Cell Communication

1. Cell Communication Unit 3 Notes

2. Intercellular Signaling—Local • Cell Junctions—signaling substances in cytosol pass freely between cells • Gap Junctions in Animals • Plasmodesmata in Plants • Cell-Cell Interaction—interaction between molecules that portrudefrom cell surface (animals) • Important in embryonic development and immune responses

3. Intercellular Signaling—Local • Local Regulators—cell secretes a local regulator molecule which acts on specific nearby target cells • Paracrine Signaling—regulators (i.e. growth factors) are released into extracellular fluid) • Synaptic Signaling—neurotransmitters are released into synapse

4. Intercellular Signaling—Long Distance • Hormones—molecules used in plants and animals for long-distance signaling • Animals = Endocrine Signaling—hormones move through circulatory system • Plants = Plant Growth Regulators—move through vessels or (more commonly) diffuse through cells or air

5. Intercellular Signaling—Long Distance • Nervous System in Animals—uses a combination of electrical and chemical signals to send a message

6. Intracellular Signaling • Three Major Parts— • Reception • Transduction • Response

7. Reception • Signaling molecule binds to a receptor protein, causing it to change shape • Ligand—molecule that specifically binds to another molecule (messenger molecule) • Two Major Types of Receptors • Plasma Membrane Receptors • Intracellular Receptors

8. Reception • Plasma Membrane Receptors—transmembrane proteins transmit information into the cell by changing shape or aggregating • G-Protein-Coupled Receptor—works with the help of a G protein. • Receptor Tyrosine Kinases—attach phosphates to tyrosines (amino acid)…leading to activation of proteins • Ligand-Gated Ion Channels—ligand binds to gated channel protein and opens gate to let in ions, i.e., Na+, Ca2+

9. Reception G-Protein-Coupled Receptors

10. Reception Tyrosine-Kinase Receptors

11. Reception Ion Channel Receptors

12. Reception • Intracellular Receptors—chemical messengers (small & hydrophobic) enter cell and bind to a receptor in the cytoplasm or nucleus • Testosterone—small 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)

13. Reception Intracellular Receptors

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

15. Transduction Phosphorylation Cascade

16. Transduction • Second Messengers—non-protein, water-soluble molecules or ions that can pass signal to proteins (1st Messengers are the original ligands) • Involved in pathways started by G-protein-linked receptors and receptor tyrosine kinases • Most common second messengers: • Cyclic AMP (cAMP) • Ca2+

17. Transduction • Cyclic AMP (cAMP) • Adenylyl cyclase converts ATP to cAMP • cAMP activates a protein kinase

18. Transduction • Ca2+--increase in Ca2+ leads to many responses in plants and animals • [Ca2+] in blood and extracellular fluid is often 10,000x greater than in cell • Ca2+ is actively transported out of the cell and into ER • Another molecule, inositol trisphosphate (IP3) stimulates release of Ca2+

19. Response • Cell Signaling leads to regulation of transcription of cytoplasmic pathways • Response may be the regulation of protein synthesis by turning specific genes on or off • Response may be the regulation of a protein’s activity

20. Response Cytoplasmic Response Nuclear Response

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

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

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

24. Cell Cycle Life of a cell from origin through division.

25. Cell Cycle Phases Mitosis and Interphase

26. Mitosis (M Phase) • Mitosis—Division of the Nucleus • Cytokinesis—Division of the cytoplasm • Mitosis + Cytokinesis = ~10% of Cell Cycle • Mitosis Phases • Prophase • Metaphase • Anaphase • Telophase

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

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

29. Interphase

30. Phases of MitosisObjective 11 Animal Cell

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

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

33. Phases of Mitosis Summary • Anaphase • Sister Chromatids split and move to poles

34. Phases of Mitosis Summary • Telophase • New nuclei form • Microtubules degrade • Cytokinesis occurs

35. Phases of Mitosis Plant Cell

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

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

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

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

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

41. Check Points • Between G1 and S • Go ahead signal from the environment is needed (i.e. growth factors from other cells) • Then…there are checks for enough mass and the condition of the DNA • If there is no signal…cell 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 • Checks for mass and correct DNA replication • If all okay…cell commits to divide • Note: Cancer often occurs because cell is quickly pushed from G1  S without proper checks

42. Regulatory Molecules/Conditions • Regulatory Proteins/Enzymes • 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 • 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 cyclin…so no MPF…and no more dividing (Cdk concentration remains the same)

43. Regulatory Molecules/Conditions

44. Regulatory Molecules/Conditions • Other internal signals • Kinetochores must be attached before anaphase can occur—unattached kinetochores send a signal to stop sister chromatids from splitting

45. Regulatory Molecules/Conditions • External Signals • Growth Factors—proteins released by certain cells that stimulates other cells to divide • Density-Dependent Inhibition—Crowded cells stop dividing because there aren’t enough growth factors and nutrients for it to divide • Anchorage-Dependence—If cells aren’t attached to the extracellular matrix, they do not get growth factors—so don’t divide

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

47. 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

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

49. Cancer Cell Characteristics

50. 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 Benign (not cancer) tumor cells grow only locally and cannot spread by invasion or metastasis