3.1.4.1 General properties of proteins

Question 1

EQ: Protein test- lactase from lactose solution

Answer 1

• Add Biuret reagent to both solutions
• lactase (enzyme) will give purple
• lactose (reducing sugar) will remain blue

Question 2

What are proteins?

Answer 2

Molecules made up of one or more polypeptide chain

Question 3

What are example of proteins?

Answer 3

Amylase, maltase, lipase, collagen, keratin, insulin

Question 4

Amino acids

Definition

Answer 4

the monomers from which proteins are made

Question 5

Amino acids

Structure

Answer 5

Amine group (NH2)
Carbon chain
Side chain (R) 
Carboxyl group (COOH)

Question 6

What is the H₂N group called?

Answer 6

The amine/amino group

Question 7

What is the COOH group called?

Answer 7

The carboxyl group

Question 8

What is the R group called?

Answer 8

The carbon containing R Group

Question 9

What are three examples of amino acids?

Answer 9

Glycine, alanine and cysteine

Question 10

Number of amino acids that are common in all organisms

Answer 10

20

Question 11

The twenty amino acids that are common in all organisms differ only in…

Answer 11

their side group

Question 12

What do proteins contain

Answer 12

Carbon,
Hydrogen,
Oxygen,
Nitrogen

Question 13

A condensation reaction between two amino acids forms…

Answer 13

a peptide bond

Question 14

peptide bond formation

Answer 14

A condensation reaction between two amino acids

between the carboxyl group of one and amine group of another

Question 15

Dipeptide formation

Answer 15

the condensation of two amino acids

Question 16

Polypeptide formation

Answer 16

the condensation of many amino acids

Question 17

What may a functional protein contain

Answer 17

one or more polypeptides

Question 18

Bends involved in the structure of proteins

Answer 18

Hydrogen
Ionic
Disulphide

Question 19

Types of protein function

Answer 19

Structural
Enzymes / Hormones
Transport
Protective
Contractile

Question 20

Protein Function - Structural

Answer 20

Keratin - skin, feathers, hair

Collagen - connective tissue, bone, tendons

Question 21

Protein Function - Enzymes / Hormones

Answer 21

Digestive enzymes
Insulin
Glucagon

Question 22

Protein Function - Transport

Answer 22

Haemoglobin

Question 23

Protein Function - Protective

Answer 23

Antibodies etc

Question 24

Protein Function - Contractile

Answer 24

Myosin, Actin - moving muscle tissue

Question 25

Primary structure | Definition

Answer 25

The unique sequence of amino acids that makes up a protein/polypeptide chain

Question 26

Primary structure | Structure/formation

Answer 26

Amino acids joined with peptide bonds in enzyme catalysed condensation reactions

Question 27

Primary structure | Bonds involved

Answer 27

Peptide bond

Question 28

Secondary structure | Definition

Answer 28

The way in which the primary structure of a polypeptide chain folds

Question 29

Secondary structure | Structure/formation

Answer 29

Alpha helixes | Beta pleated sheets

Question 30

Secondary structure | Bonds involved

Answer 30

Hydrogen bonds

Question 31

Tertiary structure | Definition

Answer 31

The final 3D structure of a protein, entailing the shaping of the secondary structure Held together by different chemical bonds (Hydrogen [weakest], Ionic, Disulphide bridges [strongest]) -Tertiary structure depends on the primary structure

Question 32

Tertiary structure | Structure

Answer 32

Globular | Fibrous

Question 33

Fibrous protein

Answer 33

Parallel polypeptide chains are cross linked at intervals to form long fibres or sheets

Question 34

Fibrous protein | Examples

Answer 34

collagen and keratin

Question 35

Globular protein

Answer 35

Polypeptide chain - tightly folded to form a spherical shape | Soluble proteins with a specific 3D shape

Question 36

Globular protein | Examples

Answer 36

enzymes, hormones, antibodies, haemoglobin

Question 37

Tertiary structure | Bonds/interactions involved

Answer 37

``` Held by bonds/interactions Ionic └2 oppositely charged r groups Disulphide └between two cysteine amino acids Hydrogen Hydrophobic/phallic ```

Question 38

Quaternary structure | Definition

Answer 38

The structure formed when 2 or more polypeptide chains join together, sometimes with an inorganic component, to form a protein

Question 39

Quaternary structure | Structure/formation

Answer 39

Inorganic component └prosthetic group └e.g. haem in haemoglobin

Question 40

Quaternary structure | Examples

Answer 40

Collagen (3 chains) Antibodies (3 chains) Haemoglobin (4 chains)

Question 41

Test for proteins

Answer 41

biuret test

Question 42

biuret test

Answer 42

-add biuret reagent Positive result- light purple Negative result- blue

Question 43

EQ: The type of bond that joins amino acids together in a polypeptide

Answer 43

-peptide

Question 44

EQ: Name the type of bond hydrolysed when the short chain of amino acids is removed.

Answer 44

Peptide (bond)

Question 45

EQ: Competitive inhibition- why a high concentration of galactose slows down the breakdown of lactose by lactase

Answer 45

galactose is a similar shape to lactose, so are both complimentary to the active site - galactose therefore fits into the active site of the enzyme - this prevents the substrate binding with the active site so less e-s complexes are made

Question 46

EQ: Effect of temperature on reaction- graph explanation (high temp)

Answer 46

- the enzyme becomes denatured as hydrogen bonds holding the tertiary structure are broken - meaning there is a change in the active site of the enzyme - so the substrate no longer fits into the active site and fewer e-s complexes are formed - more enzyme molecules are denatured as temperature increased

Question 47

EQ: How the students make sure pH doesn’t change

Answer 47

Use a buffer

Question 48

EQ: Why an enzyme catalyses only one reaction- enzyme specificity

Answer 48

- enzyme has an active site | - and only the substrate fits the active site

Question 49

EQ: Why maltase: - only breaks down maltose - allows this reaction to take place at normal body temperature.

Answer 49

- the 3D shape of the enzyme (tertiary structure) means - the active site is complimentary to the substrate (maltose) - as shown in the induced fit model - the enzyme is a catalyst - and lowers activation energy (as it provides alternative pathway for the reaction at a lower energy level) - by forming an e-s complex(which stresses the bonds so they are more easilt broken)

Question 50

EQ: Describe competitive and non-competitive inhibition of an enzyme

Answer 50

-Inhibitors reduce binding of enzyme to substrate / prevent formation of ES complex Competitive inhibition: -inhibitor similar shape to substrate -binds in to active site of enzyme -Inhibition can be overcome by more substrate -so max product will eventually be formed/ max rate of reaction will be reached Non-competitive inhibition: -Inhibitor binds to site on enzyme other than active site - Prevents formation of active site / changes shape of active site -Cannot be overcome by adding more substrate -so max product will not be formed/ max rate of reaction will not be reached

Question 51

EQ: Maltose is hydrolysed by the enzyme maltase. Explain why maltase catalyses only this reaction

Answer 51

1. Active site (of enzyme) has (specific) shape/tertiary structure / active site complementary to substrate/maltose; 2. (Only) maltose can bind/fit; 3. To form enzyme substrate complex;

Question 52

EQ: Sometimes trypsin can become activated inside a pancreatic cell. A competitive inhibitor in the cell then binds to the trypsin and stops it working. Explain how the competitive inhibitor stops trypsin working.

Answer 52

1. Inhibitor is a similar shape to the substrate; 2. (Inhibitor) blocks active site/is complementary to the active site/binds to the active site (of trypsin); 3. Substrate can’t bind to active site / no/fewer ES complexes formed;