> Comb jellies are ancient marine predators whose hairlike extensions known as cilia refract light as they swim, giving them an iridescent shimmer. They are the largest animals known to use cilia for movement, ...
I've long wondered: What is the difference between cilia and flagella? I've found no authoritative source that differentiates them or that says they are the same (except one paper from decades ago that strongly implies they are the same). It seems like something insiders know implicitly and never bother explaining.
Because a clear distinction is lacking, I don't trust non-expert sources like Wikipedia to be consistent, tor to not confuse them or miss any nuance.
> What is the difference between cilia and flagella?
Broadly and generally:
• cilia come in large groups, in rows or in sheets; flagella come singly or in pairs (occasionally more)
• cilia are short, and they beat backwards and forwards in a coordinated way, like a Mexican wave; flagellae are long, and in prokaryotes, they spin around their axis.
(Eukaryote flagella -- e.g. spermatozoan "tails" -- are a different structure that just resembles the ones in prokaryotes. Prokaryotes are bacteria and archaea -- no cell nucleus. Eukaryotas have cell nuclei and other organelles, such as mitochondria and chloroplasts. Their flagellae bend and flap, they don't spin.)
Take 1 cell. Can you count the moving hair things? Then they're flagella. Is the beastie covered in lots of them, countless, like fur? Then they're cilia.
I read earlier this year about Berg's and Samuel et al.'s (and maybe others') amazing flagellar motor discoveries. I didn't realize they were only prokaryotes; the motor seems like a sophisticated mechanism.
True! (This stuff is since my BSc and I need to do more reading, but it isn't my job, so there's no time.)
But the thing is that, AIUI, ATP-synthase is in the mitochondria and chloroplasts, so from an evolutionary perspective it is in prokaryotes... just symbiotic ones...
They are us, though. There’s no eukaryotes without mitochondria at all. We are part prokaryote in every cell, apart from the equal number of fully prokaryotic cells in our various microbiomes. Hence the term holobiont for animals like us. We’re pretty much a walking ecosystem.
In some ways, it’s wrong to imagine the branches of life are actually branches. Loki archea and alphaproteobacter together gave us the last eukaryotic common ancestor, and then bacteria continued to live around and in eukaryotes.
That said, mitochondria can’t be called prokaryotes within us. They’ve given up too many genes, and can’t survive on their own.
Of course, the rest of us can’t survive without them either, so it’s a complete mutual situation.
mmooss · · focus · HN ↗
I've long wondered: What is the difference between cilia and flagella? I've found no authoritative source that differentiates them or that says they are the same (except one paper from decades ago that strongly implies they are the same). It seems like something insiders know implicitly and never bother explaining.
Because a clear distinction is lacking, I don't trust non-expert sources like Wikipedia to be consistent, tor to not confuse them or miss any nuance.
lproven · · focus · HN ↗
Broadly and generally:
• cilia come in large groups, in rows or in sheets; flagella come singly or in pairs (occasionally more)
• cilia are short, and they beat backwards and forwards in a coordinated way, like a Mexican wave; flagellae are long, and in prokaryotes, they spin around their axis.
(Eukaryote flagella -- e.g. spermatozoan "tails" -- are a different structure that just resembles the ones in prokaryotes. Prokaryotes are bacteria and archaea -- no cell nucleus. Eukaryotas have cell nuclei and other organelles, such as mitochondria and chloroplasts. Their flagellae bend and flap, they don't spin.)
Take 1 cell. Can you count the moving hair things? Then they're flagella. Is the beastie covered in lots of them, countless, like fur? Then they're cilia.
mmooss · · focus · HN ↗
> in prokaryotes, they spin around their axis.
I read earlier this year about Berg's and Samuel et al.'s (and maybe others') amazing flagellar motor discoveries. I didn't realize they were only prokaryotes; the motor seems like a sophisticated mechanism.
randomImmigrant · · focus · HN ↗
However, we have ATP Synthase. That’s also an ion driven molecular rotary engine. Of course, we use it to convert ionic gradients to energy (ATP).
Both are exceptionally efficient molecules for their tasks.
lproven · · focus · HN ↗
But the thing is that, AIUI, ATP-synthase is in the mitochondria and chloroplasts, so from an evolutionary perspective it is in prokaryotes... just symbiotic ones...
randomImmigrant · · focus · HN ↗
In some ways, it’s wrong to imagine the branches of life are actually branches. Loki archea and alphaproteobacter together gave us the last eukaryotic common ancestor, and then bacteria continued to live around and in eukaryotes.
That said, mitochondria can’t be called prokaryotes within us. They’ve given up too many genes, and can’t survive on their own.
Of course, the rest of us can’t survive without them either, so it’s a complete mutual situation.
lproven · · focus · HN ↗