Biological molecules

Question 1

Define a monomer

Answer 1

Smaller units that join together to form larger molecules

Monosaccharides (glucose, fructose and galactose)

Amino acids

Nucleotides

Question 2

Define a polymer

Answer 2

Molecules formed when many monomers join together

Polysaccharides
Proteins
DNA/RNA

Question 3

What happens in a condensation reaction?

Answer 3

A chemical bond forms between 2 molecules and a molecule of water is produced

Question 4

What happens in a hydrolysis reaction?

Answer 4

A water molecule is used to break a chemical bond between 2 molecules

Question 5

Name the 3 hexose monosaccharides

Answer 5

Glucose
Fructose
Galactose

Question 6

Name the type of bond formed when monosaccharides react

Answer 6

1,4 or 1,6 glycosidic bonds

2 monomers = 1 chemical bond = disaccharide

Multiple monomers = many chemical bonds = polysaccharide

Question 7

Name 3 disaccharides and describe how they form

Answer 7

Condensation reaction forms glycosidic bond between 2 monosaccharides

Maltose = glucose + glucose
Sucrose= glucose + fructose
Lactose= glucose + galactose

Question 8

Describe the structure and functions of starch

Answer 8

Storage polymer of a-glucose in plant cells

insoluble = no osmotic effect on cells
large = does not diffuse out of cells

Question 9

Describe the structure and functions of glycogen

Answer 9

Main storage polymer of a-glucose in animal cells

1,4 and 1,6 glycosidic bonds

Branched = many terminal ends for hydrolysis

Insoluble = no osmotic effect and does not diffuse out of cells

Compact

Question 10

Describe the structure and functions of cellulose

Answer 10

Polymer of b-glucose, gives rigidity to plant cell walls

1,4 glycosidic bonds

Straight chain, unbranched

Alternate glucose molecules rotated at 180 degrees

H-bond crosslinks between parallel strands form microfibrils = high tensile strength

Question 11

Describe the Benedict’s test for reducing sugars

Answer 11

1. Add an equal volume of Benedict’s reagent to a sample
2. Heat the mixture in a water bath at 100 degrees for 5 minutes
3. Positive result = colour change from blue to orange/ brick red

Question 12

Describe the Benedict’s test for non reducing sugars

Answer 12

1. Negative result = Benedicts reagent remains blue
2. Hydrolyse non reducing sugars e.g sucrose into their monomers by adding 1cm3 of HCL. Heat in a water bath for 5 minutes
3. Neutralise the mixture using sodium carbonate solution
4. Proceed with the Benedicts test as usual

Question 13

Describe the test for starch

Answer 13

1. Add iodine solution

2. Positive result = colour change from orange to blue-black

Question 14

Describe how to test for lipids

Answer 14

1. Dissolve solid samples in ethanol
2. Add an equal volume of water and shake
3. Positive result = milky white emulsion forms

Question 15

How do triglycerides form?

Answer 15

Condensation reaction between 1 molecule of glycerol and 3 fatty acids forms ester bonds

Question 16

What is a saturated fatty acid?

Answer 16

Contain only single bonds

Straight chain molecules have many contact points

Higher melting point = solid at room temperature

Found in animal fats

Question 17

What is an unsaturated fatty acid?

Answer 17

Contain c=c doubl bonds

Kinked molecules have fewer contact points

Lower melting point = liquid at room temperature

Found in plant oils

Question 18

Relate the structure of triglycerides to their functions

Answer 18

High energy:Mass ratio = high calorific value from oxidation

Insoluble hydrocarbon chain = no effect on water potential of cells and used for waterproofing

Slow conductor of heat = thermal insulation

Less dense than water = buoyancy of aquatic animals

Question 19

Describe the structure and function of phospholipids

Answer 19

Glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophobic polar phosphate head

Forms phospholipid bilayer in water = component of membranes

Tails can splay outwards = waterproofing

Question 20

Compare phospholipids and triglycerides

Answer 20

Both have a glycerol backbone

Both may be attached to a mixture of saturated, monounsaturated and polyunsaturated fatty acids

Both contain the elements C, H, O

Both formed by condensation reactions

Question 21

What are the differences between phospholipids and triglycerides?

Answer 21

Phospholipids:

2 fatty acids and 1 phosphate group

Hydrophilic head and hydrophobic tail

Used in membrane function

Triglycerides:

3 fatty acids attached

Entire molecule is hydrophobic

Used as a storage molecule

Question 22

Are phospholipids and triglycerides polymers?

Answer 22

No; they are not made from a small repeating unit. They are macromolecules

Question 23

What is the general structure of an amino acid?

Answer 23

• COOH carboxyl/ carboxylic acid group
• R variable side group consists of carbon chain and may include other functional groups
• NH2 amino group

Question 24

Describe how to test for proteins in a sample

Answer 24

Biuret test- presence of peptide bond

1. Add equal volume of sodium hydroxide to sample at room temperature
2. Add 2 drops of dilute copper sulfate solution
3. Positive result: color changes from blue to purple

Negative result: solution remains blue

Question 25

How many amino acids are there and how do they differ from one another?

Answer 25

20

Question 26

How do dipeptides and polypeptides form?

Answer 26

Condensation reaction forms peptide bond and eliminates a molecule of water Dipeptide: 2 amino acids Polypeptide: 3 or more amino acids

Question 27

How many levels of protein structure are there

Answer 27

4

Question 28

Define a primary structure of a protein

Answer 28

The sequence of amino acids Determined by sequence of codons on mRNA

Question 29

Define a secondary structure of a protein

Answer 29

Alpha helix or Beta pleated sheet

Question 30

Define the tertiary structure of a protein

Answer 30

3D structure formed by further folding of the polypeptide Disulfide bridges Ionic bonds Hydrogen bonds

Question 31

Define the quaternary structure of a protein

Answer 31

Functional proteins may consist of more than one polypeptide Precise 3D structure held together by the same bonds as the tertiary structure May involve addition of prosthetic groups e.g metal ions or phosphate groups

Question 32

Describe the structure and function of globular proteins

Answer 32

Spherical and compact Hydrophilic R groups face outwards and hydrophobic R groups face inwards Involved in metabolic processes e.g enzymes and haemoglobin

Question 33

Describe the structure and function of fibrous proteins

Answer 33

Can form long chains or fibres Insoluble in water Useful for structure and support

Question 34

What are enzymes?

Answer 34

Biological catalysts for reactions Specific tertiary structure determines shape of active site, complementary to a specific substrate Formation of enzyme substrate complexes lowers activation energy of metabolic reactions

Question 35

Explain the induced fit model of enzyme action

Answer 35

Shape of active site is not directly complementary to substrate and is flexible Conformational change enables ES complexes to form This puts strain on substrate bonds, lowering activation energy

Question 36

How have models of enzyme action changed?

Answer 36

Initially lock and key model: rigid shape of active site complementary to only 1 substrate Currently induced fit model: also explains why binding at allosteric sites can change shape of active site

Question 37

What are 5 factors that affect the rate of enzyme controlled reactions

Answer 37

``` Enzyme concentration Substrate concentration Concentration of inhibitors pH Temperature ```

Question 38

How does substrate concentration affect rate of reaction?

Answer 38

Enzymes concentration is fixed so rate increases proportionally to the substrate level Rate levels off when maximum number of ES complexes form at any given time

Question 39

How does enzyme concentration affect rate of reaction?

Answer 39

Substrates are in excess so the rate increases proportionally to enzyme concentration Rate levels off when maximum number of ES complexes form at any given time

Question 40

How does temperature affect rate of reaction?

Answer 40

Rate increases as kinetic energy increases and peaks at optimum temperature Above optimum, ionic and H bonds break so the active site is no longer complementary to the substrate

Question 41

How does pH affect rate of reaction?

Answer 41

Enzymes have a narrow optimum pH range Outside the range they denature

Question 42

What are the differences between competitive and non competitve inhibitors?

Answer 42

Competitive inhibitors: Similar shape to substrate = bond to active site Do not stop reaction; ES complex forms when inhibitor is released Increasing substrate concentration decreases their effect Non-competitive inhibitors: Bind to anywhere other than the active site May permanently stop reaction; triggers active site to change shape Increasing substrate concentration has no impact on their effect