what happens during translation
protein synthesis
mRNA--> protein
what is needed for translation
small and large ribosomal subunits, tRNA, mRNA
what does tRNA carry
has an anticodon that will pair with the codon on mRNA which is associated with a given AA also carried by tRNA
what are 3 steps of translation
initiation
elongation
termination
describe initiation
tRNA brings 1st AA (Met) in china w antibody to bind to start codon (AUG) on mRNA
describe elongation
polypeptide chain grows from the P site
-peptide bonds form between AAs by ribosomal RNA
what are 3 sites in ribosome for translation
E (exit), P, A (attachment)
what happens in termination
stop codon recognized and polypeptide released
-folds to become protein after
where do tRNAs enter
enter A site, drop AA at P site, and leave via E site
how is ribosomal structure and rRNAs similar in prokaryotes and eukaryotes
-both have small subunit (SSU) and LSU
-both have ribosomal RNAs that interact w each subunit
what does SSU rRNA do
helps w mRNA binding
what does LSU rRNA do
catalyzes peptide bond formation
how to pro and eukaryotes differ in ribosome structure
pro: 50s and 30s--> 70s ribosome
eukaryote: 60s and 40s--> 80s ribosome
how do codons differ in pro and eu
same codons BUT pro has different AA codes for by start codon
-use altered form of Met called n-formyl methionine (fMet)
what its he 3rd letter in a codon calld
wobble positin
-multiple codons code for same AA
what does tRNA have that makes it more stable
hairpin loops
how does initiation differ in pro vs eukaryotes
in eukaryotes, ribosome recognizes 5' cap of mRNA to start translation
-in pro, ribosome recognizes ribosome binding site--> Shine-Delgarno sequence (AGGAGG) that rRNA binds to
when does transcription and translation occur in pro
simultaneous!
ribosomes bind immediately bc mRNA is unstable
what types of ribosomes do prokaryotes use that we do not
why?
polyribosomes-- many ribosomes acting on single mRNA transcript
**allows bacteria to respond quickly (make multiple of the same protein)
what is bacterial molecular bio geared towards? give ex
fast response!
1. operons (multiple genes on same transcript)
2. polyribosomes
3. no transcript editing
4. shorter 1/2 life of transcript (so protein production starts immediately)
5. smaller genome
what are 2 types of gene transfer
1. vertical: parent to child (all living things do this)--> making a clone of yourself, mutation occurs at slow rate
2. horizontal: parent to parent or child to child (ppl can NOT do this--only bacteria)
-HGT is bacterial sex--move DNA from one cell to an
what does HGT allow for
quickly adapting to environment by acquiring large chunks of new DNA
-gains antibiotic resistance genes and virulence factors
what are obstacles to HGT
1. getting DNA into cell
2. getting DNA to recombine onto the genome
what does adding genes onto a chromose require
homologous regions (similar )
-happens in ppl during meiosis! crossing over (causes genetic diversity)
higher match=more likely to recombine
what catalyzes the joining of 2 strands in recombination
RecA protein
**dononr DNA is destroyed
what can recombination occur between
2 plasmids
fragment and genome
plasmid and genome
why is recombination a complicated process
involves >30 proteins
-mediated by major group of proteins called Rec (recombination)
-includes helices, nuclease, etc
*requires alignment of homologous regions
what do all successful HGT events require
recombination
what are 3 forms of HGT
transformation
transduction
conjugation
who conducted a transformation experiment
describe it
Griffith in 1928
injected virulent bacteria into mice and they died
-injected avirulent bacteria and they lived
-injected heat killed virulent bacteria and they lived
-injected heat killed virulent and live avirulent and they died
**genes were transferred
what does transformation consist of
picking up DNA form environment
purposeful!!
what is competence
ability to perform transformation (take up DNA from the environment)
what are 2 types of competence
natural
artificial
describe natural competence
-not many bacteria can do this (needs a lot of specific genes
requires pili
-highly regulated!
what is pili
hairlike structure coming out of bacteria
-allows them to stick to DNA in environment and pull it inside
why is natural competence highly regulated
requires a lot of energy (don't want to do it unless it will pay off)
-only turned on during high cell density or as a stress response
*dependent on quorum sensing! don't want to turn it on if nothing is around
how is artificial competence made
treat cells with CaCl2--> makes holes in membrane/walls
-manipulated in lab conditions
what are 2 ways to make artificial competence
1. electroporation--electroshock cells which destabilizes membrane (can take up DNA)
2. heat shock--switch form cold to hot (temporarily disrupts membrane)
does only DNA from related species enter the cell
no! all types can make it in but we only see ones that recombine so they have to have related DNA!!
-need homologous regions
what happens during transduction
viruses transfer DNA to bacteria
**accidental!
what are 2 types of transduction
general
specialized
what is general transduction
host bacterial genome can be fragmented during viral replication
-pieces of host DNA can then incorporate into phage and get transferred
what occurs in both transformation and transduction
cell has to lyse
describe specialized transduction
viral genes get incorporated into host genome during lytic cycle
-when phage separates from bacterial genome it can sometimes accidentally take host genes w it and transfer these to another bacteria (HGT!)
**bacteriophage acts as delivery system
what happens to virus if it takes up host genome
is unable to replicate and dies
what is an example of transduction
vibrio cholerae
-prob w water in 3rd world countries
-has toxin that was given by a virus that causes diarrhea
how can we use transduction as a tool since viruses infect ppl too
1. use phage as delivery system (give it something that will kill bacteria)
2. gene therapy--gene editing w CRISPR
3. vaccine delivery
4. phage therapy
what is CRISPR
came from prokaryotes and functions as their immune system against viruses
- bacterial system that bacteria use to fight viruses. It consists of an enzyme called Cas9 and a guiding RNA.
-they keep a piece of the bacteriophage DNA so when it tries to infec
what does Cas9 do
enzyme that degrades what the guide RNA binds to
how can we use CRIPSR
put guide RNA and Cas9 system into phage
-the guide RNA will bind to the specific sequence we want to remove
what have we hijacked CRISPR to do
edit genes
-can cut out unwanted genes and replace them using guide RNA
what is guide RNA
Guide RNA is a strand of RNA that helps the bacteria know what part of the genomic DNA to cut.
Guide RNA contains complementary sequences to the target DNA you want to cut/get rid of/ or change. The complementary DNA replaces what you get rid of with a ne
describe conjugation
transfer DNA by directly connecting to other bacteria
-plasmid mediated transfer
donor donates plasmid
recipient receives plasmid
what must the plasmid be for conjugation
transmissible (capable of transfer)
what is an F plasmid
example of transmissible plasmid
-codes for proteins, has orin and omit sites
what is necessary for donor to have in conjugation
sex pilus
-protein filament that attaches to recipient cell and uses to transfer plasmid
*this is encoded on the plasmid that will be transferred
what does relaxase do in conjugation
nicks and unrolls the plasmid DNA
-helps direct plasmid to the pore in the sex pilus
what is the pore in the sex pili
tunnel for DNA transfer
what does conjugation require
what is this called
requires one cell to have plasmid and other to not
**called different matin types
**also requires direct contact btwn 2 cells
how does the plasmid replicate in conjugation
rolling circle
what does F factor integrating on chromosome make
Hfr cell (high frequency of recombination)
what happens when F factor gets transferred form an Hfr cell
takes some of the donor genome with it
-accidentally grabs part of chr, so makes new recombinant F- cell during recombination because entire F factor is not transferred
what can conjugation be used to do
map out bacterial genome
-depending on how long it takes for genes to transfer, can determine where in chromosome these genes are
what else can bacteria inject DNA into via conjugation
give ex
plant cells
ex. Agrobacterium
-conjugation causes overgrowth/tumor in plants
what can injecting DNA be used to do
genetically engineered plants (GMOs)
what can be done w GMOs
-resistance to disease
-add extra nutrients
-higher yield (decreases food shortages)