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1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

7. Energy and Metabolism

Negative & Positive Feedback

7. Energy and Metabolism

Negative & Positive Feedback: Videos & Practice Problems

Video Lessons Practice Worksheet

Topic summary

Negative feedback in metabolic pathways inhibits earlier steps, acting like a red light to slow down production. For example, the final product can inhibit an enzyme, reducing the conversion of molecule A to B, thus limiting the final product F. In contrast, positive feedback stimulates earlier steps, functioning like a green light to accelerate production. The final product can enhance enzyme activity, leading to increased production of the final product. Understanding these feedback mechanisms is crucial for grasping metabolic regulation and homeostasis in biological systems.

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Negative Feedback

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Negative Feedback Video Summary

Negative feedback is a crucial regulatory mechanism in metabolic pathways, functioning to maintain homeostasis within biological systems. It occurs when the final product of a metabolic pathway inhibits an earlier step in the same pathway, effectively acting as a "red light" that slows down or stops the process. This inhibition is essential for preventing the overproduction of certain metabolites, ensuring that the cell does not create excessive amounts of the final product.

To illustrate, consider a metabolic pathway that converts molecule A into molecule F through a series of enzymatic reactions involving intermediate molecules B, C, D, and E. Each step is facilitated by specific enzymes (enzyme 1 through enzyme 5). When the cell has sufficient levels of product F, the final product can feedback to inhibit an earlier enzyme in the pathway, such as enzyme 1. This feedback mechanism is represented by a negative sign, indicating inhibition. By blocking the conversion of molecule A into molecule B, the overall production of product F is decreased.

This regulatory process is vital for cellular efficiency and resource management, allowing cells to adapt to varying metabolic demands. Understanding negative feedback is foundational for exploring other regulatory mechanisms, such as positive feedback, which will be discussed in subsequent lessons.

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Positive Feedback

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Positive Feedback Video Summary

Positive feedback is a crucial concept in metabolic pathways, functioning as the opposite of negative feedback. In positive feedback, the final product of a metabolic pathway enhances an earlier step in the same pathway, effectively acting as a catalyst for further reactions. This stimulation can be visualized as a green light, signaling the pathway to accelerate and produce more of the final product.

For instance, consider a metabolic pathway where the final product is denoted as product F. In this scenario, product F travels backward to stimulate an earlier enzyme, specifically enzyme 1. This stimulation increases the activity of enzyme 1, allowing it to produce more of an intermediate product, molecule B. As a result, the increased production of molecule B leads to an even greater accumulation of the final product F.

In situations where a cell requires a higher concentration of a final product, positive feedback becomes particularly advantageous. The positive sign in this context indicates the stimulation of the enzyme, promoting a cycle of increased production. Understanding this mechanism is essential for grasping how cells regulate their metabolic pathways effectively.

Problem

________ is when the product of a biochemical pathway activates the production of itself.
a) Negative feedback inhibition.
b) Positive feedback.
c) Substrate feedback inhibition.
d) Product feedback inhibition.

Negative feedback inhibition.

Positive feedback.

Substrate feedback inhibition.

Product feedback inhibition.

Problem

Which of the following is TRUE about feedback inhibition?
a) Feedback inhibition has no physiological importance.
b) Multiple products are required for feedback inhibition.
c) Feedback inhibition of a pathway can only be accomplished by the products of that pathway.
d) Feedback inhibition involves products binding to the active site to prevent enzyme activity.

Feedback inhibition has no physiological importance.

Multiple products are required for feedback inhibition.

Feedback inhibition of a pathway can only be accomplished by the products of that pathway.

Feedback inhibition involves products binding to the active site to prevent enzyme activity.

Dig Deeper into Negative & Positive Feedback

Negative and positive feedback are regulatory mechanisms where the final product of a metabolic pathway either inhibits or stimulates an earlier step in the same pathway.

Key Terminology

Negative feedback: A process where the final product of a metabolic pathway inhibits an earlier step, slowing or stopping the pathway to maintain balance.
Positive feedback: A process where the final product of a metabolic pathway stimulates an earlier step, enhancing the pathway’s activity and increasing product formation.
Metabolic pathway: A series of chemical reactions within a cell, each catalyzed by a specific enzyme, leading to the formation of a final product.
Enzyme: A protein that acts as a catalyst to speed up chemical reactions without being consumed.
Activator: A molecule that increases enzyme activity, often involved in positive feedback mechanisms.
Inhibitor: A molecule that decreases enzyme activity, often involved in negative feedback mechanisms.
Activation energy: The energy required to start a chemical reaction, which enzymes help lower to facilitate metabolic pathways.
ATP (Adenosine triphosphate): The primary energy currency of the cell, often produced or consumed in metabolic pathways regulated by feedback.
Allosteric regulation: The regulation of an enzyme’s activity through binding of molecules at a site other than the active site, commonly seen in feedback control.
Signal transduction: The process by which a cell converts a signal or stimulus into a cellular response, sometimes involving feedback loops.

Real-World Applications

In human physiology, negative feedback regulates hormone levels such as insulin and glucagon to maintain blood glucose homeostasis, preventing excessive fluctuations.
Positive feedback plays a crucial role during childbirth, where the hormone oxytocin stimulates uterine contractions, which in turn promote more oxytocin release until delivery occurs.
In biotechnology, understanding feedback mechanisms allows for the design of metabolic engineering strategies to optimize production of desired compounds by controlling enzyme activity.

Common Misconceptions

Negative feedback does not mean the pathway is “bad” or harmful; it’s actually essential for maintaining balance and preventing overproduction of substances.
Positive feedback is not always beneficial or unlimited; it usually has a defined endpoint or is controlled by other mechanisms to avoid runaway reactions.
Feedback regulation involves more than just turning enzymes on or off; it often includes subtle changes in enzyme activity through allosteric sites or changes in gene expression.
Feedback loops are not exclusive to metabolic pathways; they also occur in systems like the nervous and endocrine systems to regulate complex physiological processes.

Do you want more practice?

We have more practice problems on Negative & Positive Feedback

Here’s what students ask on this topic:

What is negative feedback in metabolic pathways?

Negative feedback in metabolic pathways occurs when the final product of a pathway inhibits an earlier step in the same pathway. This inhibition acts like a red light, slowing down or stopping the pathway to prevent the overproduction of the final product. For example, if a metabolic pathway converts molecule A to molecule F through a series of enzymes, the final product F can inhibit an enzyme that converts A to B. This reduces the production of F, maintaining balance and preventing excess accumulation. Negative feedback is crucial for maintaining homeostasis in biological systems.

How does positive feedback differ from negative feedback in metabolic pathways?

Positive feedback is the opposite of negative feedback. In positive feedback, the final product of a metabolic pathway stimulates an earlier step in the same pathway, acting like a green light to accelerate production. For instance, if a pathway converts molecule A to F, the final product F can enhance the activity of an enzyme that converts A to B, leading to increased production of F. This mechanism is useful when a cell needs to rapidly produce more of a specific product. In contrast, negative feedback inhibits earlier steps to slow down production, maintaining balance and preventing overproduction.

Why is negative feedback important for homeostasis?

Negative feedback is essential for homeostasis because it helps maintain stable internal conditions by regulating metabolic pathways. When the final product of a pathway accumulates, it inhibits an earlier step, reducing its own production. This prevents the overaccumulation of substances, which could disrupt cellular functions and overall homeostasis. For example, in the regulation of blood glucose levels, insulin acts through negative feedback to lower blood sugar when it is too high. By inhibiting further glucose production and promoting its uptake and storage, negative feedback ensures that physiological parameters remain within optimal ranges.

Can you provide an example of positive feedback in biological systems?

An example of positive feedback in biological systems is the process of blood clotting. When a blood vessel is injured, platelets adhere to the site and release chemicals that attract more platelets. This accumulation of platelets continues to stimulate further platelet aggregation, rapidly forming a clot to seal the wound. The initial signal is amplified through positive feedback, ensuring a swift and effective response to injury. This mechanism is crucial for preventing excessive blood loss and promoting healing.

How do negative and positive feedback mechanisms contribute to metabolic regulation?

Negative and positive feedback mechanisms are vital for metabolic regulation. Negative feedback inhibits earlier steps in a pathway to prevent overproduction of the final product, maintaining balance and preventing resource wastage. For example, the end product of a pathway can inhibit an enzyme that catalyzes an early step, reducing its own synthesis. Positive feedback, on the other hand, stimulates earlier steps to accelerate production when more of the final product is needed. This amplification ensures rapid response and adaptation to changing cellular demands. Together, these feedback mechanisms ensure efficient and balanced metabolic processes, crucial for cellular function and homeostasis.