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Cell Communication.

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Presentation on theme: "Cell Communication."— Presentation transcript:

1 Cell Communication

2 Overview: The Cellular Internet
Cell-to-cell communication is absolutely essential for multicellular organisms Nerve cells must communicate pain signals to muscle cells (stimulus) in order for muscle cells to initiate a response to pain

3 Biologists have discovered some universal mechanisms of cellular regulation

4 Signal Transduction Pathway
External Signals Signal Transduction Pathway

5 Yeast cells identify their mates by cell signaling (early evidence of signaling)
 factor Receptor Exchange of mating factors. Each cell type secretes a mating factor that binds to receptors on the other cell type. 1 Mating. Binding of the factors to     receptors induces changes      in the cells that     lead to their     fusion. New a/ cell. The nucleus of the fused cell includes all the genes from the a and a cells. 2 3 Yeast cell, mating type a mating type  a/ a

6 Signal Transduction Pathways
Convert signals on a cell’s surface into cellular responses Are similar in microbes and mammals, suggesting an early origin

7 Local and Long-Distance Signaling
Cells in a multicellular organism (tissues, organs, systems) communicate via chemical messengers A hormone is a chemical released by a cell in one part of the body, that sends out messages that affect cells in other parts of the organism All multicellular organisms produce hormones Plant hormones are also called phytohormones Hormones in animals are often transported in the blood

8 Animal and plant cells Have cell junctions that directly connect the cytoplasm of adjacent cells Plasma membranes Plasmodesmata between plant cells Gap junctions between animal cells Figure 11.3 (a) Cell junctions. Both animals and plants have cell junctions that allow molecules to pass readily between adjacent cells without crossing plasma membranes.

9 In local signaling, animal cells May communicate via direct contact
Figure 11.3 (b) Cell-cell recognition. Two cells in an animal may communicate by interaction between molecules protruding from their surfaces.

10 diffuses across synapse
In other cases, animal cells Communicate using local regulators (a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid. (b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell. Local regulator diffuses through extracellular fluid Target cell Secretory vesicle Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses across synapse is stimulated Local signaling

11 Long-distance signaling
In long-distance signaling Both plants and animals use hormones (e.g. Insulin) Hormone travels in bloodstream to target cells (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood Hormones may reach virtually all body cells. Long-distance signaling Blood vessel Target cell Endocrine cell Figure 11.4 C

12 The Three Stages of Cell Signaling
Earl W. Sutherland Discovered how the hormone epinephrine acts on cells

13 Sutherland’s Three Steps
Sutherland suggested that cells receiving signals went through three processes Reception Transduction Response

14 Relay molecules in a signal transduction pathway
Overview of cell signaling EXTRACELLULAR FLUID Receptor Signal molecule Relay molecules in a signal transduction pathway Plasma membrane CYTOPLASM Activation of cellular response Figure 11.5 Reception 1 Transduction 2 Response 3

15 Step One - Reception Reception occurs when a signal molecule (ligand) binds to a receptor protein, causing it to change shape Receptor protein is on the cell surface

16 The binding between signal molecule (ligand) and receptor is highly specific
A conformational change in a receptor is often the initial transduction of the signal

17 Step Two - Transduction
The binding of the signal molecule alters the receptor protein in some way The signal usually starts a cascade of reactions known as a signal transduction pathway Multistep pathways can amplify a signal

18 Step Three - Response Cell signaling leads to regulation of cytoplasmic activities or transcription Signaling pathways regulate a variety of cellular activities

19 Example of Pathway Steroid hormones bind to intracellular receptors
(testosterone) EXTRACELLULAR FLUID Receptor protein DNA mRNA NUCLEUS CYTOPLASM Plasma membrane Hormone- receptor complex New protein Figure 11.6 1 The steroid hormone testosterone passes through the plasma membrane. Testosterone binds to a receptor protein in the cytoplasm, activating it. 2 The hormone- receptor complex enters the nucleus and binds to specific genes. 3 The bound protein stimulates the transcription of the gene into mRNA. 4 The mRNA is translated into a specific protein. 5

20 Other pathways regulate genes by activating transcription factors that turn genes on or off
Reception Transduction Response mRNA NUCLEUS Gene P Active transcription factor Inactive DNA Phosphorylation cascade CYTOPLASM Receptor Growth factor Figure 11.14

21 Termination of the Signal
Signal response is terminated quickly by the reversal of ligand binding

22 Receptors in the Plasma Membrane
There are three main types of membrane receptors: G-protein-linked Tyrosine kinases Ion channel

23 G-protein-linked receptors
Plasma Membrane Enzyme G-protein (inactive) CYTOPLASM Cellular response Activated enzyme Activated Receptor Signal molecule Inactivate Segment that interacts with G proteins GDP GTP P i Signal-binding site Figure 11.7

24 Receptor tyrosine kinases
Signal molecule Signal-binding site CYTOPLASM Tyrosines Signal molecule Helix in the Membrane Tyr Dimer Receptor tyrosine kinase proteins (inactive monomers) P Cellular response 1 Inactive relay proteins Activated relay proteins Cellular response 2 Activated tyrosine- kinase regions (unphosphorylated dimer) Fully activated receptor tyrosine-kinase (phosphorylated 6 ATP ADP Figure 11.7

25 Ion channel receptors Figure 11.7 Cellular response Gate open
Gate close Ligand-gated ion channel receptor Plasma Membrane Signal molecule (ligand) Figure 11.7 Gate closed Ions

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