ATE Biochemistry 1, P3

How is enzyme presence or amount usually measured in the lab?

By measuring enzyme activity rather than protein quantity, via substrate decrease or product increase.

How is enzyme activity measured?

by measuring the decrease of the substrate concentration or the increase of the new product

What are optimal conditions for enzyme activity in animals?

Temperature around 37–38 °C, optimal pH, presence of specific substrates and activators.

Which enzymes are used as models in the lab?

Amylase and sucrase.

How does pH affect enzyme activity?

Enzymes work best at optimal pH; changes can alter protein conformation or charge, reducing activity.

What is substrate specificity?

When an enzyme acts on only one particular substrate (e.g., sucrase acts only on sucrose).

What is reaction specificity?

When an enzyme acts on a specific type of bond, not a specific molecule (e.g., α-amylase hydrolyzes α-1,4-glycosidic bonds)

What are activators and inhibitors of enzymes?

Activators increase reaction speed; inhibitors decrease it. Inhibitors can be competitive or non-competitive.

Give an example of competitive inhibition.

Malonic acid inhibits succinate dehydrogenase.

Give an example of non-competitive inhibition.

DIPF inhibits serine-protease digestive enzymes.

Which enzyme hydrolyzes starch and glycogen?

α-Amylase.

α-Amylase is a … type enzyme

hydrolase

Is α-Amylase substrate specific?

no, as it can hydrolyse both starch and glycogen into maltose

Which enzyme hydrolyzes maltose into glucose?

Maltase.

Which enzyme hydrolyzes sucrose?

Sucrase.

Is sucrease substrate specific?

Yes, as it hydrolyses sucrose only

What is a reducing sugar?

A sugar that has a free aldehyde or ketone group and gives a positive Fehling’s test (e.g., glucose, maltose).

What is a non-reducing sugar?

A sugar with no free aldehyde or ketone group; gives a negative Fehling’s test (e.g., sucrose).

What does the Lugol test detect?

Presence of starch (blue color) or intermediate dextrins (blue-brown to red).

What is the Lugol solution?

aqueous solution of iodine made with potassium-iodide

What does Fehling’s test detect?

Reducing sugars; positive result is yellow to brick-red precipitate, negative remains blue

Fehling’s reagent I:

CuSO₄ solution

Fehling’s reagent II:

NaOH solution and salt of tartaric acid with sodium

How can enzyme activity be demonstrated in the lab?

By hydrolyzing starch with amylase and observing color change with Lugol solution.

How does enzyme activity change with temperature?

Increases with moderate rise; decreases sharply if enzyme denatures at high temperatures.

How does enzyme activity change with pH?

Highest at optimal pH; decreases when too acidic or too alkaline.

How are enzyme activators and inhibitors tested in the lab?

By comparing reaction times with activators (e.g., NaCl) or inhibitors (e.g., CuSO₄) to control.

What is a monosaccharide with six carbons and an aldehyde group called?

An aldohexose, e.g., glucose.

What happens to the aldehyde group of glucose when the ring closes?

It converts into a glycosidic OH-group, which is very reactive.

Can the glycosidic OH-group of glucose convert back to an aldehyde?

Yes, if the ring opens again.

Does glucose give a positive Fehling’s test? Why?

Yes, because it is a reducing sugar.

What defines the α- and β-isomers of glucose?

The position of the glycosidic OH-group on the first carbon.

How are D- and L-glucose defined?

By the configuration of the 5th carbon.

What are disaccharides?

Two monosaccharides connected by an O-glycosidic bond.

What is maltose made of?

Two α-D-glucose units connected by α-1,4-glycosidic bond.

Is sucrose reducing or non-reducing? Why?

Non-reducing, because both glycosidic OH-groups are bonded; rings cannot open.

What is starch made of?

Hundreds of α-D-glucose molecules, composed of amylose (α-1,4 bonds) and amylopectin (α-1,4 and α-1,6 branchings).

How does glycogen differ from starch?

Similar structure, but with more frequent α-1,6-branchings.

non-specific inhibition is caused by

high concentration of heavy metal ions