SIG - Signaling Pathways [OVERVIEW]

Signaling Pathways

Introduction

As a society, we are connected by an intricate network of communication with people who are close by and far away. Cells also communicate in a similar way. Cell-to-cell signaling can occur by direct contact or from a long distance through chemical signaling. The molecular details of cell signaling in bacteria, plants, and animals are very similar, even though their last common ancestors lived millions of years ago. These similarities suggest that early versions of today's cell-signaling mechanisms probably developed before the evolution of the first multicellular organisms. In this module, we will explore the similarities between all signaling pathways as well as look at diverse examples scattered throughout the kingdoms of life.  We will also look at the signals that control the cell cycle, cell division, and how minor changes in these pathways can lead to big changes, such as cancer.

List of Lessons

In this module, we will study the following topics:

    1. Cell Communication – this lesson will provide an overview of what cell communication is and discuss the three types of signaling based on distance.
    2. Introduction to Signal Transduction - this lesson looks at each of the three parts of all signaling pathways and multiple possibilities for each one.
    3. Illustrative Examples of Signal Transduction - this lesson will cover some of the most commonly studied examples of signaling: the nervous system, immune system, and plant signaling.
    4. Feedback Mechanisms - this lesson will differentiate positive and negative feedback mechanisms.
    5. Cell Cycle - in this lesson you will learn about the three major parts of the cell cycle as well as the parts of mitosis. You’ll also look at how DNA moves during mitosis.
    6. Regulation of the Cell Cycle - in this lesson you will learn about the major checkpoints that control the cell cycle as well as details of the cyclin-CDK mechanism for entry into mitosis. Then, you’ll learn about the basics of cancer and its relationship to cell division.

Module Objectives

By the end of this module, students will be able to:

    • Describe the ways that cells can communicate with one another.
    • Explain how cells communicate with one another over short and long distances.
    • Describe the components of a signal transduction pathway.
    • Describe the role of components of a signal transduction pathway in producing a cellular response.
    • Describe the role of the environment in eliciting a cellular response.
    • Describe the different types of cellular responses elicited by a signal transduction pathway.
    • Explain how a change in the structure of any signaling molecule affects the activity of the signaling pathway.
    • Describe positive and/ or negative feedback mechanisms.
    • Explain how negative feedback helps to maintain homeostasis.
    • Explain how positive feedback affects homeostasis.
    • Describe the events that occur in the cell cycle.
    • Explain how mitosis results in the transmission of chromosomes from one generation to the next.
    • Describe the role of checkpoints in regulating the cell cycle.
    • Describe the effects of disruptions to the cell cycle on the cell or organism.

Key Terms

Receptor Protein – protein that the signaling molecule (ligand) binds to which initiates transduction

Signal Transduction – process by which a chemical or physical signal is transmitted through a cell to initiate a response by the cell

Ligand – molecule that binds with receptor protein to initiate a transduction pathway

G-Protein – group of proteins that are activated by GTP and transmit signals from the receptor protein to the interior of the cell

Kinase – protein that phosphorylates another protein or molecule by transferring a phosphate (usually from ATP)

Phosphatase – protein that dephosphorylates another protein or molecule by removing a phosphate

Second Messenger – any molecule released during transduction that is NOT a protein and initiates the next step in the pathway

Phosphorylation – transferring a phosphate group (usually from ATP) to a protein or other molecule

Quorum Sensing – when a group of organisms collectively respond to a signal once their numbers reach a certain size

Positive Feedback – feedback where the cellular response works to amplify the change over time

Negative Feedback – feedback where the cellular response works to reduce the change or to bring the system back to stability

Tropism – movement towards a stimulus as a cellular response

Cell Cycle – series of events that leads to cellular division

Interphase – preparatory stages before cellular division

Mitosis – stages of the cell cycle where the cell is actively dividing into two identical daughter cells

Chromatin – a complex of DNA wrapped around histone proteins

Chromosome – a linear segment of DNA typically condensed during cell division

Binary Fission – cell division in prokaryotes

Cyclin – protein released during interphase that controls the progression of the cell through the cell cycle once bound to CDK

Cyclin-Dependent Kinase (CDK) – binds with cyclin to promote progression through the cell cycle

Cancer – uncontrolled cell division in a part of the body that can sometimes spread to other parts of the body

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