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
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College Board: 2.C – Organisms Use Feedback Mechanisms to Regulate Growth and
Reproduction, and to Maintain Homeostasis
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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
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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
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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
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Homeostasis• Cells/organisms use energy to maintain homeostasis• Two mechanisms:– Negative feedback– Positive feedback
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Feedback• __________________=
hypothalamus, detects a stimulus beyond the threshold (cold/hot)
• ___________________= brain
• ___________________= muscle, sweat gland
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Examples of Negative Feedback Loops
TRH
Anteriorpituitary
T3 T4
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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 _________________
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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
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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’)
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Trp Operon• Repressible – normally ____ must be turned ____• If _______________________is present it attaches to
regulatory protein • Regulatory protein + ___________________attaches
to operator site blocking transcription
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Negative Feedback - Temperature Regulation
• Receptors• Integrator• Effectors• Fever
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Negative Feedback - Plant Responses to Dehydration
• ___, ________
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Positive Feedback• A stimulus causes ____________________ response to
an activity that is already happening– Ex. ________________, _______________________
• Can be dangerous (fever)
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Positive Feedback - Ripening of Fruit
• _____________________Gas stimulates production of enzymes
• ‘One bad apple spoils the bunch’
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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
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Regulation by ADH• ADH– Stored and secreted by the posterior pituitary
• Concentrates nitrogenous wastes as urine– Urea with less _______________
• Diabetes insipidus
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Aquaporins
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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
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Alterations of Feedback• Blood clotting• Hemophilia – genes for clotting factors VIII and IX
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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