Biological Molecules

Question 1

What is the evidence for evolution?

Answer 1

• Information that supports theory of evolution- all organisms on earth are descended from one or a few common ancestors and that they have changed and diversified over time
• Life is based on carbon
• All have same carbon-based compounds that interact in similar ways (use same nucleic acids as genetic material and same amino acids to build proteins)
• Similarities suggest that animals and plants have a common ancestor

Question 2

Polymers

Answer 2

Large, complex molecules composed of long chains of monomers joined together (carbohydrates, proteins and nucleic acids)

Question 3

Monomers

Answer 3

Small, basic molecular units that can form a polymer (monosaccharides, amino acids and nucleotides)

Question 4

Condensation reaction

Answer 4

Forms a chemical bond between monomers by releasing a molecule of water

Question 5

Hydrolysis reaction

Answer 5

Breaks a chemical bond between monomers by adding a water molecule

Question 6

Monomers of carbohydrates

Answer 6

Monosaccharides (glucose,galactose and fructose)

Question 7

Starch

Answer 7

• Found in many parts of plants like small granules and starch
• Plants store excess glucose as starch
• When a plant needs energy, starch is broken down to release the energy
• Starch is a mixture of 2 a-glucose polysaccharides= amylose and amylopectin

Question 8

Amylose

Answer 8

• Long, unbranched chain of alpha glucose
• Angles of glycosidic bonds give it a coiled structure, almost like a cylinder
• Makes it compact so it’s really good for storage because you can fit it into a small space
• Hydrogen bonds between alpha glucose molecules helps to hold amylose in its helical structure

Question 9

Amylopectin

Answer 9

• Long, branched chain of alpha glucose
• It’s side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily
• Means that glucose can be released quickly

Question 10

Starch Properties

Answer 10

• Insoluble in water so doesn’t affect water potential and cause water to enter cells by osmosis, which would make them swell (this is good for storage)
• Main role is energy storage
• Large and insoluble- can’t diffuse out of cells
• Compact- lots can be stored in a small space
• Branched form has many ends so glucose released rapidly
• Alpha glucose easily transported and readily used in respiration

Question 11

Glycogen

Answer 11

• Highly branched and shorter chains
• Animals store excess glucose as glycogen (another polysaccharide of alpha glucose)
• Structure similar to amylopectin, except more side branches
• Loads of branches means stored glucose can be released quickly, which is important for energy release in animals
• Very compact molecule so good for storage

Question 12

Polysaccharide formation

Answer 12

• Large,insoluble molecules
• Formed when more than 2 monosaccharides join together by condensation reactions (loads of a-glucose molecules joined together by glycosidic bonds to form amylose)

Question 13

Hydrogen Bonding

Answer 13

• Electrons within a molecule are unevenly distributed
• One side is more negative (polarised so polar molecule)
• Weak electrostatic bond between positive of one molecule and negative of another
• Gives water its physical properties

Question 14

Metabolism

Answer 14

All the chemical processes that take place in living organisms

Question 15

Molar solution

Answer 15

Solution that contains one mole of solute in each litre of solution (mole is molecular mass expressed as grams)

Question 16

Reduction

Answer 16

Chemical reaction involving gain of electrons or hydrogen

Question 17

Reducing sugar

Answer 17

Can donate (or reduce) another chemical (benedict’s reagent)

Question 18

Why should an excess of Benedict’s be used?

Answer 18

To make sure all the sugar reacts

Question 19

What should you do if sample is solid in sugars test?

Answer 19

Grind with water and filter out solid

Question 20

What is Benedict’s?

Answer 20

Alkaline solution of copper (II) sulfate

Question 21

What conditions won’t BR work in?

Answer 21

Acidic conditions (test to see if alkaline using pH paper)

Question 22

Test for Reducing sugars

Answer 22

• Reducing sugars include all monosaccharides and some disaccharides (maltose and lactose)
• Add blue BR to a sample and heat it in a water bath which has been brought to boil
• If positive a coloured precipitate will be formed (green-yellow-orange-brick red)

Question 23

Measuring amount of sugar

Answer 23

• Higher concentration of reducing sugar, the further the colour change goes (can use this to compare amounts in different solutions)
• Could filter solution and weigh precipitate or remove precipitate and use colorimeter to measure absorbance of remaining BR

Question 24

Testing for Non-reducing sugar

Answer 24

• (sucrose) First have to break down sugar into monosaccharides
• Get a new sample and add dilute hydrochloric acid (hydrolysed disaccharides into monosaccharides), carefully heat it in a water bath that’s been brought to boil
• Then neutralise it by adding sodium hydrogencarbonate
• Carry out benedict’s as usual

Question 25

Disaccharide formation

Answer 25

• When 2 monosaccharides join together by a condensation reaction (glycosidic bond forms)
• Sucrose forms from glucose and fructose
• Lactose forms from glucose and galactose
• 2 a-glucose molecules forms maltose

Question 26

Glucose

Answer 26

• Hexose sugar- monosaccharide with 6 carbon atoms in each molecule
• Have alpha and beta glucose (isomers of each other)