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Ch. 18.4, 47.2-3, 35.5 Regulation of gene expression that orchestrates development Activities of the cell depend on the genes it expresses and the proteins it produces All cells have the same genome, but genes are regulated in each cell type ◦ Depends on activators present Induction: changes in the target cells (communicated via surface proteins and cell receptors) Homeotic (Hox) genes: regulate pattern formation in the embryo (direct the developmental process)—what genes, and where located Morphogen: determines an embryo’s axes, stimulate differentiation and development Apoptosis: programmed cell death Differentiation: process by which cells become specialized in structure and function Determination: process by which a group of cells becomes committed to a particular fate Morphogenesis: process that gives an organism its shape Induction: changes in the target cells by environmental stimuli or other cell contact (induce differentiation) In multicellular organisms a fertilized egg must give rise to cells of many different types, each with different structure/function ◦ Cell tissue organ organ system organism ◦ Mutations result in abnormal development Animal Embryonic Development…in general… Fertilization (zygote) Cleavage (mitosis—produce blastula) Gastrulation (folding of cells into 3 layers—gastrula) Organogenesis (changes in cell shape/location— rudimentary organs) Developing embryo (grow and develop, specialized cells) First zygote divides into a large number of cells (ball of cells--blastula) ◦ It then divides and folds to form a gastrula Then differentiation occurs, cells become specialized (organogenesis) ◦ Results from the expression of specific genes for that tissue/organ type Morphogenesis occurs next, specialized cells become organized into tissues and organs ◦ Occurs throughout embryo’s development Begins with egg cytoplasm. ◦ “Cytoplasmic Determinants”—molecules that will trigger development of different cells (unevenly distributed) Results in division of cells with different information ◦ Induction. Changes that induce differentiation and timing of developmental events “Hedgehog”—signaling molecule (limb bud development) ◦ Observable differentiation marked by expression of genes for tissue specific proteins Gives characteristic structure and function, regulated by transcription Body plan (cytoplasmic determinants) ◦ Spatial organization of tissues and organs Determine where/when segments will be (embryo has cues to determine this) ◦ Controlled by “Homeotic (Hox) Genes” and “morphogens” Growth, morphogenesis, differentiation ◦ All controlled by gene expression Plant organs: roots, stems, and leaves “Root” or “Shoot” systems ◦ Made of tissue layers Vascular (xylem and phloem) Dermal (epidermis) Ground Apoptosis: programmed cell death ◦ Cells die and are engulfed by neighboring cells Tadpole tail Webbing between digits microRNAs (miRNA): bind to mRNA and blocks translation by degrading the mRNA ◦ RNA interference (RNAi): regulate gene expression at transcription Important in development of organisms and control of cellular functions Single-celled organisms use signals to influence their response to the environment Multi-cellular organisms use signals to coordinate activities within cells Cells most often communicate by chemical signals ◦ Secretion of messenger molecules that target nearby cells Hormones (fight-or-flight—epinephrine) Mating pheromones (yeast) Quorum sensing (bacteria density) Growth factors (stimulate division) Neurotransmitters (signaling at synapses) Cells also communicate via cell-cell contact ◦ Cytoplasmic materials can pass through junctions in cell wall/membrane between cells ◦ Surface molecules on membrane aid in cell recognition Important in embryonic development and immune system! “Signal Transduction Pathway”—Three stages ◦ Reception: detection of a signaling molecule by the cell (binds to receptor protein in membrane) ◦ Transduction: receptor protein changes with binding of signaling molecule; converts signal to specific cellular response (sequence of changes) ◦ Response: specific cellular response is triggered Ligand (signaling molecule) binds to receptor protein, causing a change in shape ◦ This activates the receptor allowing it to interact with other molecules (initiates transduction) ◦ Each signaling molecule has specific target cells ◦ Some signaling molecules are small enough to pass through cell membrane and interact with proteins in the cytoplasm or nucleus Example: Ion-Gated Channel Signal is converted into a cellular response ◦ “signal transduction pathway” The binding of the signaling molecule triggers transduction pathway ◦ A chain reaction is started that produces a “cascade”, leading to cellular response Often controlled by phosphorylation (taking P from ATP)…this drives the reaction forward this helps amplify the signal and response Second messengers: small molecule that help to transmit signals (Ca++ and cAMP); spread via diffusion Response at the end of the pathway that occurs in the nucleus or cytoplasm ◦ Regulate protein synthesis (on/off) ◦ Affect activity of enzymes ◦ May be altered by blocked or defective transduction pathways Results in diseases such as diabetes, heart disease, neurological issues, autoimmune diseases, cancer, cholera Long distance ◦ Electrical to chemical signals—nervous system Electrical signal travels down nerve, converted to chemical signal to stimulate other end of nerve ◦ Endocrine system and hormones Specialized cells release molecules and travel through blood stream to target cells Plant hormone ethylene—stimulates ripening Hormone: molecule secreted into bloodstream (or hemolymph) to communicate regulatory messages ◦ Each has specific receptors, only some cells have them May either be water (amino acid based—bind to outside) or lipid-soluble (steroids—pass thru membrane to nucleus) ◦ Elicits a response from target cells ◦ Maintains homeostasis, respond to environment, regulate growth and development, trigger physical changes Negative or positive feedback Pituitary gland: growth hormone, thyroid stimulating hormone, luteinizing hormone, folliclestimulating hormone, oxytocin, antidiuretic hormone Pineal gland: melatonin Thyroid gland: thyroxine (T4), Triiodothyronine (T3) Adrenal gland: cortisol, epinephrine Pancreas: glucagon and insulin Ovaries/testes: testosterone, estrogen and progesterone Controlled by the hormones insulin and glucagon, produced by Islets of Langerhans in pancreas ◦ negative feedback ◦ Two hormones are antagonistic When BG is high—insulin triggers body cells to take up glucose from blood stream; also inhibits glucose production/release from liver ◦ Target cells: muscles, adipose tissue, liver When BG is low—glucagon triggers the release of glucose from storage (liver and fatty tissue) ◦ Target cell: liver, adipose tissue Normal blood sugar is 70-120 mg/ml Hyperglycemia: High blood sugar ◦ Symptoms include increase thirst/urination, glucose present in urine ◦ Extreme cases result in ketoacidosis (body breaking down fat for energy—releasing ketones leading to acidic blood), if untreated results in diabetic coma! Hypoglycemia: Low blood sugar ◦ Shakiness, irritability (extreme mood changes), lightheaded, headache, seizures, unconsciousness Increased blood glucose, fat is broken down for energy because cells don’t take up glucose effectively or at all ◦ Ketoacidosis results (decreased blood pH, Na+, K+) ◦ Kidneys filter some glucose and release in urine Lots of water consumed, glucose in urine Type 1 “juvenile diabetes” Type 2 ◦ Insulin-dependent, autoimmune disorder that destroys pancreatic cells that produce insulin ◦ Target cells don’t respond normally to insulin, don’t take up glucose ◦ Most common type. Seen in adults mostly…resulting from excess weight. Thyroxine (T4) and Triiodothyronine (T3) ◦ Target nearly all cells in the body Affect metabolism, growth and development ◦ Hormone production is stimulated by TSH from pituitary ◦ Iodine helps to regulate production Absence results in overproduction of TSH and enlarged thyroid gland (goiter) Hyperthyroidism (excess of hormone) ◦ “overactivce thyroid”; symptoms: mood changes, increased heart rate, weight loss, muscular weakness High T4 and low TSH Hypothyroidism (lack of hormone) ◦ Symptoms: weight gain, fatigue; more common in women Low T4 and high TSH