Enzymes

Lab 7

Enzymes

Enzymes – proteins that are the catalysts used by cells to initiate chemical reactions.

Cells can regulate which reactions occur and how quickly by regulating which enzymes are present.

Enzymes

An enzyme works by binding to a specific molecule and stressing the bonds of that molecule to make the reaction more likely.

Shape of the enzyme is key. An enzyme is specific for a

particular reactant.

Enzymes

Active site – place on enzyme where reactant fits.

Binding site – place on reactant where it binds to enzyme.

Enzymes

An enzyme lowers the activation energy of a particular reaction.

It may encourage the breaking of a particular chemical bond in the reactant.

3 Catalyzed reaction

Course of reaction

Energyis released.

Activationenergy

Uncatalyzed

Catalyzed

Product

Reactant

Enzymes

Or, an enzyme may encourage the formation of a link between 2 reactants holding them near each other.

Regulating Enzymes

Enzymes must have a precise shape to work properly.

Cells can control when an enzyme is active by altering its shape.

Calories for Energy

Carbohydrates are used for energy. Fats are used to construct cell membranes &

other cell structures, to insulate nervous tissue, and to provide energy. Fat-soluble vitamins that are essential for

proper health are also absorbed with fats. Proteins are used as building materials for

cell structures, enzymes, hemoglobin, hormones, and muscle & bone tissue.

Digestion

Chemical digestion breaks down larger food particles of polysaccharides, fats, & proteins into smaller subunits: Monosaccharides Fatty acids Amino acids

Amylase

In the mouth, food is mixed with saliva. It moistens & lubricates the food. Saliva contains amylase, an enzyme

that breaks down starch.

Pepsin Gastric glands have 2 kinds of

secretory cells: Parietal cells secrete HCl. Chief cells secrete pepsinogen.

Pepsinogen is a weak protease (protein-digesting enzyme) that only works at very low pH, which is supplied by the HCl.

Activated pepsinogen molecules become pepsin which is a stronger protease.

Lipase

Liver – secretes bile which consists of bile pigments and bile salts which are delivered to the duodenum during digestion. Bile salts work like a detergent to

disperse fats into tiny droplets in a process called emulsification, resulting in a greater surface area for the enzyme lipase to break fats down into fatty acids.

Digestion Large molecules are broken down into

small molecules as digestion is completed. Acid from the stomach gets neutralized. Digestion is completed.

Carbohydrates sugars Proteins amino acids Fats fatty acids

Small molecules pass through the epithelial layer and are absorbed into the bloodstream.