Unit 4 Objectives

Describe the components of a signal transduction pathway

-Signal transduction pathways link signal reception with cellular responses -Many signal transduction pathways include protein modification and phosphorylation cascades

Explain how cells communicate with one another over short and long distances

Cells communicate over short distances by using local regulators that target cells in the vicinity of the signal-emitting cell— a. Signals released by one cell type can travel long distances to target cells of another cell type.

Describe the ways that cells can communicate with one another

Cells communicate with one another through direct contact with other cells or from a distance via chemical signaling— a. Cells communicate by cell-to-cell contact.

Describe positive and/ or negative feedback mechanisms

Organisms use feedback mechanisms to maintain their internal environments and respond to internal and external environmental changes

Explain how positive feedback affects homeostasis

Positive feedback mechanisms amplify responses and processes in biological organisms. The variable initiating the responseis moved farther away from the initial set point. Amplification occurs when the stimulus is further activated, which, in turn, initiates an additional response that produces system change.

Describe the different types of cellular responses elicited by a signal transduction pathway

Signal transduction may result in changes in gene expression and cell function, which may alter phenotype or result in programmed cell death (apoptosis)

Describe the role of the environment in eliciting a cellular response

Signal transduction pathways influence how the cell responds to its environment.

Explain how mitosis results in the transmission of chromosomes from one generation to the next

Mitosis is a process that ensures the transfer of a complete genome from a parent cell to two genetically identical daughter cells— a. Mitosis plays a role in growth, tissue repair, and asexual reproduction. b. Mitosis alternates with interphase in the cell cycle. c. Mitosis occurs in a sequential series of steps (prophase, metaphase, anaphase, telophase).

Explain how negative feedback helps to maintain homeostasis

Negative feedback mechanisms maintain homeostasis for a particular condition by regulating physiological processes. If a system is perturbed, negative feedback mechanisms return the system back to its target set point. These processes operate at the molecular and cellular levels.

Describe the role of checkpoints in regulating the cell cycle

-A number of internal controls or checkpoints regulate progression through the cycle. -Interactions between cyclins and cyclin- dependent kinases control the cell cycle.

Explain how a change in the structure of any signaling molecule affects the activity of the signaling pathway

-Changes in signal transduction pathways can alter cellular response— a. Mutations in any domain of the receptor protein or in any component of the signaling pathway may affect the downstream components by altering the subsequent transduction of the signal. -Chemicals that interfere with any component of the signaling pathway may activate or inhibit the pathway.

Describe the events that occur in the cell cycle

-In eukaryotes, cells divide and transmit genetic information via two highly regulated processes. -The cell cycle is a highly regulated series of events for the growth and reproduction of cells— a. The cell cycle consists of sequential stages of interphase (G1, S, G2), mitosis, and cytokinesis. b. A cell can enter a stage (G0) where it no longer divides, but it can reenter the cell cycle in response to appropriate cues. Nondividing cells may exit the cell cycle or be held at a particular stage in the cell cycle.

Describe the role of components of a signal transduction pathway in producing a cellular response

-Signaling begins with the recognition of a chemical messenger—a ligand—by a receptor protein in a target cell— a. The ligand-binding domain of a receptor recognizes a specific chemical messenger, which can be a peptide, a small chemical, or protein, in a specific one-to-one relationship. b. G protein-coupled receptors are an example of a receptor protein in eukaryotes. -Signaling cascades relay signals from receptors to cell targets, often amplifying the incoming signals, resulting in the appropriate responses by the cell, whichcould include cell growth, secretion of molecules, or gene expression— a. After the ligand binds, the intracellular domain of a receptor protein changes shape, initiating transduction of the signal. b. Second messengers (such as cyclic AMP) are molecules that relay and amplify the intracellular signal. c. Binding of ligand-to-ligand-gated channels can cause the channel to open or close.

Describe the effects of disruptions to the cell cycle on the cell or organism

Disruptions to the cell cycle may result in cancer and/or programmed cell death (apoptosis).