What is the role of dideoxynucleotides in DNA sequencing?

Which of the following statements about antibody molecules are true and which are false?  A single cell always makes only one unique antibody

During HIV viral infection, the Tat protein acts to: 

The structure of DNA has the following properties The bases are directly attached to the deoxyribose

A ribonucleotide triphosphate used in RNA synthesis has an OH group on this carbon in the sugar portion of the nucleotide:      4′

  This DNA sequence occurs within the coding sequence of a gene. The first three nucleotides (underlined) code for glutamic acid (Glu).  The following DNA mutation is likely to result in a shorter than normal mRNA: G -> C at position 70  

Which of these DNA alterations can be repaired by base excision repair? 

x   This DNA sequence occurs within the coding sequence of a gene. The first three nucleotides (underlined) code for glutamic acid (Glu).  The following DNA mutation is likely to result in a shorter than normal mRNA: A -> T at position 82

RNA contains uracil instead of cytosine

A ribonucleotide triphosphate used in RNA synthesis has an OH group on this carbon in the sugar portion of the nucleotide:      2′