IB Biology3 Chemistry of Life

3.2 Carbohydrates, Lipids and Proteins

Jason de Nys

All syllabus statements ©IBO 2007All images CC or public domain or link to original material.

http://commons.wikimedia.org/wiki/File:Burger_King_Angus_Bacon_%26_Cheese_Steak_Burger.jpg

Carbs

Fats

Proteins & Fats

Rabbit food

3.2.1 Distinguish between organic and inorganic compounds

Organic molecules are based on carbon and are in living things.

Inorganic compounds are everything else plus carbonates (e.g. HCO3⁻ and CaCO3), carbon dioxide (CO2 )and carbon monoxide (CO).

http://commons.wikimedia.org/wiki/File:GraphiteUSGOV.jpg

3.2.2 Identify amino acids, glucose*, ribose* and fatty acids from diagrams showing their structure

ArginineAlanine Leucine

http://commons.wikimedia.org/wiki/File:Alanine.pnghttp://commons.wikimedia.org/wiki/File:Arginine.pnghttp://commons.wikimedia.org/wiki/File:Leucine.png

Here are three of the twenty-one amino acids found in eukaryotes. Identify what parts of their structures are identical.

*glucose and ribose shown in 3.2.3

ArginineAlanine Leucine

Yeah, that bit…

http://commons.wikimedia.org/wiki/File:AminoAcidball.svg

Drawn slightly differently you can see the bit that is always the same and the R Group. The R group is like x in an equation. It is a variable that stands in for a bunch of different side chains

The amine group (NH2)

The acid group (COOH)

A simple H group

Cent

ral (

α) ca

rbon

atom

Look out for this structure

Hmmm… an amine group and an acid group…

What shall we call this classof molecule?

http://commons.wikimedia.org/wiki/File:Filos_tercer_logo.JPG

The amine and acid groups could be at opposite ends, the R could be on top, bottom or side depending on orientation.

Or it could be represented differently:

http://commons.wikimedia.org/wiki/File:Amino_Acids.svg

Don’t freak out, you don’t need to know them all, just the general formula

General structural formula for a fatty* acid

*I prefer “big boned”

Carboxylic group

Chain (or ring) of carbon and hydrogen atoms

H3C (CH2)n C

O

OH

http://www.eufic.org/article/pt/nutricao/gorduras/expid/23/

Glucose has the formula C6H12O6

It forms a hexagonal ring (hexose)

http://commons.wikimedia.org/wiki/File:Glucose_crystal.jpg

5 of the carbons form corners on the ring with the 6th corner

taken by oxygen

3.2.3 List three examples each of monosaccharides, disaccharides and polysaccharides

Glucose is the form of sugar that fuels

respirationGlucose forms the base unit for many

polymers

Monosaccharide #1

Monosaccharide #2

http://commons.wikimedia.org/wiki/File:Galactose-3D-balls.png

Spot the difference

Galactose Glucose

Galactose is also a hexose sugar

It has the same formula C6H12O6

but is less sweet

http://commons.wikimedia.org/wiki/File:Alpha-D-glucose-3D-balls.png

Most commonly found in milk, but also found

in cereals

Monosaccharide #3

Original owner of image unknown

Ribose is a pentose sugar, it has a

pentagonal ring

It forms the backbone of RNA

Deoxyribose differs as shown in the diagram,

and forms the backbone of DNA

Monosaccharide #4You only need 3, this is a bonus!

Fructose is another pentose sugar

It is the sweetest naturally occurring

carbohydrate

http://commons.wikimedia.org/wiki/File:3dfructose.png

Commonly found in fruits and honey

http://commons.wikimedia.org/wiki/File:Red_Apple.jpg

http://www.flickr.com/photos/max_westby/4045923/

Disaccharide #1(Literally “two sugars”)

Lactose (C12H22O11) is most commonly found in milk

http://commons.wikimedia.org/wiki/File:Alpha-lactose-from-xtal-3D-balls.png

The two subunits that make up lactose are

glucose and galactose, our friends from a

couple of slides ago.

http://www.flickr.com/photos/vermininc/2764742483/

Disaccharide #2

The two subunits that make up sucrose are glucose and fructose.

http://commons.wikimedia.org/wiki/File:Sucrose.gif

Sucrose (C12H22O11) is also known as table sugar

http://www.flickr.com/photos/carowallis1/4388310394/

The two monosaccharides that make it up are

glucose and fructose

Disaccharide #3

Gosh! Isn’t it sweet?! The two glucose molecules are holding hands.

Maltose (C12H22O11) is a dimer of glucose

http://commons.wikimedia.org/wiki/File:Maltose_Haworth.svg

http://commons.wikimedia.org/wiki/File:Maltose_syrup.jpg

Polysaccharide #1Glycogen (C6H10O5)n is a

polymer made of repeating glucose subunits

http://en.wikipedia.org/wiki/File:Glycogen_spacefilling_model.jpg

It is not just a simple chain, it branches many times

Polysaccharide #2

http://commons.wikimedia.org/wiki/File:Amylose3.svg

Amylose is a form of starch, and is

made of repeating glucose units

http://www.flickr.com/photos/caroslines/5534432762/

Typically an amylose molecule is made up of 300-3000 glucose units, but it can be many more

Polysaccharide #3

http://en.wikipedia.org/wiki/File:Cellulose_spacefilling_model.jpg

Cellulose (C6H10O5)n is a linear molecule made of repeating glucose

units

http://www.flickr.com/photos/caroslines/5534432762/

Multiple hydrogen bonds form between adjacent strands. Making strong microfibrils.

3.2.4 State one function of glucose, lactose and glycogen in animals, and of fructose, sucrose and cellulose in plants

After expending 10 slides on a “List” question, let’s answer this one in a table!

Carb. Molecule FunctionGlucose Monosaccharide Used in respiration to

produce ATP

Lactose Disaccharide Energy source in milk

Glycogen Polysaccharide Short term energy storage in liver and muscles

Fructose Monosaccharide Energy source in fruits and honey

Sucrose Disaccharide Convenient form for transferring energy around plants

Cellulose Polysaccharide Structural component of the cell wall

http://www.flickr.com/photos/93387088@N04/8527309132/

http://www.flickr.com/photos/pasma/575078217/

3.2.5 Outline the role of condensation and hydrolysis in the relationships between monosaccharides, disaccharides and polysaccharides; between fatty acids and triglycerides; and between amino acids and polypeptides.

Two ways to help you remember what happens in condensation:• Water (H20) is formed, like condensation on a glass• The former separate molecules have “squished up“

together and are “condensed”http://www.flickr.com/photos/good_day/315807334/

Hydrolysis(water- splitting)

H2O is split in the process of breaking apart a polymer, typically one H will bind to one of the resultant molecules and OH will bind to the other.

Original source of glucose maltose image unknown

Condensation reactions joining two glucose molecules to

make maltose + water

The bond between saccharide units is called a glycosidic bond

You might see the term “dehydration reaction” mentioned interchangeably with condensation reaction.

Technically a dehydration reaction is when the water molecule has come from one of the reactants.

Whereas for a condensation reaction, part of each water molecule has come from each reactant.

In the case of the previous slide, OH from one glucose and H from the other.

http://www.flickr.com/photos/zachd1_618/5738829330/

http://commons.wikimedia.org/wiki/File:Amylase_reaction.png

http://commons.wikimedia.org/wiki/File:Lactose_hydrolysis.svg

Hydrolysis reactions break starch down into maltose

molecules.

Amylase in saliva at work

See 6.1

Hydrolysis of lactose into galactose and

glucose

Lactase at workSee 3.6.5

http://commons.wikimedia.org/wiki/File:Peptidformationball.svg

Condensation reactions between amino acids lead to dipeptide molecules

Keep adding amino acids and you end up with a polypeptide.

These reactions are catalysed by ribosomes in cellsSee 3.5 and HL 7.4

http://commons.wikimedia.org/wiki/File:Amino_acid4.png

Hydrolysis reactions break peptides down into their constituent

amino acids. The body can then use

those amino acids to make new

peptides/proteins.

Pepsin is an enzyme in the stomach that hydrolyses proteins

See 6.1

Glycerol Three Fatty Acids

3H2O

Triglyceride

Condensation reaction between glycerol and fatty acids

Lipids are glycerol combined with 1, 2 or 3 fatty acids, therefore triglycerides are lipids

Hydrolysis is the reverse of this process, catalysed by lipase

3.2.6 State 3 functions of lipids

1) Insulation: look how round

this seal is!http://www.flickr.com/photos/ucumari/2585053774/

2) Energy Storage: the fat on this bacon was a piggy’s bank

of energyhttp://www.flickr.com/photos/johnnystiletto/5411371373/

3) Cell membranes: look all those lovely phospholipids!

Take a moment to review 2.4 cell membranes and name all of the bits in this diagram

http://commons.wikimedia.org/wiki/File:Cell_membrane_detailed_diagram_blank.svg

3.2.7 Compare the use of carbohydrates and lipids in energy storage

http://www.flickr.com/photos/markscott/162791929/

Energy Ratio by mass Fat : Carbs : Protein

2 : 1 : 1So it makes the most sense for

animals to store long term energy reserves as fat. The same amount of energy stored as carbohydrates

would mass twice as much.The energy stored in lipids is primarily in the fatty acid side

chains, so triglycerides are used for energy storage rather than diglycerides or monoglycerides

Glycogen is the medium-term energy storage molecule in animals. It is stored in the liver and muscles. The energy stored in glycogen is

more readily available than the energy stored in fat.

Glucose in the bloodstream is for immediate use and will either be used in respiration to yield ATP or converted to glycogen or fat

An analogy:

You arepaid in cash

Wallet

Bank

Spend it!

Deposit in the

Put it in your

(Glycogen)

(Fat)

(Glucose)

(Respiration)

easy to get to, would be too big if you put

in all your money

Can put lots of money here, more of a hassle to get it back out

Unlike most animals, most plants do not

need to move, so they store their energy as

carbohydrates.

http://www.flickr.com/photos/87106931@N00/8359169832/

Especially plants with storage roots, shoots or tubers

Seeds are the exception, they need to disperse to spread the species. So

they use lipids for energy storage.

Thus sunflower oil, canola oil etc

Further information:

Three of the best sites for IB-specific Biology information. The top link takes you to the PPT by Stephen Taylor