Eukaryotes, cell structure Flashcards
1
Q
How do bacteria replicate/divide?
A
Binary fission
2
Q
What is a membraneless cellular compartment called?
A
A biomolecular condensate
3
Q
Give an example of a biomolecular condensate
A
Rubisco enzyme
4
Q
What 2 structures do biomolecular condensates require?
A
Scaffold macromolecules and client proteins
5
Q
Give the overall structure of the nuclear envelope
A
Outer nuclear membrane
Perinuclear space (20-40nm)
Inner nuclear membrane
6
Q
How do proteins enter the nucleus? What do they require?
A
They require a Nuclear Localization Signal (NLS) and are transported by importin through nuclear pores
7
Q
What can passively diffuse through the nuclear pore?
A
Small molecules like metal ions and ATP (cutoff: ~30,000 Da or ~9 nm diameter)
8
Q
What is the role of importin in nuclear import?
A
It binds to NLS-containing proteins and facilitates their entry into the nucleus
9
Q
What regulates nuclear import and export? Briefly state how
A
Ran-GTPase, a protein that switches between GTP- and GDP-bound states
10
Q
What gradient does nuclear export require?
A
Gradient of Ran-GTP and Ran-GDP across nuclear membrane
11
Q
What is the NES?
A
Nuclear Export Signal; required for protein export via exportin and Ran-GTP
12
Q
What is the nuclear lamina?
A
A fibrous mesh of intermediate filaments beneath the inner membrane, maintaining nuclear shape
13
Q
How is chromatin organised in the nucleus?
A
Each chromosome occupies a distinct “territory,” and associates with the nuclear lamina
14
Q
What are the 3 types of endoplasmic reticulum?
A
Rough ER, Smooth ER, and Transitional ER
15
Q
What is the function of the rough ER?
A
Protein production and folding
16
Q
What is the function of the smooth ER?
A
Lipid biosynthesis, detoxification (e.g., cytochrome P450), and calcium storage in muscle (sarcoplasmic reticulum)
17
Q
What is the transitional ER?
A
Specialized regions that form vesicles to transport proteins/lipids to the Golgi
18
Q
What is the basic structure of the golgi?
A
Stacked cisternae: cis (entry), medial, and trans (exit)
19
Q
What happens to the Golgi during cell division?
A
It breaks up and later reforms
20
Q
What is the function of the Golgi apparatus?
A
Modifying, sorting, and packaging proteins and lipids for transport
21
Q
What is the vesicular transport model?
A
Cargo moves between stable cisternae via vesicles; enzymes stay in place
22
Q
What is the cisternal maturation model?
A
Cisternae themselves mature and move; enzymes move backward via vesicles
23
Q
What determines where a vesicle goes?
A
Specific protein coats and signals on cargo/vesicle
24
Q
Name the 4 types of coated vesicles and their roles
A
Clathrin-coated: Golgi/endosome to membrane.
COPI-coated: Retrograde transport from Golgi.
COPII-coated: Anterograde from ER.
Retromer-coated: Endosome retrieval to Golgi.
25
What structure constitutes more than half the total membrane of the average animal cell?
The endoplasmic reticulum
26
What is the role of the transitional ER?
To produce vesicles with proteins or lipids for transport to Golgi apparatus
27
What is the cis-complex of the Golgi apparatus?
Adjacent to ER - receives proteins from the ER
28
Where does the trans complex of the Golgi apparatus sit?
Toward the plasma membrane
29
In 1 word, what is the structure of a clathrin coated vesicle?
Triskelion
30
What is an SRP?
A signal recognition particle
31
What are the 3 main modes of protein transport across a membrane?
Gated transport (e.g., nuclear pores)
Protein translocation (e.g., into the ER lumen during synthesis)
Vesicular transport (using membrane-bound vesicles)
32
What guides a protein with an ER signal into the ER?
SRP (Signal Recognition Particle), which brings the ribosome to the ER translocator via the SRP receptor
33
What are the key steps of co-translational translocation?
ER signal sequence on the new peptide is recognized by SRP.
SRP binds to SRP receptor on the ER membrane.
Ribosome is guided to the translocator channel.
Protein is synthesized directly into the ER lumen.
Protein unfolds during entry and refolds inside the ER.
34
What are the 4 steps in vesicle formation?
Cargo selection
Membrane bending
Protein coating
Coat disassembly
35
What prevents complete entry of a transmembrane protein into the ER lumen?
The Stop-transfer sequence
36
What happens to the protein during translocation into the ER?
It unfolds to pass through the translocator and refolds afterward
37
What mediates vesicle fusion?
v-SNAREs (on vesicle) and t-SNAREs (on target membrane) zip together, forcing membrane fusion
38
How is SNARE pairing highly specific?
Only complementary v-SNAREs and t-SNAREs can interact and zip together
39
What proteins are involved in vesicle tethering and docking?
Rab GTPases interact with tethering proteins on the target membrane
40
What 3 things determine a vesicle's location?
Coat proteins = address label
Phospholipid profile = postcode
Rab GTPases = postman
41
What are the 2 types of exocytosis?
Constitutive: continuous delivery of membrane components.
Regulated: vesicles released in response to a stimulus (e.g. insulin, histamine)
42
How is insulin secretion regulated in terms of exocytosis?
High glucose → ATP ↑ → K⁺ channel closes → Ca²⁺ influx → vesicles with insulin fuse with membrane
43
What triggers histamine release from mast cells?
A stimulus detected by surface receptors triggers regulated exocytosis of histamine granules
44
What are the 2 main types of endocytosis?
Phagocytosis: uptake of large particles ("eating")
Pinocytosis: uptake of fluid and small molecules ("drinking")
45
How does a cell balance volume while pinocytosing its own membrane?
Through membrane recycling and regulated surface area dynamics
46
What is ACE2?
A receptor for SARS-CoV-2 and a regulator of blood pressure and fluid homeostasis, highly expressed in lung, heart, and kidney cells
47
What are endosomes?
Intracellular sorting organelles in eukaryotic cells that play a crucial role in the endocytic pathway, transporting molecules and lipids between the plasma membrane, Golgi apparatus, and lysosomes
48
What are early and late endosomes?
Early: near the plasma membrane; Late: deeper in cytoplasm. Endosomes acidify over time (pH 5–6) via H⁺ pumps
49
What are lysosomes?
Acidic compartments with hydrolytic enzymes (≈40 types) to degrade proteins, lipids, nucleic acids, and sugars
50
How is the acidic environment in lysosomes maintained?
Using an ATP-driven proton (H⁺) pump
51
What is the plant vacuole and what are its functions?
Large, fluid-filled organelles (30–90% of cell volume) used for storage, degradation, turgor pressure regulation, and pH homeostasis
52
What do peroxisomes contain?
Oxidative enzymes like catalase and urate oxidase
53
What is a key product and function of peroxisomes?
Hydrogen peroxide (H₂O₂), used to oxidize lipids and detoxify compounds (e.g., alcohol)
54
How are peroxisomes formed?
Via vesicular transport of peroxisomal membrane proteins from the ER
55
What kind of cell has no mitochondria?
Red blood cell
56
What kind of cells have over 1000 mitochondria per cell?
Liver
57
What is the inner mitochondrial membrane folded into?
Cristae
58
How many protein complexes and proton pumps are there in the ETC?
4 complexes and 3 pumps
59
What enzyme converts ADP to ATP in the ETC?
F1 ATPase
60
What 3 components do chloroplasts have in common with mitochondria?
Double membrane, highly permeable outer membrane, tight intermembrane space
61
What compartment contains the molecular machinery for photosynthesis?
Thylakoid
62
What is a thylakoid stack called?
Granum
63
What is the thylakoid membrane impermeable to?
ATP and NADH
64
What simple 3 carbon sugar is produced in the stroma as a precursor for other molecules?
Glyceraldehyde-3-phosphate
65
What is the most abundant enzyme in the world?
RUBISCO
66
What is a ribosome made up of?
RNA and proteins
67
What is the size of the eukaryotic ribosome? What is each subunit?
80S ribosomes
40S (small) subunit
60S (large) subunit
68
What is the Svedberg unit?
Sedimentation rate in ultracentrifugation
69
What is the size of the prokaryotic ribosome? What is each subunit?
70S
Small subunit 30S
Large subunit 50S
70
How many tRNA binding sites are there on a ribosome?
3
71
What are the names of the tRNA binding sites on a ribosome?
EPA
72
What is the advantage of having the A and P sites of a ribosome very close together?
No stray base in between (maintain
correct reading frame)
73
What enzyme has a large amount of activity in the ribosomal translation mechanism?
Peptidyl transferase
74
What bonds connect amino acids?
Peptide
75
How many protofilaments are there per microtubule?
13
76
What is the basic building block of a microtubule?
⍺ & β tubulin heterodimer
77
Which end of the microtubule is beta-tubulin?
Plus end
78
How similar % are yeast and human tubulin to each other?
75%
79
Which tubulin-bound GTP gets hydrolysed to GDP in microtubule growth? Alpha or beta?
Beta-tubulin bound GTP is hydrolsed to GDP
80
What are the 2 terms used commonly to describe microtubule dynamics?
Nucleation
Polymerisation
81
What 3 things does microtubule nucleation require?
Gamma-tubulin
Accessory proteins
High concentrations of alpha beta tubulin heterodimers
82
What complex promotes microtubule nucleation?
Gamma-tubulin ring complex
83
What is the primary MT organising centre in most cells?
Centrosome
84
What does the Dynamic Instability behaviour of MT require?
Constant energy input - GTP
85
How does microtubule catastrophe occur?
When GTP in β-tubulin is hydrolysed, GDP-bound β-tubulin makes MT unstable
86
What does a growing microtubule contain?
A GTP cap
87
How can the plus end of a growing MT be stabilised?
Attaching to another molecular or cellular structure
88
What does taxol do?
Stabilises microtubules, so there is no shrinkage
Works as a very potent anti-cancer drug
89
What does colchicine do?
Binds free tubulin dimers
prevent MT polymerisation
Used for gout
90
What are the motor proteins that bind MTs? What directions do they take?
Kinesin (plus-end directed)
Dynein (minus-end directed)
91
What process do motor proteins use to move?
ATP hydrolysis
92
What part of chromosomes do MTs attach to?
Kinetochore
93
What structure forms the base of cilia and flagella?
A centriole
94
Describe the organisation of microtubules in cilia and flagella
“9 + 2” arrangement
9 outer MT doublets + 2 central MT pairs
95
What proteins connect the outer doublets of microtubules in cilia and flagella?
Nexins
96
How do cilia and flagella move?
MT doublets are linked (by linking proteins)
Dynein movement results in MT bending of
doublets, rather than sliding
Creating waves or beating motions
97
What 5 places can you find actin filaments?
Microvilli (e.g. intestinal epithelial cells)
Contractile Bundles in cytoplasm
Filopodia of migrating cells
Contractile ring during cell division
Contractile bundles stained with fluorescently-labelled Phalloidin
98
Describe the structure of actin filaments
Made up of actin monomers
Actin monomer within the filaments have the same orientations
Two-stranded helical protofilament with a
twist repeating every 37nm
Extensive lateral interactions between two
strands prevent strand separation
99
What does the head to tail structure of actin monomers create?
Polarity
100
What is bound in the deep cleft of an actin monomer?
Either ADP or ATP
101
Which end do microfilaments grow faster?
Plus end (barbed)
102
Describe the process of polymerisation of an actin filament (treadmilling)
Actin monomer in cytosol carry ATP,
ATP is hydrolysed to ADP when actin monomer assembles into growing actin filament
ADP remains trapped within filament until the actin monomer dissociates from filament
103
Why does actin treadmilling occur?
Actin-ATP & Actin-ADP have different conformation and binding affinities
Actin-ADP is less stable, so has a lower affinity to neighbour, easier to dissociate from filament
104
When does actin treadmilling occur?
When actin monomer concentration is intermediate
Rate of addition at plus end = Rate of
loss at minus end
105
What are the 4 steps of the general cell migration model?
Protrusion
Adhesion
Contraction
Release
106
What is the role of bundling proteins in actin structures?
Bundling proteins stabilize actin filaments in structures such as filopodia and microvilli
107
Which bundling protein is specifically associated with filopodia?
Fascin
108
What are filopodia?
Slender, finger-like cytoplasmic extensions that protrude from the cell membrane, primarily composed of actin filaments
109
Which bundling protein is found in the microvilli of gut epithelium?
Vilin
110
What are myofibrils composed of?
Multiple sarcomeres
111
What are muscle fibres composed of?
Multiple myofibrils
112
What structure does Myosin-II form in skeletal muscle?
Dimers that assemble into the thick filament
113
How does myosin-II generate force?
By coupling ATP hydrolysis to conformational changes that allow it to "walk" along actin filaments
114
What is the most durable kind of cytoskeleton?
Intermediate filaments
115
Describe the structure of an intermediate filament
1. Alpha-helical monomer (no nucleotide binding)
2. Coiled-coil dimers (Two parallel coils wound together)
3. Two dimers side-by-side
- antiparallel tetramer
- Tetramer held by lateral interactions
4. Association with another tetramer
5. 8 tetramers twisted into filament
116
What are the 4 families of intermediate filaments?
Keratin
Vimentin
Neurofilaments
Nuclear lamins
117
How do keratin filaments link directly through cells?
Through desmosomes
118
What acts as the glue between different cytoskeletons?
Plectin
119
Why is binary fission important for prokaryotes?
It allows rapid asexual reproduction roughly every 20 minutes.
120
What limits the size of prokaryotic cells?
Surface area to volume ratio diffusion rates and the need to maintain high concentrations of enzymes and substrates.
121
How does SA:vol ratio affect prokaryotic cells?
Smaller cells have a higher surface area relative to their volume allowing efficient exchange of nutrients and gases.
122
Why does diffusion limit prokaryotic cell size?
As cell size increases diffusion rates decrease making molecular transport inefficient.
123
Why are high concentrations of compounds needed in cells?
To allow biochemical reactions to occur efficiently.
124
What is compartmentalisation in eukaryotic cells?
Division of the cell into membrane-bound organelles allowing localisation and concentration of cellular processes.
125
Why is compartmentalisation important?
It enables differentiation and specialisation of cell functions and supports complex multicellular organisms.
126
What are organelles?
Subcellular compartments often membrane-bound with specific structures and functions.
127
What do transport systems in eukaryotic cells require?
ATP and organisation for cell signalling and intracellular movement.
128
What are biomolecular condensates?
Non-membrane compartments formed by aggregation of macromolecules like proteins or nucleic acids.
129
How do biomolecular condensates form?
Scaffold molecules like RNA or proteins form weak reversible interactions creating dynamic liquid-like droplets.
130
What is phase separation?
The coexistence of different biomolecular condensates within a larger structure.
131
Give an example of a biomolecular condensate
Rubisco enzyme compartments in photosynthetic bacteria or the pericentriolar material of centrosomes.
132
What microscopes have advanced our study of cells?
From Hooke's microscope to light confocal and electron microscopes.
133
What does digitisation allow in microscopy?
Still images and live-cell imaging.
134
What is GFP and why is it useful?
Green fluorescent protein from jellyfish used to label proteins in living cells.
135
What is the origin theory for mitochondria and chloroplasts?
Endosymbiosis where an archaeon engulfed bacteria leading to a symbiotic relationship.
136
Why do mitochondria and chloroplasts support endosymbiosis theory?
They have double membranes and their own DNA.
137
What makes archaea like Asgard lineage important?
Their genomes resemble eukaryotes and they divide slowly and form protrusions.
138
What is the nuclear envelope?
A double membrane that encloses the nucleus.
139
What is the structure of the nuclear envelope?
Outer membrane perinuclear space inner membrane.
140
What are nuclear pores?
Fusion points of inner and outer membrane gated by nuclear pore complexes.
141
What is the nuclear pore complex (NPC)?
A large protein structure that controls transport into and out of the nucleus.
142
How do small molecules move through NPCs?
They diffuse freely.
143
How are large proteins transported into the nucleus?
They must have a nuclear localisation signal (NLS) recognised by importins.
144
What is importin?
A receptor protein that binds NLS-containing proteins and transports them into the nucleus.
145
What regulates nuclear import?
Ran-GTPase system with Ran-GTP in nucleus and Ran-GDP in cytosol.
146
How does Ran-GTPase work?
Ran-GTP binds importin in nucleus to release cargo Ran-GDP releases importin in cytosol.
147
What is nuclear export?
Transport of RNA and proteins out of the nucleus using exportin and Ran-GTPase.
148
What is the nuclear lamina?
A fibrous mesh supporting the inner nuclear membrane and nuclear shape.
149
What happens to the nuclear lamina during division?
It disassembles and reforms.
150
What associates with the nuclear lamina?
Chromatin associates in discrete non-random locations.
151
What is the nucleolus?
A membraneless biomolecular condensate that synthesises rRNA and assembles ribosomes.
152
What is the endoplasmic reticulum (ER)?
An organelle continuous with the outer nuclear membrane with rough and smooth regions.
153
What is the function of rough ER?
Protein synthesis and folding with ribosomes on the surface.
154
How are proteins processed in rough ER?
They are translocated into the ER lumen modified and quality-checked.
155
What is the function of smooth ER?
Lipid synthesis metabolism and detoxification.
156
What is the sarcoplasmic reticulum?
Specialised smooth ER in muscle storing calcium ions.
157
What is the transitional ER (t-ER)?
ER region forming vesicles to send proteins and lipids to the Golgi apparatus.
158
What is the structure of the Golgi apparatus?
Stacks of flattened membrane sacs called cisternae.
159
What is the cis face of the Golgi?
The side facing and receiving vesicles from the ER.
160
What is the trans face of the Golgi?
The side directing vesicles toward the plasma membrane or other locations.
161
What are the functions of the Golgi?
Protein modification sorting and directing cellular traffic.
162
What are the two models of Golgi trafficking?
Vesicular transport model and cisternal maturation model.
163
What is the vesicular transport model?
Cargo moves through Golgi cisternae while resident enzymes stay in place.
164
What is the cisternal maturation model?
Cisternae move forward carrying cargo while enzymes are recycled.
165
What are coated vesicles?
Vesicles with protein coats for directed transport between organelles.
166
What are clathrin-coated vesicles?
Vesicles from Golgi or plasma membrane with triskelion structures.
167
What are COPI vesicles?
Vesicles for retrograde transport from Golgi to ER.
168
What are COPII vesicles?
Vesicles for anterograde transport from ER to Golgi.
169
What is the retromer complex?
A coat system that returns cargo from endosomes to the Golgi or plasma membrane.
170
What is the VSVG-GFP experiment?
A temperature-sensitive protein model to study protein trafficking.
171
How does temperature affect VSVG-GFP?
Misfolded at 40C trapped in ER refolds at 32C and moves to Golgi.
172
What does the VSVG-GFP experiment show?
The dynamic process of protein movement through ER Golgi and out to membrane.
173
What guides a newly made peptide with an ER signal sequence?
Signal recognition particle (SRP)
174
What does SRP do?
Binds the ribosome and guides it to the ER translocator via the SRP receptor
175
Where does protein translation occur during co-translational translocation?
Through the translocator into the ER lumen
176
What happens to the protein structure during translocation?
It unfolds while entering and refolds once inside
177
What does co-translational mean?
Translation and translocation happen simultaneously
178
What does a stop-transfer sequence do?
It halts translocation so the protein becomes anchored in the membrane
179
What is a transmembrane protein?
A protein with one part in the ER lumen and one part in the cytosol
180
What are the 3 major types of protein transport across membranes?
Gated transport
181
What is vesicle coating?
A process that selects cargo
182
What components help determine vesicle destination?
Phospholipid profile (postcode)
183
What does Ran GTPase do?
Helps tether vesicles to target membranes and coordinates docking
184
What are SNARE proteins?
v-SNAREs (vesicle SNAREs) and t-SNAREs (target SNAREs) that mediate vesicle fusion
185
How do v-SNAREs and t-SNAREs interact?
They pair specifically via complementarity to ensure vesicle fuses with the correct membrane
186
What does SNARE zipping do?
It brings the two membranes close together to initiate fusion
187
Why is SNARE pairing highly specific?
Ensures vesicles fuse only with the correct target compartment
188
What is the pathway of exocytosis?
ER → Golgi → plasma membrane
189
What is constitutive exocytosis?
A continuous
190
What is regulated exocytosis?
Triggered release of vesicles in response to a signal or stimulus
191
Describe insulin secretion via regulated exocytosis
Glucose → ↑ ATP → closes K+ channels → membrane depolarization → Ca²⁺ influx → vesicle fusion
192
What is endocytosis?
Internalization of material by engulfing it into vesicles
193
What is phagocytosis?
Uptake of large particles like bacteria by immune cells using lysosomes
194
What is pinocytosis?
Nonspecific uptake of extracellular fluid and membrane into small vesicles
195
What is receptor-mediated endocytosis?
Selective uptake of specific molecules using surface receptors (e.g. cholesterol via LDL)
196
How does LDL enter cells?
LDL binds receptor → vesicle forms → fuses with lysosome → cholesterol released → receptors recycled
197
How do viruses exploit endocytosis?
They mimic ligands and bind host receptors to enter via receptor-mediated endocytosis (e.g. SARS-CoV-2)
198
How are neurotransmitters released and retrieved?
Exocytosis releases neurotransmitters; endocytosis retrieves vesicles for reuse
199
200
What happens in early endosomes?
Sorting of internalised cargo and receptor recycling
201
How do endosomes become late endosomes?
Via maturation and acidification using proton pumps (ATP-driven H⁺ influx)
202
Why is acidification important in endosomes?
It enables dissociation of ligands from receptors and prepares for lysosomal degradation
203
What happens in late endosomes?
Cargo is either recycled or sent for degradation
204
205
What do lysosomes degrade?
Proteins
206
What enzymes are in lysosomes?
Hydrolytic enzymes (about 40 types)
207
What pH do lysosomes work best at?
pH 5 (acidic environment)
208
How is acidic pH maintained in lysosomes?
Via proton pumps that import H⁺ ions into the lumen
209
What else do lysosomes do?
Export useful metabolites back into the cytosol via transporters
210
211
What are the functions of the plant vacuole?
Storage
212
What materials do plant vacuoles store?
Ions
213
How do vacuoles affect plant structure?
They maintain turgor pressure for rigidity
214
Do plant vacuoles have digestive functions?
Yes
215
216
What are peroxisomes?
Single-membrane organelles that detoxify harmful substances
217
What enzymes do peroxisomes contain?
Oxidative enzymes like catalase and urate oxidase
218
What does catalase do in peroxisomes?
Breaks down hydrogen peroxide (H₂O₂) into water and oxygen
219
Why is H₂O₂ breakdown important?
H₂O₂ is toxic; breaking it down protects the cell
220
What do peroxisomes detoxify?
Fatty acids
221
How much ethanol is detoxified by peroxisomes?
~25% of consumed ethanol
222
How are proteins targeted to peroxisomes?
Proteins are directly imported from the cytosol using targeting signals
223
Do peroxisomes rely on the Golgi for protein import?
No
224
What type of membrane structure does the mitochondrion have?
Double membrane
225
What does the outer mitochondrial membrane contain?
Large channel forming proteins permeable to small molecules
226
What is the inner mitochondrial membrane specialized for?
Electron transport chain and ATP synthase and transport proteins
227
Why is the inner membrane folded into cristae?
To increase surface area
228
What is found in the mitochondrial matrix?
Mitochondrial DNA ribosomes tRNAs and enzymes for the citric acid cycle and fatty acid oxidation
229
What happens in the intermembrane space of mitochondria?
Contains small molecules like the cytosol and proteins like cytochrome C that trigger apoptosis
230
What are the steps of mitochondrial ATP production?
Acetyl CoA production electron carrier activation electron transport chain proton gradient ATP synthase activation ATP production
231
What is oxidative phosphorylation?
Process where ATP is made using electron transport and a proton gradient
232
How many complexes are in the ETC?
Four protein complexes only three pump protons
233
What does the F0 rotor do?
Spins due to proton flow and powers the stationary F1 ATPase
234
What does F1 ATPase do?
Converts ADP to ATP
235
How is ATP exported from mitochondria?
It is pumped into the intermembrane space and exchanged via the ADP ATP carrier
236
What diseases are caused by mitochondrial dysfunction?
MERRF LHON MELAS syndrome
237
What is MERRF?
Myoclonic epilepsy and ragged red fibre disease
238
What is LHON?
Leber hereditary optic neuropathy
239
What is MELAS?
Mitochondrial encephalopathy lactic acidosis and stroke like episodes
240
What is the relationship between chloroplasts and mitochondria?
Sugars made in chloroplasts can be broken down in mitochondria for ATP synthesis
241
What gases are exchanged between mitochondria and chloroplasts?
Chloroplasts release oxygen mitochondria release carbon dioxide
242
What membrane structure do chloroplasts have?
Double membrane with inner thylakoid membranes
243
What do thylakoid membranes contain?
Chlorophyll and proteins for photosynthesis
244
What light does chlorophyll absorb and reflect?
Absorbs red and blue light reflects green
245
What enzyme splits water in PSII?
Water splitting enzyme in photosystem two
246
What does PSII produce?
Oxygen
247
Where are electrons passed after PSII?
Down electron carriers to photosystem one
248
What is the result of electron transfer in chloroplasts?
Proton gradient that drives ATP synthesis
249
Where does carbon fixation occur?
Stroma of the chloroplast
250
Why can't ATP and NADPH diffuse back into the thylakoid lumen?
Thylakoid membrane is impermeable to them
251
What enzyme catalyzes carbon fixation?
RUBISCO
252
What is RUBISCO's role?
Fixes carbon dioxide into organic molecules
253
Where are ribosomes found?
In the cytosol and on the rough endoplasmic reticulum
254
What is the function of ribosomes?
Translate messenger RNA into proteins
255
How many ribosomes are in a typical eukaryotic cell?
Millions
256
What are ribosomes made of?
Two thirds ribosomal RNA and one third protein
257
What is a ribozyme?
RNA molecule that acts as an enzyme
258
What are the subunits of eukaryotic ribosomes?
Forty S small and sixty S large subunits making eighty S total
259
What determines ribosome structure?
Folding of ribosomal RNA into a compact three dimensional shape
260
How many RNA binding sites do ribosomes have?
Four total one for messenger RNA and three for transfer RNA
261
What are polyribosomes?
Multiple ribosomes translating a single messenger RNA simultaneously
262
How is translation different in bacteria?
Transcription and translation happen at the same time
263
What is the role of the ADP ATP carrier protein in mitochondria?
Imports ADP and exports ATP across the inner membrane
264
What are the key gradients created during the electron transport chain?
Membrane potential and pH gradient
265
How is a hydride ion from NADH used in ATP production?
It is split into a proton and two electrons for the electron transport chain
266
What is the function of cytochrome C in mitochondria?
Transfers electrons and triggers apoptosis if released
267
How do photosystems contribute to ATP synthesis?
Transfer excited electrons that pump protons and drive ATP production
268
What prevents reverse diffusion of ATP and NADPH into the thylakoid?
Thylakoid membrane is impermeable to them
269
What is the structure of a microtubule
Hollow tube made of 13 protofilaments
270
What is the building block of a microtubule
Alpha and beta tubulin heterodimer
271
Which tubulin is found at the plus end of the microtubule
Beta tubulin
272
How are tubulin dimers arranged
Head to tail
273
How many lateral and longitudinal contacts does each tubulin dimer make
Two lateral and two longitudinal
274
How conserved are alpha and beta tubulin between species
75 percent similarity between yeast and humans
275
Which tubulin subunit hydrolyzes GTP
Beta tubulin
276
What is microtubule nucleation
Initiation of microtubule formation
277
What is microtubule polymerisation
Growth or elongation of microtubules
278
Why is spontaneous nucleation rare
Requires very high concentration of tubulin dimers
279
What catalyzes microtubule nucleation in vivo
Gamma tubulin ring complex
280
Where is the gamma tubulin ring complex enriched
At the microtubule organizing center or centrosome
281
Which direction does the microtubule grow from the centrosome
Plus end grows outward
282
What is dynamic instability
Microtubules switch between growing and shrinking states
283
What is required for dynamic instability
Constant GTP input
284
What stabilizes a growing microtubule
GTP cap
285
What happens when GTP on beta tubulin is hydrolyzed
Microtubule becomes unstable and can shrink
286
What is a microtubule catastrophe
Rapid shrinking due to GDP bound beta tubulin
287
How can microtubule plus ends be stabilized
By attaching to another molecule or structure
288
Why is dynamic instability useful
Allows microtubules to explore the cell space
289
What is an example of dynamic instability in action
Mitosis where microtubules attach to kinetochores
290
What does taxol do to microtubules
Stabilizes them and prevents shrinkage
291
What is the use of taxol
Anti cancer drug and research tool
292
What does colchicine do
Binds free tubulin dimers and prevents polymerisation
293
What is the result of taxol and colchicine treatment
Mitotic arrest and cell death
294
What do microtubules help position
Organelles in eukaryotic cells
295
What proteins are involved in vesicle transport on microtubules
Motor proteins
296
What are the two main motor proteins for microtubules
Kinesin and dynein
297
Which direction does kinesin move
Plus end directed
298
Which direction does dynein move
Minus end directed
299
What powers motor protein movement
ATP hydrolysis
300
How many motor domains do motor proteins have
Two
301
Where do microtubules nucleate from during mitosis
Centrosomes at opposite poles
302
What structure stabilizes microtubules during mitosis
Kinetochore
303
What proteins help stabilize interpolar microtubules
Microtubule associated proteins
304
What forces act on the mitotic spindle
Pulling and pushing forces from motor proteins
305
What structures grow from centrioles
Cilia and flagella
306
What do centrioles become in cilia and flagella
Basal bodies
307
What is the structure of a basal body
Cylinder of nine microtubule triplets
308
What is the structure of a motile cilium
Nine outer doublets and two central microtubules
309
What connects outer microtubule doublets
Nexin proteins
310
What motor protein is found in cilia
Axonemal dynein
311
What system is used for cilia assembly and maintenance
Intraflagellar transport
312
How do microtubules cause ciliary movement
Dynein causes bending of linked microtubules
313
Why don't cilia microtubules undergo dynamic instability
They are stabilized by linking proteins
314
What is the function of cilia in sensory cells
Convert environmental signals into neural signals
315
What are ciliopathies
Disorders due to defects in cilia or basal bodies
316
What is Bardet-Biedl syndrome
Genetic ciliopathy with polydactyly kidney dysfunction and retinal defects
317
What is primary ciliary dyskinesia
Ciliopathy affecting respiratory tract sperm and fallopian tube function
318
What is the structure of actin filaments
Thin flexible protein threads made of actin monomers
319
How are actin monomers arranged in filaments
Head to tail in the same orientation
320
What is the shape of an actin filament
Two stranded helical protofilament with a twist every 37 nanometers
321
What stabilizes actin strands
Extensive lateral interactions between the two strands
322
What nucleotide does actin bind
ATP or ADP in a central cleft
323
What happens to ATP in actin after polymerization
It is hydrolyzed to ADP which stays trapped until dissociation
324
Which end of the actin filament grows faster
Plus end
325
How does actin ADP affect filament stability
It is less stable and more likely to dissociate
326
What is treadmilling
When filament length stays constant as plus end grows and minus end shrinks at equal rates
327
What promotes actin filament growth
High concentration of free actin monomers
328
What does intermediate actin concentration lead to
Treadmilling behavior
329
What are the steps of cell migration
Protrusion adhesion contraction release
330
What structures are formed by actin protrusion
Lamellipodia and filopodia
331
What do crosslinking proteins do in actin networks
Promote three dimensional actin gels
332
What causes membrane blebbing
Absence of cortical actin crosslinking
333
What is the role of bundling proteins
Stabilize actin in filopodia and microvilli
334
How is myosin organized in muscle
Myosin two dimers form thick filaments
335
What do myofibrils consist of
Repeated sarcomeres made of actin and myosin
336
How does myosin generate force
ATP hydrolysis and conformational change
337
What happens to sarcomere length during contraction
Sarcomeres shorten but filament length stays the same
338
What bacterium hijacks the actin cytoskeleton
Listeria monocytogenes
339
What is the primary role of intermediate filaments
Provide mechanical strength
340
Where are intermediate filaments absent
In arthropods and echinoderms
341
How are intermediate filaments assembled
Coiled coil dimers form tetramers which assemble into filaments
342
What crosslinks keratin networks
Disulfide bonds
343
How do keratin filaments provide mechanical strength
Link to neighboring cells via desmosomes
344
What happens in cells without intermediate filaments
They rupture under mechanical stress
345
What are neurofilaments
Intermediate filaments in axons providing tensile strength
346
What are nuclear lamins
Intermediate filaments forming a mesh under the nuclear envelope
347
What happens when nuclear lamins break down
Nuclear envelope breaks during cell division
348
What disease is caused by lamin A mutation
Premature aging with symptoms like aged skin and cardiovascular disease
349
What cytoskeletal element is found in microvilli
Actin filaments
350
What cytoskeleton enables apical to basal transport
Microtubules
351
What cytoskeleton provides mechanical strength against tearing
Intermediate filaments
352
What protein links different cytoskeletal systems
Plectin
353
What does plectin connect
Intermediate filaments to microtubules and actin
354
What proteins link the nucleus to the cytoskeleton
SUN and KASH proteins
355
Where is the SUN protein located
On the nuclear envelope connected to chromatin or nuclear lamina
356
Where is the KASH protein located
In the outer nuclear membrane linked to actin and microtubules
357
What is the role of SUN KASH bridge
Mechanical coupling between the nucleus and the cytoskeleton
358
What are the three types of cytoskeletal filaments
Microtubules Microfilaments Intermediate filaments
359
What protein subunits make up microtubules
Alpha and beta tubulin heterodimers
360
What protein makes up microfilaments
Actin monomers
361
What proteins make up intermediate filaments
Various proteins like keratin vimentin and lamins
362
What is the structure of microtubules
Hollow tubes with 13 protofilaments
363
What is the structure of microfilaments
Two stranded helical actin filaments
364
What is the structure of intermediate filaments
Rope like filaments of 8 twisted protofilaments
365
What is the diameter of microtubules
25 nanometers
366
What is the diameter of microfilaments
7 nanometers
367
What is the diameter of intermediate filaments
10 nanometers
368
Do microtubules have polarity
Yes plus and minus ends
369
Do microfilaments have polarity
Yes plus and minus ends
370
Do intermediate filaments have polarity
No
371
Which cytoskeletal filament is highly dynamic and undergoes dynamic instability
Microtubules
372
Which cytoskeletal filament undergoes treadmilling
Microfilaments
373
Which cytoskeletal filament is the most stable
Intermediate filaments
374
What energy source do microtubules use
GTP bound to beta tubulin
375
What energy source do microfilaments use
ATP bound to actin
376
Do intermediate filaments use ATP or GTP
No
377
What motor proteins interact with microtubules
Kinesin and dynein
378
What motor protein interacts with microfilaments
Myosin
379
Do intermediate filaments use motor proteins
No
380
What are the main functions of microtubules
Intracellular transport mitotic spindle cilia and flagella
381
What are the main functions of microfilaments
Cell movement shape changes cytokinesis
382
What are the main functions of intermediate filaments
Mechanical support and resistance to stress
383
What is the microtubule organizing center called
Centrosome
384
Do microfilaments require a central organizing center
No
385
Do intermediate filaments have a central organizing site
No
386
Where are microfilaments commonly found
Lamellipodia filopodia microvilli contractile ring
387
Where are intermediate filaments found
Keratins in skin neurofilaments in axons lamins in nucleus
388
Where are microtubules used in cell division
Mitotic spindle and kinetochore attachments
389
Which cytoskeletal filament is critical for muscle contraction
Microfilaments with myosin
390
Which cytoskeletal filament links to desmosomes for cell cell adhesion
Intermediate filaments
391
Which cytoskeletal filament forms cilia and flagella
Microtubules
392
Which cytoskeletal filament supports nuclear shape
Nuclear lamins
393
What cytoskeletal linker protein connects all three systems
Plectin
394
What proteins connect the nuclear interior to cytoskeleton
SUN and KASH proteins
395
What direction do kinesins move on microtubules
Plus end directed
396
What direction do dyneins move on microtubules
Minus end directed
397
What direction does myosin move on actin filaments
Usually plus end directed
398
What cytoskeletal filament resists tensile stress best
Intermediate filaments
399
Which cytoskeletal filament has the fastest turnover
Microfilaments
400
Which cytoskeletal filament is the stiffest but most brittle
Microtubules
401
Which cytoskeletal filament is the most flexible
Intermediate filaments
