Biological Molecules

Question 1

Examples of monosaccharides

Answer 1

Glucose

Fructose

Galactose

Question 2

Examples of disaccharides

Answer 2

Sucrose

Maltose

Lactose

Question 3

Examples of polysaccharides

Answer 3

Starch

Cellulose

Glycogen

Question 4

In alpha glucose, where is the OH group positioned?

Answer 4

Below

Question 5

In beta glucose, where is the OH group positioned?

Answer 5

Above

Question 6

What is the acronym for remembering where the OH group is positioned in alpha/beta glucose?

Answer 6

ABBA

Alpha
Below
Beta
Above

Question 7

What is the type of reaction that joins glucose molecules together?

Answer 7

Condensation reaction

Question 8

Glucose + Glucose = ?

Answer 8

Maltose

Question 9

Glucose + Galactose = ?

Answer 9

Lactose

Question 10

Glucose + Fructose = ?

Answer 10

Sucrose

Question 11

What can a reducing sugar do?

Answer 11

A reducing sugar can donate electrons

Question 12

Testing for reducing sugars

(All monosaccharides and some disaccharides are reducing sugars)

Answer 12

Benedict’s solution contains Cu2+ and sodium hydroxide

Reducing sugars, e.g. glucose, can donate electrons to the Cu2+, turning it into Cu+, which is insoluble

This forms a red precipitate

Heat at 80-90°c with a water bath to see results

Question 13

Testing for non-reducing sugars

(Some disaccharides and all polysaccharides are non-reducing sugars)

Answer 13

Add Benedits reagent to sample in test tube and place in water bath for 5 mins

If the solution remains blue, a reducing sugar is NOT present

Sample is gently boiled for 5 mins in HCL

Neutralised by adding drops of alkaline e.g. sodium hydrogen carbonate

Benedict’s test is then done

If a orange-brown precipitate forms, non-reducing sugar was present

Question 14

Properties of starch, where it is found and how it is used

Answer 14

Plant soluble polysaccharide

Made of many a-glucose molecules joined together by condensation reactions

Insoluble

Found in seeds, potato tubers

Can be broken down into glucose and used as an energy source

Question 15

What affect does amylose have on starch

Answer 15

Makes it compact, hydrogen bonds hold the spiral in shape so it doesn’t interfere with osmosis

Question 16

What affect does amylopectin have on starch

Answer 16

Makes it branched so larger SA so it can be quickly hydrolysed

Question 17

How is starchs’ structure suited to its function

Answer 17

Insoluble and large so it doesn’t diffuse out of cells , doesn’t affect water potential

Compact so a lot of it can be stored

When hydrolysed forms a-glucose, easily transported & used in respiration

Branched form has many ends, can be acted on by enzymes, glucose monomers are released very rapidly

Question 18

How is glycogens structure related to its function ?

Answer 18

• Insoluble so doesn’t affect water potential or diffuse out of cells

• Compact so a lot of it can be stored

• More highly branched than starch, more rapidly hydrolysed into glucose monomers -> used in respiration ( important to animals which have a higher metabolic & respiratory rate than plants )

Question 19

What monomers make up cellulose?

Answer 19

B-glucose

Question 20

What chains does cellulose form?

Answer 20

Straight, unbranched chains

They run parallel to one another, allowing hydrogen bonds to form cross-linkages between adjacent chains

This makes it a valuable structural material

Question 21

What is cellulose a major component of?

Answer 21

Plant cell walls

It provides rigidity to the plant cell

Prevents the cell from bursting (lysis) as water enters by osmosis as it exerts an inward pressure that stops further influx of water

Question 22

How is the structure of cellulose suited to its function?

Answer 22

Made up of B-glucose and so from long, straight, unbranched chains

These chains run parallel to each other and are cross linked by hydrogen bonds which add collective strength

These molecules are grouped to form microfibrils, which in turn are grouped to form fibres, which provides more strength

Question 23

Characteristics of lipids

Answer 23

Contain carbon, hydrogen and oxygen

Insoluble in water

Soluble in organic solvents e.g. alcohols and acetone

Question 24

Roles of lipids

Answer 24

Source of energy: When oxidised, provide more than 2x the energy of the same mass of carbohydrate & release water

Waterproofing: Insoluble in water

Insulation: Fats are slow conductors of heat & stored beneath the body surface to retain body heat - also act as electrical insulators in the myelin sheath around nerve cells

Protection: Fat often stored around delicate organs e.g. kidney

Question 25

Triglycerides made of?..

Answer 25

3 fatty acids 1 glycerol Each fatty acid forms an ester bond with glycerol in a condensation reaction

Question 26

When is a fatty acid described as saturated?

Answer 26

If the carboxyl (—COOH) group has no carbon-carbon double bonds All the carbon atoms are linked to the maximum number of hydrogen atoms

Question 27

When is a fatty acid described as mono-unsaturated?

Answer 27

If the carboxyl (—COOH) group has one carbon-carbon double bond

Question 28

When is a fatty acid described as polysaturated?

Answer 28

If the carboxyl (—COOH) group has more than one carbon-carbon double bond

Question 29

The structure of triglycerides related to their properties

Answer 29

• Large, non-polar molecules = insoluble in water, do not affect osmosis/WP • Low mass:energy ratio, good storage molecule -> much energy can be stored in a small volume (in animals, reduces mass they have to carry around) • Release water when oxidised due to high ratio of hydrogen to oxygen atoms, important source of water

Question 30

Structure of a phospholipid

Answer 30

2 fatty acids (hydrophobic) • Hydrophobic “tail” which orients itself away from water, readily mixes with fat 1 phosphate molecule (hydrophilic) • Hydrophilic “head” which interacts with water but not with fat

Question 31

Why are phospholipids described as polar molecules?

Answer 31

They have two ends (poles) that behave differently When phospholipid molecules are placed in water they position themselves so that they hydrophilic heads are as close to the water as possible and the hydrophobic tails are as far away from the water as possible

Question 32

The structure of lipids related to their properties

Answer 32

Phospholipids are polar molecules, meaning that in aqueous environments, they form a bilayer within cell-surface membranes (hydrophobic barrier is formed between the outside and inside of a cell) The hydrophilic phosphate “heads” help to hold at the surface of the cell-surface membrane The phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane -> glycolipids important in cell recognition

Question 33

Test for lipids (emulsion test)

Answer 33

1. Completely dry test tube 2. 2cm3 of the sample, 5cm3 of ethanol 3. Shake the tube to dissolve any lipid 4. Add 5cm3 of water and shake gently 5. A milky-white emulsion indicates presence of a lipid

Question 34

Structure of an amino acid

Answer 34

• Central carbon atom , attached to: • Amino group (—NH2) • Carboxyl group (—COOH) • Hydrogen atom (—H) • R (side) group ——each amino acid has a different R group

Question 35

Formation of a peptide bond

Answer 35

Condensation reaction Water is made by combining an —OH from the carboxyl group of one amino acid with the —H group from the amino group of another amino acid The two amino acids become linked by a new peptide bond

Question 36

Primary structure of proteins

Answer 36

Sequence of amino acids in a polypeptide chain

Question 37

Secondary structure of proteins

Answer 37

Hydrogen bonds form The long polypeptide chain twists into a 3D shape e.g. a-helix

Question 38

Tertiary structure of proteins

Answer 38

a-helixes of the secondary structure twist and fold into complex, specific 3D structures Disulphide bridges , ionic , hydrogen bonds can form depending on the primary amino acid sequence

Question 39

Quaternary structure of proteins

Answer 39

Combination of a number of different polypeptide chains and associated non-protein (prosthetic) groups into a large, complex protein molecule e.g. haemoglobin

Question 40

Test for proteins

Answer 40

Biuret test Sample of solution in a test tube and add an equal volume of sodium hydroxide solution at room temp Add a few drops of dilute copper sulphate solution and mix gently A purple colouration indicates the presence of peptide bonds

Question 41

Enzymes are…

Answer 41

Globular proteins that act as catalysts

Question 42

Inducted fit model of enzyme action

Answer 42

Proposes that the active site forms as the enzyme and substrate interact The proximity of the substrate leads to a change in the enzyme that forms the functional active site The enzyme is flexible and can mould itself around the substrate As it changes its shape, the enzyme puts a strain on the substrate molecule This strain distorts a bond/bonds in the substrate and lowers the activation energy needed to break the bond(s)

Question 43

Why are enzymes effective in small quantities?

Answer 43

Can be reused repeatedly

Question 44

Competitive inhibitors

Answer 44

Have a molecular shape similar to that of the substrate Allows them to occupy the active site of an enzyme & compete with the substrate for the available active sites The difference between the concentration of the inhibitor and the concentration of the substrate that determines the effect that this has on enzyme activity The inhibitor is not permanently bound to the active site, so when it leaves, another molecule can take its place

Question 45

Non-competitive inhibitors

Answer 45

Attach themselves to the enzyme at a binding site which is not the active site This alters the shape of the enzyme and thus it’s active site in such a way that substrate molecules can no longer occupy it This means the enzyme cannot function An increase in substrate concentration does not decrease the effect of the inhibitor