Proteins And Enzymes

Question 0

Who do two amino acids bond and what is formed?

Answer 0

Condensation reactions and a dipeptide

Question 1

What is the structure of amino acids?

Answer 1

Amino group
R group
Carboxyl group

Question 2

What are the bonds called between amino acids?

Answer 2

Peptide bonds

Question 3

What are the two types of proteins?

Answer 3

Fibrous and globular proteins?

Question 4

What are fibrous proteins?

Answer 4

These are parallel polypeptide chains held together by cross links (forming rope like fibres)

Question 5

What are the properties of fibrous proteins and give some examples?

Answer 5

High strength, insoluble in water, high tensile

Collagen, keratin and silk

Question 6

What are globular proteins?

Answer 6

Spherical, tightly folded polypeptide chains. Hydrophobic groups inside, hydrophilic groups outside

Question 7

What are some examples of globular proteins and give some properties?

Answer 7

Soluble in water
Spherical due to tight folding of the polypeptide chains

Transport proteins, enzymes and hormones

Question 8

What are proteins used for?

Answer 8

Structural, catalytic, signalling, immunological

Question 9

Describe the primary structure of proteins

Answer 9

A simple sequence of amino acids in the polypeptide chain. Held together by peptide bonds

Question 10

Describe the secondary structure of proteins

Answer 10

Hydrogen bonds form between the polypeptide chain. This makes the chain either coil (alpha helix) or fold (beta pleated sheet)

Question 11

Describe the structure of tertiary structure of proteins

Answer 11

A polypeptide chain coiled or folded even more. This forms a 3D structure. The bonds that cause this are disulphide bonds (covalent)

Question 12

Describe the structure of quaternary proteins

Answer 12

Made of more than one polypeptide chain held together by more bonds. This results in a final 3D shape. Examples include haemaglobin, insulin, collagen

Question 13

What is collagen and what gives it, it’s properties?

Answer 13

Collagen is the main consonant of connective tissues in animals.

It has three polypeptide chains tightly coiled, which makes it strong. Good for support

Question 14

What is keratin and what gives it, it’s properties?

Answer 14

Main component of hard structures in animals.

Examples are hair, nails and claws

Question 15

What is silk?

Answer 15

Ask

Question 16

What is the test for proteins and how is it done?

Answer 16

Biuret test

Test solution needs to be alkaline so add a few drops of sodium hydroxide solution
Then add some copper (2) sulfate solution

Colour change from blue to purple

Question 17

What are enzymes?

Answer 17

Enzymes are biological catalysts. They speed up chemical reactions

Question 18

Describe the structure of enzymes?

Answer 18

Tertiary structure, roughly spherical due to tight folding of polypeptide chains. Soluble as there hydrophilic groups are outside.

They have an active site which are specific to certain substrates

Question 19

How do enzymes work?

Answer 19

They lower the activation energy of a reaction. When an enzyme substrate complex forms. This reduces the activation energy of a reaction

Question 20

How does the enzyme substrate complex lower the activation energy where two substrates are joining?

Answer 20

The enzyme holds the substrate close together, reducing the repulsion between the molecules so they can bond more easily.

Question 21

How does the enzyme substrate complex lower the activation energy where a substrate is breaking down?

Answer 21

Fitting the substrate into the enzyme puts strain on the bonds in the substrate, so it breaks up more easily

Question 22

How are enzymes specific to substrates?

Answer 22

Only one substrate will fit into the active site of an enzyme. The active site shape is determined by the enzymes tertiary structure (which is determined by it’s specific primary structure)

Question 23

What is the primary structure of a protein determined by?

Answer 23

A gene (determines the sequences if amino acids). If a mutation occurs in that gene, it could change the tertiary structure of the enzyme produced (so it cannot carry out it’s function as the active site shape has changed and is no longer complimentary of the substrate)

Question 24

How do you measure the rate if an enzyme controlled reaction?

Answer 24

Measuring the amount of product produced (measuring the amount of product present at different times during the experiment, the reaction rate can be calculated)

Measuring the amount of substrate left (measure the substrate at different points of the experiments)

Question 25

What is the effect of temperature on enzyme controlled reactions?

Answer 25

The rate of reaction increases as the temperature increases. The molecules vibrate more so the molecules move faster and are more likely to collide with the enzymes active sites.

It reaches the optimum temperature where the rate of the reaction is the largest.

If the temperature increases above this then the vibrating breaks more bonds in the enzyme and thus the active site of the enzyme changes shape, no longer complimentary of the substrate and the enzyme denatures.

Question 26

How does pH affect the rate of an enzyme controlled reaction?

Answer 26

Enzymes are very specific to pH. If above or below this optimum pH, the H+ or OH- ions (in acids or alkalis) can disrupt the ionic or hydrogen bonds in enzymes, breaking their tertiary structure apart, denaturing the enzyme

Question 27

How does the substrate concentration affect the rate of an enzyme controlled reaction?

Answer 27

The higher the substrate concentration, the higher the rate of reaction (more substrate molecules means more likely collision with substrate and enzyme so more active sites will be used)

This is true up to the saturation point where there are so many substrate molecules, there are not enough enzymes to catalyse substrate quicker (all active sites are full)

Question 28

How does the enzyme concentration affect the rate of enzyme controlled reactions?

Answer 28

The more enzymes, the quicker the reactants are catalysed

Question 29

Describe the lock and key model

Answer 29

Describes how enzymes and substrates bind
The enzymes are specific so there active site is rigid and are exactly complementary of the substrate and so binds to form an enzyme substrate complex. COMPLIMENTARY SHAPE

This was first thought, but then scientists realised this does not give a complete coverage of the formation of an enzyme substrate complex

Question 30

Describe the induced fit model

Answer 30

Helps to explain why enzymes are so specific and so bond to only one substrate.

When binding to a substrate, the active site changes shape slightly so the substrate fits exactly forming an enzyme substrate complex.

This is widely accepted now

Question 31

What are enzyme inhibitors?

Answer 31

They are molecules that bind to enzymes, inhibiting their actions (slowing down the rate of the reaction they catalyse)

Question 32

How do competitive inhibitors work?

Answer 32

A molecule of the inhibitor has a similar structure to the substrate. This means they compete with the substate to bind with the enzyme. They bind with the enzyme but no reaction occurs, preventing the formation of enzyme substrate complexes, by blocking active sites. Slowing the rate of reaction.

Question 33

How do non-competitive inhibitors work?

Answer 33

Non competitive inhibitors bind to the enzyme away from it’s active site (ask about it’s name). This causes the shape of the active site to change so that substrates can no longer bond to it, so less enzyme substrate complexes can form.

Question 34

What does increasing the concentration of substrates have on an enzyme controlled reaction in the presence of non-competitive inhibitors?

Answer 34

No effect, enzyme activity is still inhibited