Unit 6: Gene Expression and Regulation Flashcards
Griffith Experiment
experiment: injected mice with strains of pneumonia, some died some didn’t
Conclusion: something survives heat treatment and becomes a “Transformation Factor”
Avery, McCarthy, Macleod
built off of Griffith (wanted to figure out what the transformation factor was)
Conclusion: DNA is the transformation factor
Hershey and Chase
sole purpose was to back up results from Avery, McCarthy, and Mcleod
used bacteriophage virus + radiation
Conclusions: exact same as Avery, just proved it in a different way (DNA not proteins are the source of genetic information)
Franklin, Watson, and Crick
used x-ray to determine structure of DNA (Photo 51)
Conclusion: DNA is a three-dimensional double helix structure
Eukaryotic vs Prokaryotic DNA
Eukaryotes have multiple LINEAR chromosomes and cannot have plasmids
Prokaryotes have a SINGLE CIRCULAR chromosome and can have plasmids
Plasmid
small, circular piece of DNA that can be transferred between bacteria
Recombination
the mixing of DNA from two different sources (aka sex)
Bateriophaege
virus that specializes in infecting and killing bacteria in order to reproduce
Bacterial Reproduction
when conditions are good, they prefer ASEXUAL reproduction through binary fission (this is the most efficient option)
- problem: NO GENETIC DIVERSITY (any change could kill whole population)
when the environment is less ideal and tough, bacteria must have sex (mix DNA) and use either Transformation, Conjugation, or Transduction
Transformation (bacterial sex)
- when prokaryotes acquire new genetic information from the environment (pick it up from dead bacteria/find it lying around)
BENEFITS: free genes, could provide new traits to overcome evolutionary and environmental challenges
COSTS: not all genes are useful to species. Also, it could waste energy and possibly harm the bacteria itself or it’s host (it might need the host to live to survive)
Conjugation (bacterial sex)
- requires TWO LIVING CELLS
- the transfer of DNA between 2 living cells
HOW: a plasmid containing genes is copied and transferred to a new cell that didn’t have the plasmid (cells connect using a pilus b/c they need to be in direct contact)
BENEFITS: creates a new donor cell that can give the genes to more cells, these genes could help the bacteria survive
CONS: it takes a lot more work and energy to find other bacteria and do this process - only worth it when conditions aren’t as favorable
Transduction (bacterial sex)
- transfer of DNA by viruses (viruses accidentally transfer bacterial DNA instead of the virus and don’t kill the cell)
Viruses (purpose, shape, and cycles)
viruses aren’t dead or alive, they’re somewhere in between (virus = more virus + super organized, but they can’t reproduce themselves and don’t respond to the environment)
PURPOSE: Spread disease (infect cell, make more, kill cell, continue cycle)
SHAPE: protein shell/coat = CAPSID (genetic information is stored in the capsid, viruses can have DNA or RNA and both can be single and doubled stranded)
LYTIC CYCLE: virus hacks cellular machinery to rapidly make more viruses that will explode/ lyse out of the host cell
- basically, turns cell into a virus factory making thousands - millions of new viruses
LYSCOGENIC CYCLE: the viral genome is incorporated to the host DNA through recombination. So, when the host replicates its DNA, the viral DNA is also copied and passed to the daughter cell
- these viruses take a long time to detect
- these cells eventually enter the lytic cycle and spread rapidly
Topoisomerase
enzyme that uncoils DNA
Helicase
enzyme that unzips DNA
DNA Polymerase
enzyme that builds new strands of DNA (only can build new strand in the 5’ to 3’ direction - moves 3’ to 5’ direction on the old strand)
NEEDS RNA primer as a landing pad on DNA strand to start synthesis. once it gets started it keeps going until something stops it.
Primase
enzyme that builds RNA primers
Ligase
enzyme that covalently bonds the backbone together
Exonuclease
enzyme that removes RNA primers
DNA Polymerase III
enzyme that “proofreads” DNA strand and fixes mistakes by replacing the mistake with a new base
DNA Replication Process
Semi Conservitive (half-keeping) and results in two identical strands of DNA that have one strand from the old DNA and one newly synthesize strand.
STEP 1: Topoisomerase uncoils the DNA to form a ladder like structure
STEP 2: Helicase unzips the DNA by breaking hydrogen bonds (single strand binding proteins - SSBs - prevent the strand from rebinding with itself) - creates a REPLICATION FORK
STEP 3: Leading strand and lagging strand synthesis happen at the SAME TIME
STEP 4: Exonuclease goes back and removes RNA primers, creating gaps in strands
STEP 5: DNA poly comes back and fills in the gaps left by Exonuclease (DNA poly can land on the newly synthesized DNA instead of an RNA primer now)
STEP 6: DNA Ligase comes through and creates covalent bonds to glue strands together
THERE ISN’T JUST ONE REPLICATION FORK, THIS PROCESS HAPPENS AT MULTIPLE SPOTS AT ONCE - ALL STEPS ARE OCCURING BASICALLY SIMULTANEOUSLY
Leading Strand Synthesis
When DNA polymerase attaches to an RNA primer (on the 3’ of old strand) on and builds one continuous strand of DNA in the 5’ to 3’ direction (this follows closely behind the helicase as it unzips the DNA)
Lagging Strand Synthesis
When helicase is unzipping DNA in the opposite direction of synthesis. Requires DNA poly to build DNA backwards
- RNA primers land on DNA as helicase unzips DNA, DNA poly lands on primers and creates a short section of DNA called an Okazaki Fragment
- DNA poly waits for helicase to unzip another section then RNA primer lands and DNA poly can fill in that next section until it hits the other RNA primer
- the lagging strand has a lot more gaps in the new DNA than the leading strand once exonuclease goes through and removes RNA primers
Telomeres
Regions at the end of chromosomes with non-coding sequences of DNA (allows cells to replicate and then destroys the single strand parts leftover without destroying important codes)
Necessary because DNA Poly can fill in backwards so the areas with the first RNA primers are left as gaps and our bodies are programmed to destroy any single strand DNA so those ends are destroyed.
