cell bio exam Flashcards
(247 cards)
1
Q
Membrane lipids are important components of the “fluid” part of the __________________
A
fluid mosaic model
2
Q
The fluid mosaic model of membrane structure…
A
retains the lipid bilayer of earlier models
However, there is a greater diversity and fluidity of lipids than originally thought
3
Q
The main classes of membrane lipids are
A
phospholipids, glycolipids, and sterols
4
Q
most abundant lipids in membranes ?
A
phospholipids
5
Q
glycerol-based phosphoglycerides
sphingolipids
are examples of what?
A
Phospholipids
6
Q
alcohols have –
A
1 hydroxyl (OH) group
7
Q
chemical compounds with one hydroxyl group
A
alcohols
8
Q
chemical compounds with two hydroxyl groups
A
diols
9
Q
chemical compounds with three hydroxyl group
A
triols
10
Q
chemical compounds with four hydroxyl groups
A
tetrols
11
Q
chemical compounds with multiple hydroxyl groups
A
polyols
12
Q
smooth ER stores ____ because [blank] is ______
A
smooth ER stores calcium bc Ca is highly reactive
13
Q
function of Ca?
A
another on/off mechanism like phosphorylation
14
Q
give example of Ca on/off mechanism
A
muscle contractions
15
Q
ATP driven pumps take Ca to _______ where it’s stored and then released
A
smooth ER
16
Q
________ take Ca to the smooth ER where it’s stored and then released
A
ATP driven pumps
17
Q
smooth ER also produces
A
lipids, i.e. sterols
18
Q
what does cortisol do
A
suppresses inflam & immune response
19
Q
chronic stress preserves ________-
A
sugar for brain
20
Q
chronic stress preserves sugar for brain. how?
A
breaks down muscle into AAs which are deaminated (broken down for energy) in Kreb’s cycle
this increases blood glucose
21
Q
what do statins do
A
lower cholesterol
22
Q
vitamin d is actually
A
a steroid hormone
23
Q
to be a ‘secretion’ it probably requires
A
exocytosis
24
Q
how do statins work
A
HMG-CoA reductase targeted
decreases smooth ER in liver’s ability to generate cholesterol
25
lipid rafts components?
cholesterol and sphingomyelin
26
define plasma membrane
membrane surrounding cell separating it from extracellular environment
27
lipid rafts are mainly found in which membranes
plasma membranes
28
Golgi analogy
post office (shipping and receiving side
29
CGN and TGN give acronyms
cis-golgi network and trans-golgi network
30
2 golgi models:
cisternae are stationary. mvmt around outside with vesicles
cisternal maturation model
31
Golgi -- glycoproteins (many proteins you know)
A & B antigens in blood, insulin...
32
2 modifications where you can stick a carb to a protein -- happens where
Golgi
33
2 modifications where you can stick a carb to a protein -- give both
N-linked
| O-linked
34
N-linked vs O-linked
| define
N-linked -- nitrogen
| O-linked -- oxygen
35
N-linked vs O-linked give all examples
N-linked -- nitrogen -- asparagine
| O-linked -- oxygen -- serine or threonine
36
what's a glycan
the carb portion of a glucoconjugate
37
glycosidic bond joins ___________
carb to another group
38
N-Linked glycans:
are attached in the endoplasmic reticulum to the nitrogen (N) in the side chain of asparagine (Asn) in the sequon
39
In _______, O-linked glycans are:
eukaryotes
assembled one sugar at a time on a serine or threonine residue of a peptide chain in the Golgi apparatus.
40
only AAs that can attach sugars
sugars ________
asparagine
serine and threonine
can accept a phosphate group
41
if something dissolves in H2O it can be subjected to ________
____ dissolve in water
therefore ______ are water-soluble
if something dissolves in H2O it can be subjected to osmosis
sugars dissolve in water
therefore glycoproteins are water-soluble
42
removal of misfolded proteins e.g. CFTR happens where
rough ER
43
phosphorylation of lysosomes happens where
Golgi
44
sulphonation =
add sulphate to tyronsine
45
give 3 things that happen in golgi
stick carb to protein (n-linked vs o-linked)
phosphorylation of lysosomes
LAST: sulphonation of tyrosine
46
mechanism for prevention of loss of rough ER proteins
retention vs retrieval tags
47
define constitutive
relating to an enzyme or enzyme system that is continuously produced in an organism, regardless of the needs of cells.
After budding from the TGN, some vesicles move directly to the cell surface and immediately fuse with the plasma membrane
This unregulated process is continuous and independent of external signals
48
2 examples each of constitutive vs NON constitutive production
constitutive:
albumin
intestinal mucosa
NON constitutive:
pancreatic enzymes
neurotransmitters
49
opposite of constitutive system
regulative
| e.g. neurotransmitters
50
proteins and nuclear envelope?
proteins must be escorted in and out of nucleus
51
membranes are organised in ________ called _________
microdomains
lipid rafts
52
signal transduction =
binding to receptors
Simplified representation of major signal transduction pathways in mammals.
Signal transduction is the process by which a CHEMICAL OR PHYSICAL SIGNAL IS TRANSMITTED THRU A CELL as a series of molecular events,
-->most commonly protein phosphorylation catalysed by protein kinases,
-->which ultimately results in a cellular response.
Proteins responsible for detecting stimuli are generally termed receptors, although in some cases the term sensor is used.[1]
The changes elicited by ligand binding (or signal sensing) in a receptor give rise to a biochemical cascade, which is a chain of biochemical events known as a signalling pathway.
53
______ is missing from lipid and carb
N
54
limiting factor for protein synthesis
nitrogen
55
what small cellular molecules contain nitrogen
DNA, AAs
56
lipid
carb
protein
which cannot be converted in liver
you cannot convert lipid and carb into protein
57
3 time release fuel types
glucose -- immediate
glycogen -- intermediate (later)
fat -- long (much later)
58
Golgi address labels are
proteins
59
can water go thru membrane? explain.
water can go through membrane, but there's so much
you can leave class through the door or you can leave through the wall
AQUAPORIN
60
____ controls expression of proteins
RNA
61
AT -- active transport
| give 3 purposes
- - expend energy to collect vital nutrients
- - remove waste products (metabolic by-products can build up to toxic levels)
- -generate a concentration gradient
62
biggest ATP drain in cell
Na-K pump
63
I would pit a lysosome against anything small except (3)**
TB, prions, viruses
**not really crucial
64
TB turns off _________-
H+ pump of lysosomes
| theyre not at optimal pH
65
active transport: a pump ______ running
always
66
direct AT ____ATP
| indirect AT ____ATP
direct active transport USES atp
| indirect active transport doesn't use atp
67
indirect AT=
active transport on one side
| facilitated diffusion on the other
68
indirect and direct AT vs concentration gradient
indirect AT uses facilitated diffusion syn concentration gradient
direct AT moves against concentration gradient
69
simple diffusion, facilitated diffusion, & AT
| give solutes transported
simple diff:
- small polar (H2O, glycerol)
- small nonpolar (CO2, O2)
- large nonpolar (oils, steroids)
facilitated diff:
- small polar (H2O, glycerol)
- large polar (glucose)
- ions (Na+, K+, Ca 2+)
active transport:
- large polar (glucose)
- ions (Na+, K+, Ca 2+)
70
simple diffusion, facilitated diffusion, & AT
direction related to electrochemical gradient?
simple diff: down
facilitated diff: down
AT: up
71
simple diffusion, facilitated diffusion, & AT
metabolic energy required?
no, no, yes
72
simple diffusion, facilitated diffusion, & AT
intrinsic directionality?
no, NO, yes
73
simple diffusion, facilitated diffusion, & AT
saturation kinetics?
no, yes, yes
74
simple diffusion, facilitated diffusion, & AT
competitive inhibition?
no, yes, yes
75
simple diffusion, facilitated diffusion, & AT
| membrane protein required?
no, yes, yes
76
cancer cells can mutate to _____________ of chemo drugs
pump out or evacuate entire categories
77
saturation point -- simple diffusion
No saturation point
78
describe simple diffusion
going thru semipermeable membrane
no transport proteins
no saturation point
79
give examples of diffusion **
milk in instant coffee
| air freshener
80
saturation kinetics implies **
whether or not x substance is waiting to cross membrane (if x saturation has been met)
81
thermodynamic properties **
do you need to add energy to get them to react or will concentration gradient -- direction relative to electrochemical gradient -- render the change spontaneous
82
compare concentration gradient and intrinsic directionality
if following the concentration gradient there's no intrinsic directionality
83
give properties of intrinsic directionality
desire to build a concentration gradient
will X always diffuse into the cell
will X always diffuse out of the cell
84
hypertonic solution has
more solute
85
ADH
antidiuretic hormone
| more aquapores on membranes of kidneys
86
aquapore is made of
aquaporin protein
87
inside of cell is normally _______ charged
______ keeps charge more neutral
negatively
K+
88
action potential
____ floods in
____ floods out
previously ________ charge becomes ________
Na floods in
K floods out
previously -- charge becomes ++
89
sodium is attracted to
negative charge inside cell
90
simple diffusion, facilitated diffusion, & AT
Na-K pumps are which
AT
91
AT is needed to move __________ _____ the concentration gradient
AT is needed to move large particles & ions against the concentration gradient
92
AT protein acts like ______
| explain a little
an enzyme
saturation kinetics: same
competitive inhibition
93
indirect AT _______ require ATP
doesn't necessarily
94
indirect AT eg
| using diffusion of Na (from what?) to drive _______
using diffusion of Na following concentration gradient built by Na-K pump to drive glucose into cell
95
simple diffusion, facilitated diffusion, direct & indirect AT
mitochondrial membrane building a gradient is which
indirect active transport
96
v inward = PΔ[S] represents
permeability
97
PΔ[S] -- define Δ[S]
concentration of substance outside cell minus concentration of same substance inside cell
98
v inward = PΔ[S]
facilitated diffusion?
at small concentration gradient (= ____ difference)
increased chance to ________
(per sec)
at small concentration gradient (small difference) there's an increased chance (v fast) to bind
99
define uniport
port carries one type of substance
100
give two other types of ports besides uniport
2 types of coupled transport
symport
antiport
101
simple diffusion, facilitated diffusion, direct & indirect AT
symport and antiport are which types?
can be facilitated diff
can also be AT
(simultaneously)
102
v inward = PΔ[S]
full description
.
v inward = rate of diffusion in moles/sec-cm^2
Δ[S] = [S] outside – [S] inside
P = permeability coefficient, which depends on thickness and viscosity of the membrane
Simple diffusion has a linear relationship between inward flux of solute and the concentration gradient of the solute
103
ATPases are
Transport proteins driven by ATP hydrolysis!
a class of enzymes that catalyse the decomposition of ATP into ADP and a free phosphate ion or the inverse reaction. This de-phosphorylation reaction releases energy, which the enzyme (in most cases) harnesses to drive other chemical reactions that would not otherwise occur. This process is widely used in all known forms of life.
Some such enzymes are integral membrane proteins (anchored within biological membranes), and move solutes across the membrane, typically against their concentration gradient. These are called transmembrane ATPases.
104
dephosphorylation reaction ______ energy
releases energy
105
ATPases are a class of enzymes that catalyse the:
decomposition of ATP into ADP and a free phosphate ion or the inverse reaction.
106
ATPases use energy derived from:
to power:
which in terms of a membrane looks like:
de-phosphorylation of ATP into ADP and PO4
other chem reactions that wouldn't otherwise occur
ATPase is an integral membrane protein moving solutes across against concentration gradients
107
name four classes of ATPase*
identify which pertain to the plasma membrane
P-type
plasma membrane!
V-type
F-type
ABC-type
plasma membrane!
*to assist with another question not important by itself
108
name four classes of ATPase and give examples of solutes transported by each
P-type
cations including bigger metals and H+, phospholipids
V-type
H+
F-type
H+
ABC-type
in eukaryotes: exporters only
exports antitumour drugs, toxins, abx, and lipids
109
give details about P-type ATPases
p for phosphorylation
| enzymes and also transporters (AT)
110
phosphorylation?
on/off switch
111
ptype atpases -- P2 cotransporters
Ca makes muscle cells contract. don't want it floating freely in cytosol
112
give details about V-type ATPases
what's the v for
what do they do & how
v for vacuole
acidify compartment
pump in H+
113
give details about F-type ATPases
what's the f for
classic example
how does it work
where
f for factor
classic: ATP synthase
uses H+ gradient to drive atp synthesis
across inner mitochondrial membrane
114
give details about ABC-type ATPases
ABC stands for ?
name subtypes
powered by ?
example discussed?
ABC for ATP binding cassette (cassette -- something you plug in)
importers and exporters
powered by ATP hydrolysis
e.g., multidrug resistance (MDR)
MDR transport protein
115
ATP hydrolysis is
the catabolic reaction process by which chemical energy that has been stored in the high-energy phosphoanhydride bonds in adenosine triphosphate (ATP) is released after splitting these bonds, for example in muscles, by producing work in the form of mechanical energy. The product is adenosine diphosphate (ADP) and an inorganic phosphate (Pi).
116
MDR transport protein in human cells
| e.g.?
MDR1 -- pump out hydrophobic rx
| e.g., makes cancer resistant to chemo
117
in bacterial cells, transcription and translation is
simultaneous
118
cystic fibrosis affects ______
| give some examples
secretions
respiratory, digestive, integumentary (salty skin?)
119
cystic fibrosis life expectancy
CF usually kills very young
120
CF mutation?
1 single gene
| CFTR protein
121
CF is
a lethal genetic disorder caused by a mutation in a single gene
there are a few other examples of these including sickle-cell anaemia
122
CF mutation details
CFTR
genetic mutation & upshot
pathophysiology
CFTR -- transport protein
Cl- transporter
uses ATP to transport Cl- (it's actually facilitated diffusion that uses ATP; just let it be. a zebra in a herd of horses)
2/3 CF sufferers have same mutation: ΔF508 (f for phenylalanine)
Δ meaning deleted
phenylalanine should be there but it's been deleted in the genetic code
protein won't fold
Cl- ions can still go thru but because cell thinks it's misfolded --> retained in rough ER and sent for destruction
Cl- secreted & water goes with it
water follows charge
mucus secretions not diluted
can't breathe d/t phlegm
123
Δ in a genetic mutation indicates
deletion
124
masked gene -- don't say dormant (it sounds like latent)
won't express
| masked by dominant and recessive allele
125
masked gene -- don't say dormant (it sounds like latent)
won't express
| masked by dominant and recessive allele
126
Na concentration increases, what happens to AAs and sugars' relative transport rate
what does this imply
what type of transport is this
Na conc. increase, AA conc. increase, sugars conc. increase
this implies symport of AAs and sugars into cell
indirect AT -- uses diffusion of sodium, takes in both
facilitated diffusion of Na AND active transport of glucose
127
Na-K-ATPase
cell type
enzyme type
exchange rate
do they happen simultaneously ?
sodium potassium pump
eukaryotic (might be animal cells only)
P-type ATPase
3 sodium out 2 potassium in
not simultaneous -- phosphorylation
128
Na-K pump details
(mark as studied if you know it undergoes conformational change)
trimeric protein
α β γ subunits
The pump has a higher affinity for Na⁺ ions than K⁺ ions, thus after binding ATP, binds 3 intracellular Na⁺ ions.[2]
ATP is hydrolyzed, leading to phosphorylation of the pump at a highly conserved aspartate residue and subsequent release of ADP. This process leads to a conformational change in the pump.
The conformational change exposes the Na⁺ ions to the extracellular region. The phosphorylated form of the pump has a low affinity for Na⁺ ions, so they are released; by contrast it has high affinity for the K⁺ ions.
The pump binds 2 extracellular K⁺ ions, which induces dephosphorylation of the pump, reverting it to its previous conformational state, thus releasing the K⁺ ions into the cell.
The unphosphorylated form of the pump has a higher affinity for Na⁺ ions. ATP binds, and the process starts again.
129
Na-K pump conformational change
remove phosphate from ATP, release sodium, and add it back, take in K
130
Na and glucose symport -- how does it happen
they don't bind to each other but Na changes shape of transport protein
indirect AT of glucose
facil. diff of Na
131
what's signal transduction (long answer)
the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellular response.
The changes elicited by ligand binding (or signal sensing) in a receptor give rise to a biochemical cascade,
When signaling pathways interact with one another they form networks, which allow cellular responses to be coordinated, often by combinatorial signaling events.[2] At the molecular level, such responses include changes in the transcription or translation of genes, and post-translational and conformational changes in proteins, as well as changes in their location.
132
signal transduction
binding to receptors
133
bile salts do what
emulsify lipid so it can be digested
134
albumin does what
water loves it; pulls water into vessels
135
rough and smooth ER together do what (give 2 answers)
build membrane
lipid synthesis
136
ascites is caused by
HTN in hepatic portal vein
137
vacuole & lysosome: pump in _______ constantly
why?
H+
maintain acidity so they can break down accumulated wastes
138
vacuole can fuse w/ an _________ to form a __________ (endocytosis)
early endosome
larger compartment
139
describe v basic animal cell endocytosis
endosome fuse w/ lysosome
| lysosome contains digestive enzymes
140
lysosomal pH?
v low
| 4-5
141
____ are too small for endocytosis
instead, what happens?
viruses
destroy host cell
142
describe self-antigen ?
and the reverse?
the correct version is a 'do not destroy' sign to immune system
DNA/RNA not being transcribed as usual -- self antigen may not be present and cell might be targeted
143
give some components of receptor-mediated endocytosis
example of a coat that forms on vesicles
receptors bind to adaptor proteins then to CLATHRIN
dynamin squeezes off the new vesicle
clathrin
144
which small protein forms football-like structures (hexagon pentagon hexagon) in coated vesicles?
clathrin
145
what cuts off a new vesicle?
| 'boa constrictor' ????
dynamin
146
self-assembling therefore own energy source
| regardless of contents it makes a ---
clathrin
football shape
147
triskelion & relation to endocytosis
a Celtic symbol consisting of three legs or lines radiating from a centre.
-->isle of man flag
clathrin spontaneously forms the lowest-energy shape
148
alcoholism impairs ________
| which causes ?
endocytosis
| decrease in nutrition
149
besides ATP we have GTP
| what uses GTP for energy source?
dynamin eg
150
chronic inflammation leads to mutations why?
required to reproduce cells often
151
pro-inflammatory (esp chronic inflam) assoc with deficiency in _______-
vit B12
152
address labelling on ______ is a ______which indicates ________
vesicle
protein
destination
153
SNARES
hooks
| SNAP receptors
154
_________ bind where it's supposed to go
| every compartment coated with ______
RABs and tethers
| RABs
155
Tay–Sachs disease
an inherited metabolic disorder in which certain lipids accumulate in the brain, causing spasticity and death in childhood.
156
Tay–Sachs disease is a class of
lipid storage disorder / lysosome storage disease
insufficiency of enzyme -- found in lysosomes -- to break down sphingolipids
157
give another lysosome storage disease
hunter syndrome
| large sugar molecules called glycosaminoglycans (or GAGs or mucopolysaccharides) build up in body tissues.
158
transport of O2 necessary for __________
cell respiration
159
natural product of cell respiration found in peroxisomes
h2o2 hydrogen peroxide
160
peroxisomes are not simply like lysosomes
they're a different organelle
161
peroxisomes' function
catabolism of unusual substances
162
N-containing compounds
toxic if formed
| N wants to react
163
these cellular components normally have nitrogen
DNA and proteins
164
these cellular components normally have nitrogen
DNA and proteins
165
resolution limit of light microscope
~200 nm
| 1/2 wavelength 400 nm (blue/violet light)
166
microtubules
thickest
| water inside
167
microfilaments
smallest
| just under surface of cell to periphery
168
mitotic spindle made of _________
microtubules
169
what's a mitotic spindle
cells divide and pull chromosomes apart using this
170
mitotic spindle attaches to ______-
centrosomes
171
centrosomes go where _______is
golgi
| golgi- near nucleus
172
part of cytoskeleton which independently grows and shrinks
microtubules
173
MTOCs?
microtubule organising centres
174
plus and minus end of ________
protofilament (microtubules)
| fast and slow growing end
175
during mitosis what happens to microtubules
break
use tubulin to make mitotic spindle
then after division use same tubulin in microtubules
176
colchicine effects
stop from building mitotic spindle
177
two ways to stop cell division ?
px mitotic spindle from forming
| or break it apart
178
two ways to stop cell division ?
px mitotic spindle from forming
| or break it apart
179
drugs that attack cells which divide rapidly have what problem ?
no discrimination
| also attack other fast-dividing cells eg bone marrow
180
define exergonic
accompanied by the release of energy.
181
facilitated diffusion -- 4 characteristics
transport proteins
down conc grad (towards equilibrium)
large or polar substances
(exergonic -- release energy)
182
Carrier proteins
(transporters or permeases) bind solute molecules on one side of a membrane, undergo a CONFORMATIONAL CHANGE, and release the solute on the other side of the membrane
183
Channel proteins
form hydrophilic channels through the membrane to provide a passage route for solutes
(facil diff)
184
Pores are formed by transmembrane proteins called
porins that allow passage of solutes up to a certain molecular weight to pass (600)
Most channels are smaller and highly selective
ION CHANNELS
quicker than transport -- no conformational change
185
Some channels are large and nonspecific, such as
the pores on the outer membranes of bacteria, mitochondria, and chloroplasts
186
allosteric
allo -- different
steric -- solid (arrangement of atoms in molecule)
--> relating to or denoting the alteration of the activity of an enzyme by means of a conformational change induced by a different molecule.
187
which type of transmembrane proteins act like enzymes?
carrier proteins
| in specificity, saturation kinetics...
188
coupled transport list two types (4 names)
symport (cotransport)
| antiport (countertransport)
189
Channel proteins
list 3 types
ion channels
porins
aquaporins
190
ion channels
gated -- open and close in response to stimulus
muscle contractions
action potential in nerves
191
list 3 types of gated ion channels
voltage
mechanical
ligand
192
The transmembrane segments of porins cross the membrane as
β barrels
| water-filled pore at centre
193
Active transport couples endergonic transport to an exergonic process
, usually ATP hydrolysis
194
Indirect active transport depends on
the simultaneous transport of two solutes
Favorable movement of one solute down its gradient drives the unfavorable movement of the other up its gradient
simultaneous inward movement of Na+ (animals) or protons (plants, fungi, bacteria) down their gradients
195
Direct Active Transport Depends on WHICH FOUR Types of Transport ATPases
P
V
F
ABC
196
AT important example
Na - glucose
sodium symporter
sodium dependent glucose transporters
2 Na -- 1 glucose
release of glucose allows to return to outward facing conformation
197
components of the endomembrane system
The endoplasmic reticulum and the Golgi complex are sites for protein synthesis, processing, and sorting
Endosomes carry and sort material brought into
the cell
Lysosomes digest ingested material and unneeded cellular components
198
ER
The membrane-bound sacs are called ER ______, and the space inside them is the ER _____
cisternae
| lumen
199
ER functions
PROTEIN SYNTHESIS
- membrane proteins
- organelles (including in endomembrane system)
- exports
LIPID SYNTHESIS
200
cytosol
the aqueous component of the cytoplasm of a cell, within which various organelles and particles are suspended.
201
Rough endoplasmic reticulum (rough ER) is characterized by
ribosomes on the cytosolic side of the membrane
202
A subdomain of rough ER, the transitional elements (TEs)
plays a role in the formation of transition vesicles that shuttle lipids and proteins from the ER to the Golgi complex
203
Variation in Amounts of Rough and Smooth ER
Cells involved in synthesis of secretory proteins have prominent rough ER networks
Cells producing steroid hormones tend to have extensive networks of smooth ER
204
Rough ER functions
add carb to glycoprotein
fold protein
remove misfolded protein (QUALITY CONTROL)
assemble multimeric protein
205
In ER-associated degradation (ERAD), proteins that are incorrectly folded, modified, or assembled are exported for degradation
Degradation occurs in cytosolic proteasomes
206
Smooth ER Is Involved in
Drug Detoxification
Carbohydrate Metabolism
Calcium Storage
Steroid Biosynthesis
207
drug detoxification often involves
hydroxylation
Adding hydroxyl groups to hydrophobic drugs increases their solubility, making them easier to excrete from the body
cytochrome p-450 (monooxygenases)
208
The liver stores glucose as
glycogen in granules associated with smooth ER
209
When glucose is needed by the body, glycogen is broken down by
phosphorolysis, producing glucose-6-phosphate
210
smooth ER that specializes in calcium storage
sarcoplasmic reticulum of muscle cells
211
site of cholesterol and steroid hormone synthesis
Smooth ER in some cells
212
Cholesterol, cortisol, and steroid hormones share a _________ but differ in the:
four-ring structure
number and arrangement of carbon side chains and hydroxyl groups
213
committed step in cholesterol biosynthesis
Hydroxymethylglutaryl-CoA reductase (HMG-CoA reductase)
214
In eukaryotic cells, ______ is the primary source of membrane lipids, with a few exceptions:
Mitochondria synthesize phosphatidylethanolamine
Peroxisomes synthesize cholesterol
Chloroplasts contain enzymes for chloroplast-specific lipids
the ER
215
The Golgi complex is functionally and physically linked to the ______
ER
Here, glycoproteins and membrane lipids from the ER undergo further processing and are sorted and packaged for transport
MEMBRANE AND PROTEIN TRAFFICKING
216
anterograde transport
Movement of material toward the plasma membrane
217
Retrograde transport
is the flow of vesicles from Golgi cisternae back to the ER
This allows the cell to balance the flow of lipids toward the plasma membrane
218
glycosylation
the addition of carbohydrate side chains to proteins
219
retention tag
Arg X Arg
| RXR
220
N-methyl-D-aspartate
(NMDA) receptor, important in mammalian neurotransmission, has the RXR tag
It is thought that the tripeptide causes subunits of NMDA to be retained in the ER until the complex is completely assembled
The RXR tag must be masked to allow the assembled complex to leave the ER
221
Golgi Complex Proteins May Be Sorted
according to the Lengths of Their Membrane-Spanning Domains
| hydrophobic domain length vs membrane length
222
The thickness of cellular membranes increases progressively
from the ER (5 nm) to the plasma membrane (8 nm)
223
All Golgi-specific proteins are
integral membrane proteins with one or more membrane-spanning domains
224
Two methods (unique to eukaryotes) for transporting materials across the plasma membrane are
Exocytosis, the process by which secretory vesicles release their contents outside the cell
Endocytosis, the process by which cells internalize external materials
225
secretory granules
Secretory pathways move proteins from the ER through the Golgi complex to secretory vesicles and secretory granules
The secretory granules then discharge their contents to the exterior of the cell
226
pinocytosis
liquids are taken up
227
phagocytosis
solid particles are ingested
228
endocytic vesicles develop into
early endosomes, which fuse with vesicles from the TGN
| They acquire digestive enzymes and form new lysosomes
229
receptor-mediated endocytosis
or clathrin-dependent endocytosis
230
ligand
what is bound (receptor-mediated endocytosis)
| receptor-ligand complexes
231
Fluid-phase endocytosis
is a type of pinocytosis for nonspecific internalization of extracellular fluid
This process does not concentrate the ingested material, and contents are routed to early endosomes
It proceeds at a fairly constant rate and compensates for membrane segments added by exocytosis
232
coated vesicles
proteins on outside give specificity to the vesicle
clathrin cop i cop ii
233
caveolae
another coat protein
lipid raft
cholesterol uptake
234
promote assembly of clathrin coat
adaptor protein complexes
235
dynamin
GTPase
| GTP hydrolysed; dynamin rings tighten
236
clathrin uncoat
uncoating requires ATP
| uncoating ATPase
237
SNARE Proteins
Mediate Fusion Between Vesicles and Target Membranes
238
Rab GTPases
When a vesicle reaches its destination, Rab GTPases (specific for different destinations) lock the complementary SNARE proteins together
This facilitates membrane fusion
239
There are numerous enzymes inside lysosomes;
| all are
acid hydrolases
240
what are each composed of:
microtubules
intermediate filaments
microfilaments
tubulin (dimers)
various
actin
241
critical concntration
The tubulin concentration at which MT assembly is exactly balanced by disassembly
242
Centrosomes have large ring-shaped protein complexes in them; these contain γ-tubulin
γ-tubulin is found only in centrosomes
γ-tubulin ring complexes (γ-TuRCs) nucleate the assembly of new MTs away from the centrosome
Loss of γ-TuRCs prevents a cell from nucleating MTs
243
centrosome is an
mtoc
basal bodies too
244
MAPs
microtubule associated proteins
Tau -- MT form tight bundles in axons
245
keratins
give one more
intermediate filaments
lamins
246
The Cytoskeleton Is a Mechanically Integrated Structure
Microtubules resist bending when a cell is compressed
Microfilaments serve as contractile elements that generate tension
Intermediate filaments are elastic and can withstand tensile forces
247
Animal cells have three common types of junctions
Adhesive junctions -- attach
Tight junctions -- seal spaces between cells
Gap junctions -- gaps directly from cell to cell
