Biological molecules

Question 1

What are the three carbohydrate monosaccharides

Answer 1

Glucose
galactose
fructose

Question 2

difference between alpha and beta glucose

Answer 2

alpha glucose has the OH below the ring whereas beta glucose has the OH above

Question 3

How is a disaccharide form and thus, a polysaccharide

Answer 3

Condensation reaction of two monosaccharides forms a glycosidic bond, condensation of disaccharides forms a polysaccharide

Question 4

What are the 3 carbohydrate disaccharides and how are they formed

Answer 4

sucrose, lactose, maltose
Condensation of
glucose + fructose = s
glucose + galactose = l
glucose + glucose = m

Question 5

Properties of starch (and adaptations) and where its found

Answer 5

-polymer of a-glucose (branched form is amylopectin)
- helical structure ( so is compact )
- insoluble (doesn’t affect water potential)
- large (cannot leave cells)

• found in plants

Question 6

Test for starch

Answer 6

-add iodine to sample
-bluey black shows presence
-orange colour shows absence

Question 7

Properties of glycogen and where is found (+adaptations)

Answer 7

• Highly branched so can be readily broken down into glucose for respiration
• found in animal cells

Question 8

Properties of cellulose and where is found (+adaptations)

Answer 8

• Polymer of beta glucose
• every other glucose molecule is inverted
• can form cross links by H bonds with other cellulose chains to form fibrils, providing strength and rigidity in PLANT CELL WALLS
• long straight chains (difficult to break down)

Question 9

Test for reducing sugars

Answer 9

• Add Benedict’s reagent
• heat mixture
• brick red precipitate shows presence of reducing sugars
• will remain blue if not

Question 10

test for non reducing sugars

Answer 10

-Add HCl and boil sample
- add alkali to neutralise
- re perform benedicts test
- brick red precipitate shows presence

Question 11

Examples of reducing sugars

Answer 11

glucose
fructose
galactose
(monosaccharides)

Question 12

5 differences between starch and cellulose

Answer 12

-Starch is helical shaped whereas cellulose is straight chains
-starch is alpha glucose molecules whereas cellulose is beta glucose molecules
- starch is used for energy storage for respiration whereas cellulose is used for strength and rigidity in cell walls
- Cellulose forms fibrils/macrofibrils whereas starch does not
- all glucose molecules in starch are the same orientation whereas in cellulose every other is inverted

Question 13

What are the 3 main functions of lipids

Answer 13

Insulation
protection
energy storage

Question 14

How does the structure of lipids relate to their functions

Answer 14

High ratio of C-H bonds to C-C bonds(energy storage)

Insoluble - doesn’t affect the water potential

Low mass - useful for storage

phospholipid bilayer ( prevention of water movement through the layer)

Question 15

how is a triglyceride formed

Answer 15

condensation reaction between a glycerol and 3 fatty acids forms 3 ester bonds and 3 H2O

Question 16

how is a phospholipid different to a triglyceride

Answer 16

phospholipid has a phosphate containing group rather than one fatty acid

Question 17

Difference between saturated and unsaturated fatty acid

Answer 17

Unsaturated has one or more C=C bond whereas a saturated fatty acid has none

Question 18

Describe the test for lipids
(EMULSION TEST)

Answer 18

add ethanol to the sample and shake

then add water

milky white layer shows presence of lipid

Question 19

How much more energy per gram do lipids release than carbs

Answer 19

2x

Question 20

Why is water dipolar

Answer 20

as both bonds in H2O have polarity due to the slight -ve charge on oxygen and slight +ve charge on hydrogen

Question 21

Properties of water (x5)

Answer 21

• important metabolite
  -universal solvent due to its dipolar nature
  -relatively high heat capacity so acts as a buffer in nature
  -relatively high latent heat of vaporisation
  -cohesion between water molecules

Question 22

how is water cohesive and why is it important

Answer 22

The hydrogen bonding between molecules means that they will stick together and this is important in formation of water columns (mass transport in plants)
and provides surface tension of water bodies