mechanisms of microbial genetics Flashcards
what are the functions of DNA
store genetic material
direct and regulate the construction of proteins necessary to a cell for growth
what is a gene
dna that is read or transcribed to produce an RNA molecule through transcription
what is translation
when mRNA provides information for the ribosome to catalyze protein synthesis
what is gene expression
the synthesis of a specific protein with a sequence of amino acids that is encoded in the gene
what are the stages of replication, transcription and translation
initiation
elongation (polymerization)
termination
What is central dogma
the flow of genetic information from DNA to RNA
what is the process from dna to a protien
DNA>transcription>RNA>translation
What is replication
the process of DNA being copied
what is the semiconservative replication model
when 2 strands of the double helix separate and each strand is the template for for a complementary strand
what did meselson and stahl use in their dna experiments
a heavy isotope of nitrogen (15N) that was incorporated into nitrogenous bases and then DNA and E. coli
what medium was the e coli cultured in for dna testing
one with 14N and allowed to grow for one generation
how is dna separated
using and ultracentrifuge where dna forms bands according to its desity
what was expected of dna after being ultracentrifugated
15n would form a band at higher density than those grown in 14N
what were the results of the first generation dna
the band was between 15n and 14n
what happened to cells grown as a second generation in 14n
one band was between 14n and 14 and the second band corresponded to th second band of DNA
how long does it take E. coli dna to replicate
42 minutes
what DNA polymerase is required for DNA synthesis
DNA pol 3
what are DNA pol 1 and DNA pol 2 used for
repair
what does DNA pol 3 do
adds deoxyribonucleotides to a nucleotide on the template strand
where does DNA get the energy for replication
the bonds of the 3 phosphate groups attached to each nucleotide, when the bond is broken diphosphate is released allowing phophpdiester to bond
what is DNA wrapped around
histones in eukaryotes and arches and histone like proteins in bacteria
what relaxes a supercoiled DNA molecule
topoisomerase 2
what is another name for topoisomerase 2
DNA gyrase
what does helicase do
separats dna strands by breaking the hydrogen bonds between base pairs.
what are replication forks
y shaped structures that are formed at the origin of replication allowing for bidirectional replication and a structure that looks like a bubble
what prevents single stranded DNA from rewinding into a double helix
the dna near the replication fork being coated with single stranded binding proteins
what direction is DNA pol 3 able to add nucleotides
only in the 5’ to 3’ directions
why can dna pol 3 only work in the 5’-3’ directions
because DNA polymerase requires a free 3’ -OH to add nucleotides too
can DNA pol 3 add a nucleotide if a 3’ is not available
no
Describe th primer
an RNA sequence that provides free 3’ ok end and is 5-10 nucleotides long and complementary to the parental or template dna
what is the primer synthesized from
RNA primase an RNA polymerase
what makes RNA polymerase different from DNA polymerase
RNA polymerase does not need a free 3’ -oh group to synthesize an RNA molecule
what is the leading strand
the continuously synthesized DNA strand. the 5’-3’ strand
what are Okazaki fragments
fragments of DNA replicated on the 3’-5’ DNA strand (lagging strand)
how many primers does the lagging strand need
one for each Okazaki fragment
what is the sliding clamp
a protein that holds the DNA polymerase in place as it adds nucleotides to the lagging side
how does topoisomerase prevent overwinding of DNA at the replication fork
it causes temporary nicks in the dna helix and the resealing it
what happens to RNA primers during DNA replication
it is replaced by dna
how are RNA primers removed
the exonuclease activity of DNA polymerase 1 removes it and the gaps are filled in
what does DNA ligase do
fills the gaps seals the gaps between the dna that replaced RNA Primer and the previously synthesized dna
how are the DNA chromosomes separated from eachother
bacterial topoisomerase 4
what makes dna replication in bacteria from eukaryotes
DNA gyrase and topoisomerase 4
DNA pol 1 function
exonuclease activity removes RNA primer and replaces it with newly synthesized DNA
DNA pol 3 function
main enzyme that adds nucleotides in the 5’ to 3’ direction
helicase function
opens the DNA helix by breaking hydrogen bonds between the nitrogen bases
ligase function
seals the gaps between Okazaki fragments on the lagging strand to create one continuous dna strand
primase function
synthesizes RNA primers needed to start replication
single stranded binding proteins function
bind to single-stranded DNA to prevent hydrogen bonding between DNA stranded DNA
sliding clamp function
helps hold DNA pol 3 in place when nucleotides are being added
topoisomerase 2 (DNA gyrase) function
relazes supercoils chromosome to make DNA more accessible for the initiation of replication, helps relieve the tress on dna when unwinding, by causing breaks and the resealing dna
topoisomerase 4 function
introduces single stranded break into concatenated chromosomes to release them from each other, and then reseals the dna
how is dna replication in eukaryotes different than bacteria
it is slower, has multiple points of origin, uses RNase h instead of dna pol 1 for a primer removal, uses pol8 and pol e for strand elongation instead of dna pol 3
what is ribonuclease h
the enzyme that removes RNA primer in eukarotes instead of dna polymerase in Bactria
what are telomeres
the ends of linear chromosomes that consist of noncoding repetitive sequences
what do telomeres do
protect coding sequences from being lost as cells continue to divide
what does telomerase contain
a catalytic part and a built in RNA template
where does telomerase attach
to the end of the chromosome and complementary bases to the RNA template on the 3’ end of the DNA strand
What is rolling circle replication
another process of dna replication used by bacteria, plasmids, bacteriophages and some eukaryote viruses
what happens in rolling circle replication
one strand of dna is nicked at the double stranded origin site
dna polymerase binds to the 3’ oh of the nicked trans and replicates unidirectionally
look it up more it doesn’t make sense
what is transcription
when information encoded within the dna sequence of one or ore genes is transcribed into a strand of dna
what is a transcription bubble
the partially unwound portion dna where rna synthesis is taking place
what is the antisense strand
the strand of dna that is acting as a template
what is the sense strand
the non template strand of dna that is almost identical to the rna
what is a critical difference between dna polymerase and rna polymerase
dna polymerase requires a 3’ oh group requiring a primer where rna polymerase does not
what does rna polymerase comprise in ecoli
6 polypeptide subunits, 5 that compose the polymerase core enzyme responsible for adding rna nucleotides and a sigma factor
what does the sigma factor do
enables RNA polymerase to bind to a specific promoter for the trascription of genes
where does the initiation of transcription begin
the promotor
what is a promoter
a dna sequence onto which the transcription machinery binds and initiates transcription
what nucleotide is transcribed as the initiation site for transcription
the first 5’ nucleotide in what’s being copied
what is upstream?
the nucleotides preceding the initiation site
what is down stream
the nucleotides following the initiation site
when does elongation in transcription begin
when the sigma subunit dissociates from the polymerase allowing the core enzyme to synthesize rna complementary to dna
how does polymerase differ between prokaryotes and eukaryotes
eukaryotes use polymers 1, 2, 3 that are different from bacterial rna polymerase
what do polymers 1,2,3 transcribe
each a different subset of genes
what type of rna polymerase do arches contain
just one more closely related rna polymerase 2 than bacterial rna polymerase
what does monocistronic mean
eukaryotic mRNA that only encodes a single polypeptide
what does polycistronic mean
prokaryotic mRNA that encode s multipolypeptide
