Protein cheat sheet
Rho: Small GTP-ase
Ran: A protein that is involved in the transport of proteins across the nuclear envelope by interacting
with karyopherins and changing their ability to bind or release cargo molecules. Inside the nucleus,
RanGTP binds to importin and releases the import cargo. Cargo that needs to get out of the nucleus into
the cytoplasm binds to exportin which is connected with RanGTP. Upon hydrolysis of RanGTP to RanGDP
outside the nucleus, the activation of exportin is undone and export cargo is released.
GTP-ases: GTPases function as molecular switches or timers in many fundamental cellular processes. It
does this by catalysing the reaction of GTP to GDP where a GTP-bound protein is switched 'on', and a
GDP-bound protein is switched 'off'. This means that GTP-ases switch proteins from 'on' to 'off'.
GAP: GTP-ase activating protein is a protein that activates GTP-ases.
GEF: Guanine nucleotide exchange factor is the counter protein of GTP-ase. It catalyses the reaction
from GDP to GTP and can therefore switch the protein from 'off' to 'on'
DNA Gyrase: A protein that helps the DNA unwind from a double helix to a single helix of DNA by
relieving the tortional strain.
Helicase: A protein that splits open the base pairs by breaking the hydrogen bonds between them.
SSB: Single strand binding protein. It stops the re-annealing; AKA stops the DNA from binding to itself.
DNA primase: A protein that makes a 'flag' of RNA so that the DNA knows where to bind and has
something to bind to.
DNA polymerase: Polymerase 1 is a protein that synthesizes the new DNA by sticking the corresponding
base pair on a base pair. It can only add to the synthesizes new DNA from 5' to 3'. Polymerase 3 is a
protein that replaces the primers with DNA by cutting them out and synthesizing a little but more DNA
to place back. Pol 3 also proofreads the DNA when synthesis is done to scan for errors.
Exonuclease: A protein that can remove nucleotides. This is useful for if the DNA polymerase makes a
mistake or for when introns need to be cut out of the pre-mRNA.
DNA ligase: A protein that facilitates the joining of DNA strands together. This is useful to bind parts of
DNA together (Seal the gap between the existing DNA and the DNA that DNA Pol I created. It does this
by catalysing a phosphate and hydroxyl reaction resulting in a phosphodiester.
Topoisomerase (DNA gyrase): A protein that reliefs tortional strain (overwinding of the DNA) in the
double DNA helix.
Signal peptidase: A protein that converts secretory and some membrane proteins to their mature or pro
forms by cleaving their signal peptides from their N-termini.
Importins and Exportins: Proteins that recognize the NLS (Nuclear localisation signal sequence) and NES
(Nuclear export signal sequence) respectively. Importins makes sure that larger proteins can be
imported into the nucleus and exportins makes sure that they can be exported out of the nucleus.
, NPC: Nuclear pore complex is a protein complex that makes pores in the nucleus through which small
proteins, that don’t have to be unfolded, can passively be diffused.
TOM and TIM: Translocase of the outer membrane (TOM) is a protein complex on the mitochondrial
wall that makes it possible for proteins to enter the mitochondria. Translocase of the inner membrane
(TIM) is a second gateway located on the inner membrane through which the proteins must move.
SRP: Signal recognition particle is a protein that recognizes and targets specific proteins to the
endoplasmic reticulum in eukaryotes.
BiP: Binding immunoglobulin protein is a molecular chaperone located in the lumen of the endoplasmic
reticulum (ER) that binds newly synthesized proteins as they are translocated into the ER, and maintains
them in a state competent for subsequent folding.
Calnexin: Calnexin is a chaperone, characterized by assisting protein folding and quality control,
ensuring that only properly folded and assembled proteins proceed further along the secretory
pathway. It specifically acts to retain unfolded or unassembled N-linked glycoproteins in the ER.
Calrectulin: Calreticulin binds to misfolded proteins and prevents them from being exported from the
endoplasmic reticulum to the Golgi apparatus.
Ubiquitin: A protein that marks other proteins for degradation (shredding)/recycling. The shredding is
done by proteases.
Translocon: A complex or proteins that works as a pathway for proteins through the ER membrane. It
sort of makes a pore just like the NPC. A key component of the translocon is Sec61.
Peptidase: An enzyme specialized in breaking down proteins into smaller polypeptides or single amino
acids and spurring the formation of new protein products. It does this by using a hydrolysis reaction
(using water) to break the bonds in the proteins. It is for example used to integrate proteins into the ER
membrane.
SNARE Proteins: A group of proteins of which the primary role is to mediate the fusion of vesicles with
the target membrane; this notably mediates exocytosis (the cell exporting molecules out of the cell) but
can also mediate the fusion of vesicles with membrane-bound compartments (such as a lysosome).
SNARE proteins are heavily ATP dependent.
Kinesin: A motor protein found in eukaryotic cells. Kinesins move along microtubule filaments and are
powered by ATP. The active movement of kinesins supports several cellular functions including mitosis,
meiosis, and transport of cellular cargo. Kinesin moves to the positive end of the microtubule which in
most cells means towards the cell membrane.
Dynein: A motor protein that transports various cellular cargos, provides forces and displacements
important in mitosis, and drives the beat of eukaryotic cilia and flagella. All these functions rely on
dynein's ability to move towards the minus-end of the microtubules.
Clathrin: A protein that plays a key role in the formation of coated vesicles. It performs critical roles in
shaping rounded vesicles in the cytoplasm for intracellular trafficking. Clathrin-coated vesicles (CCVs)
selectively sort cargo at the cell membrane, trans-Golgi network, and endosomal compartments for
multiple membrane traffic pathways.
Rho: Small GTP-ase
Ran: A protein that is involved in the transport of proteins across the nuclear envelope by interacting
with karyopherins and changing their ability to bind or release cargo molecules. Inside the nucleus,
RanGTP binds to importin and releases the import cargo. Cargo that needs to get out of the nucleus into
the cytoplasm binds to exportin which is connected with RanGTP. Upon hydrolysis of RanGTP to RanGDP
outside the nucleus, the activation of exportin is undone and export cargo is released.
GTP-ases: GTPases function as molecular switches or timers in many fundamental cellular processes. It
does this by catalysing the reaction of GTP to GDP where a GTP-bound protein is switched 'on', and a
GDP-bound protein is switched 'off'. This means that GTP-ases switch proteins from 'on' to 'off'.
GAP: GTP-ase activating protein is a protein that activates GTP-ases.
GEF: Guanine nucleotide exchange factor is the counter protein of GTP-ase. It catalyses the reaction
from GDP to GTP and can therefore switch the protein from 'off' to 'on'
DNA Gyrase: A protein that helps the DNA unwind from a double helix to a single helix of DNA by
relieving the tortional strain.
Helicase: A protein that splits open the base pairs by breaking the hydrogen bonds between them.
SSB: Single strand binding protein. It stops the re-annealing; AKA stops the DNA from binding to itself.
DNA primase: A protein that makes a 'flag' of RNA so that the DNA knows where to bind and has
something to bind to.
DNA polymerase: Polymerase 1 is a protein that synthesizes the new DNA by sticking the corresponding
base pair on a base pair. It can only add to the synthesizes new DNA from 5' to 3'. Polymerase 3 is a
protein that replaces the primers with DNA by cutting them out and synthesizing a little but more DNA
to place back. Pol 3 also proofreads the DNA when synthesis is done to scan for errors.
Exonuclease: A protein that can remove nucleotides. This is useful for if the DNA polymerase makes a
mistake or for when introns need to be cut out of the pre-mRNA.
DNA ligase: A protein that facilitates the joining of DNA strands together. This is useful to bind parts of
DNA together (Seal the gap between the existing DNA and the DNA that DNA Pol I created. It does this
by catalysing a phosphate and hydroxyl reaction resulting in a phosphodiester.
Topoisomerase (DNA gyrase): A protein that reliefs tortional strain (overwinding of the DNA) in the
double DNA helix.
Signal peptidase: A protein that converts secretory and some membrane proteins to their mature or pro
forms by cleaving their signal peptides from their N-termini.
Importins and Exportins: Proteins that recognize the NLS (Nuclear localisation signal sequence) and NES
(Nuclear export signal sequence) respectively. Importins makes sure that larger proteins can be
imported into the nucleus and exportins makes sure that they can be exported out of the nucleus.
, NPC: Nuclear pore complex is a protein complex that makes pores in the nucleus through which small
proteins, that don’t have to be unfolded, can passively be diffused.
TOM and TIM: Translocase of the outer membrane (TOM) is a protein complex on the mitochondrial
wall that makes it possible for proteins to enter the mitochondria. Translocase of the inner membrane
(TIM) is a second gateway located on the inner membrane through which the proteins must move.
SRP: Signal recognition particle is a protein that recognizes and targets specific proteins to the
endoplasmic reticulum in eukaryotes.
BiP: Binding immunoglobulin protein is a molecular chaperone located in the lumen of the endoplasmic
reticulum (ER) that binds newly synthesized proteins as they are translocated into the ER, and maintains
them in a state competent for subsequent folding.
Calnexin: Calnexin is a chaperone, characterized by assisting protein folding and quality control,
ensuring that only properly folded and assembled proteins proceed further along the secretory
pathway. It specifically acts to retain unfolded or unassembled N-linked glycoproteins in the ER.
Calrectulin: Calreticulin binds to misfolded proteins and prevents them from being exported from the
endoplasmic reticulum to the Golgi apparatus.
Ubiquitin: A protein that marks other proteins for degradation (shredding)/recycling. The shredding is
done by proteases.
Translocon: A complex or proteins that works as a pathway for proteins through the ER membrane. It
sort of makes a pore just like the NPC. A key component of the translocon is Sec61.
Peptidase: An enzyme specialized in breaking down proteins into smaller polypeptides or single amino
acids and spurring the formation of new protein products. It does this by using a hydrolysis reaction
(using water) to break the bonds in the proteins. It is for example used to integrate proteins into the ER
membrane.
SNARE Proteins: A group of proteins of which the primary role is to mediate the fusion of vesicles with
the target membrane; this notably mediates exocytosis (the cell exporting molecules out of the cell) but
can also mediate the fusion of vesicles with membrane-bound compartments (such as a lysosome).
SNARE proteins are heavily ATP dependent.
Kinesin: A motor protein found in eukaryotic cells. Kinesins move along microtubule filaments and are
powered by ATP. The active movement of kinesins supports several cellular functions including mitosis,
meiosis, and transport of cellular cargo. Kinesin moves to the positive end of the microtubule which in
most cells means towards the cell membrane.
Dynein: A motor protein that transports various cellular cargos, provides forces and displacements
important in mitosis, and drives the beat of eukaryotic cilia and flagella. All these functions rely on
dynein's ability to move towards the minus-end of the microtubules.
Clathrin: A protein that plays a key role in the formation of coated vesicles. It performs critical roles in
shaping rounded vesicles in the cytoplasm for intracellular trafficking. Clathrin-coated vesicles (CCVs)
selectively sort cargo at the cell membrane, trans-Golgi network, and endosomal compartments for
multiple membrane traffic pathways.
