Principles of Cellular Architecture Flashcards
Lecture 2
What are the two domains of prokaryotes?
archaea and eubacteria
What are metazoans?
multicellular animal cells and organisms
How has the data utilized for evolutionary trees changed over time?
Initially, the rDNA (specific DNA sequences used to encode rRNA) was examined.
Later, as technology developed, we began sequencing genomes rather than individual DNA sequences.
How has cellular biology’s thoughts on the chloroplasts’ arrival to the eukaryotic lineage changed as technology developed? What data was used initially and what data is used currently?
Initially, based on individual rDNA sequences, it was believed that chloroplasts arose 3-4 different times in the eukaryotic lineage.
Now, by sequencing entire genomes, it is currently believed that chloroplasts only arose once.
What are prokaryotes?
organisms with a nucleoid not enclosed by a membrane
What are eukaryotic cells?
cells with a membrane-bound nucleus
Archaea and eubacteria both lack membrane-bound DNA. What evidence indicates the assumption that archaea is more closely related to eubacteria than eukarya is incorrect?
- Archaeal enzymes that impact the central dogma are more similar in structure and function to enzymes found in eukarya. Archaea and eukarya are molecularly similar.
- Archaea has proteins only previously found in eukarya, never in eubacteria.
Describe Margulis’s endosymbiotic hypothesis. What evidence led her to this conclusion?
Margulis believed a primitive ancestor of eukaryotic cells enveloped a bacterial cell capable of oxidative phosphorylation. Over evolutionary time, the bacterial cell developed into the mitochondria.
This is evidenced by mitochondria having their own DNA.
What four pieces of evidence lend credibility to the endosymbiotic hypothesis?
- Mitochondria and chloroplasts have their own autonomously replicating DNA genomes.
- RNA polymerases and ribosomes found in mitochondria and chloroplasts more closely resemble prokaryotes than eukaryotes.
- Mitochondria deviate from an otherwise universal genetic code. Codons that encode an amino acid in eukaryotic cells don’t encode for the same amino acids in mitochondria.
- Mitochondria and chloroplasts divide by fission, like many bacteria.
What weakens the theoretical outside-in origins of the nucleus?
Both models rely significantly on supplemental models without concrete evidence.
Name the two potential theories for the nucleus’s arrival to eukaryotic cells from the outside-in perspective.
Endosymbiotic origin and autogenous origin
Describe the hypothetical endosymbiotic origin of the nucleus.
A eubacterium engulfs an archaeal cell. Overtime, they form a relationship and the two become one cell. The eubacterium provides the cytoplasm and the archaea becomes the nucleus.
Describe the hypothetical autogenous origin of the nucleus.
A prokaryotic cell’s plasma membrane begins to fold inward. Over time, the enfolded plasma membrane surrounds the DNA of the cell.
Why would the nucleus having an autogenous origin be useful for the cell?
It increases surface area of the cell, providing greater contact with the exterior environment, which could be useful for increasing the uptake of resources, promotes growth
Describe Baum & Baum’s inside-out model of nucleus development.
Rather than a membrane brought into the cell, the cytoplasm and membrane are moved outwards together as a fingerlike structure.
The ancestral cell develops a symbiotic relationship with epibiotic bacterium and, over evolutionary time, projects its membrane outward to increase contact with bacteria; eventually, the membrane begins to expand around the bacteria, forming a double membrane around its DNA (and around the bacterium it surrounds).
Why is the inside out model of nucleus development so popular?
Parsimonious, uses fewer supplementary models than others
Answers questions of how mitochondria and nucleus formed simultaneously and why both have a double membrane
Supported by molecular data, seen in nature
Do eukaryotes or prokaryotes have membrane-bound organelles?
Trick question! Both can have membrane-bound organelles. Eukaryotes are more likely to, however.
What are the six consequences of compartmentalization?
- Organelles contain distinct pH and ionic environments.
- Proteins encoded by nuclear genes must be targeted.
- Organelles have distinct functions.
- Cell size is not diffusion limited.
- Toxic metabolic intermediates are isolated.
- Reduced competition along biochemical pathways.
Describe a liquid-phase condensate.
oil drops on water, where like molecules coalesce to form a phase separation, separating themselves from unlike molecules
a membrane-less organelle that functions as an intracellular compartment
