Question

1. Describe how attaching an enzyme to the cell membrane regulates the rate of a specific reaction

2. Describe the type of reaction that is typically regulated by an allosteric enzyme based on DG for the reaction.

3. Differentiate between positive and negative feedback loops based on sequence of reactions resulting the formation of a final product, “F”

4. Differentiate between the [S] that gives half maximum velocity based on an allosteric enzyme without and with an allosteric activator

Answer 1

1.

Membrane-bound enzymes have certain specific differences compared with soluble enzymes. Membrane-binding often enables greater catalytic activity of associated enzymatic reactions, their regulation by low molecular weight substances (substrates and allosteric effectors, hormones) and compartmentation, etc.

Some peripheral proteins on the surface of intestinal cells, for example, act as digestive enzymes to break down nutrients to sizes that can pass through the cells and into the bloodstream.

2.

allosteric regulation (or allosteric control) is the regulation of an enzyme by binding an effector molecule at a site other than the enzyme's active site.

The site to which the effector binds is termed the allosteric site or regulatory site. Allosteric sites allow effectors to bind to the protein, often resulting in a conformational change involving protein dynamics. Effectors that enhance the protein's activity are referred to as allosteric activators, whereas those that decrease the protein's activity are called allosteric inhibitors.

Allosteric regulations are a natural example of control loops, such as feedback from downstream products or feedforward from upstream substrates. Long-range allostery is especially important in cell signaling. Allosteric regulation is also particularly important in the cell's ability to adjust enzyme activity. Allosteric regulation occurs when DG is negative.

3.

The key difference between positive and negative feedback is their response to change: positive feedback amplifies change while negative feedback reduces change. This means that positive feedback will result in more of a product. Negative feedback will result in less of a product. Positive feedback moves away from a target point while negative feedback moves towards a target.

Without feedback, homeostasis cannot occur. This means that an organism loses the ability to self-regulate its body. Negative feedback mechanisms are more common in homeostasis, but positive feedback loops are also important.