphorylates glucose
ATP is the phosphoryl donor
step 1: is it reverisble
no
step 1: what is the purpose of phosphorylation
it “primes” glucose for subsequent reactions
step 1: what effect does phosphorylation have on glucose (hint: think location)
phosphorylation traps glucose in the cell
step 1: what enzyme is used for glucose phosphorylation from ATP
hexokinase
step 1: describe the G’o
relatively large G’o (because energy in this step was raised)
step 1: does hexokinase need a substrate
yes
step 1: what substrate does hexokinase (and all the other kinases) need
(MgATP)^2-
step 1: since MgATP2- is the substrate for hexokinase, what does that make Mg2+. What is the purpose of Mg2+
it’s an essential cofactor. It shields negative charges in the active site
step 2: what enzyme is used
phosphohexose isomerase (requires Mg2+)
step 2: what is the reagent and product
glucose-6-phosphate –> fructose-6-phosphate
aldose to ketose
step 2: is it reversible
yes
step 2: what is the purpose of aldose to ketose
C1 is now able to be phosphorylated just like C6 was
because the goal is to have glucose as a mirror image
step 2: what is required to convert the aldose to the ketose
we need to open the ring in the active site to temporarily revert glucose to linear form, then we can form the ketose
step 3: what is the reagent and product
fructose-6-phosphate –> fructose 1,6-bisphosphate
step 3: what happens to make the product
F6P is phosphorylated to make the product
step 3: where does the phosphate come from to phosphorylate F6P
ATP
step 3: what enzyme uses the P from ATP to phosphorylate F6P
phosphofructokinase-1
step 3: is it reversible
no! phosphofructokinase-1 commits these carbons to glycolysis
step 3: what does phosphofructokinase-1 need for proper kinase activity
Mg2+
step 4: what is the reagent and product
fructose 1,6-bisphosphate –> glyceraldehyde 3-phosphate AND dihydroxyacetone phosphate
step 4: what is glyceraldehyde 3-phosphate
aldose, phosphorylated version of glyceraldehyde
step 4: what is dihydroxyacetone phosphate
ketose, phosphorylated version of dihydroxyacetone
step 4: what happens to fructose 1,6-bisphosphate in this step
it is cleaved into the two products, which requires the ring opening
step 4: when the ring is opened to make the two products, is there a tetrahedral intermediate
yes
step 4: what enzyme is used
aldolase
step 5: what is the reagent and product
dihydroxyacetone phosphate –> glyceraldehyde 3-phosphate
step 5: how does DHAP become G3P
isomerization
step 5: what are we left with + why
2 molecules of G3P, because one was made in this step and one was pre existing from the last step
step 5: what enzyme is used
triose phosphate isomerase
step 6: what is the reagent and product
glyceraldehyde 3-phosphate –> 1,3-bisphosphoglycerate
step 6: how does the conversion of G3P to 1,3BPG occur
oxidation with the help of Pi and NAD+
step 6: what enzyme is used
glyceraldehyde 3-phosphate dehydrogenase
step 6: other than 1,3BPG, what is produced
2 NADH and 2 H+
step 6: what is the role of the electron carrier NAD+
it’s a co-substrate of the dehydrogenase enzyme
step 6: how are NADH and H+ formed
two electrons and a proton from the oxidation of G3P to 1,3BPG are transferred to the NAD+
step 6: what happens to NAD+ levels after this step
NAD+ levels in the cell are very low, so NAD+ is eventually regenerated down the road
step 6: endergonic or exergonic
endergonic (non-spontaneous)
how do we make step 6 spontaneous (exergonic)
by coupling it with step 7
step 7: what is the reagent and product
1,3-bisphosphoglycerate –> 3-phosphoglycerate
step 7: how is 3-phosphoglycerate formed
hydrolysis of the high energy phosphoryl group from 1,3BPG
step 7: where does the hydrolyzed phosphoryl group go (came from 1,3BPG)
it is transferred to ADP –> ATP
step 7: what enzyme is used
phosphoglycerate kinase
step 7: how many ATP are produced
2
step 7: 1,3BPG was one of the molecules with a large negative G’o from bioenergetics. What does this mean for glycolysis
the products of this step (3-phosphorglycerate) are stabilized (due to ionization and resonance), and this step is super exergonic
step 7: what is the term for the transfer of a phosphoryl group from a high energy compound (ie BPG) to ADP by a soluble enzyme in the cytosol
substrate level phosphorylation
step 7: does the enzyme require Mg2+
yes
what does coupling of steps 6 and 7 achieve
makes the endergonic step 6 into an exergonic step
step 8: what is the reagent and product
3-phosphoglycerate –> 2-phosphoglycerate
step 8: how is 2-phosphoglycerate made
the phosphoryl group on 3-phosphoglycerate is shifted to C2 from C3 to produce 2-phosphoglycerate
step 8: what enzyme is used
phosphoglycerate mutase
step 8: does phosphoglycerate mutase require Mg2+
yes
step 9: what is the reagent and product
2-phosphoglycerate –> phosphoenolpyruvate
step 9: how is phosphoenolpyruvate produced
water is removed from 2-phosphoglycerate to produce phosphoenolpyruvate
step 9: what enzyme is used
enolase
step 9: phosphoenolpyruvate was one of the molecules with a large negative G’o from bioenergetics. What does this mean for glycolysis
the hydrolysis product (pyruvate) is stabilized by isomerization
step 10: what is the reagent and product
phosphoenolpyruvate –> pyruvate
step 10: how is pyruvate produced
hydrolysis
step 10: what enzyme is used
pyruvate kinase
step 10: does pyruvate kinase require Mg2+
yes
step 10: what else is produced
ATP
step 10: how much ATP is produced
2
step 10: how much of the standard free energy is retained in the ATP
half; the other half is released
T or F: for all 10 steps, the gibbs free energy is either negative or zero
true
describe the delta G value for the overall sum of the reactions
negative
which of the 10 reactions has a large negative delta G value
1, 3, and 10
for reactions 1, 3, and 10 (ones having large negative G), why are they considered regulatory points in metabolism
they’re both metabolically irreversible and regulated
describe the feeder pathway for starch
broken down by a-amylases in salivary glands = short oligosaccharides. Pancreatic a-amylases continue = maltose. Maltose is degraded to glucose by intestinal enzymes
describe the feeder pathway of dietary glycogen (animal products)
very similar to starch
describe the feeder pathway of endogenous glycogen (glucose in our bodies)
broken down via phosphorylases in the liver/muscle. Glucose 1-phosphate is cleaved off, which isomerizes to glucose 6-phosphate
(this is phosphorolysis, not hydrolysis)
describe the feeder pathway of sucrose
sucrose is cleaved by sucrases into glucose and fructose. Fructose can enter glycolysis via the muscle and kidney, or by the liver
describe the feeder pathway for fructose in the muscle/kidney
fructose is phosphorylated by hexokinase and enters glycolysis
describe the feeder pathway for fructose in the liver
fructose is phosphorylated by fructokinase at C1 (not C6). F 1-P is then cleaved into two products that enter glycolysis via G3P
describe the feeder pathway for mannose
mannose is phosphorylated by hexokinase to mannose 6-phosphate. M6P is then isomerized to fructose 6-phosphate
