Chapter 3 - proteins

Question 1

what is the structure of an amino acid?

Answer 1

• amine group (H-N-H)
• variable R group (diff R group=diff amino acids)
• carboxyl group (O=C-O-H)

Question 2

how are peptides synthesised?

Answer 2

1) peptide bond formed between two amino acids by a condensation reaction (carboxyl + amine group)
resulting in a dipeptide
2) many amino acids joined=polypeptide formed (catalysed by peptidyl transferase)
3) R groups interact forming bonds - causes long chains of amino acids folding in proteins
4) diff sequences of amino acids=diff structures=diff shapes

Question 3

how to separate amino acids using thin layer chromatography?

Answer 3

1) stationary phase
- layer of silica gel applied to rigid surface
- add amino acids to one end of gel
- submerge this end in organic solvent
2) mobile phase
- organic solvent moves through silica gel

Question 4

what is the primary structure of protein?

Answer 4

• the sequence in which amino acids are joined
• bonds involved=peptide bonds

Question 5

what is the secondary structure of proteins?

Answer 5

• oxygen, hydrogen, and nitrogen atoms of amino acids interact
• can form alpha helix or beta pleated sheet
• bonds involved=peptide bonds, hydrogen bonds

Question 6

what is the tertiary structure of proteins?

Answer 6

• the folding of a protein into its final shape
• R groups interact
• bonds involved=peptide bonds, hydrogen bonds, ionic bonds, disulfide bonds

Question 7

what is the quaternary structure of proteins?

Answer 7

• results from association of two or more individual proteins (subunits)

Question 8

hydrophilic and hydrophobic interactions?

Answer 8

• the way a protein folds depends on whether R groups are hydrophilic or hydrophobic
• hydrophilic groups=outside, hydrophobic groups=inside

Question 9

how are peptides broken down?

Answer 9

• proteases (enzymes) catalyse the breakdown
• water molecule used in hydrolysis reaction

Question 10

what is the Biuret test for proteins?

Answer 10

1) mix equal volume of sample and 10% sodium hydroxide solution
2) add 1% copper sulfate solution until solution turned blue
3) mix solution
positive=purple

Question 11

what are globular proteins?

Answer 11

• compact, water soluble, spherical shape, soluble
• essential in regulating many of the processes needed for life

Question 12

what is insulin?

Answer 12

• a globular protein
• a hormone
• involved in the regulation of blood glucose concentration
• soluble

Question 13

what are conjugated proteins?

Answer 13

• globular proteins that contain a non protein component (prosthetic group)

Question 14

what is haemoglobin?

Answer 14

• red, oxygen carrying pigment found in red blood cells
• quaternary protein (four polypeptides subunits)
• each subunit contains a prosthetic haem group
• iron in haem groups enable haemoglobin to carry oxygen

Question 15

what is catalase?

Answer 15

• an enzyme
• quaternary protein (four haem prosthetic groups)
• iron allows catalase to interact with hydrogen peroxide and speed up its reactions

Question 16

what are fibrous proteins?

Answer 16

• formed from long, insoluble molecules
• contain a limited range of amino acids
• tend to make strong, long molecules

Question 17

what is keratin?

Answer 17

-group of fibrous proteins
- present in hair, skin and nails
- large proportion of sulfur containing amino acids=many strong disulfide bonds=strong, inflexible, insoluble materials

Question 18

what is elastin?

Answer 18

• fibrous protein
• found in elastic fibres
• present in the walls of blood vessels and alveoli=give these the flexibility to expand and return
• quaternary protein

Question 19

what is collagen?

Answer 19

• a fibrous protein
• connective tissue found in skin, tendons, ligaments, nervous system
• made of 3 polypeptides wound together
• long, rope-like structure
• has flexibility