Host Defense pt.1 Flashcards
What did Thucydides notice about survivors of the plauge
Once they already had the plague they were resistant to reinfection and most suited to care for the ill
-The survivors had some form of protection against plague
Being infected once and then having resistance to it
immunological memory
What is the immune system
Complex groups of mechanisms that provide defense against infection
Allows for survival with relentless exposure to parasites
but defense is imperfect
What is the restriction modification system
Uses two key enzymes to kill and invading material
How does the restriction modification system work
-Endonuclease cut and disables invading viral DNA at specific sequence
-Modification enzyme (methyltransferase) protects the bacteria’s DNA by adding a methyl group so it does not get cut by the endonuclease and destroy itself
How does the phage protect itself from the prokaryotes immunity
-Phages have evolved to avoid DNA sequences targeted by bacterial enzymes so some don’t have DNA that gets endonuclease
-Also have unusual nucleotides, cloak DNA in proteins so the endonuclease can not get in, or hijack the methyltransferases to protect their own DNA
Arms Race
Ongoing battle between bacteria and phages to constantly evolve new strategies to defend/protect itself
What is CRISPR
bacterial defense mechanism against DNA and viruses
How does CRISPR work
-The CAS gene cuts up the viral gene
-A piece of the viral DNA gets put into the palindromic sequence as a spacer
-That piece acts like a memory
-Infection occurs again
-Stored DNA makes a matching RNA called crRNA
-The CAS complex cuts the crRNA
-CAS Complex and piece memory piece attack the viral DNA
-Viral DNA is recognized and quickly cleaved and inactivated
What are plants defense mechanisms
Constitutive Defenses
Inducible Defenses
Constitutive Defenses
always active within the plant
Inducible Defenses
Activated when an infection occurs, needing a stronger defense
Example of constitutive defenses
Plant cells express pattern recognition receptor (PRR) which recognize common molecules associated with pathogens (PAMPs)
-When PRR detect PAMPs they trigger a immune response called PTI
-This causes cell walls to strengthen, production of lytic enzymes or antimicrobial compounds
Inducible Defense Example
-Effector get injected into plant cells and weaken the defenses
-Effector triggered immunity (ETI) happens using special proteins to recognize and disable effectors
What can ETI lead to
Hypersensitive response, where the plant cells around the infection die to stop the spread of the parasite
