Lesson 2: Reactions and Stability of Proteins Flashcards
Protein Structure: two dimensional (length and height)
Primary
Protein Structure: three-dimensional spatial arrangement (around the carbon chain/skeleton)
Secondary
Protein Structure: shape in which the entire protein chain folds together in three-dimensional space
Tertiary
Protein Structure: two or more folded protein chains come together to form a ‘superstructure’
Quaternary
__________ and __________ interactions contribute to the structure of proteins, mainly their __________.
Peptide bonds; side chain; tertiary structure
The form is determined mainly by their _________ and is stabilized by _________ and _________ .
amino acid sequence; inter-chain; intra-chain hydrogen bonding
Side chains of various amino acids may also interact via the following
- Hydrogen Bonding
- Hydrophobic Interactions
- Salt Bridges
- Disulphide Bridges
- Dipole-Dipole and Ion-Dipole Forces
The amino acid sequences greatly affect the _____________ of proteins.
physico-chemical properties
physico-chemical properties of proteins
- Solubility
- Molecular weight
- Shape
- Isoelectric pH
- Precipitation
__________ is the term used for any change in the three-dimensional structure of a protein that renders it incapable of performing its
assigned function.
Denaturation
Denaturation: Physical means
heat,
violent shaking,
very high pressures,
UV radiation
Denaturation: Chemical means
pH,
high salt concentrations,
heavy metal ions,
organic solvents,
surface active agents,
high concentrations of urea.
Displays number and types of amino acids and number of peptide chains
Primary
Bonds involved in primary
H-bonds
Bonds involved in Secondary
Functional <-> R group
Bonds involved in Quarternary
(Functional <-> R group) 2 or more
Salt bridges other name
Electrostatic interaction
cysteine residue thiol group + another cysteine residue thiol group
Disulfide Bridges (Intra)
Primary Structure maintained by _______, peptide bonds
covalent
Any change in the ________ of amino acids may cause abnormal function of the polypeptide.
sequence
__________ is caused by the change in amino acid sequence of __________
Sickle anemia; hemoglobin
Hemoglobin in sickle cell anemia lacks ________and has ________ instead
Glutamate; valine
arrangement in space adopted by the backbone portion of a protein
Secondary Structure
Backbone portion of amino acids
Amino group
cardial Carbon
Carboxylic group
Hydrogen
coiled shape held in place by hydrogen bonds between the amide groups (-NH) and the carbonyl (-C=O) groups attached to the α-carbon.
R groups are not involved in this level of structure.
alpha helix (α-helix)
consists of polypeptide chains arranged side by side
held together by hydrogen bonding between the amine and the carbonyl oxygen within the amino acid backbone.
beta-pleated sheet (β-pleated sheet)
results from the interactions between amino acid side chains that are widely separated from each other within a peptide chain.
Tertiary Structure
three-dimensional spatial “arrangements”
secondary structures of proteins
specific three-dimensional “shape”
tertiary structure of a protein
Side chain <-> Side chain
Hydrogen bonding
relatively weak and are easily disrupted by changes in pH and temperature.
Hydrogen bonding (Intra)
Nonpolar side-chains are attracted to other nonpolar side-chains
“water-free pockets” in the interior region
nonpolar R groups aggregate in the interior portion of the polypeptide chain, leaving the polar portion in the exterior.
Hydrophobic interactions (inter)
Hydrophobic interactions (inter) example
London forces
between an acidic side chain (R group) and a basic side chain (R group)
Electrostatic interaction/Salt bridges (Intra)
highest level of protein organization
found only in multimeric proteins
two or more peptide chains
Quaternary structure
Quaternary structure Example:
hemoglobin
(two subunits
dimer
four subunits
tetramer
Color and Taste
colourless and usually tasteless
Shape and Size
simple crystalloid spherical structures to long fibrillar structures.
globular
(insulin)
oval
(albumin)
fibrous or elongated
(fibrinogen)
Solubility
▪ influenced by pH
▪ lowest at isoelectric point
__________ instead of true solutions in water
colloidal solutions
Molecular weight
110
Molecular weight majority of proteins/polypeptides:
40 to 4,000 amino acids
molecular weight Insulin
5,700
molecular weight Myoglobin
17,000
molecular weight Hemoglobin
64,450
Molecular weight Serum albumin
69,000
Precipitate
Flocculum
act as acids and alkali
Amphoteric
can form salts with both cations and anions based on their net charge
Ion binding capacity
Pepsin (pI) -
1.1
Casein (pI)
4.6;
Human albumin (pI)
4.7;
Urease (pI)
5.0;
Hemoglobin (pI)
6.7;
