BIO 272 EXAM 2 QUESTIONS AND
ANSWERS
Active Transport types - Correct Answers -- coupled pump (symport and anitiport) -
couple movement down gradient with against (uniport is most simple, always high to low
concentration)
- ATP driven pump - ex Na/K - 3 Na+ out, 2 K+ in or Ca2+ into sarcoplasmic reticulum
or Glucose/Na+ syporter in epithelial cells (high Na+ in, link glucose out). ATP changes
conformational shape, release ADP, Pi to return to original shape
ion channels - Correct Answers -- in selectivity filter, ion dehydrated, electrostatic group
placement must perfectly fit ion to replace H2O. C=O for positive ions (K+), amine group
for neg ions (Cl-)
Protein fates - Correct Answers -remain in cytosol
co/post-translational import into ER
post-translational import into mitochondria/plastids
import into peroxisomes
import into nucleus
N-glycosylation trimming - Correct Answers -- used to monitor if ER proteins folded
correctly
- associate with membrane bound calnexin - glucosidase removes glucose, properly
folded protein leaves ER
ER associated degradation (ERAD) - Correct Answers -- ER proteins unable to fold
properly, redirected to be degraded by cytosolic protease - 26S proteasome
- misfolded protein exported via secretory Sec61 Complex into cytoplasm
- N-glycosylations removed, proteins ubiquitin-modified (signal for degradation by 26S
proteasome
unfolded protein response - Correct Answers -signal transduction pathway to activate
chaperone genes (HSP), increase folding capacity
signal sequence hypothesis - Correct Answers -protein targeting info contained in short
polypeptide sequences to confer targeting to distinct cellular organelles - cleaved from
proteins once at destination
, single sequence - Correct Answers -amino terminal stretch 15-20 AA form hydrophobic
a-helix to target to ER
presequence - Correct Answers -amino-terminal sequence 18-36 AA form amphiphilic
a-helix for mitochondrial targeting
transit peptide - Correct Answers -N-terminal stretch 40-50 AA do NOT form a helix,
enriched in Ser, Pro - target to plastids
nuclear localization signals, peroxisomal targeting - Correct Answers -internal or C-
terminal sequences
Co-translational import to ER - Correct Answers -1) N-terminal sequence recognized by
signal-recognition particle (SRP)
2) when SRP binds to peptide and ribosome, translation stops, SRP receptor (SR) on
ER recognizes ribosome
3) SR brings ribosome into contact with translocation channel (Sec61 Complex), SRP
released, translation resumes
4) peptide chain threaded through translocation channel into ER lumen
Post-translational ER import - Correct Answers -same translocation channel complex
(Sec61 Complex), but instead of SRP-SR, Sec62/63 Complex recognizes signal
sequence, coordinates recruitment of ER lumen. HSP70 chaperones (BiP) not
ribosomes, assist in directional protein translocation (use ATP)
ER import of soluble proteins - Correct Answers -signal peptidase cleaves signal
sequence, closes channel, release protein into ER
Type I integral membrane protein - Correct Answers -Membrane protein with C-terminus
inside and N-terminus outside, can have N terminal start sequence. Hydrophobic a-helix
in middle (stop sequence)
Type II Integral Membrane Protein - Correct Answers -Membrane protein with N-
terminus inside and C-terminus outside,
Bind so + in cytosol, - in ER lumen
Mitochondrial protein import - Correct Answers -Presequence - amphiphilic a-helix (+AA
every ~4 residues to make positive strop, bind to TIM23 complex (use HSP70 pull outer
membrane closer))(need membrane potential)
TIM22 complex non conserved (newer evolutionarily), use chaperones, to inner
membrane
OXA for export out to IMS, conserved trafficking
Chloroplast protein import - Correct Answers -- no membrane potential needed
- added signal sequence for thylakoid membrane
- GTP binds to outer membrane, hydrolyzed to GDP, protein threaded through pore
ANSWERS
Active Transport types - Correct Answers -- coupled pump (symport and anitiport) -
couple movement down gradient with against (uniport is most simple, always high to low
concentration)
- ATP driven pump - ex Na/K - 3 Na+ out, 2 K+ in or Ca2+ into sarcoplasmic reticulum
or Glucose/Na+ syporter in epithelial cells (high Na+ in, link glucose out). ATP changes
conformational shape, release ADP, Pi to return to original shape
ion channels - Correct Answers -- in selectivity filter, ion dehydrated, electrostatic group
placement must perfectly fit ion to replace H2O. C=O for positive ions (K+), amine group
for neg ions (Cl-)
Protein fates - Correct Answers -remain in cytosol
co/post-translational import into ER
post-translational import into mitochondria/plastids
import into peroxisomes
import into nucleus
N-glycosylation trimming - Correct Answers -- used to monitor if ER proteins folded
correctly
- associate with membrane bound calnexin - glucosidase removes glucose, properly
folded protein leaves ER
ER associated degradation (ERAD) - Correct Answers -- ER proteins unable to fold
properly, redirected to be degraded by cytosolic protease - 26S proteasome
- misfolded protein exported via secretory Sec61 Complex into cytoplasm
- N-glycosylations removed, proteins ubiquitin-modified (signal for degradation by 26S
proteasome
unfolded protein response - Correct Answers -signal transduction pathway to activate
chaperone genes (HSP), increase folding capacity
signal sequence hypothesis - Correct Answers -protein targeting info contained in short
polypeptide sequences to confer targeting to distinct cellular organelles - cleaved from
proteins once at destination
, single sequence - Correct Answers -amino terminal stretch 15-20 AA form hydrophobic
a-helix to target to ER
presequence - Correct Answers -amino-terminal sequence 18-36 AA form amphiphilic
a-helix for mitochondrial targeting
transit peptide - Correct Answers -N-terminal stretch 40-50 AA do NOT form a helix,
enriched in Ser, Pro - target to plastids
nuclear localization signals, peroxisomal targeting - Correct Answers -internal or C-
terminal sequences
Co-translational import to ER - Correct Answers -1) N-terminal sequence recognized by
signal-recognition particle (SRP)
2) when SRP binds to peptide and ribosome, translation stops, SRP receptor (SR) on
ER recognizes ribosome
3) SR brings ribosome into contact with translocation channel (Sec61 Complex), SRP
released, translation resumes
4) peptide chain threaded through translocation channel into ER lumen
Post-translational ER import - Correct Answers -same translocation channel complex
(Sec61 Complex), but instead of SRP-SR, Sec62/63 Complex recognizes signal
sequence, coordinates recruitment of ER lumen. HSP70 chaperones (BiP) not
ribosomes, assist in directional protein translocation (use ATP)
ER import of soluble proteins - Correct Answers -signal peptidase cleaves signal
sequence, closes channel, release protein into ER
Type I integral membrane protein - Correct Answers -Membrane protein with C-terminus
inside and N-terminus outside, can have N terminal start sequence. Hydrophobic a-helix
in middle (stop sequence)
Type II Integral Membrane Protein - Correct Answers -Membrane protein with N-
terminus inside and C-terminus outside,
Bind so + in cytosol, - in ER lumen
Mitochondrial protein import - Correct Answers -Presequence - amphiphilic a-helix (+AA
every ~4 residues to make positive strop, bind to TIM23 complex (use HSP70 pull outer
membrane closer))(need membrane potential)
TIM22 complex non conserved (newer evolutionarily), use chaperones, to inner
membrane
OXA for export out to IMS, conserved trafficking
Chloroplast protein import - Correct Answers -- no membrane potential needed
- added signal sequence for thylakoid membrane
- GTP binds to outer membrane, hydrolyzed to GDP, protein threaded through pore
