Question

Which has a wider array of structures: proteins, DNA, or RNA? Explain why.

In your own words, explain common functional relatedness, structural relatedness, and ancestral gene relatedness of conserved regions of proteins.

Explain why protein domains that contain structurally or functionally important amino acid sequences would be conserved between organisms that are very distantly related.

Why are cysteines important to the structure of a protein?

Explain the role of p53 and how its mutation leads to increased growth rate in the cell.

Which mutations most commonly lead to cancer – somatic cell or germ-line?

How do mutations lead to natural selection?

Answer 1

Proteins have wider array of structures. The structural conformations include primary (1⁰), secondary (2⁰) tertiary (3⁰) and quarternary (4⁰). Primary structure constitute linear chain of amino acids. Secondary structures include alpha helix and beta pleated sheet. Some proteins have alpha helix and some other have beta sheet structure. Collagen has triple helix and hemoglobin has a quarternary structure.

Conserved sequences are similar or identical sequences in nucleic acids (DNAand RNA) or proteins across species or within a genome. Conservation indicates that a sequence has been maintained by natural selection. A highly conserved sequence is one that has remained relatively unchanged far back from the ancestors in the phylogenetic tree, and hence far back in geological time. Proteins descending from a common ancestor usually conserve certain features of sequence, structure or function. These features can often be used to assess evolutionary relationships. High sequence similarity implies protein homology,

Conserved amino acid sequences and structural similarity between proteins or protein domains in organisms that are very distantly related is an indication of their divergent evolution from a common ancestor, in other words, it is evidence of homology.

Presence of amino acid cysteine lead to the formation of a disulfide bond with another cysteine. Because it has a very reactive sulfhydryl group at its side chain. This puts cysteine in special position that cannot be replaced or substituted by any other amino acid. Because disulfide bridges formed by cysteine residues are permanent component of protein primary structure.

The TP53 gene provides instructions for making a protein called tumor protein p53. This protein prevents the cell from dividing and signals it to undergo apoptosis or the death of such cells with mutated or damaged DNA. By stopping cells- with mutated or damaged DNA - from dividing, p53 helps prevent the development of tumors.

Inactivation of the p53 tumor suppressor gene is a frequent event in tumorigenesis or tumor formation. In most cases, the p53 gene is mutated, giving rise to a stable mutant protein whose accumulation is regarded as a hallmark of cancer cells. Mutant p53 proteins not only lose their tumor suppressive activities but often gain additional oncogenic functions that endow cells with growth and survival advantages. Studies suggest that mutations in the p53 gene were shown to occur at different phases of the multistep process of malignant transformation, thus contributing differentially to tumor initiation, promotion, aggressiveness, and metastasis.

A somatic mutation occurs in a single cell in developing somatic tissue. A germinal or germ-line mutation which occurs in sex cells is passed on to the next generation. In a study of "Differences between germline and somatic mutation rates in humans and mice" by Brandon Milholland et al. suggest that somatic mutation rate is higher than germ-line mutation rate. This could be because of the accumulation of unrepaired somatic damages, as aging progresses.

Mutation and natural section are key factors of evolution. If the mutation makes the individual adaptable with its environment, it leads to the existence of the same as naturally selected. But if the mutation adversely affects the organism for its existence with the environment, the mutation is to be removed.