What Is Inside a Cell?

Compare the structure, function and the relationships of cell organelles in eukaryotic cells and prokaryotic cells. For example, nucleus, chromosome, mitochondria, cell membrane, cell wall, chloroplast, cilia, flagella.


Organelles
Cell Type Prokaryote

Eukaryote

Kingdom

Monera (Bacteria)

Protist

Plant

Fungus

Animal

Nucleus?

No

Yes

Yes

Yes

Yes

Mitochondria?

No

Yes

Yes

Yes

Yes

Multicellular?

No

No

Mostly

Mostly

Mostly

Chloroplasts?

No

No

Yes

Sometimes

No

Cell Wall?

Yes

Yes

Yes

Yes

No

Osmosis: The smaller molecules are water and the middle is a cell membrane

Open up your phone. No, not really. You’ll probably get into trouble. But think about opening up your phone. It’s made up of quite a few parts: computer chip, SIM card, battery, keypad, case, microphone, speaker and much more. If all of those parts don’t work together, then the phone doesn’t work. Well, living cells work the same way. Without all of the parts (organelles) of a cell working together, the cell itself won’t work.

As we’ve seen before, there are two major types of cells, prokaryotes and eukaryotes. The main difference, remember, is that prokaryotes have no true nucleus while eukaryotes have a nucleus (and can be multicellular). Prokaryotes came before eukaryotes, by about 3 billion years. While there are many theories as to how this happened, scientists are certain that the prokaryote is the older organism.

Archaea, a type of prokaryote. To its friends, it likes to be called Bob.

There are two types of prokaryotes, bacteria and a type of organism called “archaea”. We will only be focused on bacteria, as they are more well-known (even though archaea can be found in every corner of the world, too). Bacteria, even though they are very simple, still have DNA organized into one or more chromosomes. Bacteria have ribosomes and are surrounded by both a cell (plasma) membrane and then a cell wall. The cell membrane decides which nutrients and other materials can come into and out of the cell. If the cell membrane doesn’t let important nutrients in, the cell itself will die. At the same time, if the cell membrane doesn’t let waste leave the cell, the cell will also die very quickly.

The cell membrane doesn’t always have to use energy to let certain things go into and out of the cell. One of those things is water; water moves into and out of the cell because of osmosis. Osmosis is when water molecules move from a higher to a lower concentration. In the picture of osmosis, the smaller molecules are water, which pass from the left to the right-hand side until they are equal because they are in a lower concentration on the right-hand side. Osmosis is a type of diffusion. Diffusion is where molecules spread out until they are evenly distributed in a medium, such as the air.

The cell wall gives shape and structure to the cell. Inside all living cells, including bacteria, there are one or more chromosomes. These chromosomes contain all of the genetic information needed for the cell to stay alive and carry out all of the things that a cell does. Sometimes, cells like bacteria also have things called cilia or flagella. These are like tails for the cell and help it move around in liquids. Human sperm cells have flagella so that they can move toward the egg.

Since plants use the energy from the sun, they need to have specific organelles to capture that energy. The organelles that do this are called chloroplasts. The chloroplasts are green themselves because of chlorophyll, which captures sunlight. It is inside the chloroplasts that photosynthesis happens where carbon dioxide and water gets turned into sugar and oxygen.

As you can see in the chart at the beginning of this chapter, there are many differences between prokaryotes and eukaryotes. Eukaryotes have a nucleus which contains the DNA (that is made up of chromosomes). Also, they have mitochondria which are responsible for producing the energy that the cell needs. The nucleus, chloroplasts and mitochondria have membranes surrounding them (like the cell membrane) that decide which materials can enter and leave the organelle.

Going back to the comparison between cells and phones, we can see that there are a lot of similarities. The nucleus is like the computer chip: it contains the information necessary to keep the phone working and the chromosomes are like the instructions on the computer chip. The case of the phone acts like the cell wall; the microphone and speaker allow sound to enter and leave the phone just like the cell membrane in a cell. The battery, of course, is like the mitochondria. Phones don’t have anything that’s like chloroplasts, but wouldn’t it be cool if they did? Think about it: a cell phone with a solar panel so that you could charge it by leaving it in the sun!

Questions
Remember
1. Which kingdom of living things does not have a cell wall?
2. How is DNA organized?
3. What is the role of chloroplasts?
Put it together
4. Differentiate prokaryotes and eukaryotes in three ways (from this chapter).
5. Predict the consequences of eukaryotes not having a nucleus to hold their DNA.
Think about it
6. Draw a sample plant cell.
Review
7. Name the four layers of the Earth and describe briefly what is inside each one.
8. Define the four major roles of the biotic part of the ecosystem in your own words.
9. Explain natural selection using terms from this chapter.
10. State how new cells come about.
The Ultimate Basketball Player

By Devin M.

A guy named LeKobe Paul wanted to know more about what happens every day inside of his body. He went to a science lab to ask professionals. There, he met Dwayne Garnett, a Cells Specialist. Garnett had a PhD in the study of cells, so he could tell LeKobe anything about cells.

LeKobe began asking a series of questions and Garnett stopped him. Garnett could see that LeKobe was very anxious to learn more about cells. So Garnett said he would go over a couple organelles in the cell of an animal and a plant. Garnett began by saying that all animal cells have a cell membrane and that it was the security guard of the cell; only certain substances could pass. Next, he said that all cells have DNA and it works like a computer because it contains all of the information for the cell’s genetic code. Garnett then said cells have ribosomes which are inventors because they create proteins. LeKobe was eager to learn more because he had never known all of this happens inside of him. Garnett continued to share his knowledge by saying that some prokaryotic cells have flagella and that this is like the car because it helps the cell move. Garnett also said a plant cell has a cell wall which works as the frame of the plant cell. Inside of that cell wall you’ll find cytoplasm which works like junk because it just takes up space.

LeKobe was fascinated by the cells in his body but now he wanted to know more about plant cells. So Garnett told him that since plants use energy from the sun, they need chloroplasts. Chloroplasts are fishnets of the cell: they capture sunlight. Garnett ended his long lecture by giving one more fact, this one about eukaryotes. He said eukaryotic cells have mitochondria which work like an engine and provide all of the energy the cell needs.

LeKobe was grateful and he shook Garnett’s hand, then waved goodbye. On the way home, some scrubs challenged LeKobe to a basketball game. LeKobe dropped 150 points in 10 minutes and only allowed 2 points because he was distracted by a beautiful young lady walking down the street.

Interview with a Ribosome

By Cyen Tiss

Shaw High School

Recently, I had the pleasure of being shrunk down to microscopic size and traveling through a human skin cell. I was able to talk to many of the organelles, but by far my most interesting conversation was with Robert, a ribosome. The following is what we talked about.

Robert, left, and two other ribosomes on a strand of DNA

CT: Thank you for taking the time out of your busy schedule to talk to us!

R: No problem – I’m just going to finish up making this protein, and I’ll get with you.

CT: Okay.

[There is a two-minute delay while Robert releases the DNA he has a hold onto and lets go of the protein he just made.]

R: Now. What did you want to talk about?

CT: Well, I hardly know where to begin. Why don’t you tell me about where you grew up, what your childhood was like, you know, how things started?

R: Cyen, that was a few hours ago now, but let’s see what I can tell you. I was born over in the nucleolus, you know, that small ball in the middle of the nucleus. I spent the first minutes of my life in the nucleus, hanging out with DNA. It was there that I met older ribosomes and they showed me how to make proteins.

CT: Really! Now, what’s that like?

Stereoscopic image of a protein: to see it in 3 dimensions, cross your eyes to merge the two images into one

R: Making proteins? It’s quite fun. You see how I have two halves, a small and a large half? Well, what they showed me is how to get a hold of the strings of DNA like this [Robert grabs a long, thin string of DNA between both halves, see picture above] and peel the two strands apart. Then, I read one of the strands and build a protein.

CT: How do you make the protein?

R: The process is pretty complicated, but all you really need to know is that the DNA has all of the instructions that I need. The older ribosomes all showed me how to make proteins really well.

CT: Now, I see proteins floating around all over the place in this cell. Where do they end up going?

R: The proteins? Oh, that’s easy. These proteins are made by me and my ribosome friends in the nucleus, you see, and then they leave the nucleus for the rest of the cell. There’s a story told by all the ribosomes that the proteins just used to leave the cell membrane and that was it, until Golgi came along.

CT: Gol … what?

R: Oh, Golgi. Rhymes with “Mole G..”

Golgi apparatus

CT: Golgi! But what the heck is a “Mole G”?

R: Never mind. So these Golgi apparatus came along and they decided that they would come up with a solution. The Golgi hang out in the cytoplasm of the cell and package up all of these proteins so that they can make their way outside of the cell. There’s a Golgi apparatus right over there [Robert points with his small half to a green object that looks like a stack of pancakes]. The proteins start out at that smallest layer and then work their way through all of the layers. By the time they’ve gotten to the last layer, they’re all wrapped up and ready to go.

CT: Nice.

R: Yeah, I think it’s pretty cool.

CT: But what happens when you make too many? I see a huge pile-up at this Golgi apparatus right over here?

Endoplasmic Reticulum

R: Oh, well, what happens is that those extra proteins go over to one of those weird-looking vacuoles [see picture to the left]. They’re in charge of storage. In fact, I made a protein this morning that went straight to the vacuole – all because this one Golgi apparatus got stressed out and couldn’t handle his load of proteins. I hope they make it through the day or the whole cell will die.

CT: Wow! It’s that serious?

R: For real. All the ribosomes over there are talking about it [Robert points to a group of ribosomes hanging out on a strange, folded object].

CT: What’s that hang-out spot called?

R: That’s the endoplasmic reticulum. I don’t really know why we call it that, but everyone just says “E.R.” for short. And when we’re hanging out on it, it’s called “rough E.R.” When there’s no ribosomes there, we call it “smooth E.R.” because you never run into any trouble.

CT: What happens on the E.R.?

R: Well, that’s what we like to call the kitchen. All the chemicals in the cell get processed there, so everything gets cooked up nice and neat. In fact, I just had lunch on that E.R. right next to you. Cooks up a nice carbohydrate that one, let me tell you. Speaking of, it’s dinner time and then I have to go make some more proteins.

CT: OK, I’ll let you go! Thanks a lot for talking to us!

R: My pleasure.

Respond

  1. Name the eight organelles mentioned in this interview. For each one, write down its name and function in your own words.
  2. In detail, how is a protein made?
  3. In your own words, explain what happens to a protein after it is made until it leaves the cell.
  4. What are two questions you would ask a ribosome (or any other organelle in the cell)?
Cells Under the Microscope

You will get three slides, one by one. Each slide represents a different kingdom of life. For each slide:

  1. Zoom in on a cell as far as you can. Sketch the cell.
  2. What kingdom does it belong to?
  3. Do you see the presence of a nucleus in the cells? Why or why not?

 

Kingdoms of Life

In this activity, you will do research to complete the following chart:

Name Kingdom Multi- or single-celled? Does photosynthesis? Has a centriole?
Bed bug
House fly
Yeast
Yogurt
E. coli
Corn
Moss
Beans
Mushroom
Fern
Cheese
Amoeba
The Jelly Bean Problem

By Glenn Westover

How can large particles of food and other nutrients get into cells? The cell is full of cytoplasm, a fluid, and the cell membrane has to remain intact. It is like a water balloon; the cell membrane cannot break, because if it does, the entire cell will burst.

  1. How do large particles, those too large to diffuse, get into cells?
  2. Do cells have mouths?
  3. Does swallowed food mingle or mix with the organelles?
  4. Which cell organelle could function as a mouth?
  5. Get the following materials (per group): 1 plastic shopping bag, 1 pair of scissors, 15 cm of string, 4 pieces of wrapped candy.With the materials in hand, you must get the candy into your bag according to the following rules:
    1. The candy must enter through a solid part of the bag.
    2. The inside of the bag may not be directly open to the external environment.
    3. The candies entering the bag must remain clustered together.
    4. Students may work with their hands in the bag to act as the inside of a cell.
    5. The candy may be eaten only if it enters the bag “cell” under the specified conditions.
  6. What you just accomplished is called endocytosis. Make a drawing of endocytosis.
Functions of the Cell

Cell Wall

The cell wall is responsible for maintain the shape and structure of the cell. Bacteria often have a chemical called peptidoglycan in their cell wall. The cell wall also is responsible for maintaining the correct balance of water in the cell.

  1. What do you think would happen if there were a large hole in the cell wall?
  2. Peptidoglycan is produced by the ribosomes inside the cell. When this protein reaches the cell wall, what does the cell wall do? [HINT: Does the cell need it or not?]
  3. Suppose that a bacteria in a pond is very dehydrated. What will the cell wall do, and why?

Cell Membrane

The cell membrane (or plasma membrane) is referred to as being “selectively permeable,” meaning that it allows some substances to pass through while it prevents other substances from leaving. State whether the cell membrane allows the following materials to pass through and why or why not:

  1. Waste is produced by the ribosomes inside the cell.
  2. The cell wall allows sugar (which contains energy) to reach the cell membrane.
  3. The DNA hits the cell membrane.

Ribosome

The ribosomes are small organelles that float around the inside of the cell, looking for DNA. They are made up of two parts, a small and a large part. When they trap the DNA between the two parts, they read the DNA’s code and create proteins. These proteins go on to make up everything in the prokaryotic cell.

  1. Let’s say that there’s a disease which only affects the ribosomes in a prokaryotic cell. What do you think will happen to this cell?
  2. Why is it important that the ribosomes and DNA are both in the same part of the cell?
  3. Can ribosomes leave the cell membrane? Why or why not?

DNA

The DNA (or deoxyribonucleic acid) contains all of the genetic information for the cell.

  1. The DNA contains two copies of the cell’s genetic information. When a bacterial cell splits into two cells, what do you think will happen with the DNA?
  2. A new bacterial cell will produce a copy of its own DNA. What is it called when there is an error in the copy? [Hint: You may need to use the biology book for this!]

The genetic information that is contained by DNA will help to create proteins. What organelle needs to join the DNA in order to create proteins?

Flagella

The flagella is a tail-like structure that some prokaryotic cells have in order to help them move.

  1. Most, but not all bacteria have flagella. In what environment is there bacteria that need to have a flagella? Why?
  2. Think about what we’ve learned about natural selection. What advantage does having a flagella give over bacteria that do not have it?
  3. Again, think about what we’ve learned about natural selection. Why do some bacteria not have a flagella? In other words, what advantage does it give to a bacteria to not have a flagella?

Mitochondria

The mitochondria of a cell are responsible for producing ATP, which contains the energy that the cell uses. ATP is a molecule that has to be used immediately in order to get the energy from it. In fact, every molecule gets used about three times per minute.

  1. Why do you think that the energy gets used up so quickly?
  2. Where in the human body would you expect to see the highest concentration of mitochondria in cells?
  3. Mitochondria have been found to have their own DNA! Scientists think that means mitochondria were once independent cells that were really good at storing and making usable energy. Since bacteria don’t have mitochondria, but all other kingdoms of life do, then what do you know about mitochondria?

Chloroplasts

The chloroplasts of plant cells are able to capture energy from the sun and convert it to usable energy.

  1. As you can see in the above diagram, chloroplasts reflect green light, which makes them appear to be green. What colors of light do they absorb?
  2. Should you try to grow plants under green lights? Why or why not?
  3. Imagine what would happen if our cells had chloroplasts. What would that be like? Describe at least three effects.

Cytoplasm

The cytoplasm is the jelly-like substance that takes up space on the inside of the cell. It is mainly composed of salty water and proteins. Organelles move easily through the cytoplasm, and it pushes on the cell membrane like water in a water balloon.

  1. Why, do you think, is the cytoplasm mainly made up of salty water? [Hint: Think of what else is made up of salty water and where the first cells evolved.]
  2. Why is it important that the organelles move easily through the cytoplasm?
  3. What would happen if the cytoplasm did not push on the cell membrane at all?
Prokaryotic Cells

Use play-doh so that you can make a model of the prokaryotic cell. You will need the following information:

Organelle Function Shape
Cell Wall Structure & strength Almost rectangular and defines the size of the cell
Cell Membrane Decides what comes in & out of cell Fits on inside of cell wall
DNA Contains all information necessary for life Coiled string
Ribosomes Makes proteins Small balls that are made up of two halves, one half bigger than the other
Flagella Movement Tail-like, can be as long as the cell
Cytoplasm Allows for protein transportation Jelly-like substance that fills the cell
  1. Make a model of the cell with the play-doh
  2. Sketch and label the cell, putting the functions of each organelle on the sketch
  3. In your own words, what does “prokaryote” mean?
Eukaryotic Cells
  1. What is the major difference between prokaryotes and eukaryotes (do not give book definitions)?
  2. Using the Play-Doh, create, sketch and label a eukaryote, keeping in mind that a eukaryote has all of the organelles as a prokaryote (cell wall, cell membrane, DNA, ribosomes) plus all of the following:
Organelle Function Shape
Nucleus Controls cell, contains DNA Large ball in the middle of the cell
Nucleolus Makes ribosomes Small ball in the nucleus
Endoplasmic reticulum Site of chemical reactions, attachment of ribosomes Folded paper outside nucleus
Golgi apparatus Packages proteins Stack of pancakes outside nucleus
Vacuoles Storage Various shapes outside nucleus
Ribosomes Protein production Small balls made up of two halves, with one half bigger than the other
Cell Metaphor

The purpose of this activity is to create a metaphor for the major organelles of the eukaryotic cell. A metaphor is a useful way to remember the functions of the cell. For example, if my metaphor was that a cell can be like a school:

Cell organelle Metaphor: School
Nucleus The main office, because it directs the actions of the school
Cell Wall The outer walls of the school, because they keep out cold, heat
Cell Membrane The security guards, because they choose who to let through
DNA The teachers and books, because they have the information
Ribosomes The students, because they make the school function
Mitochondria The cafeteria, because it’s where the energy comes from
  1. Choose the topic for your metaphor and write it down.
  2. Choose six of the organelles in a eukaryotic cell and make the metaphor, as I did above.
  3. Either write a short story (two paragraphs) about something fictional that happens with your metaphor or make a drawing of your metaphor.
Carrot Diffusion

In this activity, you will be discovering how water can affect carrots by entering or leaving the cells of the carrot.

  1. Get the following materials: Two beakers or containers, string, measuring tape, salt, balance, carrots
  2. Fill two beakers with equal amounts of water.
  3. Add 15 g salt to one beaker and label it “Salt Water”.
  4. Cut a carrot in half. Tightly tie a piece of string two cm below the cut end of both pieces.
  5. Place one carrot half (cut end down) in the “Salt Water” beaker. Place the other carrot with cut end down in the “Fresh Water” beaker.
  6. Form a hypothesis about what you think will happen in each beaker.
  7. After 24 hours, remove carrots and observe them and the tightness of the strings. Record data.
  8. What was the purpose of having you tie thread on each carrot?
  9. Did the thread become loose in fresh water or salt water?
  10. Did the thread become tight thread in fresh water or salt water?
  11. Did the carrot develop a soft texture in fresh water or salt water?
  12. Did the carrot develop a firm texture in fresh water or salt water?
  13. In which type of water did the carrot cells increase in cell size (freshwater or salt water?)
  14. In which type of water did the carrot cells decrease in cell size (freshwater or salt water?)
  15. What evidence supports your conclusion?
  16. What do you think would happen to human blood cells if they were placed in a beaker of salt water?
Edible Cell

You will make a model of a cell. This cell should be able to be mostly eaten, meaning that you can have some inedible parts. If it can’t be eaten at all, then other students will be disappointed in you and you may not be able to have a part of their cell on the day of the cell party. Ideas include: Jello molds, cakes, different types of candies, etc. If you know what you want to make but do not have the resources, let your teacher know as soon as possible.

  1. You will make a bacterial, animal or plant cell. You must include a legend which describes the different parts and functions of your cell, along with how they are represented in your cell (see example below).
  2. You must include at least six organelles in your cell. Organelles include (but are not limited to): Cell wall, cell membrane, mitochondria, chloroplasts, flagella, cilia, Golgi apparatus, lysosomes, ribosomes, rough and smooth endoplasmic reticulum, nucleus, nucleolus, vacuoles, DNA, and cytoplasm.

Sample legend (don’t copy – it won’t be right!):

Item Organelle Function
Jolly Rancher Mitochondria Makes power
Sprinkles DNA Holds genetic information
Toothpick Flagella Helps the cell move
Peppermint Ribosome Makes proteins
Frosting Cell wall Provides structure to the cell
Jello Cytoplasm Fills the cell
Plant and Animal Cells

Make a Venn diagram to fill up a sheet of plain paper. Label one side “Plant Cell” and the other side “Animal Cell”. Include at least three items in each part of the Venn diagram, including a quick sketch to illustrate each point.

Discovering Enzymes

Discovering Enzymes

By Pascale Chenevier and Gil Toombes

Overview

Students use hydrogen peroxide to view reactions between enzymes and proteins and thank about the results.

Materials

  • Hydrogen peroxide
  • Acetone
  • Pipettes
  • Test tubes
  • Gloves
  • Safety goggles
  • Potatoes
  • Eggs (egg whites)
  • Carrots
  • Dirt
  • Leaves
  • Wood
  • Rocks

Introduction

Fresh potato shows an interesting chemical activity. When dipped in a solution of hydrogen peroxide, it triggers bubbling of oxygen. This activity is due to a special protein produced by the potato to protect itself against oxidative stress. Oxidative stress is very common on our planet because of our oxygen rich atmosphere. Iron is oxidized into rust by oxygen from the air, a process accelerated by water and salt. The skin is sensitive to oxidative agents called “free radicals” for which cosmetic manufacturers design special “anti-age” creams (often containing vitamin C as the anti-oxidizer). UV light shining on oxygen turns it into an even stronger oxidant, ozone (O3), which is in the ozone layer or in copiers, and that ozone is dangerous (everybody can recognize the smell of ozone because of copiers). The enzyme in potato is called catalase. An enzyme makes a reaction happen faster. If you let hydrogen peroxide sit in a container for long enough (months at room temperature) bubbles of oxygen would be released. The catalase in potato juice breaks the hydrogen peroxide down much, much faster.

Put a small amount (about 1-inch high) of hydrogen peroxide into a test tube. Cut a small sliver of fresh potato and drop it into the hydrogen peroxide. Bubbles will start to form around the potato sliver. What’s going on? There are lots of questions you could ask about this reaction but this activity addresses two chief questions.

What things make bubbles when immersed in hydrogen peroxide?

As a group, design experiments to test which things (milk, carrots, earth, leaves, wood, hair, spit, rocks, etc.) make bubbles in hydrogen peroxide. Think about how to make the comparison as accurate as possible. Predict (or guess) what you think will
happen? Write down a description of your experiments, predict (or guess) the results you expect, carry out the experiments and summarize the results.

Can we speed up, slow down or stop the reaction of hydrogen peroxide and potato juice?

We will blend and separate potato juice. Mixing potato juice and hydrogen peroxide makes foam filled with bubbles. As a group, design a protocol to test the effect of different chemicals and conditions on the reaction. Don’t forget to do a proper “control” experiment.

Summarize the results of all the tests to show the effect of chemicals and conditions on the reaction.

To conclude, we’ll do one last test of the stability/fragility of proteins. Shake potato juice with acetone (best known as nail polish remover) and test for activity: no activity. The potato juice doesn’t change appearance when we add acetone because the concentration of the active protein, catalase, is very small. Try the same thing on egg white that contains a far greater concentration of proteins (in particular albumin). This time the egg white turns into a white hard solid just like cooked egg white. Acetone has completely changed the structure of the proteins in egg white. Bad conditions destroy the complex structure of proteins. When the proteins in egg white lose their structure, they turn white and gel together. When the catalase in potato juice loses its structure, it can no longer break down hydrogen peroxide.

Enzymatic Browning of Apples

Apples and other fruit will turn brown when they are cut and the enzyme contained in the fruit (tyrosinase) and other substances (iron-containing phenols) are exposed to oxygen in the air. The purpose of this chemistry laboratory exercise is to observe the effects of acids and bases on the rate of browning of apples when they are cut and the enzymes inside them are exposed to oxygen. A possible hypothesis for this experiment would be:

Acidity (pH) of a surface treatment does not effect the rate of the enzymatic browning reaction of cut apples.

Materials

  • Five slices of apple (or pear, banana, potato, or peach)
  • Five plastic cups or other clear containers
  • Vinegar (or dilute acetic acid)
  • Lemon juice
  • Solution of baking soda (sodium bicarbonate) and water (you want to dissolve the baking soda. Make the solution by adding water to your baking soda until it dissolves.)
  • Solution of milk of magnesia and water (ratio isn’t particularly important – you could make a mixture of one part water one part milk of magnesia. You just want the milk of magnesia to flow more readily.)
  • Water
  • Graduated cylinder or measuring cups

Procedure

  1. Label the cups:
    • Vinegar
    • Lemon Juice
    • Baking Soda Solution
    • Milk of Magnesia Solution
    • Water
  2. Add a slice of apple to each cup.
  3. Pour 50 ml or 1/4 cup of a substance over the apple in its labeled cup. You may want to swirl the liquid around the cup to make sure the apple slice is completely coated.
  4. Make note of the appearance of the apple slices immediately following treatment.
  5. Set aside the apple slices for a day.
  6. Observe the apple slices and record your observations. It may be helpful to make a table listing the apple slice treatment in one column and the appearance of the apples in the other column. Record whatever you observe, such as extent of browning (e.g., white, lightly brown, very brown, pink), texture of the apple (dry? slimy?), and any other characteristics (smooth, wrinkled, odor, etc.)
  7. If you can, you may want to take a photograph of your apple slices to support your observations and for future reference.
  8. You may dispose of your apples and cups once you have recorded the data.
  9. What does your data mean? Do all of your apple slices look the same? Are some different from others?
  10. If the slices look the same, this would indicate that the acidity of the treatment had no effect on the enzymatic browning reaction in the apples. On the other hand, if the apple slices look different from each other, this would indicate something in the coatings affected the reaction. First determine whether or not the chemicals in the coatings were capable of affecting the browning reaction. Were they?
  11. Even if the reaction was affected, this does not necessarily mean the acidity of the coatings influenced the reaction. For example, if the lemon juice-treated apple was white and the vinegar-treated apple was brown (both treatments are acids), this would be a clue that something more than acidity affected browning. However, if the acid-treated apples (vinegar, lemon juice) were more/less brown than the neutral apple (water) and/or the base-treated apples (baking soda, milk of magnesia), then your results may indicate acidity affected the browning reaction. What affected the browning reaction?
  12. Was the hypothesis supported or not? If the rate of browning was not the same for the apples and the rate of browning was different for the acid-treated apples compared with the base-treated apples, then this would indicate that the pH (acidity, basicity) of the treatment did affect the rate of the enzymatic browning reaction. In this case, the hypothesis is not supported. If an effect was observed (results), draw a conclusion about the type of chemical (acid? base?) capable of inactivating the enzymatic reaction.
  13. Based on your results, what substances in each apple treatment affected the enzyme activity responsible for the browning of the apples? Which substances did not appear to affect the enzyme activity?
  14. Vinegar and lemon juice contain acids. Baking soda and milk of magnesia are bases. Water is neutral, neither an acid nor a base. From these results, can you conclude whether acids, pH neutral substances, and/or bases were able to reduce the activity of this enzyme (tyrosinase)? Can you think of a reason why some chemicals affected the enzyme while others didn’t?
  15. Enzymes speed the rate of chemical reactions. However, the reaction may still be able to proceed without the enzyme, just more slowly. Design an experiment to determine whether or not the apples in which the enzymes have been inactivated will still turn brown within 24 hours.
Protein Structure and Folding

Purpose
To demonstrate how polypeptides may become folded through interactions between the side chains of amino acids.

Background Information

Proteins make up all of the important parts of our body: hair, skin, muscle, eye color, and more! As we have learned previously, proteins are chains of amino acids. We can call these chains polymers, which simply means that they are molecules that are joined to each other. Technically, we can even call proteins a type of polypeptide, since they are polymers of amino acids.

Humans only use 20 different amino acids, which we get from the food we eat. We break down polypeptides (proteins) from animals or vegetables, then recombine those amino acids to make new polypeptides that we need. Those amino acids are very similar to each other, but are different in one way. They are similar because they all have an amino group which is made up of a nitrogen and two hydrogens and a carboxylic group made up of a carbon bonded to an oxygen and also an alcohol group (oxygen and hydrogen). They are different because they all have different side chains (or “R” groups).

Depending on the side chains, amino acids can be classified as being non-polarpolaracidic, or basic.

  • Non-polar: Has no clear positive and negative charges on the molecule
  • Polar: Has a clear negative and positive side
  • Acidic: Is negatively charged
  • Basic: Is positively charged

These side chains influence how an amino acid interacts with other amino acids. This is important because those amino acids will be packed tightly together in a polypeptide, causing the protein that it forms to fold and have a very specific shape.

Materials

You will need about 34 cards cut from poster board of five different colors, one for each of the major classes of amino acids and a special color for cysteine. Make two copies of each amino acid:

  • 10 Blue polar (hydrophilic) Asn, Gln, Ser, Thr, Tyr
  • 14 Red nonpolar (hydrophobic) Gly, Leu, Met, Phe, Pro, Trp, Val
  • 2 Yellow cysteine Cys
  • 4 Black acidic (negatively charged) Asp, Glu
  • 4 White basic (positively charged) His, Lys

Once you have cut out the rectangular cards, you will need to label each of them with the name of the amino acid it represents. If desired, the structural formula of the side chain may also be drawn on the card (Figure 1).

Procedure

  1. You will now make the following sequence: Met, Lys, His, Val, Ser, Leu, Asp, Glu, Cys, Asn, Tyr, Val, Phe, Trp, Pro, Ser, Thr, Gln, Cys, Gly. Identify these cards and link them together. These links are the peptide bonds formed between the amino acids.
  2. Now you will demonstrate the folding process. The strongest interaction between the side chains is a covalent bond formed between cysteine molecules. Identify the cards that represent cysteine. Bend the polypeptide chain so that the two side chains will be attracted to each other. Make sure that the links stay together. Make a sketch of what you have right now. You do not need to label all of the amino acids.
  3. The next strongest interaction will be between the acidic and basic amino acids. Identify these two areas and manipulate your chain so that the positively charged groups are near the negatively charged groups. Sketch the molecule at this point.
  4. The weakest interaction will be between hydrophobic interactions (meaning that they dislike water). Nonpolar side chains of amino acids try to get away from water. There is water completely surrounding the protein, so fold the protein so that the nonpolar side chains clump together in order to stay away from the water. Sketch and label the molecule.
  5. Now make up your own molecule, following these same rules that you followed in steps #2 – 4. Sketch and label the final molecule, then challenge another group to fold your protein, given the order that you created.
  6. Find another group and fold their protein, sketching and labeling your final product.
  7. Are proteins simply long chains of amino acids? Why or why not?
  8. Why do you think the folding of proteins is important to their function in living things?
Defend Your Organelle

By Amy Stuhm

  1. From the teacher, you will draw a random organelle from the following list: Cell Membrane, Mitochondria, Lysosome, Cytoplasm, Ribosome, Golgi Apparatus, Endoplasmic Reticulum, Nucleus, Vacuole.
  2. Use your textbook, the internet, and any other materials to research your organelle and and answer the following questions:
    1. State the function/s.
    2. Describe what it looks like.
    3. What would happen if it did not exist?
    4. Describe what diseases/conditions occur in the body if it malfunctions.
  3. Defend why the cell needs this organelle (you). Prepare a presentation that will convince the rest of the class that they should keep you!