biochem glycolysis.docx

8/13/2019 biochem glycolysis.docx

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1. How many ATPs are generated by Aerobic respiration? Please work itout in a table form.

PathwayCoenzyme

yield

ATP

yield Source of ATP

Glycolysis

preparatory

phase

-2

The inputs of two ATP from the cytoplasm

are required to begin glycolysis. To start this

reaction needed the activation energy.

Glycolysis

pay-off

phase

4

ATPs made by glycolysis. Note the Net Yield

for glycolysis would be 2ATPs (4 ATP-

2ATP).

2 NADH 4 (6)

These molecules are created by glycolysis,

but they can only be converted into ATP inthe mitochondrial electron transport chain.

This requires them to enter the mitochondria.

A step that is free in some organisms, and

costs 2ATP in others. This is what causes the

differences in the Net yield of aerobic

respiration.

Pyruvate

Oxidation

2 NADH 6 electron transport chain (ETC)

Krebs cycle 2 Substrate-level phosphorylation

6 NADH 18 ETC

2 FADH2 4 ETC

Total yield

36

(38)

ATP

From the complete breakdown of one glucose

molecule to carbon dioxide and oxidation of

all the high energy molecules.


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2. What is the purpose of anaerobic and aerobic respiration?Aerobic respiration requires oxygen, anaerobic does not. The sugar

glucose is the major food molecule in the cell, but it is too energetic to use

directly in most chemical reactions. Glucose is broken down into an energy

storing molecule (ATP) that can be used throughout the cell.

Anaerobic respiration occurs in the cytoplasm when no oxygen is present for

the cell to continue respiration after glycolysis. Each pyruvate is converted to

a molecule of ethanol and one NADH is used in the reaction. Lactate

fermentation occurs in animals. Each pyruvate is converted to lactate and one

NADH is used. The purpose of both fermentation processes is to free NADH

for use in glycolysis.

3. What are the steps in glycolysis? Draw the diagram.

A glucose molecule is energized by the

addition of a high-energy phosphate from

ATP, forming glucose-6-phosphate.

A rearrangement of the molecule forms

fructose-6-phosphate.

Using the available energy of a second ATP

molecule, a second phosphate is added to the

fructose.


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The fructose-1,6-biphosphate is split into two

three-carbon molecules, each having onephosphate group attached. The

dihydrooxacetone (DHAP) quickly rearranges

to form another G3P molecule, so the net

result is two G3P molecules.

In near-simultaneous reactions, each G3P

molecule gains an inorganic phosphorous

while contributing two electrons and a

hydrogen ion toNAD+ to form the energized

carrier molecules NADH. The resulting

molecules have two high-energy phosphates.

Two molecules of low energy ADP are

elevated to ATP molecules by phosphates

from the biphosphoglycerates. This recovers

the energy invested in the first step of the

glycolysis. The remaining phosphorous is

relocated to the center position.

The final phosphate is transferred to ADP to

form ATP, and this step represents the net

yield of 2 ATP for the glycolysis process as a

whole.
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4. Why do cells need to ferment if they already get 2 ATP fromglycolysis?

When there is not enough oxygen to conduct oxidative phosphorylation, some cells

resort to fermentation to produce Adenosine Triphosphate (ATP) by substrate-level

phosphorylation. These pathways both utilize pyruvate as an electron acceptor to

recycle Nicotinamide Adenine Dinucleotide (NAD+) so that it can be reused in

glycolysis.

In Fermentation, Pyruvate is transformed into another molecule using the energy

provided by NADH. It does not usecellular respiration or any ETC, therefore, it does

not require oxygen to generate ATP.Fermentation does require a sufficient supply of

NAD+to accept electrons to sustain the process.

NADH gets converted to NAD so that it can be used again in glycolysis, and pyruvate

becomes lactic acid in animal cells, or ethanol and carbon dioxide in plants, yeast, and

bacterial cells.

The anaerobic pathway is glycolysis and fermentation. This pathway recycles the

NADH generated, so the only energy molecules made from the breakdown of sugar

by this pathway is 2ATP for every glucose molecule.

5. What pathways make up aerobic respiration?

The breakdown of glucose begins with an anaerobic pathway known as glycolysis. In

both eukaryotic and prokaryotic cells this pathway occurs. The products of this

pathway can be introduced into anaerobic pathways, referred as fermentation, or into

aerobic respiration which involves the pathways known as the Kreb's cycle,

the electron transport chain, and chemiosmosis.

During glycolysis and the Kreb's cycle, high energy electrons are released. These

electrons reduce NAD+to NAD- which is then converted to NADH. The high

energy electrons are carried by NADH to the electron transport chain (ETC).

Coenzyme A joins to pyruvate causing a loss of one carbon and the generation of

NADH. The acetyl-CoA formed enters the Krebs cycle and the acetyl group is

transferred to a molecule of oxaloacetic acid making a molecule of citric acid. The
https://www.boundless.com/biology/definition/cellular-respiration/https://www.boundless.com/biology/definition/fermentation/https://www.boundless.com/biology/definition/fermentation/https://www.boundless.com/biology/definition/cellular-respiration/


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Krebs cycle releases CO2and the high energy molecules NADH, and FADH2 which

are converted into ATP by the mitochondrial electron transport chain. The ETC

requires oxygen at the final step to accept the electrons from the last cytochrome

in ETC. Without oxygen the ETC and the Kreb's cycle stop functioning.

6. Why do we need oxygen to break down glucose completely byaerobic respiration?

Oxygen is the main requirement in aerobic respiration because in the mitochondria,

oxygen is the final electron acceptor of the electron transport chain. The electron

transport chain stops working if there is no oxygen to accept electrons and then the

high energy molecules NADH and FADH2cannot be converted back into NAD and

FAD. Without these molecules, the glucose biochemical pathway will stop. These

molecules become the limiting reagents needed for glucose break down to continue,

and when they run out, the pathway discontinue.

7. How does the electron transport chain convert NADH and FADH2into ATP?The mitochondria contain two compartments, the matrix and the intermembrane

space. The Kreb's cycle occurs in the matrix of the mitochondria. This is where

NADH and FADH2are produced. They travel to the inner membrane and dump their

electrons onto the membrane. This loss of electrons is a redox reaction and converts

NADH back into NAD while FADH2changes back into FAD.

The membrane proteins in the Electron Transport Chain are protein pumps. The

passage of electrons across them makes them change shape and pump protons across

the inner membrane from the matrix to the intermembrane space. Each NADH pumps

three protons whereas each FADH2pumps two protons.

This pumping of electrons across the inner membrane causes a concentration gradient

of hydrogen atoms across the membrane. By diffusion, the hydrogen ions will want to

travel back into the matrix to reach equilibrium. They can do so by traveling through

a special channel found in the membrane called ATP synthase. This channel uses the


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energy of the passage of the Hydrogen ions to make ATP. For each proton that passes,

one ATP is made. This is why each NADH makes three ATP and each FADH2makes

2 ATP.

8. Which enzyme regulates the glycolysis? How?Glycolysis can be divided into two phases which are energy investment phase

and energy payoff phase. During the energy investment phase, hexokinase in

step 1 transfers a phosphate group from ATP to glucose, making it more

chemically reactive. The charge on the phosphate also traps the sugar in the cell.

Glucose 6-Phosphate is converted to its isomer, Fructose 6-Phosphate with the

help of phosphoglucoisomerase.

Phosphofructokinase transfers a phosphate group from ATP to the opposite end

of the sugar, investing a second molecule of ATP. This is a key step for regulation

of glycolysis.

Aldolase cleaves the sugar molecule (Fructose 1,6-Bisphosphate) into two

different three-carbon sugars (isomers) which are Dihydroxyacetone Phosphate

and Glyceraldehydes 3-Phosphate.Isomerase catalyzes the reversible conversion between the two isomers. This

reaction never reaches equilibrium. Glyceraldehyde 3-Phosphate is used as the

substrate of the next reaction (step 6) as fast as it forms.

During the energy payoff phase, triose phosphate dehydrogenase in step 6

catalyzes two sequential reactions. First, the sugar is oxidized by the transfer of

electrons to NAD+ , forming NADH. Second, the energy released from this redox

reaction is used to attach a phosphate group to the oxidized substrate, making aproduct of very high potential energy.

The phosphate group added in the previous step is transferred to ADP

(substrate-level phosphorylation) in an exergonic reaction. The carbonyl group

of a sugar has been oxidized to the carboxyl group of an organic acid (3-

Phosphoglycerate) with the help of phosphoglycerokinase.

Enzyme phosphoglyceromutase relocates the remaining phosphate group,

forming 2-Phosphoglycerate.


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Enolase causes a double bond to form in the substrate by extracting a water

molecule, yielding phosphoenolpyruvate (PEP), a compound with a very high

potential energy.

The phosphate group is then transferred from PEP to ADP with the help ofpyruvate kinase, forming pyruvate.

biochem glycolysis.docx

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