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

2. 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

3. 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

4. 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

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

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

7. Examples of Negative Feedback Loops
TRH
Anterior
pituitary T3 T4

8. 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 _________________

10. 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

11. 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’)

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

13. Negative Feedback - Temperature Regulation
Receptors
Integrator
Effectors
Fever

14. Negative Feedback - Plant Responses to Dehydration
___, ________

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

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

17. 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

18. 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

19. Aquaporins

20. 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

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

22. 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