Proteins, Enzymes and Digestion Flashcards
How would you test to see if a food contained lipids?
By doing the emulsion test.
Add water and shake. If an emulsion forms, a protein is present.
Why do lipids form an emulsion in water?
Because fats are soluble in ethanol but insoluble in water. So when you shake in water, the globules disputes forming a white emulsion.
What’s the letter that denotes the variable group of an amino acid?
R
What is the bond between amino acids in polypeptides called?
Peptide bonds.
How does temperature affect enzymes?
- The rise in temperature makes enzyme’s molecule vibrate more
- If the temperature goes above a certain level, the vibration breaks the bonds that hold the enzymes in shape.
- The active site changes shape and the enzyme and substrate no longer fit together.
- At this point, the enzyme is denatured, so no longer functions as a catalyst.
What happens if the enzyme goes above or below the optimum pH?
The H+ and OH- ions found in acids and alkalis can damage the ionic and hydrogen bonds that hold the enzyme’s tertiary structure in place. This makes the active site change, so the enzyme is denatured.
How does enzyme concentration affect the rate of reaction?
The more enzyme molecules there are in a solution, the more likely a substrate molecule is to collide with one and form the enzyme substrate complex.
So increasing the concentration of the enzyme increases the rate of reaction.
What happens if the amount of substrate is limited?
There is no further effect. Because there’s enough substrate to enzyme molecules, so adding more enzymes wouldn’t do anything.
What happens if there is a greater amount of substrate concentration?
Higher substrate concentration = faster reaction. Because more substrate concentration means a collision between substrate and enzyme is more likely and so more active sites will be used.
For substrate concentration, what happens after the saturation point is met?
There are so many substrate molecules that the enzymes have as much as they can cope with - all the active sites are full - so adding more makes no difference.
How could you prevent the rate of reaction decreasing over time?
Add more substrate concentration.
What do competitive inhibitors look like?
The molecule have a similar shape to that of substrate molecules.
What do competitive inhibitors do?
They compete with the substrate molecules to bind the active site, but no reaction takes place. Instead, they block the active site so that no substrate molecule can fit in it.
How much the enzyme is inhibited by a competitive inhibitor depends on…
The relative concentration of the enzyme and substrate.
High concentration of inhibitor = nearly all active sites take up. Not much substrate will reach the enzyme.
High concentration of substrate = increased ROR (up to a point) because there is a higher chance of substrate getting to an active site before the inhibitor does.
How could you test to see if a food contains proteins?
Perform the biuret test.
Add biuret solution (sodium hydroxide and copper sulphate). If a protein is present, it would turn purple.
What are the transport proteins?
Channel and carrier protein
What does a channel protein do?
Carries small, charged molecules eg Na+
What does a carrier protein do?
Carries large, polar molecules (ie have -ve and +ve areas). For example, glucose, glycerol, amino acids.
What is the only difference between the 20 amino acids?
Their R group
Enzymes are…
Globular proteins that act as catalysts
What does the indicted fit model propose?
That the active site forms as the enzyme substrate interact. The proximity of the substrate (a change in the environment of the enzyme) leads to a change in the enzyme that forms a functional active site.
(Basically the enzyme is flexible and can mound itself around the substrate).
What does the lock and key model propose?
A substrate will only fit the active site of one particular enzyme. The shape of the substrate (key) exactly fits the active site (lock) of the enzyme.
What is the lock and key model supported by?
The observation that enzymes are very specific in the regions that they catalyse.
Why are enzymes very specific and usually only catalyse 1 reaction?
Because they only have one complementary substrate which will fit into the active site.
What is the active site of an enzyme determined by?
It’s tertiary structure (which is determined by its primary structure)
Why do enzymes all have different shaped active sites?
Because each different enzyme has a different tertiary structure
What happens if the tertiary structure of an enzyme is altered?
The active site will change shape, so the substrate won’t fit into the active site and an enzyme substrate complex won’t be formed.
What can rage tertiary structure of an enzyme be altered by?
Changes in pH or temperature
An increase in temperature increases the _______ ______ of molecules.
Kinetic energy
In an enzyme-catalyst reaction, what would an increase in kinetic energy result in?
The molecules moving around more rapidly and colliding more often. This means that the enzyme and substrate molecules come together more often in a given time.
How can an increase in temperature cause an enzyme to change its active site?
Because the temperature rise causes hydrogen bonds and other bonds in the enzyme to break. At first, this causes the substrate to fit less well into the active site.
What happens if the temperature becomes too high in an enzyme-catalysed reaction?
The enzyme becomes denatured.
What is the pH of a solution?
A measure of its hydrogen ion concentration.
What does the optimum pH of an enzyme mean?
The pH at which it works fastest
What does a change in pH mean in an enzyme-catalysed reaction?
A change in the pH alters the amino acids that make up the active site of an enzyme. As a result, the substrate can no longer become attached to the active site and the enzyme substrate complex cannot be formed.
In an enzyme catalyse reaction, what can a significant change in pH cause?
The bonds maintaining the enzyme’s tertiary structure to break, so the active site changes shape.
Increasing the enzyme concentration __________ the rate of reaction
Increases
Why does increasing the enzyme concentration increase rate of reaction?
Because the more enzyme substances there are in a solution, the more likely a substrate molecule is to collide with one and form an enzyme substrate complex
The higher the substrate concentration, the ______ the enzyme catalyst reaction.
Faster
What happens after the saturation point of adding more substrate?
All the active sites are full and adding more substrate makes no difference.
What is the shape of a competitive inhibitor?
They have a similar shape to that of substrate molecules
What do competitive inhibitors do?
They compete with the substrate molecules to bind to the active site, but no reaction takes place. Instead, they block the active site so that no substrate molecule can fit in it.
For competitive inhibitors, how much the enzyme is inhibited depends on…
The relative concentration of the inhibitor and the substrate. If there is a high concentration of the inhibitor, it’ll take up most of the active sites, so hardly any of the substrate will reach the enzyme.
How do non-competitive inhibitors work?
- they bind to the enzyme, away from the active site.
- this causes the active site to change shape so the substrate can no longer bind to it
Why don’t non-competitive inhibitors compete with substrate molecules to bind to the active site?
Because they are a different shape
What does increasing the concentration of a substrate do with non-competitive inhibitors?
It makes no difference, enzyme activity will still be inhibited.
