Chapter 25 Reading Questions
Metabolism

Let's experience The Louvre as a chapter overview

    Housed in the Louvre are the treasures and masterpieces of the world, the legacy of every civilization. The tombs of Egypt's pharaohs, early Greek and Roman art, the Italian paintings of the Middle Ages, Realism and Impressionism, and art representative of the individualism of contemporary life. Housed within the cell, are numerous enzymes and coenzymes that began evolving long before the formation of the Louvre's treasures. These cellular enzymes are images of mankind's diversity as well as the controlling factors of chemical reactions.

    The term Louvre means lower. It was a fortified chateau along the banks of the Seine River. As a symbol of strength, it has served in the past as a prison, banquet hall, and part-time home of royal families. In this Chapter you will visit the mitochondria, the cellular chateau fortified with enzymes used to manufacture large quantities of ATP, the cell's useable energy source.

    The food you digest is used to restore body cell parts. In 1515, Francis I began restoring the Louvre for use as a royal palace. Subsequent rulers of France increased the size of the buildings and turned the Louvre into a repository of treasures; the life's work of architects, painters, and craftsman. As a matter of fact, under Louis XIV, the promotion of art became such an obsession that the government bankroll was depleted. Much like Louis XIV, with improper diet, you can bankrupt your energy supply and cell functions.

    Not only was the infamous Guillotine used in the courtyard of the Louvre, but the French Revolution opened the museum to the public world. You are about to learn how oxidation and reduction reactions, similar to the Guillotine, cut hydrogen atoms from molecules. Napoleon's conquests added vast holdings to the Louvre. Today France is very much preoccupied with the growth and collections of the Louvre. Restorations and aquisitions continue to be gathered as monuments to mankind.

    In this chapter on metabolism, you will work with the digested nutrients and how they are used in a complex of energy deriving reactions. It will be like a walk through the Louvre, step by step, viewing the processes that reflect all body functions.

Part 1: Introduction to Metabolism
    A. Catabolism vs anabolism
    B. Oxidation/reduction reactions
    C. Oxidative phosphorylation

Recall in Chapter 23 the Respiratory System's role in O ₂ and CO₂ exchange.
You will see the role of these two gases in metabolism. You have just finished
studying the breakdown of carbohydrates, proteins and fats in Chapter 24, you
will now apply these chemicals to the role of metabolism. The respiratory and
digestive systems supply the raw materials for all the body's chemical reactions
under the heading of metabolism. If you include the transport of these gases and
nutrients, then the role of the cardiovasular system is also vital to metabolism.

1. Define, in your own words, the two processes that depend upon each other in metabolism: anabolism and catabolism.

A. Catabolism is _____________________________________________________________
_____________________________________________________________
_____________________________________________________________

B. Anabolism is _____________________________________________________________
_____________________________________________________________

C. Identify the molecule that links anabolism and catabolism._______________

2. Illustrate the structure of the ATP molecule by referring to your textbook.

3. Identify the properties of enzymes. No way can the body's metabolic reactions
occur without enzymes that are not involved in digestion. These large proteins have
a tertiary structure that is cabable of locking onto molecules and loosening their bonds.
Hence, a chemical reaction. List five characteristics of enzymes.

1.__________________________________________________________
2.__________________________________________________________
3.__________________________________________________________
4.__________________________________________________________
5.__________________________________________________________

4. Contrast oxidation and reduction reactions.  If your car is five years old, is it rusting? Is your family lucky enough to have silver, if so does it tarnish? Did your boyfriend give you a gold bracelet that turned your arm green? (All that glitters is not gold, Honey!) These annoyances are due to the oxidation of the metals.

A. Define, in your own words, an oxidation reaction. _____________________________________________________
_____________________________________________________
_____________________________________________________

B. Illustrate the oxidation of lactic acid and name the chemical formed.

C           C
|            |
C --------->   C
|            |
CH3         CH3

C. The opposing reaction to oxidation is called ______________________.
To illustrate reduction in the reaction above, in which direction would you draw
an arrow? ____

D. If one substance is oxidized, then the other must be___________________.
Which is the energy producing reaction? _____________________________

5. Describe the characteristics of coenzymes. The hydrogen ions released in an oxidation
must be attached to another molecule.

Name the non-protein ions attached to an enzyme ________________________
The role of a coenzyme is to ________________________________________
There are two coenzymes that carry __________________________________
List below these common coenzymes and the vitamins from which they are derived.

coenzyme	vitamin source

6. Explain what happens to the hydrogen atoms released from oxidations or received in reductions. For every action there is a reaction! If there is an oxidation reaction, there must be a corresponding reduction reaction. A coenzyme can aid these reactions by accepting or donating hydrogen atoms. The molecules that serve this purpose are NAD and FAD. The wonder of these two coenzymes is that they can be oxidized or reduced depending upon the reactions in the body.

Illustrate these below in their oxidized and reduced form.
                                                                                                                                                     

oxidized form	reduced form

7. Let's use deductive reasoning to see where we are going with this introduction to
metabolism.

Are glucose and fatty acids highly oxidized or highly reduced
compounds? ___________________________________
When a substance is oxidized is energy released or used? __________________
Therefore, if these two end products of digestion undergo _________________
then energy can be produced.

8. Describe the generation of ATP through the process of   oxidative phosphorylation.

Identify the symbol that represents a high energy bond._____
Where is this bond appropriately placed on the ATP molecule. ____________________________________________________________
Define, in your own words, oxidative phosphorylation. ____________________________________________________________ ____________________________________________________________ ____________________________________________________________

9. Summarize the steps involved in oxidative phosphorylation.

1. a pair of H₂ is removed from substrates, coenzymes NAD⁺ or FAD⁺
2. each hydrogen atom is ionized into H ⁺ and an electron
3. the electrons are passed over a series carriers by reductions then oxidations
4. the H⁺ move across the mitochondrial membrane and then diffuse back
5. the H⁺ and electrons pass over the carrier chain releasing energy
6.. This energy is captured in the ATP molecule.

ADP + P + E ---> ATP

Focus Question
Describe oxidative phosphorylation.

Part 2: Carbohydrate metabolism
    A. The fate of carbohydrates
    B. Catabolism of glucose

10. You must realize by now that all those digested nutrients: glucose, amino acids and
fatty acids, are rich with C-H bonds (reduced) which supply the high energy bond to ATP.
How does this happen? If you describe carbohydrate metabolism, you are really describing __________________________________________________________________
__________________________________________________________________

List the four steps involved in carbohydrate metabolism.

1. _____________________________________

2. _____________________________________

3. _____________________________________

4. _____________________________________

THE FATE OF THE MILKY WAY BAR

A. The fate of carbohydrates

Since a Milky Way bar is mostly composed of the disaccharide sucrose,
by the time it reaches the small intestine sucrose has been hydrolyzed to
                1. _______________________
                2. _______________________
Molecules of glucose pass through the columnar cells of the small intestine
and enter the villi capillary. The blood is flooded with sugar.
The blood vessel that carries glucose molecules to the liver is the ___________________________________.
The fate of glucose can now follow five different pathways.

1. Glucose can be used immediately by cells as an ___________ source.
2. Glucose can be converted to subunits of proteins called.___________________
3. The liver can convert glucose into ___________________ in a process called _________________________________. The other body cells that can store
glucose in this form are ________________________________.
Later, when blood glucose levels are low, a process called ___________________
converts glycogen to glucose and restores blood glucose levels.
4. When all glycogen bins are filled, the liver and fat cells can convert glucose into _______________ and store this in _______________ tissue.
5. Any excess glucose spills into the ________________________.

The milky way bar is an immediate energy source. You have to get this glucose
inside of the cell. Glucose moves through the cell membrance  by ____________.
The rate is increased fivefold by the hormone ________________________.
In order for a cell to hold onto glucose, a phosphate group is attached to glucose.

B. Catabolism of glucose: Step 1:  The process of glycolysis
You will now trace the breakdown of glucose molecules through the four steps
listed above. In order to make this appealing, let's call this section:

Oh! How that Milky Way bar loves a phosphate group!

This first series of reactions, called glycolysis, occurs in the cytoplasm of all cells.
There are ten reactions in all each  requiring a specific ________________(ase)
to oxidize glucose.

Glycolysis produces:

    1. _______________________________________
    2. _______________________________________
    3. _______________________________________

Illustrate the part of the glucose molecule that is the end product of glycolysis .

C
|
C
|
CH3

 

• How many molecules of ATP are generated in glycolysis?________________
• How many molecules of NAD were reduced in this process?______________
  (These are saved for the electron transport chain.)
• Is ther another name for glycolysis? __________________________________
• Glycolysis does not require the presence of oxygen, and is designated as an ________________________________ reaction.

C. Catabolism of glucose: Step 2:  The formation of acetyl coenzyme A.

Now your Milky Way bar has become 2 molecules of pyruvic acid, with 95% of the energy still residing in the reduced H-C bonds. In the presence of OXYGEN, the next series of reactions, the Krebs cycle and the electron transport chain take place in the cell's mitochondria. In order for the mitochondria to utilize the Milky Way bar, it must again be prepared in a reaction which forms acetyl coenzyme A. This is called the transition reaction because it occurs between the anaerobic and the aerobic reactions. This process involves the removal of carbon dioxide and hydrogen from pyruvic acid. Again that famous molecule NAD⁺ is reduced to NADH + H⁺. The two carbon fragment is called the acetyl group and is linked to Coenzyme A.

To reinforce your understanding of the transition reaction, fill in the missing parts to the reaction illustrated below.

NAD⁺ becomes __________
Indicate where CO₂ is released

____                                                                                                     CoA
|                                                         |                                                    |
C=O -----------------------------> C=O + ______________ -----> _____
|                                                         |                                                    |
CH3                                                 CH3                                              _____    

pyruvic                                              _______                                      acetyl
acid                                                   _______                                      coenzyme A

Explain the above reaction in your own words. ____________________________
________________________________________________________________
________________________________________________________________
________________________________________________________________

D. Catabolism of glucose: Step 3:  The merry-go-round called the Krebs Cycle.

By now this candy bar is travelling in great circles. It is ready to enter a series of reactions
that keep repeating, the Krebs Cycle. Again, the Milky Way bar is going to go through
oxidations, reductions, and the removal of CO₂. The process begins with coenzyme A
carrying the _____________________________ to the mitochondrion.
The acetyl group combines with _________________________ to form a six carbon
compound called __________________________________ and the cycle begins.
Citric acid undergoes a series of seven conversions in which CO₂ and H₂ are removed.

                                                                oxaloacetic acid +

                                                                                                       citric acid

                                     malic acid

                               fumaric acid

                                                                                                              isocitric acid

                                      succinic acid

                                                                 aketoglutaric acid

Add the following events to the Kreb's Cycle :

1. Note that in this illustration citric acid eventually becomes the four carbon molecule
of ________________________________ to repeat the cycle over and over again.

2. Place an arrow and the CO₂ symbol in the areas where carbon dioxide is removed
during the Krebs cycle. Imagine this! The fate of the carbon atoms in your Milky Way
bar is to become molecules of CO₂.  Is this candy bar contributing to the greenhouse
effect on the environment?)

3. Describe the body removal CO2 in the Respiratory System. ________________________________________________________________
________________________________________________________________

5. In the Krebs cycle, some acids undergo oxidations, the hydrogens removed reduce
NAD⁺ and FAD⁺. Illustrate the four oxidation/reduction reactions in the cycle.

Summary of the Krebs Cycle,

1. There are _____ NADH + ____ H⁺ and ______________ FADH₂
2. How many ATP (GTP) are formed?________________________
3. how many CO₂ are released? ____________________________

E. Catabolism of glucose: Step 4:  The bucket brigade called the electron transport chain.

The electron transport chain is a series of oxidation/reduction reactions setting
up an  electrochemical gradient using  H⁺.  Most of the ATP is produced in this
oxidative phosphorylation. List the five types of carrier molecules below.

1._______________________________
2._______________________________
3._______________________________
4. _______________________________
5. _______________________________

In this series of events, hydrogen atoms are ionized into H⁺ and electrons. Electrons are passed from one carrier molecule to the next, similar to the way a bucket of water may be passed from one person to the next to put out a fire. Each carrier is oxidized when the electrons are passed to the next carrier. H⁺ are pumped from the mitochondrial matrix, just as water would spill in a bucket brigade, as the H⁺ spill back, energy is released and captured in the third phosphate bond of the ATP molecule. This is a simple way of explaining chemiosmosis. In this way, 34 molecules of ATP are generated. The end product of the Milky Way bar is 38 molecules of ATP for each glucose molecule that goes through this entire series of reactions.

Glycolysis produces ____________ ATP molecules.
Krebs Cycle produces ___________ ATP molecules.
Electron transport chain produces ______________ATP molecules.

Illustrate the overall reaction for aerobic respiration below.

There is one last piece to this aerobic reaction. Aerobic means oxygen is present.
This is the same oxygen you are always inhaling, the same oxygen the hemoglobin
molecule is carrying, and the same oxygen your cells will "DIE" without.

Describe the role of oxygen in aerobic respiration. ______________________________________________________________
_____________________________________________________________

So now you know! In summary, the fate of the Milky Way bar is to obtain glucose
to start a series of energy producing reactions.

1. Each molecule of glucose can produce up to ___________ molecules of ATP
which will be used as the energy source for ______________________ reactions.

2. In glycolysis, there is a net gain of ________ ATP, and this reaction does not
require the presence of oxygen, it is said to be ___________________________.

3. The main purpose of the Krebs Cycle is to "pick off" ___________________ from
the acetyl group using vitamin related carriers called _________________________,
these are transfered to the ____________________________________________.

4. In this cycle, glucose is broken down and its carbon atoms are released as ______.

5.Finally, through a series of reactions called _______________________________
in which electrons are passed down an ___________________________________
almost half of the energy in the glucose is captured in _________________________.

6.The final molecule to be reduced is ____________________________________.

All that is left is the empty wrapper!

Focus Question
How do you obtain that empty wrapper.

Essay Alert: Summarize the energy producing reactions that are part of the cell's carbohydrate metabolism.