8.2 The light reactions convert light energy into chemical energy

Vocab

wavelength: distance between adjacent waves

electromagnetic spectrum: range of electromagnetic types of energy from gamma waves to radio waves

pigment: chemical compound that determines a compounds color

paper chromatography: lab technique used to observe the different pigments in a material

photosystem: cluster of chlorophyll and other molecules in a thylakoid

Summary

• Sunlight is a form of electrogmagnetic energy
  
• Different forms of electromagnetic energy have characteristic wavelengths
  
• Shorter wavlengths have more energy than longer wavelengths


• Visible light, which can be seen in different colors by our eyes, only make up a small fraction of the electromagnetic spectrum
  
• Visible light ranges from wavelengths of about 400 nanometers, violet, to about 700 nanometers, red


• Wavelengths shorter than those of visible have enough energy to damage organic molecules such as proteins and nucleic acids
  
• When light hits a substance with pigments, three things can occur with the different wavelengths: they can be absorbed, transmitted, or reflected


• The pigments in leaf chloroplasts absorb blue-violet and red-orange light very well


• The cholorplast convert some of the light into chemical energy


• However, green light is either transmitted (pass through) or reflected on the chloroplast; thus, giving leaves their green color


• Paper chromatography is a lab technique that can be used to observe the different pigments in a green leaf

Steps of Paper Chromatography

1. the leaf is pressed on a piece of filter paper to deposit a "stain"


2. the paper is then sealed in a cylinder containing solvents, and is worked on under a vented hood
   
3. As the solvents move up the paper, the different pigments are dissolved and move up the paper


4. Different pigments dissolve at different rates, depending on how easily they dissolve and how strongly they are attracted to the paper
   
5. Several pigments spread out on the paper

• Chlorophyll A mainly absorbs blue-violet and red light, and reflects green light; plays a major role in light reactions
  
• Chloroplasts also contain "helper" pigments, including: chlorophyll B that mainly absorbs blue and orange light and reflects yellow-green light; and several types of carotenoids, which mainly absorb blue-green light and reflect yellow-orange light
  
• Within a thylakoid membrane, clusters of chlorophyll and other molecules make up photosystems; each containing a few hundred pigment molecules including chlorophyll A, B, and carotenoids.




• Each time that a pigment molecule obtains light energy, one of its electrons turns from "ground state" to "excited state"; which is very unstable


• Almost immediately, the pigment molecule returns to its ground state, and passes the energy to the next pigment molecule


• This cycle continues until the energy is transferred to what is called the reaction center of the photosystem


• Within the reaction center is a chlorophyll A molecule located adjacent to a molecule called a primary electron acceptor


• The primary electron acceptor traps the excited electron from the chlorophyll a molecule


• Other groups of molecules inside the thylakoid membrane use the trapped energy to make ATP and NADPH


• In light reactions, two photosystems are involved

Steps of Light Reactions:

1. first photosystem traps light energy and transfers the light-excited electrons to an electron transport chain; this photosystem can be considered as a "water-splitting photosystem" since the electrons are replaced by the splitting of a molecule of water. This process releases oxygen as a waste product, as well as hydrogen ions


2. excited electrons travel along an electron transport chain, and pump H+ ions across the membrane into the thylakoid


3. light-excited electrons in the second photosystem are transferred to NADP +, and are replaced by the electrons coming from the electron transport chain


4. the "backflow" of hydrogen ions out from the thylakoid provide power for ATP production

• The electron transport chain linking the two photosystems releases energy which the chloroplasts use to make ATP; this mechanism of ATP production is similar to that of cellular respiration


• In both systems, H+ ions are pumped across a membrane through an electron transport chain; the inner mitochondrial membrane in respiration and the thylakoid membrain in photosynthesis


• Second photosystem also can be thought of as "NADPH-producing photosystem"








• This photosystem produce NADPH through transferring excited electrons and hydrogen ions into NADP+

Concept Check

1. A leaf appears green since certain pigments in a leaf reflect or transmit green light from the sun.

2. When a molecule of chlorophyll a absorbs light, it transfers the excited electron to the electron transfer molecule; it absorbs blue-violet and red light, and reflects mainly green light.

3. Besides oxygen, two other molecules produced by light reaction are NADPH and ATP.

4. The light reactions take place in the thylakoid membranes in the chloroplast.

Concept 8.1 Photosynthesis uses light energy to make food

Vocab

chloroplast: organelle in plant cells and certain unicellular organisms where photosynthesis takes place

chlorophyll: pigment that gives chloroplast its color and uses light energy to split water molecules during photosynthesis

stroma: thick fluid contained within the inner membrane of chloroplast

thylakoid: disk-shaped sac in the stroma where light reactions of photosynthesis take place

light reactions: the reactions which the sun's energy is converted into chemical energy, takes place in the thykaloid membrane

Calvin's cycle: cycle in plants that makes sugar from carbon dioxide, H+ions, and high energy electrons carried by NADH

Summary

• In most lants, the leave contain the most chloroplasts are the major sites for photosynthesis
  
• Chloroplasts are concentrated in cells of mesophyll, the inner layer of tissuechloroplasts are concentrated in cells of mesophyll, the inner layer of tissue
  
• Tiny pores on the surface of the leaf allow carbon dioxide to enter and oxygen to leave


• Veins carry water and other nutrients from the roots to the leaves, as well as deliver organic molecules produced in the leaves to other parts of the plant
  
• The chloroplasts structure is key to its function

Structuer of chloroplast:

-inner and outer membrane

-inner membrane encloses a thick fluid called stroma

-suspended in the stroma are disk-shaped sacs called thylakoids; each thylakoid is enclosed by a membrane

-thylakoids arranged in stacks called grana (singular, granum)

• Some steps of photosynthesis occur within the thylakoid membranes, while others occur in the stroma


• In contrast to the falling of electrons during cellular respiration, electrons from water are "boosted uphill" by the energy of sunlight


• Chloroplasts use these "excited" electrons along with carbon dioxide and water to produce sugar molecules
  
• Photosynthesis occurs in two main stages: the light reactions, and the Calvin cycle
  
• The light reactions convert energy in sunlight into chemical energy


• These reactions rely on the molecules built into the thylakoid membrane

Steps of light reaction:

1. chlorophyll molecules in the membrane capture energy from the light


2. chlorophyll then remove electrons from water using the captured light (this splits the water into oxygen and hydrogen ions)
   
3. oxygen is a waste product of photosynthesis
   
4. chloroplast uses electrons and hydrogen ions to make an energy-rich molecule called NADPH (electron carrier), similar to NADH in cellular respiration


5. chloroplast also use light energy to produce ATP


6. Overall result of light reactions: the conversion of light energy into chemical energy stored in two compounds: NADPH and ATP.

• The Calvin cycle creates sugar from the atoms in carbon dioxide plus the hyrdogen ions and the high energy electrons carried by NADPH


• Enzymes of the Calvin cycle are outside the thykaloid and dissolve in the stroma
  
• The ATP produced by the light reactions provides energy for making sugar in the Calvin cycle


• The Calvin cycle does not directly need light, but it relies on the light reactions for two inputs: ATP and NADPH

Concept Check

1) Draw and label a simple diagram of a chloroplast that includes the following structures: outer and inner membranes, stroma, thylakoids.

2) What are the reactants for photosynthesis? What are the products?

The reactants for photosynthesis are water and carbon dioxide and the products are sugar and oxygen.

3) Name the two main stages of photosynthesis. How are the two stages related?

The two main stages of photosynthesis are the light reactions and the Calvin cycle. The NADPH and ATP that are produced in the light reactions are used in the Calvin cycle for creating sugar. The Calvin cycle then returns certain substances and some electrons back to the light reactions.

Questions (Set One)

p.106 1~12
1. Which of the following is not an organic molecule?
a)cellulose
b)sucrose
c)water
d)testosterone

2. Which of the following terms includes all the other terms on this list?
a)polysaccharide
b)carbohydrate
c)monosaccharide
d)glycogen

3. Which term is most appropriate to describe a molecules that dissolves easily in water?
a)hydrocarbon
b)hydrophobic
c)hydrophilic
d)organic

4. Cholesterol is an example of what kind of molecule?
a)protein
b)lipid
c)amino groups
d)lipid groups

5. The 20 amino acids vary only in their
a)carboxyl group
b)side groups
c)amino groups
d)lipid groups

6. A specific reactant an enzyme acts upon is called the
a)catalyst
b)sucrase
c)active site
d)subtrate

7. An enzyme does which of the following
a)adds heat to a reaction, speeding it up
b)lowers the activation energy of a reaction
c)cools a reaction, slowing it down
d)raises the activation energy of the reaction

8. Besides satisfying your hunger, why else mights you consume a big bowl of pasta the night before a race? Another reason why people may consume pasta the night before a race is to store sugar stockpiles (potential energy). When the body needs this energy, it will break down the stored sugar and use the energy.

9. How are glucose, sucrose, and starch related?
Glucose, sucrose, and starch are related because they are all sugars. Sucrose is formed from a glucose monomer connected with a fructose monomer. Starch is a polysaccharide that is formed by many glucose molecules.

10. What are steroids? Describe two functions they have in cells.
A steroid is a lipid with a carbon skeleton of four fused rings. One way in which steroids function in cells is through giving chemical signals throughout the body. Another function is that a certain kind of steroid called cholesterol is part of the membrane that surrounds our cells.

11. How are polypeptides related to proteins?
Proteins consist of one or more polypeptide chains. These chains are formed from a combination of amino acids.

12. How does denaturation affect the ability of a protein to function?
Denaturation affects the ability of a protein to function by causing the protein to either not function well, or not function at all.

p.107 14~15
14.
a) The one product represented with a question mark is a water molecule.
b)This kind of reaction is called a dehydration reaction because in order for the two amino acids to bond, a water molecule is removed.
c)If amino acids were added to this chain, the two places in which they could be attached would be to the OH molecules.

15.
a)At about 39 degrees enzyme A performs the best.
b)I would hypothesize that enzyme A is found in humans because the temperature range in which it performs well is about the average human temperature.
c)If the temperature rises above 40 degrees, then denaturation of the enzyme occurs, causing the rate of the reaction catalyzed by the enzyme to slow down.

Summary 5.5

In order to start a chemical reaction the chemical bonds in the reactant molecules have to be weakened. In this process it is required that energy is absorbed by the molecules. This "start-up" energy is referred to as activation energy, as it is the energy that activates the reactants and initiates a chemical reaction.

Cellular reactions rely on catalysts, compounds that speed up reactions. In the chemical reactions of organisms the main catalysts are specials proteins called enzymes. Enzymes do not supply activation energy, but lower the the energy required to start a reaction; thus, allowing reactions to occur faster at room temperature. Specific enzymes cause specific kinds of chemical reactions.

• if enzymes were to supply activation energy, the tempertaure would increase
  
• the lower the energy required to start a chemical reaction, the faster and more possibly it can occur
  

An enzyme catalyzes only one kind of reaction. The reason for this is that shape of each enzyme only fits the particular shape of reactant molecules. Furthermore, the reactant that is acted upon by the enzyme is defined as the enzyme's subtrate. The specific region in which the subtrate fits into is the activate site. The subratate's fit into the enzyme is not rigid. When a subtrate enters an enyzme, the enzyme slightly changes shape in order to fit the subrate snuggly.

Another way in which enzymes lower the activation energy is by accepting two subrates in adjacent areas. The holding of reactants together enables them to react more easily. Through this process, enzymes can catalyze the making of larger molecules from smaller molecules. Just like any protein, an enzyme's shape and structure are crucial to its functin. Furthermore, factors such as pH and temperature change can affect how an enzyme works, or if it works at all.

Concept Check

1. Explain the role of activation energy in a reaction. How does an enzyme affect activation energy? The role of activation energy in a reaction is that this is the initial energy with which a reaction starts. This energy activates reactants to start a chemical reaction. An enzyme lowers the activation energy, thus speeding up the chemical reaction.

2. Describe how a subtrate interacts with an enyzme. A subtrate interacts with an enzyme by entering the active site of the enzyme. The fit between the subtrate and the enzyme is not rigid, but instead the enzyme's active sight slightly changes shape to fit the subtrate.

Summary 5.4

Proteins execute most of the functions in cells. A protein is a polymer that is built up from a set of 20 kinds of monomers called amino acids. Furthermore, proteins play an important role in many of our daily functions; such as proteins that form hair, make up muscle, etc.

Amino Acid:
-monomer that consists of a central carbon atom, bonded to four other partners
-three of these four partners are common to all amino acids (amino group, carboxyl group, and hydrogen atom)
-the last group is the side group (AKA the "R-group), which determines the particular chemical properties of an amino acid

Long chains of amino acids linked together are called a polypeptide. Each link between the amino acids is connected through the process of dehydration. Proteins are created from one or more polypeptide chains. By arranging different amino acids into different orders, the body can compose an enormous variety of proteins. Every protein has a unique amino acid sequence.

Every protein is a series of precisely coiled, twisted, and folded polypeptides. The answer to how the proteins fold in the exact way is not fully understood. Certain side groups bond with others, which helps to fold polypeptides and to keep them folded. A protein is also affected by its environment, which in usual circumstances is aqueous. Thus, the hydrophillic amino acids tend to move to the edges of the protein, while the hydrophobic amino acids cluster in the middle.

When a protein undergoes unfavorable changes in temperature, pH, and other qualities, it could cause the protein to unravel and lose its shape; this process is called denaturation. Heating causes proteins to unfold because it breaks apart the weak bonds between side groups, and between side groups and water. After a protein goes through denaturation, it loses its power to function properly.

Concept Check

1.Give at least two examples of proteins you can "see" in the world around you. What are their functions? Two proteins that I can see are the proteins that make up fur, hair, and muscles. The function of fur is to keep animals warm, and muscles are used to perform daily things, such as moving and eating.

2.Relate amino acids, polypeptides, and proteins. Polypeptides (polymers) are longs chains of amino acids (monomers), and these polypeptides form in specific folds creating proteins.

3.Explain how heat can destroy a protein. Heat can destroy a protein by overcoming the weak bonds that are between the side groups, and between the side groups and water. Once this occurs, it changes the shape of the protein, and causes it not to function well.

4.Which parts of an amino acid's structure are the same in all amino acids? Which part is unique? The parts of an amino acid's structure that are the same in all amino acids are the carboxyl group, the amino group, and the hydrogen atom. The unique part is the side group, which determines the particular chemical properties of the amino acid.

Summary 5.3

Lipids play an important role in our bodies. In more detail, lipids are also compounds that avoid water. The term used for water-avoiding molecules is hydrophobic (water-fearing). Lipids surround and contain the watery contents of our cells, circulate in our bodies and send chemical signals to cells, and store energy in our bodies.

A fat is made up of a three-carbon backbone, glycerol, which is attached to three fatty acids (long hydrocarbon chains). A saturated fat is a fat in which all its three fatty acid chains have the maximum number of hydrogen atoms. In contrast, an unsaturated fat has one or more fatty acid chains with molecules that don't bond with the maximum possible number of hydrogen atoms.

• diets high in saturated fat could be unhealthy
• lipid containing deposits may form (plaques), attaching to blood vessels walls, which may reduce the blood flow and cause heart disease

Steroids are another type of lipid. Steroid molecules are formed from carbon skeletons which make four fused rings. Although steroids are classified as lipids (since they are hydrophobic), they are very different in structure and function from fats. Certain steroids circulate around the body as chemical signs. A commonly known steroid is cholesterol. This steroid is an essential molecule as it is part of the membranes that surround your cells. Cholesterol often has a bad image, since high levels of specific cholesterol-containing substances are linked to cardiovascular disease.

Concept Check

1.What property do lipids share? The property that lipids share is that they are hydrophobic.

2.What are the parts of a fat molecule? The parts of a fat molecule are the glycerol (three-carbon backbone), and the three fatty acids attached to it.

3.Describe two ways that steroids differ from fat.
a)steroids differ from fats in the way they are structured in a four fused ring, while fats are structured with a three-carbon backbone, with three fatty acids attached to it.
b)steroids differ from fats in that steroids circulate in our bodies as chemical signals.

4.What does the term unsaturated fat on a food label mean? The term unsaturated fat on a food label means that the fat within the food have less than the maximum possible number of hydrogen atoms. Unsaturated fat foods are probably more healthy than saturated fat foods.

Summary 5.2

Carbohydrates provide fuel and building material

A carbohydrate is a type of organic compound made from sugar molecules. Sugars are made up of elements carbon, hydrogenm and oxygen in the ratio 1 carbon: 2 hydrogen: 1 oxygen.

Simple sugars are called monosaccharides, and contain just one sugar unit. Some examples of monosaccharides are fructose, glucose, and galactose. Sugary molecules are the main fuel supply for cellular work. Cells break down the sugars and absorb the energy within them. Furthermore, cells also use the carbon skeletons of monosaccharides as raw ingredients for making other kinds of organic molecules. The glucose molecules that are not used right away are put into larger carbohydrates, or used to make fat molecules.

A disaccharide is made from the dehydration reaction. Disaccharides ("double sugar") are made up of two monosaccharides. The commonly known dissaccharide is sucrose. Sucrose is made up of a glucose monomer linked with a fructose monomer. Furthermore, sucrose is a major carbohydrate in plant sap that nourishes all parts of the plant. When sucrose is consumed, it breaks down into fructose and glucose, and these can be used right away.

Polysaccharides are long polymer chains that are made from simple sugar monomers (complex carbohydrates). Starch is a type of polysaccharide found in plants, and consists if only glucose monomers. When starch is consumed, it is kept as sugar stockpiles. Glycogen, like starch, consists only of glucose molecules. Yet, they are different in that glycogen is more highly branched. When the body requires energy, it breaks apart glycogen granules in order to release glucose. Cellulose are also made only from glucose molecules. They are found in plants cells, and protect, stiffen, and prevent the plant cell from flopping over. People, and most animals, cannot digest cellulose because the molecules necessary for breaking down cellulose are lacking. Thus, cellulose from plant foods, known as "fiber", pass through our digestive systems unchanged.

Most carbohydrates are hydrophillic due to the many hydroxyl groups within their sugar units. Yet, certain carbohydrates such as cellulose and forms of starch do not dissolve in water.

Concept Check

1.Explain the difference between a monosaccharide and a disaccharide.Give an example of each. The difference between a monosaccharide(eg.glucose) and disaccharide(eg.sucrose) is that a monosaccharides are simple sugars with just one unit of sugar, while disaccharides are two monosaccharides placed together.

2.Compare and contrast starch, glycogen, and cellulose. All starch,glycogen, and cellulose are made from glucose. Starch is found in plants and animals, and serves as a sugar storage. When a starch molecule is broken down, the glucose becomes available. Similarly, glycogen is stored as granules, and can be broken down to release glucose. Unlike starch, glycogen is more highly branched. Finally, cellulose is also made up from glucose. Cellulose serves as a building material, and unlike starch and glycogen, cannot be broken down by human bodies to extract the nutrients.

3.How do animals store excess glucose molecules.Animals store excess glucose molecules in the form of the polysaccharide glycogen.