Cell And Molecular Biology (Alberts) Exam
Questions And Answers Verified 100% Correct
what is a physical property of granulocytes that can be used to identify them under the
microscope? - ANSWER-they do not have round nuclei. Polymorphonuclear
what does the nucleus of a eosinophil, a neutrophil and a basophil look like? -
ANSWER-e: u shaped
n: multiple joined by thin strands
b: like a sausage balloon twisted in the middle
what are megakaryocytes - ANSWER-produce platelets in the bone marrow
what are the forms of nuclear DNA - ANSWER-Heterochromatin: Highly condensed
form
Euchromatin: less condensed form--> composed of 30nm fibres and looped
chromosome domains
Signal Patch - ANSWER-sorting signal composed of multiple internal amino acid
sequences that form a specific 3D arrangement of atoms on the proteins surface.
Nuclear disassembly and reassembly during the cell cycles - ANSWER-when a nucleus
disassembles during mitosis, the nuclear lamina depolymerises
-phosphorylation of the nuclear lamina by the cyclin dependent kinases (cdk) activated
at the onset of mitosis
- proteins of the inner nuclear membrane are phosphorylated, and the nuclear pore
complexes disassemble and disperse in the cytosol.
- nuclear envelope membrane proteins diffuse throughout the ER membrane
JAK-STAT pathway - ANSWER-Essential pro inflammatory signalling pathway initiating
the acute response to an infection --> fever
Regulation of nuclear import via phosphorylation
JAK is activated upon ligand mediated receptor dimerisation which causes
transphosphorylation.
Activated JAK phosphorylates STATs at the conserved tyrosine in the c terminus.
phosphorylation allows STAT dimerisation and entry into the nucleus using importin
,alpha 5 and the ran nuclear import pathway. once in the nucleus, STAT1 binding
with DNA competes with the importin a5 binding.
the Nuclear export signal of STAT is masked when the dimers are bound to DNA, the
DEphosphorylation of STAT by a nuclear phosphatase causes DNA release and NES
becomes accessible for CRM1 mediated nuclear export
NF-AT signalling pathway - ANSWER-Nuclear Factor of Activated T-cells
Pathway triggered if antigen is recognised on a DC
In a resting Tcell, NFAT is phosphorylated (on nuclear import signal)
Activation of the pathway leads to Ca influx which leads to calmodulin activation. act
Calmodulin binds the protein phosphatase calcineurin which dephosphorylates the
nuclear import signal of NFAT and binds the nuclear export signal.
the NFAT calcineurin complex enters the nucleus and activated transcription
REGULATION VIA DEPHOSPHORYLATION
Regulation of nuclear RNA export. mi, sn, t, r and mRNA - ANSWER-sn, r, t and
miRNAs are exported via the ran GTP/ exporting system
sn and rRNA with CRM1
t and miRNA with Xpot 1 and 5 respectively
mRNA is unknown, exported as large mRNP complexes
Structure of ER - ANSWER-the rough ER form oriented stacks of flattened cisternae
each having a luminal space of 20-30nm the smooth er membrane is connected to
these cisternae and forms a fine network of tubulus 30-60nm in diameter.
this together forms a net like labyrinth
the smooth ER - ANSWER-portion of the endoplasmic reticulum that is free of
ribosomes. usually scant in normal cells. in specialised cells however, like cells that
specialise in lipid metabolism, it is abundant and has additional functions
what are the two pathways of protein transport into the ER. characteristics -
ANSWERcotranslational with the SRP through a water filled aqueous channel in the
translocator, sec 61, and post translational. post translational requires atp. also uses
sec 61 but also a host of accessory proteins that associate to sec61 complex. (Sec62,
Sec 63, sec 71 and sec 72) Bip chaperone important
Sec A in eukaryotes
difference between eukaryotic and prokaryotic post translational translocation? -
ANSWER-in eukaryotes ATP hydrolysis occurs in the er and pulls the protein in, in
bacteria hydrolysis outside pushes the protein in
what is the SRP - ANSWER-signal recognition particle. is a ribonucleoprotein consisting
of one RNA and 6 protein subunits. Binds to the ER signal sequence and halts
,translation until the ribosome mRNA complex is attached to the ER
ER signal sequences vary greatly. how is it possible that the SRP can bind all of them?
- ANSWER-each er signal sequence has 8 or more non polar amino acids at its core.
The crystal striation of SRP allows us to understand how it can bind different
sequences. the signal sequence binding site is a large hydrophobic pocket lined by
methionines. due to the unbranched flexible side chains of the methionines, the pocket
is sufficiently plastic to accomodate different hydrophobic signal sequences.
structure and binding of SRP. - ANSWER-SRP has a rod like structure that wraps itself
around the large subunit of the ribosome. one one end it binds the signal sequence of
the emerging peptide and at the other end it binds the elongation factor binding site
how does SRP independent post translational translocation occur? - ANSWER-in
eukaryotes, the chaperone BiP and ATP are needed. sec61 complex is used alongside
associated proteins, sec 62, 63, 71 and 72. these proteins span the membrane and use
a small domain on the luminal side to deposit the chaperone BiP onto the polypeptide
chain as it emerges into the ER lumen. the removal of BiP is ATP dependent
What types of transmembrane proteins do you know? - ANSWER-Type I: the NH2
terminus is on the luminal side of the ER
Type II: the carboxy terminus is at the luminal side of the ER
How are proteins inserted into the ER membrane? - ANSWER-the proteins contain stop
transfer sequences alongside the initial start transfer sequence.
how is the orientation of protein in the membrane determined? - ANSWER-the charge of
the amino acids on either side of the stop transfer sequence determine the orientation.
positive outside and negative inside
Important multipass proteins in the immune system - ANSWER-Tetraspannins have
four transmembrane segments. CD9, CD81, CD82 and CD63
expressed in professional APC. crucial regulators of antigen presentation. involved in
both loading and trafficking of MHCII
What is GPI? - ANSWER-GLycosylphosphatidylinositol. It anchors proteins to the
membrane. attached to the C terminus of the protein and may be used to redirect
proteins to lipid rafts
BCR and lipid rafts - ANSWER-in the resting state, the BCR is not in a lipid raft. upon
antigen engagement, the BCR relocated within rafts
, what is FcyIIIb? - ANSWER-a GPI linked neutrophil specific IgG FC-receptor affinity
receptor for polyvalent immune complex IgG and decoy receptor that binds IgG
complexes without triggering activation. Basically you can have signal transduction
without activation of neutrophils
what is the most common post translational modification in the ER - ANSWER-N linked
glycosylation on Asparagine. 90% of glycoproteins. All membrane proteins are
glycosylated
most common method of glycosylation - ANSWER-a 14 sugar precursor containing
glucose, n-acetylglucosamine and mannose is added en bloc to the protein. this
precursor is on the transmembrane protein dolichol and is transferred by the membrane
bound enzyme oligosaccharyl transferase.
O-Glycosylation - ANSWER-less common. the oh group of serine or threonine. IgA
antibodies are o-glycosylated
how is correct folding ensured? - ANSWER-with the help of the ER chaperones calnexin
and calreticulin. they bind to incompletely folded proteins, retain them in the ER and
prevent them from irreversible aggregating they recognise N-linked oligosaccharides
that only have one of the original three precursor glucoses on the core. When the third
glucose is removed, the chaperones release the protein and it can leave the ER. The
chaperones can distinguish properly folded proteins from incompletely folded proteins
with the help of glycosyl transferase which continuously adds a glucose to
oligosaccharides that have lost their last glucose. it only however adds glucose to
unfolded proteins.
an unfolded protein undergoes continuos cycles of glucose trimming (glucosidase) and
glucose addition ( glucose transferase), maintaining affinity for calnexin and calreticulin
until it is fully folded.
How are misfolded proteins distinguished from incompletely folded proteins? -
ANSWER-with the help of N-linked oligosaccharides. they serve as timers to measure
how long a protein has been in the ER the slow trimming of a particular mannose on
the core oligosaccharide tree by mannosidase creates a new oligosaccharide structure
that ER luminal lectins of the retrotranslocation apparatus recognise. Proteins that fold
and exit the er faster than the mannosidase can remove its target mannose escape
degradation
What is the common feature of the multiple translocator complexes that move different
proteins from the ER into the cytosol? - ANSWER-They all contain a E3 ubiquitin ligase
that attaches ubiquitin the the unfolded protein as they are exiting the er, marking them
for destruction
Questions And Answers Verified 100% Correct
what is a physical property of granulocytes that can be used to identify them under the
microscope? - ANSWER-they do not have round nuclei. Polymorphonuclear
what does the nucleus of a eosinophil, a neutrophil and a basophil look like? -
ANSWER-e: u shaped
n: multiple joined by thin strands
b: like a sausage balloon twisted in the middle
what are megakaryocytes - ANSWER-produce platelets in the bone marrow
what are the forms of nuclear DNA - ANSWER-Heterochromatin: Highly condensed
form
Euchromatin: less condensed form--> composed of 30nm fibres and looped
chromosome domains
Signal Patch - ANSWER-sorting signal composed of multiple internal amino acid
sequences that form a specific 3D arrangement of atoms on the proteins surface.
Nuclear disassembly and reassembly during the cell cycles - ANSWER-when a nucleus
disassembles during mitosis, the nuclear lamina depolymerises
-phosphorylation of the nuclear lamina by the cyclin dependent kinases (cdk) activated
at the onset of mitosis
- proteins of the inner nuclear membrane are phosphorylated, and the nuclear pore
complexes disassemble and disperse in the cytosol.
- nuclear envelope membrane proteins diffuse throughout the ER membrane
JAK-STAT pathway - ANSWER-Essential pro inflammatory signalling pathway initiating
the acute response to an infection --> fever
Regulation of nuclear import via phosphorylation
JAK is activated upon ligand mediated receptor dimerisation which causes
transphosphorylation.
Activated JAK phosphorylates STATs at the conserved tyrosine in the c terminus.
phosphorylation allows STAT dimerisation and entry into the nucleus using importin
,alpha 5 and the ran nuclear import pathway. once in the nucleus, STAT1 binding
with DNA competes with the importin a5 binding.
the Nuclear export signal of STAT is masked when the dimers are bound to DNA, the
DEphosphorylation of STAT by a nuclear phosphatase causes DNA release and NES
becomes accessible for CRM1 mediated nuclear export
NF-AT signalling pathway - ANSWER-Nuclear Factor of Activated T-cells
Pathway triggered if antigen is recognised on a DC
In a resting Tcell, NFAT is phosphorylated (on nuclear import signal)
Activation of the pathway leads to Ca influx which leads to calmodulin activation. act
Calmodulin binds the protein phosphatase calcineurin which dephosphorylates the
nuclear import signal of NFAT and binds the nuclear export signal.
the NFAT calcineurin complex enters the nucleus and activated transcription
REGULATION VIA DEPHOSPHORYLATION
Regulation of nuclear RNA export. mi, sn, t, r and mRNA - ANSWER-sn, r, t and
miRNAs are exported via the ran GTP/ exporting system
sn and rRNA with CRM1
t and miRNA with Xpot 1 and 5 respectively
mRNA is unknown, exported as large mRNP complexes
Structure of ER - ANSWER-the rough ER form oriented stacks of flattened cisternae
each having a luminal space of 20-30nm the smooth er membrane is connected to
these cisternae and forms a fine network of tubulus 30-60nm in diameter.
this together forms a net like labyrinth
the smooth ER - ANSWER-portion of the endoplasmic reticulum that is free of
ribosomes. usually scant in normal cells. in specialised cells however, like cells that
specialise in lipid metabolism, it is abundant and has additional functions
what are the two pathways of protein transport into the ER. characteristics -
ANSWERcotranslational with the SRP through a water filled aqueous channel in the
translocator, sec 61, and post translational. post translational requires atp. also uses
sec 61 but also a host of accessory proteins that associate to sec61 complex. (Sec62,
Sec 63, sec 71 and sec 72) Bip chaperone important
Sec A in eukaryotes
difference between eukaryotic and prokaryotic post translational translocation? -
ANSWER-in eukaryotes ATP hydrolysis occurs in the er and pulls the protein in, in
bacteria hydrolysis outside pushes the protein in
what is the SRP - ANSWER-signal recognition particle. is a ribonucleoprotein consisting
of one RNA and 6 protein subunits. Binds to the ER signal sequence and halts
,translation until the ribosome mRNA complex is attached to the ER
ER signal sequences vary greatly. how is it possible that the SRP can bind all of them?
- ANSWER-each er signal sequence has 8 or more non polar amino acids at its core.
The crystal striation of SRP allows us to understand how it can bind different
sequences. the signal sequence binding site is a large hydrophobic pocket lined by
methionines. due to the unbranched flexible side chains of the methionines, the pocket
is sufficiently plastic to accomodate different hydrophobic signal sequences.
structure and binding of SRP. - ANSWER-SRP has a rod like structure that wraps itself
around the large subunit of the ribosome. one one end it binds the signal sequence of
the emerging peptide and at the other end it binds the elongation factor binding site
how does SRP independent post translational translocation occur? - ANSWER-in
eukaryotes, the chaperone BiP and ATP are needed. sec61 complex is used alongside
associated proteins, sec 62, 63, 71 and 72. these proteins span the membrane and use
a small domain on the luminal side to deposit the chaperone BiP onto the polypeptide
chain as it emerges into the ER lumen. the removal of BiP is ATP dependent
What types of transmembrane proteins do you know? - ANSWER-Type I: the NH2
terminus is on the luminal side of the ER
Type II: the carboxy terminus is at the luminal side of the ER
How are proteins inserted into the ER membrane? - ANSWER-the proteins contain stop
transfer sequences alongside the initial start transfer sequence.
how is the orientation of protein in the membrane determined? - ANSWER-the charge of
the amino acids on either side of the stop transfer sequence determine the orientation.
positive outside and negative inside
Important multipass proteins in the immune system - ANSWER-Tetraspannins have
four transmembrane segments. CD9, CD81, CD82 and CD63
expressed in professional APC. crucial regulators of antigen presentation. involved in
both loading and trafficking of MHCII
What is GPI? - ANSWER-GLycosylphosphatidylinositol. It anchors proteins to the
membrane. attached to the C terminus of the protein and may be used to redirect
proteins to lipid rafts
BCR and lipid rafts - ANSWER-in the resting state, the BCR is not in a lipid raft. upon
antigen engagement, the BCR relocated within rafts
, what is FcyIIIb? - ANSWER-a GPI linked neutrophil specific IgG FC-receptor affinity
receptor for polyvalent immune complex IgG and decoy receptor that binds IgG
complexes without triggering activation. Basically you can have signal transduction
without activation of neutrophils
what is the most common post translational modification in the ER - ANSWER-N linked
glycosylation on Asparagine. 90% of glycoproteins. All membrane proteins are
glycosylated
most common method of glycosylation - ANSWER-a 14 sugar precursor containing
glucose, n-acetylglucosamine and mannose is added en bloc to the protein. this
precursor is on the transmembrane protein dolichol and is transferred by the membrane
bound enzyme oligosaccharyl transferase.
O-Glycosylation - ANSWER-less common. the oh group of serine or threonine. IgA
antibodies are o-glycosylated
how is correct folding ensured? - ANSWER-with the help of the ER chaperones calnexin
and calreticulin. they bind to incompletely folded proteins, retain them in the ER and
prevent them from irreversible aggregating they recognise N-linked oligosaccharides
that only have one of the original three precursor glucoses on the core. When the third
glucose is removed, the chaperones release the protein and it can leave the ER. The
chaperones can distinguish properly folded proteins from incompletely folded proteins
with the help of glycosyl transferase which continuously adds a glucose to
oligosaccharides that have lost their last glucose. it only however adds glucose to
unfolded proteins.
an unfolded protein undergoes continuos cycles of glucose trimming (glucosidase) and
glucose addition ( glucose transferase), maintaining affinity for calnexin and calreticulin
until it is fully folded.
How are misfolded proteins distinguished from incompletely folded proteins? -
ANSWER-with the help of N-linked oligosaccharides. they serve as timers to measure
how long a protein has been in the ER the slow trimming of a particular mannose on
the core oligosaccharide tree by mannosidase creates a new oligosaccharide structure
that ER luminal lectins of the retrotranslocation apparatus recognise. Proteins that fold
and exit the er faster than the mannosidase can remove its target mannose escape
degradation
What is the common feature of the multiple translocator complexes that move different
proteins from the ER into the cytosol? - ANSWER-They all contain a E3 ubiquitin ligase
that attaches ubiquitin the the unfolded protein as they are exiting the er, marking them
for destruction
