Proteins

Question 1

What are amino acids made up of?

Answer 1

(alpha) Carbon bonded to a:
hydrogen
R group
NH2- Amine group (amino)
COOH- carboxyl group (acid)

Question 2

How many naturally occurring amino acids is there?

Answer 2

20- vary according to side groups
10 of these are essential amino acids in humans because the human body cannot produce them and they are obtained from the diet

Question 3

what can the NH2 group do?

Answer 3

They can act as a base, which means it can accept an H+ in acidic conditions

so sometimes an NH2 group becomes an NH3+ group

Question 4

what can the COOH group do?

Answer 4

The COOH group acts as an acid, which means it can donate an H+ in alkaline solutions

so sometimes a COOH group becomes a COO- group

Question 5

Where does a peptide bond occur?

Answer 5

Between the carboxyl and the amine group of an amino acid

Question 6

what do we call many polypeptide which are combined together into one molecule?

Answer 6

a protein

Question 7

what are the two end terminals at the end of each polypeptide chain?

Answer 7

The N-terminal: amine terminal
The C-terminal: carboxyl terminal

Question 8

what is the primary structure of a protein?

Answer 8

The primary structure of a protein is the sequence of amino acids in a polypeptide chain.
The primary structure is determined by the gene encoding the protein

Question 9

what is the primary structure of a protein?

Answer 9

The primary structure of a protein is the sequence of amino acids in a polypeptide chain.
The primary structure is determined by the gene encoding the protein

Question 10

what happens if there is a change in the nucleotide sequence of the genes encoding region?

Answer 10

It may lead to a different amino acid being added to the growing polypeptide chain
A change in the amino acids in a protein could change the proteins structure and function

Question 11

what happens in the polypeptide chain with the oppositely charged ions?

Answer 11

Thé oxygens have a partial negative charge whilst the hydrogens have a partial positive charge meaning they are polar.
Due to these attractions they form hydrogen bond pulling the polypeptide chain collider together.

Question 12

what types of secondary structures are there?

Answer 12

the beta pleated sheet
the alpha helix
dependant on the primary structure in the polypeptide chain

Question 13

why does the secondary structure fold?

Answer 13

The folding happens because the hydrogen bonds form between the groups of peptide bonds

Question 14

what type of bonds are present in the tertiary structure?

Answer 14

side groups of any two amino acids can form:
hydrogen bonds (partial negative + partial positive)
ionic (negative +positive charge)
Disulfide (bridges) bonds (cysteines, sulfhydryl groups)

Question 15

what is the tertiary structure caused by?

Answer 15

It is caused by bonds between the side groups of amino acids int he polypeptide chain

Question 16

what is the tertiary structure?

Answer 16

The 3 dimensional folding of the whole polypeptide chain

Question 17

what is the quaternary structure?

Answer 17

the shape we get when two or more 3D polypeptide chain join together

Question 18

Haemoglobin

Answer 18

Found in red blood cells of our blood

It has a quaternary structure that is made up of four polypeptide chains, called globins.

Now, because harm groups contain iron, each of them can bond one molecule of oxygen
every one molecule of haemoglobin, can carry four molecules of oxygen to all the vital organs in our body

Question 19

Haemoglobin

Answer 19

Found in red blood cells of our blood

It has a quaternary structure that is made up of four polypeptide chains, called globins.

Now, because harm groups contain iron, each of them can bond one molecule of oxygen
every one molecule of haemoglobin, can carry four molecules of oxygen to all the vital organs in our body

Question 20

what do scientists call a non-protein part in a protein? such as a haem group

Answer 20

A prosthetic group
a protein with a prosthetic group is called a conjugated protein

Question 21

what structure do globular proteins have?

Answer 21

Globular proteins are compact, roughly spherical (circular) in shape
-soluble in water

Question 22

why do globular proteins form a spherical shape when folding into their structure?

Answer 22

Their non-polar hydrophobic R groups are orientates towards the centre of the protein away from the aqueous surroundings

Their polar hydrophilic R groups orientate themselves on the outside of the protein

Question 23

What structure do fibrous proteins have?

Answer 23

Long strands of polypeptide chains that have cross- linkages due to hydrogen bonds

They have little or no tertiary structure

Due to large number of hydrophobic R groups fibrous proteins are insoluble in water

Limited number of amino acids which are highly repetitive

Question 24

Why does the ionic break in acidic conditions?

Answer 24

Adding acid to the solution makes more protons available

These protons bind to the negatively charged COO- group, turning it into neutral COOH. The uncharged carboxyl group can’t form and ionic bond to the NH3+

Question 25

why does the ionic bond break in alkali conditions?

Answer 25

If we added alkali to the solution, this would reduce the availability of protons so protons would be removed from the positively charged NH3+ group, turning it into neutral NH2 This uncharged amino group then can’t form an ionic bond

Question 26

what type of bond are disulfide bridges?

Answer 26

covalent

Question 27

which bonds are easily broken by changes in pH?

Answer 27

Hydrogen bonds Ionic bonds

Question 28

what type of test is used to test for proteins?

Answer 28

biuret test

Question 29

steps for the biuret test

Answer 29

First, add some of the food sample to a test tube add an equal volume of sodium hydroxide solution Second, add a few drops of copper sulfate solution to the test tube and mix gently

Question 30

what colour indicates a positive biuret test?

Answer 30

purple colour negative- blue

Question 31

what are enzymes?

Answer 31

proteins that catalyse reactions

Question 32

what are enzymes?

Answer 32

proteins that catalyse reactions

Question 33

what are the chemical reactants that enzymes bind to called?

Answer 33

substrates

Question 34

what is a catalyst?

Answer 34

a substance that speeds up a chemical reaction without being used up itself

Question 35

what is the activation energy?

Answer 35

the specific amount of energy needed for a chemical reaction to start

Question 36

what do enzymes do in terms of activation energy?

Answer 36

Enzymes lower the activation energies of chemical reactions inside the cell to increase the rate of reactions Enzymes lower the activation energy by binding to the reactant molecules (substrate) and allowing chemical bond-breaking and bond-forming processes to happen more easily

Question 37

what type of protein are enzymes?

Answer 37

globular proteins

Question 38

where do enzymes operate?

Answer 38

Enzymes can be intracellular or extracellular (inside/outside of the cell) Intracellular enzymes- produced and function inside the cell Extracellular enzymes- secreted by cells and catalyse reactions outside cells

Question 39

what do enzymes catalyse?

Answer 39

specific reactions

Question 40

why do enzymes catalyse only specific reactions?

Answer 40

Due to the active site of the enzyme having a specific shape which only bind to substrates with a complementary shape This forms an enzyme-substrate complex The shape of the active site is determined by the tertiary structure of the polypeptide

Question 41

what are the two different types of enzyme reactions?

Answer 41

catabolic reactions-anabolic reactions catabolic- involve the breakdown of complex molecules into simpler products, which happens when a single substrate is drawn into the active site and broken apart into two or more distinct molecules anabolic- involve the building of more complex molecules from simpler ones by drawing two or more substrates into active site, forming bonds between them and releasing single product

Question 42

Catabolic reactions: Examples

Answer 42

cellular respiration hydrolysis

Question 43

Anabolic reactions:Examples

Answer 43

Protein synthesis Photosynthesis

Question 44

Emil Fischer- 1890 Lock and key hypothesis

Answer 44

He suggested that both enzymes and substrates were rigid structures that locked into each other very precisely, like a key going a lock this was later modified and adapted to our current understanding of enzyme activity

Question 45

The induced fit model

Answer 45

States that as an enzyme and substrate coke together, their interaction causes a small shift in the enzymes structure These changes are known as conformational changes This ensure an ideal binding arrangement between the enzyme and substrate is achieved This maximises the ability of the enzyme to catalyse the reaction

Question 46

Factors affecting Enzyme activity Temperature

Answer 46

Increasing the Temperature will increase the kinetic energy of the molecules This increases the chance of a collision between the enzyme and substrate- more collisions are likely to take place in a set period of time. The rate of reaction is faster Increasing the temperature by 10°C will approximately double the rate of reaction for most enzyme- controlled reactions

Question 47

what happens to the enzyme activity when the temperature is increased to high?

Answer 47

The rate at which an enzyme catalysed a reaction drops sharply, as the enzyme begins to denature: Bonds holding the enzyme molecule in its precise shape start to break this causes the tertiary structure of the protein to change permanently damaging the active site, preventing the substrate from binding (dénaturation)

Question 48

Factors affecting enzyme activity: pH

Answer 48

Changing the pH changes the number of hydroxide ions (OH- and H+) All enzymes have an optimum pH

Question 49

Factors affecting enzyme activity: pH

Answer 49

Changing the pH changes the number of hydroxide ions (OH- and H+) All enzymes have an optimum pH

Question 50

what happens to enzyme activity at an extreme pH?

Answer 50

Hydrogen and ionic bonds hold the tertiary structure of the protein Below and above the optimum pH of an enzyme, solutions with an excess of H+ (acidic solutions) and OH- (alkaline solutions) can cause these bonds to break this alters the shape of the active site when an enzyme-substrate cannot form complete dénaturation has occured

Question 51

Factors affecting enzyme activity: Substrate concentration

Answer 51

Increasing the concentration of the substrate molecules that can form enzyme-substrate complexes at one time this increases the initial rate of reaction but when all the enzyme molecules are engaged in enzyme-substrate complexes the rate cannot increase further the rate will then plateau as the enzyme is said to be saturated the enzyme is the limiting factor

Question 52

Factors affecting enzyme activity: enzyme concentration

Answer 52

more available enzyme molecules available to catalyse the substrate in a given amount of time the higher the enzyme concentration in a reaction mixture, the greater the number of active sites available and the greater the likelihood of enzyme-substrate complex formation the substrate is the limiting factor

Question 53

what is reaction rate influenced by?

Answer 53

by the presence of competitive or non-competitive inhibitors

Question 54

What is the function of competitive inhibitors?

Answer 54

Have a similar shape to that of the substrate molecules and therefore compete with the substrate for the active site enzyme-substrate complexes cannot be formed or are at a much lower rate

Question 55

what are non-competitive inhibitors?

Answer 55

bind to the enzyme at an alternative site,which alters the shape of the active site and therefore prevents the substrate from binding to it the active site is no longer complementary to the substrate molecules some non-competitive inhibitors have a reversible effect but others are irreversible and dénature the enzyme