Biological molecules: proteins

Question 1

how are there different amino acids?

Answer 1

different r groups result in different amino acids

Question 2

when amino acids react, what is the bond called?

Answer 2

peptide bond

Question 3

when two amino acids react what is the reaction called and what molecule is formed?

Answer 3

a dipeptide molecule is formed from a condensation reaction so a molecule of water is released. This takes place in ribosomes where proteins are synthesised.

Question 4

when three or more amino acids are joined, what is the molecule called?

Answer 4

polypeptide

Question 5

how do you break the peptide bond?

Answer 5

add water, hydrolysis reaction which is carried out by protease enzymes

Question 6

at what point is the polypeptide considered a protein?

Answer 6

a polypeptide has to fold into a complex, 3 D shape. Therefore it can carry out its function e.g as a hormone or enzyme.

Question 7

what is the first level of protein structure called?

Answer 7

primary structure. It is the sequence in which amino acids are joined.

Question 8

why is the primary structure very important?

Answer 8

it determines the final 3D shape of a protein molecule which is critical for its function.

Question 9

why do twists and folds form in the secondary structure?

Answer 9

the oxygen atoms in the C=O group are slightly negative and the hydrogen atoms in the N-H group are slightly positive. These opposite charges attract forming hydrogen bonds in between amino acids.

Question 10

name the common secondary structure found in proteins?

Answer 10

alpha helix

Question 11

describe the structure of a beta pleated sheet

Answer 11

the polypeptide chains fold into a sheet like structure. Hydrogen bonds hold the shape in place. Many proteins have regions with alpha helix structures and beta pleated sheets. The secondary structure depends of the primary structure in that region.

Question 12

what is the tertiary structure?

Answer 12

it is the folding of a protein into its final shape which is critical for its function.

Question 13

what do scientists call polypeptides?

Answer 13

subunits

Question 14

what is the quaternary structure?

Answer 14

the association of two or more subunits. The subunits can interact. The quaternary structure also shows us the position of prosthetic groups.

Question 15

what are prosthetic groups?

Answer 15

molecules that help the protein to carry out its role

Question 16

what are proteins with a prosthetic group called?

Answer 16

conjugated proteins

Question 17

bonding which are important in tertiary and quaternary structures depend on what?

Answer 17

the R group of the amino acid

Question 18

If there is a hydroxyl group in the R group, what can occur between the polypeptides? and what can it be broken by?

Answer 18

hydrogen bonds occur which contributes to the 3D shape. However these bonds are weak and can be easily broken by high temp and by pH changes.

Question 19

how does hydrophobic and hydrophilic interactions occur in proteins?

Answer 19

un charged, non-polar R groups are hydrophobic. They tend to cluster together in the centre of proteins, well away from water molecules. Hydrophilic amino acids tend to be on the surface of proteins where they can interact with water molecules. However hydrophobic and hydrophilic interaction tend to be weak.

Question 20

how do ionic bonds occur in proteins? are they broken down by changes in ph?

Answer 20

amino acids with oppositely charged R groups can attract forming ionic bonds. This ionic bond holds different parts of the polypeptide chain together, contributing to the structure of the protein. Ionic bonds are broken by changes in pH.

Question 21

how does a disulphide bond occur in proteins? can it be broken down by high temp and ph change?

Answer 21

some R-groups contain cysteine molecules. Cysteine molecules contain a sulphur atom. Two sulphur atoms from two cysteine molecules can form a covalent bond. This is called a disulphide bond which can’t be broken down by high temp or pH change.

Question 22

Globular proteins are usually spherical shaped and are water soluble, why?

Answer 22

Globular proteins have hydrophilic amino acids on the surface and the hydrophobic amino acids are deep within the centre. E.g haemoglobin, hormones (insulin) and enzymes

Question 23

what is a heam group?

Answer 23

it is an example of a prosthetic group, they contain iron 2. Haemoglobin contains heam groups.

Question 24

describe the structure of haemoglobin

Answer 24

Haemoglobin contains four polypeptides in a quaternary structure, two beta beta and two alpha subunits. Oxygen binds to each heam group which is present in each subunit. Therefore each haemoglobin binds to four oxygen molecules. Secondary structure- mix of alpha helix and beta pleated sheet

Question 25

describe the structure of insulin and what is the function of insulin?

Answer 25

insulin is a hormone in the bloodstream that regulates blood glucose concentration. It consists of two polypeptide chains which are linked by disulphide bonds.

Question 26

How do hormones like insulin carry out their function?

Answer 26

they bind to specific receptor molecules which are proteins found on the cell membrane of target cells. The shape of the insulin molecule perfectly fits to its receptor. Slight changes in shape can prevent binding.

Question 27

Describe the structure of fibrous proteins and name the three examples

Answer 27

fibrous proteins often play a structural role e.g bones, tendons and the walls arteries. Fibrous proteins tend to form long rope like molecules. They tend to have a large proportion of amino acids with hydrophobic small R groups therefore, unlike globular proteins, fibrous proteins are insoluble in water. They are strong, long molecules. Fibrous proteins: Collagen, Keratin and elastin.

Question 28

Describe the structure of collagen

Answer 28

The polypeptide chains in collagen wrap tightly together to forma triple helix. Every third amino acid is glycine and the R group of glycine is a hydrogen atom. This is very small so it allows collagen polypeptides to wrap very tightly around each other. Large numbers of hydrogen bonds form between the polypeptide chains which stabilise the quaternary structure. The chain is also linked by strong cross links. Collage is further strengthened by the staggering arrangement where weak spots are avoided.

Question 29

where is collagen found?

Answer 29

in tendons (connects bone to muscle), ligaments (connects bones to each other) and in skin.

Question 30

where is keratin found and describe its properties

Answer 30

keratin is found in hair, fingernails and the outer surface of skin. It is very strong and insoluble in water.

Question 31

why is keratin so strong?

Answer 31

it contains a high proportion of cysteine which forms disulphide bonds which are strong covalent bonds.

Question 32

where is elastin found?

Answer 32

In the skin which makes it elastic and in the walls of arteries. Elastin fibres stretch when blood pulses through the artery and recoil in between pulses.

Question 33

describe the structure of elastin

Answer 33

long strands containing hydrophobic regions which are cross linked to each other. Hydrophobic regions on different strands associate causing elastin molecules to group. However when they are stretched, the strands move apart but are still cross linked

Question 34

how may lipids from mycoproteins differ from lipids from animals?

Answer 34

lipids from mycoproteins may have less unsaturated fat and overall less fat

Question 35

Describe formationn of peptide bond?

Answer 35

condensation reaction(1) between amine groups(1)

Question 36

Describe ways in which collagen is similar to the structure of haemoglobin?(4marks)

Answer 36

-amino acid sequence
-peptide bonds
-helical structure
-more than one subunit

Question 37

Describe and explain why collagen is a fibrous protein? (3marks)

Answer 37

-non- polar R-groups makes collagen insoluble
-long chain of amino acids
-little/no tertiary structure
-small range of amino acids (glyciene and proleine)

Question 38

suggest why collagen is such a strong molecule? (1 mark)

Answer 38

MANY strong hydrogen bonds

Question 39

Outline the method of chromatography that will separate the amino acids in collagen? (3 marks)

Answer 39

-hydrolyse collagen to release amino acids
-on chromatography plate, draw pencil line and spot the samples of amino acid
-put solvent in beaker below the pencil line
-dry and repeat

Question 40

what is special about glycine?

Answer 40

does not have a stereoisomer, its R group is hydrogen

Question 41

what is special about proline?

Answer 41

R group bonds back onto the amino group

Question 42

what is special about cysteine?

Answer 42

can form disulfide bonds between the side chains in a protein