1.1.5 - Proteins - structure

Question 1

describe the primary structure of proteins

Answer 1

• amino acids joined together by peptide bonds
• its the order of amino acids in a polypeptide chain
• determined by the base sequence on 1 strand of the DNA molecule

Question 2

explain the secondary structure of proteins

Answer 2

• the shape the polypeptide chain forms as a result of hydrogen bonding and between =O on -CO groups and the -H on -NH groups
• this causes the long polypeptide chain to be twisted into a 3D shape
• spiral shape is called the ⍺-helix
• less common arrangement is the β-pleated sheet

Question 3

give an example of a protein which contains a high proportion of ⍺-helix

Answer 3

keratin

Question 4

give an example of a protein fibroin that has a high proportion of β-pleated sheet

Answer 4

the protein fibroin in silk

Question 5

describe the tertiary protein structure

Answer 5

• the ⍺-helix of the secondary structure can be folded and twisted to give a more complex, compact 3D structure

Question 6

what is the shape of tertiary structure maintained by?

Answer 6

• hydrogen bonds
• ionic bonds
• disulphide bonds
• hydrophobic interactions

peptide bonds are also present

Question 7

why are multiple bonds needed to maintain the shape of tertiary structure proteins?

Answer 7

• important in giving globular proteins their shape

GLOBE shape

Question 8

give an example of tertiary structure proteins

Answer 8

• enzymes > fold to form the active sites

Question 9

describe hydrophobic interaction

Answer 9

R groups of some amino acids contain
-CH₃ and -C₂H₅ groups
which are hydrophobic

these groups cluster in the middle of the protein molecule

their positioning together away from water molecules is called hydrophobic interaction

Question 10

explain quaternary structure in proteins

Answer 10

• some polypeptide chains are not functional unless in combination
• sometimes they may combine with another polypeptide chain such as insulin molecule which has 2 chains
• may also be associated with non-protein groups and form large complex molecules such as haemoglobin

Question 11

what is haemoglobin?

Answer 11

globular protein
4 polypeptide chains
Fe in the middle

Question 12

summarise all 4 protein structures

Answer 12

PRIMARY >
the order of amino acids in the polypeptide chain

SECONDARY >
sequence of amino acids causes parts of a protein molecule to twist into ⍺-helix or fold into β-pleated sheet
peptide bonds + hydrogen bonds

TERTIARY >
protein is further folded
to form a unique 3D shape
held in place by ionic, H and disulphide bonds

QUATINARY >
more than one tertiary
more than one polypeptide chain

Question 13

what bonds are in the primary structure

Answer 13

peptide bonds

Question 14

what bonds are in the secondary structure

Answer 14

• peptide bonds
• hydrogen bonds

Question 15

what bonds are in the tertiary structure

Answer 15

• peptide bonds
• hydrogen bonds
• ionic bonds
• disulphide bonds
• hydrophobic interaction

Question 16

in a secondary structure, where are the hydrogen bonds formed between?

Answer 16

• the O in a C=O
• a H in the NH₂

Question 17

in a tertiary structure, where are the ionic and disulphide bonds formed between?

Answer 17

• between the R groups of different amino acids