metabolic control Flashcards
What is the need for regulating metabolism in cells?
To provide products at the rate they are needed.
To maintain steady-state concentrations of metabolites (homeostasis).
To prevent large changes in metabolites that could harm the cell.
To respond rapidly to changes in supply or demand (e.g., hormones).
What are the levels of metabolic regulation?
Modulation: Rapid but modest changes in enzyme activity in response to metabolite levels.
Interconversion: Slower activation or suppression of enzyme pools.
Changes in enzyme biosynthesis: Slow but major changes in gene expression via transcription and translation.
What is enzyme inhibition?
Competitive Inhibition: The inhibitor mimics the substrate and competes for the enzyme’s active site.
Non-competitive Inhibition: The inhibitor binds the enzyme-substrate complex, altering the enzyme’s function.
What is feedback inhibition in metabolic pathways?
Feedback inhibition occurs when the end product of a pathway inhibits an early enzyme in the pathway.
Example: In a linear pathway A → B → C → D → E, the product E inhibits enzyme 1, which controls the conversion of A to B.
What is the role of covalent modification in enzyme regulation?
Covalent modifications (e.g., phosphorylation) can activate or inhibit enzymes.
Example: Phosphorylation of glycogen phosphorylase activates it, while phosphorylation of glycogen synthase inhibits it.
How does phosphorylation affect glycogen metabolism?
Glycogen Phosphorylase b (inactive) is converted to Phosphorylase a (active) via phosphorylation, stimulated by hormonal signals like adrenaline.
Glycogen Synthase: Phosphorylation inhibits its activity, preventing glycogen synthesis.
What are protein kinases and their role in signal transduction?
Protein kinases transfer a phosphate group from ATP to specific amino acids (serine, threonine, tyrosine) on target proteins.
This phosphorylation can activate or deactivate proteins, playing a key role in signaling pathways (e.g., activating glycogen breakdown).
What is signal transduction in response to hormones?
Hormones (like adrenaline) activate adenylate cyclase, which produces cAMP.
cAMP activates Protein Kinase A (PKA), which activates downstream enzymes, including glycogen phosphorylase, to break down glycogen into glucose.
How can signaling pathways affect gene expression?
Protein Kinase A (PKA) can phosphorylate transcription factors (e.g., CREB), influencing the transcription of specific genes.
Other signaling pathways can involve Ca²⁺ and Protein Kinase C (PKC) to regulate gene expression.
How is gene expression regulated at the transcription level?
Transcription factors bind to specific DNA sequences near the gene promoter (e.g., TATA box, CAAT box, GC box).
These transcription factors can either activate or repress gene expression.
What are transcription factors?
Transcription factors are proteins that bind to DNA and regulate gene expression by either activating or repressing transcription.
Example: SP1 binds to the GC box and controls housekeeping genes.
What is the structure of a typical transcription factor?
Transcription factors often have:
DNA Binding Domain
Dimerization Domain
Activation Domain (sometimes includes ligand binding sites).
How is the albumin gene controlled in the liver?
The albumin gene is regulated by several transcription factors like NF1, C/ERB, and HNF1, which bind to the promoter and enhancer regions of the gene.
What are the key stages in gene expression regulation?
Transcription: DNA is transcribed into RNA.
Translation: mRNA is translated into protein.
How does the structure of a gene influence its expression?
The promoter region (e.g., TATA box) and enhancer regions control the initiation of transcription.
Interaction with RNA polymerase and transcription factors determines whether the gene is transcribed.
