Proteins and Nucleic Acids. Also featuring amino acids and polypeptides…. Nucleic Acids. DNA and RNA are informational molecules in eukaryotic cells.
Also featuring amino acids and polypeptides…..
(As with other polymers, the linkage reaction involves hydrolysis. In this case a phosphodiester bond is formed.)
Hydrogen bonds stabilize the pairs of nucleotides in the DNA double helix.
Highly condensed DNA, known as heterochromatin: Arrows indicate the condensed X chromosome (Barr body) at the periphery of the nucleus of a female mammal.
The relationship between nucleic acids and proteins was forged over a period of time in the dim past, and recent appreciation that some mitochondria, protoza and the Archaea differ from multicellular animal cells in details of the triplet code amino acid specification attest to splits in the ancestry during the period of “experimentation”.
A different text gives a different breakdown: 9 nonpolar, 6 polar, etc. It is cysteine that seems to not know where to go... .
Small chains of amino acids (fewer than 40 amino acids – the smallest is 3 amino acids) serve as peptide hormones and neurotransmitters. Examples :
1. messenger RNAs
(mRNAs) code for
the amino acids of a
on a triplet code.
There are 3 stop codons and one initiation codon.
(Note that there is not a 1:1 match of triplets and amino acids – there are 64 triplets and only 20 amino acids, so the code is redundant – some amino acids are coded for by multiple triplets.)
2. Transfer RNAs (tRNAs)
recognize amino acids (actually, a specific enzyme is required to make the attachment) and bring them to
ribosomes, where they line them up based on their complementarity to the mRNA: GUG with CAC, etc.
Post-translational processing of proopiomelanocortin (POMC). POMC in mammals consists of 3 exons, of which exons 2 and 3 are translated. Prohormone convertases 1 and 2 (PC1/2) break the parent POMC peptide into successively smaller peptides by cleavage at paired dibasic amino acid residues consisting of lysine (K) and/or arginine (R). The final products are generated in a tissue specific manner, for example α-MSH and ACTH are not produced by the same cells in the pituitary. The final products include the melanocortins (MSHs and ACTH), β-endorphin (β-end) and corticotrophin-like intermediate peptide (CLIP). There are intermediate peptides whose biological function remains unclear, such as β and γ lipotrophins (β-LPH, γ-LPH).
Millington, Nutrition & Metabolism 2007, 4:18.
In this process, the immature protein is secreted into the endoplasmic reticulum as it is synthesized. Within the ER, the signal sequence is then removed. The segments of the original gene product that will become the alpha and beta chains of the final hormone are folded by a chaperone protein and inked by disulfide bonds to form proinsulin. Removal of the C-peptide loop connecting the two chains results in the final hormone.
Nucleic acids store information (DNA) and
transfer this information into proteins (mRNA, tRNA, rRNA)
Proteins are the most diverse class of molecules in cells; their roles are to execute the information carried in the DNA
Protein function depends on protein structure. The 1o structure of a protein is established by posttranscriptional and posttranslational processing, and provides the basis for higher structural orders, which generally cannot be attained without the assistance of other proteins.