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