What is non allosteric enzymes?

Answer 1

A second and reversible form of regulation is known as allosteric regulation

In allosteric regulation, regulatory molecules bind reversibly to the protein, altering

its confirmation, which in turn alters its activity. Such allosteric effectors are not

covalently attached to the protein.

Here, the activity of a protein is

positively regulated by the

binding of a factor.

This factor could be a small

molecule or another protein.

What is important is that the

allosteric binding site is distinct

from the enzyme's catalytic site.

That is what allosteric means,

other site.

An allosteric effector can also act

negatively, inhibiting enzyme activity.

Because allosteric regulators do not

bind to the same site on the protein

as the substrate, changing substrate

concentration generally does not

alter their effects.

Of course there are other types of

regulation as well.

Active site inhibitors: An inhibitory factor may bind to and block the active site.

If this binding is reversible, then increasing the amount of substrate can over-come

the inhibition. An inhibitor of this type is known as a competitive inhibitor.

In some cases, the inhibitor chemically reacts with the enzyme, forming a covalent

bond. Because this type of inhibitor is essentially irreversible, increasing substrate

concentration can not overcome inhibition. These are therefore known as a noncompetitive

inhibitors.

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Allosteric effectors are also non-competitive, since they do not compete with

substrate for binding to the active site.

A protein binds an allosteric regulator - what happens to the

protein?

Why are allosteric regulators not "competitive"?

What makes an inhibitor that binds to the active site of an

enzyme "non-competitive" ?

Post-translational regulation: Proteins may be modified after synthesis - this

process is known as post-translational modification. A number of posttranslational

modifications have been found to occur within cells.

The first type involve the covalent addition of specific groups to the protein - these

groups can range from phosphate groups (phosphorylation), an acetate group

(acetylation), the attachment of lipid/hydrophobic groups (lipid modification), or

carbohydrates (glycosylation) .

Often post-translational modifications are reversible, one enzyme adds the

modifying group, and another can act to remove it. For example, proteins are

phosphorylated by enzymes known as protein kinases, while protein

phosphatases remove phosphate groups.

Post-translational modifications act in much the same way as do allosteric effectors,

they modify the activity of the polypeptide to which they are attached. They can

also modify a proteins interactions with other proteins, the protein's localization

within the cell, or its stability.

Proteolytic processing: Another method for

regulating protein activity involves the cleavage of

the polypeptide chain.

Many proteins are originally synthesized in a longer,

and inactive "pro-form". To become active the propeptide

must be removed - it is cut by a protease.

This proteolytic processing activates the protein.

Proteolytic processing is itself often regulated.

A protein is normally found free in the cytoplasm; where would

you expect it would be found following addition of a lipid group?

What are the advantages/disadvantages of using proteolytic

activation, compared to allosteric activation of a protein?

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activation, compared to allosteric activation of a protein?

Why are enzymes required for post-translational modification?

Do you think post-translational modification requires energy?

Telling proteins where to go: Translation of proteins occurs in the cytoplasm,

where mature ribosomes are located. If no information is added, a newly

synthesized polypeptide will remain in the cytoplasm, that is its default location.

Yet even in the structurally simplest of cells, the prokaryotes (bacteria and archaea),

there is more than one place that a protein may end up: it can remain in the

cytoplasm, it can be inserted in the plasma membrane or it may be secreted from the

cell.

Both membrane and secreted polypeptides must be inserted into, or pass through,

the plasma membrane.

Polypeptides destined for the

membrane or for secretion are generally

marked by a specific tag, known as a

signal sequence. The signal

sequence consists of a stretch of

hydrophobic amino acids, often at the

N-terminus of the polypeptide.

As the signal sequence emerges from

the ribosome it interacts with a signal

recognition particle or SRP - a

complex of polypeptides and a

structural RNA.

The binding of SRP to the signal

sequence causes translation to pause.

The mRNA/ribosome/nascent polypeptide/SRP complex will find (by diffusion), and

attach to, a ribosome/SRP receptor complex on the cytoplasmic surface of the

plasma membrane.

This ribosome/SRP receptor is associated with a polypeptide pore. When the

ribosome/SRP complex docks with the receptor, translation resumes and the

nascent polypeptide passes through a protein pore and so through the membrane.

As the polypeptide emerges on the extracytoplasmic side of the membrane, the

signal sequence is generally removed by an enzyme, signal sequence peptidase.

If the polypeptide is a membrane protein, it will remain within the membrane. If it is a

secreted polypeptide, it will be released into the periplasmic space.

_armanfiroz_

Answer 2

Allostery means "different shape." Allosteric enzymes change between active shapes and inactive shapes as a result of the binding of substrates at the active site and of regulatory molecules at other sites.

Answer 3

Allosteric just means that the enzyme can be activated somewhere else than the active site. So, these enzymes can be initiated and inhibited by the binding of an allosteric molecule at these specific sites.

Answer 4

These enzymes do not have allosteric, other place, adjuncts to activation. Such as not needing some types of vitamins to dock at the allosteric site for the active site to be active.

Answer 5

An allozyme is either form of an enzyme specified by an allelic gene.