Biology - Chapter 4 - Enzymes

What is another name for an anabolic reaction? Does it require or release energy?

Endergonic reaction. They require energy

If the factors that affect an enzymes ability are optimal, what does that mean for the enzyme?

Enzyme activity is at its highest and the rate of reaction is at its fastest

What can happen to an enzyme if its temperature gets too cold? Is this change permanent?

Inactivation. It is not permanent, when the enzyme is returned back to its normal temperature they will become functional again.

Describe the bonds in reversible inhibition. What does this therefore mean?

The bonds formed between the enzyme and the inhibitor are weak (i.e hydrogen bonds) so they are easily broken and the inhibition is reversed. This means the inhibitor can move in and out of the active site, which reduces the activity of the enzyme because the substrate will not be able to bind as often.

What is a coenzyme? Describe its make

They are organic COFACTORS. For certain enzymes, a specific coenzyme is required to catalyse reactions. Often the coenzyme is structurally altered during the reaction, but afterwards reverts back to its original form and can be reused. Examples include vitamins, ATP, NAD

What do most enzymes end in and what name do they often take after?

They generally end in 'ase' and take the name of the substrate involved in the reaction.

How do enzymes speed up a reaction?

They lower the activation energy

Describe competitive inhibition

This occurs when the shape of the inhibitor is similar to the shape of the substrate that normally binds to the active site. Due to this, the inhibitors are able to bind to the active site of an enzyme and block the substrate from binding

How is an active site created?

Via the tertiary folding of the protein

What factors regulate the activation and inhibition of enzymes and determine whether they can catalyse reactions at all, rather than the rate?

- Inhibitors - Phosphorylation - Cofactors - Coenzymes

List 4 factors that affect an enzymes ability

- Temperature - pH - Concentration of enzyme - Concentration of substrate

What number on the pH scale is neutral? What is the most common neutral molecule and therefore are humans neutral?

7. Water. Because humans are primarily made up of water we are said to be neutral

How many types of reversible inhibition are there? Name them

2. Competitive and competitive inhibition

Provide an example of an anabolic reaction

A condensation reaction

What is biochemical pathway?

A sequence of reactions in which each reaction is catalysed by a specific enzyme and the product of one reaction becomes the substrate for the next reaction

What is a key structure on the enzyme?

Active site

What is a cofactor? Describe their make

An additional component to enable an enzyme to catalyse a reaction. They a non protein compounds that bind to the enzymes that are NECESSARY for the functioning of that enzyme. Co factors are INorganic ions such as FE2+, Mg2+ or organic molecules such as proteins, vitamins and ATP

What is it called when the active site binds to the substrate?

An enzyme-substrate complex

Is the inhibition of an enzyme by an inhibiting factor reversible or irreversible?

Can be either

What do coenzymes such as ATP, NADH, FADH2 and NADPH do?

Carry chemical groups between different reactions

What is an anabolic reaction? Are they endergonic or exergonic?

Are reactions that require the input of energy in order to produce larger molecules from smaller substrates. They are endergonic because they require energy.

Why, as a general rule, does the rate of catalysed reactions increase as temperature increases?

Because the warmer particles become during a reaction, the more rapidly they move which makes successful collisions between them more likely to occur

What is another name for a catabolic reaction? Does it require or release energy?

Exergonic reaction. They release energy

What major role to the coenzymes ATP, NADH, FADH2 and NADPH play?

In maintaining cellular processes such as cellular respirations and photosynthesis. These coenzymes can store and transport chemical groups, protons and electrons from one reaction to another.

What can happen if an enzyme is taken EITHER above or below its optimal pH?

It can denature. There is no such thing as inactivation when it comes to pH

What can happen to an enzyme if its temperature gets too hot? Is this change permanent?

It can denature. This is permanent

Describe feedback inhibition. Is it a good or a bad thing?

It is a good thing. It occurs when a product produced late in the biochemical pathway acts as an inhibitor of an enzyme acting earlier in the pathway, stopping the action of the enzyme. This means the product will not continue to be produced

What structure do enzymes have?

Most enzymes have a tertiary structure, but some have a quaternary structure.

Descrive non-competitive inhibition

Occurs when an inhibitor binds to the enzyme in a place other than the active site. Binding to the allosteric site either changes the shape of the enzymes active site such that the substrate cannot bind, or it blocks the changes in shape needed for the reaction to progress once the substrate is bound

Enzymes and their active site are highly specific in their action. Each enzyme acts on how many particular substrates?

One

What do we call compounds that are irreversible inhibitors of enzymes? Give an example

Poisons. An example is cyanide. It is a irreversible inhibitor of the key enzyme in the electric transport chain. This stops the production of ATP by aerobic respiration, resulting in death

What do we described enzymes as?

Protein molecules that act as biological catalysts

What is a catabolic reaction? Are they endergonic or exergonic?

Reactions in which substrates are broken down and energy is released. They are exergonic as they release energy

Describe the bonds in irreversible inhibition. What does this therefore mean?

The bonds between the inhibitor and the enzyme are very strong (i.e covalent bonds). This means that the inhibitor blocks the enzymes active site permanently.

What does a catalyst do?

Speed up the rates of reaction

Describe the induced fit model

States that when a substrate binds to the active site of an enzyme, a change in shape of the active site occurs.

How is energy transferred?

Stored in the chemical bonds between the coenzymes and the chemical group, proton or electron they carry.

Describe the lock and key model

The complementary fitting of the enzyme and the substrate. The enzymes active site had a rigid shape that the substrate fits into (like a lock and a key). If they 'key' does not fit into the 'lock' then no reaction occurs.

What is activation energy?

The energy required to begin a chemical reaction

What actually occurs when an enzyme is denatured?

The hydrogen bonds and hydrophobic interactions that create the tertiary and quaternary structure of the enzyme are broken and the shape of the enzyme is changed (including the active site) and the substrate cannot bind to it.

What model is the most current theory?

The induced fit model

What model is more accurate and why?

The induced fit model because we know that the active site is flexible and capable of changing its shape in order to conform to the shape of the substrate and achieve a tighter fit

What does the active site bind to?

The substrate molecule

Many of the reactions catalysed by enzymes involve what?

The transfer of chemical groups (eg phosphates) from one molecule to another.

What does the phrase 'cycling of a coenzyme' mean?

The unloaded form of a coenzyme is free to accept a proton, electron or chemical group, and once it has accepted it, it is considered to be loaded. The cycling between loaded and unloaded forms is called the cycling of a coenzyme.

A chemical reaction will only occur if . . . ?

There is sufficient energy to begin the reaction

How many models are there to describe how enzymes and their substrates interact? Name them

Two. The lock and key model and the induced fit model

Are enzymes recycled?

Yes

Are coenzymes recycled?

Yes, as they move a chemical group from one molecule to another molecule in different enzymatic reactions

Can the optimal pH of an enzyme vary? Give and example

Yes. Pepsin is secreted by the human stomach and it has a pH of 2, whereas amylase, found in saliva has a pH of 7