BIOS 44 - Eukaryotic Cell

Lecture 3

Eukaryotic Cell

Advanced cells, which evolved later than prokaryotes. Contain plasma membrane, some with cell walls, flagella and cilia, and other various organelles that prokaryotes do not have.

Endosymbiotic Theory

Endo: Within

Symbiotic: Together

Endosymbiotic theory:

The theory that some eukaryotic organelles we know now, such as chloroplasts and mitochondria, were originally derived from bacteria that resided within other cells; these cell organelles evolved from ingestion of early bacteria.

Endosymbiont

Cell living within another cell

Where did chloroplast evolve from?

Photosynthetic bacteria, bacteria that perform photosynthesis for energy/ATP.

Evolved into the chloroplast

Where did mitochondria evolve from?

Non-photosynthetic bacteria

Evolved into mitochondria, providing the cell with ATP

Unicellular Eukaryotes

1. Algae

2. Protozoa

3. Yeast

Multicellular Eukaryotes

1. Algae

2. Molds (fungi)

3. Helminths

4. Plants

5. Animals

Endocytosis

Endocytosis is the process of a eukaryotic cell engulfing cell materials/liquids via the plasma membrane.

3 Types of Endocytosis

1. Pinocytosis

2. Phagocytosis

3. Receptor-mediated endocytosis

Pinocytosis

Pino: To drink

Cyto: Cell/hollow vessel

Osis: Condition

Cell “drinking”, the plasma membrane folds in and around liquids/solutes, creating a endosome to engulf water.

Phagocytosis

Phago: Eating

Cyto: Cell/hollow vessel

Osis: Condition

Cell “eating”.

The cell extends the plasma membrane creating a pseudopod; “pseudo” = false, “pod” = feet. (The projections resemble cell feet/arms).

The pseudopod surrounds any particles/bacteria, slowly engulfing it- once inside the cell, it creates a phagosome, a cell vesicle, where the material is then digested in the cell.

Phago: eating

Some: Structure

Receptor-Mediated Endocytosis

As the name states, endocytosis occurs only when a specific molecule binds onto receptors on the cells surface.

Once bound, this triggers a formation of an endosome to take in the material that has bound to the receptors.

Lysosomes

Lysosomes are vesicles containing various hydrolytic enzymes which break help digest/break down cell material.

Lyso: Breaking down

Some: Structure

How do lysosomes function?

The endosomes from endocytosis fuse with lysosomes within the cell, and the hydrolytic enzymes begin to degrade the particles.

In phagocytosis (eating), phagosomes fuse with lysosomes to form phagolysosomes.

In pinocytosis (drinking), or receptor-mediated endocytosis, the endosomes fuse with lysosomes to form endolysosomes.

In the end, the purpose of fusing is to digest any material brought into the cell via the endosomes.

Exocytosis

The reverse of endocytosis, which is to expel cell material outside the cell.

Exocytosis is done to expel waste material, secrete substances like hormones and enzymes, etc.

How does exocytosis work?

Exocytic vesicles are formed inside the cell, containing the waste material- this is called a secretory vesicle.

The secretory vesicle fuses with the plasma membrane, and the contents are then released outside the cell.

Eukaryotic Flagella

Eukaryotic flagella/flagellum

A structure resembling a tail that helps the cell move. Unlike prokaryotic flagellum, they are made with microtubules covered with plasma membrane.

Prokaryotic: Flagelin protein

Eukaryotic: Tubulin protein w/ plasma membrane covering

Eukaryotic Cilia

Small hairlike structures on the exterior of the cell; also composed of microtubules that beat/flow in the same direction, for various biological functions.

Prokaryotes: Pili/pilus

Eukaryotes: Cilia/Cilum

Eukaryotic Cytoplasm

The cytoplasm/cytosol is the fluid inside the cell that suspends the organelles/cellular components.

Eukaryotic Cytoskeleton

Protein filaments that provide structural support, aid in cell movement, and aids in cell division.

Membrane Bound Organelles (Eukaryotes only)

1. Nucleus

2. Mitochondria

3. Endoplasmic reticulum

4. Golgi apparatus

Nucleus

The nucleus is a organelles that contains DNA.

In the nucleus, transcription occurs, the process where DNA → mRNA.

Within the nucleus is also the nucleolus, which creates ribosomes.

rRNA exits the nuclear pores, and become ribosomes in the cytoplasm.

mRNA exits the nuclear pores, and bind onto ribosomes in the cytoplasm. This process then becomes translation, mRNA → proteins.

Mitochondria

The mitochondria is a membrane bound organelle, it creates ATP via cellular respiration and oxidative phosphorylation.

It contains cristae, inner folds, that increase the cells surface area for more space to be covered by ribosomes and DNA. More ATP.

Eukaryotic ribosomes are 80S (large subunit 60S, small subunit 40S).

Prokaryotic ribosomes are 70S (large 50S, small 30S).

Smooth and Rough ER

Rough ER has ribosomes on the exterior that receive, transport, and store proteins

Smooth ER synthesizes, transports, and stores lipids

Golgi apparatus

Amazon warehouse of the cell, assembles raw materials, sends end products on route to where it needs to be via vesicles