Biological Molecules

Question 1

Covalent bond between two adjacent amino acids in chain of amino acids

Answer 1

Peptide bond

Question 2

Reaction involved in breaking bonds and what happens during reaction

Answer 2

Hydrolysis

H20 added

Question 3

Describe how enzyme such as pepsin breaks down a substrate

Answer 3

1. substrate shape is complementary to active site
2. substrate fits into active site
3. induced fit
4. enzyme-substrate complex formed
5. destabilising/staining of bonds in substrate then forms enzyme-product compex
6. products/amino acids then leave active site

Question 4

Repeats

Answer 4

Improve reliability
Assess spread of results
Allow calculation of mean

Question 5

Pepstatin acts as a competitive inhibitor of pepsin

What can you conclude about the structure of pepstatin

Answer 5

Similar shape to substrate/protein

Complementary to active site

Question 6

Triglyceride

Answer 6

Contains only the the elements carbon, hydrogen and oxygen

Insoluble in water

Contains glycerol

Contains ester bonds

Contains fatty acids

Question 7

Phospholipid

Answer 7

Insoluble in water
Contains glycerol
Contains ester bonds
Important in membrane structure
Contains fatty acids

Question 8

Cholesterol

Answer 8

Contains only carbon, hydogen and oxygen
Insolube in water
Important in membrane structure

Question 9

Describe how to do the emulsion test for lipids and how a positive result would be identified

Answer 9

Mix with ethanol and add water

Goes cloudy

Question 10

Mycoproteins produced by microorganisms

How might lipid content of mycoprotein fiffer from food that comes from animals

Answer 10

Less overall lipid/fat
Less/no saturated fat/lipid
More unsaturated fat/lipid

Question 11

Primary structure

Answer 11

Peptide bonds

Sequence of amino acids

Question 12

Secondary but not primary

Answer 12

Hydrogen bonds
Initial folding of polypeptide chain
(alpha helix AND B pleated sheets)

Question 13

Tertiary but not primary or secondary

Answer 13

Overall 3D shape
Ionic bonds
Supercoiled shape (fibrous)
Or
Spherical shape (globular)

Question 14

Quaternary structure ONLY

Answer 14

a and B subunits

Multiple polpeptide chains arranged to make complete protein molecule

Question 15

Describe formation of hydrogen bonds between 2 molecules of water and explain why water can form these bonds

Answer 15

1. Between O and H (of adjacent molecules)
2. Between, electropositive H and electronegative O
3. Water molecule is polar/has unequal charge distribution

Question 16

Hydrogen bonds allow water to act as a solvent

Why is ability of water to act as a solvent important for survival of survival of organisms

Answer 16

1. medium for reactions
2. allows ionic compounds to seperate
3. transport
4. apoplast-transport of water
5. Organism can absorb minerals
6. Able to dilute toxic substances

Question 17

Name given to sequence of amino acids in a protein molecule

Answer 17

Primary structure

Question 18

Structure if amino acid molecule

Answer 18

NH2 at one end
COOH at oposite end
C in centre bonded to one R and one H

Question 19

One property of collagen that makes it useful component of blood vessel walls

Answer 19

Strength/toughness/insolubility

Question 20

Describe structure of collagen molecule

Answer 20

1. peptide bonds between amino acids
2. every 3rd amino acid is same
3. coil/twist/spiral/helix
4. left handed heliz
5. glycine/small R group allows closeness/twisting of polypeptide chains
6. three polypeptide chains
7. hydrogen bonds between polypeptide chains
8. no/few hydrophilic (R) groups on outside of molecule
9. Adjacent molecules joined by crosslinks
10. Crosslinks/ends of molecules, being staggered
11. fibril

Question 21

Function if haemoglobin

Answer 21

Transport if oxygen

Question 22

3 ways in which haemoglobin differs from that of collagen

Answer 22

Haemoglobin has/is:

1. globular
2. hydrophobic (R) groups on inside/ hydrophilic (R) groups on outside
3. 4 subunits
4. Two alpha and 2 beta chains
5. Alpha helix
6. Proportion of glycine similar to that of other amino acids

Question 23

Testing for proteins

Answer 23

Biuret test
If protein present, colour change form blue to lilac
Add biuret reagent

Question 24

Testing for lipids

Answer 24

Emulsion test
Add ethanol/alcohol
Add distilled water
Cloudy white emulsion indicates presence of lipids

Question 25

Testing for carbohydrates

Answer 25

Starch
Add iodine solution
Starch present
Colour change from yellow-brown to blue-black

Question 26

Reducing sugars

Answer 26

Place sample of food to be tested in a noiling tube
Add benedict’s solution then heat in a water bath at 80°c for 3 minutes
Orange-red precipitate indicates a reducing sugar is present (low levels of sugar-contents yellow or green)

Question 27

Functions of triglycerides

Answer 27

Energy source
Energy store
Insulation
Buoyancy
Protection

Question 28

Amylose

Answer 28

Plants
Alpha glucose
1-4 glycosidic bonds
Coiled 
Hydrogen bonds
Unbranched

Question 29

Amylopectin

Answer 29

Plants
1-4 and1-6 glycosidic bonds
Coiled 
Hydrogen bonds
Branched

Question 30

Gylcogen

Answer 30

Animals
1-4 and 1-6 glycosidic bonds
Branched
Coiled
1-4 bonded chains smaller than amylopectin
Less tendecy to coil
Morw branched
More compact
Easier to remove monomer units as there are more ends