Metabolic Regulation Flashcards
What is the most common control strategy in bacteria?
Transcriptional control of protein synthesis
The cell senses that it has too little or too much of a particular protein and responds by increasing or decreasing the rate of transcription of that gene
Give the names of the 2 types of regulation and describe what they do briefly
feedback repression - the end product of enzymatic activity accumulates and blocks transcription
Induction - a metabolite (often a substrate for a pathway) accumulates and acts as an inducer of transcription.
Diagram of repression and induction metabolic regulation
Referring to figures A and B. In both cases, a repressor protein is required. The repressor can bind to the operator region and hinder RNA polymerase binding. For repression, a corepressor (typically the end product of the pathway) is required, and the repressor can block transcription only when bound to the corepressor. For induction, the inducer (typically a substrate for a reaction) will combine with the repressor and the complex is inactive as a repressor. In figure B several genes are under the control of a single promoter. A set of contiguous genes, encoding proteins with related functions, under the control of a single promoter-operator is called an operon
Describe Lac operon regulation
The lac operon controls the synthesis of three proteins involved in lactose utilization as a carbon and energy source in E.coli.These genes are laz, lacy and laca. Lacz for example encodes b-galactosidase (or lactase)which cleaves lactose to glucose and galactose. When E.coli senses the presence of a carbon-energy source preferred to lactose, it will not use lactose until the preferred substrate (glucose) is fully consumed. This control mechanism is exercised through a protein called CAP (cyclic-AMP-activating protein). Cyclic AMP (c-AMP)levels increase as the amount of energy available to the cell decreases. Thus, if glucose or a preferred substrate is depleted, the level of c-AMP will increase. Under these conditions,c-AMP will readily bind to CAP to form a complex that binds near the lac promoter. Enhancer regions exist in both procaryotes and eucaryotes
Diagram of catabolic repression
catabolic repression is the inhibition of the expression of specific enzymes or metabolic pathways in repsonse to presense of prefered energy source
How do cells communicate with the outside world
Cell surface receptors
These are present on almost all cells and can bind chemicals in the extracellular space. They play a crucial role in providing cells with information about their environment. In animals, these receptors are essential for facilitating cell-to-cell communication and are involved in signal transduction for processes like growth and cellular differentiation
What is the chemotaxis process?
Happens in motile bacteria where receptors binding to specific compounds, and this binding reaction results in changes in the direction of movement of the flagella. Normally motile cells move in a random-walk fashion; the binding of an attractant extends the length of time the cell moves on a “run” toward the attractant. Similarly, repellents decrease the length of runs towards danger.
What does the chemotaxis process explain?
Explains how motile bacteria know how to move towards nutrients and away from dangerous territory
Diagram representation of chemotaxi
Sometimes a response is only useful when it occurs in concert by a large number of cells in close proximity to each other. The question is, how do bacteria count?
They produce a chemical known as a quorum sensing molecule, whose accumulation is related to cell concentration.
How does quorum work?
When the quorum sensing molecule reaches a critical concentration, it activates a response in all the cells present. Thus for example in bioluminescence, the internal energy of a cell in isolation or in small numbers is not wasted in generating light that no one will see until a critical threshold of cells is reached.
The mechanism of quorum sensing depends on an intracellular receptor protein, while chemotaxis, as we saw, depends on surface receptor proteins.
What is required for cells to initiate DNA synthesis and replication
Growth factors (small proteins)
Growth factors act as signalling molecules that bind to specific receptors on the cell surface. This binding triggers a conformational change in the receptor, activating its catalytic activity. This activated receptor initiates a cascade of intracellular signalling pathways, ultimately leading to cellular division.
Is controlling of cell growth by binding of an external agent to a cell receptor intracellular or extracellular modulation?
Extracellular modulation
