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Flashcards in Biochem Lecture 12 Deck (28)
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1
Q

Why is it important to be able to control enzyme reactions?

A

Every process has a way of being controlled. This allows the ability to start and stop processes and to accelerate or slow them down.
Control helps the cell to be more efficient by only doing things when they are needed.
Control is necessary for homeostasis. This is achieved through maintain a constant cell environment despite changing external conditions.

2
Q

What are multi-enzyme pathways?

A

Most metabolic pathways in the body require multiple steps. This means that the product of one process is the substrate for another process.

3
Q

What is the rate limiting step in a pathway?

A

It is always the slowest step in the process.

4
Q

How are complex and multi-enzyme processes controlled?

A

Multi-step processes are usually controlled by making changes to the rate limiting step only. This affects the entire pathway. Rate limiting enzymes catalyze an irreversible step.

5
Q

What are the four basic categories of enzyme regulation?

A
  1. Compartmentalization
  2. Substrate availability
  3. Enzyme quantity
  4. Enzyme activity
6
Q

What are the two ways that compartmentalization can control an enzyme’s activity?

A

Separation in space and in time.

Organelles create ideal environments for a reaction to happen, so the reaction won’t happen elsewhere.

7
Q

In relation to substrate concentration, when will changes have significant influences on the rate, and when will they have minimal impact on the rate?

A

When substrate concentration is near the Km value, any change in [S] will have a significant effect on rate.
When [S] is near Vmax, changes cannot have a significant impact on rate.

8
Q

What is the absolute quantity of an enzyme?

A

It results from the net balance between the rate of synthesis and degradation of the enzyme itself.

9
Q

What are inducers in regard to enzyme concentration?

A

Inducers promote the synthesis of enzymes.

10
Q

Is enzyme quantity a fast or slow way to regulate the rate of an enzymatic process?

A

It is a slow way because it takes time to build new enzymes and to degrade them.

11
Q

What are the passive means of enzyme regulation?

A

Compartmentalization and substrate availability.

12
Q

What are the active means of enzyme regulation?

A

Enzyme quantity and enzyme activity.

13
Q

What is product inhibition?

A

The product of the enzymatic reaction inhibits the function of the enzyme itself. Products often are similar to their precursors and can sometimes bind to the active site of the enzyme and prevent it from doing its job.

14
Q

What is allosteric regulation?

A

A different effector or modulator molecule binds to a different site on the enzyme, causing a conformational change that affects the enzyme’s function.

15
Q

What are the 5 characteristics shared by allosteric enzymes?

A
  1. Effector binds to a regulatory site and not to the active site.
  2. Effector binds reversibly
  3. No need for structural similarity between substrate and effector
  4. Allosteric enzymes have quaternary structure
  5. Sigmoidal curve of enzymatic activity
16
Q

What does oligomeric mean?

A

Two or more subunits.

17
Q

What is the equivalent Km value for allosteric enzymes?

A

It is the K0.5 value because allosteric enzymes don’t follow michaelis-menten kinetics which have a hyperbolic curve.

18
Q

How are allosteric effectors classified?

A

Homotropic=same chemical nature as true substrate
Heterotropic=different chemical

Activators=have positive effect and increase enzyme activity
Inhibitors=neg effect and decrease activity

19
Q

What is feedback inhibition?

A

Downstream product of a multi-enzyme pathway inhibits an upstream enzyme.

20
Q

What is feedforward activation?

A

Upstream substrate of a multi-enzyme pathway activates a downstream enzyme.

21
Q

What is the difference between feedback inhibition and product inhibition?

A

Feedback control happens through a regulatory site on the enzyme and product inhibition has structural similarities to the original substrate and binds to the active site to inhibit the enzyme activity.

22
Q

Many enzymes have a T and an R conformation. One is active and the other is not. How do activators and inhibitors interact with these conformations, and how do these interactions influence the reaction rate chart?

A

Activators bind to the R configuration and stabilize it. This is a left shift on the graph.
Inhibitors stabilize the T conformation and cause a right shift on the graph.

23
Q

What is cooperativity?

A

The binding of one substrate to a subunit has an effect on neighboring subunits so they are more likely to bind the substrate. This is called positive cooperativity.

24
Q

What are the most common types of enzyme regulation?

A

Allosteric and covalent regulation.

25
Q

What is covalent regulation?

A

Addition or removal of specific chemical groups via covalent bonding that have an immediate effect on the enzyme.
Examples of reversible modifications are:
phosphorylation
adenylation
uridylylation
ribosylation
methylation

26
Q

What are the two protein enzymes involved in phosphorylation?

A

Protein kinase: transfers a phosphorus group from ATP to the enzyme
Protein phosphatase: catalyzes hydrolysis of the phosphate group off the enzyme

27
Q

What amino acids are phosphorylated?

A

The phosphorus group is added to the hydroxyl group of serine threonine and tyrosine.

28
Q

What is an example of irreversible covalent modification of an enzyme?

A

Limited proteolysis. Many proteins are built as an inactive precursor called a proenzyme or zymogen. In order to become active, part of the protein must be cleaved. This causes an irreversible conformational change in the protein.