Session 5-Protein Structure And Function

Question 1

Give examples of biological processes for which proteins are needed

Answer 1

Catalysts (enzymes)
Transporters (eg O2, Fe)
Structural support (eg collagens)
Machines (eg muscular contraction and motion)
Immune protection (eg immunoglobulins)
Ion channels
Receptors (for hormones, neurotransmitters etc)
Ligand in cell signalling (growth factors etc)

Question 2

What is a peptide bond formation?

Answer 2

The linking of two AA accompanied by the removal of a molecule of water

Question 3

What is the primary structure of a protein?

Answer 3

Linear AA sequence of the polypeptide chain

Question 4

What is the secondary structure of a protein?

Answer 4

Folding of AA chain, stabilised by H bonds, alpha helix and beta pleated sheet

Question 5

What is the tertiary structure of a protein?

Answer 5

Extensive coiling and folding of AA chain with hydrophobic side chain folded inside (3D configuration)

Question 6

What is the quaternary structure of a protein?

Answer 6

Two or more polypeptide chains to form multi-subunit protein (eg Hb with 4 chains)

Question 7

True or false: peptide bonds are planar so the alpha C, C, O, N, H all lie in the same plane?

Answer 7

TRUE

Question 8

True or false: peptide bonds are rigid?

Answer 8

TRUE

Question 9

What is the isoelectric point (pI) of a protein?

Answer 9

pH at which there is no overall net charge

Question 10

What is the pI of basic proteins?

Answer 10

> 7

Question 11

What is the pI of acidic proteins?

Answer 11

<7

Question 12

What happens if the pH>pI?

Answer 12

Protein is deprotonated

Question 13

What is the difference between peptides/oligopeptides and polypeptides/proteins?

Answer 13

Peptides/oligopeptides are only a few AA in length whereas polypeptides/proteins are many AA in length

Question 14

What is a conjugated protein?

Answer 14

A protein that contains covalently linked chemical components in addition to AA

Question 15

Give two examples of conjugated proteins

Answer 15

Lipoproteins

Glycoproteins

Question 16

Which small hydrophobic resides are strong alpha helix formers?

Answer 16

Alanine and leucine

Question 17

Why does proline act as a helix breaker?

Answer 17

The rotation around the N-C bond is impossible

Question 18

Why does glycine act as a helix breaker?

Answer 18

The tiny R-group supports other conformations

Question 19

True or false: the alpha helix is a left-handed helix

Answer 19

FALSE - it is right-handed

Question 20

What is an antiparallel beta sheet?

Answer 20

Adjacent beta strands run in opposite directions with multiple interstrand H bonds stabilising the structure

Question 21

What are the roles of fibrous proteins? (3)

Answer 21

Support
Shape
Protect

Question 22

What are the roles of globular proteins? (2)

Answer 22

Catalysis

Regulation

Question 23

True or false: fibrous proteins consist of a single type of repeating secondary structure

Answer 23

TRUE

Question 24

Give an example of fibrous proteins

Answer 24

Collagen

Question 25

Complete the sentence: Collagen is a ______ helical arrangement of collagen chains

Answer 25

Triple

Question 26

Which AA is present in this repeating sequence in collagen: AA - X - Y?

Answer 26

Glycine

Question 27

What is domain in a tertiary structure of a protein?

Answer 27

Part of the polypeptide chain that folds into a distinct shape and often has a specific functional role

Question 28

Which force is involved in maintaining the primary structure of a protein?

Answer 28

Peptide (covalent)

Question 29

Which force is involved in maintaining the secondary protein structure?

Answer 29

H-bonds

Question 30

Which forces are involved in maintaining the tertiary and quaternary protein structures?

Answer 30

``` Peptide Ionic H-bonds Van der Waals Hydrophobic Disulphide ```

Question 31

Between which AAs do disulphide bonds form?

Answer 31

Between cysteine residues

Question 32

True or false: the interaction between hydrophobic side chains due to the displacement of water is called hydrophobic interaction, not hydrophobic bond

Answer 32

TRUE

Question 33

Complete the sentence: A normally folded protein that is functional is said to be in its ______ conformation

Answer 33

Native

Question 34

The disruption of protein structure is known as?

Answer 34

Denaturation

Question 35

How does heat cause denaturation?

Answer 35

Increased vibrational energy

Question 36

How does incorrect pH lead to denaturation?

Answer 36

Alters the ionisation states of AA and changes ionic/H bonds

Question 37

How do detergents lead to denaturation?

Answer 37

Disrupt hydrophobic interactions

Question 38

True or false: folding of proteins is random

Answer 38

FALSE - it would take too long if folding was random therefore it is ordered and driven by entropy (in order to find most stable conformation)

Question 39

How can protein misfolding cause disease?

Answer 39

Altered conformation of normal human protein promotes conversion of existing protein into diseased state

Question 40

Give examples of diseases caused by protein misfolding

Answer 40

Transmissible spongiform encephalopathies eg BSE, kuru and CJD