Chapter 2: biological molecules

Question 1

reagent used for reducing sugars

Answer 1

Benedict’s reagent

Question 2

reducing sugars test

Answer 2

• Benedict’s reagent contains copper ions
• when heated with reducing sugars, the copper ions are reduced to copper compounds
• the colour changes from blue to brown
• this test can be used for a range of concentrations of sugars

Question 3

reagent used for non-reducing sugars

Answer 3

Benedict’s reagent, following acid hydrolysis

Question 4

non-reducing sugars test

Answer 4

• sucrose is a commonly occurring non-reducing sugar
• when heated with dilute acid, sucrose is hydrolysed into its constituent monosaccarides, glucose and fructose, which are both reducing sugars
• excess acid is then neutralised by the addition of sodium hydrogen carbonate and the mixture is then tested with Benedict’s reagent. This will show the production of reducing sugars

Question 5

reagent used for starch

Answer 5

iodine in potassium iodide solution

Question 6

starch test

Answer 6

iodine solution turns from brown to blue black in the presence of starch

Question 7

proteins reagent

Answer 7

biuret reagent

Question 8

‘macromolecule’ definition

Answer 8

a large biological molecule

Question 9

‘monomer’ definition

Answer 9

a simple molecule which is used as a basic building block for the synthesis of a polymer

Question 10

‘polymer’ definition

Answer 10

a giant molecule made from many similar repeating subunits joined together in a chain

Question 11

monosaccharides function

Answer 11

• source of energy in respiration

- building blocks for larger molecules

Question 12

monosaccharide definition

Answer 12

a molecule consisting of a single sugar unit with the general formula (CH20)n

Question 13

‘disaccharide’ definition

Answer 13

a sugar molecule consisting of two monosaccharides joined together vy a glycosidic bond

Question 14

‘polysaccharide’ definition

Answer 14

a polymer whose subunits are monosaccharides joined together by glycosidic bonds

Question 15

what is starch made up of?

Answer 15

a mixture of amylose and amylopectin

Question 16

what is the storage carbohydrate in animal cells?

Answer 16

glycogen

Question 17

why are hydrogen bonds strong?

Answer 17

they are individually weak but collectively they provide enormous strength

Question 18

describe the characteristics of cellulose fibres:

Answer 18

• very high tensile strength so that they can withstand the high pressures caused by osmosis
• freely permeable, allowing water and solutes to reach or leave the cell surface membrane

Question 19

what chemical group do fatty acids contain?

Answer 19

-COOH

Question 20

acid + alcohol produces what chemical?

Answer 20

an ester

Question 21

what is the bond between an acid and an alcohol called?

Answer 21

an ester bond

Question 22

what are the most common lipids?

Answer 22

triglycerides

Question 23

describe the solubility of triglycerides

Answer 23

insoluble in water but soluble in certain organic solvents

Question 24

describe the roles of triglycerides

Answer 24

• energy reserves
• insulator against loss of heat
• metabolic source of water

Question 25

describe the unusual property of phospholipids

Answer 25

- one end is soluble in water | - one of the three fatty acid molecules is replaced by a phosphate group, which is polar

Question 26

describe the phosphate group in a phospholipid in one word

Answer 26

hydrophilic (water-loving)

Question 27

describe three functions of proteins

Answer 27

- enzymes - some hormones (eg insulin) - antibodies

Question 28

describe the general structure of all amino acids

Answer 28

- central carbon atom - bonded to an amine group NH2 - and a carboxylic acid group, COOH

Question 29

how do amino acids differ from each other?

Answer 29

by the R group

Question 30

when two amino acids join together, they form a...

Answer 30

peptide bond

Question 31

what is a polypeptide?

Answer 31

a molecule made up of many amino acids linked together by peptide bonds

Question 32

where are polypeptides formed?

Answer 32

in the ribosomes

Question 33

'primary structure' definition

Answer 33

the sequence of amino acids in a polypeptide or protein

Question 34

'secondary structure' definition

Answer 34

the structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids

Question 35

'tertiary structure' definition

Answer 35

the compact structure of a protein molecule resulting from the dimensional coiling of the already-folded chain of amino acids

Question 36

hydrogen bonds form between...

Answer 36

strongly polar groups eg -NH-, -CO- and -OH groups

Question 37

disulfide bonds form between...

Answer 37

cysteine molecules

Question 38

disulfide bonds are...

Answer 38

strong covalent bonds

Question 39

ionic bonds form between...

Answer 39

- ionised amine (NH3+) groups | - ionised carboxylic acis (COO-) groups

Question 40

how are disulfide bonds broken?

Answer 40

by reducing agents

Question 41

how are ionic bonds broken?

Answer 41

by pH changes

Question 42

weak hydrophobic interactions occur between...

Answer 42

non-polar R groups

Question 43

what structure does haemoglobin have?

Answer 43

a quaternary structure

Question 44

describe the structure of haemoglobin

Answer 44

- four polypeptide chains - each chain is a protein called a globin - two chains are alpha-globin, two are beta-globin - each chain contains a haem group (a prosthetic group) - each haem group contains an iron atoms - one 02 molecule can bind with each iron atom

Question 45

describe the structure of collagen

Answer 45

- three polypeptide chains wound round each other - every third amino acid in each polypeptide is glycine - covalent bonds form between the R groups of amino acids lying next to each other - these cross links form fibrils - they form fibres

Question 46

water as a solvent

Answer 46

- water molecules are attracted to the ions and polar molecules - they collect around and separate them

Question 47

the high specific heat capacity of water

Answer 47

- the amount of heat required to raise its temperature by a given amount - hydrogen bonds need to be broken to allow free movement

Question 48

high latent heat of vaporisation of water

Answer 48

- a measure of the heat energy needed to vaporise a liquid, changing it from a liquid to a gas - it means that living organisms can use evaporation as a cooling system

Question 49

high surface tension and cohesion of water

Answer 49

- the molecules tend to stick together - water can move through long, unbroken columns through the vascular tissue in plants - the surface of water is a habitat for small organisms