Chapter 6- Secondary Structures of Proteins Flashcards
What happens in sickle cell?
a glutamine is replaced with a valine= alters hemoglobin structures and function.
What does protein function depend on?
on protein structure
What is the relationship of protein sequence to function dependent on?
the 3D folding of proteins and inferring protein functions from these 3D structures (binding sites, catalytic activities, interactions w/ other molecules)
What are the importance of proteins ?
motor proteins, structural components of cells, enzymes, antibodies, hormones, hemoglobin/ myblobin, transport proteins in blood.
What are the 4 levels of protein structure and define them?
primary- amino acid linear sequence (from n term to c term) determines structure and function
secondary- regions of regularly repeating conformation of the peptide chain (a-helices ad beta sheet). joined by turns and loops
tertiary- describes shape of fully folded folded polypeptide chain
quaternary- arrangement of two or more polypeptide chains into a multi subunit molecule
What are the first 5 amino acids residues in lysozyme?
Lys-Val-Phe-Gly-Arg (2,3,4- hydrophobic-faces in)
What makes polypeptides fold in water into 3D structues? (tertiary )
bond rotation within the polypeptide backbone
What causes secondary structure?
regularly spaced hydrogen bonds (a-helix, beta sheet, beta turn, loop)
are alpha helices right or heft handed?
right handed
describe the a-helix structure. shape? what bonds? between what?
cork screw, telephone cord held by H bonds rom -N-H groups and the O- of c+o of the fourth amino acid along chain
what stabilizes the helix ?
the H bonds between back bone atoms Not R groups
which way do the r groups of a helix face?
perpendicular to helix axis
What is a triple helix?eg.
why are they so strong?
typical of what ?
3 polypeptide chain woven together ?
Glycine, Proline, Hydroxyproline, Hydroxylysine
because of the H bonding between -OH groups
collagen, connective tissue, skin, tendons, cartilage (cccts)
Why are helices short and why do they overlap?
so they are strong
a-helices are major components of many proteins, connected by turns. some interesting a helices are…
small DNA binding helices -
Membrane- spanning helices
amphipathic helices
coiled coils
how are a-helices are major component of small DNA binding helices?
fit in the major groove of double stranded DNA
how are a-helices are major component of membrane- spanning helices
?
they have hydrophobic amino amine in the central region that allow the helices to enter the bilayer
how are a-helices are major component of amphipathic helices?
the helices have some hydrophilic amino acids on one side and hydrophobic ones on the other side - integral protein.
Most amino acids like to in an a-helix except for?
Glycine and proline
proline is not an amino acid but a?
imino acid (secondary amino acid, N-bonded to 2 carbons, not bonded to any H )
what do proline residues do?
they act as a-helix breakers
where are proline residues normally found?
at the boundaries of a-helices and in turns
describe beta sheets? shape? what bonds?
the are like an accordion, they can join distant parts of the protein together due to H-bonds
how are beta pleated sheets arranged ?where residues face? bonds? where do r groups extend? eg.
the polypeptide chains are side by side and H bonds forms between chains (residues are rotated 180 from neighbour-side chains protrude on opposite ends). R groups extend above and below sheet. Silk
beta sheets can be parallel or anti parallel
anti= 2 bond close the gap etc.
beta sheet unit, what is the super structure they can form?
beta strand
beta barrels- strands are twisted and at an incline, r groups stick out on either face. r groups inside the barres are often beta-branched or hydrophobics
where do b-sheets fit?
In the minor groove of DNA double helix , can also used in DNA binding but are less common
