Biology Homework

CHAPTER 11

CELL COMMUNICATION

An Overview of Cell Signaling

READ: Skim Overview, Section 11.1 all subsections, carefully read“The Three Stages of Cell Signaling: A Preview

1. Describe the basic signal-transduction pathway used for mating in yeast.

See section 11.1 for a description of the example

2. Explain how plant and animal hormones travel to target cells.

Plant= through plasmodesmata

Animal = through gap junctions

3. List and briefly define the three stages of cell signaling.

4. 1. RECEPTION- Hormones bind to target cell receptors

5. 2. TRANSDUCTION-Relays signal

6. 3. RESPONSE-Specific cell responses (cytoplasmic or nuclear)

Signal Reception and the Initiation of Transduction

READ: Skim Section 11.2 (all subsections)

7. Describe the nature of a ligand-receptor interaction and state how such interactions initiate a signal-transduction system.

Ligand is a generic term for the signal that binds to the receptor in the first step of a signal transduction pathway. A ligand can be a hormone (as discussed in the examples given in class) a neurotransmitter (ex: serotonin), ions (ex: Na+, Ca2+)

8. State where signal receptors may be located in target cells.

Receptors are located:

A. on the plasma membrane- bind with water-soluble signals (signals that are hydrophilic and cannot move through the plasma membrane of the cell)

B. inside the cell; in the cytoplasm or in the nucleus- bind with fat-soluble signals (signals that are hydrophobic and can easily move through the plasma membrane of the cell)

Signal-Transduction Pathways

READ: Skim Section 11.3 all subsections EXCEPT “Calcium Ions, Inositol Triphosphate, and “Cyclic AMP”

9. List two advantages of using a multistep pathway in the transduction stage of cell signaling.

1- Higher level of control over the pathway (increased accuracy of the cellular response to a signal)- For example, imagine that your liver cell is responding to the insulin signal to take in glucose from the blood after a meal. As your blood glucose drops so will the amount of insulin in your blood. Once the insulin is no longer in the blood the signal transduction pathway is immediately stopped and glucose is no longer taken into the cell. If the transduction stage was not present, your cell might have opened more glucose channels than it needed to take the glucose from your meal out of your blood. This could lead to a life threatening condition called hypoglycemia (low blood sugar). Therefore, the transduction step in a signal transduction pathway allows your cell to correctly titrate a response to a signal.

Cellular Responses to Signals

READ: Section 11.4 (ONLY subsection “Nuclear and Cytopasmic Responses”)

10. Describe how signal information is transduced into cellular responses in the cytoplasm and in the nucleus.

We will cover this topic in greater detail in chapter 17 when we discuss protein production. For now you just need to know the difference between a cytoplasmic response (activation of a protein that already exists) and a nuclear response (production of a new protein).

Chapter 45: Endocrine System Examples

READ: pages 978-979, carefully read “Cellular Response Pathways”, “Pathway for Water Soluble Hormones”, and “Pathway for Lipid-Soluble Hormones”, Figures 45.6 & 45.7

11. How do the mechanisms that induce responses in target cells differ for water-soluble and lipid soluble hormones?

Water-soluble signals-

Reception: receptors are on the plasma membrane

Transduction: transduction events occur in the cytoplasm and/or nucleus

Response: either cytoplasmic if a protein that already exists is activated or nuclear if a new protein is made.

Lipid-soluble signals- receptors are inside the cell; in the cytoplasm or in the nucleus

Reception: receptors are inside the cell; in the cytoplasm or in the nucleus

Transduction: transduction events occur in the cytoplasm and/or nucleus

Response: nuclear-a new protein is made.

12. Describe the signal transduction pathway initiated by epinephrine. Is epinephrine a water-soluble or lipid-soluble hormone? How can you tell? Include all three steps of the signal transduction pathway in your description.

Reception: Epinephrine (water-soluble) binds to a receptor located on the plasma membrane of the target cell.

Transduction: The binding of epinephrine to the receptor triggers a series of protein activations including: G protein, Adenylyl cyclase, and cAMP second messenger.

Response: Protein kinase A is activated (cytoplasmic response) which leads to the breakdown of glycogen (storage form of glucose) and glucose is released into the blood.

13. Describe the signal transduction pathway initiated by estradiol. Is estradiol a water-soluble or lipid-soluble hormone? How can you tell? Include all three steps of the signal transduction pathway in your description.

Reception: estradiol binds to a receptor located in the liver cell cytomplasm (= estradiol is a lipid-soluble hormone)

Transduction: The binding of estradiol to the receptor triggers a series of protein activations involving the binding of the receptor-estradiol complex to the DNA in the nucleus.

Response: A new protein, vitellogenin, is produced (nuclear response).

Suggested end of chapter SELF-QUIZ questions:

#4, 6, 7