How do cells “talk” to each other? Cell Communication How do cells “talk” to each other?

Overview of Cell Communication Even single-celled organisms communicate with each other. Bacteria use quorum sensing. This involves the release of signal molecules into the environment that allow bacteria to respond to changes in the environment.* * gene expression – what genes get turned on or off

Overview of Cell Communication Mating in yeast (fungi) cells – intracellular signal transduction Response to presence of extracellular peptide mating pheromone in environment Occurs only in haploid cells and will only happen between opposite mating types (a & alpha or α)

Overview of Cell Communication Growth of a projection (known as a shmoo, due to its distinctive shape) towards source of the mating pheromone (a to α-mating pheromone & vice versa) Produces a diploid cell and increases genetic variation.

What’s shmoo with you?

What’s shmoo with you?

What’s shmoo with you?

Types of Communication Why do cells in multicellular organisms “talk” to each other? What are the topics of their conversations?

Multicellular organisms I. The cells of multicellular organisms communicate with each other. Cells signal one another with chemicals. These chemicals include peptides, proteins, amino acids, nucleotides, steroids, and other lipids. Dissolved gases like NO (nitric oxide) are also used as signals.

Multicellular organisms (Some signaling molecules are attached to the surface of the signaling cell. Other molecules are secreted through the cell membrane or released via exocytosis.

Types of Cell Signaling Who is “talking” to whom and why?

Types of Cell Signaling Paracrine signaling Direct contact Endocrine signaling Synaptic signaling **See Table 9.1 Cell-Communicating Mechanisms – be able to name types of mechanism used by cells to communicate, function, and give examples.

Cell Signaling Virtual Cell Animation Cell signaling pathways - Insulin Signaling http://vcell.ndsu.nodak.edu/animations/

Cell Surface Receptors Who’s that knocking at my door? No entry needed

Gated Ion Channels Receptor proteins form a pore. The pore is opened or closed by chemical signals Signal molecule (ex: a neurotransmitter) must bind to the protein in order for pore to open. Channels are very specific; only 1 type of ion will go through. Ions include Na+, K+, Ca2+, and Cl-.

Gated ion channel

Enzymatic Receptors* Surface receptors act like enzymes or are directly linked to an enzyme. A signal molecule attaches outside and activates the protein. Part of the protein inside the cell carries out enzymatic activity. *Kinases

Enzymatic Receptors

G-Proteins and Extracellular Messengers G-proteins have GTP (guanosine triphosphate) attached. Act like mediators between outside and inside of a cell Work with trans-membrane protein receptor (GPCR)

G-Proteins and Extracellular Messengers This is how it works: signal molecule binds to GPCR change in GPCR shape causes change in G-protein, GDP released & GTP binds G-protein diffuses away from receptor

G-Proteins and Extracellular Messengers 3 subunits in G-protein – alpha, beta, and gamma (Alpha is only one different* for each type of G-protein.)

G-Proteins and Extracellular Messengers This is how it works: Activated G-protein travels along inner side of cell membrane until it reaches an effector. GTP GDP + Pi and energy released is used to activate various pathways within cell

G-Proteins and Extracellular Messengers

G-Proteins and Extracellular Messengers Very short-lived, unless a continuous source of extracellular messengers is available. Over 100 different types identified

G-Proteins and Extracellular Messengers Visual amplification – Rhodopsin (visual purple) Adrenalin “rush” Skeletal muscle contraction

G-Proteins and Extracellular Messengers

Intracellular Signaling What is a second messenger? What is the role of these molecules?

Second messengers Substances that initiate changes within the cell when activated by G-proteins or kinases. Examples: cAMP, IP3, calcium Calcium-calmodulin system Figures 9.8 a & b, 9.11, 9.12, 9.13 and 9.15

Second messengers

Kinase Cascades Amplify the signal received at cell surface in the cytosol Why? What? Where? RESULT?

Kinase Cascades Visual amplification – night vision, 100,000 second messengers in 1 second! Cell division amplification – Ras proteins and cancer

Cell Identity Recognizing self

Cell Identity All cells have the same genetic code. Gene regulation Cells form highly specialized tissues. All cells have the same genetic code. Gene regulation How do cells “know” where they are, and how do they “know” what type of tissue they belong to?

Cell Identity Tissue specific identity markers – self v non-self

Cell Identity Glycolipids MHC proteins – Major Histocompatibility Complex MADGE

Cell Identity Antigen-antibody interaction in the immune response - An antigen-antibody complex forms.

Hormones that Enter the Cell “What happens in the cell stays in the cell.”

Intracellular response Hormones that enter cells: Steroid hormones Water-soluble hormones Hormones travel attached to protein carriers Hormones reach target cells & get released by carriers Hormones that do NOT enter cells

Intracellular response