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 polymerase

3. ______________________site – blocks/unblocks RNA polymerase

4. 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