Microbial Genetics

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Microbial Genetics
2015-10-25 23:43:23
Microbiology Microbial Genetics Lecture
Microbiology lecture exam 2
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  1. Give the role of each of these enzymes during DNA replication:
    1. Helicase
    2. Primase 
    3. DNA polmerase III
    4. DNA polymerase I
    5. DNA ligase
    • Helicase: seperates the DNA strands
    • Primase: provides a starting place for DNA polymerase III
    • DNA Polymerase III: synthesizes the new strands of DNA complementary to the original
    • DNA polymerase I: Cleans RNA out of the new DNA
    • DNA ligase: seals the breaks in the backbone of the new DNA
  2. Fill in the blanks:
    The first step in DNA replication is to seperate the original 2 strands. This occurs within the bacterial chromosome at a specific sequence called the __a__. The enzyme that disrupts the hydrogen bonds that hold the twostrands together is called __b__. Two teams of enzymes begin to copy the DNA, moving away from each other.
    • A. Origin of replication
    • B. Helicase
  3. Fill in the blanks: 
    The area called the replication fork is where the original DNA has been newly separated and replication is just beginning. The enzyme that synthesizes the new DNA strands is __a__, which makes polymers of DNA.  First, it needs a template for the ordering of the new nucleotides, provided by the __b__, plus it cannot start on its own. The enzyme that helps the first enzyme get started can start new chains of nulceotides on its own and is called __c__. However, the chains it synthesizes are RNA, which is complimentary to the original strand.
    • A. Polymerase III
    • B. Original DNA strand
    • C. Primase (RNA polymerase)
  4. Fill in the blanks:
    After the primers are in place, DNA polymerase III synthesizes new DNA strands complimentary to the parental strand. It brings in new nucleotides at the __a__ end of the primer and __a__ of the growing chains. There are two strands growing simultaneously, one strand growing towards the replicatioin fork, called the __b__. On the other side, a strand is growing away from the fork, called the __c__. The strand growing away from the fork has polymerase III synthesizing small pieces at a time, called the __d__ fragments. After the work of primase and polymerase are completed, the RNA polymers that were created by primase need to be removed and replaced with the new DNA. This is the job of the __e__. Lastly, because the new DNA is being synthesized in pieces, there are places in the DNA where fragments are next to each other but not attached by covalent bonds. This is the job of __f__, an enzyme that forms the covalent bonds between the fragments.
    • A. 3'
    • B. Leading strand
    • C. Lagging strand
    • D. Okazaki 
    • E. DNA polymerase I
    • F. DNA ligase
  5. Fill in the blanks of this transcription process:
    During the process of transcription, the info in the DNA is copied into a molecule of __a__. The enzyme that reads the DNA and synthesizes the complementary molecule for transcription is called __b__. This enzyme locates the beginning of the gene by finding the __c__, which is a specific DNA sequence that marks the beginning of the gene. Beginning at the __c__, the enzyme unwinds the DNA strand to build the complementary strand, which detaches from the DNA as it is growing. The enzyme continues to grow the new complimentary strand, until it reaches the end of the gene sequence, called the __d__. Here it detaches from DNA, releases the new strand into the cell. The new strand is released as __e__, where it will to into the __f__ to be translated into protein.
    • A. RNA
    • B. RNA polymerase
    • C. Promoter
    • D. Transcription terminator.
    • E. mRNA
    • F. Ribosomes
  6. Fill in the blanks of this translation process:
    Once mRNA enters the ribosome, it must be decoded and read, bringing the correct amino acids into position. This decoder is called the __a__. The amino acid sequence grows into a __b__, which eventually folds together to form a protein. The mRNA code is read in __c__, which are groups of 3 nucleotides, which represent specific amino acids.
    • A.. tRNA
    • B. Polypeptide chain
    • C. Codons
  7. T or F: When reading mRNA, you read from 3' to 5' end.
    False: 5' to 3'
  8. This is the process of reading mRNA. Fill in the blanks:
    When reading mRNA, you begin at the __a__ codon closest to the __b__ (3' or 5') end. Each codon is representative of an __c__, which there are 21 in all. Reading is finished when you get to the __d__ codon.
    • A. Start
    • B. 5'
    • C. Amino acid
    • D. Stop
  9. This part of the tRNA binds to the codons in mRNA, which are also specific to an amino acid.
  10. What is the mutation called that results in a small change in a single gene.
    Point mutation
  11. What is it called if a point mutation has no effect in DNA sequence?
    Silent mutation
  12. What kind of mutation is this:
  13. What kinds of changes can a substitution mutation make?
    • Silent Mutation: change of codon that produces the same amino acid. no change in protein synthesis
    • Change in codon that produces a single different amino acid. Small change in protein (ex: sickle cell anemia)
    • The most serious change is if a codon is changed to a stop codon. This will stop the protein from functioning.
  14. What kind of mutation is this:
  15. What does recombinant mean?
    When a bacteria receives DNA from a donor and it includes it in its own DNA
  16. What is the difference between vertical gene transfer and horizontal gene transfer?
    • Vertical: when parents pass genes to offspring through sexual reproduction
    • Horizontal: When genes are passed to cells of the same generation
  17. How did Frederick Griffiths use mice to discover the existance of DNA?
    • If a bacterial cell dies, it can leave behind its DNA as free DNA fragments. He heat killed a deadly bacteria, injected them into mice, and the mice survived. He then took the heat killed bacteria, and mixed it in with non-fatal bacteria.
    • The non-fatal bacteria were injected into the mice, and the mice ended dying.
    • He proved that something was passed on from the first set of bacteria, turning the non-lethal bacteria, into a lethal one.
  18. What is conjugation?
    When bacteria acquire DNA from other living bacteria, which reuires direct contact between two bacterial cells
  19. T of F: Many gram-positive bacteria connect to each other via sex pili.
    False: many gram-negative bacteria do
  20. Cells that can make a sex pilus are called __a__, and will conjugate only with cells that are __b__.
    • A. F+
    • B. F-
  21. What happens to the F- cell after the donor cell sends a copy of the F factor to it?
    The F- cell becomes a F+ cell
  22. In conjugation, cells that insert the F factor into the main chromosome are called what?
    Hfr (high-frequency recombination)
  23. T or F: Hfr cells cannot initiate conjugation with F- cells
    False: They do have that potential, but now they can pass portions of their main chromosome through the sex pilus.
  24. This process of gene transfer is the simplest, where cells pick up naked fragments of DNA that are released from neighboring bacteria.
  25. How does an Hfr cell transfer its genes?
    • It has a sex pilus and attaches to the recipient cell.
    • It starts copying its DNA, beginning at one end of the integrated F factor.
    • The receiving cell can actually receive the entire chromosome of the donor cell, but this process takes 90 minutes and will usually be interrupted.
    • Interruptions means the receiving cell will only receive fragments of the chromosome, and usually remains F-, unless the entire chromosome does get transferred (in that case the receiving cell becomes F+)
    • If this happens, the cell becomes recombinant.
  26. What does transduction mean in gene transfer?
    It involves the movement of genes from one bacteria to another by a virus.
  27. Viruses that attack bacteria are called ___.
  28. How does transduction work?
    • When a phage attacks a bacterial cell, it can destroy the cell and the cell's DNA. 
    • Once the components of the new phage are manufactured, the assemble themselves and leave the host cell, and then move on to another host.
    • Sometimes during assembly, they make pick up fragments of the host's DNA, which can then be inserted into a new host cell's DNA
    • This means the destroyed cell was the donor, and the recipient cell (the invaded cell) becomes recombinant.