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: Nucleur EnvelopeIt’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 NucleusThe 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: Nucleolus 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

The NucleusSTRUCTURE: ChromosomesInside 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

Quick ThinkThe 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

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 will usually be exported from the cell

*Found in both prokaryotes & eukaryotes

RibosomesEach 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

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)

6.4: The Endomembrane SystemThe 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 ER

Structure: lacks bound ribosomes

Function:

*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

Two distinct kinds of ER:• Rough ERFunction: 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 Apparatus

The Shipping and Receiving CenterFunction: Modifies, stores, &

ships the products of the ER. The Golgi also makes certain macromolecules itself. (pectins and polysaccharides)

Structure: Stacks of flat membranous sacs= cisternae.

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

Describe the flow of molecules through 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. Lysosomes: Digestive Compartments

• Under what circumstances might lysosomes be utilized?Recycle the cells own organic material= autophagyWhen 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. Vacuoles Diverse Maintenance CompartmentsFunction: 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