1.2 Carbohydrates

Question 1

Define monosaccharide.

Answer 1

the monomers from which larger carbohydrates are made
single sugar units

Question 2

Name the type of reaction that joins monosaccharides together.

Answer 2

condensation reaction

Question 3

What type of bond does a condensation reaction between two monosaccharides form?

Answer 3

glycosidic bond

Question 4

how are disaccharides formed

Answer 4

condensation of two monosaccharides

Question 5

what are 3 examples of disaccharides

Answer 5

maltose
Sucrose
Lactose

Question 6

What type of molecule is lactose and how is it formed?

Answer 6

a disaccharide
formed by condensation of a glucose molecule and a galactose molecule

Question 7

What type of molecule is maltose and how is it formed?

Answer 7

a disaccharide
formed by condensation of two glucose molecules

Question 8

What type of molecule is sucrose and how is it formed?

Answer 8

a disaccharide
formed by condensation of a glucose molecule and a fructose molecule

Question 9

What molecule is formed by condensation of two glucose molecules?

Answer 9

maltose

Question 10

What molecule is formed by condensation of a glucose molecule and a galactose molecule?

Answer 10

lactose

Question 11

What molecule is formed by condensation of a glucose molecule and a fructose molecule?

Answer 11

sucrose

Question 12

what are 3 common monosaccharide.

Answer 12

glucose
fructose
galactose

Question 13

what are the 2 isomers of glucose

Answer 13

alpha glucose and beta glucose

α-glucose and β-glucose

Question 14

What are the only elements that carbohydrates contain?

Answer 14

carbon
hydrogen
oxygen

Question 15

Draw the structure of alpha glucose.

Answer 15

Question 16

draw the structure of beta glucose

Answer 16

Question 17

How are polysaccharides formed?

Answer 17

the condensation of many monosaccharide/ glucose units

Question 18

3 examples of polysaccharides

Answer 18

glycogen and starch and cellulose

Question 19

What monomer is cellulose made of?

Answer 19

beta glucose

Question 20

What monomer is starch made of

Answer 20

alpha glucose

Question 21

What monomer is glycogen made of

Answer 21

alpha glucose

Question 22

Where is glycogen found?

Answer 22

animals (especially muscle and liver cells) and bacteria (but never in plant cells)

Question 23

Describe how the structure of glycogen is related to its function. 4 marks

Answer 23

1. branched so compact;
2. Polymer of glucose so easily hydrolysed;
3. Branched so more ends for faster hydrolysis;
4. Glucose (polymer) so provides respiratory substrate for energy (release);
5. Insoluble - not affect water potential/osmosis;

Question 24

basic structure starch

Answer 24

2 polyscharides

alpha glucose

amylopectin - long branded chain of alpha glucose

side branches - enzymes break down molecules to get glucosidic bonds easily
Glucose resale quickly

Amylase
long unbranded chain of alpha glucose

coiled structure
compact - good for structure - fit more in small space

Question 25

How is starch's structure suited to storage? (5 ways)

Answer 25

Insoluble - doesnt affect osmosis in the cell Large and insoluble - doesnt diffuse out of cell Compact - lots can be stored in a small space WHen hydrolysed it forms alpha glucose - alpha glucose is easliy transported and used in respiration Branched form has many ends - enzyme act as an ends simultaneously so glucose monomers are released very rapidly

Question 26

starch adaptations

Answer 26

insoluble - doesn't affect wp water doesn't enter by osmosis swells good for storage stores glucose as starch

Question 27

What is the main role of starch?

Answer 27

energy store

Question 28

What type of structure does starch form and why? Why is this good for its use?

Answer 28

a helix structure because of hydrogen bonds in the chain makes it compact which is good for storage

Question 29

Where is starch found?

Answer 29

plant cells (never animal cells)

Question 30

How is glycogen's structure different to starch's structure?

Answer 30

starch is made up of branched molecules (amylopectin) and unbranched molecules (amylose) but glycogen is only made of branched molecules (amylopectin) so glycogen is more highly branched and has shorter chains

Question 31

starch is made of

Answer 31

amylose (unbranched molecules) makes up gycogen / branched form of starch)? amylopectin (branched molecules)

Question 32

cellulose basic structure

Answer 32

long unbranded chain of Beta glucose from strong fibres microfibrils linked via weak hydrogen bonds alternate glucose molecules flipped upside down joined with 1, 4 glycosidic bonds flipped molecules- cellulose cannot exist as a helix parrallel chains of beta glucoses- croslinked with very large numbers of hydrogen bonds form microfibrils which together form fibrils NOTE - hydrogen bonds are very weak but there are very large numbers of them

Question 33

How is the structure of starch and glycogen related to its function?

Answer 33

polymer of glucose - can provide the respiratory substrate (glucose), helical/ spherical - compact and can store more energy in a small space, branched - large surface area and multiple enzymes - can act on them at one time, insoluble - doesn't affect water potential of the cell, large- so cannot diffuse out of the cell

Question 34

Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the figure.

Answer 34

Starch formed from α-glucose but cellulose formed from β-glucose; Position of hydrogen and hydroxyl groups on carbon atom 1 inverted;

Question 35

Compare and contrast the structure of starch and cellulose

Answer 35

both 1- polysaccharides 2- glycose polymers 3- made of glucose monomers 4- contain glycosidic bonds between molecules 5- contain C, H, O 1- s made of alpha glucose, c- beta glucose 2- s- coiled, C - straight molecule 3- s- branched c- not branched 4- s- no fibrils, c- yes 5- s- 1-6 glycosidic bonds c- doesn't 6- S- 2 types of molecules c - one type 7- S- amylose and amylopectin C - one type

Question 36

(c) Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar, lactose, attached. Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein. 4 marks

Answer 36

1. Glucose and galactose; Ignore α or β for glucose 2. Joined by condensation (reaction); 3. Joined by glycosidic bond; 4. Added to polypeptide in Golgi (apparatus);;

Question 37

Describe how the structures of starch and cellulose molecules are related to their functions. 5 marks

Answer 37

Starch (max 3) 1. Helical shape so compact; 2. Large (molecule)/insoluble so osmotically inactive; 3. Branched so glucose is (easily) released for respiration; 4. Large (molecule) so cannot leave cell/cross cell-surface membrane; Cellulose (max 3) 5. Long, straight/unbranched chains of β glucose; 6. Joined by hydrogen bonding; 7. To form (micro/macro)fibrils; 8. Provides rigidity/strength;

Question 38

How is cellulose's structure suited to its function? (4 ways)

Answer 38

Beta glucose unbranched chains - crosslinked by hydrogen bonds (beta-plated sheets) grouped to form microfibrils and then strong fibres this makes it rigid so it can act as a cell wall

Question 39

What type of bond is formed when two alpha glucose molecules react together to form maltose?

Answer 39

1,4 glycosidic bond

Question 40

What type of bonds are in amylopectin (makes up gycogen / branched form of starch)?

Answer 40

1,4 glycosidic bonds and 1,6 glycosidic bonds (due to branching)

Question 41

What type of bonds are in amylose

Answer 41

1, 4 glycosidic bonds

Question 42

What are the two functions that carbohydrates could have?

Answer 42

1) Respiratory substrates - providing energy e.g. Glucose + Oxgyen ------> Carbon dioxide + Water 2) Structural molecues - providing structure e.g. cellulose in plant cell walls

Question 43

Describe the Benedict's test for reducing sugars

Answer 43

1- add an equal vol of Benedict's regent to a sample 2- heat mixture in electric water bath at 100 degrees for 5min 3- positive result - colour change from blue to brick red and orange precipitate

Question 44

Describe the bendicts test for non reducing sugars

Answer 44

1- negative result - Benedict's regent remains blue 2- Hydrolyse non reducing sugars 3- add sucrose into monomers by adding 1cm3 of HCl (- The acid will hydrolyse the disaccharide to monosaccharides 4- heat in water bath for 5mib 5- neutrals mixture using sodium carbonate solution 6- processed benedicts test add 2cm3 of Benedict's reagent and heat it in a water bath for 5 minutes. orange if present

Question 45

Describe the biochemical test for starch.

Answer 45

Add 2cm3 of food sample to a test tube. Add two drops of iodine solution and shake. Positive test is a blue-black colour.

Question 46

Outline how colorimetry could be used to give qualitative results for the presence of sugars and starch.

Answer 46

1- Make standard solutions with known concentrations. Record absorbance or % transmission values. 2- Plot calibration curve: absorbance or % transmission (y-axis), concentration (x-axis). 3- Record absorbance or % transmission values of unknown samples. Use calibration curve to read off concentration.

Question 47

How does cellulose prevent a plant cell from bursting by osmosis?

Answer 47

Cell wall is rigid due to cellulose Cell wall exerts pressure that stops the further influx of water.

Question 48

Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar, lactose, attached. Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.

Answer 48

1. Glucose and galactose; 2. Joined by condensation (reaction); 3. Joined by glycosidic bond; 4. Added to polypeptide in Golgi (apparatus);