3.1.2 carbohydrates

Question 1

describe the process of benedicts test for reducing sugar:

Answer 1

1. add 2cm3 of the food sample to be tested in a test tube. If the sample, is not already in liquid form, grind and add water
2. add an equal amount of reagant
3. heat the mixture in gently boiling water for 5 minutes

if a reducing sugar is present: a red soluable precipitate forms of copper oxide

Question 2

what are all monosaccharides and disaccharides?

Answer 2

reducing sugars

Question 3

what makes glucose alpha or beta?

Answer 3

glucose has two isomers (formed by the same chemical)

alpha and beta
depends on where the OH group is on Carbon 1

OH below the plane of the ring = alpha

OH above the plane of the ring = beta

alpha and beta provide very different biological consequences

Question 4

what is the structure of alpha gluclose?

Answer 4

see diagram on notes

draw on whiteboard

Question 5

how is a monosaccaride classified?

Answer 5

classified between number of carbon atoms in each molecule

Question 6

how do monosaccharides dissolve easily?

Answer 6

dissolve easily (soluable) in water to form sweet solutions

Question 7

what is the formula for a monosaccaride?

Answer 7

(CH2O)n

n = 3 - 7

Question 8

what is glucose structural formula?

Answer 8

see diagram in notes
draw on whiteboard

Question 9

what are the 9 sugars?

Answer 9

glucose = grans
galactose = great
fructose = funny
sucrose = sweet
maltose = monkey
lactose = likes
ribose = runny
ribulose = rice
mannose = mixed

Question 10

what is the format of carbohydrates?

Answer 10

single monomer = monosaccharide

the reaction between 2 monosaccharides is a disaccharide

many monosaccharides can also be combined to form larger molecules called polysaccharides

Question 11

what is a disaccharide?

Answer 11

two monosaccharide molecules

Question 12

what is a monosaccharide?

Answer 12

class of sugars that cannot be hydrolysed to give a simpler suagr

Question 13

what is a macromolecule?

Answer 13

large number of atoms

Question 14

what is a polymer?

Answer 14

multiple units of monomers

Question 15

what is a monomer?

Answer 15

molecules of compounds

Question 16

describe how carbon are building blocks:

Answer 16

readily forms bonds with other carbon atoms

allows a sequence of carbon atoms to build again which forms a backbone that other molecules bind to, THIS LEADS TO HUGE VARIETY

molecules that contain oxygen are known as organic molecules

Question 17

what are carbohydrates made of?

Answer 17

carbohydrates are made up of carbon, oxygen and hydrogen

Question 18

describe the test for non reducing sugars (if not present):

Answer 18

add 2cm3 of food sample to 2cm2 of dilute hydrochloric acid in a boiling water bath for 5 minutes

EXAM MARK: HYDROLYSE BY BOILING WITH HCL

2. slowly add some sodium hydrocarbonate solution. test with litmus paper to check its alkaline

EXAM MARK: NEUTRALISE WITH NAHCO3

3. re test the solution by heating 2cm3 of benedicts reagent for 5 minutes

Question 19

how do you break down a disaccharide?

Answer 19

reverse of a condensation reaction is a hydrolysis reaction

disaccharide forms two monosaccharide

glycosidic bond is broken by the addition of a molecule by water

Question 20

list 3 examples of disaccharides

Answer 20

sucrose = used in many plants for transporting food reserves around

lactose = glucose and galactose/sugar found in milk

maltose = glucose and glucose/ first production in starch digestion

Question 21

how do disaccharides form?

Answer 21

two monosaccharides
(alpha glucose)

joined with a glycosidic bond

Question 22

what is a disaccharide?

Answer 22

two monosaccharides joined together

reaction is a condensation reaction

involves the removal of a water molecule

bond that forms is called a glycosidic bond

Question 23

describe the features present in cellulose and plant walls

Answer 23

cell wall is 20-40%

cellulose and has several different fibres which have different lengths

high tensile strength
can withstand large pressure due to osmosis

Question 24

summary of cellulose:

Answer 24

structural role as it is mechanically strong

formed from long unbranched chain of beta glucose molecules

between 60-70 cellulose molecules become tightly crossed linked to form bundles of microfibrilis

freely permeable to water and dissolved substances

Question 25

summary for glycogen:

Answer 25

found in animal cells
chains of 1,4 alpha glucose with 1,6 linkages

similar structure to amylopeptin but there are many more branches

molecules clump together in liver and muscle cells forming granules which act as an energy reserve

Question 26

characteristics for starch:

Answer 26

insoluable = does not draw in water by osmosis and does not diffuse water out of cells
inert = does not disrupt metabolism of the cell
compact = can be stored in a small space
amylopeptin is branched = increases SA in which enzymes work
forms alpha glucose on hhydrolysis, which can be used for respiration

Question 27

summary for amylopeptin ( branches in glucose molecule)

Answer 27

have branches between some of the alpha glucose form bonds between 1,6 instead of 1,4
molecule branches

Question 28

summary for amylose (helix in glucose molecule)

Answer 28

amylose is alpha glucose linked by 1,4 glycosidic bonds
causes the chain of alpha glucose molecules to coil into spirals
there’s an average of 8 glucose residues per turn

Question 29

what is the test for starch?

Answer 29

use iodine in potassium iodine solution to test for starch

1. place 2cm3 of sample being tested into a test tube
2. add two drops of iodine solution and shake/stir

A BLUE BLACK COMPLEX IS PRODUCED IF STARCH IS PRESENT

Question 30

starch in plants:

Answer 30

found in many parts of the plant as small granules (bulbs and tubers)
mixture of two substances - amylose and amylopeptin
made from alpha glucose molecules, joined by 1,4 glycosidic molecules

Question 31

what are the most important polysaccharides?

Answer 31

1.starch
2.glycogen
3.cellulose
polysaccarides are insoluble in water and do not interfere with normal cell metabolism