- 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

Microbe Genetics Flashcards by Cal Schiller

the entire complement of genes on all chromosomes normally found in an organism;
the hereditary information

Genome

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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

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a segment of DNA that contains the genetic code (blueprint) for a functional product (e.g.
code for a specific protein)

Gene

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The genetic code is translated into proteins for structural, catalytic, or regulatory functions
within the cell with the aid of

messenger RNA and ribosomes

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Genetic code for each protein is carried as a sequence of ____
macromolecule

nucleotide molecules in the nucleic acid

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Genes contain

instructions for making proteins

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Composition of Nucleic Acids (nucleotide)

5-carbon sugar – either Ribose or Deoxyribose

nitrogenous base (Bound to 1`)

phosphate group (bound to 5` carbon)

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Nitrogenous base

Purine (adenine, guanine)

pyrimidine (thymine, cytosine, uracil)

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Adenine binds

Thymine (or uracil)

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Guanine binds

cytosine

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5 is oriented to lateral on one side and 3 is the lateral portion on the opposite side…

makes sense?

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Adds next nulceotide to 3`C side ONLY

DNA polymerase

will not add to 5`C

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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.

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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

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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)

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binds to DNA and inserts complementary nucleotides thereby

generating a new strand

DNA polymerase

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Unwinding (and rewinding) is due to action of

enzymes such as

helicase, DNA gyrase, and topoisomerase

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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.

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DNA polymerase ____ with accuracy of about 1 error in a billion base
pairs replicated

edits for errors

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“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)

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The newly developing strand grows toward the

replication fork, i.e. “leads into” the

fork

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The leading strand is ____ because of enzymatic simplicity and ease of
access to the molecule

continuously replicated

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______ 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

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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

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_____ 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

Microbe Genetics Flashcards

(77 cards)