biochem exam 1

Question 1

gluconeogenesis

Answer 1

pyruvate to glucose
first step: pyruvate to PEP

Question 2

do not have to remember

Answer 2

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

Question 3

malate aspartate shuttle

Answer 3

can change NADH to NAD
and then NAD to NADH

Question 4

cost/benefit of bypass

Answer 4

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

Question 5

there is another way to bypass rxn #1

Answer 5

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

Question 6

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

Answer 6

D
Oxaloacetate

malate is an intermediate
the real thing in the middle is oxaloacetate :)

Question 7

7 & 10 rxn shared

Answer 7

bypasses for the 3 very exergonic (irreversible)

for glycolysis: focus on 1, 3 & 10

gluconeogenesis

Question 8

bypass #2

Answer 8

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

Question 9

glycolysis and gluconeogenesis

Answer 9

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

Question 10

bypass #3 reverse of step #1 of glycolysis

Answer 10

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

Question 11

gluconeogenesis is expensive

Answer 11

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

Question 12

notes on precursors of gluconeogenesis

Answer 12

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

Question 13

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

Answer 13

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

Question 14

from catabolism to anabolism

Answer 14

catabolic pathway is glycolysis
ATP, NAD(P)H
Precursors

divergent anabolic pathways

Question 15

pentose phosphate pathway

Answer 15

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

Question 16

pentose phosphate pathway

Answer 16

G6P to

6-phosphogluconate to

ribulose 5 phosphate

ribose 5 phosphate

fructose 6 phosphate

glycolysis

Question 17

pentose phosphate pathway

Answer 17

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

Question 18

PPP, NADPH, anti-oxidation

Answer 18

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

Question 19

NADPH determines the fate of G6P

Answer 19

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

Question 20

Storage Homopolysaccharides – Starch (Glycogen)

Answer 20

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

Question 21

Glycogen

Answer 21

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?)

Question 22

Glycogen – Why Branching?

Answer 22

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

Question 23

glyconeogenesis vs glycolysis comparison :)

Answer 23

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

Question 24

why do glycolysis
why do gluconeogenesis

Answer 24

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.

Question 25

insulin & glucagon

Answer 25

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!