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.
A restriction enzyme is a protein that recognizes a specific, short nucleotide sequence and cuts the DNA only at that specific site, which is known as restriction site or target sequence.More than 400 restriction enzymes have been isolated from the bacteria that manufacture them. The number of cuts in an organism's DNA made by a particular restriction enzyme is determined by the number of restriction sites specific to that enzyme in that organism's DNA. 2  A fragment of DNA produced by a pair of adjacent cuts is called a RESTRICTION FRAGMENT.