Posts Tagged ‘Biol1362’

The following is a review on a published article, “The Effect of Enzymes on Digestion.”, by Michael R. Bedford. Please note that his writings dealt with digestion in Birds.

Contrary to popular belief, that nutrients are always fully digested and absorbed in the blood stream, it is very unlikely that they ever do. Nutrients digestibilities vary between different dietary substances, however there are fours processes that help aid with digestibility. These four mechanisms are:

  • Deteriorating the cell wall 
  • Destroying ANF’s (supplements)
  • Supplying the Host’s Enzymes
  • Using intestinal bacteria

Destroying the cell wall.

Taken from www,newscenter.lbl,gov.

In this mechanism, Beta-glucanase, an enzymes, was used to break down the complex cell wall, rapidily allowing amylases and proteases to break down the cell’s content.

Getting rid of the ANF’s.

ANFs’ are supplements such as, non-starch polysaccharides, proteins, and amino acids.

It was observed that Beta-glucanase turned out to be soluble in barley. This was due to the Beta-glucan component being dissolved completely by the endosperm of the cell wall. ANF’s create viscosity, which reduces the effect of enzymes. Enzymes used to reduce intestinal viscosity are believed to improve digestion in the intestinal tract.

Viscosity. Taken from

Supplying the Host’s Enzymes.

Latest investigations has lead researchers to believe that the digestive tract may not have adequate enzymatic and absorption capacity to deal with all kinds of diets. However, work done by Bedford and Classen, proves that by adding the host enzymes, through means of supplements do in fact increase the rate at which these substances are digested.


Microbial presence?

The are millions of microbes present in your digestive tract. These microbes aid in digestion by breaking down the digestive substances to feed their own needs and produce, in some cases, helpful by products. Evidence to support the presence of microbes in our digestive tract is due to the presences of their by products in faeces.

Bacteria on the walls of the intestines


Bedford. Michael. R. 1996. ” The Effects of Enzymes on Digestion.” The Journal of Applied Poultry Research. Applied Poultry Inc, 1996. Accessed on April 11 2013.

Classen, H.L, T.A. Scotl, G.C. Irish, P. Hucl, M, and M.R Bedford, 1995.”The relationship of chemical and physical measurements to the apparent metabolize energy (AME) of wheat when fed to broiler chickens with and without and enzyme source”.Proc. of 2nd European Symp. on Feed Enzymes, Pages 65-77 Noordwijkerhout, NL. Accessed on April 11 2013.



This quiz is purely on enzymes only.

1. What class of enzymes breaks down substrates by adding or losing, hydrogen and oxygen?

A) Hydrolases

B) Transferases

C) Oxidoreductases



2. Ligases is the only one of the six major classes of enzymes to

A) Undergo hydrolysis

B) Combine molecules

C) Oxidise a substrate

D)Rearrange the structure of a substrate.


3.Uncompetitive Inhibitors binds to

A) Active site only

B) Enzyme-substrate complex only

C) Both the free enzyme and enzyme-substrate complex

D) To the substrate molecule only


4. Mixed Inhibitors binds to either the free enzyme or to the enzyme-substrate complex. How does this affect Vmax and Km?

A) Nothing is affected

B) Vmax increases and Km can increase and decrease

C) Vmax is reduced and Km can increase and decrease

D) Vmax remains constant, while Km increases


5) Which type inhibitor binds only to the active site?

A) Non-competitive

B) Uncompetitive

C) Competitive



Best of luck.

Thank you for you time.

What is an Inhibitor?

An inhibitor is any substance that diminishes the velocity of an enzyme catalysed reaction.

There are two main categories of inhibition- Reversible and Non-reversible. This entry deals with reversible inhibitors only. There are four types of reversible enzymes.

These are:

  • Competitive Inhibtors
  • Non-competitive Inhibitors
  • Uncompetitive Inhibitors
  • Mixed Inhibitors


Competitive inhibitors.

These inhibitors compete with the substrate molecules for the active site of the enzyme. Competitive inhibitors only bind to the active site of the free enzyme, note that it never binds to the enzyme-substrate complex. Competitive inhibitors do not change the Vmax, maximum velocity, of the reaction, however the substrate affinity binding to the active site of the enzyme, decreases. This means Km increases. (Remember high affinity = low Km and vice versa) .

In the case of allosteric enzymes. Both substrate and inhibitor cannot bind to the enzyme at the same time. When the Inhibitor binds to one active site, it temporarily changes the shape of the other active site, preventing the substrate from binding.

Taken from "Describe an Induced fit model" ,

Taken from “Describe an Induced fit model” ,


Non-Competitive Inhibitors.

Unlike competitive inhibitors,which only bind to the active site of the enzyme, non-competitive inhibitors can bind to the free enzyme as well as the enzyme substrate complex. Since the substrate can still bind to the enzyme, this tells us that Km is unchanged, however Vmax is reduced as the enzyme does not function with the inhibitor.


Uncompetitive Inhibitors.

These inhibitors only bind to the enzyme substrate complex. This means that the substrate can bind to enzyme although the inhibitor is already bound to it. This also tells us that both Vmax and Km are reduced.


Mixed Inhibitors.

Mixed inhibitors get the term “mixed” because they can act as competitive inhibitors, and only bind to the active site, or act and uncompetitive inhibitors and bind to the enzyme substrate complex. As a result of this, substrate affinity to the enzyme can either increase or decrease,(i.e. low or high Km values). From uncompetitive inhibitors, Vmax will always be reduced as the presence of the inhibitor decreases the velocity.

There are six classes of enzymes and they should be learnt in this specific order:

  1. Oxidoreductases
  2. Transferases
  3. Hydrolases
  4. Lyases
  5. Isomerases
  6. Ligases

This is the order in which we assign an enzyme commission number (EC), which is a numerical number, based on the reactions they catalyse. For example, Adenosinekinase (E.C. is used to transfer a phosphate group from ATP. The two in the E.C number means that it belongs to the group transferases.


These enzymes catalyses all redox reactions in which oxygen or hydrogen are gained or lost.  Examples of these are peroxides, lactate dehydrogenase.


These enzymes are responsible for the transportation of functional groups of molecules such as amino groups, acetyl groups or phosphate groups. Examples of these are alanine kinase. (Kinase’s transfers phosphate groups)


These enzymes , affect substrates via hydrolysis. (i.e Adding water.) Eg. Lipase or sucrase.

Lyases break down molecules by removing groups of atoms without going throught the process of hydrolysis. For example, Oxalate dehydrogenase.


Enzymes of this class re-arrange the atoms of the substrate they bind to. Example, Glucose phosphate isomerase.


These enzymes combine two molecules together using energy received through the break down of ATP to ADP. Most common example, DNA ligase.

They do, in fact there are four levels of protein structures: primary, secondary, tertiary and quaternary.

Primary structure of proteins.


Fredrick Sanger was the first scientist to discover the primary structure of proteins, by looking at the protein, insulin. The specific sequence of amino acids in a polypeptide chain is known as the primary structure of proteins. Peptide bonds are the only bonds involved in this sequence.

Secondary structure of proteins.


Secondary proteins, are the shape taken up by the polypeptide chain due to hydrogen bonding. The two most common shapes of secondary proteins are the α-helix and the β-pleated sheets.

An α-helix chanin twist every 3.6 amino acid. It is formed due to the formation of hydrogen bonds  between the CO of one amino acid to the NH of the fourth amino acid.

β-pleated sheet are formed among adjacent polypeptides chains. Like α-helices, hydrogen bonds form between the CO and NH of neighbouring chains, which results in a stronger, yet less elastic structure.


Tertiary structure of Proteins.

Three types of bonds, formed between R-groups, are responsible for the shape of these proteins. These bonds are hydrogen bonds, ionic bonds, and disulphide bonds.

Hydrogen bonds, most common, is formed when an electronegative oxygen is attracted to the electropositive hydrogen of another R-group.


Ionic bonds are formed between an charged amino acid and carbonyl group.


Disulphide bond is a covalent bond formed through oxidation of two -SH groups.


These bonds cause proteins to fold into compact, globular shapes. These proteins are soluble and are called globular proteins, for example, insulin is a globular protein.

Note: Proteins such as keratin or collagen are insoluble and do not fold into tertiary structures, instead they remain unfolded into non-fibrous structures. These are called fibrous proteins.


Quaternary structure of proteins.

Quaternary structure of proteins is the combination of two or more proteins. An example of this type of structure is haemoglobin, which is a combination for four proteins.


Proteins are huge molecules made up of many polypeptide chains. They are seven classes of proteins. Proteins for storage, channel proteins, structural proteins, proteins for immune responses, enzymes, transport proteins, and receptor proteins. Proteins can be globular, fibrous, or membranous.

Receptor proteins are used to sense stimuli.


Channel proteins aid in controlling molecules in and out of the cell. Channel proteins allows simple diffusion into the cell.

Transport proteins carry valuable resources around the body eg. Haemoglobin transport oxygen.


Structural proteins, cartilage made up of the protein collagen, helps prevent bones from rubbing together and cause damage.

Proteins in charge of immune responses, such as antibodies, fight off infection and foreign contaminants from harming the body.

Enzymes are used to speed up biochemical reactions in the body, that may take too long than life itself.



A peptide bond (C-N) is formed when the α-amino group of one amino acid and the carboxyl group of the other amino acid combines, covalently, via condensation.



Peptides get their name from the peptide bonds between two or more amino acids. They are grouped accordingly to the number of amino acids found in the chain.