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 Nucleus FUNCTION: Contains most of the DNA in eukaryotic cells. Some DNA can be found in the mitochondria and/or chloroplasts

The Nucleus STRUCTURE: Nucleur Envelope 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 Nucleus The nuclear envelope has nuclear pores. Proteins around the pores regulate the entry/exit of molecules into the nucleus The shape of the nucleus is maintained by a net of filaments called the nuclear lamina

The Nucleus STRUCTURE: Nucleolus When it’s not dividing, a nucleus contains a nucleolus The nucleolus is a dense region where rRNA is made In the nucleolus, rRNA combines with proteins to form ribosomes

The Nucleus STRUCTURE: Chromosomes 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

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

Ribosomes *Found in both prokaryotes & eukaryotes FUNCTION: The site of protein synthesis Two 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 Cells will have more of 1 kind of ribosome than the other depending on the function of the cell

Ribosomes 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

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

6.4: The Endomembrane System The 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 System 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 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 ER Structure: has ribosomes bound to the outer side of the membrane

Two distinct kinds of ER: Rough ER 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 ER Function: 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 Center Function: 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. Lysosomes Digestive 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= 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. Vacuoles Diverse 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 Compartments Function: 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