Biochemistry

Part 4 Biochemistry

What Happens in a Chemical Reaction? 

Chemical reactions occur when  atoms rearrange.

Methane (CH4) and oxygen (O2) (reactants) react to form carbon dioxide (CO2) and water (H2O) (products) Notice how atoms have switched partners or rearranged. 2

What is Storing More Energy? • If energy was released, it means that the products store less energy than the reactants. This is an exothermic reaction.

Reactants

E N E R G Y

Products

Energy is released

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What is Storing More Energy? • If energy is absorbed, it means that the products store more energy than the reactants. This is an endothermic reaction. 

Products

E N E R G Y

Energy is absorbed

Reactants

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Some Chemical Reactions are VERY FAST

Click on the Hyperlink below to view the full video with audio of this very fast exothermic reaction. Reaction between chlorine, Cl 2 (green gas) and sodium metal, produces NaCl, salt

2 Na +Cl 2 →2 NaCl

Let’s Go Back to the Reaction Between Methane and Oxygen

When the oxygen and methane molecules collide, the collision has to be STRONG enough to break the bonds that already exist. If the collision does not have enough energy, the reaction does not happen. At room temperature molecules of methane gas and oxygen collide but not STRONGLY enough for the reaction to happen. 6

Activation Energy • The minimum amount of energy necessary to get a reaction going is called the activation energy, EA. 

• All reactions have a certain amount of activation energy that must be overcome for the reaction to occur

Applet showing collision of particles with different energy (<E Aand > or = EA) and orientation. 7

Exothermic Reaction and EA

Before the reaction gets to the lower level of the products, it must get over the hump of the activation energy. 8

Endothermic Reaction and EA

For the reaction to get to the higher energy level of the products, the activation energy must be supplied and stored in the bonds of the products. 9

Activation Energy Affects the Rate of a Reaction • The greater the required activation energy of a reaction, the slower the reaction will proceed. • • If the required activation energy is lowered, a reaction will proceed faster.

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Catalysts • A catalyst is a substance that makes a reaction go faster by lowering the required activation energy. 

• A catalyst IS NOT changed or used up in a reaction.

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Effect of a Catalyst The blue line represents a reaction without a catalyst. The red line represents a reaction where a catalyst was added. The activation energy is lower so the reaction will go faster.

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Decomposition of Hydrogen Peroxide Hydrogen peroxide H2O2 decomposes by itself into hydrogen gas and water.

2 H 2O2 → 2 H 2O + O2 This reaction normally happens VERY SLOWLY. If a catalyst such as potassium iodide ( KI) is added, the reaction occurs much faster. Click Here for Reaction Video 13

Biological Catalysts Enzymes • Living organisms also have catalysts that speed up reactions. 

• These catalysts are called enzymes. 

• Enzymes in the blood catalyze the decomposition of hydrogen peroxide. That is why applying hydrogen peroxide on a wound makes it foamy. •

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REVIEW Factors That Affect Reaction Rate • Temperature: 

more collisions means faster reaction rate

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• Concentration: 

more reactants means faster reaction rate

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• Pressure: 

more collisions means faster reaction rate

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• Catalyst: 

lower activation energy means faster reaction rate

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• Surface Area 

Greater surface area means more collisions for a faster reaction rate

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• pH 

Optimal pH means faster rate of reaction

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Multiple Choice (MC) FCAT Question Catalysts may reduce the amount of activation energy required for a chemical reaction to occur. Platinum (Pt) is a catalyst that is used in the catalytic converters in automobiles. In the graphs below, pathway xis a solid line representing the uncatalyzed reaction. The dotted line shows the catalyzed reaction. Which graph best illustrates the changes in a reaction when the catalyst reduces the amount of energy required?

Short-Response (SR) FCAT Released Question

REPORT ON THE 2006 FCAT SCIENCE RELEASED ITEMS

Student Responses

SCORE:

1

Catalysts are not used up in a reaction!

Key Concept: What Kinds of Biochemical Reactions Occur in Cells? • • • • •

What is photosynthesis? How does photosynthesis occur? What is glucose? What is cellular respiration? Why do organisms need to perform respiration?

• •

Click here to view animations about the relationship between photosynthesis and cellular respiration: 1. http://glencoe.mcgraw-hill.com/sites/0078695104/student_view0/brain_p 

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Technology LAB: GIZMOS- www.explorelearning.com 1. Cell Energy Cycle (Photosynthesis/Cell Respiration) 2. Interdependence of Plants and Animals 

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Sample FCAT Questions Energy from food is made available to cells by the process of cellular respiration. In this biochemical reaction, water and carbon dioxide are produced from the breakdown of: 



A. B. C. D.

   

minerals glucose ATP vitamins

–  

What do you need to know in order to answer this question?

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Sample FCAT Questions

Energy from food is made available to cells by the process of cellular respiration. In this biochemical reaction, water and carbon dioxide are produced from the breakdown of 

    

A. B. C. D. –

minerals glucose ATP vitamins

 

Correct answer: B

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Key Concept: What is the Role of Glucose? • •

It is found in plant and animal material that is used for food. Glucose molecules are broken down through a series of chemical reactions known as cellular respiration so that energy can be released and used by the cells.

• • • Click for Glucose Song  Karaoke  

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Key Concept: What is the Role of Proteins in Cells?

• •

The structure of a protein determines its function in a cell. Proteins: – Act as transporters – Can form enzymes – Control chemical reactions in cells 

Technology Lab: GIZMOS- www.explorelearning.com  Dehydration Synthesis (Proteins) 

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Sample FCAT Question One function of cell membrane proteins is the active transport of material across the membrane. What does this do for the cell? 

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A. The transport proteins only allow dissolved salts into the cell. B. The transport proteins only allow complex external proteins into the cell. C. The transport proteins regulate quantities of internal chemicals. D. The transport proteins allow water to flow in and out of the cell easily. – –

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What do you need to know in order to answer this question?

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Sample FCAT Question One function of cell membrane proteins is the active transport of material across the membrane. What does this do for the cell? 

 





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A. The transport proteins only allow dissolved salts into the cell. B. The transport proteins only allow complex external proteins into the cell. C. The transport proteins regulate quantities of internal chemicals. D. The transport proteins allow water to flow in and out of the cell easily. –

 

Correct Answer: C

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Group Discussion Question for Key Concept #1 • •

What kinds of biochemical reactions occur in cells?

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Click for Answer:

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Many biochemical reactionsoccur in cells. One familiar biochemical reaction is photosynthesis, in which plant cells create the sugar glucose (the major source of energy for living things) from the energy of the sun. As a result of photosynthesis, plant and animal cells use glucose molecules in the biochemical process of cellular respiration in order to obtain useful energy for cells.

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• • • • •

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Group Discussion Question for Key Concept #2 • What is the role of glucose in cells?  

Click for Answer:

 

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Glucose is a simple sugar produced by photosynthesis, and is found in plant and animal material that is used for food. Glucose is the molecule that is broken apart during cellular respiration so that energy from this molecule can be released and used by cells.

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Group Discussion Question for Key Concept #4 • What is the role of proteins in cells?  

Click for Answer:

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Proteinsare important to cells for several reasons. First of all, the shape and structure of a proteinsdetermines its function in a cell. Most enzymes are proteins. In addition, proteins act as transporters, helping cells pump in certain needed materials such as specific hormones, potassium, salts, etc. Through active transport. In other words, proteins control chemical reactionswithin cells. In addition, proteins form structures for long-term nutrient storage.

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Group Discussion Question for Key Concept #5

• How does DNA tell a cell what to do?  

Click for Answer:

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DNA is the genetic code found in the nucleus of the cell and makes special proteinsfor the cell to use. All biochemical reactions are based on the coded information on molecules of DNA. DNA is literally the set of direction by which cells functions. 29

Short Response SC.A.1.4.4 To produce sulfuric acid (H2SO4), one industrial plant uses the “contact process,” which consists of several reactions. The initial reaction in this process uses sulfur dioxide (SO2 ) and oxygen (O2 ) in the presence of vanadium oxide (V2 O5) pellets to produce sulfur trioxide (SO3) as shown below.  V2O5  Pellets  2S02 (g) + O2 (g) ---------------- 2SO3 (g) 

 

Sulfur Dioxide

Oxygen

Sulfur trioxide

Part A In the reaction between SO2 and O2, what is the role of the V2O5 pellets? The vanadium oxide pellets serve as a catalyst in the reaction between SO 2 and O 2 . Part B Explain what the industrial chemist could do to increase the efficiency of the reaction. To increase the reaction ’ s efficiency , the chemists could increase the temperature at which the reaction occurs .

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Short Response SC.A.1.4.4 Magnesium (Mg) in solid form can chemically react with chlorine(Cl2) gas to form magnesium chloride (MgCl2). This reaction is exothermic. 

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Mg + Cl2 ------------- MgCl2 + Heat

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In the reaction between Mg and Cl2 , what determines how quickly the reaction will occur? Explain your answer. 

The rate of a reaction depends on the surface area of the Mg and the concentration of the Cl2 . Also, the pressure and temperature of the reactants will have an effect on the rate of reaction. The number of molecules interacting and the energy in those molecules will determine the rate of reaction. 31

Short Response SC.D.1.4.2 T h e M id - A tla n tic R id g e in th e A tla n tic O ce a n h a s b e e n stu d ie d b y scie n tists fo r m a n y ye a rs. T h e fo rm a tio n s p ro d u ce d b y th e M id - A tla n tic R id g e yie ld s clu e s to th e co m p o sitio n o f E a rth ’ s cru st.

Part A In w h a t d ire ctio n a re th e tw o o ce a n ic p la te s a t the Mid - Atlantic Ridge moving in relation to each other? Part B Explain how a volcano can the movement of these plates . P a rt A :

be

produced by

T h e o ce a n ic p la te s a re m o v in g a w a y fro m e a ch o th e r.

Part B : When only a thin layer of crust is present between these spreading plates , magma may be released . The larva may then rise and spread upward and outward , forming a volcano . 32