The general features of carbohydrates
Carbohydrates are organic molecules composed of one or
more monosaccharides
They include sugar and polysaccharides
Sugars include monosaccharides (single sugars)
disaccharides (double sugars)
Sugars taste sweet
Sugars are small and soluble
Sugars are the most important source of energy for many
cells
Two monosaccharides can be joined to make a disaccharide
If monosaccharides continue to be added, a poly saccharide
is formed
Polysaccharides are large, complex molecules
Usually they do not taste sweet
Polysaccharides are insoluble
Word equations for the formation of dissacharides
glucose + glucose → Maltose + Water
glucose + Galactose → lactose + Water
glucose + Fructose → sucrose + Water
These are all examples of condensation reactions
Condensation reactions join two molecules together with
the release of water
Hydrolysis reactions split up two molecules using water
(hydro=water; lysis=splitting).
Form maltose by joining two alpha-glucose molecules.
Highlight which parts of the molecules form water in this
condensation reaction.
Carbons 1 and 4 are linked via an oxygen atom to form a 1,4 glycosidic link (a
covalent bond)
Water is formed from the two hydroxyl groups (-OH) groups linked to carbon 1 and 4
Title
Polysaccharides
Monosaccharide monomers are linked together by
condensation reactions to form disaccharides and
polysaccharide polymers
Task
Draw a simple diagram of a linear chain of polysaccharides
Draw a simple diagram of a branched chain of polysaccharides
Polymers are formed in …………../polymerisation reactions.
They can continue to create long chains of s………… (a
carbohydrate). These building reactions are part of ……………..
metabolism.
Task
3 polysaccharides we will study are
1. Starch
2. Cellulose
3. Glycogen
2.3.U1 Monosaccharide monomers are linked together by condensation
reactions to form disaccharides and polysaccharide polymers.
Starch is only found in plants
Starch is made from two polysaccharides: amylose and
amylopectin
Amylose is a chain of alpha-glucose monomers joined by 1-4
glycosidic bonds
It is unbranched.
The long chains of alpha glucose monomers forms a helix.
Amylopectin is a chain of alpha-glucose monomers joined by
1,4 glycosidic bonds and some 1, 6 glycosidic bonds
The 1, 6 glycosidic bond causes amylopectin to be
branched.
Explain how the structure of starch relates to function
The function of starch is to store glucose.
Starch is a very large molecule, so it is insoluble
This means starch does not cause water to enter cells, where it
is stored, (it has no osmotic effect).
The helix is a compact shape to allow storage
The branched structure of amylopectin, means that it has
many ends.
This allows starch to be more rapidly made or broken down.
Title
Glycogen – how structure suits function
Structure
• Glycogen has a similar structure to amylopectin
• It is a chain of alpha-glucose monomers joined by 1,4
glycosidic bonds and 1,6 glycosidic bonds
• There are more 1,6 glycosidic bonds than there are in
amylopectin
• Hence, glycogen is more highly branched
Function
• Glycogen is a large and compact store of glucose in
mammalian muscle and liver cells
• It is insoluble and so it will not cause water to move into
cells where it is stored
• More branches allow glycogen to be broken down very
rapidly, to supply glucose for respiration
•
•
•
•
Describe the structure of cellulose
Cellulose is a chain of beta-glucose molecules joined by 1,4
glycosidic bonds
It is unbranched
Due to the position of the hydroxyl group (-OH) on carbon 1 in
beta-glucose, every other glucose monomer must be rotated
by 180 degrees to form 1,4 glycosidic bonds
The long chain of beta glucose monomers is straight rather
than in a helix
Function
• Groups of long, straight, cellulose molecules can line up close
to each other
• This allows many hydrogen bonds to form between polar –OH
groups in neighbouring molecules
• Cellulose molecules associate to form strong myofibrils
• Microfibrils have great mechanical strength and form the cell
wall of plant cells
Compare the structure of starch, glycogen, and cellulose as
viewed using Jmol software.
Key features to view:
Amylose – No branches and helix structure
Amylopectin – Branches and 1,6 glycosidic bonds
Glycogen – Similar to amylopectin but more branches
Cellulose – No branches and straight molecule. Alternate flipping
of glucose monomers in the polymer
Title
Name and describe the main types of lipids
Type of lipid Description
Triglyceride Composed of one glycerol and three fatty acids
Joined by condensation reactions
Examples include fats and oils
Fats are solid and oils are liquid at room
temperature (20oC)
Are hydrophobic
Phospholipid Like triglycerides but one fatty acid is replaced
with a phosphate group
Form the phospholipid bilayer of membranes
Are amphipathic
Steroids
Characteristically contain four co-joined carbon
rings in their structure (three hexagons and one
pentagon)
Include cholesterol and the male and female sex
hormones
Distinguish the structures of:
1. Saturated and unsaturated fatty acid
2. Monounsaturated and polyunsaturated fatty acids.
Saturated fatty acid
All the carbons in the
hydrocarbon chain are linked
by single bonds
Unsaturated fatty acid
At least one double bond in
the hydrocarbon chain
All carbons in the hydrocarbon More hydrogen could be
chain are fully saturated with added (a process called
hydrogen
hydrogentatio
Monounsaturated fatty acids
Polyunsaturated fatty acids
One double bond present in the Two or more double bonds
hydrocarbon chain
present in the hydrocarbon
chain
Title
Lipids are better long-term stores of energy than carbohydrates
Energy storage molecules in humans
- Carbohydrate: glycogen is stored in liver and muscle cells
- Lipids: triglycerides are stored in adipose tissue
Feature
Advantages of lipids over carbohydrates
Energy released
per gram
Lipids release approximately twice the amount of energy
per gram compared to carbohydrates
Storage space
An equivalent amount of energy will take up less storage
space if lipids are used
Energy stored per Although both are insoluble, unlike lipids, carbohydrates
gram of body mass will attract more water molecules
This increases the mass of stored carbohydrate
In terms of body mass, this makes lipids able to store
more than six times as much energy
Lipids enable organism to transport large energy stores
in a small mass
This advantage of lipids is excellently demonstrated by
migrating birds, which fly long distances without eating
2.3.S2 Determination of body mass index by calculation or use of a
nomogram.
1. A man has a mass of 75 kg and a
height of 1.45 metres.
a. Calculate his body mass index.
(1)
BMI
= mass in kilograms ÷ (height in
metres)2
= 75 kg ÷ (1.45 m)2
= 75 kg ÷ 2.10 m2
= 35.7 kg m-2
a. Deduce the body mass status of
35.7 kg m-2 is above 30.0 (see table below)
this man using the table. (1)
therefore the person would be classified obese.
BMI
Status
a. Outline the relationship
between height and BMI for a
fixed body mass. (1)
Below 18.5
Underweight
18.5 – 24.9
Normal
The taller a person the smaller the
BMI;
25.0 – 29.9
Overweight
30.0 and Above
Obese
(negative correlation, but not a
linear relationship)
Title: Provide evidence supporting the statement that saturated fatty acids and trans fatty acids (trans –
fats) increase health risks
Saturated fatty acids
Trans-fats
Source
Naturally found in animal fats
and dairy produce
Artificially made by adding
hydrogen to polyunsaturated
fatty acids
Scientific evidence for health
risk
Positive correlation with
coronary heart disease
(CHD) in many population
studies
Positive correlation with
coronary heart disease
(CHD) in many population
studies
Conflicting evidence:
- The Maasai people of
East Africa have a high
saturated fat intake but a
low incidence of CHD
One study showed that
swapping 2% of the energy
intake from trans fats with
cis-unsaturated fats more
than halves the risk fo CHD
-
All evidence points towards a
casual relationship
Other studies suggest
there is a casual link
between saturated fatty
acids and CHD
Evaluate evidence supporting the statement that saturated fatty acids and trans fats increase health risks
Trans-fats and Saturated fatty acids
Methods to obtain evidence
-
Population studies (epidemiology)
Clinical studies
Animal experiments
Evaluation of evidence
Correlation in population studies do not establish a casual link
Sample size and genetic backgrounds should be considered
Effects of other dietary components should be considered
- There is evidence that some foods protect against CHD
- There is evidence that foods with high glycemic index increase
CHD
Casual link between trans fats and CHD has been largely
established. This has led to trans fats being banned in some
countries.
Casual link between saturated fatty acids and CHD is disputed