biology by bradford · grade 9 biology

Biological molecules: function

How monomers join and split, and then the project: a four room pop-up museum, one room per biomolecule.

Lesson objectives

By the end of the lesson you should be able to:

Identify the elements that make up carbohydrates, lipids, proteins and nucleic acids, and name the element that distinguishes each: nitrogen in proteins and nucleic acids, phosphorus in nucleic acids and phospholipids.

Represent the monomer of each biomolecule with a labelled drawing.

Describe how monomers join by condensation and separate by hydrolysis, showing where water is released or used.

Identify two example polymers for each biomolecule and describe the function of each.

Explain the roles each biomolecule plays in living organisms.

Identify dietary sources of each biomolecule.

Starting point

The four biological macromolecules, what they are built from, and what they build.

Macromolecule	Elements	Monomer (sub-unit)	Polymer
Carbohydrates	Carbon, hydrogen, oxygen	Monosaccharide	Polysaccharide
Proteins	Carbon, hydrogen, oxygen, nitrogen, sulfur	Amino acid	Polypeptide
Lipids	Carbon, hydrogen, oxygen (phosphorus in phospholipids)	Glycerol and fatty acids	Not true polymers
Nucleic acids	Carbon, hydrogen, oxygen, nitrogen, phosphorus	Nucleotide	DNA, RNA

Lipids are the odd one out: glycerol and fatty acids are building blocks, but they do not repeat in a chain, so lipids are not polymers.

How can two monomers join or separate?

Two glucose molecules. Press the buttons and watch where the water goes.

Two separate glucose molecules. Look at the OH on carbon 1 of the left glucose and the HO on carbon 4 of the right glucose.

Condensation

Two molecules join to form one larger molecule, releasing a molecule of water.

glucose + glucose → maltose + water
glucose + fructose → sucrose + water
glucose + galactose → lactose + water

Hydrolysis

hydro (water) + lysis (splitting). A bond is broken by adding a molecule of water.

maltose + water → glucose + glucose
sucrose + water → glucose + fructose
lactose + water → glucose + galactose

The same two reactions build and break every biomolecule: monosaccharides into disaccharides, glycerol and three fatty acids into a triglyceride, amino acids into a dipeptide. Condensation releases water, hydrolysis uses it. They are opposites.

your turn

Make a phospholipid

You have one glycerol, two fatty acids and one phosphate group. Sketch the molecule and show every condensation reaction needed to join them.

Before you draw, predict: how many water molecules will be released?

Check your answer

Each fatty acid joins onto glycerol in its own condensation reaction, forming an ester bond. That is two reactions.
The phosphate group joins onto the third carbon of glycerol in a third condensation reaction.
Three reactions, so three water molecules are released.
Compare a fat (a triglyceride): three fatty acids, three reactions, three waters. A phospholipid swaps one fatty acid for a phosphate group.

The project: a four room pop-up

One room for each biomolecule, built into a single display.

Imagine the rooms are part of a museum. An art museum? A science museum? A children's museum? Make it fun and be creative.

Type or use your best handwriting. Use the floor as well as the walls. Every room needs everything on the rubric, and at least two interactive elements: pop outs, pull downs, flaps, fold outs, spinners.

step 1

Make a square

Fold the top corner down to the opposite edge. Cut off the strip underneath.

step 2

Crease it both ways

Fold in half top to bottom, unfold, then side to side. You now have four equal squares.

step 3

Cut to the centre

Cut along one crease, from the bottom edge to the centre point. Stop there.

step 4

Overlap the bottom panels

Pull one bottom square over the other so they sit exactly on top. Glue them together.

step 5

Stand it up

Crease so the room stands on its own: two walls and a floor. That is one room.

step 6

Make four, join them

Repeat for all four biomolecules, then glue the rooms wall to wall, back to back.

The rubric

Tick each criterion as your room meets it. The score adds up as you go, so you can see what is missing before you hand it in.

Criterion	Carbs	Lipids	Proteins	Nucleic acids

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