MICR 271 Midterm Exam with All Actual
Detailed Answers 2026 Updated.
3 Domains of life - Answer Bacteria, Archaea, Eukarya
Endosymbiont theory - Answer - eukaryotes evolved more complex structures and metabolic
processes by building upon prokaryotic attributes
- evolutionary connection between prokaryotes and eukaryotes
- similarities between bacteria and mitochondria
- mitochondria and chloroplasts evolved from free-living bact via symbiosis w/in a eukaryotic
host cell to have 2 key differences: these organelles contain their own DNA and a distinct
translation system
- likely that an alpha-proteobacteria member is the ancestor of mitochondria, however, there is
little agreement as to which member
Microbe - Answer microscopic living organism that may be single-celled or multicellular
Links between prokaryotes and eukaryotes highlighting functional independencies - Answer 1.
N is abundant in atmosphere but only a few species of microbes can use it in this form, all other
organisms depend on these N-modifying bact
2. More and more complex pathways arose with ancestral microorganisms and a microbe was
the source of mitochondria
3. Humans contain 10x more bact cells than human cells and 100x more microbial genes than
human genes
4. Total biomass on earth of bact is approaching that of plants
5. ~50 mil bact in 1g of soil and 1 million bact in 1mL of fresh water
6. Photosynthetic bact (cyanobacteria) living in bodies of water like lakes, ponds, and shallow
oceans produces 50% of the oxygen we breathe
Eukaryotic vs prokaryotic cells - Answer - prokaryotes have nucleoids
- eukaryotes have membrane-encoled nuclei
- eukaryotes are much more complex
- allow for functional difference in transcription, translation, how they generate energy, etc.
- eukaryotes have membrane-bound orgnalles and prokaryotes do not
Bacteria - Answer - prokaryote
- single-celled microorganisms characterized by peptidoglycan-containing cell walls
,Archaea - Answer - domain of single-celled prokaryotic microorganisms which do not have
peptidoglycan in their cell walls
Eukaryota - Answer - organism whose cells contain a nucleus and other organelles enclosed in
membranes
Archezoan scenario - Answer - primitive amitochondrial euk cell phagocytosed an alpha-
proteobacterium, leading to mitochondrion evolution
- this hypothesis has fallen out of favor
Symbiogenesis scenario - Answer - complexity of euk cell and its defining features emerged
after the mitochondrial symbiosis
- a single endosymbiotic event involing the uptake of an alpha-proteobacterium by an archaeal
cell led to the generation of the mitochondria, followed by the evolution of the nucleus and
compartmentalization of the euk cell
Phylogenomics - Answer - analysis of whole genomes
Phylogenetics - Answer - genetic distinctions
Phylogeny - Answer - evolutionary history of a group of organisms
- the more similar an organism is to another, the closer their genetic relationship are
- initial efforts to map phylogenetic relationships compared rRNA between organisms to create
a tree of life
- genetic similarities btwn organisms can help us understand the phylogeny of the organisms
- tree of life represents the phylogeny of organisms and the history of the organismal lineages as
they change thru time
Tree from 1987 by Carl Woese - Answer - compare rRNA sequences
- major finding: close relationship between archaea and eukaryota
Bacteria vs archaea vs eukaryota - Answer 1. Bacteria = no nucleus, 3-4 subunits of rna
polymerase, 70s ribosomes, murein cell wall
2. Archaea = no nucleus, 8 - 12 subunits of rna polymerase, 70s ribosomes, no murein cell wall
3. Eukaryota = nucleus present, 12 - 14 subunits, 80s rna polymerase, no murein cell wall
Phylogenetic tree of life - Answer - we now compare entire genomes
,- recent tech advances in dna sequencing allow whole genomes to be pieces together without
culturing organisms
- bact and archaebact together based on their cell wall structures
- now with dna sequencing, their rna was found to be more distantly related than previously
thought
- in 1990, archaea was suggested
- tree used to show too great of evolutionary distance between arachaea and eukaryotes, the
revised tree shows a much closer evolutionary distance
- red dots show lineages lacking an isolated and cultured representative, a distinct genome has
been sequenced from an environmental sample but the organism has never been grown in pure
culture in a lab setting
- many organisms are yet to be characterized as they are difficult to create in lab
- tree assumes that the higher the level of genetic similarity between two organisms, the more
they are related evolutionarily
- this assumption is less problematic with the whole gene pool than if it was based only on rRNA
sequence
Web of life - Answer - there are multiple connections between branches of the tree of life that
create extensive networks of untree-like links btwn 3 traditional domains
- tree-like structure at the top acknowledges that euks obtained mitochondria and chloroplasts
from bact
- lacks a single cell at the root, early life likely evolved from a population of primitive cells with
different genes
- links symbolize horizontal gene transfer of single/multiple genes that have always occurred
between unicellular organisms i.e. transfer of genes via viruses
Where do viruses come from - Answer - obligate intracellular parasites = their reproduction
cannot occur outside of a host cell, it relies on intracellular resources
- important contributors to web of life
- capable of interacting with all 3 domains and carry genetic info between dif kinds of organisms
and between the domains
- constant interacs btwn viral and cellular 'empires'
How do viruses fit in the picture? - Answer - small infectious agents that only replicate inside
living cells of other organisms
- in ocean water and soil, the number of viral particles exceeds the number of cells by 10:100
- genetic diversity substantially exceeds that of cellular life forms
- cells contain many antiviral defence systems
, - viral genomes consist of many forms of nucleic acids and use diverse replication processes like
rna replication and reverse transcription, unlike cellular life which uses a rep-express strategy
via dsdna
- viruses are the 'empire of life' though it is debated whether or not they are actually alive
- chicken pox, HIV, cold, COVID-19 = viral
- pneumonia, meningitis, diarrhea = viral/bacterial
- strep, uti, tuberculosis = bacterial
Virus basics - Answer - small infectious agents
- once assembled, virus progeny are able to leave the host cellular environment and infect new
cells and/or hosts
- viruses can infect animals, plants, bacteria and archaea
Virions - Answer - when not inside a host, viruses exist in the form of virions, these consist of
2, sometimes 3 parts
1. genetic material (DNA or RNA)
2. capsid (protein coat)
3. Envelope (some virsuses have a layer of lipids surrounding the protein coat)
- seem to predate "living" forms of life
Virus-first theory - Answer - viruses are ancestral to cells, they evolved from mixtures of
macromolecules (e.g. nucleic acids, proteins) before the first cells appears on earth
- existed as self-replicating units in a pre-cellular world
- self-replicating units of RNA that were first in existence may have gained the ability to infect
early forms of cells
- some RNA molecules can catalyze chemical reactions
Escape theory - Answer - cells came before viruses
- viruses derived from bits of cellular RNA and/or DNA fragments that leaked/escaped from cells
- when these acquire a protein coat they can become independent entities with the ability to
interact with other cells
- viruses are derived from genetic elements that may have resembled genetic sequences known
as retrotransposons
- during asymmetric cell fission a vesicle could have formed, engulfing a self-replicating RNA
with a coat-encoding RNA segment, this particle would continue to evolve through interactions
with additional early cell types
Reduction theory - Answer - cells came before viruses
Detailed Answers 2026 Updated.
3 Domains of life - Answer Bacteria, Archaea, Eukarya
Endosymbiont theory - Answer - eukaryotes evolved more complex structures and metabolic
processes by building upon prokaryotic attributes
- evolutionary connection between prokaryotes and eukaryotes
- similarities between bacteria and mitochondria
- mitochondria and chloroplasts evolved from free-living bact via symbiosis w/in a eukaryotic
host cell to have 2 key differences: these organelles contain their own DNA and a distinct
translation system
- likely that an alpha-proteobacteria member is the ancestor of mitochondria, however, there is
little agreement as to which member
Microbe - Answer microscopic living organism that may be single-celled or multicellular
Links between prokaryotes and eukaryotes highlighting functional independencies - Answer 1.
N is abundant in atmosphere but only a few species of microbes can use it in this form, all other
organisms depend on these N-modifying bact
2. More and more complex pathways arose with ancestral microorganisms and a microbe was
the source of mitochondria
3. Humans contain 10x more bact cells than human cells and 100x more microbial genes than
human genes
4. Total biomass on earth of bact is approaching that of plants
5. ~50 mil bact in 1g of soil and 1 million bact in 1mL of fresh water
6. Photosynthetic bact (cyanobacteria) living in bodies of water like lakes, ponds, and shallow
oceans produces 50% of the oxygen we breathe
Eukaryotic vs prokaryotic cells - Answer - prokaryotes have nucleoids
- eukaryotes have membrane-encoled nuclei
- eukaryotes are much more complex
- allow for functional difference in transcription, translation, how they generate energy, etc.
- eukaryotes have membrane-bound orgnalles and prokaryotes do not
Bacteria - Answer - prokaryote
- single-celled microorganisms characterized by peptidoglycan-containing cell walls
,Archaea - Answer - domain of single-celled prokaryotic microorganisms which do not have
peptidoglycan in their cell walls
Eukaryota - Answer - organism whose cells contain a nucleus and other organelles enclosed in
membranes
Archezoan scenario - Answer - primitive amitochondrial euk cell phagocytosed an alpha-
proteobacterium, leading to mitochondrion evolution
- this hypothesis has fallen out of favor
Symbiogenesis scenario - Answer - complexity of euk cell and its defining features emerged
after the mitochondrial symbiosis
- a single endosymbiotic event involing the uptake of an alpha-proteobacterium by an archaeal
cell led to the generation of the mitochondria, followed by the evolution of the nucleus and
compartmentalization of the euk cell
Phylogenomics - Answer - analysis of whole genomes
Phylogenetics - Answer - genetic distinctions
Phylogeny - Answer - evolutionary history of a group of organisms
- the more similar an organism is to another, the closer their genetic relationship are
- initial efforts to map phylogenetic relationships compared rRNA between organisms to create
a tree of life
- genetic similarities btwn organisms can help us understand the phylogeny of the organisms
- tree of life represents the phylogeny of organisms and the history of the organismal lineages as
they change thru time
Tree from 1987 by Carl Woese - Answer - compare rRNA sequences
- major finding: close relationship between archaea and eukaryota
Bacteria vs archaea vs eukaryota - Answer 1. Bacteria = no nucleus, 3-4 subunits of rna
polymerase, 70s ribosomes, murein cell wall
2. Archaea = no nucleus, 8 - 12 subunits of rna polymerase, 70s ribosomes, no murein cell wall
3. Eukaryota = nucleus present, 12 - 14 subunits, 80s rna polymerase, no murein cell wall
Phylogenetic tree of life - Answer - we now compare entire genomes
,- recent tech advances in dna sequencing allow whole genomes to be pieces together without
culturing organisms
- bact and archaebact together based on their cell wall structures
- now with dna sequencing, their rna was found to be more distantly related than previously
thought
- in 1990, archaea was suggested
- tree used to show too great of evolutionary distance between arachaea and eukaryotes, the
revised tree shows a much closer evolutionary distance
- red dots show lineages lacking an isolated and cultured representative, a distinct genome has
been sequenced from an environmental sample but the organism has never been grown in pure
culture in a lab setting
- many organisms are yet to be characterized as they are difficult to create in lab
- tree assumes that the higher the level of genetic similarity between two organisms, the more
they are related evolutionarily
- this assumption is less problematic with the whole gene pool than if it was based only on rRNA
sequence
Web of life - Answer - there are multiple connections between branches of the tree of life that
create extensive networks of untree-like links btwn 3 traditional domains
- tree-like structure at the top acknowledges that euks obtained mitochondria and chloroplasts
from bact
- lacks a single cell at the root, early life likely evolved from a population of primitive cells with
different genes
- links symbolize horizontal gene transfer of single/multiple genes that have always occurred
between unicellular organisms i.e. transfer of genes via viruses
Where do viruses come from - Answer - obligate intracellular parasites = their reproduction
cannot occur outside of a host cell, it relies on intracellular resources
- important contributors to web of life
- capable of interacting with all 3 domains and carry genetic info between dif kinds of organisms
and between the domains
- constant interacs btwn viral and cellular 'empires'
How do viruses fit in the picture? - Answer - small infectious agents that only replicate inside
living cells of other organisms
- in ocean water and soil, the number of viral particles exceeds the number of cells by 10:100
- genetic diversity substantially exceeds that of cellular life forms
- cells contain many antiviral defence systems
, - viral genomes consist of many forms of nucleic acids and use diverse replication processes like
rna replication and reverse transcription, unlike cellular life which uses a rep-express strategy
via dsdna
- viruses are the 'empire of life' though it is debated whether or not they are actually alive
- chicken pox, HIV, cold, COVID-19 = viral
- pneumonia, meningitis, diarrhea = viral/bacterial
- strep, uti, tuberculosis = bacterial
Virus basics - Answer - small infectious agents
- once assembled, virus progeny are able to leave the host cellular environment and infect new
cells and/or hosts
- viruses can infect animals, plants, bacteria and archaea
Virions - Answer - when not inside a host, viruses exist in the form of virions, these consist of
2, sometimes 3 parts
1. genetic material (DNA or RNA)
2. capsid (protein coat)
3. Envelope (some virsuses have a layer of lipids surrounding the protein coat)
- seem to predate "living" forms of life
Virus-first theory - Answer - viruses are ancestral to cells, they evolved from mixtures of
macromolecules (e.g. nucleic acids, proteins) before the first cells appears on earth
- existed as self-replicating units in a pre-cellular world
- self-replicating units of RNA that were first in existence may have gained the ability to infect
early forms of cells
- some RNA molecules can catalyze chemical reactions
Escape theory - Answer - cells came before viruses
- viruses derived from bits of cellular RNA and/or DNA fragments that leaked/escaped from cells
- when these acquire a protein coat they can become independent entities with the ability to
interact with other cells
- viruses are derived from genetic elements that may have resembled genetic sequences known
as retrotransposons
- during asymmetric cell fission a vesicle could have formed, engulfing a self-replicating RNA
with a coat-encoding RNA segment, this particle would continue to evolve through interactions
with additional early cell types
Reduction theory - Answer - cells came before viruses
