FHMP 008 Amino acids, protein structure and function

Question 1

what is the structure of an amino acid?

Answer 1

Amino group (N-terminus = left), Carboxyl group (right side), Side chain (R-group), H atom and central C atom

Question 2

What is the R group?

Answer 2

• it is the variable group (has 20 variations)

- each amino acid has a different R group

Question 3

what is the peptide bond and how is it formed?

Answer 3

• Amino acids are polymerised by Condensation to form Peptide Bond
• forms between the N- terminus (NH3) and the C- terminus (COO) and produces water

Question 4

How are R groups classified

Answer 4

• 20 R groups in total
• 9 = hydrophobic ( mostly C-H)
• 11 = hydrophilic
• 6 hydrophilic are neutral ( all have O, OH or NH groups that form bonds with H2O) (mostly in active sites)
• 2 hydrophilic are acidic ( have COO- group)( in active sites and salt bridges)
• 3 hydrophilic are basic ( have N-H ) (some act as buffers)

Question 5

What are the 4 levels of protein structure?

Answer 5

primary, secondary, tertiary, quaternary

Question 6

What is the primary structure of a protein?

Answer 6

sequence of amino acids in a polypeptide chain

Question 7

What is the secondary structure of a protein?

Answer 7

• 3D arrangement of a polypeptide chain
• alpha helix or beta-pleated sheet
• hydrogen bonding

Question 8

describe the bonding in alpha helix structure

Answer 8

• helical arrangement, main protein chain repeats itself about every 4th turn
• R groups stick outwards
• carboxyl and amine groups hydrogen-bonded
• all H bonds are parallel to the helical axis

Question 9

describe the bonding in beta pleated sheet

Answer 9

• main chain is extended: the R groups alternate up and down
• all carboxyl and amine main chain groups are hydrogen bonded
• all H bonds are perpendicular to main chain
• parallel sheets = N-terminus are at same end
• antiparallel sheets = N -terminus are at opposite ends

Question 10

What is the tertiary structure of a protein?

Answer 10

• 3D folding of a polypeptide chain due to interactions between side chains of amino acids that lie in different regions of the primary sequence
• hydrogen bonding, salt bridges/ionic bond between opposite charges, hydrophobic/hydrophilic interactions and disulphide bridges

Question 11

What is the quaternary structure of a protein?

Answer 11

3D arrangment due to interactions between different polypeptide chains in proteins composed of more than one polypeptide (subunit interaction)

Question 12

what are the 3 types of protein?

Answer 12

fibrous, globular, hybrid

Question 13

What are fibrous proteins?

Answer 13

• strong/insoluble/inflexible material e.g. collagen and keratin
• structural support e.g. tendons, bones, muscle, ligament, hair, skin…
• long strong fibers
• insoluble in water
• quaternary structure is held by covalent bridges
• more stable (less effected by environment)

Question 14

give 3 examples of fibrous proteins

Answer 14

keratin, elastin, collagen

Question 15

describe collagen

Answer 15

Fibrous protein.
3 polypeptides wound in rope-like structure (triple helix), very strong.
Every third amino acid in glycine (small).
tropocollagen assembles together to make collagen fibre
cross linking to increase strength
- skin, tendons, cartilage, bones, connective tissue

Question 16

describe elastin

Answer 16

Fibrous protein in elastic fibres.
Quaternary.
Made of small, soluble tropoelastin molecules linked together via interactions between hydrophobic areas.
Alternate hydrophobic and lysine-rich areas.
Cross-linking covalent bonds between lysine.
- arteries, lungs, bladder, ligament

Question 17

Describe keratin

Answer 17

Fibrous protein.
Large proportion of cysteine (containing sulfur).
Many strong disulfide bridges between alpha helices
- hair, nails, outer skin

Question 18

What are globular proteins?

Answer 18

• water soluble proteins with a specific 3D shape e.g. enzymes, hormones, antibodies, haemoglobin
• spherical compact shape
• quaternary structure is held together by non-covalent forces
• used a lot in metabolism
• less stable (more effected by environment)

Question 19

give 4 main types of globular proteins

Answer 19

• enzymes = catalase, trypsin
• transporters = haemoglobin, transferrin
• protection = antibodies (immunoglobulins)
• hormones = insulin
• DNA binding
• storage
• cell signalling

Question 20

Describe haemoglobin structure

Answer 20

• 4 polypeptide chains held together by disulfide bonds, globular protein
• conjugated protein - contains a haem group ( iron ion ) to bind to O2
• 2 alpha, 2 beta chains
• binds to and carries/transports oxygen around the body

Question 21

describe immunoglobulin structure

Answer 21

• antibodies, bind to antigens on pathogen and kills the pathogen
• 2 light chains, 2 heavy chains, Fab and Fc region
• Beta sheet structure ( 2 sheets)
• Y shaped
• hydrogen bonding, disulfide bridhes

Question 22

what are hybrid proteins?

Answer 22

• proteins with both fibrous and globular proteins

Question 23

give 3 examples of hybrid proteins

Answer 23

actin, myosin, fibrinogen