1. CARBOHYDRATE S & LIPIDS
Compounds of carbon, hydrogen and oxygen are used to supply and store energy.
Topic 2.3
IB Biology
Miss Werba

2. TOPIC 2 – MOLECULAR BIOLOGY
2.1
MOLECULES TO METABOLISM
2.2
WATER
2.3
CARBOHYDRATES & LIPIDS
2.4
PROTEINS
2.5
ENZYMES
2.6 STRUCTURE OF DNA & RNA
2.7 DNA REPLICATION, TRANSCRIPTION & TRANSLATION
2.8 CELL RESPIRATION
2.9 PHOTOSYNTHESIS
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3. THINGS TO COVER U.1 U.2 U.3 U.4 Statement Guidance
Monosaccharide monomers are linked together by condensation reactions to form disaccharides and polysaccharide polymers.
The structure of starch should include amylose and amylopectin.
Sucrose, lactose and maltose should be included as examples of disaccharides produced by combining monosaccharides.
U.2
Fatty acids can be saturated, monounsaturated or polyunsaturated.
Named examples of fatty acids are not required
U.3
Unsaturated fatty acids can be cis or trans isomers.
U.4
Triglycerides are formed by condensation from three fatty acids and one glycerol.
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4. THINGS TO COVER A.1 A.2 A.3 A.4 S.1 S.2 IM.1 Statement Guidance
Structure and function of cellulose and starch in plants and glycogen in humans.
A.2
Scientific evidence for health risks of trans fats and saturated fatty acids.
A.3
Lipids are more suitable for long-term energy storage in humans than carbohydrates.
A.4
Evaluation of evidence and the methods used to obtain the evidence for health claims made about lipids.
S.1
Use of molecular visualization software to compare cellulose, starch and glycogen.
S.2
Determination of body mass index by calculation or use of a nomogram.
IM.1
Variation in the prevalence of health problems around the world.
NOS 5.2
Evaluating claims
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5. MONOSACCHARIDES
U.1
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6. MONOSACCHARIDES Glucose Galactose Fructose Examples Details
Example use in plants
Example use in animals
Glucose
C6H12O6
hexose sugar
5C form the ring, with the 6th corner taken by oxygen
Source of energy for cellular respiration
Galactose
same as glucose but one set of side chains are reversed
Found in cereals
Found in milk
Fructose
pentose sugar
Component of fruits;
Sweet so it attracts animals for seed dispersal.
Component of honey; Good energy source.
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7. MONOSACCS  DISACCS Condensation reaction Water is removed
U.1
Condensation reaction
Water is removed
Glycosidic bond formed
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8. MONOSACCS  DISACCS
U.1
glucose + glucose  maltose + water glucose + galactose  lactose + water glucose + fructose  sucrose + water
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9. DISACCHARIDES
U.1 d
Maltose O
Lactose
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10. DISACCHARIDES Maltose Lactose Sucrose Examples Details
Example use in plants
Example use in animals
Maltose
C12H22O11
glucose dimer
Intermediate in the digestion of starch.
Sweet;
Lactose
glucose and galactose
Found in some seeds as a energy storage molecule.
Found in milk to provide newborns with energy.
Sucrose
table sugar
glucose and fructose
Transport form for carbon;
Provides energy for plants unable to photosynthesise.
Sweet; Good energy source.
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11. MONOSACCS  POLYSACCS Condensation reaction
U.1
Condensation reaction
Water is removed (no. of water = no. of monomers – 1)
Glycosidic bonds formed
Often very long and may be branched
Examples:
Starch – used as an energy storage molecule in plants
Glycogen – used as an energy storage molecule in animals
Cellulose – structural component of plant cell walls
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12. POLYSACCHARIDES: Cellulose
Function: structural component of plant cell walls
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13. POLYSACCHARIDES: Cellulose
Structure:
Made of β-glucose molecules linked together
Condensation reactions link C1 of one glucose to C4 of the next
The molecule is a straight chain (not curvy)
The molecule is unbranched
Cellulose can adhere to itself through hydrogen bonding  forming cellulose myofibrils with a high tensile strength
It’s this strength that allows the cell wall to resist turgor pressure.
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14. POLYSACCHARIDES: Starch
U.1
A.1
Function: used as an energy storage molecule in plants
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15. POLYSACCHARIDES: Starch
U.1
A.1
Structure:
Made of α-glucose molecules linked together
Condensation reactions link C1 of one glucose to C4 of the next
The molecule is a curvy chain (not straight)
Starch is hydrophilic, but are not soluble due to their large size
There are two forms of starch:
Amylose – contains only C1-C4 bonds and forms linear helices
Amlyopectin – also contains C1-C6 bonds, which causes branching
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16. POLYSACCHARIDES: Glycogen
U.1
A.1
Function: used as an energy storage molecule in animals
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17. POLYSACCHARIDES: Glycogen
U.1
A.1
Structure:
Made of repeating glucose molecules linked together
Condensation reactions link C1 of one glucose to C4 of the next and potentially C1 to C6.
The molecule is a compact
Hydrophilic but insoluble – therefore does not upset the osmotic balance of the cells
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18. POLYSACCHARIDES: Glycogen
U.1
A.1
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19. MOLECULAR VISUALISATION SOFTWARE
Use jmol from the biotopics website to compare the structure of cellulose, starch and glycogen:
Instructions:
Select the glucose molecule and identify the colours used to represent carbon, hydrogen and oxygen.
Compare the glucose, sucrose and fructose molecules.
Look at the amylose model and zoom out. Describe it’s shape.
Zoom in on amylose. Describe the glycosidic bonds here. Are they all the same?
Look at the amylopectin model and zoom in on a branchpoint. Describe the glycosidic bonds here.
Investigate glycogen and cellulose in a similar way.
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20. LIPID STRUCTURE Monomer unit: fatty acid
Polymer: triglyceride (3 fatty acids & glycerol)
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21. LIPID STRUCTURE
U.4
Triglycerides (3 fatty acids & glycerol) are formed by condensation reactions
3 reactions are needed ∴ 3 water molecules are produced
covalent bond
= ester bond
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22. FATTY ACID STRUCTURE Fatty acids can be:
saturated
monounsaturated or
polyunsaturated
Saturation determined by the number of double bonds:
saturated = 0 double bonds
monounsaturated= 1 double bond
polyunsaturated = 2+ double bonds
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23. FATTY ACID STRUCTURE
U.2
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24. FATTY ACID STRUCTURE Unsaturated fatty acids can be: cis or
trans isomers
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25. FATTY ACID STRUCTURE
U.3
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26. FATTY ACID STRUCTURE Cis- isomers Trans- isomers very common in nature
rare in nature – produced artificially to produce solid fats (eg. margarine)
H atoms on same side
H atoms on different sides
double bond causes a bend
double bond
does not cause a bend
loosely packed
closely packed
triglycerides with cis-isomers have low melting points
triglycerides with trans-isomers have highmelting points
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27. HEALTH CLAIMS ABOUT LIPIDS
The relative amounts of different types of fatty acid in a person’s diet can be correlated with health issues.
Western diets tend to be high in saturated fatty acids
Linked to an increased risk of coronary heart disease (CHD)
But correlation ≠ causation – could be linked to another factor
The Maasai people of Kenya do not fit this correlation.
Diet is high in saturated fatty acids (from milk, meat, etc) but CHD is almost unknown in this population
Mediterranean diets also tend to be high in fatty acids – but cis-monounsaturated fatty acids
Linked to an lower incidence of CHD
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28. HEALTH CLAIMS ABOUT LIPIDS
Genetic factors could be involved
All fatty acids are high in energy
Excess of fat in the diet linked to an increased risk of obesity
Positive link between diets high in trans-fats and Coronary Heart Disease (CHD)
Link between low levels of omega-3 saturated fatty acids and affected brain and nerve development
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29. HEALTH CLAIMS ABOUT LIPIDS
Evaluation of evidence and the methods used to obtain the evidence for health claims made about lipids.
Evaluation = make an appraisal by weighing up the strengths and limitations of the evidence
Evidence = from research; some more scientifically valid than others.
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30. HEALTH CLAIMS ABOUT LIPIDS
Evaluation of evidence and the methods used to obtain the evidence for health claims made about lipids.
Strengths?
Has a positive or negative correlation been determined?
Has the standard deviation or statistical significance of the difference between the two means tested?
Has the range of data been considered?
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31. HEALTH CLAIMS ABOUT LIPIDS
Evaluation of evidence and the methods used to obtain the evidence for health claims made about lipids.
Limitations?
What was the definition of “health” being tested?
What was the sample size?
Was the sample representative of the general population?
Was the data gathered from human or animal trials?
Was it a realistic study?
What methods were used to gather the data?
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32. LIPIDS FOR LONG-TERM ENERGY STORAGE
Functions of lipids include:
Structure: phospholipids in cell membranes
Hormonal signalling: steroid hormones are lipids (eg. oestrogen, testosterone)
Insulation: fat is an insulator; lipids also insulate neurons
Protection: fats protect internal organs from damage
Storage of energy: fats can be used as a long-term energy storage source
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33. LIPIDS FOR LONG-TERM ENERGY STORAGE
Carbohydrates and lipids contain a lot of chemical energy and can be used for energy storage
Lipids less readily digested so they are more suitable for long-term storage
These lipids are stored as fats in adipose tissue (cf. Topic 1) under the skin and around organs, including the kidneys.
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34. LIPIDS FOR LONG-TERM ENERGY STORAGE
Lipids release more energy per gram than sugars (or proteins).
Lipids are therefore lighter than sugars of equal yield:
Lipids add 1/6 as much to body mass as sugars
Glycogen is stored with water (b/c it’s soluble), while fats are not
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35. LIPIDS FOR LONG-TERM ENERGY STORAGE
So why use glycogen at all????
Breakdown of sugars is much faster, making them ideal for short-term energy storage
Sugars are soluble in water (cf. blood plasma), making them easy to transport to sites of use
Glucose can be used aerobically (with O2) or anaerobically (without O2) but fats can only be utilised in aerobic conditions
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36. BODY MASS INDEX (BMI) CALCULATION
Body Mass Index (BMI) is a screening tool to identify potential weight issues.
It should be used in conjunction with other measures, such as a skinfold thickness test, diet evaluations, fitness assessments and family history.
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37. BODY MASS INDEX (BMI) CALCULATION
BMI is calculated in the same way for kids and adults.
Units for BMI = kg m-2
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38. You can also use a BMI chart to assess BMI
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39. BODY MASS INDEX (BMI) CALCULATION
An alternative method uses a nomogram.
Draw a line between the weight and weight.
It will cross a third axis, a BMI scale.
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40. BODY MASS INDEX (BMI) CALCULATION
Q1 A woman has a mass of 72kg and a height of 1.69m.
Calculate her BMI.
Deduce the body mass status of this woman using the table.
Outline the relationship between height and BMI for a fixed body mass.
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41. BODY MASS INDEX (BMI) CALCULATION
A1 A woman has a mass of 72kg and a height of 1.69m.
BMI = 72 ÷ (1.69)2 = 25.2 kg m-2
The woman would be classified as overweight.
The taller the person, the smaller their BMI; negative correlation.
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42. BODY MASS INDEX (BMI) CALCULATION
Q2 A man has a height of 150cm and a BMI of 40.
Calculate the minimum amount of body mass he must lost to reach normal body mass status. Show your working.
Suggest 2 ways in which the man could reduce his body mass.
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43. BODY MASS INDEX (BMI) CALCULATION
A2 A man has a height of 150cm and a BMI of 40.
BMI = mass / height = mass / mass = 40 x = 90 kg
BMI = mass / height = mass / mass = 24.9 x = 56 kg
Weight loss needed = 90 – 56 = 34kg
Reduce calorie intake/reduce fat intake/diet; Exercise/increase activity level.
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44. CARBOHYDRATES & LIPIDS
Q3 What is the difference between galactose and lactose?
Lactose is a disaccharide and galactose is a monosaccharide.
Lactose is the product of anaerobic respiration in humans and galactose is the product of anaerobic respiration in yeast.
Lactose is an enzyme and galactose is a hormone.
Galactose is a sugar found in milk but lactose is not found in milk.
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45. CARBOHYDRATES & LIPIDS
Q4 What chemical is shown in the diagram below?
Saturated fatty acid
Cis-monounsaturated fatty acid
Trans-monounsaturated fatty acid
Polyunsaturated fatty acid
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46. CARBOHYDRATES & LIPIDS
Q5 Outline the role of condensation and hydrolysis in the relationship between fatty acids, glycerol and triglycerides.[6]
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