biological molecules

Question 1

disaccharide formation

Answer 1

-a disaccharide is formed when two monosaccharides join together.
-monosaccharides are joined together by condensation reactions.
-a glycosidic bond forms between the two monosaccharides as a molecule of water is released.

Question 2

maltose

Answer 2

disaccharide formed by condensation of two glucose molecules

Question 3

sucrose

Answer 3

disaccharide formedby condensation of a glucose molecule and a fructose molecule

Question 4

lactose

Answer 4

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

Question 5

test for reducing sugars

Answer 5

Add Benedict’s solution (blue) to a sample and heat in a water bath that has been brought to boil.
If test is positive it will form a coloured precipitate. brick red.
can use a colorimeter to measure absorbance of remaining benedicts to see how much reducing sugar present

Question 6

test for non reducing sugars

Answer 6

add dilute hydrochloric acid and carefully heat in waterbath that has been brought to the boil. then you neutralise it by adding sodium hydrogen carbonate. then carry out benedicts test.

Question 7

condensation of a-glucose forms

Answer 7

glycogen and starch

Question 8

amylose structure + features

Answer 8

long, unbranched chain of a-glucose.
the angles of the glycosidic bonds give coiled structure.
compact- good for storage

Question 9

amylopectin

Answer 9

long, branched chain of a-glucose.
its side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily.
this means glucose can be released quickly.

Question 10

features of starch

Answer 10

insoluble in water- doesn’t affect water potential
doesn’t cause water to enter cells through osmosis
this makes it good for storage.

also large meaning it cannot leave the cell- good storage

Question 11

glycogen

Answer 11

acts as an energy store or reserve.
animals store excess glucose as glycogen. (polysaccharide)
long with more side branches than amylopectin. loads of branches means that stored glucose can be released quickly, which is important for energy release in animals.
also very compact - so good for storage.

Question 12

cellulose

Answer 12

made of long unbranched chains of beta-glucose.
when beta glucose molecules bond, they form straight cellulose chains.
the cellulose chains are joined together by hydrogen bonds to form strong fibres. called microfibrils.
these strong fibres mean that cellulose provides structural support for cells.

Question 13

iodine test for starch

Answer 13

-add iodine dissolved in potassium iodide solution to the test sample.
-if starch is present, the sample changes from browny-orange to a dark , blue-black colour.

Question 14

what are triglycerides

Answer 14

Consist of one molecule of glycerol with three fatty acids attached to it.
Fatty acid molecules have long ‘tails’ made of hydrocarbons.
The tails are ‘hydrophobic’- making lipids insoluble in water.

Question 15

saturated fatty acids

Answer 15

no double bonds between their carbon atoms

Question 16

unsaturated fatty acids

Answer 16

contains double bonds between some carbon atoms.
causes chain to kink

Question 17

how to make triglyceride

Answer 17

3 condensation reaction between glycerol and fatty acids forming ester bonds. molecule of water released.

Question 18

what are phospholipids

Answer 18

one glycerol, two fatty acids and phosphate group.
phosphate group is hydrophilic whilst fatty acid tails are hydrophobic. important in cell membrane.

Question 19

properties of triglycerides

Answer 19

-mainly energy storage molecules due long hydrocarbon tails of fatty acids containing lots of chemical energy- so a load of energy released when they’re broken down.
-insoluble in water so don’t affect water potential of cell and water doesn’t enter into cell through osmosis(which would make them swell).
-triglycerides bundle together as insoluble droplets in cells because the fatty acid tails are hydrophobic- the tails face inwards, shielding themselves from water with their glycerol heads.

Question 20

properties of phospholipids

Answer 20

-make up bilayer of cell membranes. cell membranes control what enters and leaves a cell.
-phospholipid heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on either side. the centre of the bilayer is hydrophobic, so water soluble substances can’t easily pass through it=membrane acts as a barrier to these substances.

Question 21

emulsion test for lipids

Answer 21

-Shake the test substance with ethanol for about a minute.then pour solution into water
-Any lipid will show up as a milky emulsion
-The more lipid there is, the more noticeable the milky colour will be.

Question 22

why is it an advantage that glycogen is more branched than starch

Answer 22

more branched= more ends
more glucose at ends so can hydrolyse at faster rate= more respiration