AP Bio Exam Review: Unit 2 – Cells & Cell Communication

Comparisons of Scopes Visible light passes through specimen Compound Light Electron Visible light passes through specimen Light reflects light so specimen is magnified Magnify up to 1000X Specimen can be alive/moving color Focuses a beam of electrons through specimen Magnify up to 1,000,000 times Specimen non-living Black and white

Prokaryote Vs. Eukaryote “before” “kernel” No nucleus DNA in a nucleoid Cytosol No organelles other than ribosomes Small size Primitive i.e. bacteria “true” “kernel” Has nucleus and nuclear membrane Cytosol Has organelles with specialized structure and function Much larger in size More complex i.e. plant/animal cell

Parts of plant & animal cell p 108-109

Cells must remain small to maintain a large surface area to volume ratio Large S.A. allows increased rates of chemical exchange between cell and environment

Animal cells have intercellular junctions: Tight junction = prevent leakage Desmosome = anchor cells together Gap junction = allow passage of material

Cell Membrane

6 types of membrane proteins

Passive vs. Active Transport Little or no Energy Moves from high to low concentrations Moves down the concentration gradient i.e. diffusion, osmosis, facilitated diffusion (with a transport protein) Requires Energy (ATP) Moves from a low concentration to high Moves against the concentration gradient i.e. sodium/potassium pumps, exo/endocytosis

hypotonic / isotonic / hypertonic

Apoptosis = cell suicide Cell is dismantled and digested Triggered by signals that activate cascade of “suicide” proteins (caspase) Protect neighboring cells from damage Animal development & maintenance

Sodium potassium pump Endocytosis Exocytosis

Exocytosis and Endocytosis transport large molecules 3 Types of Endocytosis: Phagocytosis (“cell eating” - solids) Pinocytosis (“cell drinking” - fluids) Receptor-mediated endocytosis Very specific Substances bind to receptors on cell surface

Cell Communication

Multicellular Organisms Behave as a community – “Cells talk” Neighbors carry on private conversations Messages are sent over distances Phone Mail Public announcements are made Alarms are rung when there is danger

Signal Transduction Pathways Conversions of signals from one form to another in a cell Verbal instructions  written text  email  voice mail  action Eventually a response will occur due to the original signal

Communication Signal cell  Target cell Cell to cell recognition Cell Junctions Local Regulators Distance Regulators

Cell to cell recognition Glycoproteins, glycolipids, and other molecules on plasma membranes serve as recognition markers. Important for immune response and embryonic development

Cell Junctions Plasmodesta – plant cells Gap Junctions – animal cells Allow communication between the cytoplasm of neighboring 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.

Local Regulators Communicate and influence cells in close proximity Figure 11.3 (b) Cell-cell recognition. Two cells in an animal may communicate by interaction between molecules protruding from their surfaces. Communicate and influence cells in close proximity Growth factors – cause multiplication and growth of target cells Paracrine Signaling – simultaneous response by more than one cell Synaptic Signaling – Nervous system Neurotransmitters diffuse from one nerve cell to stimulate the next

diffuses across synapse (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 Figure 11.4 A B

Long-distance signaling Distance Regulators 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 Hormones Carried in the bloodstream of animals Endocrine System  Circulatory System Carried in the vesicles of plants

Relay molecules in a signal transduction pathway 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 Transduction Response 1. Reception – detection of message by a receptor protein on a target cell (several different receptors) 2. Transduction – receptor changes and initiates a cascade of events 3. Response – activation of target

Plasma Membrane Receptors G-protein-linked receptor Receptor tyrosine kinase (kinase is an enzyme that phosphorylates other proteins to activate them) Ligand-gated ion channel

a) G-Protein-Linked Receptor Signal molecule attaches to receptor and activates G-protein is activated G-protein activates an enzyme which triggers a cascade in the cell to the target. Used for vision and smell 60% of medicines activate G-proteins Secondary structure

b) Tyrosine Kinase Receptor Signal molecule Signal-binding sitea 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 6 ADP Figure 11.7

c) Ligand-Gated Ion Channels Cellular response Gate open Gate close Ligand-gated ion channel receptor Plasma Membrane Signal molecule (ligand) Figure 11.7 Gate closed Ions Signal molecule attached to ligand opening a gate for specific ions Once Ions enter specific reactions take place Na+ Ca+

Transduction Cascade Step 1 step 2  step 3  step 4  reaction Activated by phosphorylation ATP  ADP + P Protein Kinases Deactivated by dephosphorylation P removed Protein phosphatases

Second Messengers Small, non protein, water soluble, ions Cyclic AMP Levels regulate gene expression in bacteria Calcium Ions – Ca2+ Receptors on the outside of the membrane are the 1st messengers

Cyclic AMP Created from ATP from adenyl cyclase Used with G proteins 1st or 2nd messenger Figure 11.9 O –O N O P OH CH2 NH2 ATP Ch2 H2O HO Adenylyl cyclase Phoshodiesterase Pyrophosphate Cyclic AMP AMP i

Response Reception Transduction Response mRNA NUCLEUS Gene P Active transcription factor Inactive DNA Phosphorylation cascade CYTOPLASM Receptor Growth factor Figure 11.14 Signals are amplified as they are sent from messenger to messenger. Signals are specific to target cells and enzymes Not all cells respond to a signal

Amoeba sisters cell-to-cell communication video https://www.youtube.com/watch?v=-dbRterutHY