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Lecture 16
Glycolysis II
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Glycolysis & Human
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Glucose
Cytoplasm
Transporter(Malfunction is related to Diabetes)
HOH
Before Step 1 of Glycolysis:
Inherited Diseases:
Deficiency of Phosphoglycerate Kinase (Step 7)Deficiency of Pyruvate Kinase (Step 10)
Inability of exercise due to muscle pains
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Arsenate Poisoning
Arsenate (AsO43-) is structural analog of inorganic
phosphate Pi (HPO42-) Competes with phosphate for binding site inglyceraldehyde 3-phosphate dehydrogenase (Step 6)
Very unstable!
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Questions & Answers
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Quest ion:
What is the net outcome per molecule of
glucose during glycolysis?
1. 2 ATP consumed; 4 ATP produced; 2 pyruvate produced
2. 4 ATP consumed; 2 ATP produced; 2 pyruvate produced
3. 2 ATP consumed; 4 ATP produced; 1 pyruvate produced
4. 4 ATP consumed; 2 ATP produced; 1 pyruvate produced
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Quest ion:
Why is the PFK-1 step of glycolysis
called the first commi t tedstep?
1. It is the first regulated step of the pathway.
2. It is the only metabolically irreversible step.
3. It is the first step through which all hexoses entering thepathway must pass.
4. It is the step bridging the hexose and triose phases.
5. It is the first step to produce ATP.
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Quest ion:
Which is true about the four isozymes of
hexokinase?1. They all have approximately the same Kmvalue.
2. Hexokinases I and II catalyze the reverse of the
reaction catalyzed by hexokinases III and IV.3. All four hexokinases are usually saturated at normal
blood glucose concentrations.
4. Hexokinase I is active mostly in the liver.
5. Hexokinase IV has a much higherKmthan the others.
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More Quest ions :
1. What are the three irreversible steps of
glycolysis?
2. The product of aldolase is dihdroxyacetone
phosphateand ______. Give name and chemical
structure.
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Fate of Pyruvate,
Horto n Chapter 11.3
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The Fate
of Pyruvate
10 Steps of Glycolysis
(See Lecture 11)
Citric Acid
Cycle CO2H2O
Animals, Plants
& many Microbesunderaerobicconditions
(see later)
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The Fate
of Pyruvate
Anaerobic:
Fermentation to Ethanol
in yeast & some bacteria
Anaerobic:
Fermentation to Lactate
in exercising muscles,
red blood cells
and lactic acid bacteria
Precursor in
Gluconeogenesis
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Fermentation
In the absence of aerobic respiration(=membrane-associated electron transport system, see later)
Fermentation regenerates NAD+(Oxidizes NADH to NAD+)
If NAD+ would not be regeneratedglycolysis would stop!
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~ ~~
NADH + H+NAD+
Step 6:The addition of a phosphategroup is coupled to an oxidation,
generating NADH and a
high-energy phosphate bond.Step 7:ATP is produced by
substrate-level
phosphorylation.
Step 8:A chemicalrearrangement occurs.
Step 10:ATP is produced bysubstrate-level
phosphorylation.
Step 9:Water is removed, causingthe phosphate bond tobecome high-energy.
Glyceraldehyde
3-phosphate
1,3-bisphospho-
glycerate
3-phospho-
glycerate2-phospho-
glycerate
Phospho-
enolpyruvate
Pyruvate
~
H2O
~ ~~
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Reoxidation of NADH
during alcoholic Fermentation
In yeast & some bacteria (Zymomonas)
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Reoxidation of NADH
during alcoholic Fermentation
In yeast & some bacteria (Zymomonas)
Production of alcoholic
beverages (beer & wine)
and bread
Hangover
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THE OVERALL REACTION
Glucose + 2 ADP3-
+ 2 Pi2-
+ 2 H+
2 Ethanol + 2 CO2 + 2 ATP4- + 2 H2O
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Auto-Brewery Syndrome
Consumption of carbohydrate-rich foods (sugar)
the patient appears drunk
Ethanol production in the gut by yeast
Caused by infection (e.g. antibiotic poisoning)
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Reoxidation of NADH
during Lactic Acid Fermentation
in exercising muscles,
red blood cells, and
lactic acid bacteria
(Strepto coc cus, Lactob aci l lus)
Exercise
Tooth decay
Cheese, Yogurt,
Sauerkraut, Pickles
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THE OVERALL REACTION
Glucose + 2 ADP3-
+ 2 Pi2-
2 Lactate- + 2 ATP4- + 2 H2O
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Alligator:
Quick burst ofenergy by lactic
acid fermentation
Generate ATP inthe muscle quickly
without O2
Needs long
recovery to clear
excess lactate(source of sourness
after exercise)
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The Pasteur Effect
Facultative microbes have both
fermentation and aerobic
respiration With O2 - Consumes less
glucose
Without O2 - Consumes moreglucose
S
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Summary
Under anaerobic conditions:
Pyruvate Ethanol & CO2or Pyruvate LactateBoth processes regenerate NAD+ from NADH.