biochem exam 1 part II Flashcards
glucose
the major fuel for most organisms
if totally oxidized, delta G = -2840 kJ/mol
versatile precursor: from it, can synthesize C=skseltons of most major molecules
fates in higher plants & animals:
- stored (polysaccharides, sucrose)
- oxidized to a 3-C compound (pyruvate): glycolysis
- oxidized to pentoses
fates of glucose
storage
- can be stored in polymeric form (starch, glycogen)
- when there’s plenty of excess energy
- glycogen, starch, sucrose
oxidation via glycolysis
- generates energy via the oxidation of glucose
- short-term energy needs
- pyruvate
oxidation via pentose phosphate pathway
- biosynthesis of lipids and nucleotides
- generates NADPH via oxidation of glucose
- ribose 5-phosphate
synthesis of structural polymerase
- cell walls of bacteria and plants
- ECM & cell wall of polysaccahrides
glycolysis
the almost-universal central pathway for carbohydrate catabolism (breakdown)
results in the storage of energy n atp and NADH
the first part of the catabolism of glucose, either anaerobic (fermentation - alcoholic or lactic acid) or aerobic
A 2-phase process
phase 1: preparatory (investment) phase
- glucose is phosphorylated and cleaved to form 1 molecule of glyceraldehyde3-phosphate. 2 ATP molecules are invested
phase 2- payoff phase
- 2 glyceraldehyde 3-phosphates are converted to 2 pyruvates. The payoff of 4 ATP and 2 NADH molecules
another representation:
energy investment phase:
2 ATP + glucose -> 2 ADP
energy payoff phase
4 ADP -> 4 ATP
2 NAD+ -> 2 NADH (reduction, step 6)
net:
glucose -> 2 pyruvate + 2 H2O
2ADP + 2Pi -> 2atp
2 NAD+ -> 2 NADH + 2H+
Fates of Pyruvate (More Later)
Aerobic Conditions: pyruvate is oxidized to yield the acetyl group of acetyl-coenzyme A.
That acetyl group is then oxidized completely to CO2 by the citric acid cycle
Pyruvate→Acetate→CO2 + H2O
NADH + O2 + 2H+ → NAD+ + H2O
Anaerobic Conditions:
Animals and microbes convert pyruvate into lactate when O2 is lacking
Through transforming pyruvate into lactate, NADH is oxidized to replenish NAD+
Replenishing NAD+ allows glycolysis (ATP production) to continue for a short time
Summary of Glycolysis and Energetics
how much of the energy in glucose is removed through glycolysis?
C6H12O6 (glucose) + 6O2 -> 6CO2 + 6H2O
delta G = -2840 kJ/mol
Glc + 2 NAD+ -> 2 pyruvate + 2 NADH + 2H+
delta G = -146 kJ/mol
146/2840 = 5.2%
much energy remains in pyruvate
Summary of Glycolysis and Energetics
glc + 2 NAD+ + 2 ADP + 2Pi
-> 2 PYRUVATE + 2NADH + 2H+ + 2ATP + 2H2O
glycolysis is very exergonic:
delta G = -85 kJ/mol
you can also think about glycolysis as a 2part process
Glc + 2 NAD+ ->. 2pyruvate + 2NADH + 2H+
delta G = -146 kJ/mol
2 ADP + 2Pi -> 2ATP + 2H2O
delta G = +61 kJ/mol
(-146 + 61 = -85 kJ/mol)
this shows that 146 kJ/mol are removed from glucose and 61 kJ/mol are stored as ATP
Summary of Glycolysis and Energetics
Glc + 2ATP + 2NAD+ 4ADP + 2Pi -> 2pyruvate + 2ADP + 2NADH + 2H+ +4ATP + 2H2O
or the net rxn:
Glc + 2NAD+ 2ADP + 2Pi -> 2 pyruvate + 2 ATP + 2 H2O
used:
1 glucose
2 ATP
2 NAD+
made:
2 pyruvate - various different fates
4 ATP - used for energy requiring processes within the cell
2 NADH - a high energy molecule, must be reoxidized to NAD+ in order for glycolysis
Glycolysis
1- 5: “preparatory phase”
Phase 1: - Preparatory (Investment) Phase Glucose is phosphorylated and cleaved to form 2 molecules of glyceraldehyde-3-phosphate. Two ATP molecules invested
Glycolysis: Step 1
Glucose-6-phosphate is produced
from blood glucose by hexokinase
Glucose phosphorylated at C-6
It keeps glucose in the cell!! because the phosphate is negatively charged and cannot pass through the phospholipid bilayer.
Glucose is now Charged - due to a negative charge from phosphate
Exergonic → irreversible
delta G = -16.7 kJ/mol
Uses/stores energy of ATP. First ATP invested! (other ATP investment is step 3 I think)
Hexokinase allosterically regulated by glucose-6-phosphate
Mg2+ lowers activation energy
(Ch #6 Biochem I – Enzyme Mechs)
1 - exergonic
2 - energy stored in the phosphate bond
3- regulated, steps 1,3,10
4 - induced fit
Glycolysis: Step 2
Isomerase converts glucose-6- phosphate to fructose-6- phosphate
6-membered ring to 5
Reversible (small ∆G) of 1.7 kJ/mol
Mg2+ lowers activation energy (Ch #6 Biochem I – Enzyme Mechs)
Glycolysis: Step 3
Fructose-6-phosphate is phosphorylated by phosphofructokinase-1 (PFK-1)
Fructose phosphorylated at C-1 Symmetrical☺now, 1,6-biphos.
Keeps all later products in the cell!! Charged.
Exergonic → irreversible Uses/stores energy of ATP
Second ATP invested!
Mg2+ lowers activation energy
(Ch #6 Biochem I – Enzyme Mechs)
1 - exergonic
2 - energy stored
3- regulated, steps 1,3,10
4 - induced fit
Glycolysis: Step 4
Fructose-1,6-bisphosphate is cleaved into two, 3-C molecules by aldolase:
- Glyceraldehyde-3-phosphate (G-3-P) ☺
- Dihydroxyacetone phosphate (DHAP) Gotta change this!
1 -> 2 molecules: endergonic, but coupled to later rxns
- FROM HERE ON, EACH REACTION IS HAPPENING TWICE! (except Step 5 – ha!)
Glycolysis: Step 5
Dihydroxyacetone phosphate (DHAP) from Step 4 is converted to Glyceraldehyde-3-phosphate (G-3-P)☺ through triose phosphate isomerase
Now we have two G-3-Ps from 1 glucose!
Prep. Phase Done!
Glycolysis
6 - 10: payoff phase
Phase 2: - Payoff Phase
2 molecules of glyceraldehyde- 3-phosphate are converted to two molecules of pyruvate.
Four ATP molecules and 2 NADH molecules were produced.
Glycolysis: Step 6
Glyceraldehyde 3-phosphate is phosphorylated/oxidized to 1,3-bisphosphoglycerate
NAD+ is reduced to NADH
1,3-Bisphosphoglycerate has a phosphate group we can cleave, and release energy to drive reactions (remember reaction coupling?). Also storing energy in the NADH.
G3P is oxidized and NAD+ is reduced (a redox rxn!!!)
NAD+ is reduced to NADH
Glycolysis: Step 7
ATP is synthesized (2 ATPs come back→net = zero at this point) as phosphoglycerate kinase transfers the phosphate group from 1,3-Bisphosphoglycerate to ADP
1,3-Bisphosphoglycerate → 3-Phosphoglycerate + ATP
Energy released used to pull previous rxns 4, 5 & 6
