Metabolic pathways are a balance between anabolic and catabolic processes and need to be regulated to meet requirements in the cell.

Metabolic pathways are comprised of anabolic pathways (building up) and catabolic pathways (breaking down) and their regulation is essential to ensure the metabolic needs of the cell are made. Regulation can occur due to irreversible reactions (where the product cannot go back to its reactant state), using rate-limiting enzymes or negative feedback (where products of a process inhibit enzymes earlier in the pathway. This regulation of metabolic pathways helps to control reactions that progress pathways and makes use of the dynamic between thermodynamic favorability and also the spontaneity of the reactions, enzymes and catalysts play a large role in controlling these processes to ensure reactions are only spontaneous when required.

Regulation of metabolic pathways exists in a dynamic steady state, where the levels of the metabolites are kept at a constant level due to the continual work of the metabolic processes taking place in the cell. To maintain this consistent level key cell components are required in abundance such as amino acids, ATP and glucose, all of which are examples of substances kept in dynamic steady state. For example, blood glucose circulates and is directly linked to levels of ATP production. This has a knock-on effect on the break down of glycogen to produce more blood glucose to meet the increased needs of cells during times of high respiration.

Another example of this is the control of gene expression where the genes that code for certain enzymes can be upregulated by the presence of molecules related to the metabolic pathway that increases transcription such as transcription factors. This could be in response to increase levels of metabolites, drug or hormones. 

 

Practice Questions

 

Khan Academy   

Regulating electron carrier molecules

 

 

MCAT Official Prep (AAMC)

Official Guide B/B Section Passage 5 Question 18

Section Bank B/B Section Passage 2 Question 9

Section Bank B/B Section Passage 5 Question 38

Practice Exam 4 B/B Section Passage 1 Question 3

 

Key Points

• Metabolic pathways are a balance between anabolic and catabolic processes and need to be regulated to meet requirements in the cell

• Regulation can occur due to irreversible reactions, using rate-limiting enzymes or negative feedback.

• Regulation of metabolic pathways exists in a dynamic steady state, where the levels of the metabolites are kept at a constant level due to the continual work of the metabolic processes taking place in the cell.

Key Terms

Anabolic: the process of building up chemical compounds in cells

Catabolic: the process of breaking down chemical compounds in cells

Rate–limiting enzymes: have a relatively lower velocity than other enzymes in the same pathway

Thermodynamic: related to heat energy and changes

Negative feedback: the counteraction of an effect by its own influence on the process giving rise to it

Dynamic steady-state: remains constant over time, but that constant state requires continual work