biochem exam 1 Flashcards
gluconeogenesis
pyruvate to glucose
first step: pyruvate to PEP
do not have to remember
get from pyruvate to PEP but we have to get through another molecule which is oxaloacetate!
really focus on 1, 3 & 10 these are highly exergonic, irreversible and regulated through its enzymes hexokinase, PFK-1 & pyrvuate kinase which are also influenced by insulin, epinephrine and glucagon
malate aspartate shuttle
can change NADH to NAD
and then NAD to NADH
cost/benefit of bypass
benefit: pyruvate to PEP
cost: break 2 high energy phosphate bonds (ATP and GTP) to form PEP
benefit: NADH is used up in mitochondria (where it is relatively plentiful), rxn #2) and reformed in the cytosol (where it is needed later n gluconeogenesis rxn #3) it is like an NADH shuttle
there is another way to bypass rxn #1
lactate can turn into pyruvate and eventually to glucose, which is what your muscles needs
this takes place when lactate is abundant (ex: anaerobic muscle)
its first rxn produces NADH in the cytosol, so no need to transport NADH equivalent
In gluconeogenesis, instead of reversing the PEP pyruvate reaction, pyruvate is converted to ___, which is then converted to PEP.
A
Ethanol
B
Malate
C
Lactate
D
Oxaloacetate
D
Oxaloacetate
malate is an intermediate
the real thing in the middle is oxaloacetate :)
7 & 10 rxn shared
bypasses for the 3 very exergonic (irreversible)
for glycolysis: focus on 1, 3 & 10
gluconeogenesis
bypass #2
Simplehydrolytic reaction
- What does a phosphatase do? - removes pi
- Fructose-1,6- biphosphate to fructose-6-phosphate
- What makes this exergonic? - breaking the phosphate bonds, to release energy
G3P to DHAP
F2,6P
F6P
G6P
glucose
use phosphatase to remove phosphate
glycolysis and gluconeogenesis
bypass of 10
bypass of 3
bypass of 1
so in gluconeogenesis
bypass #1 is the reverse of step 10
- pyruvate to oxaloacetate to PEP
bypass #2 is the reverse of step 3
- Fructose-1,6- biphosphate to
fructose-6-phosphate
bypass #3 is the reverse of step 1
- so G6P to glucose
all of these are highly exergonic and therefore are regulated
bypass #3 reverse of step #1 of glycolysis
Simplehydrolytic reaction
- What does a phosphatase do?
- Glucose-6-phosphate to glucose
- What makes this exergonic?
- Substrate is converted as it passes into the ER of the liver and kidney. Later glucose is released into the blood.
G6P to glucose
the enzyme that catalyzes this rxn is found in hepatocytes and renal cells, but not in muscle or brain so in muscle or the brain glucose cannot be synthesized by this pathway. glucose for these organs must come from other sources
gluconeogenesis is expensive
and not just glycolysis reversed
the input of energy makes gluconeogenesis - irreversible
6 energy equivalents used!!!! for gluconeogenesis while 2 energy equivalents (or ATP, in steps 1 & 3 :) but then we end up getting 4 ATPs back in the payoff phase!) is used for glycolysis
notes on precursors of gluconeogenesis
many amino acids (the glucogenic amino acids) can be converted to pyruvate or intermediates of the citric acid cycle which can enter gluconeogenesis
amino acids can be turned into sugar
in animal, fatty acids which are converted to acetyl COA cannot be net-converted to glucose
so amino acids can turn into sugar and fatty acids cannot turn into sugar
For the synthesis of 1 molecule of glucose from pyruvate, how many ATP equivalents are required and produced, respectively?
A
2, 4
B
4, 0
C
4, 2
D
6, 0
E
6, 2
D
6, 0
this is talking about gluconeogenesis where we use 6 energy equivalents and 0 energy is produced :) because this is an anabolic and not a catabolic process
from catabolism to anabolism
catabolic pathway is glycolysis
ATP, NAD(P)H
Precursors
divergent anabolic pathways
pentose phosphate pathway
Parallel to glycolysis
- Anabolic(like gluconeogenesis)
- Occurs in the cytoplasm
- Generates NADPH (reducing agent/electron acceptor – 60% generated here)
- Generates pentoses as well as ribose 5-phosphate. A precursor for nucleotide synthesis
NADH oxidized = NAD+ reduced = NADH
pentose: 5 carbon sugar
- nucleic acids
and now we can add phosphates to them
functions of NADH
- reduction of glutathione (protects the cell from ROS)
- cholesterol synthesis
- fatty acid synthesis
pentose phosphate pathway
G6P to
6-phosphogluconate to
ribulose 5 phosphate
ribose 5 phosphate
fructose 6 phosphate
glycolysis
pentose phosphate pathway
do not have to know the pathway
G6P to nucleotides coenzymes, DNA, RNA
if the tissue doesn’t need pentose phosphates, they can be ‘recycled’ into G6P
NADPH: important reducing agent (energy source) for anabolic pathways
especially important for rapidly dividing cells (newborns, cancer)
NADPH as an anti-oxidant
so this process uses G6P to make nucleotides, DNA & RNA
if pentose phosphates are not needed then it gets recycled to G6P
NADPH can decide if G6P will go PPP or glycolysis
- if the tissue does not need nucleotides then the G6P is recycled and can go into glycolysis to be broken down
PPP, NADPH, anti-oxidation
NADPH as an anti-oxidant: very important in cells exposed to high [O2], such as RBCs - reduces glutathione (GSH) and prevent oxidative damage which helps with DRUG/TOXIN METABOLISM
so NADPH is an anti-oxidant that prevents oxidative damage. It is also an important reducing agent for anabolic processes
NADPH determines the fate of G6P
glycolysis vs PPP
Glucose
G6P
6 Phospho-gluconolactone
pentose phosphates
so NADPH is important because it determines whether or not G6P goes to glycolysis to be made into pyruvate or if it goes into the PPP to make made into pentose phosphates for DNA & RNA
Storage Homopolysaccharides – Starch (Glycogen)
Main storage polysaccharide in animals
- Greatest abundance in the liver (100g) and muscle cells (400g)
- Similar in structure to amylopectin, but with more branch points
- Unbranched glucose polymer (α1→4 linkage)
- Branches out every 8-12 residues (glucoses) using α1→6 linkages our body cannot digest beta
- It is more compact. Why?
- can break off glucose faster
Glycogen
Not as energy-rich as fatty acids, why? - because fatty acids have a lot of hydrocarbons which means they are very reduced and have a lot of energy
- What are the advantages of glycogen? - not as osmotically active
- Maintains blood-glucose levels between meals
- Keeps brain supplied with glucose
- Energy for sudden, strenuous activity (fast breakdown)
- Energy in the absence of O2
- Helps maintain osmotic balance in cells (remember?)
Glycogen – Why Branching?
to use polysaccharides as sources of energy, degradative enzymes must degrade polymers into monomers - is this what glycogen phosphorylase does?
these degradative enzymes act only on non-reducing ends
each branch ends with a non-reducing sugar
branching makes possible more rapid degradation
glyconeogenesis vs glycolysis comparison :)
focus on steps 1, 3 & 10 for glycolysis and apply it to gluconeogenesis
bypass #1
gluconeogenesis step 1 = bypass of glycolysis step 10:
- pyruvate + bicarbonate
to
- oxaloacetate
to
- PEP
or when lactate is abundant
- lactate
to
- pyruvate
to
- oxaloacetate
to
- PEP
bypass #1 is the reverse of glycolysis step 1
bypass #2 is the reverse of glycolysis step 3
bypass #3 is the reverse of glycolysis step 10
bypass #2
gluconeogenesis step 2 = reverse of step #3 of glycolysis:
- Fructose-1,6- biphosphate to fructose-6-phosphate via a phosphatase :) (Fructose-1,6- biphosphase)
bypass #3
gluconeogenesis step 3 = reverse of step #10 of glycolysis
- Glucose-6-phosphate to glucose via a phosphatase :) (G6P phosphatase
why do glycolysis
why do gluconeogenesis
why do glycolysis
- for when we need energy
- requires energy but also produces energy
- when we have a lot of glucose
Glycolysis is a central metabolic pathway that is used by all cells for the oxidation of glucose to generate energy in the form of ATP (Adenosine triphosphate) and intermediates for use in other metabolic pathways.
why do gluconeogenesis
- for when we have enough energy to make
- for when we need to make glucose
Gluconeogenesis refers to the synthesis of new glucose from noncarbohydrate precursors, and provides glucose when dietary intake is insufficient or absent.
insulin & glucagon
insulin
- favors glycolysis
- favors glycogen synthesis
glycolysis produces G6P from glucose (once insulin pushes the glucose into the cells after you just ate), that G6P can be turned into G1P which can be used for a growing glycogen chain
G1P is what is used for the glycogen chain!!!!!
glucagon
- favors gluconeogenesis
- favors glycogen breakdown
gluconeogenesis produces glucose for it to go into the blood and raise your blood sugar when you have not eaten in a while
glycogen breakdown breaks off the glucose bits off of glycogen to produce glucose for it to go into your blood stream!
