BI 164 Final Exam- Endosymbiosis Theory

Prokaryote

Lack a membrane bound nucleus and unicellular, virtually all bacteria and archaea

Eukarya

Organisms that have cells with membrane bound nuclei

Binary fission

A type of asexual reproduction where a single parent cell divides into two identical daughter cells, used by bacteria and archaea

Lateral gene transfer

Transfer of DNA between 2 species (bacteria/archaea)

• Bacteria/archaea take DNA from environment (another strain)

• Virus or agent can move DNA among species

• Direct physical contact between cells → exchange of DNA and results in genetic recombination

ex: Cyanobacteria

2 keys points about bacterial “sex” - lateral gene transfer

1. One way transfer of genetic material instead of an exchange between individuals

2. Instead of involving all genes present, transfer is limited to a plasmid or small portion of the genes in the main chromosome

Protist

All eukaryotes that are not land plants, fungi, or animals

Logical to conclude the first eukaryote was a single-celled organism

Yes, virtually all bacteria and arches are unicellular and so are most subgroups of major lineages of eukaryotes

Mitochondria

Organelles that generate ATP aerobically → energy

Endosymbiosis Theory

Mitochondria originated when a bacterial cell took up residence inside another cell about 2 billion years ago

Symbiosis

When individuals of 2 different species live in close and prolonged physical contact

Endosymbiosis

One species lives inside another

Evidence of Endosymbiosis Theory

1. Several similarities between mitochondria and chloroplasts

   • Mit. and chond. DNA match more closely with bacterial DNA

   • M and C have their own DNA, mRNA, and ribosomes

   • M and C have a plasma membrane → similar to those in bacteria

   • M and C divide/replicate by binary fission (same as bacteria)

2. Mitochondria and chloroplasts have double membranes

3. Genes from M and C have moved to eukaryotic genome (lateral gene transfer)

4. Mitochondria similar in size to a-proteo bacteria

Extension of Endosymbiotic Theory

Eukaryotic chloroplasts originated when a protist engulfed a cyanobacterium

Significance ~ Why do endosymbiotic systems persist? Adaptive function?

• Bacteria are protected

• Host energy capacity (host cells bigger, faster, capture more prey…)

• Chloroplasts → only need sunlight to produce energy

• Negative effect on host (ex. evolution of immunity)

Why loose a mitochondria?

Organism lives in an area with low oxygen, and mitochondria are expensive to maintain

Result of endosymbiosis

2 membranes in chloroplasts and mitochondria

2 vs 4 membranes on a tree…

Indicate that secondary symbiosis event occurred, traits that evolved after secondary symbiosis

Secondary endosymbiosis

Eukaryotic non-photosynthesizing cell engulfs a photosynthetic eukaryotic cell and retains chloroplasts

Any cell that has a mitochondria…

= eukaryotic cell (not archaea ancestor)

2 different forms of multicellular development

1. Clonal development

2. Aggregative development

Clonal development

Multicellularity arises when cells stay connected or encased with one another after division from multicellular spore or zygote

→ *cells stay together*

Aggregative development

Cells that live independently for most of their life, episodically associate to form a multicellular organism

→ *cells come together*

Fitness effects (good/ bad) of multicellularity:

• (+) specialization of cells, multitasking

• (+) longevity → one cell dies, organism still remains, allows for apoptosis

• (+) lower surface area: volume → takes on different shapes, different interaction with outside world

• (-) how to move/transport when larger

2 different types of multicellularity:

1. Simple multicellularity

2. Complex multicellularity

Simple multicellularity

Simple shapes, (filaments, cluster, sheet of cells… 1 layer thick), arise via mitotic division

• cell adhesion

• multicellular state can persist

• minor specialization: somatic and germ cells

→ aggregative and mostly clonal

Complex multicellularity

Cells with persistent multicellularity and:

• Cell adhesion

• Intercellular communication

• Differentiation of tissue

• Programmed cell death

3D structure, same cells don’t interface with environment

→ only clonal development

Include:

• Animals

• Fungi

• Plants

• Red/brown algae