BIOL 371 Unit 1

What are the main divisions of the living world defined by?

cell characteristics

What are the domains of life?

Bacteria, Archaea, Eukarya

What did bacteria give rise to? How?

Archaea, bacteria and mitochondria through horizontal gene transfer

What is the nucleus made up of?

nuclear pore complex, nuclear envelope, chromatin and the nucleolus

Eukaryotic vs prokaryotic cell examples

animals plants and fungi vs bacteria and archaea

Are eukaryotes or prokaryotes larger?

eukayotes

Eukaryotic vs prokaryotic cell number

usually multicellular vs usually unicellular

Eukaryotic vs prokaryotic cell nucleus

present vs absent

Eukaryotic vs prokaryotic cell wall

only in plants and fungi vs in all (usually complex)

Eukaryotic vs prokaryotic cell genetic recombination

meiosis and fusion of gametes vs DNA transfer between organisms

Eukaryotic vs prokaryotic cell microtubules

present vs absent

Eukaryotic vs prokaryotic cell endoplasmic reticulum

present vs absent

Eukaryotic vs prokaryotic cell cytoskeleton

extensive and complex vs minimal

Eukaryotic vs prokaryotic cell mitochondria pr

present vs absent but most bacteria carry our cellular respiartion

Eukaryotic vs prokaryotic cell ribosomes

present vs present

Eukaryotic vs prokaryotic cell vesicles

present vs absent

Eukaryotic vs prokaryotic cell golgi apparatus

present vs absent

Eukaryotic vs prokaryotic cell chloroplasts

present (in plants) vs absent (but some bacteria carry out photosynthesis)

Eukaryotic vs prokaryotic cell vacuoles

presenr vs absent

Eukaryotic vs prokaryotic cell flagella

complex vs simple

What are protists?

eukaryotes that are not an animal, plant, or fungus, usually unicellular

What can multicellularity help determine?

How related organisms are and their different kingdoms

What do lysosomes do?

degrade macromolecules

What does the golgi apparatus do?

modifies and sorts proteins and lipids as they move to their final destination into or out of the cell

What is the plasma membrane made up of?

phospholipids and proteins

What is the cytoskeleton?

protein fibre networks support the plasma membrane and organelles within cytoplasm

What is the cytoskeleton used for?

allows movement and maintenance of spatial relationships within the cell among its elements

allows cell to control its shape and move

Microtubules

hollow tube formed from tubulin dimers, very mobile and can depolymerize easily (build and dissemble)

What would happen if the microtubule is affected?

can affect cell division

Intermediate filament

a strong fiber composed of intermediate filament proteins

Microfilament

a double helix of actin monomers, important in movement and intracellular transport

What is phagocytosis and how does it happen?

a type of endocytosis in which a cell engulfs large solid particles, such as bacteria, dead cells, or food particles, by surrounding them with its plasma membrane

Why is the cytoskeleton essential for phagocytosis?

cytoskeleton is essential for phagocytosis because it provides the force and structure needed for the cell to change shape and engulf particles

What is the purpose of the cilia and flagella?

Cytoskeletal elements allowing cell to move faster or create currents

What is the eukaryote endomembrane system?

made up of the nuclear envelope, lysosomes, golgi apparatus, vacuoles, endoplasmic reticulum

• series of flattened sacs and tubes formed by lipid bilayer membranes directly interconnected or connected by moving vesicles

General functions for eukaryotic endomembrane

• compartmentalization: isolation of biochemical processes and transfer of products between compartments

• greatly increase of surface area for synthesis

How is movement of the cell controlled?

Using the cytoskeleton

How are prokaryotic genomes organized?

a single loop of DNA - good for replication but regulation must be simple since everything is on the same structure

How are eukaryotic genomes organized? Why?

divided between a number of linear chromosomes

• allows for complex gene regulation

• allows recombination and production of different gametes

• chromosome rearrangement can take place during meiosis

How does sexual reproduction generate genetic diversity?

independent assortment ad recombination

What is the weight of a eukaryotic ribosome?

large 60S and small 40S subunits creating the 80S ribosome

What are ribosomes?

complexes of RNA and proteins (rRNA, ribosomal RNA)

What are ribosomes responsible for?

Protein synthesis

Are eukaryotic or bacterial ribosomes larger and more complex?

eukaryotic (80S), bacterial are 70S

Where are eukaryotic ribosomes?

either freely suspended in cytosol or attached to membrane

Where can proteins that are made on free ribosomes go?

remain in cytosol, pass through nucleus or become parts of cytoplasmic structures

Where can proteins that are made on ribosomes attached to the endoplasmic reticulum go?

they follow a special path to other organelles in the cell

What is the mitochondria a site for?

cellular respiration

What is the chloroplast site for?

photosynthesis

Where are mitochondria and chloroplasts found and what do they help with?

both greatly increase surface area for processes in eukaryotic cells

Do only eukaryotic cells preform cellular respiration and photosynthesis?

no, there are prokaryotic cells that engage in oxidative phosphorylation and photosynthesis

What are the 6 evidence of endosymbiotic origins?

• circular DNA

• independent replication (mitochondria and plastids removed from a cell means cell won’t be able to produce new ones)

• size (bacteria size 1-10 microns)

• double membrane

• certain proteins specific to bacteria cell membrane are also in mito/chloro membranes

• 70S ribosomes

Endosymbiotic theory

Explains how eukaryotic cells originated. It proposes that ancestral, larger prokaryotes engulfed smaller, free-living prokaryotes (like aerobic bacteria and cyanobacteria). Instead of being digested, these smaller cells formed a mutually beneficial relationship and eventually evolved into modern organelles, such as mitochondria and chloroplasts.

Endosymbiotic origins of mitochondria and plastids

The first eukaryotic cells likely formed when an ancestral archaeal cell engulfed an aerobic alphaproteobacterium. This symbiotic relationship eventually produced the mitochondrion, making those early eukaryotes heterotrophic (endosymbiotic hypothesis part I). Later, some of these cells acquired chloroplasts through a second endosymbiotic event involving a cyanobacterium making autotrophic eukaryotes. (endosymbiotic hypothesis part II)

What is the endomembrane-first hypothesis for eukaryotic evolution?

An ancestral archaeon first evolved the endomembrane system (nucleus, ER, Golgi).

It then engulfed an aerobic α-proteobacterium.

The α-proteobacterium became the mitochondrion.

What is the mitochondria-first hypothesis for eukaryotic evolution?

An ancestral archaeon first formed a symbiosis with an α-proteobacterium.

Membrane outgrowths enclosed the bacterium (not phagocytosis).

The α-proteobacterium became the mitochondrion.

The endomembrane system evolved afterward, possibly as a result of the same membrane-enclosing event.

What is the most widely accepted hypothesis for the evolution of the eukaryotic endomembrane system?

Mitochondria-first hypothesis because it explains how mitochondria and the endomembrane system could evolve without requiring phagocytosis, which modern archaea lack.

What did the invagination of the plasma membrane do?

The invagination hypothesis proposes that the eukaryotic endomembrane system evolved when the plasma membrane folded inward, enclosing portions of the cytoplasm. These membrane-bound compartments gradually developed different lumen compositions (different enzymes, proteins, and conditions), allowing them to specialize into organelles such as the nucleus, endoplasmic reticulum, Golgi apparatus, and lysosomes.

What is endosymbiotic gene transfer, and why is it important?

During endosymbiosis, genes from the bacterial ancestor (future mitochondrion or chloroplast) were transferred to the eukaryotic nuclear genome.

These genes became part of the host cell's DNA.

Their proteins are made in the cytoplasm and then imported into the mitochondria or chloroplast.

Result: Organelles retain only a small genome, while the nucleus controls most of their functions.

What does Braarudosphaera bigelowii tell us about endosymbiosis?

It is a unicellular eukaryotic alga that acquired a nitrogen-fixing bacterium by endosymbiosis.

The bacterium evolved into a nitrogen-fixing organelle (~100 million years ago).

Shows that new organelles can still evolve through endosymbiosis.

Why was the origin of Braarudosphaera bigelowi esier than mitochondria?

because the host was already a eukaryote with phagocytosis and internal organelles.

What is secondary endosymbiosis and how did it create major eukaryotic groups?

A heterotrophic eukaryote engulfed an autotrophic eukaryote (alga).

The algal chloroplast was retained and became part of the host cell.

Produced new photosynthetic eukaryotic lineages 3 independent times

What is the cube-square relationship?

Surface area increases with the square of length (L²).

Volume increases with the cube of length (L³).

As size increases, volume grows faster than surface area.

Important in biology because larger cells/organisms have difficulty exchanging materials efficiently.

How do internal membranes allow eukaryotic cells to be larger and more energetic than prokaryotic cells?

Internal membranes and folded surfaces of mitochondria and chloroplasts increase membrane area.

Folding of membranes provides more space for energy cellular respiration and photosynthesis.

Allows eukaryotic cells to produce more ATP, make more complex molecules, and become larger/more complex than prokaryotes.

What is simple multicellularity and what is its distinct traits (5)?

• adhesion

• communication

• structurally simple

• no bulk flow

• most in direct contact with the environment (no inner/outer cells)

What is bulk flow?

movement of fluids or gases through an organism, rather than cell-to-cell

What are volvox?

Volvox demonstrates multicellularity because it consists of many permanently attached cells that cooperate and exhibit division of labor, with specialized flagellated somatic cells for movement and photosynthesis and reproductive cells (gonidia) for reproduction. This makes it an important model for studying the evolution of multicellular life.

Slime molds relation to multicellularity?

Slime molds are an example of facultative (temporary) multicellularity, where independent cells aggregate under environmental stress to form a multicellular structure with specialized functions.

What is complex multicellularity and what is its distinct traits (4)?

• adhesion

• communication

• differentiate and specialize

• formation of bulk flow mechanisms

Most to least accepted theories of origins of multicellular life

Colonial theory, syncytial theory, and symbiotic theory

Symbiotic Theory

Different species of single-celled organisms came together and permanently lived as one organism.

Why isn’t the symbiotic theory supported?

Different species usually have different genomes.

Hard to explain how they would become one organism with identical DNA in every cell.

Very little evidence.

• One cell divides its nucleus many times.

• The cell doesn't split.

• Now there is:

  • one giant cell

  • many nuclei

  • shared cytoplasm

• Eventually:

  • membranes form

  • separate cells are created

  • all cells have identical DNA

  This explains why every cell has the same genome.