Bio H – Energy – Handout 1
What type of work does a cell do? You have just learned that a cell can actively transport substances across membranes. The cell also builds the phospholipid bilayer and the proteins embedded in them that make up the cell membrane. A cell is really a miniature “molecule factory” in which thousands of reactions occur within a microscopic space. Some of these reactions release energy while others require energy.
To understand how the cell “does work” you must first have a basic knowledge of the forms of energy and an idea of how energy can be transformed (become another type of energy).
Energy is defined as the capacity to cause change or to perform work. Energy can be grouped into two basic forms:
1.
Kinetic energy –the energy of movement: the motion of objects (people, planets, water, wind), the vibrations of atoms by sound waves or in thermal energy (heat), the electromagnetic energy of the movements of light waves, and the motion of electrons in electricity a.
Moving objects perform work by transferring the energy of their motion into other
matter i.
Example: your legs push pedals which turn wheels, which allows you to move up a hill (on your bike!) ii.
Thermal energy causes atoms to move faster. The transfer of thermal energy is called heat (heat of your body into sweat, etc). iii.
Light is a type of kinetic energy which can be utilized to power the process of photosynthesis, making it very important to all living organisms since it is energy that is transformed (by photosynthesis) into chemical energy (a form of potential energy)
2.
Potential Energy a.
Energy that MATTER possesses as a result of its location or its structure. i.
Water behind a dam or you at the top of a hill sitting on a bicycle are examples of potential energy due to location. ii.
Chemical energy is potential energy available for release in a chemical
reaction.
1.
It is the energy that can be transformed to power the work of the cell a.
Chemical energy is found in the electrons that form bonds between elements.
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Bio H – Energy – Handout 1
The study of energy transformations is called thermodynamics. To study energy transformations we define a system (the matter that is under study) and everything outside the system (surroundings).
A system can be an electric power plant, or a cell, an organism, or an entire planet. Systems can also be closed or open systems. Closed systems exchange energy, but not matter with the surroundings. An example would be Earth. It obtains lots of energy from the sun, but virtually no matter (remember that energy “flows” but matter “cycles”. On the other hand, an organism is an open system; it exchanges both energy and matter with its surroundings (think of the matter that goes in and out of your body!).
In the world of thermodynamics, we must concern ourselves with two laws
First Law of Thermodynamics (AKA Law of Energy Conservation)
1.
Energy IN THE UNIVERSE is constant. ENERGY cannot be created nor destroyed, BUT
ENERGY can be transferred or transformed. a.
Example: a power plant doesn’t create energy, it converts it from coal (chemical to electrical energy) or, in the case of a dam, the water flows through a turbine
(converting the kinetic energy of the water to kinetic energy in the turbine  electricity. b.
A chloroplast in a plant cell converts light energy into chemical energy (so producers
really TRANSFORM light energy to chemical energy).
WAIT A MINUTE….if energy is neither created nor destroyed, why
can’t organisms recycle energy? If we look at the diagram below, we see that every transfer or transformation of energy results in
some energy being converted to thermal energy (random molecular motion) and is released as HEAT. ENTROPY is a measure of disorder or randomness.
Second Law of Thermodynamics (Law of Entropy)
1.
While the amount of energy in the universe remains the same, the quality of the energy (ability to use it for work) decreases with each transformation or transfer). a.
Example: The C-C and C-H bonds in glucose are taken apart by a multistep process in cellular respiration, and about 34% of the energy is transferred to ATP for use in chemical reactions. The rest (66%) is lost as heat (think of your body during an active workout).
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Bio H – Energy – Handout 1
The figure below compares a car and a living cell to show how energy can be transformedor transferred and how entropy increases as a result. Amazingly, car engines and cells use the same basic process to make the chemical energy in their fuel available for work.
The engine mixes oxygen with energy rich gasoline reactants in the equation) in an explosive chemical reaction that moves the pistons which turn the car wheels. The waste (products in the equation) are carbon dioxide and water, which are two simpler molecules (as compared to gasoline) and are very energy poor. Only 25% of the energy available in the bonds of gasoline are converted to the kinetic energy of the car’s movement. The rest is lost as heat.
The cell also uses Oxygen and an organic molecule (this time containing oxygen as well as carbon and hydrogen. This process, called cellular respiration transfers the chemical energy stored in glucose into another molecule, ATP. ATP is the only molecule that can be used in living organisms to do work. The waste products are still CO2 and H2O, but this process manages to transfer about 34% of the energy, while the other 66% generates heat. We have lost 2/3 of the energy stored, but can use the remaining
34% to maintain order (and structure) in the cell, and thus in living things..
Fuel
Gasoline C
8
H
18
Oxygen (O
2
)
Glucose (C6H12O6)
Oxygen (O
2
)
Heat
Energy Conversion
Combustion
Energy conversion in a car
Heat
Cellular Respiration
ATP ATP
Energy for cellular work
Energy conversion in a cell
Waste Products
CO
2
H
2
O
CO
H
2
2
O
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Bio H – Energy – Handout 1
QUESTIONS:
1.
What are three ways that molecules can get into or out of cells that utilize energy?
2.
Why is energy required for these molecules (what are the conditions that require the use of energy)?
3.
Provide three examples of work a cell does (besides making membranes and transporting molecules through the membrane).
4.
Using the terms kinetic energy and potential energy explain how a plant transforms the energy of the sun into glucose.
5.
What is the difference between transformation and transference? Provide and example of each.
JOURNAL ENTRY: Unlike open and closed systems, an isolated system is a system in which neither energy nor matter can enter or leave. Can this type of system exist in nature? Provide some reasoning, based on what you have read (in this handout) and what you know from previous classes/experiences.
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Bio H – Energy – Handout 1
1.
EXERGONIC REACTIONS
Living cells carry out thousands of reactions every day. Some reactions release energy. This energy can be in the form of heat (remember these are called exothermic), or the energy can be transferred (often via electrons and “new bonds”) to a new molecule. Because the release of energy isn’t always in the form of heat, we call chemical reactions that release energy exergonic (means energy outward)
reactions.
Cells release energy from glucose molecules in a process called cellular respiration. However, unlike the wood that we burn in the fireplace, the energy is not released in a single step. Cellular respiration involves many steps, each a separate chemical reaction; you can think of it as a slow, controlled, burn.
During this process, some of the energy escapes as heat (about 66%), but a substantial amount is stored in ATP. Energy transferred to an ATP molecule can now be utilized to provide activation energy for chemical reactions in the body.
2.
ENDERGONIC REACTIONS
In order to STORE energy (like sunlight) in molecules (like glucose) , we begin with energy poor reactants
(CO2 and H2O) and transfer absorbed energy into the chemical bonds of the “energy rich” products.
When products contain more chemical energy than the reactants, this type of reaction is called an
endergonic (energy inward reaction. This process (which involves many steps and many reactions) is called photosynthesis.
This energy includes energy in ATP
This energy is energy captured from sunlight
Amount of energy required
(

G > 0)
Exergonic reaction (cellular respiration) Endergonic reaction (photosynthesis)
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Bio H – Energy – Handout 1
The total of all of an organisms exergonic and endergonic reactions (in other words all chemical reactions) is called metabolism. As we learned earlier this year, these reactions will occur in either catabolic (breakdown) or anabolic (building up) processes (also called biochemical or metabolic
pathways).
The use of energy released from exergonic reactions to drive endergonic reactions is called energy
coupling and is very important in all cells. ATP molecules are the key to energy coupling, so lets look at the structure and function of ATP.
Catabolic and anabolic pathways in cell metabolism
Catabolic pathways involve the breakdown of nutrient molecules (Food: A, B, C) into usable forms (building blocks). In this process, energy is either stored in energy molecules for later use, or released as heat. Anabolic pathways then build new molecules out of the products of catabolism, and these pathways typically use energy. The new molecules built via anabolic pathways (macromolecules) are useful for building cell structures and maintaining the cell.
Nature Education, 2010
JOURNAL ENTRY: Use the diagram above as a starting point. Provide an explanation AND expanded diagram) for what happens in the digestive system, and within the cells that allows the cell to create proteins for the cell membrane from a turkey sandwich (meat and bread). The vocab in your paragraph should include words like catabolic, anabolic, exergonic, biochemical pathway, synthesis (or synthesize) , protein, amino acid, starch, glucose, ATP and heat in your explanation. Use the small white boards to create the diagrams as a lab group, and copy your final diagram into your journal BEFORE writing your paragraph. Check your diagram with Ms. Landa BEFORE beginning your paragraph.
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Bio H – Energy – Handout 1
ATP is the abbreviation for adenosine (the bracketed portion of the ATP molecule ) triphosphate (the circled area of the ATP molecule. The phosphates for bonds with each other that are unstable and are easily broken by hydrolysis (the addition of water). The easiest bond to break is the one between the
2 nd and 3 rd phosphate groups. This allows energy to be “donated” to a new molecule and results in the formation of an ADP (adenosine Diphosphate) and an inorganic phosphate group.
So, how do we use that “released energy” from this exergonic reaction to power another reaction? The third phosphate is actually transferred to another molecule (phosphorylation) before the phosphate is released (and the energy then transferred to the new molecule). Most cellular work depends on ATP energizing molecules through phosphorylation.
Three types of work are shown in the pictures below. The work shown includes mechanical work (A), chemical work (B), and transport work (C). First determine what is happening in each diagram below.
Then label the diagrams according to the type of work done and identify what symbols represent ATP,
ADP and inorganic phosphate (P i
).
_____ ______ ______
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Bio H – Energy – Handout 1
As shown in the reaction below, ATP can be regenerated (so the Pi and the ADP are reusable and can be joined. The energy released during cellular respiration from glucose is used to create ATP from ADP and
Pi. The release of the energy is exergonic, but the formation of ATP from ADP and Pi is endergonic. ATP transfers energy (through phosphorylation) and this energy will be used to drive other chemical reactions. So…how fast is this ATP to ADP reaction? A working muscle cell may use and regenerate 10 million ATP molecules per second.
It is important to remember that ATP is NOT an enzyme. An enzyme lowers the activation energy. ATP brings the energy that is required for the activation of the reaction. Our next step is to better understand how cells “harvest” energy from glucose (at least the basic steps) and produce ATP.
QUESTION:
Do exergonic processes require energy? Explain.
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Bio H – Energy – Handout 1 http://www.ncbi.nlm.nih.gov/books/N
BK26882/
Glucose and other food molecules are broken down by controlled stepwise oxidation to provide chemical energy in the form of ATP and NADH. These are three main sets of reactions that act in series—the products of each being the starting material for the next: glycolysis (which occurs in the cytosol ), the citric acid cycle (in the mitochondrial matrix), and oxidative phosphorylation
(on the inner mitochondrial membrane ). The intermediate products of glycolysis and the citric acid cycle are used both as sources of metabolic energy and to produce many of the small molecules used as the raw materials for biosynthesis. Cells store sugar molecules as glycogen in animals and starch in plants; both plants and animals also use fats extensively as a food store.
These storage materials in turn serve as a major source of food for humans, along with the proteins that comprise the majority of the dry mass of the cells we eat.
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Bio H – Energy – Handout 1
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