Unit Iv Cell Energy

Name ______Test Date______

UNIT IV – CELL ENERGY

I. CHEMICAL ENERGY AND LIFE (pp. 201, 202)

A. Energy and Life

Energy is the ability to dowork_. 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-phosphatebonds__.

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 _sametime and _all the time in a cell.

II. ENZYMES (pp. 47-53)

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 upin

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.

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:

Glycolysis – Means _”sugar-breaking”__. Occurs in the _cytosol__ of thecell. Glycolysis does not require _oxygen_. The splittingof 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__

Oxidative Respiration – Glycolysis releases less than ¼ of the chemical

energy stored in glucose. Most of its potential energyremains bound in the

_pyruvic acid_ formed from glycolysis. In aerobic conditions, meaning

_O2__ is available, the pyruvic acidformed from the breakdown of

_glucose__ during _glycolysis__ enters the _mitochondria___ of the cell

where the _enzymes__ ofoxidative 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:

Krebs Cycle – series of reactions that occur in the mitochondrial matrix,

in which the energy stored in _pyruvic acid___ isreleased 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____

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

*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_

II. FERMENTATION - __ANAEROBIC_ ENERGY PRODUCTION (pp. 223, 224)

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_andH2O 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 musclecells, it is felt as _pain and fatigue__. This is referred to as _oxygen debt___. As activity slows, and oxygen is re-supplied, themuscle 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 oxygensupplies 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. 232)

PHOTOSYNTHESIS

/ CELLULAR RESPIRATION
Function / Capture energy / Release energy

Cell Location

/ Chloroplasts / Mitochondria

Occurs In

/ 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