L10: Microbial Genetics Flashcards
the “central dogma” of molecular biology
genetics
genetics
the science of heredity: what genes are, how they carry information, how that info is expressed, and how genes are replicated
vertical gene transfer
the passing of genes to progeny (offspring)
gene expression
process of a gene becoming functional
DNA to protein
what are the 3 steps of gene expression?
replication (DNA doubles)
transcription (DNA to RNA)
translation (RNA to protein, ribosome)
genome
all the genetic material in a cell; all organisms have one
chromosomes
structures containing DNA that physically carry hereditary information; they contain genes
gene
a segment of DNA that encodes a functional product (usually a protein)
genomics
the molecular study of genomesgen
genotype
the genes of an organism
phenotype
the expression of an organism’s genes
DNA is a polymer of the nucleotides: adenine, thymine, cytosine, and guanine, which are…
dATP
dTTP
dCTP
dGTP
DNA is the genetic material of _____ cells
all
the backbone of DNA is the…
deoxyribose-phosphate
strands of DNA are held together by ________ between base-pairs of AT and GC
hydrogen bonds
DNA strands are _________ in direction
antiparallel
TRANSCRIPTION (eukaryotes): step 1?
starting at an RNA primer, DNA polymerase copies DNA in the 5’ to 3’ direction
TRANSCRIPTION (eukaryotes): step 2?
leading strand synthesized continuously
lagging strand synthesized discontinuously
TRANSCRIPTION (eukaryotes): the lagging strand comprises…
Okazaki fragments
TRANSCRIPTION (eukaryotes): Okazaki fragments
segmented pieces of the lagging strand in the 3’ to 5’ direction since DNA polymerase can only go in the 5’ to 3’ direction
TRANSCRIPTION (eukaryotes): step 3?
RNA primers are removed and Okazaki fragments are joined together by DNA ligase
TRANSCRIPTION (eukaryotes): step 4?
the energy comes from cutting the outermost 2 phosphate groups off of each nucleotide as it is added to the growing DNA chain
TRANSCRIPTION (eukaryotes): step 5?
stops when DNA polymerase reaches the terminator sequence on DNA
cellular organisms have ________ w/ proofreading abilities, so mutation rate is low under most conditions
DNA polymerase
DNA replication is ___________, meaning that each new DNA has 1 old and 1 new strand
semiconservative
bacterial DNA replication differs from eukaryotic DNA replication in the sense that…
it is bidirectional
RNA
produced via transcription of DNA; contains ribose instead of deoxyribose, and is single-stranded
what are the 3 main types of RNA?
mRNA
rRNA
tRNA
mRNA
messenger RNA, which is the carrier of information between DNA and protein synthesis (translation)
rRNA
ribosomal RNA, which is structural RNA that comprises part of the ribosome (translation)
tRNA
transfer RNA, which brings amino acids to the ribosome to construct proteins (translation)
true or false: in bacteria, transcription and translation can occur simultaneously
true
operons
a unit made up of linked genes that regulate other genes responsible for protein synthesis
operons comprise…
promoters and operators
in bacteria, there can be up to ______ genes organized in operons
4 to 5
promoter
a specific DNA sequence located at the start of a gene that acts as a binding site for RNA polymerase, marking where transcription should begin
what is the difference between eukaryotic and bacterial promoters?
there can be several genes under the control of 1 promoter in an operon
the promoter controls/activates…
transcription
________ is often induced by a specific stimulus
transcription of an operon
transcription of a gene produces…
mRNA
transcription can also be induced by the removal of a ________from an operator
repressor
repressor
protein that acts as an on/off switch for gene expression
induction of an operon definition
the process where a group of genes within an operon are turned on (activated) in response to the presence of an inducer/operator
exons
coding regions of eukaryotic genes
introns
noncoding regions of eukaryotic genes
true or false: bacterial genes are split into exons and introns
false; they are NOT
in eukaryotes, after genes are transcribed to mRNA, the introns are _________ before the mRNA is translated by the ribosome
spliced
true or false: there is no splicing in bacteria
true; bacteria have no nucleus so splicing cannot occur
TRANSLATION: mRNA is translated into…
codons
codons
series of 3 nucleotides, which code for 1 amino acid
what is the start codon for translation of mRNA?
AUG - methionine (eukaryotes); formylmethionine (prokaryotes)
what are the stop codons for translation of mRNA?
UAA, UAG, and UGA (no amino acid to code for)
differences between bacterial and eukaryotic ribosomes allow us to use drugs that specifically affect…
bacterial ribosomes
why can mRNA be translated while still being transcribed from DNA in prokaryotes?
prokaryotic chromosomes are NOT in a separate compartment (nucleus)
what 4 things are required for translation?
amino acids
ribosomes
mRNA
tRNA
mutation
a permanent change in the genetic material; can be neutral, beneficial, or harmful
mutagen
agent that causes mutations
spontaneous mutations
mutations that occur in the absence of a mutagen (i.e. RNA viruses)
example of a spontaneous mutation?
SARS-CoV2/COVID-19; mutates spontaneously at a rapid rate
base substitution (point) mutation
change in 1 base of DNA; is a type of silent mutation
missense mutation
base substitution that results in an amino acid change; is a type of point mutation
silent mutation
a change in a codon that does NOT result in a change of amino acid
nonsense mutation
base substitution that results in a “nonsense” stop codon; puts a stop codon in the wrong place
nonsense mutations cause…
a short, “truncated” and probably non-functional version of the protein
frameshift mutation
occurs when the 3-letter code is disrupted w/ an insertion or deletion of 1+ nucleotide pairs
what are the 4 main types of mutagens?
ionizing radiation
UV rays
chemicals
DNA repair
ionizing radiation
causes the formation of ions that can react w/ nucleotides and the deoxyribose-phosphate backbone and form breaks in the DNA
UV rays
creates thymine dimers; covalently links the 2 bases together and causes mispairing
chemical mutagens
chemicals that damage DNA bases, become intertwined in the DNA double-helix, and cause mispairing of bases
DNA repair
multiple mechanisms for DNA repair, but they can’t always keep up with the damage
translesion synthesis
a type of “last resort” DNA repair by adding a random nucleotide to create a “sloppy copy” of the original gene
often causes mutation, but saves the live of the cell
spontaneous mutation rate
1 in 10^9 replicated base pairs
1 in 10^6 replicated genes
mutagens increase the mutation rate to…
1 in 10^5 or 1 in 10^3 per replicated gene; depends on the potency of the mutagen
Ames test
a bacterial mutation test used to measure the potency of a mutagen
