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AOHS Foundations of Anatomy and Physiology I

Lesson 3 Biochemistry

Student Resources

Resource Description

Student Resource 3.1 Notes: Atoms, Molecules, and Bonds

Student Resource 3.2 Reading: Atoms, Molecules, and Bonds

Student Resource 3.3 Notes: Electrolytes, pH, and Homeostasis

Student Resource 3.4 Reading: Electrolytes, pH, and Homeostasis

Student Resource 3.5 Reading: The Chemistry of Spaghetti and Meatballs

Student Resource 3.6 Notes: Cell Membranes

Student Resource 3.7 Reading: Cell Membranes

Student Resource 3.8 Observations: Diffusion and Osmosis

Student Resource 3.9 Reading: Transport across Cell Membranes

Student Resource 3.10

Glossary: Lessons 1‒3 (separate Word file)


Lesson Review: Biochemistry

Copyright © 2014‒2016 NAF. All rights reserved.

AOHS Foundations of Anatomy and Physiology I Lesson 3 Biochemistry




Notes: Atoms, Molecules, and BondsStudent Name: _______________________________________________________ Date:___________

Directions: As you watch the presentation on atoms, molecules, and bonds, practice taking notes by filling in this resource.

1. What is an element?

2. Give three examples of elements. Include their chemical symbols.

3. What is the difference between an atom and a molecule?

4. What is a compound? Name an example.

5. Label the parts of an atom on this diagram.



6. This diagram shows the electron shells for magnesium, which has the chemical symbol Mg. Mg has 12 electrons. Illustrate where these electrons would be located on this diagram.

7. What is the difference between a covalent bond and an ionic bond?

8. What is an ion?

9. What is a polar molecule?

10. Why can a spoon hold more water than the level of its rim?




Reading: Atoms, Molecules, and Bonds



Taking in substances like air, food, and water is what keeps us going. When these things enter our bodies, they undergo different processes so that our organs can use them. The food we eat provides us with energy, and we use oxygen to help release it. Water helps carry wastes away after food has been digested, and it’s part of every cell in our bodies. In fact, 60% of our body weight is water.

Many parts of our body also play a role in protecting us from harmful things. Our skin protects us from weather, wind, and toxins in the environment. Our lungs filter particles from the air we breathe. Our immune system hunts down and fights organisms that cause infection.



The air we breathe is a mixture of several different gases. Almost 80% of the air in our atmosphere is nitrogen. Oxygen is the second most prevalent gas and makes up 20% of the atmosphere. There is more argon in the air than carbon dioxide.



Oxygen is an element. Elements can’t be broken down into any other substance by a chemical reaction.

There are 118 elements known to exist, and about 90 of them occur naturally. Everything in the universe, including you, is made from these elements.

The periodic table lists all the elements that exist. The rows and columns give us different kinds of information about each element, like what their characteristics, or properties, are. In this version of the periodic table, the colors indicate one way some elements are similar.

What’s important for us is to note is that each element has a number. That number is based on the structure of that element.

The elements that don’t occur naturally are created by physicists in order to study matter. They only exist for fractions of a second in huge complicated machines called particle accelerators.



We take oxygen into our bodies in two ways. We breathe in oxygen gas and there is also oxygen in the food we eat. Much of the oxygen in our bodies is in water molecules.

Carbon is the building-block element that many of the substances in our body are made from.

Hydrogen is also in many substances in our bodies. Most importantly, it’s in water.

Nitrogen is an important element in DNA and proteins. Even though the air we breathe is almost 80% nitrogen, we can’t break it down and make use of it. All the nitrogen we use in our bodies comes from the food we eat.

There are about 20 other elements that play important roles in our health:

• Iron in our blood cells carries oxygen through our bodies.

• Sodium regulates how much water we retain and how much we lose.

• Calcium is important in the structure of our bones and teeth.



Atoms rarely exist just as single atoms. They’re almost always bonded to other atoms. Two or more atoms bonded together are called molecules.

Molecules can be very small and simple, like the oxygen molecule, or they can be huge and complex. A protein molecule, for example, can have thousands of atoms.

To explain what atoms are in a molecule, we write out the chemical formula of the molecule. The formula consists of the letters that represent the elements and the number of atoms of each element.

O2 is the chemical formula for oxygen, the molecule we breathe. The O stands for oxygen and the 2 tells us that there are two atoms.



Here are examples of formulas for other molecules that keep your body working. You can also see the shapes of these molecules.

In the drawings, the size of the balls shows how big the atoms are relative to each other. Hydrogen is a much smaller atom than carbon. We’ll see why later in this presentation.

The formula for sugar, C6H12O6, can represent many different sugar molecules, each having a different shape. Here, we picture glucose because glucose is the molecule the body uses to get energy.

How many atoms does the glucose molecule have?

With 24 atoms, sugar is considered a small molecule by biological standards.

Sugar is a chemical compound. A compound is any substance that consists of two or more elements that occur in fixed proportion to each other.

For example, water is also a compound. As we see here, it has two H atoms bonded to every O atom.



The smallest amount of an element that exists is an atom. Atoms are made of even tinier particles. These are called subatomic particles.

The center of the atom, called the nucleus, is made of protons and neutrons.

Neutrons have no charge, only weight.

Protons have a positive charge.

Electrons orbit around the nucleus. Electrons have a negative charge.



Electrons orbit the nucleus in a series of rings called electron shells. Each shell is farther away from the nucleus, and each one can hold a certain number of electrons. The electrons always fill the shells closest to the nucleus of the atom.

The innermost ring, closest to the nucleus, holds up to 2 electrons.

The second ring holds up to 8 electrons.

The third ring holds up to 18 electrons. In the sodium atom we see here, the inner shell is full, the second shell is full, and there is one electron left over. That electron goes into the third shell all by itself.

There can be up to 7 electron shells, depending on how many are needed to hold the electrons.

Note: There are many different ways to depict atoms, and we use different kinds of drawings depending on what we want to show. In reality, atoms don’t look like any of these pictures. In fact, atoms are too small to see, even with the strongest light microscope. We use these models to help us illustrate and understand ideas about atoms.



An atom’s atomic number is determined by the number of protons it has. The number of electrons is the same as the number of protons, giving the atom a neutral charge. This is true even if the atom’s outer ring isn’t completely full of electrons.

If an atom’s outer ring has exactly as many electrons as it can hold, that atom is very stable and doesn’t usually react with other atoms. Neon, element 10, is an example of that kind of atom. If you go back to the periodic table on Slide 4, you’ll see neon (Ne) in the far right column. All the elements in that column have full outer shells and are not very reactive.

If the outer shell isn’t full, the atom is much more likely to bond with other atoms.



Most atoms are likely to bond with other atoms. Atoms bond only with other atoms that will make them more stable. You can learn more about how atoms become more stable if you take a course in chemistry.

There are two types of atomic bonds that are important in anatomy and physiology. In a covalent bond, atoms share electrons. For example, in O2 (pictured above), the two oxygen atoms each share two electrons with the other. This way, the outer shell of each atom is complete, with eight electrons.



In another type of bond, called an ionic bond, some atoms give up electrons to other atoms. This is the kind of bond we see above between sodium and chlorine, which we call sodium chloride, or table salt. Because negatively charged electrons are lost or gained in this kind of bond, the charge of the atoms is affected. An atom with either a positive or negative charge is called an ion.



In a water molecule, each hydrogen (H) is sharing its sole electron with the oxygen (O), and the oxygen is sharing one electron with each hydrogen. The H’s electrons are attracted to the O nucleus, though, because the O nucleus is much bigger than the H nucleus. Because the negative charge of the electrons is being pulled away from the H and toward the O, the H atoms are slightly positive and the O slightly negative. We call molecules that contain slightly charged atoms polar molecules.

The fact that water is polar is very important in anatomy and physiology. Because our bodies are 60% water, almost all the processes that take place in our bodies happen in water. The fact that water is a polar molecule is central to a large proportion of the things our bodies do to keep us alive.



The hydrogen bond is important to stabilizing the structures of many things in the body, from large molecules to organs. It also affects how your body carries out some chemical reactions.

When we’re referring to water, the hydrogen bond is a bond between molecules rather than between atoms, and it is considered a weak bond. A weak bond requires less energy to break it. Therefore, it requires much less energy to separate molecules of water from each other than to separate the atoms in a water molecule from each other.

You can see the hydrogen bond in action in a spoonful of water. If you fill a spoon to the very brim, you’ll see that the spoon can hold water a bit higher than its rim. That’s because hydrogen bonds hold the molecules of water together and keep them from spilling over. Of course, if you shake the spoon, you disrupt the weak hydrogen bonds and the water spills. You’ve moved the water, which has put a little energy into it, and that breaks the hydrogen bonds. The water molecules themselves are still intact.



Water is just one kind of molecule that we need. Actually, every substance we take in, including air and food, is made of molecules. Some molecules we’ll encounter often are:

Sugar – The sugar we’re used to seeing on our tables is sucrose. Sucrose is actually two kinds of sugar molecules, glucose and fructose, joined together.

Fat and protein – The steak is mostly fat and protein. Steak is a muscle. When we learn about the muscle system, you will see where the protein comes from.

Vitamins – Each vitamin is a different kind of molecule. When we eat vegetables and fruit we are ingesting vitamins. Unlike sugars, fats, and proteins, vitamins often have metal ions in them. Vitamins play a variety of roles in the body to keep it healthy.



Our bodies are very complex biochemical systems. Our biochemistry is what makes us human beings, and it’s also what makes us unique: no two people are exactly alike, because no two people’s biochemistry is exactly the same.

In this course, we will learn more about the chemistry that is important to making our bodies work. While it seems like there is a lot to learn, keep in mind that we’ll only be scratching the surface of what we know, and scientists add to this body of knowledge every day. Keep an eye out for stories in the news about the substances mentioned here. There is a lot of new knowledge being gained about all of them.

We’ll also look into some aspects of our body chemistry and function that we still don’t understand. These are questions that future scientists, doctors, nutritionists, and health care professionals—like you!—will help find the answers to.




Notes: Electrolytes, pH, and HomeostasisStudent Name:_______________________________________________________ Date:___________

Directions: Fill in the diagrams and answer the questions as you watch the presentation on electrolytes, pH, and homeostasis.

1. What is an electrolyte?

2. Name four important electrolytes and at least one function for each.

Electrolyte Function

3. Explain why drinking water while you exercise is important to electrolyte homeostasis.

4. Why do we have to replace electrolytes through things we eat and drink?

5. Explain how an antacid neutralizes stomach acid.



6. Give two examples of things that are acidic and two examples of things that are basic and note their pH.

Acidic substance pH

Basic substance pH

7. Why is it important for your body to maintain pH homeostasis?




Reading: Electrolytes, pH, and Homeostasis



As you have learned, an ion is an atom that has a positive or a negative charge. Ions are extremely important substances in many of the reactions in your body that keep you alive.

For example, our muscles contract because they get an electrical signal from our brain that moves ions around in our muscles.

When we digest our food, ions help break it down. Ions are also an important factor in how our bodies figure out how much fluid to keep and how much to get rid of via sweat and urination.

Iron ions in red blood cells carry oxygen through our system.

Every thought you have is the result of electrical signals in your brain. Those signals happen because ions are moving in your brain.

Some ions in the body are positively charged, some are negatively charged, some are a single atom, and others comprise several atoms. The charge, positive or negative, on the ions is what makes them take part in reactions. Ions are so important to muscle movement that having an imbalance of them can create heart and nervous disorders.



You’ve learned that the salt on your table is sodium chloride, made of sodium and chlorine atoms held together by ionic bonds. When you put salt in water, salt dissolves because the ionic bond between the atoms is broken and they float around in the water as ions. Some ions in your body are called electrolytes. One definition that you may have heard of is that electrolytes are a set of ions that are important for your body when you’re exercising. Sports drinks and coconut water advertise that they’ll keep you supplied with electrolytes.

We need more than 15 types of electrolytes. The most familiar ones are metal ions such as sodium and potassium. All your internal cells are bathed in a solution that is mostly sodium and water, and that same solution makes up the bulk of your blood. The organelles inside your cells are bathed in a solution that contains more potassium. Calcium and magnesium, other important electrolytes you may have heard of, work together to make your muscles contract and relax and to build strong bones.

We need fairly large quantities of electrolytes like sodium and potassium, and very small quantities of others, like zinc, copper, and selenium.



As with many other substances in your body, maintaining the homeostasis of electrolyte levels is very important. Your body keeps the amount of each electrolyte within a narrow range. When the levels of a particular electrolyte are too high, your kidneys will filter out the excess and it will leave your body in your urine.

When electrolyte homeostasis is thrown out of balance, some serious problems can arise, like seizures, kidney dysfunction, and irregular heartbeats. When you become dehydrated, your electrolytes can become more concentrated because there is less water in your body, and the high concentration can make the chemical reactions happen less efficiently. So it’s important to drink water when you’re exercising to keep your electrolyte levels balanced.



There are many ways you might lose electrolytes: when your exercise intensively for a long time, you lose electrolytes in your sweat. When you have an illness that makes you throw up or gives you diarrhea, you can lose so much body fluid that you lose too many electrolytes. Water doesn’t contain electrolytes and your body can’t make them, so you have to take them in by eating or drinking them. In the hospital, many patients aren’t able to eat or drink as much as they need, so they’re given what’s called an IV of saline solution. IV stands for “intravenous,” and it means that the substance is delivered into the body through a needle that’s put into a vein. A saline solution contains dissolved sodium chloride and sometimes other electrolytes as well.



Another important ion in your body is a hydrogen ion, H+. H+ is a hydrogen atom without its electron. H+ is an example of an ion that’s not an electrolyte (you’ll learn more about what makes an ion an electrolyte when you take chemistry). H+ is the ion we associate with something that’s an acid.

An acid is a chemical that, when it meets up with water, dissolves and releases hydrogen ions, H+. As you learned earlier, a charged atom is likely to react with something near it. A good example is the H+ ions in your stomach. There is a lot of acid in your stomach, and the many H+ ions react with the food you’ve eaten and begin to break it down into the molecules that your body will absorb. These ions will also kill off many infectious organisms that might be on your food. Your stomach has special cells that can handle all that acid. If your stomach acid is too low for too long, it may lead to a peptic ulcer or other digestive conditions.



A base is a substance that, when dissolved in water, releases an OH- ion, which is also called a hydroxide ion. When you add the OH- ions to an acid that has H+ ions, the OH- and the H+ find each other and come together as water (H2O). Because the H+ ions get bound up in newly made water molecules, they’re neutralized; the plus and minus charges cancel each other out.

An important base in your body is a substance called bicarbonate. When food moves from your acidic stomach into your small intestine, digestive organs release bicarbonate into the intestine to neutralize the acidic material coming from the stomach. Bicarbonate is also important in balancing the acidity in your blood.

Many antacids, like TUMS and Rolaids, contain calcium carbonate. The carbonate part of that compound is a base that neutralizes stomach acid when you have heartburn. The calcium can contribute to bone strength.



You can think of acids and bases as opposite ends of a spectrum. We call that spectrum the pH scale: pH stands for power of hydrogen, or potential hydrogen. Essentially, it’s a measure of how readily a chemical solution will accept H+ ions. The lowest pH, 1, is very acidic; it is loaded with H+ ions and probably won’t accept more. The highest, pH 14, is very basic, and will accept lots of H+ ions (which means it will neutralize a strong acid). A solution of 7 has the same number of H+ as OH- ions. It’s neither basic nor acidic; it’s classified as neutral. Pure water has a pH of 7. Solutions at both ends of the spectrum are harsh for living things—just read the warning labels on a bottle of very basic liquid drain cleaner or on a very acidic car battery.



Just as your body maintains the concentration of electrolytes within a narrow range, it also tightly controls pH levels. If pH is too high or too low, some molecules necessary for important reactions will start to fall apart or not be able to perform the reactions very efficiently. The pH of your blood is around 7.4. Maintaining this pH is especially important, because blood is constantly flowing to all of your organs. Organs in your digestive system have a more acidic pH. The pH in your mouth is usually between 4 and 6, and in your small intestine it’s between 5 and 7.

Certain diseases and conditions such as diabetes and alcoholism can make the body go out of balance in such a way that body fluids become acidic, causing a condition called acidosis. Acidosis, if untreated, can be a very serious condition. When acidity keeps important reactions in your body from happening, a person can become short of breath, confused, and fatigued. Extreme acidosis can lead to shock and permanent organ damage.



Though you lose electrolytes when you sweat during exercise, your body is capable of adjusting to the loss as long as it’s not too great. Your kidneys act as filters for electrolytes (and many other substances). As blood flows through them, they get signals about electrolyte concentration levels and can adjust how much of each electrolyte to flush out in your urine. If you’ve been exercising for a long time, though, or are sweating a great deal, replenishing your electrolytes is likely to perk you up.

Many people turn to sports drinks or coconut water to supply these valuable ions. While either of these drinks can provide you with some necessary nutrients, use caution: coconut water is high in potassium but lacks sodium, so it may not provide what you need. And sports drinks are high in sugar, which provides instant energy and may be what you’re craving most.

Another option for getting your electrolytes, as well as other important nutrients when you’re exercising is a handful of dried fruits and nuts. Raisins, bananas, and apricots all have lots of electrolytes and the carbohydrates you need. Nuts provide fat and protein that will help sustain you beyond your immediate energy requirements. Salted nuts will also give you some sodium. Most Americans get plenty of this electrolyte, so be careful not to get too much.




Reading: The Chemistry of Spaghetti and MeatballsStudent Name: ________________________________________ Date: ________________

Directions: Complete the reading and answer the questions.

Imagine that you had a long day at school and then you went to basketball practice. By the time you get home, you’re pretty hungry. You’re in luck: your dad or mom is cooking spaghetti and meatballs. Your tasty dinner is also an opportunity to look at the basic chemistry of the foods we eat.

Sugar and Starch Are Both CarbohydratesAs was mentioned in the presentation, there are many different kinds of sugar. Several of them are in the foods we eat. Sugar provides energy that fuels chemical reactions in your body. The table sugar you might stir into a cup of tea is called sucrose. It’s made of two different sugar molecules: glucose and fructose. Your body uses only glucose to power things it does, so for that to happen, various chemical reactions occur to change other sugars into glucose.

Your spaghetti actually contains a lot of sugar, too, but in a different form called starch. Starches are very long molecules that are made of many sugar molecules (often glucose) strung together end to end.

Example of a starch:

Simple sugars like table sugar and more complex starches like those in pasta are both carbohydrates. Carbohydrates are always made of sugar, and always contain carbon, hydrogen, and oxygen.

To help you keep track of these terms, fill in the chart below.

1. Sucrose is the chemical name for:

Sucrose is made of two different kinds of sugars:

a.

b.



2. The kind of sugar our bodies use as fuel for chemical reactions is:

3. A long chain of sugar molecules is called:

Examples of carbohydrates:

a.

b.

4. Elements that all carbohydrates are made out of, along with their chemical symbols:

a.

b.

c.

PolymersA long chain of similar molecules all strung together is called a polymer. Starch is a polymer of sugar molecules. Believe it or not, we eat a lot of polymers! Bread, butter, olive oil, potatoes, even the meatballs are made of polymers.

The meatballs are polymers of protein, not sugar. Proteins are polymers of small molecules called amino acids. Proteins help make the chemical reactions in your body happen quickly, and they send signals from one part of your body to another. Some proteins take on the role of small structures that carry out jobs, like making your muscles contract. In fact, the meatballs are made of muscle from a cow or turkey or whatever animal you choose to eat.

When you cook your meatballs, you can also see that some grease melts out of them. That grease is fat that was alongside the muscle. There are many types of fat, made from many different molecules, and some fats are polymers. Even though fat sometimes gets a bad rap, it’s a very important substance in our bodies. Fat stores energy, helps you maintain your body temperature, and surrounds your vital organs to protect them like a pillow against shock.

Carbon = OrganicThree types of molecules—fat, sugar, and protein—are the main nutrients in your food. In all three of them, carbon atoms are central to their structure. Molecules that contain carbon (with the exception of carbon dioxide) are considered organic. We often think of “organic” as meaning that a food is grown without using pesticides. But in this context, organic has to do with chemical structure. Many substances, like plastic, nylon, and gasoline, are also organic, because the molecules that make them up are based in carbon.



Examples of organic molecules:

5. What similarities do you notice between the molecules? What’s different?

Salts = IonsTo bring out the flavor of his spaghetti sauce, your dad probably added some salt. What atoms make up salt? (If you don’t remember, look back at Student Resource 3.2, Reading: Atoms, Molecules, and Bonds). There isn’t any carbon in salt, so it’s an inorganic compound.

When the salt mixes with the water in the spaghetti sauce, it dissolves, meaning that the sodium and chlorine ions split up from each other. These electrolytes circulate in your body. As you’ve learned, they help regulate fluid balance, are used to initiate actions (get them started) such as muscle movement, and play other important roles in homeostasis.

6. What electrolytes are generated when table salt is dissolved in water?

Summing It UpAll living things, from pine trees to mosquitos to snails to people, use the same molecules for the basic processes of life. And what we eat always comes from something else that was alive, whether it was a plant, an animal, or a fungus, which is why our food contains the kinds of molecules we need. In fact, the entire system of life on this planet rests on molecules made mostly of carbon, oxygen, hydrogen, and nitrogen—and that’s why we need to know a little bit of chemistry to understand ourselves.




Notes: Cell MembranesName: _______________________________________ Date: _______________________

Directions: Fill in the charts and answer the questions as you watch the presentation on cell membranes.

1. Draw a phospholipid molecule and label the head, legs, polar, and nonpolar parts.

2. Explain why the phospholipids in the cell membrane arrange themselves with their heads facing out and tails facing each other.

3. What are the two ways proteins are part of the cell membrane, and what does each do?




Reading: Cell Membranes



An egg is actually one big cell. Most cells are so small we can’t see them without a microscope. A chicken egg is one of the largest cells that exists!

Even a cell covered with a hard shell needs a cell membrane as a gatekeeper. And while your cell membranes are much thinner and more delicate than the ones around a chicken egg, the two cell membranes aren’t so different from each other. In the chicken egg, and in your cells, the cell membrane helps keep out bacteria that could cause an infection. But there are tiny holes in the membrane (and in the shell) that will let in very small molecules like oxygen and water. And the way the cell membrane is put together is also key to how it does its job of controlling how and when things move into and out of the cell.



The cell membrane is extremely important to physiology. The membrane has to serve as gatekeeper for all kinds of substances: water, ions, small molecules, and big molecules. It has sophisticated machinery to allow it to deal with them all.

The structure of the membrane is related to how it carries out all its functions. Remember how form and function are tied together? We’ll see it here.

First, most of the membrane is made of molecules called phospholipids. Their shape is kind of like a stick figure, with a “head” and “legs.” The cell membrane contains two layers of these molecules, with the legs facing each other and the heads facing the inside and outside of the cell. Notice how the molecules are lined up in the magnified (zoomed-in) image of the membrane.



The head of the phospholipid molecule is polar. Remember that a polar molecule has a slight charge to it. And remember that water is polar, and water also makes up most of the fluid inside and outside of your cells. Polar molecules are slightly attracted to each other, so the polar ends of the phospholipid molecules are drawn to the water.

In contrast, the legs of the phospholipid molecule are not charged and don’t easily float in water. So they sit next to each other, forming the inside of the cell membrane, and the polar heads face the watery inside and outside of the cell.



The cell membrane also has lots of proteins embedded in it. Some of the proteins, like the one zoomed-in on here, go all the way from one side of the cell membrane to the other and have a tiny hole, or channel, running through the middle of them. That channel is how ions, like sodium ions, go in and out of the cell. We’ll learn more about how these little channels work later on. For now, it’s enough to know that when you hear people talking about sodium in their food affecting their body, these little channels in the proteins of the cell membrane are the key to that.



There are other proteins in the cell membrane that hang out on one side or the other of the membrane. These proteins latch on to larger molecules and ferry them into or out of the cells. We’ll also learn about how these work in this lesson. Glucose uses these kinds of proteins to get across the cell membrane.



While the most apparent role of the cell membrane is to control what goes into and out of the cell, researchers have learned over the last decade or so that the cell membrane also has a much more complex role. Studies done at Cornell in 2011 revealed that there are some proteins found in the cell membranes of virtually all living organisms that assist with putting particular genes in the nucleus into action. The researchers think that the genes may produce a product that moves from the cell nucleus to connect with parts of the cell membrane and then back into the nucleus again before releasing its product into the body.

Other researchers are studying the cell membranes of bacteria that have become resistant to antibiotics. The more they understand about how the cell membrane is structured and holds together, the more drugs they can develop to destroy the cell membrane of an infectious bacterium, stopping it in its tracks.

Cell membranes also contain cholesterol, and the form of cholesterol in the cell membrane is one that assembles itself rather than having to be made by cells. Researchers are also interested in the physics behind that self-assembly, because it can give them clues to how they might be able to design microscopic self-assembling machines or molecules that can be used in medical treatments.




Observations: Diffusion and OsmosisName: _______________________________________ Date: _______________________

Directions: For each demonstration, write your observations in the space provided as clearly and in as much detail as possible. For example, if you were to observe what happens when you add milk to a bowl of cereal, you might write: “When the cereal was added to the milk, it floated on top at first. But I could immediately see milk begin to cling to the edges. After about 10 seconds, I could see tiny white spots or pools forming on the flakes, and the flakes appeared to be absorbing the milk.”

Action Observations What I learned

Add food coloring to water

At start

After 5 seconds

After 20 seconds

Add tea bag to hot water

At start

After 5 seconds

After 20 seconds

Put egg cell in sugary liquid

Put egg cell in water after being in sugary liquid




Reading: Transport across Cell Membranes

In an ambulance, a paramedic starts a patient on an IV (intravenous) of 0.9% sodium chloride solution. The paramedic needs to pay attention to the concentration of sodium chloride in the IV to make sure that it’s balanced with the patient’s body chemistry, and that it will maintain the right electrolyte homeostasis.

There are a several different ways that particles, such as the sodium and chloride ions in the IV bag, make their way across the cell membrane. Many particles are dissolved in water. In these cases, water is called a solvent and the substances dissolved in it are called solutes. The cell membrane is semipermeable, meaning that while some solutes can cross it, others can’t.

Simple Diffusion across the Cell Membrane

As you learned earlier, when molecules diffuse, like the food coloring in your cup, they go from an area of high concentration (the drop of food coloring) to low concentration (into the rest of the water where little or no food coloring is present). The molecules move in this direction because they tend toward an even distribution across the whole solution. The same is true of molecules in your body fluids when they cross the cell membrane. This directed flow of molecules from high to low concentration is also referred to as moving down the concentration gradient.

For example, molecules like oxygen are small enough to squeeze their way through tiny spaces in the cell membrane, and so they move across it freely. When the concentration of oxygen outside a cell is greater than it is inside, the oxygen will diffuse across the cell membrane—in other words, down the concentration gradient—and enter the cell.



Osmosis Is Diffusion of Water across the Membrane

As you also just learned, often substances inside or outside the cell can’t cross the cell membrane. If, for example, there’s more of a particular large particle inside the cell than outside, then its concentration is much higher inside the cell. But the large particle can’t even out its concentration gradient by leaving the cell. So, what happens instead? Water flows into the cell, which decreases the concentration of the solute. To review, this flow of water across the semipermeable membrane is called osmosis.

Facilitated Diffusion across the Cell Membrane

Some particles, like ions and glucose, need a little help getting into the cells, even to move down the concentration gradient. That’s where the proteins in the cell membrane come in handy. Two different kinds of proteins in the cell membrane bring particles in and out of the cells in different ways.



Ion channelsBecause ions are charged and the central part of the cell membrane isn’t (remember the uncharged “tails”?), it’s difficult for many ions to get across. They make their way through via a channel protein, which is a clump of protein that spans the cell membrane and has a tiny channel running through it, like a tunnel that protects the charged ion and lets it through the uncharged part of the cell membrane. Some of these channel proteins will change their shape when the concentration of solute is high enough, and the result is that the channel closes and stops letting solute particles through. This is one way that cells can regulate how much of a certain substance is going in and out.

Carrier proteinsOther molecules, like glucose, catch a ride on a carrier protein. Carrier proteins, like ion channels, are embedded in the cell membrane. Each carrier protein contains a special area that matches up, like a lock and key, with one specific compound. A glucose molecule outside the cell, for example, will latch on to this part of its carrier protein. When it does so, the protein changes shape, which repositions the attached molecule so that it can move to the other side of the membrane and into (or out of) the cell.

Lots of substances enter and leave cells using carrier proteins in the membrane, and for each substance there is a unique “lock” on the protein that the substance can put its “key” into.



Active Transport Requires Energy

In all the situations mentioned so far—diffusion, osmosis, and facilitated diffusion—we’ve been talking about substances moving down their concentration gradient. Because these substances are essentially moving in the direction they would tend to naturally, the movement doesn’t require any energy from the cell. It’s sort of like if you were standing on the edge of a stair. When you put your foot out, it doesn’t take much energy to follow gravity down. Sometimes, though, a cell needs to move a substance up its concentration gradient. So the cell has to do the equivalent of taking a step up the stairs—it has to expend energy. The process of moving substances across the membrane using energy is called active transport.

One important active transport mechanism is called an ion pump, which is also a protein in the cell membrane. In most cells, some sodium ions (Na+) leak into the cells and some potassium ions (K+) leak out. Both of these ions are naturally diffusing down their concentration gradients. But the cell needs to have particular concentrations of sodium and potassium on different sides of the cell membrane in order to maintain the balance it needs to carry out its functions. Our cells are constantly actively transporting these ions across their membranes. For example, cells leak potassium and have to constantly pump potassium back into the cell. So, although active transport costs the cell energy, a great benefit is that it functions independently of concentration.

Like other membrane proteins, active transport pumps only recognize specific substances in the same way that carrier proteins do. This means that when there’s an energy cost involved, the cell can be specific about what substances it allows back and forth. If it doesn’t pump, the substance doesn’t cross the membrane.

Ion pumps and active transport are vital in keeping the necessary balance of ions inside and outside of your cells. The sodium-potassium pump is an important tool that your nerve cells use to create nerve impulses.




Lesson Review: BiochemistryName _____________________________________________________ Date _______________

Directions: Use the resources from this lesson to help you fill in the answers below. Use this information to study for the quiz.

Atoms, Molecules, and BondsHow in an atom related to an element?

How is a molecule related to a compound?

What are the three particles in an atom?

Why are ions important in the body?

Electrolytes and pHName four important electrolytes in the body.

What ions determine whether a solution is acidic or not?

What happens when an acid and a base come together?



Cell MembranesStructure

Number Name of structure Function

1

2

3



Which part of the phospholipid molecule that makes up the cell membrane is polar? Which end of the phospholipid is water attracted to?

Processes List the three ways that substances can cross the cell membrane:

Process Definition Needs energy?

Why or why not?

(Diffusion)

(Osmosis)

(Active transport)



Spaghetti and MeatballsMatch the type of molecule with its description.

Description Type of Molecule

Molecules that make up proteins Protein

A molecule that stores energy and is not soluble in water Starch

Molecules made from sugars Organic

Polymer of amino acids Glucose

Polymer of sugar molecules Amino acid

Molecules that contain carbon Fat

Simple sugar that your body uses for energy Carbohydrates


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