Biological molecules - Carbohydrates

Question 1

What are monomers?

Answer 1

Smaller units from which larger molecules are made

Question 2

What are polymers?

Answer 2

Molecules made from a large number of monomers joined together

Question 3

What are some examples of monomers?

Answer 3

Monosaccharides, amino acids and nucleotides

Question 4

What is a condensation reaction?

Answer 4

It joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water

Question 5

What is a hydrolysis reaction?

Answer 5

Breaks a chemical bond between two molecules and involves the use of a water molecule

Question 6

What are monosaccharides?
Their general formula?

Answer 6

The monomers from which larger carbohydrates are made
Typically soluble and sweet tasting
(CH2O)n where n can any number from three to seven.

Question 7

What are some examples of monosaccharides?

Answer 7

Glucose, galactose and fructose

Question 8

What bond does a condensation reaction between two monosaccharides form?

Answer 8

A glycosidic bond

Question 9

What are carbohydrates?

Answer 9

Molecules which consist only of carbon, hydrogen and oxygen
They are long chains of sugar units called saccharides

Question 10

What is a disaccharide?

Answer 10

Two monosaccharides joined through a condensation reaction, forming a glycosidic bond

Question 11

What is maltose?

Answer 11

A disaccharide formed by condensation of two alpha glucose molecules

Question 12

What is sucrose?

Answer 12

A disaccharide formed by condensation of an alpha glucose molecule and a fructose molecule

Question 13

What is lactose?

Answer 13

A disaccharide formed by condensation of an alpha glucose molecule and a galactose molecule

Question 14

Structure of alpha glucose?

Answer 14

Alcohol groups both on the bottom/same side

Question 15

Structure of beta glucose?

Answer 15

Alcohol groups on different sides

Question 16

What is a polysaccharide?

Answer 16

They are formed by the condensation of many glucose units

Question 17

What are some examples of polysaccharides?

Answer 17

Glycogen, starch and cellulose

Question 18

What is the structure and function of glycogen?

Answer 18

Main energy storage molecules in mammals
Formed from many molecules of alpha glucose joined together by 1,4 and 1,6 glycosidic bonds
Has a large number of side branches so lots of energy can be released quickly as enzymes can act simultaneously on the side branches
Large but compact so can store more energy
Insoluble so won’t affect water potential of cells and can’t diffuse out of cells

Question 19

What is the structure and function of starch?

Answer 19

Stores energy in plants
Mixture of two polysaccharides; amylose and amylopectin
Amylose - unbranched chain of glucose joined by 1,4 glycosidic bonds so it is coiled so very compact so can store a lot of energy
Amylopectin - branched and made up of 1,4 and 1,6 glycosidic bonds
Many side branches so many enzymes can act of them simultaneously so lots of energy released
Insoluble so won’t affect water potential
Compact so lots of energy can be stored in small spaces
When hydrolysed the alpha glucose molecules can be transported easily

Question 20

What is the structure and function of cellulose?

Answer 20

Made of long, unbranched chains of beta glucose which are joined by glycosidic bonds
Form microfibrils which are made of long cellulose chains running parallel to one another that are joined by hydrogen bonds forming strong cross linkages
Important in stopping cell wall from bursting under osmotic pressure as it exerts inward pressure which stops the influx of water so the cells stay rigid and turgid, helping maximise the surface area for photosynthesis

Question 21

What is the test for reducing sugars?

Answer 21

Add 2cm^3 of the food sample to be tested (needs to be in liquid form to begin with).
Add 2cm^3 of Benedict’s Reagent.
Heat the mixture gently in a water bath for five minutes. If the solution turns brick red (orange-brown) then a reducing sugar is present and it is a positive result.

Question 22

What is the test for non-reducing sugars?

Answer 22

If Benedict’s test was negative add another 2cm^3 of the same food sample and 2cm^3 of dilute hydrochloric acid is added.
The test tube is then placed in a water bath for 5 minutes.
After this some sodium hydrogencarbonate is added in order to neutralise the test tube as the Benedict’s Reagent will not work in acidic conditions.
The solution can now be retested by adding 2cm3 of Benedict’s Reagent to the solution and placing in a water bath for 5 minutes.
If a non reducing sugar is present in the original sample then a colour change from the blue Benedict’s Reagent to brick red (orange-brown) will be observed.

Question 23

What is the test for starch?

Answer 23

Add iodine/potassium iodide.
If the solution turns blue/black in colour from orange-brown then starch is present.