Organic chemistry: Why does L-albuterol produce less adverse effects in the human body compared to albuterol?
Albuterol is sold as a racemic mixture. This means that there is an equal amount of the left- and right-handed enantiomers of the chiral molecule in the mixture. L-albuterol, also called levalbuterol, is the right-handed enantiomer. Because the human body has stereoselective receptors, the right-handed enantiomer is responsible the pharmacological activity. In the racemic mixture, the inclusion of the left-handed enantiomer causes more adverse side effects.
Cell Biology: What is the role of cyclin in the cell cycle?
Cyclins act as an activating protein and bind to cyclin-dependent protein kinases (Cdks). Together they form a cyclin-Cdk complex, also called a cyclin-dependent kinase complex (CDKC) which is enzymatically active. Activity of CDKC is controlled by phosphorylation, dephosphorylation, and Cdk inhibitors.
Genetics/Genomics: What is the difference between a cis-acting element and a trans-acting factor?
Cis-acting elements, also called cis-acting sites, are regions of non-coding DNA that regulate nearby the transcription of nearby genes. For example, promoters and operators are cis-acting elements. A trans-acting factor are proteins that bind to cis-acting sites to control gene regulation. I find students get confused between cis and trans, because of familiarity with these terms from organic chemistry. It helps to remember that cis-acting sites are segments of DNA, while trans-acting factors are regulatory binding proteins.