Learning outcomes Flashcards
What is an operon? What are the advantages of a cell for organizing genes as operons?
a cluster of genes that are transcribed as a single messenger RNA.
advantages =allows many genes to be turned on or off due to specific signals.
I.e. lac operon which allows enzymes for the metabolism of lactose to only be produced when glucose is not present and lactose is.
What is a repressor protein?
A regulatory protein that binds to specific sites on DNA and blocks transcription; involved in negative control.
What is a helix-turn-helix motif?
The shape of a protein so it can bind to DNA
two segments of the polypeptide chain that have an a-helix secondary structure connected by a short sequence forming the “turn.”
Explain how the different portions of the helix turn helix structure help bind to proteins
First helix = recognition helix, which interacts specifically with DNA.
Second helix = stabilizing helix stabilizes the first helix by interacting with it by way of hydrophobic interactions.
Turn linking the two helices = consists of three amino acid residues, the first of which is typically a glycine.
When do cells break down lactose
In the absence of glucose
Which operon is used to break down lactose in many prokaryotes
Lac operon
List the key players in the lac operon
Repressor protein, An inducer (allolactose), RNA polymerase, CAP binding Site, cAMP-CAP complex,
When does the repressor fall off of the lac operon?
In the presence of allolactose which binds to it and reshapes resulting in it falling off
Why is allolactose present to bind to the repressor protein in the lac operon
Occasionally the repressor protein falls of the lac operon at the same time that DNA polymerase is present resulting in about 3 copies of the lacZ enzyme in the cell at all times. when lactose is present these proteins break it down to create the allolactose
What is the inducer in the lac operon
allolactose
Once the repressor is off the operon why doesn’t it turn on immediately
Because you still need the cAMP-CAP matrix bound to the CAP binding site.
This reshapes the DNA making it so DNA polymerase can bind
When is cAMP present in the cell?
When glucose is present any cAMP present in the cell is shipped out to be used elsewhere. Once there is no glucose is used up the ATP is broken down into cAMP is used in the cell …. = can bind to CAP
What is catabolite repression used for in regards to the lac operon?
It is used to ensure that only the most efficient fuel (glucose ) is used, once glucose is depleted then other fuels can be used.
How does the CAP binding site interact with the lac operon?
When the cAMP-CAP complex binds to the CAP binding site is straightens out the DNA which allows RNA polymerase to bind
What are two examples of global control mechanisms
- Catabolite repression - Changing the binding site to control when RNA polymerase binds
- Alternative Sigma Factors - Change the shape of RNA polymerase to control when it binds /where it binds to
What is the normal sigma factor for E. coli
Sigma ^70
What does the superscript mean in sigma proteins?
indecates the mass of the protein in kilodaltons (1 dalton = molecular weight of hydrogen)
Why does the size of the sigma protein matter?
because this is what controls where sigma (part of RNA polymerase) binds to the DNA. the shape of it is kind of like a bean so it attaches normally in two spots (on 35 base pairs upstream of the promoter site and the other 10) but if the bean is changed the size that gap will change size too.
Why aren’t alternate sigma factors constantly used by the cell
They are either destroyed very quickly or in some other way deactivated until needed
Can you explain alternate sigma factors using an example
- Heat shock response is controlled by Sigma 32 (called RpoH)
- sigma 32 is usually inactive because it is bound to DnaK
- When the cell experiences high temperatures, DnaK is denatured and lets go of sigma 32
- Then sigma 32 binds to RNA polymerase and tells it where to transcribe to make heat shock proteins.
Name the two components of a two-component system
- Sensor Kinase
2. Response protein
In a two-component system where is sensor kinase and where is the response regulator?
kinase = cytoplasmic membrane
Response regulator = cytoplasm
What are ompF porin proteins and when are they used
-Large pores used for osmotic regulation when the conditions are cold a low nutrients
What are ompC porin proteins and when are they used
-small pores under high temp high nutrient conditions
Define signal transaction
the external signal is transmitted from a surface protein to the interior of the cell.
Is histadine kinase hydrophobic or hydrophobic
Two hydrophobic ends and a hydrophilic middle
-This allows it to have a sensor outside of the cell and then components in the cell to interact with
Where does the phosphate come from in a 2 component system
The histadine kinase autophosphoralates its self
Explain the basics of a two component system when its a promoter protein
- environmental signal interacts with histidine kinase
- kinase autophosphorilates
- kinase passes phosephate to protein
- protein binds to DNA upstream of promoter site (think cap binding site)
In osmotic regulation what happens when there is high osmotic pressure?
-low nutrients
-little phosphorylation of EbvZ
-few OmpR-P
-OmpR-P only binds to the high afinity site
===Only OmpF is made
In osmotic regulation what happens when there is low osmotic pressure
- high ammounts of nutrients
- Lots of EnvZ-P is made
- lots of OmpR-P
- Binds to low and high affinity binding sites
- micF (backwards ompF) is made
- micF binds to ompF turn it off
- ompC is turned on
What is feedback inhibition
- Controls enyzmatic activity
- biosynthetic pathways are temporarily shut off because of excess products
-From what i understand its when something produces too much of something further production is stopped do to the high conc of product
in chemotaxis what is a run? (flagella)
- Flagella moving counterclockwise
- Runs
- Coherant motion
In chemotaxis what is happening in a tumble (flagella)
- Clockwise motion
- Bundle is a messs
- timbles randomly
How many types of MCP’s are there?
4
What are the proteins involved in chemotaxis
- MCP
- CheW
- CheW
- CheY
- CheB
- CheR
- CheZ
Which protein in chemotaxis is the sensor kinase
CheA
What does CheW do
ITs a coupling protein that changes the pattern of autophoshorylation of by CheA
What is the response regulator in chemotaxis
CheY and CheB
What does CheY do?
- Response regulator
- Bumps into Flagella motor
- when phosphorylated it changed the direction of the flagella motor clockwise (tumble)
What does CheB do
- Response Regulator
- Demethylates MCP’s to help reset the system once CheB is Phosphorylated
What does CheR do?
- Methylates MCP
- -Controls Adaptation to signal (idk)
What does CheZ do
- Dephosphorylates CheY-P
- Promotes Runs
Whats going on when cell is running
- MCP changes Conformation
- CheW helps attach CheA to the MCP
- When attached CheA autophosphorylates less
- Less phosphorylation of CheY
- Flagella moving clockwise
- Longer runs
- CheR decreases MCP’s responce (sensitivity to stimulant) by adding methyl groups
How does CheB reset the system
- CheR keeps adding CH3’s until its saturated
- This builds up the ammount of CheA
- CheB is methylated and removes CH3’s from MCP
What happens if a repellant binds to the MCP
-Increased formation of CheA-P
-Increased tumbling
(when the concentration of the repellant decrease the runs become longer)
Explain quorum sensing on a protein level
- Autoinducer signaling molecule that crosses membranes and responds to osmotic pressure.
- When is builds up in a cell it activates transcription of of quorum specific genes
What is quorum sensing used for
- Toxin production
- Biofilms
- Bioluminescence
What are the three possible general habitats
- Lithosphere
- Atmosphere
- Hydrosphere
Define Autochthonous
An organism that is indigenous to a habitat
Define Allochthonous
Organisms that are transient (usually lived somewhere else and then were transported there)
Lake zone: Littoral zone
Light penetrates to the bottom
Submergerd/ emergent plants
Lake zone Limnetic Zone
-Open water from surface to lowest level where photosynthesis is occuring
Lake: Benthos
- Bottom
- Lots of nutrients due to gravity
Define Oligotrophic
A low nutrient lake, usually deep, LArger hypolimnion