Chapter 2 protein composition and structure Flashcards
Why are L-amino acids most abundant in proteins
because they are more soluble than a racemic mixture of D and L-amino acids, and the racemic mixture tends to form crystals
what is the ring in prolin called and what is special about proline
pyrrolidine and the side chain bindes to the nitrogen and alpha carbon of the backbone
which one is much more reactive than the other
sulfhydryl or hydroxyl ?
sulfhydryl
what are the special groups in arginin and histidine called
guanidinium
imidazole
which amino acid is often found in the active site of enzymes and how does it function
histidine
functions by acid base cataysis the release and uptake of protons by the imidazole ring
peptide bonds are quite stable kinetically because
because the rate of hydrolysis is quite low
the mean molecular weight of amino acid is
110 g/mol
what determines the 3-dimensional structure of proteins
the primary structure (aminoacid sequences)
what is the condition of peptide bonds in terms of charge? and why is it helpful?
uncharged allowing the polymers of aminoacids to form tightly packed globular structures
which configuration is favourable by most peptide bonds
trans
what is steric exclusion
Two atoms cannot exist in the same place at the same time
most common cis peptide bonds are found in ….. linkages and why? and what is the process called?
x-prolin linkages. because the nitrogen atom is bounded to 2 tetrahedral carbon atoms. Thi makes the difference between cis and trans conformation very small and therefore, the configuration of this peptid bond can interconvert
the distance of a helical turn? how many aminoacids? the degree of rotation per amino acid in the helical structure?
5,4 Å
3,6 aminosyrer per helical turn
100 degrees
why are right-handed helices energetically more favourable than left-handed helices
because of the less steric clashes
What are supersecondary structures or motifs
certain combinations present in many proteins and exhibit similar functions
alpha-helical coiled coil
2- right handed alpha helices wound around each other in a left handed manner (left-handed superhelix)
heptad repeats
repitition of 7 amino-acids
which agents effectively disrupt a protein’s non covalent interactions
urea, guanidium chloride
How can disulfide bonds be cleaved?
reversibly by reducing agents such as B-mercaptoethanol
The function of chaperons
they step in and make sure that folding progresses seemingly + the proteins don’t form aggregates
aminoacids commonly observed in turns
glycin, asparagin and prolin
which ones tend to disrupt a-hellices and why
valine, threonin and isoleucin because of steric clashes
serine and asparagine? because their side chains contain hydrogen donors and acceptors that commpete for the side chain
prolin disrupts both alpha and B structures
because prolin lacks an NH and the ring is restricted to certain angles
Unstructured regions in intrinsically disordered proteins are rich in which types of aminoacids
charged and polar amino acids with dew hydrophobic ones
