Final 9 - Protein Flashcards
Draw the peptide bond between two amino acids
Do it
Names of essential amino acids
- Histadine
- Isoleucine
- Leucine
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Valine
How can you tell from an amino acid’s structure if it’s polar, non-polar, or electronically charged?
POLAR -
OH groups
NH groups
SH groups
NON-POLAR - Methyl groups or ring structures
ELECTRONIC CHARGED - COOH groups,
amine (NH3) groups
Describe the PRIMARY structure of a protein
Sequence of a chain of amino acids
Describe the SECONDARY structure of a protein. Describe the different forms and which type of forces they use
Local folding of the polypeptide chain into helices (a-helix) or or sheets (ß-pleated sheets)
- ß-pleated sheets - two parallel peptide chains that form H-bonds between each other
- A-helix - H and Os form hydrogen bonding between linked amino acids
Describe the TERTIARY structure of a protein. Describe the different forms
3D folding pattern of a protein due to side chain interactions from polarity
- Fibrous Protein - Often seen in connective tissues like collagen or hair
- Globular Protein - Very common (hemoglobin, whey, etc)
Describe the four stabilizing forces in tertiary proteins
- DISULFIDE BOND - when SH groups get together they form a covalent bond, completely locking the structure
- IONIC BOND - in charged groups, positive charges will attract negative changes, forming an ionic bond; hydrophilic groups will face outside surface, towards water
- HYDROGEN BOND
- HYDROPHOBIC INTERACTIONS - polar AA side chains want to be with polar, nonpolar with nonpolar, so protein eventually forms globular shape with non-polar (hydrophobic) groups hiding inside protein. When clustered together hydrophobic interactions happen
• Similar to H-bonding - weak force, not covalent bond
Describe the QUATERNARY structure of a protein
Protein consisting of more than one amino acid chain; similar interactions as are in tertiary
Provided two amino acids, be able to predict what kind of forces could occur between them (hydrophobic interaction, ionic bond, hydrogen bond and disulfide linkages)
- Hydrophobic interaction- two methyl groups
- Ionic bond - cation and anion (eg: NH3+ and O-)
- Hydrogen bond - OH group and an O
- Disulfide linkage - two S ends
What structure is lost during denaturation?
- Secondary and tertiary structures are fragile
* Primary structure is hard to change
Describe protein denaturation
Denaturation is change of shape of a protein without breaking peptide bonds
• Usually irreversible
• Denatured proteins interact with other proteins while unfolded, if forms disulfide cross-link it’s irreversible
Why does egg white (albumin) becomes opaque during boiling or frying?
• When crack the raw egg the white is transparent and a liquid/gel texture; at this point the albumin is water soluble
• Albumin contains a lot of systein (so has a lot of -SH groups)
• When start to cook it you see the egg white turning from transparent → semi transparent → opaque
- Application of heat breaks hydrogen bonds, hidden hydrophobic groups, losing its 2ndary 3rtiary structure
- Become random coils of protein
- When temperature cools, all systein is exposed to each other and forms new disulphide linkages
Describe how cheese coagulation happens using casein
Add rennin (enzyme) which works on kappa-casein of micelle and removes it, leaving only a- and ß-cassein (both of which are very hydrophobic). Because of this they cluster together, pushing water out - cheese is formed!
Describe how yogurt is formed using casein
Add a lot of acid (+ charges) into system and you will lose more and more negative charges until you reach an zero net charge on surface, thus no repelling of micelles between each other and they coagulate. pH gets as low as 4.6
Describe casein’s structure and components
Doesn’t have a regularly defined secondary or tertiary structure due to high levels of proline. So forms a ball-shaped micelle out of random coils
• Hydrophobic a- and ß-casein, and hydrophilic kappa-casein
Very heat stable
