PGS: 201 – 208 - Ms. Rooney's AP Biology



AP Biology Cell Communication Part 1

(Associated Learning Objectives: 1.14, 1.15, 1.16, 3.31, 3.32, 3.33, 3.34, 3.35, 3.36, 3.37, 3.38, 3.39, 4.5 )

Important concepts from previous unit:

1) Chemical molecules have distinct shapes and densities based upon the number of each subatomic unit.

2) Cell membranes interact with the surrounding environment.

3) The Extra Cellular Matrix (ECM) is involved in cell communication.

I. Cell – to Cell Communication

A. It is absolutely essential for multi-cellular organisms to survive and function properly.

B. Communication is accomplished mainly by chemical means.

II. Types of signaling that can occur between cell or organisms:

A. Direct

1. Involves physical contact between cells or organisms.

2. Could also involve passage from plant cell to another plant cell through the plasmademata (holes) in the cell wall of adjacent cells.

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B. Local

1. Growth factors that are released into a localized area. (Usually for normal growth or repair.)

2. Another example is at the synapses of neurons. (Not direct contact because of the synaptic cleft.)

3. Another example, a teacher speaking to a class of students.

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C. Long Distance

1. Hormones (They are released in one part of the body to travel to another part of the body.)

2. Pheromones (Chemical mate attractants released into the environment.)

III. Signal Transduction Pathway (It is analogous to talking on the phone.)

A. Earl Sutherland won the Nobel Prize in 1971 for this discovery. He worked at Vanderbilt University.

B. Three parts to the pathway:

1. Reception - Molecule binding to membrane receptor protein. (It is like the phone ringing.)

I don’t know anything about the actual call. I only know the phone is ringing. I will need to change the ringing into something I can understand.

2. Transduction (means “to change or carry through”) (It is like answering the phone.)

a. This is a series of steps in the changing of the signal to something the cell can understand at the nucleus or in the cytoplasm.

b. It would be this series of steps: Pick the phone up, move the phone to your mouth, say hello, and wait for the conversation to begin. Now that the conversation is occurring, I can understand what the message is that was initiated by the ringing of the phone.

3. Response - This usually involves making something or turning on/off an enzymatic process.

a. Usually involves DNA transcription and translation or enzymes INSIDE the cell.

b. Now that I know what the phone message was for; I hang up the phone and do what I was asked to do. The pathway is now complete and the action/response has occurred.

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IV. Ligand - This refers to the actual signal molecule.

A. The ligand binds to the receptor protein (which are like cell “hands”) on the cell membrane or inside the cell.

Think of cells like a blind, deaf, and mute individual. They could effectively still communicate and understand their environment by using their hands to touch and feel.

B. The attachment causes a conformational shape change in the receptor protein that sets in motion the transduction pathway.

C. Different ligands can initiate different response, this is important when considering chemical based medicines.

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Watch Bozeman Science Videos and Use Freeman Chapter 8 150-170 for reference as well as the internet to help you answer the following questions.



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● List the types of signals involved in communication and where they come from.

● Describe why signal transduction pathways that are under strong selective pressure.

● Use an example to explain how signal transduction pathways influence how the cell responds to its environment in unicellular organisms.

● Using an example to explain how signal transduction pathways coordinate the activities within individual cells that support the function of the organism as a whole in multi-cellular organisms.

● Use an example to explain how cells communicate by cell-to-cell contact.

● Use an example to explain how cells communicate over short distances by using local regulators that target cells in the vicinity of the emitting cell.

● Explain how signals released by one cell type can travel long distances to target cells of another cell type.

AP Biology Cell Communication Part 2

(Associated Learning Objectives: 1.14, 1.15, 1.16, 3.31, 3.32, 3.33, 3.34, 3.35, 3.36, 4.4, 4.5, 4.22 )

Important concepts from previous units:

1) Phosphorylation occurs by the hydrolysis of a phosphate ion from ATP and attaching it to a molecule.

2) Enzymes are proteins whose names usually end in “ase”.

3) Enzymes control cellular processes by feedback (negative or positive) mechanisms.

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V. The most important receptor protein pathways in cells:

A. G- Protein Pathway - This is the most common pathway used by cells.

1. G- Protein Linked Receptor

a. This protein serves as the attachment point for the Ligand. It is found in the plasma membrane of a cell. (This acts like the “hands” for the cell.)

b. It will change shape upon attachment of the proper ligand.

c. ALL cells possess G protein receptors. This allows them to interact with and respond to the environment around them.

2. G- Protein - This protein or enzyme acts as a relay protein carrying the message to the appropriate location.

a. Phosphorylation is possible due to the shape change that occurred with the receptor protein. This process will turn on the G-protein.

b. The activated G-protein then travels to the appropriate enzyme or protein to phosphorylate it. (It is usually GTPase.)

c. The GTPase will then turn on or off the necessary process in the cytoplasm or nucleus. (Mostly transcription/translation.)

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B. Tyrosine- Kinase Pathway - This pathway is involved with growth/emergency repair most of the time.

1. It has the ability to act like a catalyst for rapidly activating several relay proteins. (6 at one time.)

2. This is a great example of structure = function. In repair, you need to get multiple processes going quickly to prevent possible cell or tissue death.

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C. Ion Channel Receptors (Such as found at synapses of neurons.)

1. A.K.A. Ligand-gated Ion Channels.

2. These act as a control of a particular signal. Like letting sodium into a post-synaptic neuron. The “gate” is opened by the attaching of the neurotransmitter (the ligand) to the receptor protein. Once the gate is opened now the charged sodium ions can enter the cell to start depolarizing that cell.

D. INTRAcellular Receptors

1. These receptors are mostly for receiving hormones and steroids. Since these molecules are lipids, they don’t need receptor proteins on the cell membrane. They travel into the cell by diffusing across the phospholipid bi-layer.

a. A.K.A. Transcription Factors – the usually start the making of mRNA within the nucleus.

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VI. Secondary Messengers - These are relay molecules within the cell’s cytoplasm.

A. Usually they are ion based molecules within a cell. These can MOVE about inside the cell.

B. Most common types:

1. Cyclic AMP (cAMP)

a. Made by Adenylyl Cyclase from ATP

2. Ca++ (Calmodulin) and IP3 (Inostol Triphosphate)

a. These are mainly involved in helping to create and control muscle contraction.

b. The ligand (first messenger) for a muscle contraction comes to the cell. It combines with the membrane bound receptor protein. A shape change occurs in the receptor protein. The shape change allows for the inactive G protein to attach to the receptor protein and become phosphorylated by ATP. The activated G-protein will then travel to the inactive PIP2. The g-protein will break a bond in the PIP2 to convert it to an active state molecule called IP3. The IP 3 will travel to the endoplasmic reticulum of the muscle cell. The endoplasmic reticulum is like a storage place for Calcium ions. To open the storage facility you need a key. The key here is the secondary messenger IP3. The IP3 binds to a receptor protein on the endoplasmic reticulum. This causes a shape change to occur in the receptor protein. The shape change now allows the calcium ions (in the form of Calmodulin) to come out into the cytoplasm. The calmodulin (a secondary messenger too) will go and attach to the myosin microfilaments and thereby initiate a muscle contraction using the sliding filament theory.

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● Describe how signals are received by cells.

● List the types of different chemical messengers and explain the specific one-to-one relationship with their receptors.

● Using an example to explain how a receptor protein recognizes signal molecules, causing the receptor protein’s shape to change, which initiates transduction of the signal.

● Describe the process of signal transduction.

● Explain the concept of signaling cascades.

● Use an example to explain how second messengers are often essential to the function of a signaling cascade.

● Explain the effects of protein modifications on the signaling cascade

● Explain the effects of phosphorylation on the signaling cascade.

AP Biology Cell Communication Part 3

(Associated Learning Objectives: 1.15, 1.16, 3.31, 3.32, 3.33, 3.36, 3.37, 3.38, 3.39, 4.17, 4.22 )

Important concepts from previous units:

1) Enzymes regulate (control) cell processes.

2) Phosphorylation is the binding of a phosphate to a molecule with the intent of making it “work”.

3) ATP is the molecule cells use for cellular “work”.

VII. Cellular Response

A. The end product of the pathway is about the regulation of some cell process.

1. The responses are usually protein synthesis or product synthesis. (Turning them on/off.)

VIII. Protein Kinase Cascades

A. KINASES turn ON processes by phosphorylating the molecule.

B. The point of the cascade is to amplify the signal. (It keeps cells from making excess ligand signals. We only need one molecule to activate a process in that cell.)

C. Each step in the cascade can amplify a signal; but it can also control the reaction rate of the process.

IX. Protein Phosphotase Cascades

A. Turn OFF processes by removing a phosphate ion from the molecule.

B. Same as “B” and “C” above.

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X. Amplification of the Signal

A. Only need small amount of the ligand to convey the message. (This conserves E and materials.)

B. The cascades amplify the signal at each step. (1 becomes 2. 2 becomes 4. 4 becomes 8, and so forth.)

Small Signal |Produces a BIG response

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XI. Structure = Function

A. Different kinds of cells have different kinds and numbers of protein receptors. Each controls a different process.

XII. Scaffolding Proteins

A. This allows for direct contact stimulation of multiple relay proteins at one time. (Similar to a Tyrosine-Kinase receptor protein. (Can you see how the scaffolding proteins might have evolved into the “one”

half of a Tyrosine- Kinase protein over time? Then putting two next to each other over time?)

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