During DNA replication, a complementary strand of DNA is made for each original DNA strand. Thus if a portion of the original strand is tcga actca, then the new strand will be

agcttgagt

Explanation:

DNA is a double helix molecule composed of two complementary DNA strands which are in turn composed of four different nucleotide bases: Adenine (A), Guanine (G), Cytosine (C) and Thymine (T). In the DNA molecule, G and C are bound together as a base pair, while A and T are bound together as another base pair. This complementary base pairing structure means that both DNA strands are complementary to each other. In this case, since the sequence of one strand is "TCGAACTCA", the complementary DNA strand would have the sequence "AGCTTGAGT".