2.3 Carbohydrates and lipids

Question 1

Monosaccharides

Carbohydrates

Answer 1

• Polar
• Soluble in water
• Examples: glucose, ribose, galactose
• Act as monomers to make larger more complex carbohydrate molecules
• Two monosaccharides are linked together by a condensation reaction which forms a glycosidic bond producing a disaccharide (and releasing one water molecule)

Question 2

Disaccharides

+ examples

Answer 2

• Made of two monomers
• Polar
• Soluble in water
• Examples: sucrose (glucose + fructose), maltose (glucose + gluctose), lactose (glucose +galactose)

Question 3

Polysaccharides

+ examples

Answer 3

• Large molecules
• Not all are polar and soluble in water
• Examples: cellulose, glycogen, starch

Question 4

Starch

Carbohydrate - polysaccharide

Answer 4

• In plants, starch is used to store enegry
• Amylose (unbranched - helical chains) and amylopectin (branched) are two forms of starch
• Starch is made by linking together alpha glucose molecules

Question 5

Glycogen

Carbohydrate - polysaccharide

Answer 5

• In animals, glycogen is used to store energy
• Stored in liver and muscles
• Can be easily broken down (unlike lipids) to glucose which can be easily transported around the body for use in cellular respiration.
• Its more accesible than energy stored in fat
• Composed of branched chains of alpha glucose

Question 6

Cellulose

Carbohydrate - polysaccharide

Answer 6

• Linear chains of beta glucose
• Structural polysaccharide, present in cell walls of plants
• Prevents cell from overexpanding and bursting
• Composed of unbranched chains of beta glucose subunits

Question 7

Lipids

Answer 7

• Hydrophobic
• Non polar
• Insoluble in water
• Less dense than water
• Excellent heat insulation (blubber)
• Water insoluble –> provides a waterproof layer in plants and animals

Question 8

Triglycerides

One of the main groups of lipids

Answer 8

• Formed by condensation reaction between one glycerol and three fatty acids
• Two types of triglycerides: oils and fats

Question 9

Fatty acids

Answer 9

• Carboxyl acids attatched to the head of a long hydrocarbon chain

Question 10

Saturated fatty acids

Answer 10

• No double bonds between any on the carbon atoms that make up the hydrocarbon chain
• Linear in structure
• Bad for health

Question 11

Unsaturated fatty acids

monounsaturated and polyunsaturated

Answer 11

• They have double bonds between the carbons that make up between the hydrocarbon chain
• Monounsaturated: one double bond
• Polysaturated: more than one double bond

Question 12

Cis and trans unsaturated fatty acids

Answer 12

Unsaturated fatty acids may occur in two different structural configurations:
- Cis: the hydrogen atoms attatched to the carbon double bond are on the same side. There is a bend in the fatty acid chain. Healthier (good cholesterol). Lower melting point
- Trans: the hydrogen atoms attatched to the carbon double bond are no opposite sides (do not commonly occur in nature, generally linear in structure). Dangerous for carbiovascular system. Higher melting point.

Question 13

Lipids and energy storage

Answer 13

• Higher energy content
• Can act as thermal insulators

Question 14

Lipid vs glycogen

Answer 14

• A gram of lipid gives twice the amount of energy as a gram of glycogen
• Lipids contribute to less body mass than carbohydrates. Using lipids as a long-term storage molecule means that animals have a ligter mass which is essential for their mobility.

Question 15

Lipids and health

Answer 15

• Eating a high content of lipids –> obesity –> type 2 diabetes, Coronary heart disease, certain types of cancer

Question 16

Unhealthy fats

Answer 16

• Saturated fats: naturally occur in many foods, the majority come from animal sources (meat and deaty products)
• Trans fats: formed by the (partial) hydrogenation of vegetable oils by adding hydrogen to unsaturated fats under pressure to increase spreadability of vegetable oils and increase shelf life of certain products (margarine)

Question 17

Trans and saturated fats –> formation of astherosclarotic plaques in arteries

Health risks of trans fats and saturated fatty acids

Answer 17

Leads to heart attack
- This hypothesis is supported by evidence obtained from patients who died from CHD that shows high concentrations of trans fats are present in fatty deposits in diseased arteries

These are POSITIVE CORRELATIONS.
NO CASUAL RELATIONSHIP has been found yet.
- A causal relationship is hard to prove as other factors may play a role (genetics, other foods, consumption of alcohol and lifestyle)
- There are populations of people such as in Kenya where they have a diet high on saturated fats and low rates of deaths caused by CHD.

Question 18

Body mass index (BMI)

Answer 18

The body mass index (BMI) provides a measure of relative mass based on the weight and height of the individual
- It is commonly used as a screening tool to identify potential weight problems in sedentary adults
- Not a diagnostic tool

BMI = mass (kg)/height^2 (m)

Question 19

Lipids vs carbohydrates in terms of energy storage

Answer 19

• Lipids can store more more energy per gram than carbohydrates
• Lipids add less body mass (useful for mobility)
• Carbohydrates, more specifically glycogen, can be broken down into glucose rapidly and then transported easily by the blood to where it is needed. Fats in adipose tissue cannot be mobilized as rapidly.
• Glucose can be used either in anaerobic or aerobic cell respiration whereas fats and fatty acids can only be used in aerobic respiration

Question 20

To use a nomogram

Answer 20

Draw a line from the body mass (weight) of the person, and their height and where it intersects the W/H^2 line the persons BMI can be determined.