proteins and enzymes Flashcards
describe the induced fit model of enzyme action and how an enzyme acts as a catalyst (3)
- substrate binds to active site
- active site shape changes so it is complementary to substrate
- reduces activation energy
suggest what scientists can do to stop enzyme reactions (2)
- boil solution
- denatures the enzyme
how does a competitive inhibitor decrease the rate of an enzyme controlled reaction (3)
- inhibitor has a similiar shape to substrate
- so it binds to active site
- prevents enzyme-substrate complex forming
when bread is stale, the starch becomes a competitive inhibitor of amylase in the small intestine, how can eating stale bread reduce weight gain? (3)
- there is less hydrolysis of starch
- into maltose
- so less absorption of glucose by the intestine
describe how the structure of a protein depends on the amino acids it contains (5)
- structure is determined by position of amino acids
- primary structure is sequence of amino acids
- secondary structure formed by hydrogen bonding
- tertiary structure formed by interactions between R groups
- this creates active site in enzymes
explain how the active site of an enzymes causes a high rate of reaction (3)
- reduces activation energy
- induced fit causes enzyme active site to change shape
- so enzyme-substrate complex causes bonds to form
a dipeptide consists of 2 amino acids joined by a peptide bond.
describe two other ways in which all dipeptides are similar and one way they differ (3)
- similar: all have amine group at the end
- similar: all have carboxyl group at end
- difference: have different R groups
describe a biochemical test for a protein (2)
- add biuret reagent
- turns from blue to purple
describe how a non-competitive inhibitor reduces rate of enzyme controlled reaction (3)
- attaches to the enzyme at allosteric site
- changes shape of the active site
- active site and substrate no longer complementary so less substrate binds- less enzyme-substrate complexes
Inhibition cannot be reduced by adding more substrate
describe how a peptide bond is formed between two amino acids to form a dipeptide (2)
- condensation reaction
- between amine and carboxyl group
the secondary structure of a polypeptide is produced by bonds between amino acids, describe how. (2)
- hydrogen bonds
- between H in amine group and O in carboxyl group
forming B-pleated sheets or a- helices
two proteins have the same number and type of amino acids but different tertiary structures, explain why (2)
- different sequence of amino acids
- ionic/hydrogen/disulfide bonds form in different places
how does formation of an enzyme-substrate complex increase rate of reaction? (2)
- reduces activation energy
- due to bending bonds
suggest two control variables when investigating effect of temperature on enzyme reaction (1)
- enzyme concentration
- pH
explain how a change in sequence of DNA bases could result in a non-functional protein (3)
- changes the amino acid sequence
- hydrogen/ ionic bonds form in different places and change tertiary structure
- changes active site shape so substrate cannot bind
what is the peptide bond between on 2 amino acids?
the C atom of one amino acid and the N atom of another amino acid
what is meant by the primary structure of a polypeptide?
the sequence of amino acids
what is meant by the secondary structure of a polypeptide?
formation of hydrogen bonds between positive H in the amine group of one amino acid and negative O in the carboxyl group of another amino acid
forms a-helices and B-pleated sheets
what is meant by the tertiary structure of a polypeptide?
the 3D folding of the chain due to interactions between R groups on different amino acids
what bonds form between R groups within the tertiary structure?
- ionic- between oppositely charged R groups
- hydrogen- between polar R groups
- london forces- between non-polar R groups
- disulfide bridges- between R groups containing sulfur
are ionic bonds stronger than disulphide bridges?
no, disulfide bridges are stronger and harder to break
ionic bonds are easily broken by changes in pH
what determines the 3D structure of a protein
the primary structure- sequence of amino acids
what is meant by quaternary structure
the interaction of two or more folded polypeptides
may contain a prosthetic group e.g haem in haemoglobin
what is the biuret reagent made up of
sodium hydroxide and dilute copper(II) sulfate
describe the differences between a fibrous protein and a globular protein and give an example of each
fibrous:
- long chains which run parallel to each other, chains are linked by cross bridges e.g. collagen
- have structural functions
- insoluble
globular:
- spherical shape
- water soluble
e.g. haemoglobin
give 3 functions of globular proteins
Enzymes- all enzymes are globular proteins as their round shape can be altered to fit their specific active site
Transport proteins- they are soluble so can cross cell membrane. e.g. haemoglobin, which transports oxygen.
Messengers proteins- they are hormones as they are soluble- Regulate the body’s metabolic processes. e.g. insulin
give 1 function of fibrous proteins
Structural proteins.- they are stable and insoluble- support and protect tissues. e.g. keratin- provides structure to hair and nails
e.g. collagen, a type of connective tissue in the body.
why is collagen a strong structural protein
- has hydrogen bonds, lots together are strong
- Collagen is present as fibres, consist of many collagen fibrils folded around each other.
explain why the quaternary structure of collagen makes it a suitable molecule for a tendon
has 3 polypeptide chains wound together
forms a strong, rope-like structure that has strength in the direction of the pull of a tendon
suggest how the cross linkages between amino acids of polypeptide chains increase the strength and stability of a collagen fibre
prevents individual polypeptide chains from sliding past one another
so they gain strength as they act as a single unit
the points where 1 collagen molecule ends and another starts is spread throughout the fibre
explain why this arrangement of collagen molecules is necessary for the efficient functioning of a tendon
the junctions between adjacent collagen molecules are points of weakness
if they all occurred at the same point, this would be a major weak point and the fibre may break
