Describe the differences and similarities between lecithin and cephalin. Match the words in the left column to the appropriate blanks in the sentences on the right. ResetHelp Lecithins and cephalins are both sphingolipids; they consist of glycerol with fatty acids forming bonds with the first and second groups. The third group of the forms a with phosphoric acid, which forms another bond with an amino alcohol. In lecithins, the amino alcohol is ; in cephalins, the amino alcohol is usually .

this protocol describes a detailed procedure for intracellular flow cytometry staining.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.