What is the act of two bacteria joining and exchanging DNA?
It is called bacterial conjugation, this is not sexual reproduction, since no exchange of gamete occurs.
many antibiotics like penicillin act on the bacterial cell wall and break the NAG-NAM bonds, so there is lysis hence death of bacteria, others like tetracyclin stop protein synthesis and so it stops growth, mitomycin and actinomycinD cause breaks in the DNA. So they can act in varied ways but their job is to kill.
What do biologists use to cut DNA molecules at a specfic sequence of nucleotides to make smalller fragments?
Restriction enzymes, also known as restriction endonucleases, are used to cut DNA into smaller fragments. Restriction enzymes are found in bacteria, where they act like molecular scissors by cutting up DNA from invading viruses or bacteriophages. Each restriction enzyme recognizes a specific nucleotide sequence and cuts the DNA at that site. This process makes restriction enzymes extremely useful in biotechnology where they are used in procedures such as DNA cloning, DNA fingerprinting, and genetic engineering…
Do you mean what is the difference between DNA w/in chromosomes and DNA that is not? the DNA in chromosomes is tightly bound up (to histones) and therefore can not be accessed to be transcribed or replicated. Also this DNA may be methylated, or otherwise made inaccessible to enzymes that might act on it