Unit IV: The Cell Membrane

Unit 4: Cell Membrane
A. Structure
B. Passive Transport
C. Active Transport / plasma membrane
impermeable
intracellular
extracellular
concentration
concentration gradient
passive transport
osmosis
diffusion
facilitated diffusion
active transport
carrier (transport) protein
pumps (ions or molecular)
endocytosis
exocytosis
homeostasis
homeostatic mechanism
system
BIO.A.4.1 - Identify and describe the cell structures involved in transport of materials into, out of, and throughout a cell.
  • BIO.A.4.1.1 - Describe how the structure of the plasma membrane allows it to function as a regulatory structure and/or protective barrier for a cell.
  • BIO.A.4.1.2 - Compare the mechanisms that transport materials across the plasma membrane (i.e., passive transport—diffusion, osmosis, facilitated diffusion; and active transport—pumps, endocytosis, exocytosis).
BIO.A.4.2 - Explain mechanisms that permit organisms to maintain biological balance between their internal and external environments.
  • BIO.A.4.2.1 - Explain how organisms maintain homeostasis (e.g., thermoregulation, water regulation, oxygen regulation).

Cell Membrane Structure

(Section 6.2 in book)

The cell membrane is the edge of life; it is the boundary that separates the living cell from its nonliving surroundings. A remarkable film only about 8 micrometers thick, the membrane surrounds the cell and controls the traffic of substances into and out of the cell. As we have seen repeatedly in our study so far, cellular structure fits function. Therefore, to understand how membranes work we will begin by examining their structures and characteristics.

SELECTIVE PERMEABILITY

The MOST IMPORTANT characteristic of the cell membrane is its ability to maintain homeostasis within the cell by regulating the passage of materials in and out of the cell. In other words, it is very "picky" about what gets in or out. This important quality is called selective permeability.

  1. Cell membrane: ______

______

  1. Define selective permeability:______

______

______

  1. Label the parts of the phospholipid with these four terms: head, tail, hydrophobic, & hydrophilic
  1. Rank the molecules according to their speed to cross the cell membrane from fastest to slowest….

Explain why you ranked them in that order.

a. b. c. d. ______

______

  1. Name the scientists who discovered the structure of the cell membrane.______
  2. What did they call their model?______
  3. What characteristic does mosaic refer to?______
  4. What characteristic does fluid refer to? ______
  1. Label these parts of the cell membrane on the diagram below:

a)Phospholipids: are arranged in a double layer and are the most numerous part of the membrane, they have round heads and 2 squiggly tails

b)Protein: each one looks like a potato

c)Cholesterol: are the dark colored chains in between the phospholipids

d)Carbohydrates: chains on the outside of the membrane that look like antennae

e)Cytoskeleton: thin structures inside the cell

THE CONNECTION BETWEEN STRUCTURE AND FUNCTION

The main job of the cell membrane is to maintain cellular ______.

The main characteristic that allows it to do this is its ______.

Other parts / characteristics of the membrane help it do its job >

  1. The phospholipids are a great barrier because they are ______which means that they will NOT mix with water, while their ‘heads’ are ______, which means they will mix with water. This helps the cell membrane keep the water on the inside of the cell separate from the water on the outside of the cell.
  2. It is ______so it won’t rupture easily. If it did break easily, the cell membrane would not be the great boundary that it is! In addition, the membrane contains ______which adds strength and stability.
  3. Most importantly, the membrane contains gates and channels (which are the ______) which help regulate what goes in and out.

TYPES OF PROTEINS IN THE MEMBRANE

Although the basic structure of a cell membrane is a lipid bilayer, most of the functions of the membrane are carried out by proteins. Proteins can function as enzymes. So far, we have seen that enzymes in the mitochondrial membrane are responsible for allowing cellular respiration to occur. Likewise, proteins in the membranes of chloroplasts allow photosynthesis to happen. When our cells need glucose, the cell membrane proteins are signaled to start breaking down a larger molecule (called glycogen) into smaller glucose molecules. Some proteins allow one cell to recognize another. For example, when our white blood cells are roaming around our body looking for invaders, they check every cell. Cell membrane proteins allow them to determine whether another cell is a cell of our body or a germ. These proteins are called marker proteins. Other proteins receive signals from hormones. These proteins are called receptor proteins. An example of this is when insulin is released from the pancreas, it travels to all the cells of the body and joins with membrane protein receptors. The receptors then open the gate that allows glucose to get into the cell. Lastly, many proteins work to transport substances either into or out of cells. Our nerve cells conduct signals by transporting sodium and potassium into and out of the cell. This happens through transport proteins.

For each type of cell membrane protein, give an example of how it works in our body.

  1. Enzyme: ______

______

  1. Cell recognition: ______

______

  1. Transport: ______

______

  1. Signaling / Receptor: ______

______

1

UNIT 4 Cell membrane

When Blood Kills………

Our blood type is directly determined by the proteins present in the membranes of our red blood cells. We’re going to explore the concept of blood typing by going to the following site, reading the content and answering the questions.

in awhile this web address does not work. If it doesn’t work, please google blood typing and nobel prize to get to the website.)

Please use the information in this chart to help you with the website:

A / /
B antibodies /
B / /
A antibodies /
AB / / None /
O / /
A & B antibodies /


BLOOD TYPE ANTIGENS ANTIBODIES PICTURE OF RBC & PLASMA

  1. Who discovered blood groups? When? ______
  2. If incompatible blood is mixed, agglutination occurs. What is agglutination? Why is this bad?

______

______

  1. With the discovery of blood groups, what was made possible? ______
  2. What are the four parts of blood and what is the job of each? ______

______

  1. The differences in human blood are due to the presence or absence of certain protein molecules called ______and ______.
  2. Where are antigens located? ______
  3. Where are antibodies located?______
  4. If you have the Rh factor protein on your red blood cells, you are called ______. If this protein is absent, you are referred to as ______.
  5. An Rh- person can develop Rh ______if they get blood from an Rh+ person.
  6. But an Rh____ person can receive blood from an Rh____ person without any problems.
  7. Play the agglutination animation. (you will need to know this information to help you play the game)
  8. How can you tell what blood type someone has? ______

______

  1. What results from agglutination? ______

______

  1. What blood type is the universal donor (meaning it can be given to all blood types without causing a reaction)?______
  2. What blood type is the universal recipient (meaning it can receive all blood types without having a reaction)?______

PLAY THE BLOOD TYPING GAME AT THE BOTTOM. Fill in this chart as you play the game.

*Hint: When you find the blood type of the patient, notice you are putting their blood into 3 testtubes. The testtubes are filled with ANTIBODIES, not bloodtypes. Use the chart from the beginning of this activity to help you.

Patient description / Blood type / Which blood type can the patient receive (it may be more than one!)

17. How many mistakes did you make during the simulation? (It will tell you at the end of the game, if it does not tell you, you made too many mistakes, and you should re-read the information & play it again) ______

THE CELL MEMBRANE PROTEINS CAN RECEIVE SIGNALS FROM HORMONES

Glucagon is a hormone that works with insulin to maintain sugar balance in the blood. When glucose is needed in between meals, the hormone glucagon is used to release stored glucose. Glucagon is produced in the pancreas (just like insulin). It travels through the bloodstream and binds to receptor proteins located in the cell membranes of liver and muscle cells. When glucagon molecules bind to receptor proteins, the receptor proteins change shape and cause enzyme proteins in the membrane to produce a molecule called cyclic AMP (which is related to ATP and ADP). Cyclic AMP relays the first message (from the hormone) into the cell. The cyclic AMP molecules activate a series of enzymes that break down a larger molecule (called glycogen) into glucose for the cell to use.

On the other hand, after we eat, insulin is released from the pancreas. The insulin hormone attaches to cell membrane receptor proteins on each cell in our body. This causes the cell to open transport protein tunnels so glucose can enter the cell. Once inside the cell, glucose is used for cellular respiration. Remember? 

Importance of Cell Membrane Proteins in the Body

Review Questions

Based on your reading and class work, answer the following questions to demonstrate your understanding of why and how the membrane is important in the body.

  1. ____ Each type of RED blood cell has a different ____ in its cell membrane.
  2. antigenb. antibody
  1. ____ A person with O blood has
  2. O antibodiesb. A antibodiesc. B antibodiesd. A & B antibodies
  1. ____ If a person with type A blood receives blood from an AB person their blood will
  2. be okayb. will agglutinate (clump)
  1. ____ The hormone that is released in-between meals and breaks down glycogen to release glucose is called
  2. glucagonb. insulin
  1. ____ Both glucagon and insulin are hormones that bind to ______proteins in the cell membrane.
  2. transportb. enzymec. markerd. receptor
  1. ____ Insulin is to glucose like
  2. key is to a person
  3. door is to a window
  4. window is to a fly

Summarize how cell membrane proteins are essential to each of the following processes.

  1. blood type and transfusions

______

______

______

  1. hormones working to maintain sugar balance

______

______

______

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Cell Membrane Function

Now that you have a picture of the plasma membrane and its structure, think about its role as a gatekeeper of the cell. Keep in mind that it is selectively permeable. In an effort to maintain homeostasis, the cell membrane must determine what enters and leaves the cell. Some substances that are either entering or leaving the cell are oxygen, carbon dioxide, water, ions, glucose, amino acids, and protein. Each of these molecules moves into or out of cells in different ways.

MOLECULAR MOTION

All molecules are constantly in motion… bumping into one another. This random motion of molecules is called Brownian motion. As molecules randomly bump into the cell membrane, there is a chance that the molecule will go through the cell membrane.

  1. Brownian Motion: ______

WHERE SUBSTANCES CROSS THE MEMBRANE

Substances cross the membrane in different ways based on their SIZE and CHARGE. Smaller molecules such as water (8 um), oxygen (5 um) and carbon dioxide (9 um) can fit through these small pores and therefore pass directly through the lipid bilayer. Charged atoms or molecules (ions such as Na+, K+, Cl-, Mg+) pass through the proteins in the membrane because they are charged. Other larger molecules such as glucose (20 um) and amino acids (25 um) must travel across the membrane through a protein tunnel because they are too big to fit through the bilayer.

  1. What two characteristics determine where a molecule will pass through the membrane?

______

  1. What type of molecules pass through the bilayer? Give examples.

______

  1. What type of molecules pass through the proteins? Give examples.

______

  1. If the size of the protein tunnels are 25 um, then would glycogen (60 um) and protein (150 um) be able to fit through the cell membrane? YES / NO

Well, if they can’t fit THROUGH the membrane, then how do they enter and leave the cell? The answer to that question is the cell membrane will actually open up and let them in or out!

HOW SUBSTANCES CROSS THE MEMBRANE: TWO GENERAL TYPES OF TRANSPORT

There are two types of transport across the membrane – passive transport and active transport. Passive transport relies on Brownian motion to automatically cause molecules to spread out without the use of any cellular energy. The three types of passive transport that we will be studying are diffusion, facilitated diffusion and osmosis. Active transport (as its name suggests) is when the cell membrane proteins use energy to actually grab molecules and pump them in or out.

  1. Describe passive transport:______

______

______

  1. Describe active transport:______

______

______

Passive Transport: Diffusion Demonstration

Substances in and around the cell are evenly distributed among water molecules. All of these particles move randomly, colliding with each other. Random collisions would tend to scatter the molecules of the substance until it was evenly mixed with the water molecules. Diffusion refers to this net movement of particles from an area of higher concentration to an area of lower concentration.

  1. Diffusion: ______

______

  1. OBSERVATION: Add a drop of dye to a beaker of water. Keep an eye on its progress while reading the rest of this section. This demonstrates what you are reading about!

Concentration refers to the amount of substance in a given area. The difference in concentration of a substance across space (or a membrane) is called a concentration gradient. Because ions and molecules diffuse from areas of higher concentration to areas of lower concentration, they are said to move with a gradient. If no other processes interfere, diffusion will continue until there is no concentration gradient (all molecules are evenly spread out). At this point, the solution is said to be in dynamic equilibrium. When the molecules are evenly spread out they continue to move around but there is no overall change in the concentration. Maintaining dynamic equilibrium is one of the characteristics of homeostasis.

  1. Concentration:______

______

  1. Gradient:______

______

  1. Concentration Gradient: ______
  2. Draw 8 X’s on the left side of the diagram and 4 X’s on the right to illustrate a concentration gradient of molecules.
  3. Draw an arrow to indicate the direction the molecules will move across the membrane by diffusion.
  1. Dynamic equilibrium:______

______

  1. Draw a diagram showing the molecules of X in dynamic equilibrium.
  1. Reexamine the beaker with the dye. Discuss what happened in the beaker incorporating what you know about diffusion.______

______

Diffusion in the Body: Gas Exchange

PART A: Use during-reading strategies (such as highlighting) to learn about how diffusion of oxygen and carbon dioxide is seen in red blood cells.

The cell obtains and excretes a variety of atoms and molecules by the process of diffusion across the membrane. Molecules of oxygen and carbon dioxide are two of these molecules. Let’s examine how they diffuse into and out of red blood cells.

OXYGEN TRANSPORT: When we take a breath, oxygen is MORE concentrated in our lungs and LESS concentrated in our red blood cells (RBCs). Therefore oxygen will diffuse from the lungs into RBCs. Inside the RBC, the protein hemoglobin soaks up this oxygen. The RBCs take this oxygen to the cells of the body. Since the oxygen is MORE concentrated in the RBC and LESS concentrated in our body cells, the oxygen diffuses out of the RBC and into the body cell.

In tissues, the presence of carbon dioxide produced by cellular respiration makes the blood more acidic and causes the hemoglobin molecules to change shape, releasing oxygen more easily. So the tissues that are working the hardest (and therefore releasing the most carbon dioxide) are the tissues that will get more oxygen. The effect of carbon dioxide on the rate of oxygen unloading is called the Bohr effect.

CARBON DIOXIDE TRANSPORT: At the same time that the red blood cells are unloading oxygen to tissues, they are also absorbing carbon dioxide. Only 7% of the carbon dioxide that the blood carries is dissolved in plasma (about 7%). About 23 percent is carried by the hemoglobin molecules inside red blood cells. The remaining 70 percent is carried within the cytoplasm of red blood cells.

How do the red blood cells manage to keep all of this carbon dioxide inside their cytoplasm? Why doesn’t it simply diffuse back into the plasma, where carbon dioxide levels are lower? And then back into the cells where there is also a lower amount of carbon dioxide? An enzyme within the red blood cells, called carbonic anhydrase, combines carbon dioxide molecules with water to form carbonic acid which breaks apart into bicarbonate ions. Ions have a harder time passing through the cell membrane – that’s how the carbon dioxide is kept in the RBC on its journey back to the lungs. Once the RBC gets back to the lungs, the opposite process occurs and the ions are converted back to carbon dioxide. Hemoglobin likes oxygen more than carbon dioxide. Therefore, the hemoglobin releases its bound carbon dioxide and takes up oxygen instead. The red blood cells, with their newly bound oxygen, then start their next journey back to the body’s tissues.

PART B: Answer these questions based on information from the reading.

  1. Which two molecules move across the membrane by diffusion?______
  2. Where do they cross (through lipid bilayer or protein channel)? Why? ______

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