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Cell Communication Unit 3 Notes

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Intercellular SignalingLocal Cell Junctionssignaling substances in cytosol pass freely between cells o Gap Junctions in Animals o Plasmodesmata in Plants Cell-Cell Interaction interaction between molecules that portrude from cell surface (animals) o Important in embryonic development and immune responses

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Intercellular SignalingLocal Local Regulatorscell secretes a local regulator molecule which acts on specific nearby target cells o Paracrine Signalingregulators (i.e. growth factors) are released into extracellular fluid) o Synaptic Signalingneurotransmitters are released into synapse

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Intercellular SignalingLong Distance Hormonesmolecules used in plants and animals for long-distance signaling o Animals = Endocrine Signalinghormones move through circulatory system o Plants = Plant Growth Regulatorsmove through vessels or (more commonly) diffuse through cells or air

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Intercellular SignalingLong Distance Nervous System in Animalsuses a combination of electrical and chemical signals to send a message

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Intracellular Signaling Three Major Parts o Reception o Transduction o Response

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Reception Signaling molecule binds to a receptor protein, causing it to change shape o Ligandmolecule that specifically binds to another molecule (messenger molecule ) Two Major Types of Receptors o Plasma Membrane Receptors o Intracellular Receptors

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Reception Plasma Membrane Receptorstransmembrane proteins transmit information into the cell by changing shape or aggregating o G-Protein-Coupled Receptorworks with the help of a G protein. o Receptor Tyrosine Kinasesattach phosphates to tyrosines (amino acid)leading to activation of proteins o Ligand-Gated Ion Channelsligand binds to gated channel protein and opens gate to let in ions, i.e., Na +, Ca 2+

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Reception G-Protein-Coupled Receptors

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Reception Tyrosine-Kinase Receptors

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Reception Ion Channel Receptors

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Reception Intracellular Receptorschemical messengers (small & hydrophobic) enter cell and bind to a receptor in the cytoplasm or nucleus o Testosteronesmall steroid hormone Activates receptor protein in cytoplasm of target cell by binding to it Activated receptor protein (with attached testosterone) enters nucleus and turns on specific genes that control male sex characteristics = transcription factor (proteins that control which genes are on and off)

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Reception Intracellular Receptors

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Transduction Cascades of molecular interactions relay signal from receptors to target molecules Information is relayed by shape changes of proteins Ex: Protein Phosphorylation & Dephosphorylation o Protein Kinasesenzymes that transfer phosphate groups from ATP to a protein (usually activating the protein) o Protein Phosphatasesenzymes that remove phosphate groups from proteins (usually deactivating protein and so turn off pathway)

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Transduction Phosphorylation Cascade

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Transduction Second Messengersnon-protein, water-soluble molecules or ions that can pass signal to proteins (1 st Messengers are the original ligands) Involved in pathways started by G-protein-linked receptors and receptor tyrosine kinases Most common second messengers: o Cyclic AMP (cAMP) o Ca 2+

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Transduction Cyclic AMP (cAMP) o Adenylyl cyclase converts ATP to cAMP o cAMP activates a protein kinase

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Transduction Ca 2+ --increase in Ca 2+ leads to many responses in plants and animals o [Ca 2+ ] in blood and extracellular fluid is often 10,000x greater than in cell o Ca 2+ is actively transported out of the cell and into ER o Another molecule, inositol trisphosphate (IP 3 ) stimulates release of Ca 2+

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Response Cell Signaling leads to regulation of transcription of cytoplasmic pathways o Response may be the regulation of protein synthesis by turning specific genes on or off o Response may be the regulation of a proteins activity

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Response Nuclear Response Cytoplasmic Response

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Fine-Tuning Responses Signal Amplification o Number of activated products increases at each catalytic step of a cascade because enzymes are active long enough to catalyze many reactions o Consequence = small number of ligands can lead to large response Specificity of Cell Signaling and Coordination of Response o Specific types of cells have specific receptors, relay proteins, and/or proteins needed for a response to occur

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Fine-Tuning Responses Signal is unique to different types of cells.

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Fine-Tuning Responses Scaffolding Proteins & Signaling Complexes o Scaffolding Proteinslarge relay proteins that other relay proteins attach to simultaneously o Same proteins can be involved in multiple pathways Termination of the Signal o Proteins must be inactivated

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Cell Cycle Life of a cell from origin through division.

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Cell Cycle Phases Mitosis and Interphase

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Mitosis (M Phase) MitosisDivision of the Nucleus CytokinesisDivision of the cytoplasm Mitosis + Cytokinesis = ~10% of Cell Cycle Mitosis Phases o Prophase o Metaphase o Anaphase o Telophase

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Mitosis (M Phase) Mitosis allows cell to go from 4n 2n Produces somatic cells (2n) Does not produce gametes (1n)

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Interphase Interphasephase in which the cell grows, metabolizes, and copies DNA Interphase = ~90% of Cell Cycle Split up into 3 smaller phases o Gap 1 Phase (G1)Takes up ~35% of Interphase Growth Cell is 2n o Synthesis Phase (S)Takes up ~35% of Interphase DNA Replication occurs Cell goes from 2n 4n o Gap 2 Phase (G2)Takes up ~ 30% of Interphase More GrowthParticularly molecules for division Cell is 4n

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Interphase

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Phases of Mitosis Objective 11 Animal Cell

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Phases of Mitosis Summary Prophase o Chromatin condenses into chromosomes (made of sister chromatids attached at centromere) o Microtubules form o Centrioles/Centrosomes move to poles

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Phases of Mitosis Summary Metaphase o Microtubules attach to the kinetochores of each sister chromatid o Chromosomes line up along the metaphase plate

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Phases of Mitosis Summary Anaphase o Sister Chromatids split and move to poles

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Phases of Mitosis Summary Telophase o New nuclei form o Microtubules degrade o Cytokinesis occurs

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Phases of Mitosis Plant Cell

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Reproduction in Prokaryotic Cells DNA, Binary Fission & Budding Objective 14

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Bacterial DNA One loop of DNA attached to Cell Membrane o Still highly folded to fit into cell o Only one set of genes (not one from mom and one from dad like in eukaryotes) May contain 1 or more Plasmids o Tiny loops of extra DNA that are able to move from 1 bacteria to another o Allows for recombination = advantage!

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Binary Fission Asexual Reproduction of most Prokaryotes Basic Steps: o DNA Replicationunzips to copy o Cell Pinches New cells should be clones o No genetic recombination o Only variation through mutations Rate = divides as fast as every 20 minutes

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Budding Some prokaryotes reproduce in this manner Asexual Reproduction Basic Steps o Cell Develops a bulge or bud o DNA copies o Bud Breaks Off Listeria monocytogenes

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Control of Cell Cycle Checkpoints & Regulatory Proteins/Conditions Objective 12

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Check Points Between G1 and S o Go ahead signal from the environment is needed (i.e. growth factors from other cells) o Thenthere are checks for enough mass and the condition of the DNA o If there is no signalcell goes to G0 (non-dividing state) Most cells in G0 never divide (i.e. nerve/muscle) or they only divide if there is an injury Between G2 and M o Checks for mass and correct DNA replication o If all okaycell commits to divide Note: Cancer often occurs because cell is quickly pushed from G1 S without proper checks

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Regulatory Molecules/Conditions Regulatory Proteins/Enzymes o Cyclin-Dependent Kinase (Cdk)enzymes needed to drive the cell cycle Cyclin-Dependent Kinase (enzyme that activates or deactivates other molecules by phosphorylation) only works when activated by cyclin a protein that rises and falls in the cell cycle o Example: Maturation Promoting Factor (MPF) Cyclin increase in concentration in G2 and bind with a specific Cdk to form MPF MPF signals the start of Mitosis At end of mitosis, enzymes break down cyclinso no MPFand no more dividing (Cdk concentration remains the same)

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Regulatory Molecules/Conditions

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Other internal signals o Kinetochores must be attached before anaphase can occur unattached kinetochores send a signal to stop sister chromatids from splitting

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Regulatory Molecules/Conditions External Signals o Growth Factorsproteins released by certain cells that stimulates other cells to divide o Density-Dependent InhibitionCrowded cells stop dividing because there arent enough growth factors and nutrients for it to divide o Anchorage-DependenceIf cells arent attached to the extracellular matrix, they do not get growth factorsso dont divide

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Cancer and the Cell Cycle Objective 13Define cancer and explain how aberrations in the cell cycle can lead to tumor formation.

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Cancer Complex collection of diseases that can arise in almost any tissue in the body. All cancers arise as a result of the loss of cell cycle control. Cytotoxic T Cell Attacking a Cancer Cell

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Cancer Cell Characteristics Uncontrolled growth Lack of response to stop signals Immortality Ability to divide infinitely Recruits food supplies (angiogenesis) Random migration

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Cancer Cell Characteristics

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Benign versus Malignant Benign (not cancer) tumor cells grow only locally and cannot spread by invasion or metastasis Malignant (cancer) cells invade neighboring tissues, enter blood vessels, and metastasize to different sites

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Cancer-Related Genes Stability Genescode for proteins that keep genetic alterations to a minimum o If mutated, mutation rates increase Oncogenescode for proteins that promote cell division o If mutated to be overly active = cancer Tumor Suppressor Genescode for proteins that inhibit cell from progressing from G1 S o If mutated to be underactive = cancer o Example TP53 codes for p53 protein = transcription factor that normally inhibits cell growth and stimulates cell death when induced by cellular stress

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Check Points