EXAM 3 Flashcards
(325 cards)
1
Q
the synthesis of proteins as directed by mRNA templates
A
Translation of mRNA
2
Q
Translation of mRNA is _____ in the formation of a functional protein.
A
the first step
3
Q
____________ must fold into appropriate conformations and often undergo various processing steps, sorting, and transport.
A
Polypeptide chains
4
Q
Gene expression is regulated at the level of _________ in both prokaryotic and eukaryotic cells.
A
translation
5
Q
these ultimately regulate all aspects of cell behavior
A
intracellular proteins
6
Q
polypeptide chains are synthesized from the __________ to the ___________
A
amino; carboxy terminus
7
Q
Each amino acid has:
A
3 bases - a codon in the mRNA
8
Q
tRNAs align amino acids with corresponding _________________________
A
codons on the mRNA template
9
Q
They are 70–80 nucleotides long and have characteristic cloverleaf structures.
A
tRNAs
10
Q
All tRNAs fold into:
A
compact L shapes.
11
Q
Which sequence is at the 3’ terminus
A
CCA
12
Q
This binds to the appropriate codon by complementary base pairing.
A
anticodon
13
Q
Attachment of amino acids to specific tRNAs by these enzymes
A
aminoacyl tRNA synthetases.
14
Q
Each of ___ enzymes recognizes a single amino acid, and correct tRNA.
A
20
15
Q
Attachment of amino acids to tRNAs occurs in two steps:
A
- Amino acid join AMP – form aminoacyl AMP.
- Amino acid is transferred to the 3′ CCA terminus of the tRNA and AMP is released.
16
Q
The amino acid is aligned on the mRNA template by:
A
complementary base pairing.
17
Q
most amino acids are specified by: (how many codons)
A
more than one
18
Q
____ different tRNAs for the 20 different amino acids.
A
40
19
Q
Some tRNAs can recognize more than one mRNA codon, as a result of:
A
nonstandard base pairing (wobble) at the 3rd codon position.
20
Q
Nonstandard base pairing allows G to pair with __, and inosine (I) to pair with ________.
A
U; U, C or A
21
Q
Ribosomes are named according to their:
A
sedimentation rates in ultra-centrifugation
22
Q
bacterial ribosome name
A
70S
23
Q
eukaryotic ribosome name
A
80S
24
Q
Amount of ribosomes in growing mammalian cells
A
ten million
25
Ribosomes have _____ subunits
Two
26
Ribosomal subunits contain:
rRNA and proteins
27
rRNA is responsible for:
catalyzing peptide bond formation
28
The large ribosomal subunit functions as a
ribozyme.
29
mRNAs have noncoding __________ at the ends.
untranslated regions (UTRs)
30
Most eukaryote mRNAs are _________, encoding a single protein.
mono-cistronic
31
Prokaryotic mRNAs are often _________, encoding multiple proteins, each of which is translated from an independent start site.
poly-cistronic
32
In both prokaryotes and eukaryotes, translation always starts with:
Methionine (encoded by AUG)
33
Initiation codons in bacterial mRNAs are preceded by a ______________, that aligns the mRNA on the ribosome.
Shine-Dalgarno sequence
34
Eukaryotic mRNAs are recognized by __________________ at the 5′ terminus.
the 7-methylguanosine cap
35
3 stages of translation:
1. Initiation
2. Elongation
3. Termination
36
First step of translation initiation
a specific initiator methionyl tRNA and the mRNA bind to the small ribosomal subunit.
37
Second step of translation initiation
The large ribosomal unit then joins, forming a functional ribosome.
38
A group of ribosomes bound to an mRNA molecule
polysome
39
In eukaryotes initiation is complex, and requires at least ____ proteins, designated eIFs (eukaryotic initiation factors).
12
40
The initiator methionyl tRNA is bound to ____ and the mRNA is brought to the complex by ______.
eIF2
eIF4E
41
Ribosome scan down the mRNA to identify:
AUG initiation codon
42
When AUG is identified, ____ triggers the hydrolysis of GTP bound to _____.
eIF5
eIF2
43
Initiation factors are released, and the ____ subunit joins the complex.
60S
44
In elongation, these are the 3 binding sites on the ribosome:
Peptidyl (P)
Aminoacyl (A)
Exit (E)
45
The initiator methionyl tRNA is bound at the ____ site.
P
46
The next aminoacyl tRNA binds to the ____ site
A
47
Which elongation factor brings the aminoacyl tRNA to the ribosome?
eEF1α
48
Translocation (3 steps)
1. Ribosome moves three nucleotides along the mRNA, positioning the next codon in an empty A site.
2. This step translocates the peptidyl tRNA from A to P, and the uncharged tRNA from P to E.
3. A new aminoacyl tRNA binds to the A site and induces release of the uncharged tRNA from the E site.
49
Translocation requires another elongation factor _______ and is coupled to GTP hydrolysis.
eEF2
50
As elongation continues, the eEF1α (or EF-Tu) released from the ribosome bound to GDP must be:
reconverted to its GTP form.
51
Regulation of eEF1α by GTP binding and hydrolysis is a common method of:
protein regulation.
52
Elongation continues until a _______ is translocated into the A site.
stop codon
53
examples of stop codon sequences
UAA
UAG
UGA
54
___________ recognize the signals and terminate protein synthesis.
Release factors
55
Some translational repressors bind to:
specific sequences in the 3′ UTR.
56
Some translational repressors bind to initiation factor _____, interfering with its interaction with eIF4G and inhibiting initiation of translation.
eIF4E
57
mediated by short double-stranded RNAs, this is used as an experimental tool to block gene expression at the level of translation.
RNAi (RNA interference)
58
RNA interference is mediated by: (2 things)
siRNAs produced from double stranded RNAs
miRNAs transcribed by RNA polymerase II
59
Most miRNAs form:
mismatches that repress translation.
60
siRNAs generally pair perfectly with their targets and induce:
cleavage of the mRNA.
61
These are important in embryonic development, and may play a role to cancer and other diseases.
miRNAs
62
Translation can also be regulated by:
modification of initiation factors
63
Phosphorylation of eIF2 and eIF2B by _______ blocks the exchange of bound GDP for GTP, inhibiting initiation of translation.
regulatory protein kinases
64
In the absence of growth factors, the nonphosphorylated 4E-BPs bind to _____ and inhibit translation.
eIF4E
65
Polypeptide chains must undergo folding and other modifications to become:
functional proteins.
66
3-D protein conformation results from interactions between:
the side chains of the amino acids.
67
act as catalysts that assist the self-assembly process without becoming part of the folded protein.
Chaperones
68
Chaperones bind to and stabilize:
unfolded or partially folded polypeptides intermediates.
69
Chaperones bind to polypeptide chains that are:
still being translated on ribosomes.
70
The chain must be protected from ___________ until synthesis of an entire domain is complete.
aberrant folding or aggregation with other proteins
71
Chaperones also stabilize ___________ during their transport into organelles.
unfolded polypeptide chains
72
Many chaperones were initially identified as ____________, expressed in cells subjected to high temperatures.
heat-shock proteins (Hsp)
73
Hsp70 proteins stabilize polypeptide chains during translation by binding to:
short hydrophobic segments.
74
The polypeptide is then transferred to a _______, where folding takes place
chaperonin
75
Chaperonins consist of:
subunits arranged in 2 stacked rings to form a double-chambered structure.
76
Chaperonin structure isolates the protein from:
the cytosol and other unfolded proteins.
77
catalyzes disulfide bond formation and is abundant in the ER, where an oxidizing environment allows (S—S) linkages.
Protein disulfide isomerase (PDI)
78
catalyzes isomerization of peptide bonds that involve proline residues.
Peptidyl prolyl isomerase
79
Isomerization between the cis and trans configurations of prolyl-peptide bonds could otherwise be a ________ in protein folding.
rate-limiting step
80
Process where cleavage of the polypeptide chain removes portions such as the initiator methionine from the amino terminus.
Proteolysis
81
Proteolytic processing includes formation of ________ by cleavage of larger precursors.
active enzymes or hormones
82
Example of proteolytic processing
Insulin is synthesized as a precursor polypeptide that goes through 2 cleavages to produce the mature insulin.
83
Most enzymes are controlled by changes in conformation, often as a result of:
binding small molecules.
84
Small molecule regulation is common in controlling metabolic pathways by:
feedback inhibition.
85
GDP- bound form of protein is:
Inactive
85
GTP- bound form of protein is:
Active
85
The regulation of translation factors such as ______ by GTP binding is a common mechanism of by which the activities of intracellular proteins are controlled.
eEF1α
85
_________ is reversible; can activate or inhibit proteins in response to environmental signals.
Phosphorylation
86
Phosphorylation is catalyzed by _________, which transfer phosphate groups from ATP to the hydroxyl groups of side chains of serine, threonine, or tyrosine.
protein kinases
87
Phosphorylation is reversed by __________, which catalyze hydrolysis of phosphorylated amino acids.
protein phosphatases
88
Protein kinases are often components of:
signal transduction pathways.
89
Sequential action of a series of protein kinases can transmit a signal from the cell surface to target proteins in the cell, resulting in:
changes in cell behavior in response to environmental stimuli.
90
Interactions between ________ can regulate protein activity.
protein subunits
91
cAMP-dependent protein kinase components
2 regulatory subunits
2 catalytic subunits
92
cAMP acts as an ________ by altering protein-protein interactions.
allosteric regulator
93
Protein levels in cells are determined by:
rates of synthesis and rates of degradation.
94
Many regulatory proteins have _______; this allows levels to change quickly in response to external stimuli.
short half lives
95
The major pathway of protein degradation in eukaryotes
ubiquitin-proteasome pathway.
96
attached to the amino group of the side chain of a lysine residue, then more are added to form a chain.
Ubiquitin
97
The specificity of ________ selectively targets proteins for degradation.
E3 enzymes
98
These are recognized and degraded by a large protease complex, the proteasome.
Polyubiquinated proteins
99
4 stages of Mitosis
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
100
Many proteins that control fundamental cellular processes are targets for:
regulated ubiquitylation and proteolysis.
101
Example of regulated ubiquitylation and proteolysis
Cyclins regulate progression through the division cycle of eukaryotic cells.
102
separates the nuclear contents from the cytoplasm
Nuclear envelope
103
The nuclear envelope controls traffic of _______ through nuclear pore complexes, and plays a critical role in regulating gene expression.
proteins and RNAs
104
The nuclear envelope consists of: (3 things)
2 nuclear membranes
Nuclear lamina
Nuclear pore complexes
105
The outer membrane of the nuclear envelope is continuous with:
endoplasmic reticulum (ER).
106
The inner membrane of the nuclear envelope has proteins that bind to the:
Nuclear lamina
107
Nuclear membranes are:
phospholipid bilayers
108
__________ are the only channels for small polar molecules, ions, and macromolecules.
Nuclear pore complexes
109
a fibrous mesh that provides structural support
Nuclear lamina
110
intermediate filament proteins that associate to form higher order structures.
lamins
111
Two lamins interact to form a:
dimer
112
the α-helical regions wind around each other to form a:
coil
113
_____________ associate with each other to form the lamina.
Lamin dimers
114
Lamins bind to:
Inner membrane proteins
Chromatin
115
________ are composed of about 30 different pore proteins (nucleoporins).
Nuclear pore complexes
116
RNAs synthesized in the nucleus must be exported to the ________ for protein synthesis.
cytoplasm
117
Proteins needed for nuclear functions must be imported from:
synthesis sites in the cytoplasm.
118
Molecules pass through pore complexes by two mechanisms:
1. Small molecules and protein (<40kd) pass freely in either direction
2. Proteins and RNAs are selectively transported; recognized by specific signals.
119
______ are connected to rings at the nuclear and cytoplasmic surfaces.
8 spokes
120
The spoke-ring assembly surrounds a:
central channel.
121
Proteins that must enter the nucleus have amino acid sequences called:
nuclear localization signals.
122
nuclear localization signals are recognized by:
nuclear transport receptors
123
The amino acid sequence responsible for nuclear localization was determined using:
T antigen mutants.
124
The T antigen nuclear localization signal is a single stretch of amino acids in rich basic amino acid residues – (2 types)
lysine and arginine.
125
The nuclear localization signal of ________ is bipartite, consisting of a Lys-Arg sequence, followed by a Lys-Lys-Lys-Lys sequence located ten amino acids farther downstream.
nucleoplasmin
126
Nuclear localization signals (NLS) are recognized by receptors called _______, which carry proteins through the nuclear pore complex.
importins
127
Importins work in conjunction with the GTP-binding protein _____, which controls directionality of movement.
Ran
128
Importins bind to the NLS of a protein, then to nuclear pore proteins and the complex is:
transported across the membrane.
129
In the cytoplasm, Ran GAP ______ the GTP on Ran to GDP, releasing the importin.
hydrolyzes
130
The Ran/GDP formed in the cytoplasm is then transported back to the nucleus by its own import receptor, where Ran/GTP is ________.
Regenerated
131
Proteins are targeted for export by amino acid sequences called
nuclear export signals (NES).
132
NES are recognized by receptors in the nucleus called ________, which direct protein transport to the cytoplasm.
exportins
133
Many importins and exportins are members of a family of nuclear transport receptors known as:
karyopherins
134
Exportins form stable complexes with ______ in association with Ran/GTP in the nucleus.
cargo proteins
135
In the cytoplasm, GTP hydrolysis and release of Ran/GDP leads to:
dissociation of the cargo protein.
136
Function of snRNA in nucleus
pre-mRNA splicing
137
Function of snoRNA in nucleus
RNA processing
138
Karyopherin exportins transport _________ in cytoplasm (3 RNA types)
tRNAs, rRNAs, miRNAs
139
mRNA transport does not involve _______ and is independent of Ran.
karyopherins
140
________ on the cytoplasm side releases the mRNA and ensures unidirectional transport.
helicase
141
In the cytoplasm, the snRNAs associate with proteins to form ___________, which are recognized by an importin and transported back to the nucleus.
snRNPs
142
Chromatin becomes highly _______ during mitosis to form the compact metaphase chromosomes.
condensed
143
During interphase, most chromatin _______ and is distributed throughout the nucleus.
decondenses
144
DNA replication and transcription take place in:
clustered regions.
145
Each chromosome occupies a:
chromosome territory
146
In interphase cells, the _______ is decondensed and transcriptionally-active, and is distributed throughout the nucleus.
euchromatin
147
_________ is highly condensed and not transcribed, and is often associated with the nuclear envelope or periphery of the nucleolus.
Heterochromatin
148
LADs
lamina-associated domains
149
NADs
Nucleolus-associated domains
150
DNA sequences found in NADs substantially ________ those in LADs.
overlap with
151
Where does transcription occur?
Transcription factories (clustered sites)
152
__________ genes may be transcribed in the same factory
Coregulated
153
__________ are organelles within the nucleus that concentrate proteins and RNAs that function in specific nuclear process.
Nuclear bodies
154
Nuclear bodies are not:
enclosed by membranes
155
The _______ functions in rRNA synthesis and ribosome production.
nucleolus
156
Transcription outside the nucleolus occurs by
RNA polymerase III
157
Transcription inside the nucleolus occurs by
RNA polymerase I
158
rRNA genes that make up nucleolar organizing regions
5.8S, 18S, 28S
159
Nucleoli consists of three regions:
Fibrillar center
Dense fibrillar component
Granular component
160
Components of ribosome formation: (3 things)
pre-rRNA
ribosomal proteins
5S rRNA.
161
_________ are produced in the cytoplasm and imported to the nucleolus.
Ribosomal proteins
162
_______ are transcribed outside of nucleolus and produced elsewhere in the nucleus.
5S rRNAs
163
Pre-ribosomal particles are then exported to the cytoplasm, yielding the __________
40S and 60S ribosomal subunits.
164
________ are involved in assembly of snRNPs and other RNA-protein complexes
Cajal bodies
165
The enzyme for _________ is concentrated in Cajal bodies.
RNA methylation
166
Following assembly and maturation in Cajal bodies, snRNPs are transferred to ________, which also contain splicing factors.
speckles
167
Speckles are recruited to actively transcribed genes where _________ occurs.
pre-mRNA processing
168
network of membrane-enclosed tubules and sacs (cisternae) - extends from nuclear membrane throughout cytoplasm.
Endoplasmic reticulum (ER)
169
Rough ER
ribosomes on the outer surface.
170
Smooth ER
lipid metabolism
171
The secretory pathway (4 parts)
Rough ER > Golgi > secretory vesicles > outside of cell
172
Proteins synthesized on ________ stay in the cytosol or are transported to the nucleus and other organelles.
free ribosomes
173
Proteins synthesized on _______________ are translocated directly into the ER through translocon.
membrane-bound ribosomes
174
Proteins move into the ER during their synthesis on membrane-bound ribosomes. (type of translocation)
Cotranslational translocation
175
Proteins move into the ER after translation has been completed on free ribosomes. (type of translation)
Posttranslational translocation
176
Ribosomes are targeted to the ER by a signal sequence at the _________ which is removed when the growing polypeptide chain enters the ER.
amino terminus
177
The role of signal sequences in targeting proteins to correct locations was determined by in vitro preparations of:
Rough ER.
178
Orientations vary—the amino (N) or the carboxy (C) terminus is on the _______ side
cytosolic
179
The lumen of the ER is topologically equivalent to the:
exterior of the cell.
180
Domains of membrane proteins that are exposed on the cell surface correspond to regions of _______ that are translocated into the ER lumen.
polypeptide chains
181
Some proteins have an _______________ signal sequence cleaved by signal peptidase during translocation through translocon.
amino terminal
182
a _____________________ in the middle of the protein halts translocation and anchors the polypeptide in the membrane.
transmembrane α helix
183
The carboxy terminal portion of the growing polypeptide remains in the:
cytosol
184
Many proteins are inserted directly into the ER membrane by:
internal transmembrane sequences.
185
Internal transmembrane sequences are recognized by SRP, but not cleaved by ______________
signal peptidase.
186
Proteins that span the membrane multiple times are inserted as a result of a series of transmembrane sequences with _______________ orientations.
alternating
187
Protein folding and processing can occur here during translocation:
(2 places)
across the ER membrane or
within the ER lumen.
188
The primary role of lumenal ER proteins is to
(2 functions)
assist folding
assembly of newly translocated polypeptides
189
Formation of _______ bonds is important in protein folding.
disulfide
190
In the cytosol, which is a ______ environment, most cysteine residues are in their reduced (—SH) state.
reducing
191
In the ER, an _______ environment promotes disulfide (S—S) bond formation, facilitated by protein disulfide isomerase.
oxidizing
192
Proteins are glycosylated on specific ________ (N-linked glycosylation) as they are translocated into the ER.
asparagine residues
193
____________ helps prevent protein aggregation in the ER and provides signals for subsequent sorting.
Glycosylation
194
Some proteins are attached to the plasma membrane by glycolipids called:
GPI anchors
195
GPI anchors are assembled in the ______ and added to the carboxy terminus of some polypeptides.
ER membrane
196
Misfolded proteins are removed from the ER by
ER-associated degradation (ERAD).
197
If an excess of unfolded proteins accumulates, a signaling pathway called the _________ is activated.
unfolded protein response (UPR)
198
UPR leads to production of:
more chaperones
199
If protein folding can’t be adjusted to a normal level, the cell undergoes:
programmed cell death.
200
Unfolded proteins activate 3 receptors in the ER membrane:
1. IRE1
2. ATF6
3. PERK
201
Hydrophobic _________ are synthesized in association with already existing membranes rather than the aqueous cytosol.
membrane lipids
202
Most lipids are synthesized in:
smooth ER
203
Eukaryotic membranes are made of 3 lipid types:
phospholipids
glycolipids
cholesterol
204
Most of phospholipids are synthesized on the ___________ side of the ER membrane from water-soluble precursors (glycerol).
cytosol
205
New phospholipids are added only to the _______ half of the ER membrane.
cytosolic
206
Some phospholipids must be transferred to the other half: requires passage of polar head groups through the membrane, called:
flippases
207
_______ is converted to glycolipids or sphingomyelin in the Golgi apparatus.
Ceramide
208
abundant smooth ER, where steroid hormones are synthesized, is found in cells of the:
testis and ovary
209
Proteins in the lumen of one organelle are packaged into _________________, then released to the lumen of the recipient organelle following vesicle fusion.
transport vesicles
210
Membrane proteins and lipids are transported in a similar way; their ________ is maintained.
topological orientation
211
Proteins that function within the ER, such as BiP, have a targeting sequence (i.e. _______) at the carboxy terminus that directs retrieval back to the ER.
KDEL or KKXX
212
Most glycolipids and sphingomyelin are synthesized in the _____
Golgi
213
2 components of the Golgi:
1. cisternae
2. associated vesicles.
214
Proteins from ER enter at convex ___ face of Golgi and exist from the concave _____ face
cis; trans
215
receives molecules from the ERGIC
Cis compartment (Golgi)
216
most modifications are done here in the Golgi
medial and trans compartments
217
the sorting and distribution center
trans-Golgi network
218
model in which proteins are carried between cisternae in transport vesicles.
stable cisternae model
219
model in which proteins are carried within the cisternae, which gradually mature and progressively move through the Golgi in the cis to trans direction.
cisternal maturation model
220
Vesicles return Golgi resident proteins back to:
earlier Golgi compartments.
221
carbohydrates added to side chains of serine and threonine
O-linked glycosylation
222
______ is synthesized by transfer of a phosphorylcholine group from phosphatidylcholine to ceramide.
Sphingomyelin
223
Addition of carbohydrates to ceramide yields:
different glycolipids.
224
Transport from the Golgi to the cell surface can occur by three routes:
Direct transport
Recycling endosomes
Regulated secretory pathways
225
In polarized cells of epithelial tissue, plasma membranes are divided into (2 domain types)
apical domains and basolateral domains
226
Transport vesicles with secretory proteins are coated with
coat proteins.
227
carry proteins from the ER to Golgi apparatus.
COPII-coated vesicles
228
bud from the ERGIC or Golgi and carry their cargo back, returning proteins to earlier compartments.
COPI-coated vesicles
229
transport in both directions between the trans Golgi network, endosomes, lysosomes, and plasma membrane.
Clathrin-coated vesicles
230
Formation of coated vesicles is regulated by small GTP-binding proteins (ARF1 and Sar1) related to:
Ras and Ran
231
The _________ recruit adaptor proteins that mediate vesicle assembly by interacting with cargo proteins and with coat proteins.
GTP-binding proteins
232
Interaction between transport vesicles and target membranes is mediated by ________ and small-GTP binding proteins (Rab proteins).
tethering factors
233
ubiquitous proteins that direct vesicular trafficking and exocytosis
SNAREs
234
SNARE proteins have a central _______ domain.
coiled-coil
235
___________ pairing of vesicle and target SNAREs; destabilize them and fuse.
SNARE-SNARE
236
membrane-enclosed organelles that contain enzymes to break down all types of biological polymers.
Lysosomes
237
lysosomal storage diseases result in:
undegraded material accumulation.
238
The enzyme deficiency in _____ disease prevents the hydrolysis of glucosylceramide to glucose and ceramide
Gaucher
239
To maintain the ______ pH, a proton pump in the lysosomal membrane actively transports protons into the lysosome.
acidic
240
Lysosomes digest material taken up from outside the cell by:
endocytosis.
241
Types of endosomes: (3 types)
early
recycling
late
242
Early endosomes separate molecules targeted for recycling from those destined for:
degradation
243
Molecules destined for degradation are transported to multivesicular bodies and then to ___________
late endosomes.
244
turnover of the cell’s own components.
autophagy
245
A small area of cytoplasm or organelle is enclosed in a vesicle (________) which fuses with a lysosome, and its contents are digested.
autophagosome
246
Autophagy can also be regulated during development and in response to _____
stress.
247
The cytoskeleton is composed of three main types of protein filaments:
Actin filaments
Microtubules
Intermediate filaments
248
Actin polymerizes to form actin filaments called
microfilaments
249
All the actin monomers are oriented in the same direction, so actin filaments have
polarity.
250
________ is the first step of actin polymerization—a trimer is formed, and monomers are then added to either end.
Nucleation
251
Actin polymerization is ________; the filaments can be broken down when necessary.
reversible
252
________ has tight binding sites that mediate head-to-tail interactions with two other actin monomers, to form ________
G actin, F actin
253
Actin bound to ATP associates with the _______, and the ATP is then hydrolyzed to ADP.
plus ends
254
___________ is critical in regulating actin filaments within the cell.
Treadmilling
255
_______ is less tightly bound than ATP-actin and dissociates at the minus end
ADP-actin
256
______ bind ATP-actin and nucleate initial polymerization of long unbranched actin filaments.
Formins
257
________ binds actin monomers and stimulates exchange of bound ADP for ATP, increasing the local concentration of ATP-actin.
Profilin
258
initiate growth of branched actin filaments, important in driving cell movement at the plasma membrane.
Arp2/3 complex
259
stabilize actin filaments by binding lengthwise along the groove of the filament.
Tropomyosins
260
severs filaments, generating new ends which are then available for polymerization or depolymerization.
Cofilin
261
Name for filaments that are cross-linked into closely packed parallel arrays.
Actin bundles
262
Name for filaments that are cross-linked in arrays that form 3-D meshworks with the properties of semisolid gels.
Actin networks
263
The fibroblasts attach to the matrix via binding of transmembrane proteins called
integrins
264
Sites of attachment
focal adhesions
265
large actin bundles
stress fibers
266
Two other proteins, _______ are involved in binding stress fibers.
talin and vinculin
267
In sheets of epithelial cells, cell–cell contacts (adherens junctions) form a _________ around each cell.
continuous adhesion belt
268
Contact is mediated by transmembrane proteins called:
cadherins
269
Cadherins bind to cytoplasmic _____, which anchor actin filaments to the plasma membrane.
catenins
270
generate energy from breakdown of lipids and carbohydrates.
Mitochondria
271
use sunlight energy to generate ATP and reducing power to synthesize carbohydrates from CO2 and H2O.
Chloroplasts
272
contain enzymes involved in a variety of metabolic pathways.
Peroxisomes
273
Mitochondria and chloroplasts also have their own
genomes
274
Mitochondria are surrounded by a
double membrane system
275
The inner membrane of the mitochondria has numerous folds called ______, which extend into the interior (matrix).
cristae
276
_______ contains genetic system and enzymes for oxidative metabolism.
The matrix
277
The _______ is transported into mitochondria, where its complete oxidation to CO2 yields the bulk of usable energy (ATP) obtained from glucose metabolism.
pyruvate
278
_______ from NADH and FADH2 are transferred through a series of carriers in the membrane to molecular oxygen.
High-energy electrons
279
The energy derived from this is converted to potential energy stored in a _______, which drives ATP synthesis.
proton gradient
280
The inner membrane of mitochondria contains a high percentage of proteins involved in: (2 things)
oxidative metabolism and transport.
281
The inner membrane of mitochondria is ________ to most ions and small molecules—this helps maintain the proton gradient.
impermeable
282
The outer mitochondrial membrane
is _________ to small molecules.
Highly permeable
283
form channels that allow the free diffusion of small molecules through the inner mitochondrial membrane
porins
284
Composition of the intermembrane space is similar to:
cytosol
285
Mitochondrial genomes consist of _____ DNA molecules, present in multiple copies
circular
286
Mitochondrial genomes encode all the rRNAs and most of the tRNAs needed for
translation
287
The human mitochondrial genome
encodes ______ proteins involved in electron transport and oxidative phosphorylation.
13
288
U in the tRNA anticodon can pair with any of the four bases in the _____ codon position of mRNA
third
289
_____ codons are recognized by a single tRNA
four
290
causes blindness; mutations in mitochondrial genes for electron transport chain.
Leber’s hereditary optic neuropathy
291
Most of the mitochondrial proteins are synthesized on
free ribosomes
292
______ bind to receptors on the mitochondria: protein complex (translocase of the outer membrane, or Tom complex).
Presequences
293
Proteins are then transferred to complex in the inner membrane called
Tim complex
294
Presequences in the mitochondria are cleaved by ________ and the polypeptide is bound by other Hsp70 chaperones that facilitate folding.
matrix processing peptidase (MPP)
295
Some proteins with multiple trans-membrane domains have _______ instead of presequences.
internal import signals
296
Some inner membrane proteins are encoded by the:
mitochondrial genome.
297
Some inner membrane proteins are synthesized on ribosomes in the mitochondrial matrix and targeted to the ______ in the inner membrane.
Oxa translocase
298
Proteins destined for the outer membrane or intermembrane space pass through the
Tom complex.
299
Proteins with single transmembrane domains are inserted via the outer membrane protein called
Mim1.
300
Most mitochondria membrane lipids are imported from
cytosol
301
________ improves efficiency of oxidative phosphorylation by restricting proton flow across the membrane.
Cardiolipin
302
Lipid transfer between ER and mitochondria is mediated by
phospholipid transfer proteins
303
Transport of ATP and ADP is mediated by an integral membrane protein, _________.
adenine nucleotide translocator. (ANT)
304
ATP carries a more negative charge than ADP (–4 compared to –3), so exchange is driven by the ________ of the electrochemical gradient.
voltage component
305
Pi is brought in as phosphate (H2PO4–) in exchange for hydroxyl ions (OH–).
This exchange is electrically _______, but is driven by the proton concentration gradient.
neutral
306
_______ within mitochondria corresponds to a higher concentration of hydroxyl ions, favoring their translocation to the outside.
Higher pH
307
fatty acids, and lipid components of their own membranes.
Nitrite (NO2–) reduction to ammonia (NH3), essential for incorporation of N into organic compounds, occurs in _______
chloroplasts
308
Chloroplasts are bounded by a double membrane called _______
the chloroplast envelope
309
An internal membrane system, the _______ membrane, forms a network of flattened discs
thylakoid
310
inside the envelope but outside the thylakoid membrane
stroma
311
Chloroplast membranes are functionally similar to those of:
mitochondria
312
The stroma is equivalent in function to the
mitochondrial matrix
313
Electron transport and chemiosmotic generation of ATP takes place in the
thylakoid membrane.
314
The chloroplast genes encode both RNAs and proteins involved in (2 things)
gene expression
photosynthesis.
315
One subunit of ______ is encoded by chloroplast DNA.
rubisco
316
________ (transit peptides), direct translocation across the two chloroplast membranes of the envelope and are then removed by proteolytic cleavage.
N-terminal sequences
317
outer stroma membrane
Toc complex
318
Inner stroma membrane
Tic complex
319
Stroma transit peptide
stromal processing peptidase (SPP).
320
Proteins that must cross the thylakoid membrane have a _________, exposed after cleavage of the transit peptide.
second signal sequence
321
Proteins are translocated into the thylakoid lumen by two different pathways:
1. Sec
2. Tat
322
Signal sequences are cleaved by:
thylakoid processing protease (TPP).
