Effect of Ascending an Ordinary Flight of Stairs on the Work of the Heart Observations on Normal Individuals and on Patients withCoronary Heart Disease By JAMESA. L. MATHERS,M.D.,HAROLD I. GRIFFEATH,M.D.,ROBERTL.LEVY,M.D., AND JOHNL. NICKERSON,PH.D.he blood pressure cuff andelectrocardiograplhic electrodes remained on the ex-tremities during the exercise to facilitate the speedof making the observations during the recovery period. All obstructions, such as closed doors andotherpersons, wereremoved fromthe path ofthesub-ject being tested.
Restriction enzymes, also known as restriction endonucleases, are enzymes that cut a DNA molecule at a particular place. They are essential tools for recombinant DNA technology. The enzyme scans a DNA molecule, looking for a particular sequence, usually of four to six nucleotides. Once it finds this recognition sequence, it stops and cuts the strands. This is known as enzyme digestion. On double stranded DNA the recognition sequence is on both strands, but runs in opposite directions.
Cutting and Splicing DNA Molecules. If you want to insert a piece of new DNA (foreign DNA) into an existing strand you'd have to cut the existing strand, somehow position the foreign DNA, and then join the strands. This joining is called ligation and can be done with the enzyme DNA ligase. Restriction enzymes are produced by bacteria and function to protect bacteria from foreign DNA (like viruses). Restriction enzymes work by degrading foreign DNA. Restriction enzymes recognize and cut the sugar phosphate backbone of the DNA molecule at specific sites on a strand of DNA. The restriction enzyme recognition site is determined by a specific sequence of nucleotides. Thousands of restriction enzymes have been isolated, although many share the same recognition sequence.