2.3 (Carbohydrates and Lipids)

Question 1

What is monosaccharide 1?

Answer 1

Glucose, C6H12O6 (hexaose). Form of sugar that fuels respiration, base unit for many polymers

Question 2

What is monosaccharide 2?

Answer 2

Galactose, also C6H12O6, less sweet than glucose

Question 3

What is monosaccharide 3?

Answer 3

Fructose, found in fruits and honey, pentose sugar

Question 4

What is monosaccharide 4?

Answer 4

Ribose, pentose sugar, backbone of RNA

Question 5

Monosaccharides are monomers of polysaccharides:

Answer 5

Glucose + glucose –condensation– maltose + water

Question 6

What is disaccharide 1?

Answer 6

Maltose, C12H22O11, a dimer of glucose

Question 7

What is disaccharide 2?

Answer 7

Lactose, C12H22O11, most commonly found in milk. Made of glucose and galactose

Question 8

What is disaccharide 3?

Answer 8

Sucrose, C12H22011, table sugar. Made of glucose and fructose

Question 9

What are polysaccharides?

Answer 9

Polymers more than two molecules. Often very long and branched. Glycosidic bonds 1-4 or 1-6

Question 10

What is polysaccharide 1?

Answer 10

1-4, glucose alternately upwards and downwards, cellulose is are straight, unbranched chains. High tensile strength, prevents plant cells from bursting

Question 11

What is polysaccharide 2?

Answer 11

1-4, glucose the same way, starch molecule is curved, size is not fixed, only made by plant cells

Question 12

Describe amylose and amylopectin.

Answer 12

Amylopectin chain is branched, has a more globular shape, consists of 2,000-200,000 units
Amylose, chain of α-glucose molecules is un-branched, forms a helix, made of 300-3,000 glucose units

Question 13

What is polysaccharide 3?

Answer 13

Glycogen, C6H10O5, a polymer made from repeating glucose subunits, consists of 30,000 units. Branches many times, made in animals (liver and muscles in humans) and some fungi

Question 14

Describe cis-isomers.

Answer 14

• Very common in nature
• Hydrogen atoms on the same side of two carbin atoms
• Double bond causes a bend in fatty acid chain
• Loosely packed
• Triglycerides from have low melting point (liquid at room temp)

Question 15

Describe trans-isomers.

Answer 15

• Rare in nature
• Hydrogen atoms on the same side of two carbin atoms
• Double bond does not cause a bend in the fatty acid chain
• Closely packed
• Transisomers formed have high melting points

Question 16

Key questions to consider for strengths.

Answer 16

• Is there a (negative or positive) correlation between intake of the lipid being investigated and rate of the disease or the health benefit?
• If instead mean values are being compared how different are they? Has this difference been assessed statistically?
• How widely spread is the data?

Question 17

Key questions to consider for limitations.

Answer 17

• Was the measure of the health a valid one?
• How large was the sample size?
• Does the sample reflect the population as a whole or just a particular sex, age, state of health, lifestyle or ethnic background?
• Was the data gathered from human or animal trials?
• Were all the important control variables effectively controlled?
• Were the levels and frequency of the lipids (or substance studied) intake realistic?
• How rigorous were the methods used to gather data?

Question 18

Scientific evidence for health risks of trans fats.

Answer 18

• Positive correlation found between saturated fatty acid intake and rates of CHD in many studies.
• Correlation ≠ causation. Another factor, e.g. dietary fibre could be responsible.
• Populations that do not fit the correlation such as the Maasai of Kenya; diet rich in meat, fat, blood and milk, therefore have a high consumption of saturated fats, yet CHD is almost unknown among the Maasai.
• Diets rich in olive oil, containing cis-monounsaturated fatty acids, traditionally eaten in countries around the Mediterranean. Populations of these countries have low rates of CHD, it has been claimed that this is due to the intake of cis-monounsaturated fatty acids.
• Genetic factors could be responsible.
• Other aspects of the diet could explain the CHD rates.
• Positive correlation between amounts of trans-fat consumed and rates of CHD.
• Other risk factors have been tested,n account for the correlation, but none did.
• In patients who had died from CHD, fatty deposits in the diseased arteries have been found to contain high concentrations of trans-fats, giving more evidence of a causal link.

Question 19

Functions lipids.

Answer 19

• Structure: Phospholipids are a main component of cell membranes
• Hormonal signalling: Steroids are involved in hormonal signalling (e.g. estrogen, progesterone, testosterone)
• Insulation: Fats in animals can serve as heat insulators while sphingolipids in the myelin sheath (of neurons) can serve as electrical insulators
• Protection: Triglycerides may form a tissue layer around many key internal organs and provide protection against physical injury
• Storage of energy: Triglycerides can be used as a long-term energy storage source

Question 20

Reasons for using long-term energy storage.

Answer 20

• Amount of energy released in cell respiration per gram of lipids is double that for carbohydrates (and protein)
• Lipids add 1/6 as much to body mass as carbohydrates: fats are stored as pure droplets whereas when 1g glycogen is stored it is associated with 2g of water. This is especially critical for active animals as energy stores have to be carried.

Question 21

Why is glycogen needed at all?

Answer 21

• Glycogen can be broken down to 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 22

Glycogen and glucose as energy storage.

Answer 22

• 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