In terms of structure: both are composed of amino acids.
A peptide is when at least two amino acid are linked together.
A protein is composed of multiple amino acids and have a secondary, tertiary and even quaternary structure.
In terms of function: larger molecules have more complex functions.
Peptides can act as a intracellular or extracellular ligands ...
much like cellulose, chitin strands are bonded to other strands by hydrogen bonds. here is a slide share with a breakdown of the structure.
It is crosslinked in the sense strands are linked to other strands in such a way that most enzymes cannot access it to break it down. this is the same thing that makes wood last untreated. In a strictly chemistry sense ...
Alternative splicing and Post translational modifications such as acetylation, methylation, phosphorylation of amino acid residues play major role in increasing the diversity found in proteome compared to genes.
If you scroll down through the uniprot entry you will come to a section with the heading PTM/Processing.
From this you can see that the first 18 amino acids are a signal peptide.
You can learn more about signal peptides from any good introductory textbook covering cell-biology — alternatively Khan Academy is a good source for learning the basics.
If you have ever used a natural bath sponge, you know that the structure of a sponge's spongin skeleton is great for absorbing water and squeezing that water back out. The sponge's skeleton contains millions of tiny holes, all connected in a massive network of internal tunnels, through which the sponge takes in food and eliminates waste. It feeds by use of ...