M2 Enzymes Flashcards
1
Q
Describe enzymes
A
- Enzymes are biological catalysts. They are globular proteins that interact with substrate molecules causing them to react at a faster rate without the need for harsh environment conditions
- Enzymes are proteins of high molecular weight
- They are sensitive to temperature changes, being denatured at high temperatures
- They are sensitive to pH
- They are specific to the reactions they catalyse as they have an active site within which chemical reactions take place
- Enzymes affect both the structure and function
2
Q
Describe the role of enzymes in reactions
A
- Anabolic (building up) reactions are all catalysed by enzymes, and are required to build different cell components
- Catabolic (breaking down) reactions are also catalysed by enzymes, as energy is required for the majority of living processes, including growth. Energy is released from large organic molecules, like glucose.
- Metabolism is the sun of all the different reactions and reaction pathways happening in a cell or an organisms, and it can only happen as a result of the control and order imposed by enzymes.
3
Q
Describe the role of enzymes in intracellular reactions
A
- Enzymes have an essential role in the structure and function of cells and whole organisms. The synthesis of polymers from monomers, eg. making polysaccharides from glucose requires enzymes
- Example: Catalase catalyses the breakdown of hydrogen peroxide to oxygen and water quickly, preventing its accumulation. It is found in plant and animal tissues.
4
Q
Describe the role of enzymes in extracellular reactions
A
- Nutrients that supply cells with components necessary for survival and growth are often in the form of polymers such as proteins or polysaccharides. These large molecules cannot enter cells directly so need to be broken into smaller components first.
- Enzymes are released from cells to break down these large nutrient molecules into smaller molecules in digestion. These enzymes work outside of cells.
- Both single-celled and multicellular organisms rely on extracellular enzymes to make use of polymers for nutrition.
- Single-called organisms release enzymes into their immediate environment, the enzymes break down larger molecules, such as proteins, and the smaller molecules produced, are absorbed by cells.
- Nutrients eaten by multi-cellular organisms are taken into the digestive system, large molecules still have to be digested so smaller molecules can be absorbed into the blood stream. From there they are transported around the body to be used as substrates in cellular reactions.
5
Q
Describe the digestion of starch
A
- Starch polymers are partially broken down into maltose (a disaccharide) by the enzyme amylase. Amylase is produced by the salivary glands and the pancreas. It is released in saliva into the mouth, and in pancreatic juice into the small intestine.
- Maltose is then broken down into glucose (a monosaccharide) by the enzyme maltase. Maltase is present in the small intestine.
Glucose is small enough to be absorbed by the cells lining the digestive system and subsequently absorbed into the bloodstream.
6
Q
Describe the digestion of proteins
A
- Trypsin is a protease, a type of enzyme that catalyses the digestion of proteins into smaller peptides, which can then be broken down further into amino acids by other proteases.
- Trypsin is produced in the pancreas and released with the pancreatic juice into the small intestine, where it acts on proteins.
- The amino acids that are produced by the action of proteases are absorbed by the cells lining the digestive system and then absorbed into the bloodstream.
7
Q
Describe the mechanism of enzyme action
A
- Molecules in a solution move and collide randomly, for a reaction to happen molecules need to collide in the right orientation.
- When high temperatures and pressures are applied the speed of molecules will increase, therefore the frequency of successful collisions and the rate of reaction increases.
- Many different enzymes are produced by living organisms, and each enzyme catalyses one biochemical reaction only (the specificity of the reaction)
- The energy needed for a reaction to start is the activation energy, sometimes the activation energy is so large it prevents the reaction from happening under normal conditions. Enzymes help molecules collide successfully, therefore reduce the activation energy required.
8
Q
Describe the lock and key hypothesis
A
- The active site is an area within the tertiary structure of the enzyme that is complementary to the shape of a specific substrate molecule. Only a specific substrate will fit the active site.
- When the substrate is bound to the active site, an enzyme-substrate complex is formed. The substrate(s) then react and the product(s) are formed in an enzyme-product complex. The product(s) are then released, leaving the enzyme unchanged and able to take part in subsequent reactions.
- The substrate is held in such a way by the enzyme that the right atom-groups are close enough to react. The R-groups within the active site of the enzyme will also interact with the substrate, which also helps the reaction along.
9
Q
Describe the induced-fit hypothesis
A
- However the induced-fit hypothesis is a modified version of the lock and key hypothesis.
- The initial reaction between the enzyme and the substrate is relatively weak, but these weak interactions rapidly induce changes in the enzymes tertiary structure (inducing that active site to change shape) that strengthen binding, putting strain on the substrate molecule.
- This can weaken a particular bond(s) in the substrate, therefore lowering the activation energy for the reaction.
10
Q
What affect does temperature have on enzyme activity?
A
- Increasing the temperature of a reaction environment increases the kinetic energy of the particles.
- As temperature increases the particles move faster and collide more frequently. In an enzyme-controlled reaction an increase in temperature increases the frequency of successful collisions between substrate and enzyme, increasing the rate of reaction.
- The temperature coefficient (Q 10) of a reaction is a measure of how much the rate of reaction increases with a 10°C rise in temperature. For an enzyme controlled reaction, this is usually 2.
11
Q
Describe denaturation from temperature
A
- As enzymes are proteins their structure is affected by temperature.
- At higher temperatures the bonds holding the protein together vibrate more. As the temperature increases these vibrations increase until the bonds strain and then break.
- The breaking of these bonds results in a change in the precise tertiary structure of the protein. The enzyme has changed shape and denatured.
- When an enzyme is denatured the active site changes shape and is no longer complementary to the substrate. The substrate can no longer fit into the active sites and the enzyme will no longer function as a catalyst.
12
Q
Describe the optimum temperature for enzymes
A
- The optimum temperature is the temperature at which the enzyme has the highest rate of activity.
- Many enzymes in the human body have optimum temperatures around 40°C, however the optimum temperatures of enzymes can vary significantly.
- Once the enzyme has denatured above the optimum temperature, the decrease in rate of reaction is rapid as there only needs to be a slight change in the active site for the substrate to no longer to be complementary. This happens to all of the enzyme molecules at the same point so the decrease in rate of reaction is relatively abrupt.
- The decrease in rate of reaction below optimum temperature is less rapid as the enzyme has not denatured, they are just less rapid.
13
Q
Describe organisms that can survive temperature extremes (extremophiles)
A
- Enzymes controlling the metabolism activities or organisms living in extremely cold environments tend to have more flexible structures, particularly at the active site, making them less stable than enzymes that work at higher temperatures therefore smaller temperature changes will denature them.
- Thermophiles are organisms adapted to living in very hot environments. The enzymes present in these organisms are more stable than other enzymes due to the increase number of bonds (particularly hydrogen bonds and sulfur bridges) in their tertiary structures. The shapes of these enzymes and their active sites are more resistant to change as the temperature rises.
14
Q
What affect does pH have on enzyme activity?
A
- Proteins (therefore enzymes) are affected by changes in pH.
- Hydrogen bonds and ionic bonds between amino acid R-groups hold proteins in their precise 3d shape. These bonds result from interactions between the polar and charged R-groups present on the amino acids forming the primary structure.
- A change in pH refers to a change in hydrogen ion concentration. More hydrogen ions are present in low pH environments and fewer hydrogen ions are present in high pH environments.
- The active site will only be in the right shape at a certain hydrogen ion concentration (the optimum pH). When the pH changes from the optimum, the structure of the enzyme (and therefore the active site) is altered. However, if the pH returns to the optimum then the protein/enzyme will resume its normal shape and catalyse the reaction again - this is called renaturation.
15
Q
How does pH alter the shape of an active site?
A
- When the pH changes more significantly the structure of the enzyme is irreversibly altered and the active site will no longer be complementary to the substrate. The enzyme is said to be denatured and substrates can no longer bind to active sites, reducing the rate of reaction.
- Hydrogen ions interact with polar and charged R-groups. Changing the concentration of hydrogen ions therefore changes the degree of this interaction. The interaction of R-groups with hydrogen ions also affects the interaction of R-groups with each other.
- The more hydrogen ions present (low pH) the less the R-groups are able to interact with each other. This leads to bonds breaking and the shape of the enzyme changing.
- The reverse is also true when fewer hydrogen ions (high pH) are present. This means the shape of an enzyme will change as the pH changes and therefore it will only function within a narrow pH range.
