organisms use feedback mechanisms
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College Board: 2.C – Organisms Use Feedback Mechanisms to Regulate Growth and Reproduction, and to Maintain Homeostasis. Organisms Use Feedback Mechanisms. - PowerPoint PPT PresentationTRANSCRIPT
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
Anteriorpituitary
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:
1._______________________ gene – produces a controller protein
2.____________________site – attachment for RNA polymerase3.______________________site – blocks/unblocks RNA
polymerase4.Structural genes – produces enzymes for a reaction
DNA
Regulatory genePromoter
Operator
Gene 1 Gene 2 Gene 3
Structural genes - enzymes
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– 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