ch 6.3 & 6.4: the organelles of eukaryotic cells
TRANSCRIPT
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