BIOL 371 Theme 1

Eukaryote Features

• Membrane Bound Nucleus

• Endomembrane system

• Primary genome of multiple linear chromosomes

• 80s ribosomes

• Organelles

  • Mitochondria (all Eukarya)

  • Plastids (In algae and plants)

• Sexual reproduction

Why Sexual Reproduction?

Allows for recombination/diversity through gamete fission

Why cytoskeleton?

Allows for faster, more agile movement

What would be the non-primary genome?

Mitochondria and Plastids

Multicellularity

Eukaryotes can be multicellular but aren’t always

What group did Eukarya evolve from

Archaea

Complex Multicellularity

Separate tissues, ploidy levels, etc

Colony

Another example of multicellularity

Microtubule

polymers of tubulin that form part of the cytoskeleton. Spindle fibers

Microtubule Structure

Formed by circles of 13 tubulin dimers (pairs of tubulins) with a + and - end. The center has a diameter of 15nm and the whole microtubule has a diameter of 25nm.

Alpha tubulin end

positive

Beta tubulin end

negative

Microfilament

A filament made up of actin subunits that reacts with myocin in the muscles. Its involved in intracellular transport in membranes. Moves faster then prokaryotes.

Flagella type of movement

smooth s-shaped waves that travel from base to tip. Usually longer but fewer

Cilia type of movement

Oarlike power stroke followed by a recovery stroke. Shorter but there are more of them

Movement of Cilia and Flagella

Waving and bending mechanism. One side shortens while the other lengthens. Powered by dynein motor proteins which slide the microtubule doublets over each other.

Process of cilia/flagella movement with structure

9 pairs of microtubules with two in the middle. Rigid spokes. Dynein arms that run up and down which move towards other microtubules and bind to the proteins (like a hug)

Benefits of a membrane

• process segregation (control certain reactions separately)

• More surface area

Nucleus benefits

• stores DNA

• Membrane bound

• DNA can replicate away from the rest of the cell

Mitochondria benefits

• ATP generation via oxidative phosphorylation

What eukaryote has cell walls?

Fungi

What is the benefit of a folded ER

Increased surface area

Benefits of cell walls in a plant cell

Can store starch as cannot always make it due to the environment

What do endomembranes allow?

• Allow the cell to engulf larger particles

• Increase internal SA

• Partition parts of all processes

  • Specialized regions

Why do chromosomes matter?

• Genes stay together

• Can evolve as a unit

• Gene clusters can do things individual genes cannot

Why do chromosomes matter?

• Context dependent gene expression (Hox genes)

• Body can turn off and on genes as needed

Reasons for Eukarya to have 80s ribosomes

• actively transcribe genetic code

• composed of 60s and 40s (large and small subunits)

• Agility

• Bigger ribosomes for generally bigger organisms

Mitochondria

• Oxidative phosphorylation (ATP generation)

• Have inner and outer membrane

• Reproduce on their own via fission

• have their own DNA - circular

• Can reproduce on their own outside of the cell cycle

• 70s ribosomes

Endosymbiosis of Mitochondria

• Were an anaerobic bacteria that moved into the cell

• Cell gave it protection and nutrients and it generated ATP for the cell

• Mutualism

• Instead of digesting the mitochondria, they were harnessed and used

Plastids

• chrloroplastids

• Acquisition of plastids happened after animal/plant split as all Eukarya have mitochondria but not all have plastids

Benefits of Sexual Reproduction for Eukarya

• diversity through gamete fission

• no two individuals have exactly the same genome

• CAN be asexual in times of great stress (only some eukarya)

Prokaryote reproduction

• Asexual reproduction

• All “clones” of each other except for plasmid traiding

Endosymbiosis does not depend on…

Other cell features

Secondary endosymbiosis

One bacterium was eaten by another Eukaryote and that eukaryote adopted some of its features

What do plant cells have that animal cells lack?

Plastids and cell walls

How old is the earth?

4.6 billion years old

When did life start?

3.8 million years ago, mainly prokaryotes (anaerobic and synthetic bacteria)

Stromatolites

Mats of photosynthetic Cyanobacteria that act as a sediment trap, then grow over the sediment. First evidence of a complex multicellular eukaryote

First evidence of multicellular organisms

• Algae and stromatolites

• Chitrakoot fossils

• 1.6 Ga (Giga Anum)

Bangiomorpha

• earliest evidence of sexual reproduction

• 1.05 billion years ago

• Evidence of gametes

• No distinct tissues (so not complex)

• Red algae

Approximately how many times has multicellularity evolved in the loosest sense

25

Great Oxygenation event

Cyanobacteria starting to produce oxygen as a biproduct to oxygenate the atmosphere

Approx 2300 ma

Carboniferous event

Where coal came from. Big spike in oxygen

Why was oxygen steady for a bit before spiking?

Photosynthetic bacteria evolved dark rxn first so not as much O2 was released.

Two reasons oxygen content became more

Big spread of photosynthetic plants OR a big bump in efficiency (light rxn evolved)

Great Rusting

2.5Ga-1.8Ga

Banded iron formations

Ocean full of iron, reacted with oxygen

Iron never made it to atmosphere

Why didn’t bigger eukaryotic organisms evolve until there was more oxygen?

No oxygen = no oxydative phosphorylation = no ATP = no complexity. Key to adaptive radiation

Symbiotic origin of multicelluarity

Single cells attach to one another (different genomes), compartmentalism tasks and sync genomes

Syncytial rise of multicelularity

Cell duplicates nucleus, subdivides but doesn’t divide, multiple nuclei in one cytoplasm, then subdivides into separate processes and tissues, no evidence for this fully happening

Colonial rise of multicellularity

Same genome, same species, stick together and live as a colony. Functions shift ans express different parts of the genome. What happened in animals

Choanoflagellates

Colonially cooperative, what animals evolved from

Advantages of multicellularity

• division of labour and economy of scale

• Increased size (protection, and can eat bigger things)

• Can do more stuff with the energy

• Exploit new environments

• Storage (starch, fat)

• More feeding opportunities

• Protected internal environment (disease resistance)

• Share information with other cells

• Complexity (visible protection, chemical protection, internal transport)

• Predator/prey host/parasite interaction

• Specialized immune system

Daphnia example

1. Daphnia eats an algae that retains or rejects offspring under normal conditions

2. With the predator present, the algae gets bigger and retains more offspring

3. Predator removed but algae remains the same. Bigger was good!

Light Sensing: Cyanobacteria

• Single photosynthetic pigment

• chromophor (acts like a switch)

• Can sense light but no direction or intensity

• Can respond

Light sensing: Marine Ragworm

• Has a layer of additional sensing pigments

• Can sense direction

• Can move towards or away from light

Light sensing: vertebrate eye

• have cornea, lens, retina

• Trichromatic (helped with foraging of brightly coloured fruits)

• Camera eye

• Sense movement and direction

• Some molluscs also have this eye

Surface Area Challenge

SA has to keep up with internal volume as volume gets bigger faster. Need the SA for processes. SA/V decreases as you get bigger.

How Eukarya adapt to SA challenge

• Mitochondria and endomembrane system (internal SA)