glycolysis

Question 1

what makes glucose a good fuel?

Answer 1

yields good amount of energy upon oxidation
can be efficiently stored in polymeric form (glycogen)
many organisms and tissues can meet energy needs on glucose alone

Question 2

glucose is a versatile biochemical precursor. bacteria can use glucose to build:

Answer 2

all of the amino acids
membrane lipids
nucleotides in DNA and RNA
cofactors needed for metabolism

Question 3

what are the four major pathways of glucose utilization?

Answer 3

storage: can be stored in polymeric form (starch, glucose) when there is excess “energy” (ATP) available
glycolysis: generates energy via oxidation of glucose for short term energy needs
pentose phosphate pathway: generates NADH via glucose oxidation for biosynthesis of lipids and nucleotides
synthesis of structural polysaccharides: in cell walls of bacteria, fungi, and plants

Question 4

what is glycolysis?

Answer 4

sequence of enzyme catalyzed reactions by which glucose is converted into pyruvate. pyruvate can be further oxidized and used in biosynthesis. synthesis of ATP and NADH also occurs

Question 5

research of glycolysis played a large role in modern biochemistry in:

Answer 5

understanding the role of coenzymes
discovery of the pivotal role of ATP
development of methods for enzyme purification
inspiration for next generation biochemists

Question 6

what are some feeder pathways for glycolysis? eg where does the glucose come from?

Answer 6

glucose molecules are cleaved from glycogen and starch by glycogen phosphorylase (yields glucose-1-phosphate)
disaccharides are hydrolyzed, such as Lactose and Sucrose, and yield glucose and other sugars (fructose, galactose, mannose) which enter glycolysis at different points

Question 7

Does glycolysis involve oxygen? explain?

Answer 7

no. glycolysis was likely one of the earliest energy-yielding pathways and developed before photosynthesis when atmosphere was anaerobic. So the early organisms had to find a way to get free energy from glucose anaerobically

Question 8

what is the general overview of glycolysis? 2 phases

Answer 8

the general reaction is
Glucose + 2 NAD+ + 2 ADP + 2 Pi –> 2 Pyruvate + 2 NADH + 2 ATP + 2 H2O
phase 1: preparatory phase, uses ATP
phase 2: payoff phase, creates ATP and NADH

Question 9

what is used and made in glycolysis? what is the net gain?

Answer 9

used: 1 glucose, 2 ATP, 2 NAD+
made: 2 pyruvate, 4 ATP, 2 NADH
net gain of 2 ATP, yayyy

Question 10

what are the potential fates of pyruvate made from glycolysis?

Answer 10

in aerobic conditions it can be oxidized to Acetyl CoA and enter the citric acid cycle, resulting in CO2 and H2O
in anaerobic conditions it is fermented to lactate (animals) or ethanol (yeast)

Question 11

what is fermentation? what’s the purpose?

Answer 11

fermentation occurs in anaerobic conditions after glycolysis and generates ATP without consuming oxygen or NAD+. It involves the reduction of pyruvate to another product (lactate or ethanol) and regenerates NAD+ for further glycolysis under anaerobic conditions

Question 12

what is the reaction for lactic acid fermentation? draw mech

Answer 12

reduction of pyruvate to lactate using NADH and lactate dehydrogenase. ∆G is spontaneous. NAD+ is also produced, important for refueling glycolysis

Question 13

what is the Cori Cycle?

Answer 13

In the muscle, ATP is produced by glycolysis for contraction. The pyruvate produced is reduced to lactate and transported to liver where gluconeogensis occurs to create glucose from lactate, but it costs 6 ATP. The glucose is transported to the muscle to allow continued glycolysis there, so the muscle is gaining 2 ATP but the whole system is losing 4 ATP

Question 14

what is the reaction for ethanol fermentation? draw

Answer 14

pyruvate is reduced to acetaldehyde and then to ethanol. enzyme pyruvate decarboxylase reduces pyruvate to acetaldehyde and releases CO2. alcohol dehydrogenase reduces acetaldehyde to ethanol and converts NADH to NAD+

Question 15

what is gluconeogensis?

Answer 15

the opposite of glycolysis, its a pathway that synthesizes glucose

Question 16

which steps differ in gluconeogenesis from glycolysis?

Answer 16

all of the spontaneous, irreversible steps require additional enzymes.
First step: pyruvate carboxylase converts pyruvate to oxaloacetate (draw mech, slide 53)
Second step: phosphoenolpyruvate carboxykinase converts oxaloacetate to PEP (draw mech, slide 54)
Fructose 1,6-bisphosphate to fructose 5-phosphate is catalyzed by fructose bisphosphatase-1 (opposite of PFK)
glucose 6-phosphate to glucose is catalyzed by glucose 6-phosphatase (opposite of hexokinase)

Question 17

where do glycolysis and gluconeogenesis usually take place in the cell?

Answer 17

glycolysis is usually in the cytoplasm and gluconeogenesis is usually in the mitochondria (or cytosol)

Question 18

gluconeogenesis is expensive, what does it cost? why are we willing to pay this cost?

Answer 18

cost: 4 ATP, 2 GTP, 2 NADH
it is physiologically necessary. important systems like the brain, nervous system, and red blood cells generate ATP only from glucose. when glycogen stores are depleted, we need to get glucose from somewhere
this mostly happens during starvation or vigorous exercise

Question 19

what is the pentose phosphate pathway? what does it generate?

Answer 19

a pathway that uses glucose 6-phosphate to generate NADPH and ribose precursors to nucleotides, coenzymes, DNA, and RNA
NADPH plays a role in reducing glutathione, which prevents oxidative stress. NADPH also plays role in synthesis of fatty acids and sterols etc.