Proteins structure Flashcards
What is the primary structure of a protein
the linear amino acid sequence of the polypeptide chain
What is the secondary structure of a protein
How is it stabilised
the local spatial arrangement of polypeptide backbone – the conformations like helices etc
stabilised by intramolecular and sometimes intermolecular hydrogen bonding of amide groups.
What is the tertiary structure of a protein
the overall 3- dimensional configuration of the protein in space
What is the Quaternary Structure of a protein?
How is it held together?
association between different polypeptides to form a multi-subunit protein
Each of the subunits has its own primary, secondary, and tertiary structure. The subunits are held together by hydrogen bonds and van der Waals forces between nonpolar side chains.
How is a peptide bond formed
Peptide bond formation:
the linking of two amino acids is accompanied by the abstraction of a molecule of water
It occurs between the COO and the NH3
This reaction is also known as a condensation reaction
What are the features of peptide bonds
- Peptide bonds are planar (Straight line)
- Peptide bonds are rigid
- Peptide bonds always adopt a Trans Configuration
- Bonds on either side of the peptide bond are free to rotate
-Why is a peptide bond planar
-What does it mean when planar
- planar bond because it has a partial double bond character.
- Ca, C, O, N, H and Ca all lie in the same plane
Why is the peptide bond RIGID
- because it has a partial double bond character between
C-N and C-O
Why is a Peptide bond always adopting a trans confirmation
The peptide bond nearly always has the trans configuration since it is more favourable than cis
the reason for this is that the cis isomer places the R groups of the two connected amino acids in close proximity to each other thus they may react with each other in cis
What does the amino acid sequence determine
The amino acid sequence of a protein determines:
* The way in which the polypeptide chain folds
* The physical characteristics of the protein
What are the key properties of proteins
- Size
* Number of amino acid residues
* Molecular weight in kDa - (weight of one H Atom) - Isoelectric point
* The isoelectric point, pI, of a protein is the pH at which there is no overall net charge
What stabilises the Alpha Helix
H-bonds between N-H and C=O stabilise the structure of the a-helix
How many amino acids are in one turn of an alpha helix structure?
3.6 amino acids
what is a pitch and how long is it in a alpha helix
The Distance of one turn
0.54 nm
What helix is alpha helix
Right handed helix
