The Eukaryotic Cell Flashcards
What are the 3 ‘super kingdoms’ in the classification system?
Bacteria, archaea, and eukarya.
What are the 6 kingdoms in the classification system?
Bacteria, Archaea, Protista, Plantae, Fungi, Animalia
Describe 3 features of the first atmosphere on Earth.
- very little oxygen
- rich in water vapour
- rich in compounds released from volcanic eruption (e.g CO2, nitrous oxides, methane, ammonia, hydrogen)
What is the most compelling theory describing how life evolved on Earth initially?
- Life evolved at hydrothermal vents located at bottom of ocean floor
- seawater mixing with rock from earths mantle created chemistry that enabled formation of amino acids and nucleotides.
First life on earth was in the form of what organism?
Prokaryotic chemotrophs
Describe the great oxidation event and what it was critical for.
- photosynthetic prokaryotes produced oxygen
- critical to the evolution of aerobic organisms
When do eukaryotic cells first appear in the fossil record?
1.8 billion years ago.
What were the first eukaryotic fossils?
Precambrian acritarch fossils.
Where do scientists believe early eukaryotes lived?
In the water column, freely suspended
List the 3 earliest eukaryotes and when they appeared in the fossil record chronologically.
1.4 billion years ago - Grypannia
(Filamentous green algae spiral thingy)
635 million years ago - early Seaweed
500 million years ago - Burgess Shale animals (Cambrian)
Compare prokaryotes and eukaryotes in terms of:
- presence of mitochondria
- DNA shape
- histone proteins with DNA
- nuclear envelope and endoplasmic reticulum
- only eukaryotes have mitochondria
- prokaryotes have circular DNA, eukaryotes linear DNA
- only some proks have histones, all euks have histones
- only euks have nuclear envelope and ER
Compare prokaryotes and eukaryotes in terms of:
- multicellular or uni
- cell size
- genome size
- gene number
- meiosis (sexual or asexual)
- proks are unicellular, euks are multicellular
- prokaryotes are <10 micrometers, euks are 3 micrometers to 10 mm
- proks have very little bases, euks have way more bases
- proks have ~4000 genes, euks have 6000-35000 genes
- proks are asexual, euks undergo meiosis (sexual)
What archaeal group are eukaryotes most closely related to?
Lokiarchaeota
What 2 features are characteristic of Lokiarchaea?
- actin homologise in cytoskeleton
- vesicular trafficking machinery
The acquisition of WHAT was key in the evolution of eukaryotes and why?
Mitochondria, gave eukaryotes power
What did eukaryotes evolve from?
Prokaryotes
Describe two key features of the most recent ancestor of eukaryotes and archaea.
- cytoskeleton
- endocytosis and/or phagocytosis
List 3 features of the most recent common ancestor of eukaryotes.
- nucleus
- mitochondrion
- membrane bound organelles
What are the two main theories describing how eukaryotes might have acquired the mitochondria?
Endosymbiosis: outside in model
Eukaryote host engulfed a purple bacterium
Endosymbiosis: inside out model
Eukaryotes and purple bacterium initially had close symbiotic relationship, over time projections of cell wall from eukaryote slowly enveloped purple bacteria.
List 7 key features that are evidence of how eukaryotes increased their genome size and complexity.
- nuclear envelope and endoplasmic reticulum
- linear chromosomes
- multiple chromosomes
- telomeres
- multiple replication origin points
- histone proteins
- gene duplication
What is the old and now inaccurate theory of how the endomembrane system evolved in eukaryotes?
- invagination (folding in) of plasma membrane to create nuclear membrane and endoplasmic reticulum
Describe the new and more accepted theory of how the endomembrane system evolved. What is the evidence for this?
- mitochondria was already in ancestral eukaryotes before the endomembrane system evolved
- bacteria secrete outer membrane vesicles containing lipids for signaling and these are the same as mitochondrial vesicles
- vesicles from the mitochondria might have fused together to generate membrane structure that evolved into the endomembrane system.
EVIDENCE: eukaryotic plasma membrane has lipid composition more similar to bacteria than ancestral archaea
Describe the origin of the nuclear envelope.
- during nuclear division, envelope disintegrates
- chromosomes divide and separate
- ER clusters around chromosomes and forms new envelope
How many chromosomes do prokaryotes have?
1 circular chromosome
How are eukaryotes able to contain so much more DNA?
Bc of histones and their packaging mechanism.
Describe the steps of how a new bacterium is made.
- Circular chromosome is attached to cell membrane at specific point
- DNA replicates the cell grows
- The two copies of DNA are separated by expansion of the cell membrane between the attachment points.
- Membrane furrows inwards to divide cell in two.
Describe a selection pressure for why bacteria have so few genes.
- bacterial chromosomes have a single replication origin
- more genes requires more time to replicate
- bacteria would therefore get out-competed by faster replicating organisms
Why don’t bacterial chromosomes have multiple origin points?
More than one origin requires multiple decatenation points, too complicated (Russian wedding ring problem)
Impossible for two chromosomes to untangle as lots of bits of DNA would be linked together
Do linear eukaryotic chromosomes have catenation (linking of strands)? Explain why.
No, because they are linear and have multiple replication origins.
What is an advantage of the evolution of linear chromosomes?
- longer piece of DNA with multiple origin points, manageable replication/generation time
- multiple chromosomes to increase DNA content and complexity
What is a disadvantage of linear chromosomes?
- a small amount of DNA at the end of chromosomes is lost with every replication
(DNA with RNA primer attached is unreplicated so it degrades) - linear chromosomes therefore less stable than circular chromosomes because of the end problem
How do telomeres solve the end problem of linear eukaryotic chromosomes?
- keep adding sacrificial non coding DNA that the RNA primer can attach to and later delete without losing cruciak genes
What did Fukui Ishikawas experiment involving fission yeast show about telomeres?
Fission yeast is eukaryotic, once genes for telomere formation were deleted, yeast nearly all died. Therefore couldn’t survive with linear chromosomes because they just got shorter and shorter
When they made the chromosomes circular, they could grow ok and divide by binary fission but unable to have sexual reproduction
What is parasitic/junk DNA?
Introns (non coding parts of DNA) that interrupts the DNA words in a gene.
Still transcribed into mRNA, but is excised before translation.
What key processes does the nuclear envelope of the nucleus separate? Why is this important?
- nucleus separates transcription and translation
- acts as barrier to prevent precocious translation that would make a dodgy protein if introns are still present
- ensures intron excision prior to translation
Since prokaryotes don’t have a nucleus, would they survive having introns in their genes? Why or why not?
No because without nucleus, transcription and translation are coupled. No time to excise introns. Therefore would not survive bc too many defunct proteins produced if introns present!
What are the two theories about the origin of the evolution of meiosis? Which one is said to be more accurate?
- From mitosis (too many changes from mitosis)
2. From bacterial transformation (more accurate)
