4. cell structure: eukaryotic cells

When did eukaryotic cells appear on earth?

approximately 2 billion years ago

processes in which eukaryotic cells appeared

-ancestral cells lost their cell wall

-autogenesis

-endosymbiosis

ancestral cells lost their cell walls due to

ingesting mitochondria

what is autogenesis?

the infolding of the plasma membrane that resulted in the development of the nucleus and the endoplasmic reticulum. The infolding caused the nucleus to have its own bubble while the endoplasmic reticulum are the leftover parts that didn’t wrap the DNA

first part of endosymbiosis

larger cells known as ancestral anaerobic cells engulfed smaller aerobic cells. Eventually, these small aerobic cells began to live as symbionts (live together)

second part of endosymbiosis

eventually, the smaller aerobic cells allowed the larger anaerobic cells to do cellular respiration while these larger cells gave the smaller cells a protective shield. This mutualism became permanent and eventually both cells merged into one singular organism.

result of endosymbiosis

The dependents of the ancient engulfed cell are known today as mitochondria

-this whole transformation formed the first eukaryotic cell, giving rise to the animal cell

second endosymbiotic event

eukaryotes with primitive (ancient) mitochondria engulfed cyanobacteria (smaller photosynthetic bacteria

-this became chloroplasts, giving rise to plant cells

evidence that supports endosymbiosis

1. Similar size and shape

Mitochondria and chloroplasts are roughly the same size as bacteria.

2. Double membranes

Both mitochondria and chloroplasts have double membranes.

This fits the idea that another cell originally engulfed them.

3. Similar inner membranes

The inner membranes of mitochondria and chloroplasts have a composition similar to bacterial membranes.

4. Their own DNA

Mitochondria and chloroplasts contain their own DNA, and the slideshow says this DNA resembles bacterial DNA.

5. Binary fission

Mitochondria and chloroplasts can replicate independently of cell division using binary fission, like bacteria. Unit 4. Cell Structure Eukaryo…

6. Bacteria-like ribosomes

Mitochondria and chloroplasts have ribosomes whose size and structure resemble bacterial ribosomes.

Characteristics of Eukaryotic Cells

Typically 100-100 m in diameter

• Have membrane bound organelles

• Have cytoskeleton

• Larger ribosomes

• Several linear chromosomes

• There are two types of eukaryotic cells:

plant cells and animal cells

organelles unique to plant cells

plasmodesmata, chloroplasts, cell wall, large central vacuole

organelles unique to animal cells

lysosomes, centrioles. centrosomes, cilia, flagella, small vacoule or no vacoule

1. Plasma membrane

selective barrier that controls what goes in and out of the cell, including waste, oxygen, and nutrients

-includes phospholipid bilayer, carbohydrates (including glycolipids and glycoproteins), proteins, and cholesterol in animal cells.

nucleus

Definition/function: Contains most of the cell's DNA and genes.

The DNA is packed as chromatin

Chromatin = DNA + histone proteins

The nucleus is surrounded by a nuclear envelope, which:

• Has two membranes

• Contains nuclear pores

• Separates the nucleus from the cytoplasm

Nucleolus

area inside the nucleus where rNA is made and ribosomes are assembled

Endoplasmic Reticulum (ER)

A membrane system that forms tubes and sacs within the cytoplasm. has two types

Rough ER (RER)

Has ribosomes attached.

Makes proteins that:

• Will be secreted from the cell

• Require sugar modification

• Become part of membranes

• Are delivered to lysosomes

These proteins can then be distributed in transport vesicles.

Smooth ER (SER)Has no ribosomes.

Has no ribosomes.

Functions:

• Synthesizes lipids, including phospholipids

• Contains enzymes that metabolize and detoxify drugs and poisons

• Can store Ca²⁺, especially in muscle cells

Golgi apparatus

Structure: Made of flattened membranous sacs called cisternae.

Functions:

• Modifies products from the ER

• Manufactures certain macromolecules

• Sorts and packages materials into transport vesicles

• Distributes them to the plasma membrane or lysosomes

Lysosomes

Definition: A membranous sac containing hydrolytic enzymes.

Function: The enzymes digest macromolecules.

The enzymes work best in the acidic environment inside the lysosome. \

• can fuse with a food vacuole and digest its molecules.

• recycle the cell's own organelles and macromolecules through autophagy.

Vacuoles

Definition: Large vesicles.

two types

Food vacuole

• Formed by phagocytosis

• Found in animal cells in your slides

Central vacuole

Function: Site of cellular respiration, which uses oxygen to generate ATP.

Structure:

• Two membranes

• Smooth outer membrane

• Inner membrane folded into cristae

• Intermembrane space

• Mitochondrial matrix

Chloroplasts

Found in plants and algae.

Function: Site of photosynthesis.

They contain:

• Chlorophyll

• Enzymes

• Other molecules needed for photosynthesis

Chloroplast structure

• Outer membrane

• Inner membrane

• Thylakoids → membranous sacs

• Granum → stack of thylakoids

• Stroma → internal fluid

Peroxisomes

Definition: Specialized metabolic compartments surrounded by a single membrane.

Functions:

• Remove toxic substances

• Remove excess toxic oxygen radicals/ROS

• Break down fatty acids, important for fat metabolism Unit 4. Cell Structure Eukaryo…

Cytoskeleton

Definition: A network of fibers extending throughout the cytoplasm.

Functions:

• Organizes cell structures and activities

• Anchors organelles

• Supports the cell

• Helps maintain cell shape

• Interacts with motor proteins for movement

• Provides tracks along which vesicles travel Unit 4. Cell Structure Eukaryo… Unit 4. Cell Structure Eukaryo…

It contains three types of structures:

MicrotubulesMicrofilamentsIntermediate filaments

Centrioles

Your slide defines them as paired, barrel-shaped organelles located in the cytoplasm of animal cells near the nuclear envelope.

are involved in developing microtubules/spindle fibers during cell division.

Centrosome

Two centrioles form the centrosome.

Cilia

Definition: Microtubule-containing extensions projecting from some cells.

According to your slide:

• Many

• Short

• Beat like a windshield wiper

• Microtubules control their beating

Flagella

Also microtubule-containing extensions involved in cell movement.

According to your slide:

• One

• Long

• Propeller-like beating

Cell wall in plants

a rigid, structural outer layer that surrounds the plasma membrane of a plant cell

. It is made primarily of the tough carbohydrate cellulose.

Its main functions are to provide mechanical support, maintain cell shape, and protect against osmotic stress (preventing the cell from bursting when it absorbs water).

Transport vesicles

transport materials between components of the endomembrane system. Your slide specifically says endomembrane components are connected through transfer by vesicles. Unit 4. Cell Structure Eukaryo…

endomembrane system

never, eat, gross, leftover, veggie, pizza

nuclear envelope, endoplasmic reticulum (smooth and rough) lysosomes, vacoules, plasma membrane

endomebrane system

Its job is the traffic of proteins and membranes through the cell, and the components transfer materials using vesicles

Lysosomes contain

hydrolytic enzymes that digest macromolecules, and those enzymes work best in an acidic environment

Autophagy

lysosomes recycling the cell's own organelles and macromolecules