Chemistry Ch 16 Flashcards
What are enzymes?
Enzymes are proteins that catalyse biochemical reactions by providing an alternative reaction pathway with a lower activation energy.
Enzymes are not changed as a result of the process of catalysis.
How generalised are enzymes?
Enzymes are highly specific; enzymes may only catalyse one specific reaction or a reaction with a particular chemical bond or functional group.
There are hundreds of enzymes in the human body to catalyse different biochemical reactions.
How do enzymes work?
Enzyme molecules have uniquely shaped active sites that interact with specific reactant molecules (substrates), weakening or breaking the bonds in the reactant molecules.
What is enantiomer?
Enantiomer each of a pair of molecules that are mirror images of each other.
In chemistry, an enantiomer, also known as an optical isomer, is one of two stereoisomers that are mirror images of each other that are non-superposable, much as one’s left and right hands are the same except for being reversed along one axis.
Why is only one enantiomer catalysed?
Because of the difference in the three-dimensional shape of the two enantiomers of an optically active substrate, only one enantiomer may be able to interact with an enzyme’s active site.
As a consequence, only a reaction with that enantiomer may be catalysed.
What are the two main models for enzyme action?
The earliest model to account for enzyme action was the lock-and-key model
A newer model for enzyme action is the induced fit model, This model accounts for the flexibility of many enzymes’ active sites.
What is a coenzyme?
Many enzymes require the presence of an additional non-protein molecule called a coenzyme in order to function.
Where do coenzymes come from & what do they do?
Coenzymes are often made from vitamins. Coenzymes can act as carriers of electrons or groups of atoms in biochemical pathways.
How do low temperatures affect enzymes?
Low temperature does not alter the tertiary structure but fewer, less energetic collisions occur per unit time between the enzyme and substrate so the rate of reactions is slower.
What is the enzyme’s optimum pH?
The pH at which the enzyme activity is greatest is the enzyme’s optimum pH.
How does pH affect enzymes?
The charges on some R groups in the polypeptide chain of an enzyme depend on the pH of the solution.
Changes to the charges on the R groups that occur as pH changes can result in a new tertiary structure for an enzyme, as intermolecular bonds are broken and new bonds are formed. The enzyme can become denatured.
How is the effectiveness determined?
The effectiveness of an enzyme can be experimentally determined by measuring the change in concentration of a reactant or product of the reaction per unit time.
What is enzyme activity?
Enzyme activity measures the ability of an enzyme to convert a substrate into products.
What are Enzyme operating conditions?
Enzymes operate over an extremely mild and narrow set of conditions when compared with catalysis by inorganic catalysts.
Enzymes are very sensitive to changes in pH and temperature.
What is denatured for an enzyme?
An enzyme is said to be denatured if its tertiary and quaternary structures are disrupted: for example, by high temperatures or pH changes.
Tertiary structure = Three dimensional shape
Quaternary structure = Peptide chain composition
How are enzymes digested?
During the hydrolysis of a protein, the primary structure is broken down as peptide links are broken. This occurs during digestion of food.
What is the optimum temperature for an enzyme?
The temperature at which the enzyme activity is greatest is the enzyme’s optimum temperature.
How do high temperatures affect enzymes?
High temperature denatures an enzyme because the increased kinetic energy of the polypeptide chain disrupts the bonds that maintain the enzyme’s tertiary and quaternary structure.
When an enzyme is denatured, the shape of its active site is changed and its catalytic activity is lost.
How are carbohydrates digested?
Carbohydrates are hydrolysed during digestion to smaller carbohydrates, often glucose.
Polysaccharides are hydrolysed to disaccharides and then to monosaccharides.
The monosaccharides can be transported in the bloodstream to cells for the production of energy or storage as glycogen
How are plant carbohydrates digested?
Enzymes play an important role in hydrolysis. Amylase and maltase hydrolyse glycosidic links in starch and maltose in the digestive process. Humans cannot digest cellulose.
However, some animals, such as cows and koalas, have bacteria in their digestive tracts that digest cellulose using the enzyme cellulase. The glucose produced from this process is a source of energy for the animal.
What causes lactose intolerance?
Lactose intolerance is often the result of a human not being able to produce the enzyme lactase to hydrolyse lactose in milk
Which parts of starch are easy to digest?
The branches in the amylopectin component of starch make it easier to hydrolyse than the amylose component
What is the glycaemic index?
The glycaemic index (Gl) of a food is a measure of its impact upon blood sugar levels.
- High-GI foods are digested easily and can cause a spike in sugar levels.
- Low-GI foods are slow to digest and they have a smaller effect upon blood sugar levels, providing energy over a longer period of time.
How are triglycerides digested?
Triglycerides are hydrolysed by enzymes during digestion. The products are glycerol and the fatty acids from which the triglyceride was originally made.
Where are triglycerides digested?
Digestion of triglycerides occurs in the small intestine where bile emulsifies the fat. which is then hydrolysed by the enzyme lipase.
What happens to triglycerides once digested?
Once hydrolysed, the glycerol and fatty acids pass into the bloodstream to the liver where triglycerides are re-formed. The triglyceride can be stored in adipose tissue or it can be oxidised in muscle cells to release energy
What happens to triglycerides over time?
Triglycerides can deteriorate with time, especially unsaturated triglycerides. When the flavour or aroma is spoilt the triglyceride is described as rancid. Oxidative rancidity occurs as a consequence of the reaction of oxygen with unsaturated fats or fatty acids.
What do antioxidants do to shelf life?
Antioxidants improve the shelf life of foods, usually by reacting with free radicals and restricting their propagation.
Where do antioxidants come from?
Some foods contain natural antioxidants. Other foods have synthetic antioxidants added to prolong shelf life. Synthetic antioxidants usually contain hydroxyl groups.
