glycolysis Flashcards
it is the first stage of glucose metabolism in organism
glycolysis
- center and the heart of carbs metabolism
- starts at the mouth, physical digestion (starts munching and chewing into smaller pieces)
- as well as chemical digestion, salivary amylase
glycolysis process
index card
how many steps are there in glycolysis
10
what is the committed step in glycolysis
Fructose-1, 6-bisphoshate
- means u rlly have to go through the slide
- no turning back
what are the reactant, products AND PROCESS of glycolysis
reactant:
1 molecule of glucose (6-C molecule)
product:
2 mol of pyruvate (3-C molecule)
2 mol of ATP
1 mol of NADH, Nicotinamide adenine dinucleotide
process:
oxidation
- each reaction in the pathway is catalyzed by an enzyme specific for that reaction
what are the difference between anaerobic glycolysis, aerobic oxidation and anerobic alcoholic fermentation
requires oxygen:
aerobic oxidation
– produces the most ATP, takes place in mitochondria
does not require oxygen:
anaerobic glycolysis (when oxygen is limited)
anerobic alcoholic fermentation
- common in yeast and bacteria
Pathway of conversion of glucose to lactate
Anaerobic glycolysis
Glucose → Pyruvate → Lactate
Occurs during intense exercise when muscles can’t get enough oxygen
The lactate buildup can cause muscle fatigue and soreness
how can the lactate be converted back to glucose
in the liver when oxygen becomes available
what is the first step of glycolysis
glucose is phosphorylated to give glucose-6-phosphate
endergonic reaction as it needs energy in the form of ATP
ATP
- serves as the energy source
- provide glucose the phosphate group hence the product of ATP is ADP
- one of the phosphate group from ATP is attached to the C6 of glucose
enzyme used:
hexokinase + co-factor of Mg2+
second step of glycolysis
isomerization:
glucose-6-phosphate to fructose-6-phosphate
third step of glycolysis
phosphorylation:
fructose-6-phosphate to
fructose-1,6-bisphosphate
enzyme used:
phosphofructokinase + MG2+
endergonic reaction to exergonic reaction
hence ATP needs to undergo hydrolysis
Key allosteric control enzyme in glycolysis
Phosphofructokinase
- at least 1 subunit of the Phosphofructokinase should be activated in order to activate the other 3
- controls how fast glycolysis can occur which can prevent wasting glucose when energy isn’t needed
Slows down when ATP is high (cell has enough energy)
Speeds up when ATP is low (cell needs energy)
step four of glycolysis
cleavage:
fructose-1, 6-bisphosphate to give 3-C fragments, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate
enzyme:
aldolase
Enzyme that catalyzes the reverse aldol condensation of fructose-1,6-bisphosphate
aldolase
*it has lysine residue and the thiol grp of cysteine
step five of glycolysis
isomerization:
DHAP to G-3-P
dihydroxyacetone phosphate to glyceraldehyde-3-phosphate
enzyme: triphosphate isomerase
endergonic reaction
- reaction has a +deltaG value (+2.41 kJ mol-1 or +0.58kcal mol-1)
- overall process is negative
step 6 to 10
index card
why do we have to transfer a phosphate group from phosphoenolpyruvate, PEP to ADP to give pyruvate
Energy Levels:
PEP has very high energy (-61.9 kJ/mol)
ATP has lower energy (-30.5 kJ/mol)
PEP is like a “stretched rubber band” - unstable and wants to release energy
PEP is unstable due to high energy
Needs to transfer this energy somewhere
The Transfer Process:
PEP → transfers phosphate → to ADP
Results in:
More stable pyruvate
Useful ATP molecule
Like converting “unstable energy” to “usable energy”
Benefits:
Stabilizes the system
Creates useful energy currency (ATP)
Completes glycolysis efficiently
Cell can use the ATP later when needed
it is the most the most important
pathway for the regeneration of NAD+ is reduction of pyruvate to lactate
anaerobic conditions
under anaerobic conditions, why is important to regenerate NAD+
It’s Like a Reusable Shopping Bag:
NAD+ picks up electrons (becomes NADH)
NADH drops off electrons (becomes NAD+ again)
This cycle must keep going for glycolysis to continue
In Glycolysis:
NAD+ is needed in step 6 (making 1,3-bisphosphoglycerate)
Without NAD+, glycolysis stops
The Problem:
Limited supply of NAD+ in cells
Need to keep recycling it
Like having only a few shopping bags that must be reused
Solution in No-Oxygen Conditions:
–Lactate Formation–
Pyruvate + NADH → Lactate + NAD+
Regenerates NAD+
Allows glycolysis to continue
similarities and differences between alcoholic fermentation and lactic acid fermentation
SIMILARITIES
Both start with glyceraldehyde-3-phosphate
Both use NAD+ and regenerate it
Both happen without oxygen
Both are ways to keep making energy when no oxygen is present
DIFFERENCES
–Final Products–
Alcoholic Fermentation → produces ethanol (alcohol)
Lactic Acid Fermentation → produces lactate (lactic acid)
STEPS
Alcoholic Fermentation:
Has an extra step (intermediate)
Pyruvate → Acetaldehyde → Ethanol
Uses enzyme alcohol dehydrogenase
Lactic Acid Fermentation:
Simpler process
Pyruvate → Lactate (direct)
Uses enzyme lactate dehydrogenase
WHERE IT HAPPENED
Alcoholic: In yeast (making bread/beer)
Lactic Acid: In human muscles during intense exercise
GOAL
Regenerate NAD+ to keep glycolysis running
Just do it in different ways with different end products
briefly explain decarboxylation of pyruvate to acetaldehyde
Pyruvate, a product of glucose breakdown, loses a carbon dioxide molecule and turns into acetaldehyde.
enzyme:
pyruvate decarboxylase
cofactor:
Mg2+
TPP, thiamine pyrophosphate
briefly explain reduction of acetaldehyde to ethanol
Acetaldehyde is then converted into ethanol by adding hydrogen
enzyme:
alcohol dehydrogenase
NADH gives up electrons turning into NAD+ which is needed to keep the fermentation process going
However, even though NADH and NAD⁺ are used in the reaction, they don’t show up in the final, simplified equation for alcoholic fermentation. Only ethanol and CO2 are shown
briefly explain the energy production in glycolysis
glycolysis release energy:
by breaking down glucose into 2 molecules of pyruvate releases energy = exergonic reaction
the total amt of energy released:
abt -74 kJ for each mole of glucose
negative value means given off
released energy is used to power other reactions that need energy (endergonic reactions)
ATP:
as glycolysis happen, 2 ADP molecules are turned into ATP which is used for source of energy and metabolic processes
briefly explain the control points in glycolysis
can be adjusted to either speed up or slow down glycolysis depending on the cell’s needs. this helps save energy if the cell doesn’t need more products right away.
- Hexokinase (Glucose → G-6-P):
Controlled by ATP: ATP can activate this enzyme when energy is needed.
Controlled by G-6-P: If too much G-6-P builds up, it inhibits (or slows down) hexokinase, preventing more glucose from being used.
2.Production of fructose-1,6-bP:
This step is called the “committed step” because once it happens, glycolysis will continue to the end.
3.Pyruvate kinase (PEP → pyruvate):
Controlled by ATP: If ATP levels are high, this enzyme is inhibited, slowing down glycolysis since the cell doesn’t need more energy.
Controlled by alanine: If there’s plenty of alanine (a building block for proteins), this step is also slowed down, saving resources for other processes.
