Feedback Systems. Feedback Loop Video Fig. 1-13 Negative feedback Excess D blocks a step D D D A B C Enzyme 1 Enzyme 2 Enzyme 3 D (a) Negative feedback.

Feedback Systems

Feedback Loop Video

Fig. 1-13

Negativefeedback

Excess Dblocks a step

D

D D

A

B

C

Enzyme 1

Enzyme 2

Enzyme 3

D

(a) Negative feedback

W

Enzyme 4

XPositivefeedback

Enzyme 5

Y

+

Enzyme 6

Excess Zstimulates astep

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. 8-22

Intermediate C

Feedbackinhibition

Isoleucineused up bycell

Enzyme 1(threoninedeaminase)

End product(isoleucine)

Enzyme 5

Intermediate D

Intermediate B

Intermediate A

Enzyme 4

Enzyme 2

Enzyme 3

Initial substrate(threonine)

Threoninein active site

Active siteavailable

Active site ofenzyme 1 nolonger bindsthreonine;pathway isswitched off.

Isoleucinebinds toallostericsite

Feedback Inhibition• Metabolic pathway• Switched off by inhibitory

binding of end product to an enzyme earlier in the pathway of production

Fig. 40-8Response:Heater turnedoff

Stimulus:Control center(thermostat)reads too hot

Roomtemperaturedecreases

Setpoint:20ºC

Roomtemperature

increases

Stimulus:Control center(thermostat)

reads too cold

Response:Heater turnedon

Nonliving Example of What type of Feedback to maintain homeostasis

Fig. 40-16Sweat 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. 40-17

Organic moleculesin foodExternal

environment

Animalbody Digestion and

absorption

Nutrient moleculesin body cells

Carbonskeletons

Cellularrespiration

ATP

Heat

Energy lostin feces

Energy lost innitrogenouswaste

Heat

Biosynthesis

Heat

Heat

Cellularwork

Blood Sugar Levels

Example of Hormonal Feedback System

Test Review Info

Every Pyruvate produces

• 3 NADH• 1 ATP• 1 FADH2

• HOW MANY PYRUVATES DO YOU GET FROM 1 SUGAR MOLECULE?

Fig. 10-9

Wavelength of light (nm)

(b) Action spectrum

(a) Absorption spectra

(c) Engelmann’s experiment

Aerobic bacteria

RESULTS

Rate

of p

hoto

synt

hesi

s(m

easu

red

by O

2 rel

ease

)Ab

sorp

tion

of li

ght b

ych

loro

plas

t pig

men

ts

Filamentof alga

Chloro- phyll a Chlorophyll b

Carotenoids

500400 600 700

700600500400

Can you fill this out?

Photosynthesis Cellular 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

Photosynthesis Cellular Respiration

Organelle for process

Chloroplast Mitochondrion

Reactants CO2 and H2O Sugars (C6H12O6) and O2

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

Products Sugars (C6H12O6) and O2

CO2 and H2O