Protein

Question 1

Elemental composition of proteins

Answer 1

Carbon, Hydrogen, Oxygen, Nitrogen, some sulphur

Question 2

Protein structure generally

Answer 2

Amino group, variable group, carboxyl group

20 different amino acids, vary by R group

Question 3

Protein behaviour in water

Answer 3

Amino acids dissolve in water, carboxyl dissociates freeing a hydrogen atom, -ve charged
Amino acid acquires H+
Amino acid has +ve and -ve charge, zwitterion

Question 4

Dipeptide formation

Answer 4

Condensation reaction form dipeptide and water

Question 5

Primary structure

Answer 5

Sequence of amino acids in polypeptide chain
Created by condensation reactions between many amino acids
Due to variation in chemical makeup of R group, interactions between amino acids in chain

Question 6

Secondary structure

Answer 6

Amino acid chain folds into alpha helix or beta pleated sheets
Due to hydrogen bonds between amino (+ve) and carboxyl group (-ve)

Question 7

Tertiary structure

Answer 7

Secondary structure folds even more
Unique 3D structure formed
Held together by disulphides bonds, ionic bonds, hydrogen bonds
Not all proteins fold into tertiary shape

Question 8

Strength of disulphide bonds

Answer 8

Fairly strong

Not easily broken

Question 9

Strength of ionic bonds

Answer 9

Weaker than disulphide bonds and easily broken by pH changes

Question 10

Strength of hydrogen bonds

Answer 10

Weakest bond

But numerous

Question 11

Quaternary structure

Answer 11

Large proteins formed from no of polypeptide chains

Can include prosthetic groups

Question 12

Types of proteins

Answer 12

Fibrous

Globular

Question 13

Fibrous protein properties

Answer 13

Structural
Large insoluble, strong, flexible
Form long parallel chains like cellulose
2ndary level of folding
Often have repeating amino acid sequences
Do not denature as easily as globular

Question 14

Examples of fibrous proteins

Answer 14

Collagen- in tendons, cartilage
Keratin- in nails, skin, horns, claws
Elastin- ligaments
Actin, Myosin- muscle fibres

Question 15

Globular proteins properties

Answer 15

Tertiary structure, resembles globule, compact shape
Often involved in controlling, cellular metabolism
Specific shape
Water soluble, colloidal solutions
Altered easily, not stable, denature more easily

Question 16

Examples of fibrous proteins

Answer 16

Enzymes
Carriers and receptors in membranes
Antibodies
Haemoglobin

Question 17

Chemical reactions

Answer 17

When reactants collide, enter transition state
Molecule become strained, molecules activated
In transition state, more chance of strained bonds breaking, new bonds forming
Under normal conditions, very few have enough KE to enter transition state

Question 18

Catalysts, activation energy

Answer 18

Catalyst provides lower energy pathway

Reacts more rapidly, bind to catalyst, speed up biological reactions

Question 19

Structure of enzymes

Answer 19

Globular
Specific 3D shape, result of amino acid sequence, R groups
Small region involved in catalysing reactions, active site
Active site made up of small no of amino acids
No change to nature of products, energy change during reaction, catalyst

Question 20

Lock and key theory

Answer 20

Specific shaped substrate fits in specific complementary
Enzyme substrate complex formed
Products formed, no change to enzyme shape

Question 21

Advantages and disadvantages of the lock and key theory

Answer 21

Explains enzyme specificity

Assumes enzyme is rigid
Not supported by observation that molecules bind to allosteric site that can alter active site shape

Question 22

Induced fit model

Answer 22

As substrate approaches enzyme, shape changes
Reaction proceeds as enzyme, substrate binds
Products released, enzyme returns to original shape
Causes conformational change in enzyme

Question 23

Advantages of the induced fit theory

Answer 23

Explains how other molecules affect enzyme activity

Explains how activation energy is lowered

Question 24

Effect of temperature on enzyme activity at optimum

Answer 24

High temperature, high KE of molecules
Greater no of successful collisions, producing enzyme substrate complexes
Greater rate of reaction

Question 25

Effect of temperature beyond optimum

Answer 25

Increased temperature cause atoms within molecule to vibrate more energetically Increased vibrations strain bonds, bonds break, active site changes shape

Question 26

Effect of pH on enzyme activity

Answer 26

Change in pH alters charges on amino acids make up active site, enzyme substrate complex cannot be formed Changes tertiary structure Denatures enzyme

Question 27

Effect of substrate concentration on enzyme activity

Answer 27

Activity of enzyme depends on no of substrate molecules/sec, bind to form enzyme substrate complexes More substrate molecules=more successful collisions, more enzyme substrate formed, more product

Question 28

Coenzymes

Answer 28

Small organic non protein molecules, carry chemical groups between enzymes Consumed in reactions in which they are substrates Regenerated, con maintained in the cell

Question 29

Prosthetic group

Answer 29

Special subset of coenzymes, non protein parts of conjugated proteins Involved in active site of enzymes

Question 30

Control of metabolic pathways

Answer 30

Series of reactions, each step catalysed by enzymes Highly structured Non competitive Level of any chemical maintained at constant level with end product inhibition

Question 31

Enzyme inhibitors

Answer 31

Directly, indirectly interferes with AS function Reversible, irreversible Competitive, non competitive

Question 32

Competitive

Answer 32

Complementary to AS shape Bind to AS, prevent substrate binding Temporary, quickly released

Question 33

Effect of competitive inhibitors on rates of reaction

Answer 33

Increase substrate concentration, more substrate binds to AS in preference to inhibitor

Question 34

Non competitive inhibitors

Answer 34

Attach to allosteric site Produce conformational change in enzyme molecule including AS Substrate will not fit completely

Question 35

Effect of non competitive inhibitors on rate of reaction

Answer 35

Increasing substrate no will not affect rate of reaction