The Origins and Functions of Mitochondria & Chloroplasts Flashcards
What are mitochondria and chloroplasts
Membrane-bound sub-compartments of eukaryotic cells responsible for major energy-related processes
Describe the membrane structure of mitochondria and chloroplasts
Both have a double membrane. The outer membrane is freely permeable, while the inner membrane is selective, containing carrier proteins for specific metabolites
What is the function of the internal membranes in mitochondria and chloroplasts
To increase surface area for biochemical processes like ATP synthesis or photosynthesis
What are the main functions of mitochondria
TCA cycle and OxPhos: ATP & NADH production
Ammonia assimilation via glutamine synthetase
Biosynthesis of branched-chain amino acids (valine, leucine, isoleucine)
Some lipid synthesis
What are the main functions of chloroplasts
Photosynthesis: ATP, NADPH, and sugar production
Synthesis of most vitamins (e.g. beta-carotene → vitamin A)
Biosynthesis of most amino acids and lipids
What percentage of total cellular protein is in the mitochondria and chloroplasts
Mitochondria: ~5%
Chloroplasts in plants: ~70% (20–50% of that is Rubisco)
Where are chloroplasts located in plant cells and why
Around the cell periphery near airspaces to minimise CO₂ diffusion path
How do chloroplasts behave in response to light
They move within the cell to optimise light capture for photosynthesis.
Why do chloroplasts resemble cyanobacteria
Due to their internal membrane structure and evolutionary origin
Who first described chloroplasts
Hugo von Mohl in 1837 (“grains of chlorophyll”)
Who proposed that chloroplasts divide like bacteria
Andreas Schimper (1883)
Who proposed the endosymbiotic theory for chloroplasts
Konstantin Mereschkowsky in 1905
Who is credited with the endosymbiotic theory for mitochondria
Lynn Margulis in 1966 (“On the Origin of Mitosing Cells”)
What is the endosymbiotic theory
The theory that mitochondria and chloroplasts originated as free-living bacteria engulfed by a host cell
Why was the endosymbiotic theory slow to gain acceptance
Similar morphology doesn’t guarantee evolutionary relatedness, similarities could be due to convergent evolution
What is convergent evolution
When unrelated organisms evolve similar traits due to similar environmental pressures
When did mitochondrial endosymbiosis occur
Before the diversification (radiation) of eukaryotes
What lineage did chloroplasts evolve from
From a cyanobacterium within the archaeplastida lineage
How are mitochondria and chloroplasts inherited
Maternally, through uniparental inheritance
Why is uniparental inheritance significant
It isolates organelle genomes from recombination, which can lead to mutation accumulation (Muller’s Ratchet)
How do mitochondrial and chloroplast genomes compare to their ancestors
They are greatly reduced compared to their free-living ancestors
What is notable about the human mitochondrial genome
Circular, codes for OxPhos proteins, rRNA genes, tRNAs, lacks ribosomal proteins
What additional genes are in plant mitochondria compared to human
Ribosomal proteins, cytochrome c biogenesis proteins, maturases, and transporters
What is found in the land plant chloroplast genome (7)
rRNA & tRNA genes
NADH dehydrogenase (Complex I)
Cytochrome b6f (Complex III)
ATP synthase (Complex V)
Ribosomal proteins
Photosystem I & II genes
Rubisco large subunit
Why do organelles now rely on the nuclear genome for many of their proteins
Genes were transferred to the nucleus over time.
It’s more efficient: nuclear genes can be inherited diploidly, reducing mutation risk and resource burden.
Organelles import proteins synthesised in the cytosol.
