IB Biology Core 2.3 Carbohydrates and Lipids

1. 2.3 Carbohydrates and
Lipids

2. Guidance
The structure of starch should include amylose and amylopectin.
Named examples of fatty acids are not required.
Sucrose, lactose, and maltose should be included as examples of disaccharides produced by
combining monosaccharides.
Understandings
• Monosaccharide monomers are linked
together by condensation reactions to
form disaccharide and polysaccharide
polymers
• Fatty acids can be saturated,
monounsaturated, or polyunsaturated.
• Unsaturated fatty acids can be cis or
trans isomers.
• Triglycerides are formed by
condensation reactions from three
fatty acids and one glycerol.
Applications/Skills
• A: Structure and function of cellulose and starch in
plants and glycogen in humans.
• A: Scientific evidence for health risks of trans fats
and saturated fatty acids.
• A: Lipids are more suitable for long-term energy
storage in humans than carbohydrates.
• A: Evaluation of evidence and the methods used to
obtain the evidence for health claims made about
lipids.
• S: Use of molecular visualization software to
compare cellulose, starch, and glycogen.
• S: Determination of body mass index by calculation
or use of a nomogram.

3. Carbohydrates
Monosaccharide: one sugar unit
Examples: glucose (C6H12O6)
deoxyribose
ribose
Fructose
Galactose
https://cdavies.wordpress.com/2009/01/27/simple-sugars-fructose-
glucose-and-sucrose/

4. Carbohydrates
Disaccharide: two sugar unit
Examples:
• Sucrose (glucose+fructose)
• Lactose (glucose+galactose)
• Maltose (glucose+glucose)
http://www.cheesescience.com/wp-content/uploads/2011/09/glulac.jpg

5. Polysaccharides
Polysaccharide Function
Cellulose Provide rigidity and support
in plants
Starch Product of photosynthesis;
stored as granules in
roots/root structures
Glycogen Stored excess glucose in liver
and muscle tissue
http://bio.classes.ucsc.edu/bio20L/glossary/struc/starch.gif
All composed of the same monomer (glucose)
1,4 linkages

6. Glycogen
An insoluble storage molecule in the liver.
When blood glucose is high, the pancreas
releases insulin, telling the liver to capture
blood glucose and combine molecules of
glucose to make the polysaccharide
glycogen, through condensation reactions.
This stores energy for later.
When blood glucose drops, the hormone
glucagon causes the glycogen to be broken
down (hydrolysis reactions) to glucose and
then released back into the blood.
Liver from: http://en.wikipedia.org/wiki/File:Leber_Schaf.jpg

7. Fatty Acids
There are two kinds of fatty acids you
may see these on food labels:
1. Saturated fatty acids: no
double bonds (bad)
2. Unsaturated fatty acids:
double bonds (good)
http://foodscienceacademy.org/wp-content/uploads/2013/06/fat_f2.jpg

8. Unsaturated Fatty Acids
• Monounsaturated
• Only one double bond present
• Animal fats
• Usually solid at room temp
• Bent shape
• Polyunsaturated
• Two or more double bonds present
• Usually from plants
• Usually liquid at room temp
• Curved shape
Adapted from http://e004777c130eade00234-5ddb36df15af65ab8482e83373c53fe5.r41.cf1.rackcdn.com/images/30.jpg

9. Cis vs trans fatty acids
Trans Fatty Acids Cis Fatty Acids
- Processed foods
- Hydrogenated
- Straightened out
- Ex: hydrogenated oils
- More curved
- Generally considered
healthier
- Ex: omega-3
http://www.nutrientsreview.com/wp-content/uploads/2014/12/Trans-cis-fatty-acid.jpg

10. Triglycerides
Formed by condensation reaction between three fatty acids and a glycerol
http://erichamber.ca/departments/science/dfung/pages/biology/biologic/fatty_acid_glycerol.gif

11. Lipids for Energy Storage
• Lipids can be hydrolyzed into 2 carbon segments for cell
respiration
• Twice the energy per gram compared to glucose
• Not soluble in water, so won’t disrupt osmotic balance in cells
• Carbohydrates are soluble in water, so water would enter the cell, causing it
to swell.

12. BMI
• Formula 1 (metric):
weight in kg/(height in m)(height in m)
• Formula 2 (imperial):
[weight in lb/(height in in)(height in in)] X
703
http://www.vertex42.com/ExcelTemplates/Images/body-mass-index-chart.gif

13. Homework
Vocab
• Triose
• Pentose
• Hexose
• Saturated fatty acid
• Monounsaturated fatty acid
• Polyunsaturated fatty acid
• Omega-3 fatty acid
• Triglyceride
• Glycogen
• BMI
Other
• Challenge yourself 3-6
• Exercises 6-8
• Nature of science (choose one)