Biological molecules

Question 1

How are large molecules formed

Answer 1

Many monomers (individual molecules) join to form longer chains called polymers

Question 2

Define monosaccharides

Answer 2

Soluble substances
General formula (CH2O)n
All end with ‘Ose’
E.g glucose

Question 3

Examples of monosaccharides

Answer 3

Triose - 3
Pentose - 5 (ribose)
Hexose - 6 (glucose galactose and fructose)

Question 4

Difference between Alpha and beta glucose

Answer 4

Alpha OH group is below
Beta OH group is above

Question 5

Describe test for reducing sugar

Answer 5

All monosaccharides and some disaccharides
2cm of food Sample
2cm of Benedict’s reagent
Heating for 5 minutes
Color change from blue to orange-brown

Question 6

Why does Benedict’s reagent turn red when heated with reducing sugar

Answer 6

Sugar donates electrons that reduce blue copper (II) sulfate to orange copper (I) oxide

Question 7

Examples of disaccharides

Answer 7

Made up of condensation reactions between 2 monosaccharides forming a glycosidic bond with molecule of water removed
Glucose and glucose = maltose
Glucose and fructose = sucrose
Glucose and galactose = lactose

Question 8

Test for non reducing sugar

Answer 8

E.g sucrose
2cm of food sample to 2cm of Benedict’s
Heating for 5 minutes with no color change

Add another 2cm of food sample to 2cm of dilute HCl and place in boiling water to hydrolyse
Add sodium hydrogen carbonate solution to neutralize HCl and test with pH paper
Retest by heating with 2cm of Benedict’s with heating
Benedict’s will turn orange as non reducing sugar hydrolysed

Question 9

Features of polysaccharides

Answer 9

Insoluble as large molecules : suitable for storage

Question 10

Test for starch

Answer 10

2cm of sample
2 drops of iodine solution
Blue-black coloration

Question 11

Starch

Answer 11

Polysaccharide found in plants
Made up of amylose and amylopectin
Main role is energy storage

Insoluble so doesn’t draw water in by osmosis & doesn’t diffuse easily
Compact so a lot can be stored in small space
Forms alpha glucose when hydrolyzed so easily transported and ready to use

Question 12

Difference between amylose and amylopectin

Answer 12

Amylose
Alpha glucose molecules unbranched : makes it compact (helical)
Only 1-4 glycosidic bonds

Amylopectin
a-glucose molecules branched
1-4 and 1-6 glycosidic bonds

Question 13

Glycogen

Answer 13

Found mainly in muscles and liver
Polymer made of many repeating alpha units
1-4 and 1-6 glycosidic bonds (similar to amylopectin)
Made of smaller chains than amylopectin so more easily hydrolyzed

Question 14

Cellulose

Answer 14

Found in plants & used for strength
Polymer of beta
OH group above ring so must be rotated 180 to form glycosidic bond
1-4 C linking
Straight unbranched chain

Prevents cell wall from bursting
Exerts pressure to allow stems and leaves to remain rigid for max S.A

Question 15

Microfibrils

Answer 15

Cellulose chains grouped tgt
Hydrogen bonds form cross linkage between each parallel layer

Question 16

Lipids properties

Answer 16

Smaller proportion of hydrogen and oxygen than carbs
Insoluble in water
Soluble in organic solvents
Main groups (triglycerides, phospholipids and waxes)

Question 17

Roles of lipids

Answer 17

In plasma membrane
Energy store
Waterproofing
Insulation
Protection around delicate organs

Question 18

Diff types of fats

Answer 18

Saturated = no double bonds
Mono-unsaturated = one double bond
Polyunsaturated = more than one double bond cause molecules to bend so oil at room temp

Question 19

Triglycerides

Answer 19

3 fatty acids (end COOH) combined with glycerol molecule (CH2OH)

Question 20

Phospholipids

Answer 20

2 fatty acids instead of 3 replaced by phosphate group (hydrophilic)
Made up of hydrophilic head and hydrophobic tail

Question 21

Test for lipids

Answer 21

2cm of sample
5cm of ethanol
Shake tube
5cm of water
white milky solution

Question 22

Structure of amino acid

Answer 22

Basic monomer units that combine to make up a polymer called polypeptide

Question 23

Formation of peptide bond

Answer 23

OH from carboxyl group on one amino acid
H from from amine group on other amino acid

Question 24

Primary structure

Answer 24

Determines the ultimate shape and function of a protein
Consists of a number of polypeptide chains

Question 25

Secondary structure

Answer 25

Describes how the polypeptide chain can fold or curl into regular repeating 3D structure Alpha helix : spiral coil with peptide bonds forming the backbone Beta pleated : sheet where the polypeptide chains fold into regular pleats held tgt by hydrogen bonds between amino and carboxyl ends or amino acids

Question 26

Tertiary structure

Answer 26

Alpha helices twisted even more to give polypeptide chain a 3D structure Has : Disulfide bonds Ionic bonds formed between any carboxyl and and amino groups Hydrogen bonds

Question 27

Quaternary structure

Answer 27

Large proteins and contain two or more polypeptide chain May contain prosthetic group

Question 28

Describe structure of proteins

Answer 28

Primary : chain of amino acids linked by peptide bonds Secondary : formed by interaction between amino and carboxyl groups form H bonds Alpha helix or beta pleated sheet forms Tertiary : folding up of the polypeptide stabilized by disulfide bridges / hydrogen / ionic Quaternary: several polypeptide subunits join conjugated proteins are proteins would which combine with non protein molecules

Question 29

Test for proteins

Answer 29

Buiret Sample places in test tube and add equal volume of sodium hydroxide Add a few drops of dilute copper II sulfate Purple color

Question 30

Why are triglycerides better way of storing energy

Answer 30

Release more energy Less soluble