Eukaryotic cells Flashcards
1
Q
Why is binary fission important for prokaryotes?
A
It allows rapid asexual reproduction roughly every 20 minutes.
2
Q
What limits the size of prokaryotic cells?
A
Surface area to volume ratio diffusion rates and the need to maintain high concentrations of enzymes and substrates.
3
Q
How does SA:vol ratio affect prokaryotic cells?
A
Smaller cells have a higher surface area relative to their volume allowing efficient exchange of nutrients and gases.
4
Q
Why does diffusion limit prokaryotic cell size?
A
As cell size increases diffusion rates decrease making molecular transport inefficient.
5
Q
Why are high concentrations of compounds needed in cells?
A
To allow biochemical reactions to occur efficiently.
6
Q
What is compartmentalisation in eukaryotic cells?
A
Division of the cell into membrane-bound organelles allowing localisation and concentration of cellular processes.
7
Q
Why is compartmentalisation important?
A
It enables differentiation and specialisation of cell functions and supports complex multicellular organisms.
8
Q
What are organelles?
A
Subcellular compartments often membrane-bound with specific structures and functions.
9
Q
What do transport systems in eukaryotic cells require?
A
ATP and organisation for cell signalling and intracellular movement.
10
Q
What are biomolecular condensates?
A
Non-membrane compartments formed by aggregation of macromolecules like proteins or nucleic acids.
11
Q
How do biomolecular condensates form?
A
Scaffold molecules like RNA or proteins form weak reversible interactions creating dynamic liquid-like droplets.
12
Q
What is phase separation?
A
The coexistence of different biomolecular condensates within a larger structure.
13
Q
Give an example of a biomolecular condensate
A
Rubisco enzyme compartments in photosynthetic bacteria or the pericentriolar material of centrosomes.
14
Q
What microscopes have advanced our study of cells?
A
From Hooke’s microscope to light confocal and electron microscopes.
15
Q
What does digitisation allow in microscopy?
A
Still images and live-cell imaging.
16
Q
What is GFP and why is it useful?
A
Green fluorescent protein from jellyfish used to label proteins in living cells.
17
Q
What is the origin theory for mitochondria and chloroplasts?
A
Endosymbiosis where an archaeon engulfed bacteria leading to a symbiotic relationship.
18
Q
Why do mitochondria and chloroplasts support endosymbiosis theory?
A
They have double membranes and their own DNA.
19
Q
What makes archaea like Asgard lineage important?
A
Their genomes resemble eukaryotes and they divide slowly and form protrusions.
20
Q
What is the nuclear envelope?
A
A double membrane that encloses the nucleus.
21
Q
What is the structure of the nuclear envelope?
A
Outer membrane perinuclear space inner membrane.
22
Q
What are nuclear pores?
A
Fusion points of inner and outer membrane gated by nuclear pore complexes.
23
Q
What is the nuclear pore complex (NPC)?
A
A large protein structure that controls transport into and out of the nucleus.
24
Q
How do small molecules move through NPCs?
A
They diffuse freely.
25
How are large proteins transported into the nucleus?
They must have a nuclear localisation signal (NLS) recognised by importins.
26
What is importin?
A receptor protein that binds NLS-containing proteins and transports them into the nucleus.
27
What regulates nuclear import?
Ran-GTPase system with Ran-GTP in nucleus and Ran-GDP in cytosol.
28
How does Ran-GTPase work?
Ran-GTP binds importin in nucleus to release cargo Ran-GDP releases importin in cytosol.
29
What is nuclear export?
Transport of RNA and proteins out of the nucleus using exportin and Ran-GTPase.
30
What is the nuclear lamina?
A fibrous mesh supporting the inner nuclear membrane and nuclear shape.
31
What happens to the nuclear lamina during division?
It disassembles and reforms.
32
What associates with the nuclear lamina?
Chromatin associates in discrete non-random locations.
33
What is the nucleolus?
A membraneless biomolecular condensate that synthesises rRNA and assembles ribosomes.
34
What is the endoplasmic reticulum (ER)?
An organelle continuous with the outer nuclear membrane with rough and smooth regions.
35
What is the function of rough ER?
Protein synthesis and folding with ribosomes on the surface.
36
How are proteins processed in rough ER?
They are translocated into the ER lumen modified and quality-checked.
37
What is the function of smooth ER?
Lipid synthesis metabolism and detoxification.
38
What is the sarcoplasmic reticulum?
Specialised smooth ER in muscle storing calcium ions.
39
What is the transitional ER (t-ER)?
ER region forming vesicles to send proteins and lipids to the Golgi apparatus.
40
What is the structure of the Golgi apparatus?
Stacks of flattened membrane sacs called cisternae.
41
What is the cis face of the Golgi?
The side facing and receiving vesicles from the ER.
42
What is the trans face of the Golgi?
The side directing vesicles toward the plasma membrane or other locations.
43
What are the functions of the Golgi?
Protein modification sorting and directing cellular traffic.
44
What are the two models of Golgi trafficking?
Vesicular transport model and cisternal maturation model.
45
What is the vesicular transport model?
Cargo moves through Golgi cisternae while resident enzymes stay in place.
46
What is the cisternal maturation model?
Cisternae move forward carrying cargo while enzymes are recycled.
47
What are coated vesicles?
Vesicles with protein coats for directed transport between organelles.
48
What are clathrin-coated vesicles?
Vesicles from Golgi or plasma membrane with triskelion structures.
49
What are COPI vesicles?
Vesicles for retrograde transport from Golgi to ER.
50
What are COPII vesicles?
Vesicles for anterograde transport from ER to Golgi.
51
What is the retromer complex?
A coat system that returns cargo from endosomes to the Golgi or plasma membrane.
52
What is the VSVG-GFP experiment?
A temperature-sensitive protein model to study protein trafficking.
53
How does temperature affect VSVG-GFP?
Misfolded at 40C trapped in ER refolds at 32C and moves to Golgi.
54
What does the VSVG-GFP experiment show?
The dynamic process of protein movement through ER Golgi and out to membrane.
55
What guides a newly made peptide with an ER signal sequence?
Signal recognition particle (SRP)
56
What does SRP do?
Binds the ribosome and guides it to the ER translocator via the SRP receptor
57
Where does protein translation occur during co-translational translocation?
Through the translocator into the ER lumen
58
What happens to the protein structure during translocation?
It unfolds while entering and refolds once inside
59
What does co-translational mean?
Translation and translocation happen simultaneously
60
What does a stop-transfer sequence do?
It halts translocation so the protein becomes anchored in the membrane
61
What is a transmembrane protein?
A protein with one part in the ER lumen and one part in the cytosol
62
What are the 3 major types of protein transport across membranes?
Gated transport, protein translocation, vesicular transport
63
What is vesicle coating?
A process that selects cargo
64
What components help determine vesicle destination?
Phospholipid profile (postcode)
65
What does Ran GTPase do?
Helps tether vesicles to target membranes and coordinates docking
66
What are SNARE proteins?
v-SNAREs (vesicle SNAREs) and t-SNAREs (target SNAREs) that mediate vesicle fusion
67
How do v-SNAREs and t-SNAREs interact?
They pair specifically via complementarity to ensure vesicle fuses with the correct membrane
68
What does SNARE zipping do?
It brings the two membranes close together to initiate fusion
69
Why is SNARE pairing highly specific?
Ensures vesicles fuse only with the correct target compartment
70
What is the pathway of exocytosis?
ER → Golgi → plasma membrane
71
What is constitutive exocytosis?
A continuous
72
What is regulated exocytosis?
Triggered release of vesicles in response to a signal or stimulus
73
Describe insulin secretion via regulated exocytosis
Glucose → ↑ ATP → closes K+ channels → membrane depolarization → Ca²⁺ influx → vesicle fusion
74
What is endocytosis?
Internalization of material by engulfing it into vesicles
75
What is phagocytosis?
Uptake of large particles like bacteria by immune cells using lysosomes
76
What is pinocytosis?
Nonspecific uptake of extracellular fluid and membrane into small vesicles
77
What is receptor-mediated endocytosis?
Selective uptake of specific molecules using surface receptors (e.g. cholesterol via LDL)
78
How does LDL enter cells?
LDL binds receptor → vesicle forms → fuses with lysosome → cholesterol released → receptors recycled
79
How do viruses exploit endocytosis?
They mimic ligands and bind host receptors to enter via receptor-mediated endocytosis (e.g. SARS-CoV-2)
80
How are neurotransmitters released and retrieved?
Exocytosis releases neurotransmitters; endocytosis retrieves vesicles for reuse
81
82
What happens in early endosomes?
Sorting of internalised cargo and receptor recycling
83
How do endosomes become late endosomes?
Via maturation and acidification using proton pumps (ATP-driven H⁺ influx)
84
Why is acidification important in endosomes?
It enables dissociation of ligands from receptors and prepares for lysosomal degradation
85
What happens in late endosomes?
Cargo is either recycled or sent for degradation
86
87
What do lysosomes degrade?
Proteins
88
What enzymes are in lysosomes?
Hydrolytic enzymes (about 40 types)
89
What pH do lysosomes work best at?
pH 5 (acidic environment)
90
How is acidic pH maintained in lysosomes?
Via proton pumps that import H⁺ ions into the lumen
91
What else do lysosomes do?
Export useful metabolites back into the cytosol via transporters
92
93
What are the functions of the plant vacuole?
Storage
94
What materials do plant vacuoles store?
Ions
95
How do vacuoles affect plant structure?
They maintain turgor pressure for rigidity
96
Do plant vacuoles have digestive functions?
Yes
97
98
What are peroxisomes?
Single-membrane organelles that detoxify harmful substances
99
What enzymes do peroxisomes contain?
Oxidative enzymes like catalase and urate oxidase
100
What does catalase do in peroxisomes?
Breaks down hydrogen peroxide (H₂O₂) into water and oxygen
101
Why is H₂O₂ breakdown important?
H₂O₂ is toxic; breaking it down protects the cell
102
What do peroxisomes detoxify?
Fatty acids
103
How much ethanol is detoxified by peroxisomes?
~25% of consumed ethanol
104
How are proteins targeted to peroxisomes?
Proteins are directly imported from the cytosol using targeting signals
105
Do peroxisomes rely on the Golgi for protein import?
No
106
What type of membrane structure does the mitochondrion have?
Double membrane
107
What does the outer mitochondrial membrane contain?
Large channel forming proteins permeable to small molecules
108
What is the inner mitochondrial membrane specialized for?
Electron transport chain and ATP synthase and transport proteins
109
Why is the inner membrane folded into cristae?
To increase surface area
110
What is found in the mitochondrial matrix?
Mitochondrial DNA ribosomes tRNAs and enzymes for the citric acid cycle and fatty acid oxidation
111
What happens in the intermembrane space of mitochondria?
Contains small molecules like the cytosol and proteins like cytochrome C that trigger apoptosis
112
What are the steps of mitochondrial ATP production?
Acetyl CoA production electron carrier activation electron transport chain proton gradient ATP synthase activation ATP production
113
What is oxidative phosphorylation?
Process where ATP is made using electron transport and a proton gradient
114
How many complexes are in the ETC?
Four protein complexes only three pump protons
115
What does the F0 rotor do?
Spins due to proton flow and powers the stationary F1 ATPase
116
What does F1 ATPase do?
Converts ADP to ATP
117
How is ATP exported from mitochondria?
It is pumped into the intermembrane space and exchanged via the ADP ATP carrier
118
What diseases are caused by mitochondrial dysfunction?
MERRF LHON MELAS syndrome
119
What is MERRF?
Myoclonic epilepsy and ragged red fibre disease
120
What is LHON?
Leber hereditary optic neuropathy
121
What is MELAS?
Mitochondrial encephalopathy lactic acidosis and stroke like episodes
122
What is the relationship between chloroplasts and mitochondria?
Sugars made in chloroplasts can be broken down in mitochondria for ATP synthesis
123
What gases are exchanged between mitochondria and chloroplasts?
Chloroplasts release oxygen mitochondria release carbon dioxide
124
What membrane structure do chloroplasts have?
Double membrane with inner thylakoid membranes
125
What do thylakoid membranes contain?
Chlorophyll and proteins for photosynthesis
126
What light does chlorophyll absorb and reflect?
Absorbs red and blue light reflects green
127
What enzyme splits water in PSII?
Water splitting enzyme in photosystem two
128
What does PSII produce?
Oxygen
129
Where are electrons passed after PSII?
Down electron carriers to photosystem one
130
What is the result of electron transfer in chloroplasts?
Proton gradient that drives ATP synthesis
131
Where does carbon fixation occur?
Stroma of the chloroplast
132
Why can't ATP and NADPH diffuse back into the thylakoid lumen?
Thylakoid membrane is impermeable to them
133
What enzyme catalyzes carbon fixation?
RUBISCO
134
What is RUBISCO's role?
Fixes carbon dioxide into organic molecules
135
Where are ribosomes found?
In the cytosol and on the rough endoplasmic reticulum
136
What is the function of ribosomes?
Translate messenger RNA into proteins
137
How many ribosomes are in a typical eukaryotic cell?
Millions
138
What are ribosomes made of?
Two thirds ribosomal RNA and one third protein
139
What is a ribozyme?
RNA molecule that acts as an enzyme
140
What are the subunits of eukaryotic ribosomes?
Forty S small and sixty S large subunits making eighty S total
141
What determines ribosome structure?
Folding of ribosomal RNA into a compact three dimensional shape
142
How many RNA binding sites do ribosomes have?
Four total one for messenger RNA and three for transfer RNA
143
What are polyribosomes?
Multiple ribosomes translating a single messenger RNA simultaneously
144
How is translation different in bacteria?
Transcription and translation happen at the same time
145
What is the role of the ADP ATP carrier protein in mitochondria?
Imports ADP and exports ATP across the inner membrane
146
What are the key gradients created during the electron transport chain?
Membrane potential and pH gradient
147
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
148
What is the function of cytochrome C in mitochondria?
Transfers electrons and triggers apoptosis if released
149
How do photosystems contribute to ATP synthesis?
Transfer excited electrons that pump protons and drive ATP production
150
What prevents reverse diffusion of ATP and NADPH into the thylakoid?
Thylakoid membrane is impermeable to them
151
What is the structure of a microtubule
Hollow tube made of 13 protofilaments
152
What is the building block of a microtubule
Alpha and beta tubulin heterodimer
153
Which tubulin is found at the plus end of the microtubule
Beta tubulin
154
How are tubulin dimers arranged
Head to tail
155
How many lateral and longitudinal contacts does each tubulin dimer make
Two lateral and two longitudinal
156
How conserved are alpha and beta tubulin between species
75 percent similarity between yeast and humans
157
Which tubulin subunit hydrolyzes GTP
Beta tubulin
158
What is microtubule nucleation
Initiation of microtubule formation
159
What is microtubule polymerisation
Growth or elongation of microtubules
160
Why is spontaneous nucleation rare
Requires very high concentration of tubulin dimers
161
What catalyzes microtubule nucleation in vivo
Gamma tubulin ring complex
162
Where is the gamma tubulin ring complex enriched
At the microtubule organizing center or centrosome
163
Which direction does the microtubule grow from the centrosome
Plus end grows outward
164
What is dynamic instability
Microtubules switch between growing and shrinking states
165
What is required for dynamic instability
Constant GTP input
166
What stabilizes a growing microtubule
GTP cap
167
What happens when GTP on beta tubulin is hydrolyzed
Microtubule becomes unstable and can shrink
168
What is a microtubule catastrophe
Rapid shrinking due to GDP bound beta tubulin
169
How can microtubule plus ends be stabilized
By attaching to another molecule or structure
170
Why is dynamic instability useful
Allows microtubules to explore the cell space
171
What is an example of dynamic instability in action
Mitosis where microtubules attach to kinetochores
172
What does taxol do to microtubules
Stabilizes them and prevents shrinkage
173
What is the use of taxol
Anti cancer drug and research tool
174
What does colchicine do
Binds free tubulin dimers and prevents polymerisation
175
What is the result of taxol and colchicine treatment
Mitotic arrest and cell death
176
What do microtubules help position
Organelles in eukaryotic cells
177
What proteins are involved in vesicle transport on microtubules
Motor proteins
178
What are the two main motor proteins for microtubules
Kinesin and dynein
179
Which direction does kinesin move
Plus end directed
180
Which direction does dynein move
Minus end directed
181
What powers motor protein movement
ATP hydrolysis
182
How many motor domains do motor proteins have
Two
183
Where do microtubules nucleate from during mitosis
Centrosomes at opposite poles
184
What structure stabilizes microtubules during mitosis
Kinetochore
185
What proteins help stabilize interpolar microtubules
Microtubule associated proteins
186
What forces act on the mitotic spindle
Pulling and pushing forces from motor proteins
187
What structures grow from centrioles
Cilia and flagella
188
What do centrioles become in cilia and flagella
Basal bodies
189
What is the structure of a basal body
Cylinder of nine microtubule triplets
190
What is the structure of a motile cilium
Nine outer doublets and two central microtubules
191
What connects outer microtubule doublets
Nexin proteins
192
What motor protein is found in cilia
Axonemal dynein
193
What system is used for cilia assembly and maintenance
Intraflagellar transport
194
How do microtubules cause ciliary movement
Dynein causes bending of linked microtubules
195
Why don't cilia microtubules undergo dynamic instability
They are stabilized by linking proteins
196
What is the function of cilia in sensory cells
Convert environmental signals into neural signals
197
What are ciliopathies
Disorders due to defects in cilia or basal bodies
198
What is Bardet-Biedl syndrome
Genetic ciliopathy with polydactyly kidney dysfunction and retinal defects
199
What is primary ciliary dyskinesia
Ciliopathy affecting respiratory tract sperm and fallopian tube function
200
What is the structure of actin filaments
Thin flexible protein threads made of actin monomers
201
How are actin monomers arranged in filaments
Head to tail in the same orientation
202
What is the shape of an actin filament
Two stranded helical protofilament with a twist every 37 nanometers
203
What stabilizes actin strands
Extensive lateral interactions between the two strands
204
What nucleotide does actin bind
ATP or ADP in a central cleft
205
What happens to ATP in actin after polymerization
It is hydrolyzed to ADP which stays trapped until dissociation
206
Which end of the actin filament grows faster
Plus end
207
How does actin ADP affect filament stability
It is less stable and more likely to dissociate
208
What is treadmilling
When filament length stays constant as plus end grows and minus end shrinks at equal rates
209
What promotes actin filament growth
High concentration of free actin monomers
210
What does intermediate actin concentration lead to
Treadmilling behavior
211
What are the steps of cell migration
Protrusion adhesion contraction release
212
What structures are formed by actin protrusion
Lamellipodia and filopodia
213
What do crosslinking proteins do in actin networks
Promote three dimensional actin gels
214
What causes membrane blebbing
Absence of cortical actin crosslinking
215
What is the role of bundling proteins
Stabilize actin in filopodia and microvilli
216
How is myosin organized in muscle
Myosin two dimers form thick filaments
217
What do myofibrils consist of
Repeated sarcomeres made of actin and myosin
218
How does myosin generate force
ATP hydrolysis and conformational change
219
What happens to sarcomere length during contraction
Sarcomeres shorten but filament length stays the same
220
What bacterium hijacks the actin cytoskeleton
Listeria monocytogenes
221
What is the primary role of intermediate filaments
Provide mechanical strength
222
Where are intermediate filaments absent
In arthropods and echinoderms
223
How are intermediate filaments assembled
Coiled coil dimers form tetramers which assemble into filaments
224
What crosslinks keratin networks
Disulfide bonds
225
How do keratin filaments provide mechanical strength
Link to neighboring cells via desmosomes
226
What happens in cells without intermediate filaments
They rupture under mechanical stress
227
What are neurofilaments
Intermediate filaments in axons providing tensile strength
228
What are nuclear lamins
Intermediate filaments forming a mesh under the nuclear envelope
229
What happens when nuclear lamins break down
Nuclear envelope breaks during cell division
230
What disease is caused by lamin A mutation
Premature aging with symptoms like aged skin and cardiovascular disease
231
What cytoskeletal element is found in microvilli
Actin filaments
232
What cytoskeleton enables apical to basal transport
Microtubules
233
What cytoskeleton provides mechanical strength against tearing
Intermediate filaments
234
What protein links different cytoskeletal systems
Plectin
235
What does plectin connect
Intermediate filaments to microtubules and actin
236
What proteins link the nucleus to the cytoskeleton
SUN and KASH proteins
237
Where is the SUN protein located
On the nuclear envelope connected to chromatin or nuclear lamina
238
Where is the KASH protein located
In the outer nuclear membrane linked to actin and microtubules
239
What is the role of SUN KASH bridge
Mechanical coupling between the nucleus and the cytoskeleton
240
What are the three types of cytoskeletal filaments
Microtubules Microfilaments Intermediate filaments
241
What protein subunits make up microtubules
Alpha and beta tubulin heterodimers
242
What protein makes up microfilaments
Actin monomers
243
What proteins make up intermediate filaments
Various proteins like keratin vimentin and lamins
244
What is the structure of microtubules
Hollow tubes with 13 protofilaments
245
What is the structure of microfilaments
Two stranded helical actin filaments
246
What is the structure of intermediate filaments
Rope like filaments of 8 twisted protofilaments
247
What is the diameter of microtubules
25 nanometers
248
What is the diameter of microfilaments
7 nanometers
249
What is the diameter of intermediate filaments
10 nanometers
250
Do microtubules have polarity
Yes plus and minus ends
251
Do microfilaments have polarity
Yes plus and minus ends
252
Do intermediate filaments have polarity
No
253
Which cytoskeletal filament is highly dynamic and undergoes dynamic instability
Microtubules
254
Which cytoskeletal filament undergoes treadmilling
Microfilaments
255
Which cytoskeletal filament is the most stable
Intermediate filaments
256
What energy source do microtubules use
GTP bound to beta tubulin
257
What energy source do microfilaments use
ATP bound to actin
258
Do intermediate filaments use ATP or GTP
No
259
What motor proteins interact with microtubules
Kinesin and dynein
260
What motor protein interacts with microfilaments
Myosin
261
Do intermediate filaments use motor proteins
No
262
What are the main functions of microtubules
Intracellular transport mitotic spindle cilia and flagella
263
What are the main functions of microfilaments
Cell movement shape changes cytokinesis
264
What are the main functions of intermediate filaments
Mechanical support and resistance to stress
265
What is the microtubule organizing center called
Centrosome
266
Do microfilaments require a central organizing center
No
267
Do intermediate filaments have a central organizing site
No
268
Where are microfilaments commonly found
Lamellipodia filopodia microvilli contractile ring
269
Where are intermediate filaments found
Keratins in skin neurofilaments in axons lamins in nucleus
270
Where are microtubules used in cell division
Mitotic spindle and kinetochore attachments
271
Which cytoskeletal filament is critical for muscle contraction
Microfilaments with myosin
272
Which cytoskeletal filament links to desmosomes for cell cell adhesion
Intermediate filaments
273
Which cytoskeletal filament forms cilia and flagella
Microtubules
274
Which cytoskeletal filament supports nuclear shape
Nuclear lamins
275
What cytoskeletal linker protein connects all three systems
Plectin
276
What proteins connect the nuclear interior to cytoskeleton
SUN and KASH proteins
277
What direction do kinesins move on microtubules
Plus end directed
278
What direction do dyneins move on microtubules
Minus end directed
279
What direction does myosin move on actin filaments
Usually plus end directed
280
What cytoskeletal filament resists tensile stress best
Intermediate filaments
281
Which cytoskeletal filament has the fastest turnover
Microfilaments
282
Which cytoskeletal filament is the stiffest but most brittle
Microtubules
283
Which cytoskeletal filament is the most flexible
Intermediate filaments
