Chemical Reactions in Cells

• To keep your body alive, your cells undergo countless chemical reactions.– Many of these reactions are occurring 24/7.

These chemical reactions drive cellular processes!

Cells in your body produce CO2, then blood carries the CO2 from the cells to your lungs (you exhale it out).

PROBLEM

• CO2 is not soluble (dissolvable) in water, so it cannot be carried through your blood.

A chemical reaction in your body converts CO2

into a soluble compound.

In blood, CO2 is converted to a soluble compound:

CO2 + H2O H2CO3

In the lungs, the reaction is reversed to exhale the CO2:

H2CO3 CO2 + H2O

Chemical Reactions & Enzymes

Chemical Reactions

• A change of one set of chemicals into another– Can be slow or fast– Require collisions between

molecules– Involves changes in chemical bonds

Chemical Reactions

• Reactants: elements or compounds that enter into a chemical reaction– Bonds of reactants are broken in a chemical reaction.

• Products: elements or compounds that are produced in a chemical reaction– Bonds of products are formed in a chemical reaction.

What are the reactants in this reaction?The products?

Chemical reactions involve changes in chemical bonds!

Whenever a reaction occurs that rearranges the atoms of molecules, bonds in the reactants must be broken & new

bonds in the products must be formed.

Chemical Reactions & Energy

• Breaking & forming chemical bonds requires energy release or absorption.

• Reactions that release energy can occur spontaneously (but not all do).– Energy is released as heat.

• Reactions that absorb energy will not occur without an energy source.

The chemical reaction of photosynthesis requires energy from the sun.

Activation Energy

• The energy needed to get a reaction started

• BUT, some chemical reactions are very slow or require lots of energy, so they cannot occur on their own.

Activation Energy Video

Catalysts

• Catalysts are proteins that speed up the rate of a chemical reaction by lowering the activation energy of the reaction.

Enzymes

• An enzyme is a protein that acts as a biological catalyst.– Enzymes speed up reactions that take place in your body.

Enzymes

• Enzymes provide a site (called the active site) where reactants (substrate) can be brought together to react.– This decreases the activation energy.

Enzymes

• The structure formed when the substrate (reactants) bind to the active site is called the enzyme-substrate complex.

Enzymes

• Enzymes can be reused, but they are specific.– The enzyme’s structure

allows only certain substrates to bind to the enzyme.

The enzyme-substrate relationship is like a lock & key!

Only the correctly shaped key will open the lock…

Enzymes

If enough substrate is present, a single enzyme can act on 1,000 molecules per second!

Disruptions in homeostasis can prevent enzymes from functioning.

• Enzymes function best in a small range of conditions.

• In the wrong conditions, an enzyme can denature (lose its structure).– Temperature changes– pH changes– Other chemicals

Why is the shape of the enzyme important?

The sugar found in milk is called LACTOSE.

• Lactose is a disaccharide.

This means that lactose is composed of 2 monosaccharides – glucose & galactose.

Remember!When you digest your food, your body breaks it up into

its smallest subunits.

Do we need the enzyme LACTASE to digest milk?