Mechanisms Of Microbial Genetics Lecture 11-13 Flashcards
DNA critical functions
Inheritance parent to offspring
- chromosomes and plasmids
- exact replication
Directs and regulates protein synthesis
- gene expression
DNA replication Model 1
Conservative replication
DNA is “unzipped” into two
individual strands. Each DNA strand is used to make a
complementary copy.
2 com copies fuse together and make NEW DNA molecule
DNA replication Model 2
Semiconservative replication
same as conservative except the
complementary copies stay with the parent strand to form a hybrid old / new DNA molecule
DNA replication Model 3
Dispersive replication
DNA stays double stranded and is
somehow copied that way in “blocks”, and resulting
DNA molecules have regions of parental DNA
interspersed with progeny DNA
DNA Rep. Bacteria
Rep starts at orgin of rep
and bidirectionally
1000 bases per second
Occurs because of Stabilizing proteins and enzymes
DUE TO DNA POLYMERASE
DNA Polymerase III
main player in DNA replication
DNA pol adds a nucleotide (a nucleoside triphosphate) that is complementary to the one
on the template strand
phosphodiester bond
Product of nucleotide and complimentary base in DNA rep
is supplied by the nucleoside triphosphate itself
• Formation of the phosphodiester bond is a
dehydration synthesis reaction
DNA REP IN BACTERIA STEP 1
STEP 1: INITIATION
1. DNA is uncoiled
Topoisomerase, DNA gyrase
2. A replication fork is formed Helicase
3. An RNA primer is synthesized RNA primase
DNA REP IN BACTERIA STEP 2
STEP 2: ELONGATION
1. The clamp structure recruits DNA polymerase III to the primer
2. The sliding clamp/DNA polymerase III complex
continuously synthesizes a complementary
DNA sequence on the leading strand, in 5’ to 3’ direction
3. This also occurs on the lagging strand, but in a discontinuous manner
DNA REP IN BACTERIA STEP 2 LAGGING STRAND
STEP 2: ELONGATION (lagging strand)
1. The clamp structure recruits DNA polymerase III to the primer
2. The sliding clamp/DNA polymerase III complex
synthesizes a short complementary DNA sequence in 5’ to 3’ direction and then
disengages
3. A new clamp complex locates to the RNA primer closer to the replication fork and synthesizes a new short sequence
DNA REP IN BACTERIA STEP 3 prokaryotes
STEP 3: TERMINATION (prokaryotes)
1. In prokaryotes, the circular chromosome is copied
2. When replication circles back to the origin of
replication, the two copies are still connected
3. Bacterial topoisomerase IV breaks the DNA backbone and separates the two copies
DNA REP IN BACTERIA STEP 3 eukaryotes
STEP 3: TERMINATION (eukaryotes)
1. In eukaryotes, chromosome is copied in a
linear fashion with multiple origins of
replication
2. When replication reaches the ends
(telomeres), there is not enough room for synthesis of a new RNA primer
3. These ends remain unrepaired in somatic cells
4. Ends are repaired by telomerase in germ cells and stem cells
Extrachromosomal DNA Replication
Replication of plasmids
Called rolling circle replication
only one strand is initially copied
• Once that copy is made and recircularized, a
new complementary strand is synthesized
What is gene expression
A gene is a sequence of DNA that spells out how to build a specific amino acid sequence
– Gene expression is the process of reading a gene
and ultimately producing that specific amino acid
sequence
Transcription and translation
Carries out gene expression
RNA TRANSCRIPTION
the first step in creating a
new protein from the instructions encoded in a gene
Complementary RNA of the DNA strand is generated into messenger RNA or RNA transcript
Eukaryotes mRNA
One mRNA made for only one gene
Prokaryotes mRNA
One mRNA can encode multiple genes
Prokaryote RNA Transcription
DNA opened and unwound
Forming a transcription bubble
RNA Polymerase located to specific region on antisense strand (template strand) and signals process to start location is called promoter
RNA prokaryotic transcription
RNA Polymerase needs no primer (unlike 3 OH in dna process)
Does not require separate clamp assembly or helicase
Uses uracil instead of thymine
Transcript is single stranded
TATA BOX prokaryotic rna transcription
