3.1.2 carbohydrates

Question 1

define monosaccharide

Answer 1

monomers from which larger carbohydrates are made

Question 2

give examples of monosaccharides

Answer 2

glucose, galactose and fructose

Question 3

what bond does a condensation reaction between 2 monosaccharides form?

Answer 3

glycosidic

Question 4

what is formed by the condensation of 2 monosaccharides?

Answer 4

disaccharide

Question 5

give examples of disaccharides

Answer 5

sucrose, maltose and lactose

Question 6

what monosaccharides make up sucrose?

Answer 6

glucose and fructose

Question 7

what monosaccharides make up lactose?

Answer 7

galactose and glucose

Question 8

what monosaccharides make up maltose?

Answer 8

glucose and glucose

Question 9

what are the two isomers of glucose?

Answer 9

alpha glucose and beta glucose

Question 10

define polysaccharide

Answer 10

molecules formed by the condensation of many glucose units

Question 11

give examples of polysaccharides

Answer 11

starch
glycogen
cellulose

Question 12

outline the structure and function of starch

Answer 12

structure : 2 polymers - amylose & amylopectin alpha glucose
function: energy source

Question 13

what type of bonds does starch have?

Answer 13

amylose : alpha 1:4 glycosidic bonds
amylopectin : alpha 1:4 and 1:6 glycosidic bonds

Question 14

how is the structure of starch suited to its function?

Answer 14

amylose : long, unbranched chains of glucose, coiled so compact and able to hold a lot of glucose good for energy storage
amylopectin : branched meaning there are free ends allowing enzymes to hydrolyse to get the glucose, faster hydrolysis= good for respiration
extra : starch is insoluble, molecules are large & compact

Question 15

outline the structure and function of glycogen

Answer 15

structure : alpha glucose
function : storage molecule (in liver & muscles )

Question 16

what type of bonds does glycogen have?

Answer 16

alpha 1:4 and 1:6 glycosidic bonds

Question 17

how is the structure of glycogen related to its function?

Answer 17

compact so more can be stored
insoluble so doesn’t allow water into cells
more branched so ends can be acted on by enzymes

Question 18

outline the structure and function of cellulose

Answer 18

structure : beta glucose
function : provides rigidity to the plant cell wall & also prevents the cell from bursting as water enters it

Question 19

what type of bonds does cellulose have?

Answer 19

hydrogen bonds

Question 20

how is the structure of cellulose related to its function?

Answer 20

cellulose is made up of beta glucose and so form long straight unbranched chains
the cellulose molecules run parallel to each other and are cross linked by hydrogen bonds
the are grouped together to form microfibrils giving more strength

Question 21

how would you test for reducing sugars?

Answer 21

add Benedict’s reagent to the sample solution
heat the test tube in a water bath
if reducing sugar is present a coloured precipitate will form (copper sulfate reduced to copper oxide)
positive result : blue to brick red

Question 22

what are the reducing sugars?

Answer 22

galactose
glucose
fructose
maltose

Question 23

how would you test for non reducing sugars?

Answer 23

add dilute hcl to the sample and heat in a water bath that has been brought to a boil
neutralise the solution with sodium hydrogen carbonate
then carry out the Benedict’s test as normal

Question 24

what is a non reducing sugar?

Answer 24

sucrose

Question 25

how would you test for starch?

Answer 25

add a few few drops of iodine to the sample
if starch is present a blue-black colour is present
(useful to see if starch has been digested by enzymes)

Question 26

how would you test for proteins?

Answer 26

add a few drops of copper sulfate solution to the sample
if a colour change from blue to lilac is observed then protein is present

Question 27

how would you test for lipids?

Answer 27

add ethanol to the sample
shake to mix and add the mixture to a test tube of water
if lipids are present a milky emulsion will form
the more lipid the more obvious the milky emulsion will be