Trypsin. Hypothesis: - I hypothesize that as the temperature increases the rate of enzyme catalysed reaction increases.

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Ali Attalla

Biology Coursework

Trypsin

PLANNING SECTION :

Aim: - To find the optimum temperature for the enzyme catalyst.

Hypothesis: - I hypothesize that as the temperature increases the rate of enzyme catalysed reaction increases.

Enzymes

Enzymes are complex protein molecules produced by living organisms. They catalyse a vast range of chemical reactions without themselves being chemically changed at the end of the reaction. These biological catalysts are important because they speed up the rate of reaction they catalyse that would otherwise be too slow to support life. For example Catalase catalysis the decomposition of hydrogen peroxide into water and oxygen.

2H2O2 → 2H2O + O2

        Enzymes bind temporarily to one or more of the reactants of the reaction they catalyse. In doing so, they lower the amount of activation energy needed and thus speed up the reaction.

        Cofactors are non-proteins components required by enzymes for their efficient functioning. An enzyme-cofactor complex is called a holoenzyme. An enzyme without its cofactor is called apoenzyme.

The Chemical Structure Of Enzymes

All enzymes are globular proteins. Proteins consist of long chains of amino acids. In a globular protein the amino acid chain is folded and wound into spherical or globular shape. While the enzyme molecule is normally larger than the substrate molecule it acts upon, only a small part of the enzyme molecule actually comes into contact with the substrate. This region is called the active site. Only a few of the amino acids of the enzyme molecule make up the active site. These so-called catalytic amino acids are often some distance apart in the protein chain but are brought into close proximity by the folding of the chain.

        Hydrogen bonds, ionic bonds and disulphide bridges hold the amino acid chain in its distinct three-dimensional shape.

        The primary structure of a protein is the actual sequence of amino acids in the chain. There are twenty naturally occurring amino acids. Since there are thousands of amino acids in one protein chain and the number of possible permutation is vast. Each type of enzyme has its own sequence of amino acids different from any other enzyme.

        The secondary structure of a protein is the way in which the amino acid chain is organized. In the globular protein here, the secondary structure involves twisting the amino acid chain into a spiral and helix.

        The tertiary structure is due to the bending and twisting of the polypeptide helix into a compact structure. All three types of bond, disulphide, ionic and hydrogen contribute to the maintenance of the tertiary structure.

        The quaternary structure arises from the combination of a number of different polypeptide chains, associated non-proteins groups, into a large complex protein molecule.

        Enzymes are very large and complex organic molecules that are synthesized by the cell to perform very specific functions. These biological catalysts are important because they speed up the rate of reaction they catalyze that would otherwise be too slow to support life. Catalase is an enzyme present in the cells of plants, animals and aerobic (oxygen requiring) bacteria. It promotes the conversion of hydrogen peroxide, a powerful and potentially harmful oxidizing agent, to water and oxygen molecule.

2H2O2  2H2O + O2

Catalase also uses hydrogen peroxide to oxidize toxins including phenols, formic acid, formaldehyde and alcohols.

Enzyme act by binding substrates, forming a complex. The complex stresses chemical bonds forming a transition state. This makes the substrate more reactive. Energy is needed to form this state and the enzyme provides it. The enzyme’s site of attachment and the parts that stress the substrate’s bonds is known as the active site.

Properties Of Enzymes

  1. All are globular proteins consisting of coiled polypeptide chains.
  2. They increase the rate of a reaction without themselves being used up.
  3. Some enzymes require another compound called a coenzyme to be bound to them before they can catalyse reactions.
  4. Their presence does not alter the nature of the end products of the reaction.
  5. Their activity varies with changing pH, temperature, and substrate concentration.
  6. The generally catalyse one specific reaction.
  7. They catalyse a reaction in either direction according to prevailing conditions.
  8. They reduce the activation energy (Ea) required for a chemical reaction to take place.
  9. The names of most enzymes end in –ase, this suffixes often being added to the name of the substrate.

The Rate Of Enzyme Controlled Reactions

The rate of an enzyme reaction is measured by the amount of substrate changed, or amount of product formed, during a period of time.

        The rate is determined by measuring the slope of the tangent to the curve in the initial stage of the reaction. The steeper the slope, the greater is the rate. If activity is measured over a period of time, the rate of reaction usually falls, most commonly as a result of a fall in substrate concentration.

Where Is Catalase Found And What Does It Do?

All aerobic organisms use molecular oxygen, 3O2, for respiration or oxidation of nutrients. During reduction of molecular oxygen to water, hydrogen peroxide is generated. It can damage DNA, protein and lipid membranes and may even be a causative factor of cancer. For defence against H2O2 cells contain Catalase. Each type pf organism has its own Catalase, which probably differs at least slightly in other species of organism.

        The rate of which enzymes catalyse reaction varies with their environment. Enzymes work best within an optimum range of physical and chemical conditions.

Catalase is located in cell organelle called the peroxisome. Peroxisomes in animal cells are involved in the oxidation of fatty acids, and the synthesis of cholesterol and bile acids. Hydrogen peroxide is a by-product of fatty acid oxidation. White blood cells produce hydrogen peroxide to kill bacteria. In both cases Catalase prevents the hydrogen peroxide from harming the cell itself. Peroxisomes in plant cells are involved in photorespiration (the use of oxygen and production of carbon dioxide) and symbiotic nitrogen fixation (the breaking apart of the nitrogen molecule N2 to retrieve nitrogen atoms). Hydrogen peroxide is produced as an intermediate during these chemical processes. And must be removed to prevent damage to cellular machinery.

        Prokaryotes organisms like bacteria that lack nuclear membrane also lack membrane bound organelles such as peroxisomes. Antioxidant enzymes like Catalase and superoxide dismutase are located in the periplasmic space, which is the space between the inner and outer membranes of the cell wall. There are numerous enzymes located here that would be toxic if they were found inside the cell. The Catalase found here can act on toxic molecules that are transported to the periplasm or the enzyme can be released outside the bacterial wall where it can act on toxic molecules in the environment. Catalase that is released by the bacteria plays a role in protecting the bacteria from being destroyed by white blood cells during an infection.

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Mechanism Of Enzyme Action

Enzymes are taught to operate on a lock and key mechanism. In the same way that a key fits a lock very precisely, so the substrate fits accurately into the active site of the enzyme molecule. The two molecules form a temporary structure called the enzyme-substrate complex. The products have a different shape from the substrate and so, once formed, they escape from the active site leaving it free to become attached to another substrate molecules. The sequence is summarized in the figure below.

Factors Affecting Enzyme Activity

A number of external factors ...

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