Molecules (carbohydrates)- topic 1

Question 1

what is the definition of carbohydrates?

Answer 1

-carbohydrates are a group of organic compounds that contain atoms of carbon, hydrogen and oxygen only

Question 2

what is the general formula for carbohydrates?

Answer 2

-C(x)H(2n)O(y)

Question 3

why can carbohydrates also be known as hydrated carbon?

Answer 3

-each carbohydrate molecule contains carbon together with hydrogen and oxygen in the same ratio as they are in water

Question 4

what are the three types of carbohydrates?

Answer 4

-monosaccharides (one single sugar molecule)
-disaccharides (two monosaccharides joined together)
-polysaccharides (many monosaccharides joined together)

Question 5

what are the 4 different types of carbohydrates and that are their functions ?

Answer 5

-glucose is used as a fuel as it is a soluble sugar
-starch and glycogen are insoluble sugars are used for storage
-cellulose is used as support in plant cell walls
-carbohydrates are used on the surface of cells to help cell to cell recognition

Question 6

what arethe appearence of monosaccharides?

Answer 6

-monosaccharides are white, crystalline solids that dissolve in water to give sweet tasting solutions

Question 7

why are reducing sugars also known as monosaccharides?

Answer 7

-they all readily reduce other chemicals and therefore are regarded as reducing sugars, this means that it takes oxygen from that chemical or donates hydrogen to it in doing so the sugar becomes oxidized

Question 8

what is the simplest carbohydrate molecule?

Answer 8

-glucose which is also known as hexose because it contains six carbon atoms

Question 9

what are the two structures of glucose?

Answer 9

-alpha glucose
-beta glucose

Question 10

what is the difference between alpha and beta glucose? what are the two different types used for?

Answer 10

-both have the same formula they have different properties because of the way the H and OH are attached to carbon 1
-alpha glucose is used to make starch and beta glucose is used to make cellulose

Question 11

what are the similarities and differences between glucose and fructose?

Answer 11

-the sugar found in fruits and is also a monosaccharide with the same chemical formula as glucose
-is carbon atoms are arranged differently compared to glucose and it has a different structural formulas which therefore means it has different physical properties

Question 12

what are the two most common disaccharides?

Answer 12

-maltose which is composed of a bond between glucose 1 and glucose 4
-sucrose which is composed of a bond between glucose 1 and fructose 2

Question 13

what does the disaccharide maltose consist of? how is it formed? what beverage does maltose make?

Answer 13

-bond between glucose 1 and glucose 4
-it is formed by digestion of starch by amylase because this enzyme breaks down starch into two units
-brewing beer starts with malt which is a maltose solution made from germinated barley

Question 14

what does the disaccharide sucrose consist of?

Answer 14

-sucrose is formed by a bond between glucose 1 and fructose 2
-common in plants because it is less reactive then glucose and it is their main transport sugar
-it is just common table sugar

Question 15

what happens when two monosaccharides join together?

Answer 15

• when the two join together a molecule of water is removed which is known as a condensation reaction

Question 16

what is the bond called when two sugar molecules called?

Answer 16

-a glycosidic bond

Question 17

what is the reaction called when bonds are broken by the addition of water?

Answer 17

-hydrolysis reaction

Question 18

when does a condensation reaction occur? what reactions are condensation?

Answer 18

-it occurs when two molecules join together which forces a water molecule out
-all polymerization reactions are condensations

Question 19

what is a glycosidic bond?

Answer 19

-the bond that holds the two molecules together is called a glycosidic bond in a carbohydrate

Question 20

what happens during a hydrolysis reaction? what reactions are hydrlysis reactions?

Answer 20

-a hydrolysis reaction occurs when a disaccharide molecule is split apart and a water molecule is added
-the glycosidic bond is broken during this reaction
-all breakdown reactions are hydrolyses (e.g. digestion of carbohydrates by enzymes)

Question 21

what is a polysaccharide?

Answer 21

-a polysaccharide (polymers) is made of many monosaccharides (monomers) all joined together by glycosidic bonds

Question 22

what are the 3 main polysaccharides?

Answer 22

-starch
-glycogen
-cellulose

Question 23

what is starch? is it soluble and what is the effect of this?

Answer 23

-starch is the plant storage polysaccharide
-it is insoluble and forms starch granules inside many plant cells
-starch because it is insoluble does not change the water potential of cells so it does not cause cells to take up water by osmosis

Question 24

what are the 2 substances that make up starch?

Answer 24

-amylose
-amylopectin

Question 25

what is amylose made up of?

Answer 25

-made up of alpha glucose molecules all joined together to form a long chain
-the chain tends to coil up known as a helix

Question 26

what is amylopectin made up of?

Answer 26

-branched chain molecule which means that not only are the alpha glucose molecules joined to form a chain but also the chains are joined together by bonds which branch between them

Question 27

what is starch broken down into? what enzyme breaks it down?

Answer 27

-both amylose and amylopectin (make up starch) are broken down by the enzyme amylase into maltose

Question 28

what is glycogen made of? why is it similar to amylopectin?

Answer 28

-it is a polysaccharide of alpha glucose and is a similar structure to amylopectin however it does contain even more branches between chains

Question 29

what is glycogen used for ?

Answer 29

-made by animals as their storage polysaccharide and is found mainly in muscle and liver cells
-because it is so highly branched it can be mobilized (broken down to glucose for energy) very quickly

Question 30

what is cellulose?

Answer 30

-cellulose is only found in plants where it is the main component of cell walls
-cellulose only contains beta glucose unlike starch and glycogen contains alpha glucose

Question 31

what is the effect of cellulose being made of only beta glucose?

Answer 31

-in beta glucose the OH group on carbon 1 points up which means that in a chain every other glucose molecule is inverted
-this tiny change makes a huge difference in the structure and the properties of cellulose
-the beta glucose polymer in cellulose forms straight chains compared to alpha glucose in starch that coils up
-hundreds of these straight chains are linked together by hydrogen bonds to form cellulose microfibrils

Question 32

what are the properties of the microfibrils that are formed on cellulose?

Answer 32

-they are very strong and rigid and give strength to plant cells and therefore to young plants and also to materials such as paper and cotton

Question 33

how is a beta glycosidic bond broken?

Answer 33

-these bonds cannot be broken by amylase but instead requires a specific cellulase enzyme

Question 34

what organisms possess the cellulase enzyme?

Answer 34

-the only organisms are bacteria
-herbivorous animals have this bacteria so that they can digest cellulose
-humans cannot digest cellulose and it is referred to as fiber