Download Unit 1 – Lectures 4 – Cellular Metabolism (Chapter 5) What is

Unit 1 – Lectures 4 – Cellular Metabolism (Chapter 5)
What is Cellular Metabolism?
Metabolism is made of all of the chemical reactions happening in an organism (even just
one cell) at a time. There are two main types of reactions
(1) Anabolic – A building up reaction that brings two molecules together to form a
bigger molecule. This requires energy to be put into it to make it form.
(2) Catabolic – A breaking apart reaction that takes a larger molecule and breaks it
apart. The energy in the bigger molecule is released and the molecule breaks up.
Cellular Metabolism is thus the sum of all the anabolic and catabolic reactions occurring at
any one time in a cell.
Energy Use in a Cell
Energy in a cell is kept in the form of chemical bonds. There is never free energy in a cell as
it is always kept in a bond.
There are two main molecules involved in energy use. Carbohydrates are important to
harvest energy from. In addition, ATP is an important carrier of energy.
ATP stands for Adenosine Tri-Phosphate. It is an Adenosine attached to three phosphates.
The
final
phosphate
bond
is
a
high
energy
bond.
A–P–PP
ATP gives energy to something by releasing that final high energy bond and transferring it
somewhere through the process of phosphorylation. In this case, the high energy
phosphate bond drives the recipient molecule to do something.
The catabolism of ATP leads to the high energy bond being released.
A–P–PP  A–P–P +
 P (ATP is broken apart and high energy bond is
released)
The anabolism of ADP leads to the high energy bond being formed into a new ATP.
A–P–P
+
 P  A – P – P  P (ATP is reformed when the high energy bond
phosphate is reincorporated)
However, the free high energy phosphate is never kept alone. Thus simultaneously, the
bond is reformed with the other molecule to make it do something. Often this is with a
protein as proteins do almost all the functions of a cell. Thus the catabolism of ATP is
coupled with the anabolism of a protein and the high energy phosphate bond.
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A–P–PP
\
X--------------------------- X  P (X is now bonded to the high energy bond of phosphate)

A–P–P
Sugars as a Source of Energy
The environment supplies sugars for cells. Sugars are simple carbohydrates that have a lot
of energy stored in their chemical bonds. Sugars end in the suffix –ose. Such as sucrose,
glucose, galactose, mannose, lactose, etc.
The most important sugar is glucose with a chemical formula of C6H12O6.
This sugar is like a hexagon with much energy stored in the chemical bonds of a closed
circle. This was the example of the 6 kindergartners holding hands and how they would
move around a lot.
This sugar is very important and all cells have fundamental metabolic process to break
down glucose in a catabolic reaction and release the energy inside of it. This process is
called glycolysis. Glycolsysis is a series of eyzymes that charges up and catabolizes glucose
to produce ATP. Glucose is the key entry point sugar for glycolysis as all other sugars must
first be turned into glucose before the process may occur. This is because glucose is the
only sugar recognized by the first enzyme in the process of glycolysis. Remember: Each
enzyme is very specific to a molecule. One enzyme will not work on any molecule other
than the one that it is meant to. Thus the first enzyme of glycolsysis specifically recognizes
glucose.
FUNDAMENTAL PROCESS: GLYCOLSYSIS
Glycolysis occurs in all cells, aerobic or anaerobic. It occurs in the cytoplasm of all cells. It
is a series of enzymes that work on glucose to energize it and allow it to catabolize into two
parts that allow the energy to be released into new ATPs.
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Metabolism
lucose:
sugar that is
e common
ntry point
to energy
oduction.
In the first part, energy is taken from ATP and put into glucose to charge it up. Each ATP
gives its high energy phosphate onto the sugar to impart energy to it. Note that sugars like
glucose are stable enough not to break apart sponateously.
Now, after the energy is put into glucose, the 6-Carbon molecule breaks apart and becomes
two three carbon molecules that each have a high energy phosphate bound to the carbons.
However, more phosphates must be places on the carbons to take off more energy. Thus
new phosphates from the environment (called inorganic phosphates) are escorted onto the
3-Carbon molecules by the escort molecule NAD. Two NADs bring a phosphate onto the
two 3-Carbon molecules. The NAD then exchanges the phosphate for hydrogens and
becomes NADH+H with each of the 3-Carbon molecules now bound to 2 phosphates. The
new phosphate immediately sucks out chemical energy from the carbon network.
Now, glycolysis enzymes come and one by one take off the phosphates from the 3-Carbon
molecules and place these high energy bonds onto an ADP. This produces 4 ATPs (2 per 3Carbon molecule). The 3-Carbon molecules at the end of the process are each called
pyruvic acid.
Inputs and Outputs of Glycolysis
Input:
1 molecules of Glucose (6-Carbon sugar)
2 molecules of ATP
2 molecules of NAD+P
4 molecules of ADP
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Output
2 molecules of Pyruvic Acid (Each a 3-Carbon molecule)
2 molecules of ADP
2 molecules of NADH+H
4 molecules of ATP
ATP Production Capacity of Glycolysis
Gross Output: 4 ATP
Input: 2ATP
---------------------------Net Output: 2 ATPs per molecule of Glucose
Glycolysis can continue forever if environmental sugar is produced. ADPs are constantly
produced as other processes in the cell use ATP. However, NAD is depleted in the process.
Thus all cells must have a way to recover (recycle) the NADH+H’s back to NAD.
FUNDAMENTAL PROCESS: FERMENTATION
Fermentation is a process that all cells are capable of that recovers NADs from NADH+H’s
to allow glycolysis to always continue. This process also occurs in the cytoplasm of any cell
that does it. However, there are many types of fermentation.
Fermentation is an anaerobic process in which no Oxygen is required. If a cell is able to
undergo aerobic (oxygen requiring) processes than fermentation will not function.
However, some bacteria can only undergo fermentation.
Fermentation uses the product of glycolysis, pyruvic acid, to function.
Lactic Acid Fermentation is simple using an enzyme that can take the H’s from NADH+H
and transfer them onto pyruvic acid to create lactic acid. NAD is released and able to go
capture another phosphate for glycolysis.
Ethanol Fermentation is the process where the fermentation enzymes work to change
pyruvic acid to acetaldehyde that can be used to change NADH+H into NAD. This occurs by
removing a Carbon by the lose of CO2. Leaving the 2-Carbon molecule Acetaldehyde.
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entry point
into energy
production.
This process does not produce ATPs but rather produces NAD For use in glycolysis.
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