Download Unit V Teacher Notes - Cell Energy

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UNIT V – CELL ENERGY
I. CHEMICAL ENERGY AND LIFE (pp. 217 - 221)
A. Energy and Life
Energy is the ability to do work_. Cells require energy for metabolic
reactions, _active __ transport, cell division, and maintaining
_homeostasis_. We obtain energy from _food__, but most energy
originally comes from the sun. Plants are able to capture the sun’s energy
and use it to produce glucose, C6 H12 O6. This process, known as
photosynthesis, occurs in the chloroplasts_ of plant cells. The reaction
for photosynthesis is: __6 CO2 + 6 H2O + sun →_ C6 H12 O6 + 6 O2_.
Although glucose is the preferred energy molecule for the cell, other
carbohydrates, _lipids__, and _proteins____ can also be broken down for
energy.
B. Chemical Energy
The chemical energy in food (and all molecules) is stored in the _covalent
bonds. This is _potential___ energy. When the bonds are broken and
the _electrons_ are released, some energy is lost as _heat___, but a
percentage of the potential energy can be converted to useable energy in
the form of _ATP__. Food molecules cannot be used as a direct energy
source for the cell because food contains too much energy – would be
wasteful and destructive.
C. ATP
_Adenosine TriPhosphate_ is a _nucleotide_ that is composed of
_adenine (nitrogen base), _ribose (5-carbon sugar), and _3 phosphate
groups___. Energy is stored in _phosphate-phosphate bonds__.
These “rechargeable batteries” are mostly present in the cell in two forms:
ATP - Adenosine TRI Phosphate. Has _3_ phosphate groups.
ADP - Adenosine DI Phosphate. Has _2__ phosphate groups.
_ATP__ has the most phosphate bonds, and therefore contains the most
_potential_ or stored energy.
Cells are able to use and recycle ATP by breaking off or adding a phosphate group.
1. Energy can be used when a phosphate bond is hydrolyzed (broken)and
_ATP__ is converted to _ADP__.
____ATP + water → ADP + P + energy___ (exergonic process)
2. Energy is stored; that is, ATP is “recharged” by _adding_ a phosphate
group to _ADP__.
____ADP + P + energy → ATP___ (endergonic)
Under normal conditions, both of these processes are occurring at the
_same time and _all the time in a cell.
II. ENZYMES
(pp. 158 - 160)
The molecular tools of the cell; proteins are instrumental in almost everything organisms
do, including support, structure, movement. One very important function of proteins is to
serve as _enzymes___. Enzymes trigger _chemical__ reactions in the body by serving
as a _catalyst__. A catalyst _triggers_ a chemical reaction without being _used up in
the reaction__. An enzyme works by lowering the activation energy, that is the
energy required to _get the reaction started_.
A. Enzymes share four common features:
1. Enzymes work best within a narrow _pH___ and _temperature___ range.
Ex: pepsin in stomach has pH of 2
2. Enzymes do not make a reaction happen that couldn’t happen on its
own; they simply make the reaction occur much _faster__.
3. Enzymes are not _used up or changed in the reaction___. The same
enzyme may be used over and over again.
4. Enzymes are _substrate-specific___. A substrate is the _reactant___.
Enzymes are substrate-specific because of their _shape____. The
substrate fits into a portion of the enzyme called the _active site__. This fit
between the active site of the enzyme and the substrate allows enzymes to
be specific for a certain type of reaction.
B. Inhibition of Enzyme Function
1. Competitive inhibitor – __Mimics_ normal substrate; prevents the substrate from
attaching to the _Active Site_.
2. Non-competitive inhibitor – attaches to _another part_ of enzyme away from
_active site_; changes shape of active site preventing substrate from attaching.
III. CELLULAR RESPIRATION - _AEROBIC_ ENERGY PRODUCTION
(pp. 221-223, 226-229)
Cellular respiration is the breakdown of _glucose__ in the presence of
_oxygen___ to “make” _ATP__. The oxygen required for cellular
respiration is _inhaled___ into the _lungs_, _diffuses___ into the _blood___,
and is delivered to the _mitochondria_ of the body cells by _red blood
cells__. The glucose needed is obtained through _eating/digestion_. The
glucose is transported in the blood and enters the body cells via
_facilitated diffusion._
There are two major parts to cellular respiration:
A. Glycolysis – Means _”sugar-breaking”__. Occurs in the _cytosol__ of
the cell. Glycolysis does not require _oxygen_. The splitting of glucose, or
glycolysis, occurs very quickly with the aid of _enzymes_, producing two
_3_ -C molecules known as _pyruvic acid_.
In addition, when the bonds of glucose are broken, the high energy electrons
that are released are caught by _NAD+ NADH, a molecule that acts as an
electron carrier. This electron energy will be converted to ATP later in the
process.
Glycolysis requires _2_ ATP to occur, but results in the formation of _4_ ATP,
for a net _gain_ of _2_ ATP.
 Reaction: C6 H12 O6 + 2 ATP → 2 pyruvic acid + 4 ATP +NADH
 Net Gain of ATP = __2 ATP__
B. Oxidative Respiration – Glycolysis releases less than ¼ of the chemical
energy stored in glucose. Most of its potential energy remains bound in the
_pyruvic acid_ formed from glycolysis. In aerobic conditions, meaning
_O2__ is available, the pyruvic acid formed from the breakdown of
_glucose__ during _glycolysis__ enters the _mitochondria___ of the cell
where the _enzymes__ of oxidative respiration complete the breakdown of
glucose to produce _carbon dioxide__, _water___, and _34 ATP___.
 Reaction: __2 pyruvic acid + O2 → CO2 + H2O + 34 ATP___
 Net Gain of ATP = __34 ATP___
Oxidative respiration is a 2-part process:
1. Krebs Cycle – series of reactions that occur in the mitochondrial matrix,
in which the energy stored in _pyruvic acid___ is released in the form of
high-energy _electrons___ when covalent bonds are broken and pyruvic
acid is completely broken down to _C, H, O_. There are only _2_
additional ATP produced in the Krebs Cycle; most of the energy released is
captured in the form of electron energy, producing additional _NADH_. In
addition, a second type of electron carrier is utilized, producing 2 “filled”
___electrons (FADH2)__________.

Net Energy Gain = _NADH, FADH2, 2 ATP____
2. Electron Transport Chain – In this step, the electron carriers, _NADH__
and _FADH2_ “dump” their electrons. These electrons are passed along a
series of molecules embedded in the inner membrane of the
_mitochondria_ of _eukaryotic_ cells. This same process occurs in the
_cell membrane_ of _prokaryotic_ cells. As the electrons “fall” down the
ETC, the energy they release is used to power an enzyme known as
_ATP synthase_, which attaches phosphate groups to _ADP_ to produce
_ATP_. This process is known as _oxidative phosphorylation_because
_oxygen_ must be present. It is the _protons_ of oxygen that “pulls” the
electrons down the ETC. As the electrons are collected by oxygen, _H2O_
is produced.
 Net Energy Gain = _32 ATP
http://www.dnatube.com/video/2354/Electron-Transport-Chain
*Combined Reactions of Glycolysis + Oxidative Respiration = Cellular Respiration*
____ C6 H12 O6 + 6O2 → 6CO2 + 6H2O + 36 ATP_________
**TOTAL ATP YIELD PER MOLECULE OF GLUCOSE**
Glycolysis = __2_ ATP
Krebs Cycle = __2_ ATP _
ETC =
32 ATP_
O2
II. FERMENTATION - __ANAEROBIC_ ENERGY PRODUCTION (pp. 232)
Glycolysis is constantly occurring in the _cytosol__ of every cell under
_anaerobic___ conditions, meaning _oxygen__ is not required. The reaction
for glycolysis is: _ C6 H12 O6 + 2 ATP → 2 pyruvic acid + 4 ATP +NADH _
Glycolysis is the first step for all cellular energy production.
 If oxygen is available, _oxidative respiration_ follows glycolysis.
Pyruvic acid is broken down to _CO2_and H2O and 36 ATP are
produced.
 If oxygen is not available, some types of cells have a back-up
mechanism for glucose metabolism called _fermentation___. If a
cell cannot switch to fermentation, it cannot survive without oxygen.
A. General Description
In fermentation, the pyruvic acid formed during glycolysis does not enter
the _mitochondria_, instead, the entire pathway takes place in the
_cytosol____. Fermentation does not produce any additional _ATP__,
but the removal of pyruvic acid from the cytosol allows the process
of glycolysis and the net gain of _2__ATP to continue.
B. Types of Fermentation - The 2 most common fermentation pathways used
by cells are:
1. Lactic Acid Fermentation – Pyruvic acid is converted to _lactic acid_.
May be utilized by:
 Human Muscle Cells – Occurs when demand on muscles exceeds
supply of oxygen. As lactic acid builds up in the muscle cells, it is felt
as _pain and fatigue__. This is referred to as _oxygen debt___. As
activity slows, and oxygen is re-supplied, the muscle cells switch back
to _cellular respiration___ and the lactic acid is sent to the _liver_ to
be broken down.
 Bacteria & Fungi – There are some types of bacteria & fungi that carry
out lactic acid fermentation in _anaerobic__ conditions. This is utilized
by the dairy industry to produce _cheese__ and _yogurt___.
C6 H12 O6 + 2 ATP → 2 pyruvic acid + 4 ATP → lactic acid___
2. Alcoholic Fermentation – Pyruvic acid is converted to _alcohol__ and
_CO2___. When oxygen supplies are depleted, _yeast__ and many
bacteria switch to alcoholic fermentation. This process is used commercially
for _brewing and baking________
_ C6 H12 O6 + 2 ATP → 2 pyruvic acid + 4 ATP → alcohol + CO2__
**TOTAL ATP GAIN IN FERMENTATION = 2 ATP **
V. ENERGY FLOW – A COMPARISON OF PHOTOSYNTHESIS & CELLULAR RESPIRATION
(p. 222 – 225, 233)
PHOTOSYNTHESIS
Function
Capture energy
CELLULAR RESPIRATION
Release energy
Cell
Location
Occurs In
Chloroplasts
Mitochondria
Autotrophs
Heterotrophs AND Autotrophs
Reactants
CO2 + H2O + energy
C6 H12 O6 + O2
Products
C6 H12 O6 + O2
CO2 + H2O + energy
Overall
Reaction
6CO2 + 6H2O +energy → C6 H12 O6 +
6O2
C6 H12 O6 + 6O2 →6CO2 + 6H2O + energy