Biological molecules

[Junaid456]

Can someone please explain to me the different levels of protein tructure in detail and their importance?

 

[beacon_of_light]

The structure of a single protein chain in its functional form can be considered on three levels:
• primary structure – the sequence of amino acids in a polypeptide chain – the direct product
of the coding sequence in the gene.;
• secondary structure – regular structural arrangements of the polypeptide chain that result
from hydrogen-bonding between peptide bond regions of the chain;
• tertiary structure – the overall folding of a polypeptide chain that arises from interactions
between the amino acid side-chains.
Tertiary structure is maintained by the following bonds :

van der Waals’ forces between non-polar side-chains,
• hydrogen bonding between polar R-groups,
• ionic bonds (salt bridges) between ionised R-groups, and
• covalent disulphide bridges formed between cysteine residues at different locations in the
primary sequence

Quaternary Structure: Linking of more than one polypeptide chains .

 

[larina]

okay...you need to now that there are 4 types of protein structures:-
1)primary structure:- this included the sequence, number and types of amino acid arranged in a poly peptide chain.
2)secondary structure:- this is when a polypeptide chain is coiled into an alpha-helix shape (note that these alpha-helix are hold tightly by hydrogen bonds between -CO and -NH groups in amino acid)
3)tertiary structure:- this is when a polypeptide has a 3D shape(and not in chain form). Different polypeptides have different 3D structure and different funtions. this is because of the different R-groups present in the amino acid.
there are 4 types of bonds in the tertiary structure:-
1. hydrogen bonds----formed between H and -OH groups.weaker than the ionic and covalent bonds. bond are broken by high temps and high pH.
2. Disulphide bonds----these are the bonds formed between the amino acids of 2 cysteine molecules. very strong bonds. bonds are broken by reducing agents.
3. Ionic bonds---bonds formed between amine groups and carboxyllic acid group. bonds broken by high temps and pH changes.
4. Hydrophobic interactions----formed between R groups of non-polar(ie hydrophobic) molecules.

4) quaternary structure:- it is the structure of polypeptide which have 2 or more polypeptide bonds....eg heamoglobin has 4 polypeptide bonds and insulin has 2 polypetide bond. the bons are hold by the bonds in the tertiary strucure

hope u get it!

 

[Junaid456]

Thank you both of you. That was really helpful. Can you please tell me one more thing, Larina. You mentioned that Ionic bonds are formed between Carboxylic and amine groups of an amino acid. Here, are you referring to the functional COOH and NH2 groups attached to the alpha carbon or, in this case, where ionic bonds exist, COOH and NH2 groups are present as part of the R group of amino acids. Can you please help me out?

 

[larina]

ok....these carboxylic acids and amine groups are ionised (they hav a charge)
eg. NH2+(from amine group)----------O-(from COOH) the dotted red line shown is the ionic bond.

 

[Junaid456]

so, these ionised amine and carboxylic groups are from the side (R) chain and not the functional group part of an amino acid?

 

[soumayya]

tertiary structure is only concerned with interactions of the R groups...thus, all the 4 types of bonds (including ionic bonds), are between the R groups of the amino acids in the polypeptide chain...
btw...the NH2 and COOH of the alpha carbon are already involved in bonding (primary structure), to form a strong covalent CONH peptide bond...so the alpha carbon no longer has amine and carboxylic groups...

Hope this helps...

 

[Junaid456]

Thanks. But the hydrogen bonding present in the SECONDARY STRUCTURE which coils (alpha helix) the polypeptide chain is present between the peptide regions (C=0-N-H) of DIFFERENT amino acids, right? :|

 

[soumayya]

yh...the secondary structure is the regular coiling due to hydrogen bonding between the C=0 of a peptide bond and the N-H of another peptide bond 5 amino acids away...