Protein structure

[deleted388502]

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Hi!

I was wondering if someone could clarify primary/secondary/tertiary/quaternary structure for me.
I know the basic definitions; primary structure is # and sequence of AA, secondary is protein conformation with alpha helix and beta pleated sheet, tertiary is 3D shape formed when chair folds, and quaternary is the interactions of multiple polypeptide chains, but I get confused about how to classify information they give you about a protein under these categories.

For example, I was under the impression that disulfide linkages were a part of the primary structure between cysteine from what I have in my class notes from biology, but EK lecture exam told me it was for tertiary structure. I'm hoping someone can just maybe just explain the different levels a little more detail.

Thanks!

 

[Czarcasm]

Hi!

I was wondering if someone could clarify primary/secondary/tertiary/quaternary structure for me.
I know the basic definitions; primary structure is # and sequence of AA, secondary is protein conformation with alpha helix and beta pleated sheet, tertiary is 3D shape formed when chair folds, and quaternary is the interactions of multiple polypeptide chains, but I get confused about how to classify information they give you about a protein under these categories.

For example, I was under the impression that disulfide linkages were a part of the primary structure between cysteine from what I have in my class notes from biology, but EK lecture exam told me it was for tertiary structure. I'm hoping someone can just maybe just explain the different levels a little more detail.

Thanks!

I've seen it presented both ways, but given what occurs naturally or spontaneously, I think the more appropriate categorization is tertiary structure for cysteine bonds. The reason being is their linkage is in large part facilitated by the interactions of the other amino acids in the folded structure. Some professors also insist that it's a primary structure if it's a cysteine linkage within the same amino acid chain and that's also technically true, but sort of disregards what we know about protein folding in general. I prefer to think of primary structure as the sequence of amino acids as opposed to all the covalent bonds linking the amino acids for this reason. I think AAMC realizes this and generally tries to avoid questions where confusion like this can happen. More than likely, it would be something straightforward, like the structure of a multisubunit protein like hemoglobin (quaternary), or the structure of an individual subunit of hemoglobin (tertiary), etc.

 

[Chrisz]

Hi!

I was wondering if someone could clarify primary/secondary/tertiary/quaternary structure for me.
I know the basic definitions; primary structure is # and sequence of AA, secondary is protein conformation with alpha helix and beta pleated sheet, tertiary is 3D shape formed when chair folds, and quaternary is the interactions of multiple polypeptide chains, but I get confused about how to classify information they give you about a protein under these categories.

For example, I was under the impression that disulfide linkages were a part of the primary structure between cysteine from what I have in my class notes from biology, but EK lecture exam told me it was for tertiary structure. I'm hoping someone can just maybe just explain the different levels a little more detail.

Thanks!

You are confused what is a disulfide linkage. disulfide linkages are formed by dehydrogenation of two cystein R groups (in this case, -SH + SH--> -S-S-.) It is not connected by peptide bond. Peptide bond is formed by condensation (removal of water molecules. The amino group of the second amino acid attacks the carbonyl carbon of the first amino acid. In the process, a water molecule is formed as a byproduct). Primary structure only considers about the sequence formed by peptide bonds. Disulfide bonds are formed to stabilize the tertiary structure or quanternary structure. For example, an amino acid sequence is folded back upon itself, and it makes a disulfide bond -S-S- to tabilize the 3 dimensional (folded upon itself) structure. Two separate polypeptides can be connected to each other by forming a disulfide linkage (in thise case, quanternary structure).

 

[deleted388502]

You are confused what is a disulfide linkage. disulfide linkages are formed by dehydrogenation of two cystein R groups (in this case, -SH + SH--> -S-S-.) It is not connected by peptide bond. Peptide bond is formed by condensation (removal of water molecules. The amino group of the second amino acid attacks the carbonyl carbon of the first amino acid. In the process, a water molecule is formed as a byproduct). Primary structure only considers about the sequence formed by peptide bonds. Disulfide bonds are formed to stabilize the tertiary structure or quanternary structure. For example, an amino acid sequence is folded back upon itself, and it makes a disulfide bond -S-S- to tabilize the 3 dimensional (folded upon itself) structure. Two separate polypeptides can be connected to each other by forming a disulfide linkage (in thise case, quanternary structure).

Mmmmmmmm. Brilliant answer. I was in fact confused about this. Thank you so much!!!