Carbohydrates and Lipids

Question 1

What is the structure of ribose?

Answer 1

Ribose is a five-carbon molecule (a carbohydrate) with 4 carbons forming the ring with one oxygen atom and another forming a side chain. The molecular formula is C5H10O5. The OH groups for carbon 1,2,3 face up, down,down respectively

Question 2

How are monosaccharides linked together to form disaccharides and polysaccharides?

Answer 2

By condensation reactions: This involves the loss of an OH from one
molecule and an H from another molecule, which together forms
H2O. Thus, it involves a combination of subunits and yields water.

Question 3

What kind of metabolic process is the linking of monosaccharides?

Answer 3

An anabolic process because it involves the formation of macromolecules from small molecules or monomer units. It needs energy to do this.

Question 4

What is formed between two or more monosaccharides when they combine to form disaccharides and polysaccharides?

Answer 4

Two monosaccharide monomers may be joined via a glycosidic linkage to form a disaccharide or vie several glycosidic linkages to form a polysaccharide

Question 5

OH groups from which carbon numbered in the glucose molecule is actually only used for linking to make polysaccharides?

Answer 5

1,4 and 6.

Question 6

What are the types of linkages formed and found in the formation of polysaccharides

Answer 6

They form two kinds of linkages which alters the structure and hence function of different polysaccharides. 1-4 glycosidic bond and 1-6 glycosidic bond

Question 7

How are branched and unbranched glucose polymers formed?

Answer 7

1-4 bond forms an unbranched sequence of glucose molecules whereas 1-6 bond form s branched chain of glucose molecules

Question 8

What are the two types of glucose molecule and how do they differ from each other?

Answer 8

Alpha glucose has the OH group of the first carbon pointing downwards or opposite direction of the carbon number 6. Whereas beta glucose has the OH group pointing upwards which means pointing towards the OH group of carbon 6.

Question 9

Cellulose is maded by linking together what type of glucose molecules and by which bond?

Answer 9

Beta glucose are linked together via 1-4 glycosidic bonds by condensation reactions

Question 10

How is the position of the OH groups of each carbon in the glucose molecule which forms cellulose? What is the issue and how is it resolved?

Answer 10

The OH groups of carbon 1 and 4 face in opposite directions. The issue is that with these OH groups distant from each other, condensation reactions can’t take place. Thus, the beta glucose molecules must align at 180 degrees to the previous one for these OH groups to link and form a polymer.

Question 11

What is the nature of the glucose polymer chain of cellulose?

Answer 11

The glucose subunits in the chain are oriented alternately upwards and downwards. This results in a straight chain rather than curved, and it is unbranched.

Question 12

How does the nature of the glucose polymer chain of cellulose gives it a characteristic nature? What is the proper name of this nature?

Answer 12

As cellulose forms an unbranched chain of beta glucose molecules, it can form bundles, with hydrogen bonds linking the cellulose molecules. These bundles are called microfibrils. They provide very high tensile strength and are the basis of plant cell wall. They prevent the plant cells from bursting, even when high pressure has developed due to entry of water by osmosis

Question 13

Starch is made by linking which type of glucose molecule? And how are the OH groups of the carbons positioned and therefore the consequence?

Answer 13

Starch contains alpha glucose subunits. Therefore the OH groups of carbon 1 and 4 point downwards in the same way, forming a 1-4 glycosidic bonds without undergoing change in positioning. As a result, starch molecule is curved

Question 14

What are the two forms of starch?

Answer 14

Amylose and amylopectin. Amylose forms an unbranched chain of glucose molecules via 1-4 linkages, and forms a helix. Amylopectin forms a branched chain via 1-4 and 1-6 glycosidic linkages, and has a more globular shape.

Question 15

What is the nature of the two types of starch in water?

Answer 15

Hydrophillic although they are too large to be soluble in water

Question 16

Therefore based on the nature of starch in general, how does it serve to be a useful function to the plant cell?

Answer 16

Starch is therefore suitable to store large amounts of glucose in plant cells as per the need, as when if a concentrated glucose would have been the storage molecule in plant cells, too much water would enter the cell by osmosis

Question 17

Where is starch usually stored and how does it help the plant?

Answer 17

Starch is used as the store of glucose and therefore of energy in seeds and storage organs such as potato, supporting their growth until they grow to a fully grown plant capable of photosynthesising to produce more glucose and other carbon compounds for cellular activities and energy.

Question 18

Where is starch made a temporary store and why?

Answer 18

Starch is stored temporarily in leaf cells when glucose is being synthesised by photosynthesis rapidly. Then it can be exported to other parts of the plant

Question 19

Which organisms have glycogen as their glucose storage component and where it is stored in humans? What’s the function of glycogen?

Answer 19

Glycogen is made by animals and fungi. It is stored in the liver cells and some muscles in humans. Glycogen has the same function as starch in plants: it acts as a store of energy in the form of glucose in cells where a large store of dissolved glucose would cause osmotic problems.

Question 20

How is glycogen different from starch?

Answer 20

Glycogen also exists as amylose and amylopectin with alpha glucose as subunits but has more branching points making its shape more compact.

Question 21

It is easy to add or remove glucose molecules in starch and glycogen. How is this done and what new characteristic it gives to both these polysaccharides of glucose?

Answer 21

This can be done at both ends of an unbranched chain or any end of a branched-chain. Thus, glycogen and starch do not have a fixed size as the number of glucose molecules they contain can be increased or decreased.

Question 22

What are lipids?

Answer 22

A diverse group of carbon compounds that share the property of being insoluble in water

Question 23

Examples of triglycerides

Answer 23

Fat in adipose tissue in humans and oil in sunflower seeds

Question 24

What are fats and oils?

Answer 24

Fats are liquid at body temperature 37 celsius and solid at room temperature 20 celsius. Whereas oils are liquid at both body and room temperature

Question 25

How are triglycerides made?

Answer 25

Triglycerides are formed by condensation from three fatty

acids and one glycerol. Each fatty acid is linked to the glycerol and thus three water molecules are produced.

Question 26

What kind of bond is present in the formation of triglycerides?

Answer 26

The linkage formed between each fatty acid and the glycerol is an ester bond.

Question 27

Where is adipose tissue?

Answer 27

Adipose tissue is a specialized group of cells for the storage of lipids in the form of fats and is found immediately beneath the skin as fats or around some organs including the kidneys.

Question 28

What makes the storage of lipids even more beneficial and different from the storage of carbohydrates besides long-term energy storage?

Answer 28

Stored lipids also have secondary roles which cannot be performed well by carbohydrates such as heat insulators (because fats are poor conductors of heat) and shock absorbers (because fats are liquids at body temperature)

Question 29

What is the importance of this massive advantage of lipids as long term energy storage?

Answer 29

As a sufficing amount of energy is stored in the body mass, it makes it importance as organisms need to carry their energy stores wherever they go. It is even more important for animals such as birds and bats that fly

Question 30

What is the massive advantage of lipids as long-term energy storage?

Answer 30

Fats form pure droplets in cells with no water associated whereas each gram of glycogen has about 2 grams of water. So lipids are actually six times more efficient in the amount of energy that can be stored per gram of body mass.

Question 31

What are the advantages of carbohydrates as a short-term or immediate energy storage and release in cells compared to fats?

Answer 31

Glycogen can be broken down into glucose quickly and then transported easily via blood plasma in dissolved forms to target organs. Whereas fats can’t be mobilized as rapidly. Glucose can be used in aerobic and anaerobic respiration whereas fats and fatty acids can only be used in aerobic respiration

Question 32

What is the basic structure of fatty acids?

Answer 32

They are a hydrocarbon chain (a chain of carbons atoms with hydrogen atoms linked to them by single covalent bonds). At one end of the chain is an acid group denoted by COOH which is the carboxyl group.

Question 33

What are the variable features in the structure of a fatty acid?

Answer 33

The length of the hydrocarbon chain. Most living organisms use fatty acids which have between 14 to 20 carbon atoms. Another variable feature is the bonding between carbon atoms; there can be single covalent bonds or double covalent bonds between carbon atoms in one or more positions the chain

Question 34

What are saturated fatty acids?

Answer 34

A fatty acid with single bonds between all of its carbon atoms, therefore, contains as much hydrogen as it possibly could and is called a saturated fatty acid.

Question 35

What are unsaturated fatty acids?

Answer 35

Fatty acids that have one or more double bonds are unsaturated
because they contain less hydrogen than they could

Question 36

What are the two types of unsaturated fatty acids in terms of bonds?

Answer 36

Monounsaturated- If there is one double bond. If there are more than one double bond it is polyunsaturated.

Question 37

Unsaturated fatty acids can be cis or trans isomers. What are cis isomers of fatty acids?

Answer 37

Hydrogen atoms which are on the same side of the two carbon atoms in a double bond are known as cis fatty acids

Question 38

Unsaturated fatty acids can be cis or trans isomers. What are trans isomers of fatty acids?

Answer 38

The alternative of cis fatty acids. Trans fatty acids have hydrogen atoms on opposite sides of the two carbon atoms double bonded.

Question 39

What is a characteristic in the hydrocaarbon chain of cis faaty acids which makes their melting point low?

Answer 39

There is a bend in the hydrocarbon chain where the double bond is situated in a cis fatty acid. This discourages the triglycerides containing cis-unsaturated fatty acids to form close and tightly packed regular arrays which are found in saturated fatty acids. This lowers its melting point, and cis unsaturated fatty acids are oils- they are usually liquid at room temperature.

Question 40

What is the nature of the hydrocarbon chain in trans fatty acids?

Answer 40

Trans fatty acids ddo have a bend in the hydrocarbon chain at the double bond so they have a high melting point and are solids at room temperature

Question 41

How are trans fatty acids produced and why?

Answer 41

Trans fatty acids are produced aritifically by partial hydrogenation of vegetable or fish oils. This is done to produce solid fats for use in margarine and other processed foods.

Question 42

There have been many claims about the effects of different types of fat
on human health. The main concern is coronary heart disease (CHD) . What is CHD?

Answer 42

In this diesease the coronary arteries become partially blocked by fatty deposits, causing blood clot formation and heart attacks

Question 43

In many research programs, what positive correlation has been found between CHD and this other factor?

Answer 43

In many research program, high saturated fat intakes account for higher CHD rates and thus a positive correlation

Question 44

What is the disadvantage of finding correlation? (in relevance to health risks of fats scientific evidence)

Answer 44

A correlation does not provide full certainty or proof for one factor investigated as there are other intervening factors in the diet or lifestyle that could cause higher CHD rates. Thus, correlation doesn’t prove that saturated fats cause the disease.

Question 45

What is another possible factor while finding correlation that could actually cause CHD?

Answer 45

low dietary fibre intake

Question 46

Diets rich in olive oils are traditionally eaten in countries around the Meditarrean. In these countries the CHD rates are quite low, why? But CHD still exists, what could be the reason?

Answer 46

The population in the countries of the Meditarrean experience typically low rates of CHD, claimed because of the presence of cis mono-unsaturated fats. Howevere CHD is still prevalent due to other factors such as genetics or other aspects of the diet such as tomatoes in many dishes explain CHD rates

Question 47

What other type of fat is correlated with increased chances of CHD?

Answer 47

trans-fats