Ch 6.3 & 6.4: The Organelles of Eukaryotic Cells

In eukaryotic cells genetic instructions (DNA) are housed in the nucleus and the instructions are carried out at the ribosomes

The NucleusFUNCTION: Contains most of the DNA in eukaryotic cells. Some DNA can be found in the mitochondria and/or chloroplasts

The NucleusSTRUCTURE: It’s surrounded by a nuclear envelope (AKA nuclear membrane)The nuclear envelope is made of a phospholipid bilayer with embedded proteins.

What other structure does this remind you of???

The nuclear envelope has nuclear pores. Proteins around the pores regulate the entry/exit of molecules into the nucleusThe shape of the nucleus is maintained by a net of filaments called the nuclear lamina

The NucleusSTRUCTURE: Inside the nucleus is the cell’s DNA. The DNA is organized and packaged into chromosomes Chromosomes are made of chromatin = a combination of DNA & protein

The NucleusSTRUCTURE: When it’s not dividing, a nucleus contains a nucleolusThe nucleolus is a dense region where rRNA is madeIn the nucleolus, rRNA combines with proteins to form ribosomes

Quick Think

The nuclear pores of the nuclear envelope allow molecules into and out of the nucleus. Think of specific molecules that would need to get into and out of the nucleus

Cells will have more of 1 kind of ribosome than the other depending on the function of the cell

Ribosomes*Found in both prokaryotes & eukaryotes

FUNCTION: The site of protein synthesisTwo types:

Free Bound

Found floating in cytosol

Found bound to the ER

Typically make proteins that’ll be used inside the cell

Make proteins that’ll become part of a membrane or that will be exported from the cell

Ribosomes

STRUCTURE: Each ribosome, whether bound or free, is made of a large and small subunit.

each subunit is composed of RNA and proteins

unlike other organelles, ribosomes

are NOT membrane bound

Cuz they’re not truly organelles

Quick Think

Suppose you observe a cell with a BUNCH of bound ribosomes. What could you deduce from this observation?

6.4: The Endomembrane SystemThe endomembrane system

(EMS) as a whole regulates protein traffic and performs metabolic functions in eukaryotic cells

Components of the EMS: nuclear envelope, ER, Golgi apparatus, lysosomes, vacuoles, and the cell membrane (even though the cell membrane is not an endomembrane)

The EMS consists of internal membranes in the cell that interact with each other either by direct physical contact, or indirectly by transferring vesicles between them

Parts of the endomembrane

system…

1. Endoplasmic Reticulum (ER)Biosynthetic Factory

• Overall basic structure: a network of membranous tubes & sacs = cisternae– The inside of the ER

tubes is called the lumen

– The ER is continuous with the nuclear envelope

Two distinct kinds of ER:• Smooth ERStructure: lacks bound ribosomesFunction:

*Enzymes of the smooth ER help synthesize lipids like oils, phospholipids, & steroids (ex: sex hormones)*Other enzymes detoxify drugs/poisons by adding –OH groups to drugs which makes them more soluble in water and easier to flush out*Stores Ca 2+ = part of the mechanism that causes cell contraction

Two distinct kinds of ER:• Rough ERStructure: has ribosomes

bound to the outer side of the membrane

Function: protein secretion*Excretory proteins are made on the bound ribosomes. As the protein is being built, it enters the ER lumen through a pore. The proteins then become enveloped in part of the ER membrane which buds off, becoming a transport vesicle:

Two distinct kinds of ER:• Rough ERFunction: the rough ER is

also a membrane factory for the cell. It can make its own phospholipids and the bound ribosomes make the membrane proteins

Parts of the endomembrane

system…

2. The Golgi ApparatusThe Shipping and Receiving Center

Function: Modifies, stores, & ships the products of the ER. The Golgi also makes certain macromolecules itself.

Structure: Stacks of flat membranous sacs= cisternae.

2. The Golgi ApparatusThe Shipping and Receiving Center

Each golgi has two distinct ends:a) the cis face receives transport vesicles from the rough ER. Cis face AKA “receiving side”b) The trans face produces different vesicles that bud off and transport their contents to other parts of the cell. AKA “shipping side”.

i. Before molecules are shipped, they’re tagged with a molecular ID

Parts of the endomembrane

system…

3. LysosomesDigestive Compartments

Structure: membranous sac of hydrolytic (think hydrolysis) enzymes digest macromolecules.

Mini quick think: why is it important to have these hydrolytic enzymes compartmentalized?

3. LysosomesDigestive Compartments

• Under what circumstances might lysosomes be utilized?Recycle the cells own organic material= autophagy

When a cell engulfs or “eats” outside particles = phagocytosis. Ex: an amoeba eating food particles, white blood cells destroying pathogens

Parts of the endomembrane

system…

4. VacuolesDiverse Maintenance Compartments

Structure: Membranous sac

Function: 1. May act as a lysosome at times

2. Food vacuoles can carry food from outside the cell to a lysosome to be digested

3. Contractile vacuoles pump excess water out of the cell in many protists

Contractile Vacuole

4. VacuolesDiverse Maintenance Compartments

Structure: Membranous sac

Function: 4. Plant cells usually have a big central vacuole, the membrane of which is called the tonoplast.

a. Central vacuoles can act as storage. They store extra organic & inorganic molecules as well as excess metabolic waste produced by the cell.

b. Central vacuoles may also contain a plant cells pigments, or poisons that deter herbivores

The spectacular symphony that is the Endomembrane System Endomembrane System

Quick Think • Think of the function of each of the

following cells. For each cell type, tell me which organelle would be relatively more abundant and WHY…– Thyroid cells (producing proteins to be

released into the bloodstream)– Liver cells– Heart muscle cells– Leaf cells