Module 2.4 - Enzymes Flashcards
Define an enzyme?
Enzymes are biological catalysts and they catalyse metabolic reactions by lowering the activation energy.
Where can enzyme action take place?
It can be both intracellular (inside the cell) and extracellular (outside the cell).
Give an example of an intracellular enzyme?
Catalase - Is an enzyme that works inside the cells to catalyse the breakdown of hydrogen peroxide (a toxic by-product of several cellular reaction and if builds up can kill cells) to harmless oxygen and water.
Give 2 examples of extracelullar enzymes?
Amylase and Trypsin.
What is the enzyme amylase’s function and where is it found/secreted from?
Works outside the cell in the human digestive system and is found in the saliva. It is secreted into the mouth by cells in the salivary glands. It catalyses the hydrolysis of starch into maltose (a sugar) in the mouth..
What is the enzyme trypsin’s function and where is it found/secreted from?
Works outside the cell in the human digestive system and catalyses the hydrolysis of peptide bonds, turning big polypeptides into smaller ones (which then get broken down into amino acids by other enzymes). Trypsin is produced by cells in the pancreas and secreted into the small intestine.
Describe how an enzyme is specific?
The specific shape of the active site is determined by the enzyme’s tertiary structure and makes up the active site which is where the substrate molecules bind to. The substrate shape is complementary to the enzyme’s shape and only works with this one or a few.
Why does the formation of the enzyme-substrate complex lower the activation energy in anabolic reactions?
If 2 substrate molecules need to be joined, attaching to the enzyme holds them close together, reducing any repulsion between the molecules so they can bond easily.
Why does the formation of the enzyme-substrate complex lower the activation energy in catabolic reactions?
If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate. This strain means the substrate molecule breaks up more easily.
State the earlier model of enzyme action and describe it?
‘Lock and Key’ model and scientists said that this model showed that substrates fit perfectly into the enzyme like a key fitting into a lock.
What is the model that replaced the ‘Lock and Key’ model and how does it differ?
The ‘induced fit’ model, where the substrate and enzymes shapes are still complementary as the enzyme and substrate form an enzyme-substrate complex, the active site changes shape slightly to fit the substrate more closely, making them so specific.
Describe why the rate of reaction of enzyme activity increases as the temperature does?
More heat means more kinetic energy, so molecules move faster and this makes the enzymes more likely to collide with the substrate molecules. The energy of these collisions also increases, which means each collision is more likely to result in a reaction.
What happens to enzyme activity if temperature gets TOO high?
The rise in temperature makes the enzyme’s molecules vibrate more and if the temperature goes above a certain level, this vibration breaks some of the bonds that hold the enzyme in shape. The active site changes shape and the enzyme and substrate no longer fit together. At this point, the enzyme is denatured - it no longer functions as a catalyst.
How does pepsin differ from other enzymes?
Most enzymes have an optimum pH level of around 7 (neutral) but pepsin works best at acidic pH 2, which is useful because it’s found in the stomach where hydrochloric acid is secreted.
How does too high or low pH’s lead to enzyme’s becoming denatured?+
H+ and OH- ions found in acids and alkalis can mess up the ionic and hydrogen bonds that hold the enzyme’s tertiary structure in place. This makes the active site change shape, so the enzyme is denatured.
How does enzyme concentration affect the rate of reaction for enzyme action?
The more enzyme molecules there are in a solution, the more likely a substrate molecule is to collide with one and form an enzyme-substrate complex. So increasing the concentration of enzymes increases the rate of reaction.
Why does the graph for enzyme concentration to rate of reaction begin to level off?
Because, if the amount of substrate is limited, there comes a point when there’s more than enough enzyme molecules to deal with all the available substrate, so adding more enzymes has no further effect.
Describe the correlation between substrate concentration and rate of reaction of enzymes?
The higher the substrate concentration, the faster the reaction - more substrate molecules means a collision between substrate and enzyme is more likely and so more active sites will be used.
Describe what the ‘saturation’ point is in terms of substrate concentration?
After that, there are so many substrate molecules all the active sites are full, and adding more substrate makes no difference.
