College Board: 2.C – Organisms Use Feedback Mechanisms to Regulate Growth and Reproduction, and to Maintain Homeostasis

Organisms Use Feedback Mechanisms Negative feedback mechanisms maintain dynamic homeostasis for a particular condition (variable) by regulating physiological processes, returning the changing condition back to its target set point. Operons in gene regulation Temperature regulation in animals Plant responses to water limitations

Organisms Use Feedback Mechanisms Positive feedback mechanisms amplify responses and processes in biological organisms. The variable initiating the response is moved farther away from the initial set-point. Amplification occurs when the stimulus is further activated which, in turn, initiates an additional response that produces system change Lactation in mammals Onset of labor Ripening of fruit

Organisms Use Feedback Mechanisms Alteration in the mechanisms of feedback often results in deleterious consequences Diabetes mellitus in response to decreased insulin Dehydration in response to decreased antidiuretic hormone (ADH) Grave’s disease (hyperthyroidism) Blood clotting

Homeostasis Cells/organisms use energy to maintain homeostasis Two mechanisms: Negative feedback Positive feedback

Feedback __________________= hypothalamus, detects a stimulus beyond the threshold (cold/hot) ___________________= brain ___________________= muscle, sweat gland

Examples of Negative Feedback Loops TRH Anterior pituitary T3 T4

Negative Feedback - _______________________ Basic unit of genetic expression in _________________ Sequence of genes that produces a series of _________________ that produce a final product Advantages: All enzymes are produced at the _______ _______ Can be controlled at one site _________________

Operons 4 parts: _______________________ gene – produces a controller protein ____________________site – attachment for RNA polymerase ______________________site – blocks/unblocks RNA polymerase Structural genes – produces enzymes for a reaction Structural genes - enzymes Regulatory gene Promoter Gene 1 Gene 2 Gene 3 Operator DNA

lac Operon Normally ___ (bacteria normally use ______________) Must be _________________ (‘turned on’) Repressor protein produced by the regulatory gene blocks operator Lactose ___________________________________of the repressor Regulatory protein is removed from operator site Operon becomes active (‘induced’)

Trp Operon Repressible – normally ____ must be turned ____ If _______________________is present it attaches to regulatory protein Regulatory protein + ___________________attaches to operator site blocking transcription

Negative Feedback - Temperature Regulation Receptors Integrator Effectors Fever

Negative Feedback - Plant Responses to Dehydration ___, ________

Positive Feedback A stimulus causes ____________________ response to an activity that is already happening Ex. ________________, _______________________ Can be dangerous (fever)

Positive Feedback - Ripening of Fruit _____________________Gas stimulates production of enzymes ‘One bad apple spoils the bunch’

Alterations of Feedback – Diabetes mellitus in response to decreased insulin Too much glucose excreted (mellitus – ‘sweet’) Role of insulin __________________________ Dehydration in response to decreased antidiuretic hormone (ADH) (vasopressin) Neuro-secretory ____________ water absorption in collecting tubule of kidneys

Regulation by ADH ADH Concentrates nitrogenous wastes as urine Stored and secreted by the posterior pituitary Concentrates nitrogenous wastes as urine Urea with less _______________ Diabetes insipidus

Aquaporins

Alterations of Feedback Grave’s disease: Autoimmune – antibodies attach to TSHR on cells of the thyroid gland causing the thyroid to overproduce thyroid hormones (T3 and T4) Most common cause of ____________________ Hereditary – mostly females Goiter

Alterations of Feedback Blood clotting Hemophilia – genes for clotting factors VIII and IX

Integration and Coordination Nervous system - brain, spinal cord, nerves, and sense organs Integrates incoming information from receptors and sends impulses to muscles and glands (electrical) Hypothalamus – neurohormonal Endocrine system - glands that secrete hormones Control metabolic functions (chemical) Review: steroid and nonsteroid hormones