Regulation of metabolic pathways

Question 1

How are metabolic pathways regulated?

Answer 1

• Through regulation of enzyme-catalyzed reactions (with allosteric regulations or covalent alterations)
• The synthesis of metabolites within the pathways and how they are interconnected (some metabolites are used in one pathway and in the other too)

Question 2

What is the pasteur effect?

Answer 2

it depends on O2 to be presence or absence. Yeast are facultative anaerobes (with O2 = growth, without O2 = fermentation)– Type and speed of glucose utilization depend on cells’ requirements. Cells respond to their environment.

Question 3

What does dynamic steady state mean? Why is it used for?

Answer 3

In result of the cell/org’s efforts, they create homeostasis– they insure that they always have enough E/nutrients to supply their cells: E due to their level of exercise/resting needs and nutrients, since O2 and other compounds are not always available.

Question 4

Stem cells produce any types of RBC. What differentiates them (E-wise and physiologically-wise)

Answer 4

Stem cells have mitochondria and nucleus + have
organelles to utilize nutrients to generate E (using O2)

RBCs do not have mitochondria, so their E generation is anaerobic; Instead, they convert glucose by glycolysis + fermentation for the generation and storage of high-energy phosphates (for survival of RBC).

Question 5

What source of E does neurons depend on? What is an alternative too?

Answer 5

Glucose.

Ketones.

Question 6

What do cardiac myocytes (muscle cells) depend on (source of E)?

Answer 6

FA

Question 7

What are all the possibilities of regulation of enzymes in a cell, that will increase or decrease its activity? (10)

Answer 7

STEPS:
1-Extracelular signal (starts regulation process)
2-Transcriptional regulation – The rate of synthesis of a protein depends on transcription factors; TF can be regulated by (de)phosphorylation or TF can interact with other TF or prots (corepressor or coactivator).
3-Stability of mRNA (the resistance of mRNA to be degraded by a ribonuclease)
4-mRNA translation (or not…) + speed at which it is translated, varies.
5-Protein stability (half-life): how long can it be maintained in the cell. Some proteins are tagged for degradation by the covalent attachment (cyclins); Some proteins are made in inactive forms and become active only with removal of inhibitory sequence in the proenzyme (inactive prot).
6-Enzyme localization. Depending where the enzyme is and where it is needed, the enzyme action could be limited. PROTEINS ARE NOT FUNCTIONAL UNTIL THEY REACH THE DESTINATION.
7-Changes of levels of substrates– affects the enzyme activity: no substrate, no activity. Too much substrate, the enzyme activity plateaus.
8-Enzyme binding ‘’allosteric effectors’’– small molecules that interact with the enzyme and change its activity.
9-Covalent modification affects enzyme activity. The addition of the phosphate gr on cyclins change the shape and activity of enzyme.
10-Interaction with regulatory prots. Activators and repressors.

Question 8

What are cyclins and why are they used for?

Answer 8

Cyclins– important for cell cycles. Various types: when they are phosphorylated, they ave a binding site that accepts kinases. The whole complex get activated and ACTIVATES OTHER PROTEINS USED IN CYCLE DIVISION such as microtubule formation and chromatin remodeling. These cyclins are synthesized and degraded, as needed.
WHen dephosphorylation, they are inactive.

Question 9

How can the amount of proteins in a cell be measured? RNA?

Answer 9

Western blot.

PCR.

Question 10

Why are regulatory mechanisms developped by the organism? (5)

Answer 10

• Maximize product/metabolites utilization ( ex. Glycolysis and Gluconeogenesis) product of one pathway inhibits the other. Pathways o opposite directions are not favored simultaneously.
• Glycolysis vs Gluconeogenesis: In liver, glucagon stimulates glycogen breakdown and gluconeogenesis while blocking glycolysis. In muscle, epinephrine stimulates glycogen breakdown and glycolysis, providing ATP to support contraction.
• Share metabolites between alternative pathways:.Ex. Glycolysis or pentosephosphate pathway; oxidative stress on cells– the 2nd pathway is favored, since 2 NAD+ will be reduced to 2 NADH, thus stripping the G-6-P of electrons to yield Ribulose-5-phosphate.
• Give fuel best suited for the need of the org. (glucose, fatty acids, glycogen, or amino acids)
• Slow down/shut down biosynthetic pathways when products accumulate. Muscles will use glucose until are no more, then they use fat are other nutrient.