Amino Acids And Proteins

Question 1

What is an amino acid

Answer 1

A compound whose molecules contain bird an amino and a carboxyl group

Question 2

How many amino acids occur naturally and in what form

Answer 2

20 occur naturally and they combine to form proteins

All naturally occurring amino acids are a amino acids

Question 3

What does alpha amino acid mean

Answer 3

NH2 and COOH are bonded to same C atom

Question 4

What is the definition of a zwitterion

Answer 4

Ions which have a permanent positive and negative charge but which are neutral overall

Question 5

Why do amino acids exist as zwitterions

Answer 5

• they all contain a basic group and an acidic carboxyl group
• undergo internal acid-base reaction
• forms a dipolar ion

Question 6

Draw the diagram of a zwitterion amino acid

Answer 6

See page 22

Question 7

State the physical properties of amino acids

Answer 7

⭕️ High mp - dipolar ions - strong forces of attraction - lot of energy
⭕️ water soluble - dipolar ions - interact w polar water molecules
⭕️ white crystalline solids
⭕️ insoluble in organic solvents

Question 8

What group is involved in the reaction when an amino acid reacts with sodium carbonate

Answer 8

The COOH group

Question 9

What are the products for the reaction of an amino acid with sodium carbonate

Answer 9

Metal salt
Water
Carbon dioxide

Question 10

What are he observations for amino acid reaction with sodium carbonate

Answer 10

Bubbles of colourless has evolved

Solid disappears

Question 11

What group is reacted when amino acids react with nitrous acid

Answer 11

The NH2 group is replaced by an OH

Question 12

What are the products when amino acid is reacted with nitrous acid

Answer 12

N2
H2O
Hydroxycarboxylic acid

Question 13

How is nitrous acid produced

Answer 13

In situ
NaNO2 and HCl
Below 5°C

Question 14

What is formed when amino acids react with copper (II) sulfate

Answer 14

A complex

Question 15

What are the observations when amino acid is reacted with nitrous acid

Answer 15

Bubbles of colourless has given off (N2)

Question 16

What are the observations when amino acid reacts with copper (II) sulfate

Answer 16

Dark blue solution formed

Question 17

Write the structural equation of amino acid reaction with copper (II) sulfate

Answer 17

See notes

Question 18

Draw the structure of an amino acid in acid conditions and alkaline conditions

Answer 18

See notes

Question 19

Describe the structure of a neutral amino acid

Answer 19

Contains one amine and one carboxyl group

Question 20

Describe an acidic amino acid

Answer 20

Contains additional carboxyl group

Question 21

Describe a basic amino acid

Answer 21

Contains additional amine group

Question 22

What kind of reaction forms a peptide (polyamide)

Answer 22

Condensation polymerisation of amino acids

Question 23

What is a peptide link

Answer 23

Link between -NH2 of one amino acid and -COOH of another

Question 24

What is a condensation reaction

Answer 24

When two molecules combine to form one single molecule. Resulting in the loss of a small molecule eg water

Question 25

Draw the peptide group

Answer 25

See notes

Question 26

What happens during acid hydrolysis of protein

Answer 26

- acids formed are protonated - NH2 ➡️ NH3+ - positive amino acid ions - COOH stays same

Question 27

What happens during alkaline hydrolysis of a proteins

Answer 27

- acids formed are deprotonated - COOH ➡️ COO- - negative amino acid ions - NH2 stays the same

Question 28

What is the definition of primary structure of proteins

Answer 28

Sequence of amino acids joined by peptide links in the chain

Question 29

What is the definition of secondary structure

Answer 29

Twisting/coiling of the chain to form a B-pleated sheet/a helix by intramolecular hydrogen bonding

Question 30

Between which parts of the molecule does H bonding occur in the secondary structure

Answer 30

NH and C=O

Question 31

What is the definition of tertiary structure in proteins

Answer 31

Bending / folding of secondary structure to give a precise 3D shape held together by Hydrogen bonding / disulphide bridges / ionic interactions / VDW forces

Question 32

How does the tertiary structure occur

Answer 32

Interactions between R-group side chains

Question 33

How to sulfer bridges form

Answer 33

- cystine | - side group of SH ➡️ oxidised to form dimer

Question 34

What type of bond is a sulfer bridge

Answer 34

Covalent - stronger than H bond

Question 35

How do ionic interactions occur in tertiary structure

Answer 35

Ionic bonds between adjacent acidic and basic amino acids

Question 36

How do VDW forces occur in tertiary structure

Answer 36

Between non polar side groups

Question 37

How do dipole dipole interactions occur in tertiary structure

Answer 37

Between polar side chains

Question 38

How do hydrophobic interactions occur in tertiary structure

Answer 38

- Between non polar side chains and water - repel water - chain folds and hydrophobic on inside folds and hydrophilic polar groups on outside

Question 39

What is the definition of an enzyme

Answer 39

A protein which is a biological catalyst

Question 40

What do enzymes do

Answer 40

- Speed up reaction without being used up | - alternative reaction pathway of lower activation energy

Question 41

What is the definition of active site

Answer 41

Site on surface of enzyme into which the substrate fits

Question 42

What is the induced fit theory

Answer 42

Substrate induces a change of the active site of the enzyme

Question 43

What does it mean that enzymes are stereospecific

Answer 43

Only one optical isomer will fit

Question 44

Why are enzymes specific

Answer 44

Due to tertiary structure - specific shape needed to fit active site

Question 45

Why are enzymes in washing powder

Answer 45

- Break down biological molecules in stains - break down by hydrolysis ➡️ makes them more water soluble so easier washed - allows powder to work at lower temp - more cost effective

Question 46

What effect does pH have on enzyme activity

Answer 46

- optimal pH - if H+ added ➡️ active site protonated - if OH- added then active side deprotonated - changes structure of active site

Question 47

What effect does temp have on enzyme activity

Answer 47

- optimal temp - changes active site - break interactions eg H bonds - v high = denatured