2.1.2 Biological Molecules

Question 1

Name the interaction between the two molecules of water

Answer 1

Hydrogen bond

Question 2

Explain how hydrogen bonds form between two molecules of water

Answer 2

Unequal sharing of the electrons in the O-H bonds of water. Oxygen atom is slightly negative and hydrogen atoms are slightly posiitve. Slightly positive hydrogen atoms in one water molecule are atracted to the slightly negative atom in another water molecule

Question 3

Describe how polymers are found from their constituent monomers

Answer 3

Polymers(long chain of induvidual monomers) formed by condensation reactions between many monomers where a water molecule is released in each of these reactions

Question 4

Define a monosaccharides

Answer 4

Monosaccharides are the simplest carbohydrates, soluble, full of carbon hydrogen bonds for energy storage

Question 5

Define an isomer

Answer 5

Molecules with the same formula but different atom arrangements in space, such as glucose

Question 6

Define a disaccharides

Answer 6

Formed when two monosaccharides react in a condensation reaction,forming a glycosdic bond

Question 7

Two glucose molecules can combine to form maltose. Describe the chemical reaction that give rise to maltose

Answer 7

Join togther covalently through a condensation reaction, relesse a water molecule, forms a glycosdic bond between 2 monosachharides to form maltose

Question 8

Describe the procedure when performing a Benedicts test

Answer 8

Sample is heated with Benedict solution (alkaline copper(2) sulfate)
Changes colour of the solution from blue to green to yellow and then orange- red
Orange red precpitate would form if reducing sugars are present

Question 9

State wether amylose or amylopectin of starch is hydrolysed faster and why

Answer 9

Amylopectin because it has branches, more free ends so can be hydrolysed more rapidly

Question 10

State the bond that link glucose molecules together in amylose molecules

Answer 10

1-4 glycosdic bond

Question 11

Give a summary of starch

Answer 11

Plant based energy storage molecule - made of 2 types of alpha glucose polymers- amylose and amylopectin
Insouble - no effect on WP
Branching - site for hydrolysis
Large molecule- many glucose molecules for respiration

Question 12

Describe the structure of glycogen and explain how its structure is related to its function

Answer 12

Polysacharide made of ALPHA glucose molecule joined together by 1-4 and 1-6 glycosdlic bond
Chains with glucose monomers joined only by 1,4 glycosdic bonds are small, glycogen has less tedency to coil
1,6 glycosdic bonds present, give gylcogen a highty branched strcuture therefore high number of acessible ends, enable many enzymes to rapidly hydrolyse glycogen

Question 13

State where glycogen is stored in humans

Answer 13

Liver and muscles

Question 14

Describe the structure of cellulose

Answer 14

Polysacharide made up of beta glucose monosacharides bonded togther by 1,4 glycosdic bonds
Chains of beta glucose straight and lie side by side
Straight due to hydroxyl and hydrogen groups being inverted on carbon-1 of beta glucose
Within a chain, rotation of sucessive beta glucose molecules by 180 for glycosidic bond formation between them

Question 15

Explain how the function of cellulose is related to its structure

Answer 15

H bonding within the chains of BETA glucose in a molecule of cellulose strengthens them and prevents spiralling
H bonding between different chains of the cellulose gives the whole structure strength
Strong glycosidic bonds within chains and h bonds between chains give the cell wall of the plant a high tensile strenght

Question 16

Compare the structure of triglyceride and phospholipids

Answer 16

Triglycerides made up of glycerol and three fatty acids joined by condesation reaction
Phospholipids made up of glycerol, 2 fatty acids and one phosphate group

Question 17

Describe the difference between saturated and unsaturated fatty acids

Answer 17

Saturated - no carbon carbon double bonds in the hydrocarbon atom, max number of hydrogen
Unsaturated - double bonds in the fatty acid chain

Question 18

What are ester bonds

Answer 18

Ester bonds ( C- O-C=O) are covalent bonds formed in condensation and broken in hydrolysis. Formed between fatty acids and glycerol 
Fatty acids can join any of the 3 hydroxyl groups on glycerol

Question 19

Describe how the structure of chlosetrol is different from triglyceride

Answer 19

Chlosterol is not made from fatty acids or glycerol

4 fused hydrocarbon rings (isoprene units) forming the steroid structure, not present in triglycerides

Question 20

State 2 different roles of lipids

Answer 20

Important component of the CSM

use as a source of energy

Question 21

Give an overal summary of AA

Answer 21

Contain an amino group, carboxyl group, hydrogen and one 20 variable R groups
Plants synthesise all thier AA, if they have enough nitrogen

Question 22

Describe the chemical reaction that links AA into a polypetide

Answer 22

Condesation reactions between carboxyl group of one AA and the amino group of the next

Question 23

Explain the importance of primary protein structure in protein functionality

Answer 23

Primary structure determines the R group and bonds that will determine the rest
Provide the protein with its unique shape
Importanr im enabling the protein to perform its specfic function

Question 24

Describe why secondary structure arise in a protein

Answer 24

Alpha helices and beta pleated sheets arise naturally due to the structure of AA, contain a carboxyl and amino group when bonded in a chain. H bond between AA because the amino group is slightly positive and the oxygen in the carboxyl group is slightly negative

Question 25

Describe 2 common features of fibrous proteins

Answer 25

Long polypeptide chains w repeating sequence of AA

AA mainly have non polar R groups, insoluble in water

Question 26

What is the function of elastin

Answer 26

Cross links and coils for strong extensible tissues such as skin or lungs

Question 27

State the structural role of collagen

Answer 27

Strengh to the skin

Question 28

What and give examples of globular protein

Answer 28

Spherical shape with a core of hydrophobic interactions and surface hydrophilic AA, water soluble
Haemoglobin,Insulin, Pepsin

Question 29

Describe how the structure of haemoglobin relates to its function with reference to the levels of protein structure

Answer 29

Globular protein, 4 polypeperide chain, primary: sequence of AA in the 4 PPC,each of the polypeptide chains is coiled into alpha and beta pleated sheets
Quaternary structure of haemoglobin is formed when all 4 PPC are linked,spherical molecule
Each polypeptide is linked with a haem group, making it a conjugated protein

Question 30

Describe what is meant by a prosthetic group, give example

Answer 30

Non proteins that are associated with the PPC of a proten

E.g haem (iron containing) group in haemoglobin

Question 31

Describe how to test for proteins in a sample

Answer 31

Biuret test confirms presence of peptide bond
1) add equal volume of sodium hydroxide to sample at room temp
2) Add drops of dilute copper sulfate solution
positive - colour changes from blue to purple
Negative - solution remains blue

Question 32

Describe how to test for lipids in a sample

Answer 32

Dissolve solid samples in ethanol
Add an equal volume of water and shake
Positive result: milky white emulsion form

Question 33

Describe how to test for reducing sugars

Answer 33

1) add an equal volume of Benedict’s reagent to a sample
2) Heat the mixture in an electric water bath at 100 for 5 min
3) positive result: blue to orange and brick red
Or use test strip coated in a reagents that changes colour If reducing sugar is present

Question 34

Describe the benedicts test for non reducing sugars

Answer 34

1) negative result: Benedicts reagent remains blue
2) Hydrolyse non reducing sugars e.g sucrose into their monomers adding 1cm of HCI
3) Neutralise the mixture using sodium carbonate solution
4) proceed

Question 35

Describe the test for starch

Answer 35

Add iodine solution

Positive , orange to blue black