DNA sequences can act as "tape measures of evolution". Scientists analyzing the human genome sequence were surprised to find that some of the regions of the human genome that are most highly conserved (similar to comparable regions in other species) don't code for proteins. What is a possible explanation for this observation? EVOLUTION CONNECTION sequences can act as "tape measures of evolution". Scientists analyzing the human genome sequence were surprised to find that some of the regions of the human genome that are most highly conserved (similar to comparable regions in other species) don't code for proteins. What is a possible explanation for this observation?

Non-coding DNA regions play important roles in regulating transcriptional activity by encoding different types of non-coding RNAs (ncRNAs), acting as scaffold attachment regions, acting as enhancer specific regions, etc.

Explanation:

Historically, it had been believed that non-coding DNA sequences were 'junk DNA' since they don't encode for proteins (beyond the sequences that are transcribed into functional non-coding RNAs, i.e., transfer RNA and ribosomal RNA). However, in the last years, it has been shown that non-coding DNA sequences play critical roles in regulating gene expression and genome function. For example, evolutionary conserved non-coding RNAs (ncRNAs) with regulatory roles on gene expression such as, for example, long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) have been mapped in non-coding DNA sequences, thereby evidencing the functional significance of these regions. In consequence, the conservative nature of certain non-coding DNA sequences evidence that mutations in such regions may have significant deleterious effects, and thereby they could have a negative impact on the fitness of the individual.

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products