IB Biology
3 Chemistry of Life
3.2 Carbohydrates, Lipids and Proteins
All syllabus statements ©IBO 2007
All 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
Lettuce makes it healthy,
right?
Proteins
& Fats
Fats
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
Alanine
Arginine
Leucine
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
http://commons.wikimedia.org/wiki/File:Alanine.png
http://commons.wikimedia.org/wiki/File:Arginine.png
http://commons.wikimedia.org/wiki/File:Leucine.png
Alanine
Yeah, that bit…
Arginine
Leucine
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
http://commons.wikimedia.org/wiki/File:AminoAcidball.svg
The amine
group (NH2)
Look out for this structure
The acid
group (COOH)
Hmmm… an amine group and an acid
group…
What shall we
call this class
of 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:
Don’t freak out, you don’t need to
know them all, just the general formula
http://commons.wikimedia.org/wiki/File:Amino_Acids.svg
General structural formula for a
fatty* acid
H3C
(CH2)n
Chain (or ring) of carbon
and hydrogen atoms
*I prefer “big boned”
O
C
OH
Carboxylic group
http://www.eufic.org/article/pt/nutricao/gorduras/expid/23/
3.2.3 List three examples each of monosaccharides, disaccharides and polysaccharides
Monosaccharide #1
Glucose has the formula C6H12O6
It forms a hexagonal ring (hexose)
Glucose is the form
of sugar that fuels
respiration
Glucose forms the
base unit for many
polymers
5 of the carbons form
corners on the ring
with the 6th corner
taken by oxygen
http://commons.wikimedia.org/wiki/File:Glucose_crystal.jpg
Monosaccharide #2
Galactose is also a
hexose sugar
It has the same
formula C6H12O6
but is less sweet
Spot the difference
Galactose
Glucose
Most commonly
found in milk,
but also found
in cereals
http://commons.wikimedia.org/wiki/File:Galactose-3D-balls.png
http://commons.wikimedia.org/wiki/File:Alpha-D-glucose-3D-balls.png
Monosaccharide #3
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
Original owner of image unknown
Monosaccharide #4
You only need 3, this is a bonus!
Fructose is another
pentose sugar
Commonly found in
fruits and honey
It is the sweetest
naturally occurring
carbohydrate
http://www.flickr.com/photos/max_westby/4045923/
http://commons.wikimedia.org/wiki/File:Red_Apple.jpg
http://commons.wikimedia.org/wiki/File:3dfructose.png
Disaccharide #1
(Literally “two sugars”)
Lactose (C12H22O11) is most
commonly found in milk
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/
http://commons.wikimedia.org/wiki/File:Alpha-lactose-from-xtal-3D-balls.png
Disaccharide #2
Sucrose (C12H22O11) is also
known as table sugar
Themonosaccharides
two subunits that
The two
make
upitsucrose
that
make
up are are
glucose
fructose.
glucose
andand
fructose
http://commons.wikimedia.org/wiki/File:Sucrose.gif
http://www.flickr.com/photos/carowallis1/4388310394/
Disaccharide #3
Maltose (C12H22O11) is a dimer
of glucose
Gosh! Isn’t it sweet?! The two glucose
molecules are holding hands.
http://commons.wikimedia.org/wiki/File:Maltose_syrup.jpg
http://commons.wikimedia.org/wiki/File:Maltose_Haworth.svg
Polysaccharide #1
Glycogen (C6H10O5)n is a
polymer made of repeating
glucose subunits
It is not just a simple chain, it
branches many times
http://en.wikipedia.org/wiki/File:Glycogen_spacefilling_model.jpg
Polysaccharide #2
Amylose is a form
of starch, and is
made of repeating
glucose units
Typically an amylose molecule
is made up of 300-3000 glucose
units, but it can be many more
http://www.flickr.com/photos/caroslines/5534432762/
http://commons.wikimedia.org/wiki/File:Amylose3.svg
Polysaccharide #3
Cellulose (C6H10O5)n is a
linear molecule made
of repeating glucose
units
Multiple hydrogen bonds form
between adjacent strands.
Making strong microfibrils.
http://www.flickr.com/photos/caroslines/5534432762/
http://en.wikipedia.org/wiki/File:Cellulose_spacefilling_model.jpg
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
Function
Glucose
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/pasma/575078217/
http://www.flickr.com/photos/93387088@N04/8527309132/
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 “
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.
 Condensation
reactions joining two
glucose molecules to
make maltose + water
The bond between saccharide units is called a glycosidic bond
Original source of glucose maltose image unknown
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/
 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 work
See 3.6.5
http://commons.wikimedia.org/wiki/File:Lactose_hydrolysis.svg
http://commons.wikimedia.org/wiki/File:Amylase_reaction.png
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 cells
See 3.5 and HL 7.4
http://commons.wikimedia.org/wiki/File:Peptidformationball.svg
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
http://commons.wikimedia.org/wiki/File:Amino_acid4.png
Condensation reaction between glycerol and fatty acids
Glycerol
Three Fatty Acids
Hydrolysis is the reverse of this
process, catalysed by lipase
Triglyceride
3H2O
Lipids are glycerol combined with 1, 2 or 3 fatty
acids, therefore triglycerides are lipids
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 energy
http://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.s
vg
3.2.7 Compare the use of carbohydrates and lipids in energy storage
Energy Ratio by mass
Fat : Carbs : Protein
2:1:1
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
So 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.
http://www.flickr.com/photos/markscott/162791929/
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
Wallet
(Glycogen)
An analogy:
easy to get to,
would be too big if you put
in all your money
You are
paid in cash
(Glucose)
Bank
(Fat)
Spend it!
(Respiration)
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.
Especially plants with storage
roots, shoots or tubers
http://www.flickr.com/photos/87106931@N00/8359169832/
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