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Microbio Test 3 Review (ch 8, 10, 11) > Ch 8 > Flashcards

Ch 8 Flashcards

1
Q

Describe how DNA serves as genetic info

A

the structure of DNA helps explain two primary features of biological info storage.

-first, the linear sequence of bases provides the actual info

-genetic info is encoded by the sequence of bases along the strand of DNA, in much the same way as our written language uses linear sequence of letters to form words and sequences

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2
Q

Describe and recognize the process of DNA replication (aka DNA synthesis), including the function of the necessary enzymes and directionality of replication. Be able to repeat the replication fork

A

DNA synthesis begins at the origin of replication (modeled
as oriC) in prokaryotes

Formation of a replication fork must occur: zone of
unwound DNA where DNA polymerization is occurring

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3
Q

steps in DNA synthesis (DNA replication)

  1. DNA topoisomerases like DNA gyrase
A

remove the supercoils in the DNA to create linear DNA

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4
Q

steps in DNA synthesis (DNA replication)

  1. DNA topoisomerases like DNA gyrase
A

remove the supercoils in the DNA to create linear DNA

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5
Q

steps in DNA synthesis (DNA replication)

  1. DNA is nicked: DNaA proteins bind to the
A

origin and cleave the hydrogen bonds between complementary strands

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6
Q

steps in DNA synthesis (DNA replication)

  1. Next, DNA helicase acts to unwind
A

the DNA for a short distance and expose it as 2 single-stranded regions

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7
Q

steps in DNA synthesis (DNA replication)

  1. next, single-stranded binding proteins (SSBs) bind to these exposed
A

regions and prevent them from re-annealing to one another

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8
Q

steps in DNA synthesis (DNA replication)

  1. an RNA primer is synthesized against the template
A

ssDNA by primase

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9
Q

steps in DNA synthesis (DNA replication)

  1. Extension of DNA or polymerization (adding 3’ end) is performed by DNA polymerase III
A

occurs continuously on the leading strand

occurs discontinuously on the lagging strand creating okazaki fragments
new primers have to be added as
the fork ‘moves’ and exposes new
DNA ahead of the primer

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10
Q

steps in DNA synthesis (DNA replication)

  1. Once DNA synthesis is complete along the template the RNA primers must be
A

removed and replaced by DNA nucleotides
the RNA primers are removed by
DNA polymerase I proofreading
after the synthesis step

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11
Q

steps in DNA synthesis (DNA replication)

  1. Okazaki fragments are sealed together by DNA ligase to form
A

a continuous piece of DNA (no RNA nucleotides)

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12
Q

semi-conservative DNA replication

A

each chromosome now has 1 single strand of parental DNA (template) and one newly synthesized strand of DNA (daughter)

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13
Q

major enzymes in DNA synthesis

helicase

A

unzipping the DNA helix

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14
Q

major enzymes in DNA synthesis

gyrase

A

helping to untangle the DNA supercoils

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15
Q

major enzymes in DNA synthesis

primase

A

synthesizing an RNA primer

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16
Q

major enzymes in DNA synthesis

DNA polymerase III

A

adding bases to the new DNA chain; proofreading the chain for mistakes

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17
Q

major enzymes in DNA synthesis

DNA polymerase I

A

removing primer, closing gaps, repairing mismatches

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18
Q

major enzymes in DNA synthesis

ligase

A

final bonding of nicks in DNA during synthesis and repair

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19
Q

Describe and recognize the differences between DNA and RNA.

A

DNA
- deoxyribose sugar
- double stranded
-bases: Adenine-Thymine Cytosine-Guanine

RNA
-ribose sugar
-single stranded
-bases: Adenine-Uracil Cytosine-Guanine

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20
Q

Transcription Steps

  1. transcription begins when RNA polymerase bind to the
A

promoter sequence

21
Q

Transcription Steps

  1. transcription proceeds in the
A

5’->3’ direction

22
Q

Transcription Steps

  1. transcription stops when it reaches the DNA-based
A

terminator sequence

23
Q

Transcription Steps

  1. the mRNA transcript looks just like the coding strand (U’s for T’s) because
A

RNA polymerase adds nucleotides complementary to the template strand (5’ to 3’)

24
Q

What enzyme performs transcription?

A

RNA polymerase

25
Q

Steps in Translation: Initiation

30S and 50S ribosomal subunits assemble with

A

mRNA and Met-tRNA

26
Q

Steps in Translation: Initiation

  1. process is aided by several proteins called
A

initiation factors (IF’s)

27
Q

Steps in Translation: Initiation

  1. begins when the AUG start codon is situated in the
A

P site (peptidyl site) of the ribosome

28
Q

Steps in Translation: Initiation

  1. allows the anticodon portion of Met-tRNA to bind to the
A

AUG of the mRNA

29
Q

Steps in Translation: Elongation

amino acids are brought into the ribosome to

A

elongate the polypeptide, then the ribosome is translocated to a new codon

30
Q

Steps in Translation: Elongation

  1. A (aka receptor) site is filled:
A

Aminoacyl tRNAs (tRNA + amino acid) are brought to the A site of the ribosome (specific amino acid selected by complementary tRNA anticodon- mRNA codon binding)

this is aided by protein elongation factors (EFs)

31
Q

Steps in Translation: Elongation

  1. Transpeptidation
A

the amino acids in the P site join the new amino acid in the A site via formation of a peptide bond between aa’s

32
Q

Steps in Translation: Elongation

  1. Translocation
A

movement of the ribosome along the mRNA occurs to move a new codon into the A site

33
Q

Steps in Translation: Elongation

  1. Translocation

how does it work?

A

A site –> P site

P site –> E site (aka exit)

A site will be emptied so a new aminoacyl tRNA can enter it

uncharged tRNA in the E site dissociates from the ribosome completely

34
Q

Steps in Translation: Termination

occurs when a stop codon enters the

A

ribosome’s A site

aided by protein release factors (RF’s) which recognize stop codon

35
Q

Steps in Translation: Termination

  1. completed polypeptide is cleaved from tRNA and ribosome subunits
A

dissociate

36
Q

Steps in Translation: Termination

  1. subunits are free to form new
A

initation complexes and repeat the entire process on a new mRNA strand

37
Q

coupled transcription/translation,

A

Prokaryotes are much more
efficient at protein expression
than eukaryotes

  • Since there is no membrane to
    separate the DNA from the
    cytoplasm, translation of
    mRNA can start as soon as a
    transcript is produced
38
Q

transpeptidation

A

the amino acids in
the P site join the new amino acid in
the A site via formation of a peptide
bond between aa’s

39
Q

translocation

A

movement of the
ribosome along the mRNA occurs to
move a new codon into the A site

40
Q

mutation:

A

change in genetic material- within the nucleotide sequence

41
Q

point mutation:

A

a single base (nucleotide) change

only affects 1 codon

42
Q

missense mutation

A

results in a different amino

43
Q

silent (aka neutral) mutation

A

results in the same amino acid code still being encoded

44
Q

nonsense mutation

A

results in the conversion of an affected codon from endoding an amino acid to becoming a stop or nonsense codon

45
Q

frameshift mutation

A

results in multiple changes

46
Q

transformation

A

Naked (free) DNA/plasmids in
the environment can be taken
up by a cell

  • For successful HGT &
    recombination: this DNA must
    recombine into chromosome
    by homologous recombination
  • Exception: a whole plasmid can
    be taken up and remain free in
    the cytoplasm!
  • Non-homologous genes will be
    degraded (= unsuccessful
    HGT/recombination)
47
Q

transduction

A

HGT mediated by a bacteriophage
(bacterial virus) carrying DNA into a host as it
‘infects’ the host

  • A incorrectly packaged bacteriophage carries bacterial
    chromosomal DNA into the cell it infects
  • Called a transducing phage
  • Cell can gain new genes via homologous recombination of
    the introduced DNA (if HGT is successful)
  • If there is no homologous genes in the new host, the
    transferred DNA could also be degraded (this would be
    unsuccessful HGT)
48
Q

transposons

A

Segments of DNA that can move from one region of DNA to
another = ‘jumping genes’

  • Contain a gene for the transposase, enzyme that helps it move
    (for cutting and resealing DNA)
  • Insertion sequences only have the transposase gene
  • Composite (complex) transposons carry other genes plus
    transposase (which is often sandwiched by two insertion
    sequence
49
Q

conjugation

A

Cell-to-cell transfer of a plasmid. The original cell retains the
plasmid and one strand moves into the recipient cell (where
the other strand is replicated)

  • Also called mating but its not sexual reproduction!

Requirements for conjugation:
* Cell-to-cell contact between donor & recipient cells via a
pilus made by the donor cell

  • tra genes - these encode the pilus and other apparatus
    necessary for conjugation
  • oriT (origin of transfer): this is the site where rolling-circle
    replication begins to make a copy of the plasmid DNA that
    is exchanged with the neighboring cell (in contact via pilus)

Microbio Test 3 Review (ch 8, 10, 11) (5 decks)

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