Microbe Genetics Flashcards
the entire complement of genes on all chromosomes normally found in an organism;
the hereditary information
Genome
- one entire double-strand of DNA containing multiple genes [The chromosome is
always DNA, except in RNA viruses.] [Also referred to as “nuclear material” or “nucleic acid”.]
Chromosome
- a segment of DNA that contains the genetic code (blueprint) for a functional product (e.g.
code for a specific protein)
Gene
The genetic code is translated into proteins for structural, catalytic, or regulatory functions
within the cell with the aid of
messenger RNA and ribosomes
Genetic code for each protein is carried as a sequence of ____
macromolecule
nucleotide molecules in the nucleic acid
Genes contain
instructions for making proteins
Composition of Nucleic Acids (nucleotide)
5-carbon sugar – either Ribose or Deoxyribose
nitrogenous base (Bound to 1`)
phosphate group (bound to 5` carbon)
Nitrogenous base
Purine (adenine, guanine)
pyrimidine (thymine, cytosine, uracil)
Adenine binds
Thymine (or uracil)
Guanine binds
cytosine
5 is oriented to lateral on one side and 3 is the lateral portion on the opposite side…
makes sense?
Adds next nulceotide to 3`C side ONLY
DNA polymerase
will not add to 5`C
antiparallel concept
antiparallel – the two strands run in opposite directions; i.e. the nucleotide
of the 3’ end of one strand pairs up with the nucleotide of the 5’ end of the adjacent
strand. Strands are not identical, but are complementary.
Strand Direction
- the end on which no phosphate is bound to the 3’ carbon of the
sugar is called the 3’ end; the end in which the phosphate is bound only to the 5’ carbon
is called the 5’ end
form where short lengths of double-stranded DNA helix unwind, thus exposing the separated strands. Unwinding (and rewinding) is due to action of enzymes such as helicase, DNA gyrase, and topoisomerase which break the hydrogen
bonds between bases and/or hold part of the strand stable.
Replication forks (think of a zipper)
binds to DNA and inserts complementary nucleotides thereby
generating a new strand
DNA polymerase
Unwinding (and rewinding) is due to action of
enzymes such as
helicase, DNA gyrase, and topoisomerase
DNA “opening” (4-step sequence)
A short length of “parental” DNA unwinds
Exposes the separated strands
Creates a replication fork
Due to action of helicases, DNA gyrase, etc.
DNA polymerase ____ with accuracy of about 1 error in a billion base
pairs replicated
edits for errors
“Leading” strand is the _____ strand having the 3’ end of the exposed
nucleotide “facing toward” (“leading into”) the replication fork
newly growing (SEE PAGE 4 on PDF)
The newly developing strand grows toward the
replication fork, i.e. “leads into” the
fork
The leading strand is ____ because of enzymatic simplicity and ease of
access to the molecule
continuously replicated
______ is the strand having the 5’ end of the exposed nucleotide facing
toward the replication fork
“Lagging” strand
lags by a fraction of a second
The newly developing “lagging” strand grows _____, which is
accomplished by replicating short fragments, then connecting them together to
form a new complementary strand
away from the replication fork
_____ are needed to initiate strand growth in the
absence of a nucleotide having a 3’ binding site
RNA primer and RNA polymerase
i.e., for the lagging strand’s exposed 5`C
After a RNA primer is in place, thus providing a 3’ site, then ______. However, DNA polymerase cannot join the final
nucleotide of the new fragment to the existing strand because it cannot facilitate
linking to both 3’ and 5’ binding sites
DNA polymerase
takes over the replication and continues to within one nucleotide of the existing,
previously generated strand
facilitates linkage of a nucleotide to both 3’ and 5’ binding
sites simultaneously, inserts a nucleotide to join the newly replicated fragment with
the existing strand
DNA ligase
The replication of the lagging strand is discontinuous because of this process of
producing short fragments and joining them to the existing strand. A new fragment
is generated each time the replication fork advances a short distance. This process
continues throughout the entire replication process until the
entire DNA has been
replicated.
The new double-stranded DNA re-winds into a ___ as the parental DNA unwinds
exposing more nucleotides to be replicated
helix
when the entire chromosome is copied, each double helix consists of one newly synthesized strand of DNA bound to one original parent strand
Semiconservative replication
Large, single stranded molecule of nucleotides
RNA
carries the genetic code
from the DNA to the ribosome
mRNA
3 Nucleotides =
Codon (or 1 amino acid)
1 Codon =
1 amino acid
site of protein
synthesis
Ribosome
transports and then transfers the amino acid to the developing peptide chain
“Transfer RNA” (tRNA)
“Triplet code” means that each set of three Nirtrogenous bases codes for an amino acid
e.g., UUU, UUC= phenylalaline
CCU, CCC, CCA, CCG = proline
Codons are interpreted at the
ribosome (for development of polypeptides)
the site on the tRNA that bonds with the codon on the mRNA (carries the three bases which complement the codon).
Anticodon
Specifies which AA will be carried by the tRNA
Assists protein synthesis by serving as a “facilitator” for the mRNA and tRNA functions
rRNA
Site where codons and anticodons come together
rRNA
Where amino acids form polypeptides (w/ mRNA)
tRNA (anticodon to codon)
code on DNA into mRNA
Transcription
code on mRNA into polypeptide
Translation
the transfer of the genetic code on DNA gene into a messenger RNA (mRNA) strand by means of DNA-dependent RNA polymerase
transcription
Transcription steps
(1) DNA double-helix unwinds a portion and strands separate thus exposing nucleotides of a gene
(2) RNA polymerase binds to the DNA at the promoter site (beginning of the gene)
(3) Complementary RNA nucleotides are joined together in sequence by the RNA polymerase
(4) Transcription ends when the RNA polymerase reaches the termination region of the gene, and the new single-stranded mRNA is released (the DNA re-winds)
Promoter site
(right before) beginning of the gene
Translation steps
(1) mRNA attaches to the ribosome with the “start” codon in place
(2) A tRNA with the complimentary anticodon matches to the codon on the mRNA, thus bringing the first
amino acid into place
(3) As the mRNA codons are matched with complimentary tRNA anticodons, the amino acids are linked together and the tRNA released
(4) Polypeptide chain is released when the reading frame reaches the “stop” codon
Multiple ribosomes can attach/read the same mRNA to simultaneously produce two versions of the same polpypeptide/protein
Neat
are constantly expressed (transcribed and translated into functional products) (60-80% of genes are in this category)
Constitutive genes
Inducible genes
can be “turned on” if the right substrate/enzyme comes along
Repressible genes
can be “turned off” (meaning they’re normally in the “on” position)
related genes that are regulated as a group/series (e.g. genes which code for the enzymes of a single metabolic pathway)
Operon
codes for a “repressor” protein which can bind to the “operator” region
Repressor gene – (located in another portion of the chromosome)
Promoter site
region of the chromosome to
which the RNA polymerase binds during transcription
region of the chromosome which controls (either permits or blocks) access of the RNA polymerase to the structural genes of the operon; site to which the repressor protein binds (or fails to bind)
Operator site
adjacent genes of the operon which direct the synthesis of proteins with related functions and which are regulated as a unit
Genes of the Operon
genes are expressed only when certain environmental conditions are present (e.g. genes for enzymes of a biosynthetic pathway are expressed only when the appropriate substrate is present, i.e. presence of substrate causes Operator site to be unblocked.)
Inducible operon
genes are expressed except when certain environmental conditions are present (e.g. presence of certain metabolic products causes genes for metabolic enzymes to be repressed, thus slowing down metabolism, i.e. presence of metabolic products causes Operator site to be blocked.)
Repressible operon
Mutation
changes (substitutions or deletions) in the sequence of DNA bases, thus changing the genetic code.
Mutation types
Base Substitution
Frameshift mutatiaon
a single base is replaced with another, thus changing the codon. May result in an improper amino acid in the protein
Base substitution
Silent (base substitution)
No change in the protein
Missense (base substitution)
Different amino acid in the protein; usually not highly significant
Nonsense (base substitution)
RNA polymerase is stopped from reading the code resulting in an incomplete, nonfunctional protein
insertion or deletion of bases may shift the codon reading frame of the mRNA in the ribosome
Frameshift mutation
Usually results in missense mutation and significantly different, nonfunctional, or incomplete protein
MUtations caused by
Spontaneous
or
Chemical mutagens, e.g. nitrous acid, base analogs (do not pair properly), (antibiotics)
or
Radiation - X-ray, gamma rays, ultraviolet light
gain, loss, or substitution of entire gene segments or inversions or transpositions of gene sequences to form new combinations of genes.
Recombination
a. Results in major change or non-functional cell.
b. Source of genes may be DNA from the same or another microbe (or RNA for certain viruses)
small, circular, self-replicating piece of DNA in bacteria
Plasmid
Plasmid is separate from the normal chromosomal DNA
These genes often code for antibiotic resistance or disease-causing factors
plasmid gene
integration of the DNA of a temperate bacteriophage (virus) into the bacterial chromosome where it replicates along with the bacterial chromosome
Lysogeny
(Lysogeny) Viral gene may code for antibiotic resistance or ___
disease-causing factors
(Lysogeny) Produces new _____ upon separation from the bacterial DNA
bacteriophage
the transfer of genetic material between donor and recipient cells involving direct cell-to-cell contact
Conjugation
A copy of DNA strand or plasmid is
transferred to the recipient cell
_____ (hollow tube extending from one bacterium to another) is used to transfer DNA from one cell to another (conjugation)
sex pilus (can be plasmid)
the direct uptake of DNA segment from one bacterium to another as “naked” DNA in solution (free DNA from one cell is incorporated into the DNA of another; usually follows cell breakdown and release of DNA after bacterial death)
Transformation
Results in new characteristics for the recipient cell
Transduction
the transfer of DNA from donor bacterium to recipient bacterium by using a bacterial virus as the vehicle (host DNA or plasmid is accidentally enclosed in a bacterial virus during exit of the virus from the bacterium)
Bacteriophage is not functional
