Feedback Systems

Feedback Loop Video

Fig Negative feedback  Excess D blocks a step D D D A B C Enzyme 1 Enzyme 2 Enzyme 3 D (a) Negative feedback W Enzyme 4 X Positive feedback Enzyme 5 Y + Enzyme 6 Excess Z stimulates a step Z Z Z Z (b) Positive feedback Negative Feedback Most common form of regulation Accumulation of end product slows the process Positive Feedback End product SPEEDS UP production of that product Blood clotting Childbirth The idea is for the process to go to completion

Fig Intermediate C Feedback inhibition Isoleucine used up by cell Enzyme 1 (threonine deaminase) End product (isoleucine) Enzyme 5 Intermediate D Intermediate B Intermediate A Enzyme 4 Enzyme 2 Enzyme 3 Initial substrate (threonine) Threonine in active site Active site available Active site of enzyme 1 no longer binds threonine; pathway is switched off. Isoleucine binds to allosteric site Feedback Inhibition Metabolic pathway Switched off by inhibitory binding of end product to an enzyme earlier in the pathway of production

Fig Response: Heater turned off Stimulus: Control center (thermostat) reads too hot Room temperature decreases Set point: 20ºC Room temperature increases Stimulus: Control center (thermostat) reads too cold Response: Heater turned on Nonliving Example of What type of Feedback to maintain homeostasis

Fig Sweat glands secrete sweat, which evaporates, cooling the body. Thermostat in hypothalamus activates cooling mechanisms. Blood vessels in skin dilate: capillaries fill; heat radiates from skin. Increased body temperature Decreased body temperature Thermostat in hypothalamus activates warming mechanisms. Blood vessels in skin constrict, reducing heat loss. Skeletal muscles contract; shivering generates heat. Body temperature increases; thermostat shuts off warming mechanisms. Homeostasis: Internal temperature of 36– 38°C Body temperature decreases; thermostat shuts off cooling mechanisms. How is this an example of feedback? Is it positive or negative feedbac

Fig Organic molecules in food External environment Animal body Digestion and absorption Nutrient molecules in body cells Carbon skeletons Cellular respiration ATP Heat Energy lost in feces Energy lost in nitrogenous waste Heat Biosynthesis Heat Cellular work

Blood Sugar Levels

Example of Hormonal Feedback System

Test Review Info Every Pyruvate produces 3 NADH 1 ATP 1 FADH 2 HOW MANY PYRUVATES DO YOU GET FROM 1 SUGAR MOLECULE?

Fig Wavelength of light (nm) (b) Action spectrum (a) Absorption spectra (c) Engelmann’s experiment Aerobic bacteria RESULTS Rate of photosynthesis (measured by O 2 release) Absorption of light by chloroplast pigments Filament of alga Chloro- phyll a Chlorophyll b Carotenoids

Can you fill this out? PhotosynthesisCellular Respiration Organelle for Process Reactants (needed material) Cycle of Chemical Reactions Electron Transport Chain Products (what is made) What is the structure of a Mitochondria? What is the structure of a Chloroplast?

Comparison of Photosynthesis & Cellular Respiration PhotosynthesisCellular Respiration Organelle for process ChloroplastMitochondrion ReactantsCO 2 and H 2 OSugars (C 6 H 12 O 6 ) and O 2 Cycle of chemical reactions Calvin cycle in stroma of chloroplasts builds sugar molecules Krebs cycle in matrix of mitochondria breaks down carbon-based molecules Electron Transport Chain Proteins within thylakoid membrane Proteins within inner mitochondrial membrane ProductsSugars (C 6 H 12 O 6 ) and O 2 CO 2 and H 2 O