134 ❯ STEP 4. Review the Knowledge You Need to Score High
Nonsense mutation:substitution of wrong nucleotide into DNA that produces an early stop
codon.
Transcription:process by which mRNA is synthesized on a DNA template.
RNA processing:introns (noncoding) are spliced out, exons (coding) glued together: 3′poly-A tail,
5 ′G cap.
Translation:process by which the mRNA specified sequence of amino acids is lined up on
a ribosome for protein synthesis.
Codon:triplet of nucleotides that codes for a particular amino acid: start codon=AUG;
stop codon=UGA, UAA, UAG. (For specifics on translation, please flip to text for a good
description.)Promoter:base sequence that signals start site for transcription.
Repressor:protein that prevents the binding of RNA polymerase to promoter site.
Inducer:molecule that binds to and inactivates a repressor.
Operator:short sequence near the promoter that assists in transcription by interacting
with transcription factors.
Operon:on/off switch for transcription. Allows for production of genes only when needed.
Remember the lac operon—lactose is the inducer, when present, transcription on; when
absent, it is off.
Viruses:Parasitic infectious agent unable to survive outside the host; can contain DNA or
RNA, or have a viral envelope (protective coat).- Lytic cycle:one in which the virus is actively reproducing and kills the host cell.
- Lysogenic cycle: one in which the virus lies dormant within the DNA of the host cell.
Retrovirus:RNA virus that carries with it reverse transcriptase (HIV).
Prion:virus that converts host brain proteins into misshapen proteins (mad cow disease).
Viroids:tiny plant viruses.
Phage:virus that infects bacteria.
Bacteria:prokaryotic cells; consist of one double-stranded circular DNA molecule; repro-
duce by binary fission (e.g., plasmid—extra circle of DNA present in bacteria that repli-
cate independently of main chromosome).Genetic Recombination
Transformation:uptake of foreign DNA from the surrounding environment (smooth vs.
rough pneumococcus).
Transduction:movement of genes from one cell to another by phages, which are incorpo-
rated by crossover.- Generalized:lytic cycle accidently places host DNA into a phage, which is brought to
another cell. - Specialized: virus leaving lysogenic cycle brings host DNA with it into phage.
Conjugation:transfer of DNA between two bacterial cells connected by sex pili.