Enzymes and Proteins Quiz

Question 1

enzymes

Answer 1

globular proteins catalysts which speed up biological reactions unchanged by the reaction specific to their substrate active site is the position on the enzyme occupied by the substrate affected by temperature and pH

Question 2

active site

Answer 2

position on the enzyme occupied by the substrate

Question 3

enzyme–substrate specificity

Answer 3

a) Large globular protein enzyme
b) Active Site where the substrate combines to the enzyme
c) Substrate which fits the active site
d) Activated complex. The substrate is weakened to allow the reaction.
e) Unchanged enzyme/ re-used at low concentrations
f) Product of the reaction

Question 4

effect of pH on the rate of an enzyme catalysed reaction

Answer 4

optimal pH (a) or (b) the maximum rate of reaction is achieved.pepsin (a)= pH3, Red curve =salivary amylase (b)= pH 7.2

Question 5

Denaturation

Answer 5

tructural change in a protein that results in the loss (usually permanent) of its biological properties either be done by Temperature or pH

Question 6

lactase in the production of lactose-free milk

Answer 6

Lactose is a disaccharide (glucose + Galactose) milk sugar

Around 90% of all humans show some kind of lactose intoler ance.

People who are lactose intolerant can drink milk if it is lactose free.

Lactase is an enzyme extracted from yeast that can digest the milk sugar to glucose and galactose.

Question 7

Primary Structure:

Answer 7

The order/ number of amino acids in a polypeptide chain.

This forms a -N-C-C-N-C-C-N-C-C- backbone to the molecules

                                                                               The pri

mary structure is read from the NH2– terminal to the –COOH terminal.

Each amino acid is identified by its specific R group

Question 8

Secondary Structure:

Answer 8

Alpha Helix:, Beta-pleated sheet,, Open Loops

Question 9

Alpha Helix:

Question 10

Beta-pleated sheet

Question 11

Open Loops

Answer 11

Alpha helices and beta-pleated sheets are often connected together by short chains of amino acids which form neither of the previous structures but simply link other sections together (see tertiary).

These loops often connect the more recognisable helices and pleated sheets.

They are in fact often important regions of proteins including the active sites of enzymes.

Question 12

Tertiary Structures:

Answer 12

Tertiary structure is the three-dimensional conformation of a polypeptide.

In other words there are folds in a polypeptide chain.

The polypeptide folds just after it is formed in translation.

The shape is maintained by intra-molecular bonds

Hydrogen bonds

Ionic Bonds

Disulphide Bridges

Question 13

Quaternary Structure:

Answer 13

Haemoglobin is a quaternary structure.

It is composed of four different polypeptide chains.

Each chain forms a tertiary structure called a haem group.

Question 14

fiborous protiens

Answer 14

Fibrous proteins are water insoluble, long and narrow proteins.

They are associated with providing strength and support to tissues.

CollagenThis is the most common protein in animals.

Keratin keratin is the major protein in hair and nail structure.

Question 15

Globular proteins

Answer 15

Globular proteins are near soluble (colloids).

They have more compact and rounded shapes.

They are associated with functions such as:

pigments and transport proteins( haemoglobin, myoglobin, lipoproteins)

immune system (Immunoglobulins).

There is now a more sophisticated method of describing protein structure called structural motifs.

Examples are haemoglobin and Immunoglobulin(antibodies)

Question 16

Polar and non polar amino acids

Answer 16

ections of the molecule that contain polar amino acids are hydrophilic and can exist in contact with water.Polar amino acids allow the positioning of proteins on the external and internal surface of a cell membrane. Both cytoplasm and tissue fluid are water based regionshe non-polar amino acids allow the same protein to site within the phospholipid bilayer.

Question 17

Functions of Protiens with examples know four

Answer 17

structure- collagen

enzymes-hemoglobin

hormones-insulin

contractile-muscles

defense-antibodies

Question 18

Metabolic pathways

Answer 18

Chemical changes in living things often occurring with a number of intermediate stages.

Each stage has its own enzyme.

Catabolic pathways breakdown molecules

Anabolic pathways build up molecules

consist of enzyme-catalysed reactions in chains and cycles

Question 19

Cyclic Pathways:

Answer 19

However cyclic pathways tend to use the last product they create to rebegin the cycle

opposit of end-product inhibiton

Question 20

induced-fit model

Answer 20

a) Note the active site is not complementary to the substrate
b) At the complexing of the enzyme and

substrate the active site changes to accommodate the substrate. The structure of the enzyme allows a certain amount of adaptation to the substrate. hence the broad specificity of some enzymes.

States (c), (d) and (e) happen in the same way as the lock and key hypothesis.

Question 21

Activation energies

Answer 21

Enzymes lower the activation energy of the chemical reaction that they catalyse.

In the activated complex or transition state energy is put into the substrate to weaken the structure. This allow the reaction to occur with a minimal amount of additional energy required.

Normal activation energy would cause damage to the proteins of the cell. Thus reduced activation energy make these reactions possible in a cell.

After the product is formed energy is released.

Exergonic reactions release more energy than the activation energy. .

Question 22

Competitive and non-competitive inhibition

Answer 22

Inhibitors are substances that reduce or completely stop the action of an enzyme

Inhibition can act on the active site (competitive) or on another region of the enzyme molecule(non-competitive). The competition in the former being for the active site of the enzyme.

Question 23

Competitive inhibition:

Answer 23

The substrate and inhibitor are chemically very similar in molecular shape.

The inhibitor can bind to the active site

Enzyme-inhibitor complexing blocks substrate from entering the active site.

This blockage reduces the rate of reaction.

However..

If the substrate concentration is increased it occupies more active sites than the inhibitor. Therefore the substrate out-competes the inhibitor for the active site.

The rate of reaction will increase again.

Example:Succinate is converted to Fumerate by Succinate dehydrogenase(SDase)

SDase can be inhibited by a later intermediate in the cycle called malonate

Question 24

Non-competitive Inhibition:

Answer 24

The substrate and the inhibitor are chemically different in molecular structure.

The inhibitor cannot bind to the active site.

The inhibitor can bind to another region of the enzyme molecule.

The bonding of the inhibitor with the enzyme causes structural changes in the enzyme molecule.

The active site changes shape.

The substrate cannot bind therefore the rate of reaction decreases.

Example: Inhibition by metal ions (Ag+)

Silver ions inhibiting the formation of sulphide bridges at the amino acid cysteine.

This changes the protein bonding and in turn the active site changes excluding the substrate

Question 25

End product inhibition of enzyme pathway

Answer 25

End product inhibition is negative feedback used to regulate the production of a given molecule.

The initial substrate is a molecule that is altered in three steps by enzymes 1,2 and 3. The end product will combine with enzyme 1 to stop the reaction so there will not be an excess production of the end product..