Enzymes and proteins

Question 1

what is a primary structure protein

Answer 1

Chains of Amino acids linked together by peptide bond, formed by condensation reactions, producing polypeptides.

Question 2

what is a secondary structure protein

Answer 2

the folding go the polypeptide chain into alpha helices and beta sheets due to hydrogen bonds

Question 3

what is a tertiary structure protein

Answer 3

it is the overall 3D shape of the polypeptide.

It is formed by hydrophobic interactions, ionic bonds, hydrogen bonds and disulfide bridges

Question 4

what is a quaternary structure protein

Answer 4

It is the overall 3D shape of more than one polypeptide in a protein (haemoglobin), Not all proteins have quaternary structure

Question 5

what type of reaction is required to form bonds between adjacent amino acid residues

Answer 5

condensation reaction

Question 6

what is structure of a globular protein

Answer 6

They are spherical in shape and soluble in water
The hydrophobic R groups of the residue face in towards the centre of the protein and hydrophilic R groups are on the outside
Example of haemoglobin

Question 7

what is the structure of a fibrous protein

Answer 7

They have regular, repetitive sequences and are usually insoluble in water, (don’t dissolve)
They form fibres which have a structural function
The primary structure is long unbranched chain which is highly wound, eventually with other fibres to form a ‘rope’
Examples are collagen, elastin and keratin

Question 8

give two examples of ways in which the properties of globular and fibrous proteins differ

Answer 8

globular proteins are almost spherical and soluble, where as fibrous proteins are insoluble and relatively straight

Question 9

what are the two types of membrane proteins

Answer 9

-Proteins which site on the outside of the membrane are called peripheral or extrinsic proteins and have hydrophilic surfaces
-Proteins which are embedded into the cell are called intrinsic or integral proteins and contain hydrophobic inner regions
Also there are other membrane proteins such as receptors, enzymes and transporter proteins

Question 10

what is a transmembrane protein

Answer 10

membrane transport protein which always spans across the whole membrane

Question 11

what are the two types of transport proteins

Answer 11

carrier proteins

Channel proteins

Question 12

what is a carrier protein

Answer 12

are closed proteins structures which undergo a conformational change to move specific molecules across the membrane (active transport)

Question 13

what is a channel protein

Answer 13

transport proteins with water filled open pored which allow specific molecules to cross
The inside of the channel protein is hydrophobic and the outside if hydrophilic

Question 14

what is passive diffusion

Answer 14

the movement of small and non-polar molecules which diffuse down their concentration gradient through the membrane
This is mainly through channel proteins; small molecules such as O and C can just pass through the membrane

Question 15

what is facilitated diffusion

Answer 15

Uses channel proteins and carrier proteins to move molecules to diffuse through, and down their concentration gradients

Question 16

what is active transport

Answer 16

Uses carrier proteins and energy from the hydrolysis of ATP to move molecules against their concentration gradient

Question 17

what is an enzyme

Answer 17

are proteins which act as biological catalysts by reducing activation energy

Question 18

what are the two explanations for the mechanism of action for enzymes

Answer 18

The Lock and key model

The induced fit model

Question 19

what is the induced fit model

Answer 19

demonstrates the mechanism of action of enzymes by saying:

• the proximity of the substrate to the enzyme results in a conformational change in the shape of the active site to make it complementary
• This allows the active site to mould itself to the substrate forming a stable enzyme-substrate complex

Question 20

what are the two ways in which enzymes can be inhibited

Answer 20

competitive

Non-competitive

Question 21

what is a competitive inhibitor

Answer 21

Inhibitors which bind to the active site of the enzyme and are affected by substrate

Question 22

what is non-competitive inhibitors

Answer 22

inhibitors which bind to an alternative site of the enzyme called the allosteric site and are unaffected by the substrate concentration (more dangerous)

Question 23

how would you quantify competitive inhibitors

Answer 23

Solutions with competitive inhibitors are Abel to reach the uninhibited maximum rate of reaction with a high enough substrate concentration
- can reach the max of the norm solution but just takes longer

Question 24

how would you quantify non-competitive inhibitors

Answer 24

solutions with non-competitive inhibitors have a reduced rate of reaction and will not reach the uninhibited maximum rate of reaction.
-plateaus on the graph lower

Question 25

why are non-competitive inhibitors unaffected by substrate concentrations

Answer 25

because they do not have to compete with the substrate to get int he active site, as they have their own allosteric site on the enzyme which results in a change in the shape of the active site

Question 26

what is the structure of haemoglobin

Answer 26

has 4 polypeptide chains - 2 alpha, 2 beta
It is a globular protein and forms a suspension in aqueous solutions
It is conjugated and contains prothetic iron-containing harm groups in each chain
Each haem group can bind one O2 molecule (four in total)

Question 27

what is the function of haemoglobin

Answer 27

in erythrocytes Haemoglobin transports oxygen from the lungs to respiring tissues to allow respiration.
It under goes conformational Changes when binding to oxygen - cooperative binding
Binding of the first O2 molecule changes the orientation of the haem groups making it more accessible to O2

Question 28

describe the role of haemoglobin in oxygen transport in mammals

Answer 28

Haemoglobin has a high affinity to O2, binding to it in the lungs (region of high partial pressure) and forming oxyhemoglobin. It then transports the bound O2 to respiring tissue where the O2 is released. On is released at low O2 partial pressure (respiring tissues) due to a reduction in haemoglobin affinity.

Question 29

what is the structure of an antibody

Answer 29

It has 4 polypeptide chains
-2 light chains
-2 heavy chains
It has 3 regions
-variable region = contain antigen binding sites
-hinge region = provides flexibility
-constant region = bind to receptors on cells
Antigen binding sites are specific to individual antigens

Question 30

what is the function of antibodies

Answer 30

They prepare the pathogen for destruction but do not destroy them:
- cause agglutination of bacterial sites
-serve as markers for phagocytosis
The 3 regions have different functions:
-variable region binds to antigens on pathogens or to toxic chemicals they may secrete
-constant region is a binding site fore phagocytes
-hinge region lets each antibody bind to 2 different phagocytes

Question 31

define the term enzyme

Answer 31

a biological catalysts made of protein that is made inside cells

Question 32

what is activation energy

Answer 32

the energy necessary to initiate a reaction

Question 33

how does subtilisin differ from trypsin in its mode of action

Answer 33

-subtilisin catalyses the hydrolysis of any peptide body within a polypeptide
-trypsin only catalyses the hydrolysis of peptide bonds between certain amino acid residues.
Trypsin has greater level of specificity than subtilisin

Question 34

explain the importance of enzymes in organisms

Answer 34

Enzymes provide an alternative pathway with a lower activation energy so reactions can occur. Reactions occur at temperatures that are suitable for organisms. Enzymes catalyse reactions to produce structural molecules, such as collagen, cellulose and keratin, and they catalyse reactions to break down food substances in digestion.

Question 35

explain how the induced fit model differs from the lock and key model

Answer 35

the induced fit model proposes that the substrate is not complementary in the shape of the active site until it is in place. When the substrate binds to the active site, the enzyme changes shape so the substrate is bound closely into the active site.

Question 36

give an example of an inorganic cofactor and discuss the importance of cofactors in enzyme-catalyses reactions

Answer 36

nickel, copper, chloride, calcium and zinc
-cofactors interact with some enzyme molecules, some stables the molecule, others take part in the reaction. Without them the reactions that the enzymes catalyse will not take place.

Question 37

describe the mode of action of non-reversible enzyme inhibitors

Answer 37

a non-reversible inhibitor combines permanently with an enzyme molecule. This totally inactivates the enzyme so it will never function again. These inhibitors can combine with any part of an enzyme, some with the active site and some with allosteric site