Chapter 4 Flashcards
average molecular weight of an amino acid
110
How do you approximate the number of amino acids in a protein?
dividing the proteins molecular weight by 110.
smallest protein
insulin: ~50
biggest protein
titin
The 3D structure of a protein is determined by…
its amino acid sequence
the most important forces stabilizing the specific structures of a given protein are…
non-covalent
low free energy means…
most stable
Folded proteins occupy a….
low-energy state
Protein folding _________ the order.
increases
denaturation
loss of activity; reversible (energy required is small)
Folding and unfolding is a ______________ process
cooperative
cooperative process
as soon as some come apart, it all comes apart
Within main-chain of the polypeptide, there is a repeating pattern of…
NCCNCC
To represent a viable form of secondary structure, the folding pattern must:
- optimize the hydrogen bonding potential of main chain carbonyl and amide groups
- represent a favoured conformation of the polypeptide chain
There are _____ numbers of hydrogen bond donors and accepts within the polypeptide main chain.
equal
most residues within biological peptides and proteins tend to be in….
trans configuration
Trans configuration can’t convert to cis without….
breaking bonds
Each alpha carbon is held within the main chain through…
single bonds with complete freedom of rotation
Phi
alpha carbon to amide nitrogen
Psi
alpha carbon to carbonyl carbon
Ramachadran Plot
Illustrates all possible combos of Phi and Psi
alpha helices are ______ handed helices
right
right handed helix
3.6 residues/turn
alpha helices are stabilized by..
many hydrogen bonds which are parallel to helix axis
All C=O groups point towards….
C-terminus
Which amino acids are usually not found in alpha helices?
proline and glycine
Stretches of similarly charged residues will ________ alpha helices due to ______________.
destabilize, electrostatic repulsion
The positioning of hydrophobic and hydrophilic residues with primary structure generates…..
an amphipathic alpha helices
conformation of beta strands
- fully extended polypeptide chains
- side chains projected alternately above and below
How are beta strands stabilized ?
by hydrogen bonds between C=O and -NH on adjacent strands
Which are more stable, parallel or anti-parallel beta sheets?
anti
Unique _______ produced at the interfaces between subunits of quaternary structure.
active sites
Keratin primary structure
-pseudo seven repeat (a and d are hydrophobic)
Keratin secondary
right handed, amphipathic alpha helices
keratin tertiary
the hydrophobic strip in alpha helical rods are looking for hydrophobic environment
keratin quaternary structure
hydrophobic surfaces interact to form coiled coils
coiled coil of keratin
-two right-handed helices wrapping in a left-handed fashion
Individual units of keratin are linked together through…
disulfide bonds
What determines overall strength of keratin?
extent of disulfide bonds
collagen makes up…
tendons, skin
collagen primary
multiple repeats of Gly-X-Y where X is often proline or hydroxyproline
collagen secondary
-formations of left handed helices (3 residues/turn)
collagen tertiary
full length helical
quaternary
coiled coils
coiled coils of collagen
three left handed helices wrapping in right handed fashion
What determines strength of collagen?
linkages from amino acid residues that undergo post-translational modification
The enzyme that performs performs the stabilizing links (involving p.t.m residues) of collagen require….
VITAMIN C
silk primary
six residue repeat (GSGAGA)
silk secondary
composed primarily from beta sheets (strength)
silk is both flexible and strong because…
- fully extended polypeptide chains (strength)
- beta sheets (flex)
- association of sheets by van der Waals and hydrophobic interactions (flex)
Hydrogen bonds hold….
beta sheets together (non-covalent)
hydrophobic and van der Waal interactions bring ________ together
beta sheets
Entire helix is a dipole with N (__) and C (__).
N=+
C= -
