BIOL2117 CELL BIOLOGY QUESTIONS AND
ANSWERS
What was theory one about how cellular life originated? Include evidence for and against.
CORRECT ANSWER - Haldane's 1929 "primordial soup" theory, further explored by the Miller-
Urey experiments, suggests life originated from a mixture of organic molecules formed by ultraviolet
light.
- Supporting evidence includes the creation of amino acids and nucleotides in lab conditions.
- However, the theory falls short in explaining the formation of complex life-essential polymers and
the role of UV light as an energy source.
What was theory two about how cellular life originated? Include evidence for and against.
CORRECT ANSWER - This theory proposes that life originated in deep-sea thermal vents,
where warm, alkaline fluids rich in minerals facilitated early biochemistry.
- Evidence for this includes lab synthesis of organic molecules like amino acids and similar
biochemistry to early methanogens.
- However, the transient nature of hydrothermal vents and the inability to synthesize all essential
molecules, like nucleotides, pose challenges to the theory.
What is the role of chemiosmosis in the theory that life originated at hydrothermal vents?
CORRECT ANSWER - Chemiosmosis at hydrothermal vents suggests that natural
electrochemical gradients could have been harnessed for energy.
- The proton motive force across membranes could have fueled ATP synthesis, providing early life
forms with an energy source.
What are the essential components needed for life and how might they have originated in alkaline
hydrothermal vents?
CORRECT ANSWER 1. An energy source: promotor chemically unfavourable reactions
2. Generation of useful chemical energy: covert light/organic molecules into something that can drive
complex chemical reactions.
3. Catalysts: make complex reactions more favourable
4. Replicator: a molecule that can make copies of itself
5. A boundary to seperate life from non-life: to enclose metabolism and chemical energy.
Describe the difference between informative character and uninformative character.
, CORRECT ANSWER - An "informative character" is a trait shared by some but not all species,
useful for determining relationships.
- "Uninformative characters" are either universal or entirely unique, offering no insight into
relationships.
How do we trace the evolutionary lineage of existing cells, and what role does LUCA play in this?
CORRECT ANSWER - Understanding cellular relationships helps us infer attributes of LUCA
which can be done by molecular by phylogeny,
- LUCA is the Last Universal Common Ancestor.
- It is the starting point for the three domains of life: Bacteria, Eukarya, and Archaea.
- However Eukarya is just specialised Archaea so it just Archaea and Bacteria.
What are the key characteristics and likely habitat of LUCA?
CORRECT ANSWER - LUCA likely utilized H2, N2, and CO2 as substrates and generated
methane.
- It had proteins with iron-sulfur co-factors and synthesized ATP using electrochemical gradients.
- These traits are consistent with LUCA residing at alkaline hydrothermal vents.
- Its genomic makeup is derived from both bacterial and archaeal genomes.
What is FECA and LECA?
CORRECT ANSWER - FECA: common features between Eukaryotes and Asgard
- LECA: common features shared amongst Eukaryotes
What are the unique features of eukaryotes?
CORRECT ANSWER 1. A nucleus (containing DNA)
2. Vesicle trafficking
3. Multiple, linear chromosomes that separate by mitosis
4. A cytoskeleton (microtubules, microfilaments)
5. Organelles
What does Asgard Archaea look like?
CORRECT ANSWER - Asgard archaea have a complex cultivation history, taking around 12
years to find correct growth conditions.
- They exhibit a slow doubling time of 14-25 days, in syntrophic co-culture with other archaea.
,- No visible nucleus or internal organelles/membranes
- featuring unique, branching protrusions created through "loki-actin."
What does the Serial Endosymbiosis hypothesis propose regarding the origin of mitochondria?
CORRECT ANSWER - The Serial Endosymbiosis hypothesis suggests that mitochondria, along
with chloroplasts and potentially flagella, originated from free-living organisms that were
incorporated into eukaryotic cells through endosymbiosis.
- This hypothesis is generally accepted for mitochondria and chloroplasts but is controversial and
less supported for flagella.
What is the evidence that mitochondria are derived from an alpha-proteobacterium?
CORRECT ANSWER 1. Shape and size (~0.5 µm). Surrounded by two membranes
2. Genome, bacterial-derived (but with greatly reduced gene content)
3. Bacterial-like 70S ribosomes (vs 80S in cytosol); inhibited by tetracycline and not cycloheximide
4. Bacterial-like metabolic pathways (TCA cycle, electron transport chain, Fe-S cluster synthesis
Eukaryotes are a composite of Archaea and Bacteria but when in eukaryotic evolution did the
mitochondrion arise?
CORRECT ANSWER - Suggests mitochondria evolved at the very onset of eukaryotes as the
common ancestor of all eukaryotes (LECA) had a mitochondrion
What characteristics do "mitochondria-related organelles" (MROs) exhibit in eukaryotes that lack
typical mitochondria?
CORRECT ANSWER - "MROs" in eukaryotes lacking typical mitochondria are surrounded by
two membranes and lack conventional mitochondrial features like the TCA cycle and mitochondrial
genome.
- However, they have hydrogenosomes convert malate and pyruvate into H2, CO2 and ATP
What is the common ancestor of all eukaryotes that had a bacterial symbiont?
CORRECT ANSWER The common ancestor of all eukaryotes had a bacterial symbiont that
became the mitochondrion.
What is the syntrophic origin of mitochondria?
CORRECT ANSWER - Hypothesizes that Asgard archaea entered a metabolic symbiosis,
termed syntrophy ("together feeding"), with a bacterium, exchanging organic molecules for ATP.
, - Protrusions possibly facilitating this interaction eventually led to the bacterium's internalization,
becoming an organelle, hinting at an intricate evolutionary process grounded in symbiotic
relationships.
What is the structure of the mitochondria?
CORRECT ANSWER Cristae:
- invaginations of the inner membrane.
- Increase surface area for electron transport chain
Matrix:
- the lumen (inside) of the mitochondrion.
- Where most metabolic reactions take place
What are the different shapes and sizes in mammalian, plant and toxoplasma cells that mitochondria
comes in?
CORRECT ANSWER - Mammalian cells (fibroblast): multiple mitochondria, very dynamic
(constantly moving, dividing and fusion)
- Plant cells (tobacco): multiple mitochondria, also dynamic
- Toxoplasma cells: single mitochondrion per parasite
Describe the process of the electron transport chain.
CORRECT ANSWER 1. TCA cycle-derived electrons are given to CoQ.
2. CoQ transfers electrons to Complex III.
3. Electrons move to Complex IV via CytC, creating a proton gradient in the intermembrane space.
4. O₂ accepts the final electron, validating the electron transport chain activity.
5. The proton gradient facilitates ATP synthesis through ATP synthase (complex V), converting ADP
and inorganic phosphate to ATP.
What is the role of ATP synthase (complex V) in ATP production?
CORRECT ANSWER 1. In chemiosmosis, the proton gradient is 'harvested' by ATP synthase
(complex V).
2. The proton gradient is coupled to the rotation of a membrane component within complex V,
enabling a mechanical to chemical energy conversion.
3. This rotational energy enables the synthesis of ATP from ADP and inorganic phosphate, playing a
crucial role in energy storage for the cell.
ANSWERS
What was theory one about how cellular life originated? Include evidence for and against.
CORRECT ANSWER - Haldane's 1929 "primordial soup" theory, further explored by the Miller-
Urey experiments, suggests life originated from a mixture of organic molecules formed by ultraviolet
light.
- Supporting evidence includes the creation of amino acids and nucleotides in lab conditions.
- However, the theory falls short in explaining the formation of complex life-essential polymers and
the role of UV light as an energy source.
What was theory two about how cellular life originated? Include evidence for and against.
CORRECT ANSWER - This theory proposes that life originated in deep-sea thermal vents,
where warm, alkaline fluids rich in minerals facilitated early biochemistry.
- Evidence for this includes lab synthesis of organic molecules like amino acids and similar
biochemistry to early methanogens.
- However, the transient nature of hydrothermal vents and the inability to synthesize all essential
molecules, like nucleotides, pose challenges to the theory.
What is the role of chemiosmosis in the theory that life originated at hydrothermal vents?
CORRECT ANSWER - Chemiosmosis at hydrothermal vents suggests that natural
electrochemical gradients could have been harnessed for energy.
- The proton motive force across membranes could have fueled ATP synthesis, providing early life
forms with an energy source.
What are the essential components needed for life and how might they have originated in alkaline
hydrothermal vents?
CORRECT ANSWER 1. An energy source: promotor chemically unfavourable reactions
2. Generation of useful chemical energy: covert light/organic molecules into something that can drive
complex chemical reactions.
3. Catalysts: make complex reactions more favourable
4. Replicator: a molecule that can make copies of itself
5. A boundary to seperate life from non-life: to enclose metabolism and chemical energy.
Describe the difference between informative character and uninformative character.
, CORRECT ANSWER - An "informative character" is a trait shared by some but not all species,
useful for determining relationships.
- "Uninformative characters" are either universal or entirely unique, offering no insight into
relationships.
How do we trace the evolutionary lineage of existing cells, and what role does LUCA play in this?
CORRECT ANSWER - Understanding cellular relationships helps us infer attributes of LUCA
which can be done by molecular by phylogeny,
- LUCA is the Last Universal Common Ancestor.
- It is the starting point for the three domains of life: Bacteria, Eukarya, and Archaea.
- However Eukarya is just specialised Archaea so it just Archaea and Bacteria.
What are the key characteristics and likely habitat of LUCA?
CORRECT ANSWER - LUCA likely utilized H2, N2, and CO2 as substrates and generated
methane.
- It had proteins with iron-sulfur co-factors and synthesized ATP using electrochemical gradients.
- These traits are consistent with LUCA residing at alkaline hydrothermal vents.
- Its genomic makeup is derived from both bacterial and archaeal genomes.
What is FECA and LECA?
CORRECT ANSWER - FECA: common features between Eukaryotes and Asgard
- LECA: common features shared amongst Eukaryotes
What are the unique features of eukaryotes?
CORRECT ANSWER 1. A nucleus (containing DNA)
2. Vesicle trafficking
3. Multiple, linear chromosomes that separate by mitosis
4. A cytoskeleton (microtubules, microfilaments)
5. Organelles
What does Asgard Archaea look like?
CORRECT ANSWER - Asgard archaea have a complex cultivation history, taking around 12
years to find correct growth conditions.
- They exhibit a slow doubling time of 14-25 days, in syntrophic co-culture with other archaea.
,- No visible nucleus or internal organelles/membranes
- featuring unique, branching protrusions created through "loki-actin."
What does the Serial Endosymbiosis hypothesis propose regarding the origin of mitochondria?
CORRECT ANSWER - The Serial Endosymbiosis hypothesis suggests that mitochondria, along
with chloroplasts and potentially flagella, originated from free-living organisms that were
incorporated into eukaryotic cells through endosymbiosis.
- This hypothesis is generally accepted for mitochondria and chloroplasts but is controversial and
less supported for flagella.
What is the evidence that mitochondria are derived from an alpha-proteobacterium?
CORRECT ANSWER 1. Shape and size (~0.5 µm). Surrounded by two membranes
2. Genome, bacterial-derived (but with greatly reduced gene content)
3. Bacterial-like 70S ribosomes (vs 80S in cytosol); inhibited by tetracycline and not cycloheximide
4. Bacterial-like metabolic pathways (TCA cycle, electron transport chain, Fe-S cluster synthesis
Eukaryotes are a composite of Archaea and Bacteria but when in eukaryotic evolution did the
mitochondrion arise?
CORRECT ANSWER - Suggests mitochondria evolved at the very onset of eukaryotes as the
common ancestor of all eukaryotes (LECA) had a mitochondrion
What characteristics do "mitochondria-related organelles" (MROs) exhibit in eukaryotes that lack
typical mitochondria?
CORRECT ANSWER - "MROs" in eukaryotes lacking typical mitochondria are surrounded by
two membranes and lack conventional mitochondrial features like the TCA cycle and mitochondrial
genome.
- However, they have hydrogenosomes convert malate and pyruvate into H2, CO2 and ATP
What is the common ancestor of all eukaryotes that had a bacterial symbiont?
CORRECT ANSWER The common ancestor of all eukaryotes had a bacterial symbiont that
became the mitochondrion.
What is the syntrophic origin of mitochondria?
CORRECT ANSWER - Hypothesizes that Asgard archaea entered a metabolic symbiosis,
termed syntrophy ("together feeding"), with a bacterium, exchanging organic molecules for ATP.
, - Protrusions possibly facilitating this interaction eventually led to the bacterium's internalization,
becoming an organelle, hinting at an intricate evolutionary process grounded in symbiotic
relationships.
What is the structure of the mitochondria?
CORRECT ANSWER Cristae:
- invaginations of the inner membrane.
- Increase surface area for electron transport chain
Matrix:
- the lumen (inside) of the mitochondrion.
- Where most metabolic reactions take place
What are the different shapes and sizes in mammalian, plant and toxoplasma cells that mitochondria
comes in?
CORRECT ANSWER - Mammalian cells (fibroblast): multiple mitochondria, very dynamic
(constantly moving, dividing and fusion)
- Plant cells (tobacco): multiple mitochondria, also dynamic
- Toxoplasma cells: single mitochondrion per parasite
Describe the process of the electron transport chain.
CORRECT ANSWER 1. TCA cycle-derived electrons are given to CoQ.
2. CoQ transfers electrons to Complex III.
3. Electrons move to Complex IV via CytC, creating a proton gradient in the intermembrane space.
4. O₂ accepts the final electron, validating the electron transport chain activity.
5. The proton gradient facilitates ATP synthesis through ATP synthase (complex V), converting ADP
and inorganic phosphate to ATP.
What is the role of ATP synthase (complex V) in ATP production?
CORRECT ANSWER 1. In chemiosmosis, the proton gradient is 'harvested' by ATP synthase
(complex V).
2. The proton gradient is coupled to the rotation of a membrane component within complex V,
enabling a mechanical to chemical energy conversion.
3. This rotational energy enables the synthesis of ATP from ADP and inorganic phosphate, playing a
crucial role in energy storage for the cell.
