Carbohydrates

Question 1

What are carbohydrates

Answer 1

Molecules that only contain the elements carbon, hydrogen and oxygen

Question 2

What are carbohydrates also known as

Answer 2

Saccharides or sugars

Question 3

What’s a single sugar unit known as

Answer 3

Monosaccharide- like glucose, fructose and ribose.

Question 4

What’s a disaccharide

Answer 4

When two monosaccharides link together- like lactose and sucrose

Question 5

What are polysaccharides

Answer 5

When two or more(usually many more) monosaccharides are linked-like glycogen, cellulose and starch.

Question 6

What is glucose

Answer 6

A monosaccharide- six carbons= hexose monosaccharide

Question 7

What’s a molecular structure diagram

Answer 7

Carbons are numbered clockwise beginning with the carbon to the right of the oxygen atom within the ring

Question 8

Two forms of glucose

Answer 8

Alpha(OH below) and beta(OH above)- OH(hydroxyl) group on carbon 1 is in opposite positions.

Question 9

Properties of glucose molecules

Answer 9

Polar and soluble in water-due to hydrogen bonds that between hydroxyl groups and water molecules. This solubility in water is important, because it means glucose is dissolved in the cystol of the cell.

Question 10

What’s a condensation reaction

Answer 10

When two alpha glucose molecules are side by side, two hydroxyl groups interact (react). When this happens bonds are broken and new bonds reformed in different places producing new molecules. Two hydrogen atoms and an oxygen atom are removed from the glucose monomers and join to form a water molecule. A bond forms between carbon 1 and 4.

Question 11

What bond forms between glucose molecules

Answer 11

Covalent bond called a glycosidic bond is formed. Called a condensation reaction because a water molecule is formed as one of the products of reaction. Known as 1,4 glycosidic bond.

Question 12

What’s maltose

Answer 12

Two glucose reacted- example of disaccharide- molecule made up of two monosaccharides

Question 13

What’s fructose

Answer 13

Naturally occurs in fruit, often in combination with glucose forming the disaccharide sucrose.

Question 14

What do galactose and glucose form

Answer 14

The disaccharide lactose-found in milk. - galactose and fructose are also hexose monosaccharides

Question 15

What are pentose monosaccharides

Answer 15

Sugars that contain five carbon atoms. Ribose is the sugar present in RNA nucleotides and deoxyribose is the sugar present in DNA nucleotides

Question 16

What is starch

Answer 16

Chemical energy store in plants- lots of glucose molecules

Question 17

What’s amylose

Answer 17

Formed by alpha glucose molecules joined by 1,4 glycosidic bonds. Angle of this bond means long chain twists to form a helix which is further stabilised by hydrogen bonding within the molecule. This makes the polysaccharide more compact, and much less soluble, than the glucose molecules used to make it.

Question 18

How is amylopectin formed

Answer 18

When glycosidic bonds form in a condensation reaction between carbon 1 and carbon 6 on two glucose molecules. Amylopectin is also made up of 1-4 glycosidic bonds between alpha glucose molecules but there are also 1,6 formed by condensation reactions. This means that amylopectin has a branched structure, with the 1,6 branching points occurring approximately once in every 25 glucose subunits.

Question 19

What is glycogen

Answer 19

The functionally equivalent energy storage molecule to starch in animals and fungi. Glycogen forms more branches than amylopectin, which means it is more compact and less space is needed for it to be stored.

Question 20

Why do animals need glycogen to be compact

Answer 20

Mobile, coiling or branching of these polysaccharides makes them very compact, which is ideal for storage. The branching also means there are many free ends where glucose molecules can be added or removed. This speeds up the processes of storing or releasing glucose molecules required by the cell.

Question 21

Key properties of glycogen and amylopectin

Answer 21

Insoluble, branched and compact.

Question 22

What reaction does starch or glycogen undergo to release glucose

Answer 22

Hydrolysis reactions- requiring the addition of water molecules. The reactions are catalysed by enzymes. These are the reverse of the condensation reactions that form the glycosidic bonds.

Question 23

Why are beta glucose unable to react in same way alpha glucose can

Answer 23

Hydroxyl groups on carbon 1 and 4 are too far away to react. The only way that beta glucose molecules can join together and form a polymer is if alternate beta glucose molecules are turned upside down

Question 24

What is cellulose

Answer 24

Made up of beta glucose- when a polysaccharide is formed from glucose in this way it is unable to form branches. A straight chain molecule is formed called cellulose.

Question 25

Cellulose microfibrils

Answer 25

Cellulose molecules make hydrogen bonds with each other forming microfibrils. These microfibrils join together forming macrofibrils, which combine to produce fibres. These fibres are strong and insoluble and are used to make cell walls. Cellulose is an important part of our diet, it is very hard to break down into its monomers and forms the ‘fibre’ or ‘roughage’ necessary for a healthy digestive system.