Which Organelle is Spicier?
SER vs RER
By Sara Escallon-Sotomayor and Madeleine Silverman-Sloan
Introduction to RER and SER
Ribosomes
Discussion
Discovery of the Endoplasmic Reticulum
- Ribosomes are tiny spheres that contain ribosomal RNA (rRNA) and ribosomal proteins.
- Sites of protein synthesis
- Free ribosomes float in the cytostol (no attachments to organelles).
- RER is studded with ribosomes: synthesize proteins for use inside the ceproteins for insertion in the plasma membrane or use outside the cell.
Structure
Why do you think the ER is found throughout the cytoplasm?
- Different regions of Eukaryotic cells were discovered towards the end of the 19th century using basic dyes: collectively named the ergastoplasm
- In 1945, Keith Porter observed a fine reticulum in cells of chicken fibroplast
- In 1952, Porter and Kallman first used the term “endoplasmic reticulum” to describe these structures.
- Greek: Endon meaning within, plasma meaning form
- Latin: Rete meaning net
- “Network within the plasma of the cell”
- The improvement of the electron microscope led scientists to differentiate in between RER and SER
- In 1974, cell biologists Albert Claude, George Palade and Christian de Duve succeeded in extracting and studying the subcellular fractions of the cells.
Diagram
Abstract
This report studies the structure and function of the Rough Endoplasmic Reticulum and the Smooth Endoplasmic Reticulum as well as the products used by these organelles in protein synthesis. It also integrates other sciences into the study of this topic.
Functions
Do you think the SER or the RER is more important? Why?
Rough Endoplasmic Reticulum
Basic Functions and Structure of all ER
Translocation
- Site of synthesis of a protein (RER vs free ribosome) is determined by the N-terminal portion of the polypeptide, which is the first part to emerge from the ribosome during protein synthesis.
- There are two types of translocation: Cotranslational and posttranslational.
Cotranslational
- Newly forming proteins are deposited into the RER lumen by ribosomes bound to RER membrane.
- These polypeptides contain a signal sequence that targets the nascent polypeptide to the RER and leads to the compartmentalization of the polypeptide within the ER.
- In cotranslational translocation, a protein is synthesized as it moves through the RER.
Posttranslational
- A protein maybe released through the ribosome after translation has been completed.
- The protein then travels through the RER to the appropriate membrane.
Structure
- System of membrane-enclosed channels that penetrates much of the cytoplasm.
- Probably evolved from invaginations of the plasma membrane.
- Channels are called cisterns.
- Enclosed within the ER is luminal (cisternal) space
- ER is a highly dynamic structure.
Two groups of ER:
- Rough (granular) ER is covered in Ribosomes.
- Smooth (agranular) ER has no ribosomes.
- The ER provides a holding spot for chemical reactions.
- Serves as a "transportation channel."
- Presence of bound ribosomes on it’s cytosolic surface.
- Typically composed of a network of flattened sacs (cisternae)
- Connected by helicoidal membranes.
- Continuous with the outer membrane of the nuclear envelope.
- Cell homogenization: RER sheets fragment into rough-surfaced vesicles.
- Contains high levels of proteins involved in the movement of nascent proteins into the ER lumen.
Function
- Synthesize of proteins and the synthesis of most of the lipids of a cell’s membrane.
- The addition of sugars to the asparagine residues of proteins begins in the RER and continues in the Golgi complex.
- The RER works closely with the ribosomes and the Golgi apparatus.
- Serves as temporary storage area for newly synthesized molecules
- Together, the rough ER and golgi complex synthesize and package molecules that will be secreted from the cell
Conclusion and Summary
Summary
RER and SER are two important organelles that have many responsibilities. Their main purpose is synthesizing products to be used throught the cell.
Conclusion
Although the RER and the SER look similar and have several common activities, their composition and the jobs they fulfill are very different. Also, proteins, amino acids, and polypeptides are important for them to do their jobs, and they must work closely with the ribosomes and the Golgi apparatus.
Integration With
Chemistry
Smooth Endoplasmic Reticulum
- The ER is the site of synthesis (proteins, lipids, sugars, etc.)
- Chemical reactions occur within the ER to synthesize these products.
In depth:
- Amino acids are the building blocks of proteins and polypeptides.
- Amino acids form chemical bonds with each other to produce polypeptides.
- Polypeptides form chemical bonds to produce proteins.
- A protein is made up of two or more polypeptide molecules.
- These chemical reactions occur within the ER.
Structure
- Composed of a long network of folded tube like structures (Cisternae)
- The interior of the SER is called the Lumen or Cisternal Space
- Lumen is surrounded by membrane
- SER is not covered in ribosomes
Functions
- In certain cells, enzymes in the smooth ER can inactivate or detoxify a variety of chemicals (e.g. alcohol, pesticides, carcinogens etc.)
- Important in the synthesis of lipids, such as cholesterol and phospholipids, which form all the membranes of the organism
- Transitional vesicle to transport ER products to various locations
- Regulates and releases calcium ions
- Largely involved in steroid and hormone production
Integration with Physics
- Before the discovery of the electron microscope, cells were studied with light microscopes.
- Light microscopes involve optics (bending of light) which is physics.
- Electron microscopes use physics to function.
Differences Between Plant and Animal Cells
Plant Cells contain more organelles than Animal Cells. Their extra organelles are as follows;
- Vacuoles
- Cell Wall
- Chloroplasts