Microbial Genetics Flashcards
In E. coli, the DNA is twisted by what enzyme?
Topoisomerase II or DNA gyrase
Define the process of DNA replication
- Two strands of parental DNA are unwound and separated from each other in one small DNA segment after another
- Free nucleotides are matched up to the exposed bases of the single-stranded parental DNA
- Then the parental DNA is unwound a bit further to allow the addition of the next nucleotides
- The original strand and the newly synthesized daughter strand rewind
What is the point at which replication occurs called?
Replication fork
Why is DNA replication called semiconservative replication?
Because each new double-stranded DNA molecule contains one original, conserved strand and one new strand
What enzyme is involved in the process of adding new nucleotide to the growing DNA strand?
DNA polymerase, which can add new nucleotides to the 3’ end only (5’ –> 3’ direction)
Function of RNA Primer
RNA primer is needed to start synthesis. DNA polymerase can then add nucleotides to the 3’ end of the RNA.
What is leading strand? What is lagging strand?
- Leading strand: the DNA stand that is continuously synthesized
- Lagging strand: since DNA polymerase can only add nucleotides to the 3’ end, one new DNA must be synthesized in pieces consisting Okazaki fragments.
What is transcription?
The synthesis of a complementary strand of RNA from a DNA template
Explain the transcription process
- RNA polymerase binds to the DNA promoter
- RNA ploymerase assembles free nucleotides into a new chain
- RNA synthesis continues until RNA polymerase reaches DNA terminator
- Single-stranded mRNA are released from the DNA
Explain the transcription process
- RNA polymerase binds to the DNA promoter
- RNA ploymerase assembles free nucleotides into a new chain
- RNA synthesis continues until RNA polymerase reaches DNA terminator
- Single-stranded mRNA are released from the DNA (and transported to ribosomal RNA)
There are 64 possible codons but only 20 AAs, what is this situation called? Why is it important?
- It’s called degeneracy of the code
- Degeneracy allows for a certain amount of change, or mutation in the DNA w/o affecting the protein ultimately produced
List the 3 nonsense or stop codons
UAA
UAG
UGA
List the start codon. What AA does it code for?
AUG
Methionine – the initiating methionine is often removed later, so not all proteins begin with Met.
Explain the translation process
- mRNA is transported to the Ribosome; a tRNA carrying the first AA is paired w/ the start codon on mRNA
- - The place on the ribosome where the first tRNA sits is called the P site - A tRNA carrying the 2nd AA approaches (at A site of the Ribosome)
- The ribosome moves along the mRNA until the wnd tRNA is in the P site, and the process continues
- When the ribosome reaches a Stop codon, the polypeptide is released
- Finally, the last tRNA is released, and the ribosome comes apart
Why can’t the RNA transcrip by used for translation in Euk. cells?
- Euk. genes are composed of Exons and Introns, which are transcribed to RNA by RNA polymerase
- - Exons: The regions of DNA which can be expressed
- - Introns: The intervening regions of DNA that do not encode protein - The long RNA transcript must be processed by ribozymes to remove the intron-derived RNA and splice together the exon-derived RNA, producing an mRNA
- The mature mRNA then travels to the cytoplasm, where it is used by rRNA to direct protein synthesis