Enzyme Quiz

quiztime

1. Which of the following best describes enzymes?

(A) Enzymes are biological catalysts that speed up a chemical reaction by providing and alternative pathway with lower activation energy.

(B) Enzymes are only proteins and usually it speeds up the rate of a reaction when required by the body.

(C) Enzymes are large biological molecules responsible for the thousands of chemical reactions for life sustenance.

(D) Enzymes influence chemical reactions in living systems by affecting the rate at which reactions occur

(E) Enzymes are protein catalysts that speed up a chemical reaction by lowering activation energy.

2. At high temperatures, the rate of enzyme action decreases because the increased heat

(A) changes the pH of the system

(B) alters the active site of the enzyme

(C) the reaction is in dynamic equilibrium

(D) the ratio of enzyme concentration to substrate concentration is 1:2

(E) increases the concentration of the enzyme

3. Which is true for the lock and key hypothesis?

1. substrate changes active site of the enzyme structure

2. enzyme’s active site has a complementary shape of to the substrate

3.  the functioning and role played by one enzyme is controlled by a single gene

4. R groups of the amino acids in the active site forms temporary bonds

(A) 1 only

(B) 1, 4

(C) 2, 3

(D) 2, 4

(E) All of the above

4. What defines a co-factor?

(A) organic co factors

(B) non-protein substances required by most enzymes for their efficient activity

(C) assist in the formation of the enzyme-substrate complex

(D) an unstable structure intermediate between the reactants and the products

(E)  hold substrate in a correct orientation for it to react with the active site

5. Competitive inhibition….

(A)  Binds at different sites on the enzyme not the active site

(B)   Only binds to the enzyme-substrate complex away from the active site

(C)   Binds to the active site only

(D)  Binds at a separate site from the active site

(E)   Km maybe increased or decreased

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Types Reversible Inhibition

Types Reversible Inhibition

Michaelis-Menten Curve:
Effect of a Competitive/Non-Competitive Inhibitor on the Reaction Velocity vs Substrate Concentration Plot

Michaelis_Menten2

Lineweaver- Burk Plot:
Effect of a Competitive/Non-Competitive Inhibitor on the Reaction Velocity vs Substrate Concentration Plot

Lineweaver_Burk2

Once a Upon an Enzyme (part 2)

Factors Affecting the Rate of Enzyme Reactions

Temperature

Over the range 0-40 degrees Celsius the rate of reaction doubles for the rise of every 10 degrees Celsius until optimum temperature. Heat supplies activation energy and kinetic energy to the reacting molecules causing them to move more quickly thus increasing the chances of collision. Hence the in a given time the more product will form than at a lower temperature. The temperature at which enzymes catalyzes a reaction at maximum rate is called OPTIMUM TEMPERATURE. Above this temperature heat causes the molecules to vibrate so violently that the hydrophobic and ionic bond that maintain the specific 3D structures break. The enzyme molecules begin to lose its shape and activity and is said to be denatured. At first the substrate molecules loosely fits into the active site until eventually it no longer fits or can no longer be held in the correct position for the reaction to occur.

enztemprate

pH

Every enzyme functions most effectively over a narrow pH range. The optimum pH is that at which the maximum rate is achieved. A pH above or below the specific value will reduce the activity of the enzyme. Changes in pH alter the ionic charge of the acidic and basic R groups thus disrupting ionic bonds that help to maintain the specific shape of an enzyme. The pH change leads to n alteration in enzyme shape particularly at the active site thus the enzyme is unable to function effectively and is said to be denatured.

enzphrate

Enzyme Concentration

If the substrate concentration is at a high level and pH and temperature are constant the rate is proportional to enzyme concentration, the larger the amount of enzyme, the greater the amount of substrate used in the time, provided its excess substrate.

Substrate Concentration

The rate increases with increasing substrate concentration up to a point where any further increases do not produce an increase in rate. As the substrate concentration increases, more and more active sites are filled so more substrate is used and more products are formed in a given time. As the concentration is increased further the active sites become saturated. Thus any extra substrate has to wait until the enzyme-substrate complex has dissociated into products and free enzyme. At high substrate concentration both enzyme concentration and the time for dissociation limit the rate of the reaction.

 

enzmichaelis

NOTE: BOTH [ENZYME] AND [SUBSTRATE] HAVE THE SAME BASIC GRAPH

for further information plz refer to Mr. J.M enzyme youtube video

Once a Upon an Enzyme (part 1)

Enzymes

 

you guys can look at this vid .. it basically sums up what is written here and is fun and kix 2 watch apart from informative

 

Enzymes are biological catalysts that speed up a chemical reaction by providing and alternative pathway with lower activation energy.

Some enzymes are RNA molecules called ribozymes.

Some antibodies have catalytic properties – abzymes.

Structure

They are globular proteins coiled into a precise 3D shape with hydrophilic R groups on the outside ensuring solubility. Most enzymes are far larger than the substrates they act on (about 100 amino acids). Only a small part of enzymes, between 3-12 amino acids comes into direct contact with the substrate. This area is called the active site and it is here that binding of the substrate takes place. The active site is always found on the cleft or crevice in the enzyme. The remaining amino acids making up the bulk of the enzyme maintain the correct globular shape of the molecule which is important if the active site is to function at an optimum rate.

Mode of Action

Enzymes act as catalysts by lowering the activation energy of the reaction. This is energy required to make substances react. Thus at a given temperature in the presence of an enzyme more reacting molecules will have energy to form product therefore more product will form in a particular time as compared to a non-catalyzed reaction.

The enzyme hold substrate in a correct orientation for them to react i.e. the active site must bind with the specific substrate. Less energy is wasted since the substrate molecules on its own will give off a lot of energy in random motion to achieve the correct orientation.

In all chemical reactions the reacting atoms or molecules pass through a transition state – an unstable structure intermediate between the reactants and the products. The amount of energy needed to get the reactants to form this transition state is the activation energy. In rearranging the bond of the reactants to form the products energy is released so the product has less energy that the reactants.

The enzyme holds the reactants properly in a precisely correct orientation to react with each other which makes bond formation and breakage easier. The formation of the enzyme-substrate complex thus lowers the activation energy for the reaction. Once the reaction has occurred the complex breaks up into enzyme and product(s) leaving the enzyme unchanged.

Lock and Key Hypothesis

This suggests that the enzyme’s active site has a complementary shape of to the substrate, into which the substrate fits exactly. Random movements of the enzyme and substrates bring the substrate into the active site forming the enzyme-substrate complex. This enzyme is like a lock into which the substrate, the key fits. The R groups of the amino acids in the active site forms temporary bonds (ionic, hydrogen and hydrophobic). This interaction can break or cause the formation of bonds in the substrate forming one or more products. When the e products form the no longer if into the active site and leave the site free to receive more substrate. Enzymes are therefor specific and will act only on one isomer. Others may act on similar molecules or break similar linkages.

lock and key

Induced Fit Hypothesis

This is when the substrate fits into the active site it causes changes in the enzyme structure such that the amino acid at the active site are molded into a precise formation allowing the enzyme to perform its catalytic function.

induced fit

Enzyme Co-factor

These are non-protein substances required by most enzymes for their efficient activity. There are three types:

  1. Inorganic ions – assist in the formation of the enzyme-substrate complex by molding the enzyme or substrate into a more suitable shape therefore increasing the chances of a reaction occurring and speeding up the rate. E.g. salivary amylase activity is increased in the presence of chloride ions. 
  2. Prosthetic groups – these are organic molecules which are tightly and permanently bound to the enzyme and act as carries of groups of atoms, single atom or electrons which are being transferred from one place to another. E.g. hem in the hemoglobin acts as an oxygen carrier.
  3. Coenzymes – these are organic molecules which are loosely attached to the enzyme and do not remain attached between reactions. They transfer groups or atoms from the active site of one enzyme to another. E.g. coenzyme A, NADP 

Properties of Enzymes

  1.  All are globular proteins
  2. They increase the rate of reaction without being used up in the reaction themselves
  3.  Their presence does not alter the nature or properties of the end product.
  4. A very small amount causes the change to large amount of substrate
  5. Their activity is affected by pH, temperature, substrate concentration, enzyme concentration and inhibitors
  6. Enzymes are substrate specific.

 

Protein Quiz

hey guys now that we have completed proteins…..its quiz time 😀

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hit it your best shot

1. How many different types of amino acid are used to make proteins?

a. 4

b. 20

c. 25

d. 40

e. 100

2. Amino acids are made up of several elements carbon, hydrogen, oxygen, ………

a. Nitrogen

b. Phosphorous, Magnesium and Sulphur

c. Phosphorous, Iron and Magnesium

d. Iron and Magnesium

e. Nitrogen and Sulphur

 

 

3. Which of these is not a globular protein?

a. The skin protein collagen

b. The hormone insulin

c. The enzyme amylase

d.  Concanavilin

e. The oxygen carrier hemoglobin

4. Disulphide bridges help to maintain which aspect of protein structure?

a. Primary structure

b. Secondary structure

c. Tertiary structure

d. Quaternary structure

e. None of the above

5. The primary structure of a protein is held together by:

a. Hydrogen bonds

b. Disulphide bonds

c. Ionic bonds

d. Glycosidic bonds

e. Peptide bonds

6. A small chain of amino acids is called a

a. Side chain

b. Peptide

c. Fatty acid

d. Muscle

e. Oligopeptide

7. Which amino acid is NOT an essential amino acid?

a. Lysine

b. Methionine

c. Aspartic Acid

d. Tryptophan

e. Valine

8. Which is true about anti parallel beta pleated sheets?

1. Strong and more stable bonds

2. Long and weak bonds

3. Polypeptide strand run in opposite direction

4. Polypeptide strand run in the same direction

a. 1 only

b. 2 only

c. 1, 2, 3

d. 1, 3

e. 3, 4

And the Nobel Prize for Biochemistry goes to….. Yes you guessed it…Christian Boehmer Anfinsen, Jr

:S …huh??….WHAT????…….WHO???????

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Christian Boehmer Anfinsen, Jr. (1916-1995), was an American biochemist who shared the 1972 Nobel Prize for work that helped explain the structure and composition of proteins in living cells. 

 Christian Boehmer Anfinsen is the founder of the Anfinsen Experiment (duhhh just by the name itself you would have guessed it).

2-mercaptoethanol (HS-CH2-CHOH) is use to interrupt the disulphide bridges in a protein. The bond linking the two sulfurs in the protein is disrupted and a new bond between two sulfurs is formed with the end of two molecules of 2-mercaptoethanol.

Anfinsen showed that the evidence for protein folding resided in the amino acid sequence of the protein. He experimented with ribonuclease A as his template for folding but didn’t denature the protein until he used urea plus 2ME to break the disulfide bridges.

The protein denatured (unfolded) under those conditions however once the urea and 2ME were removed the protein refolded and regained its biological activity. Therefore refolding could take place in in vitro.

He also ventured to remove only the 2ME and learned that it lead to recovery of 1% biological  activity of the protein. He demonstrated that correct disulphide bonds can from only after the protein folds into its native conformation.

Anfinsen EXP

Anfin

For in dept details of the Anfinsen Experiment see his published paper about it (click on the link)

Also see http://profiles.nlm.nih.gov/KK/B/B/J/T/