1. A day in the life of a protein…
Why are all of these organelles important anyway?

2. To start off, what can you recall about proteins?
Remember that proteins are macromolecules.
These large molecules are necessary for life processes.
Recall from Chapter 2 (The Chemistry of Life) that proteins contain the elements: C,H,O,N.
Recall from Chapter 2 (The Chemistry of Life) that proteins are polymers (many units) made up of monomers called amino acids.
Recall from Chapter 2 (The Chemistry of Life) that amino acids within a protein molecule form hydrogen bonds with other amino acids.
This helps give the protein its unique shape.

3. Why are proteins important anyway?
Proteins carry out many critical functions so they need to be made correctly.
The critical functions of proteins include:
Energy source for cells
Cell signaling
Enzymes
Antibodies
Cell structure

4. Organelles found inside cells make proteins.
Much of a cell is devoted to making proteins and several organelles within the cell are involved.
These organelles include the following:
Nucleus
Endoplasmic Reticulum
Smooth
Rough
Ribosomes
Golgi Apparatus
Vesicles

5. Protein Components Within Cells
Recall from Chapter 2 (The Chemistry of Life) that proteins are important for cell structure.
The cytoskeleton provides cells with important structural support and maintains the cell’s shape.
Have you ever wondered what the cytoskeleton is made of?
It is a flexible network of proteins!
The small protein subunits that make up the cytoskeleton form long threads, or fibers, that crisscross the entire cell and come in three types.
Microtubules
Filaments
Microfilaments

6. The Three Fibers that Compose the Cytoskeleton
Microtubules: long, hollow tubes that give cells their shape and act as “tracks” for the movement of organelles.
When a cell divides, the microtubules form fibers that pull half of the DNA into each new cell.
TUCK THIS INFORMATION AWAY FOR MEIOSIS.
Intermediate filaments: give the cell its strength
Intermediate filaments are smaller than microtubules
Microfilaments: tiny threads that enable cells to move and divide.
Microfilaments are the smallest of the three fibers.
Microfilaments also help muscle cells contract and relax.

7. The Nucleus
The nucleus is the storehouse for most of the genetic information (DNA) in your cells.
The nucleus has a double membrane or bi-lipid layer called the nuclear envelope.
The nuclear envelope allows for the protection of and easy access to DNA.
DNA contains genes that are the instructions for making proteins.
Molecules that could damage DNA need to be kept out of the nucleus.
Many proteins are involved in turning genes on and off.
The double membrane of the nucleus allow for proteins to access DNA when it is needed.

8. The Nucleus(cont.)
The nuclear envelope is composed of pores that allow for large molecules to pass between the nucleus and cytoplasm of a cell.
These pores are composed of proteins.
The nucleus also contains the nucleolus.
The nucleolus is a dense region where tiny organelles essential for making proteins are assembled.
These tiny organelles are called ribosomes.

9. Ribosomes What are ribosomes? What do ribosomes do?
Ribosomes are made of a combination of proteins and RNA molecules.
What do ribosomes do?
Ribosomes are the site for protein synthesis.
Ribosomes link amino acids together to form proteins.
After ribosomes are assembled in the nucleolus they pass through the nuclear pores of the nuclear envelope into the cytoplasm.
Where are ribosomes found?
Ribosomes can be found in two places within a cell.
Free floating in the cytoplasm
Bound to the endoplasmic reticulum

10. Ribosomes (cont.)
You will find free ribosomes and attached ribosomes within a cell.
Ribosomes translate mRNA into proteins for use inside or outside of the cell.
Free ribosomes synthesize proteins to be used within the cell.
Ribosomes attached to the rough ER will synthesize proteins to be embedded into the cell membrane or moved outside the cell.

11. Endoplasmic Reticulum
The endoplasmic reticulum (ER) is an interconnected network of thin, folded membranes and is classified as either rough or smooth.
Rough ER is studded with ribosomes and is where proteins are produced, processed, and distributed.
Smooth ER has no ribosomes and is where lipids are produced.
Smooth ER is also responsible for the break down drugs and alcohol.

12. ER (cont.)
The ER membranes form a maze of enclosed spaces that includes many creases and folds.
The interior of the ER membrane is called the lumen.
In the lumen, proteins can be modified to aid in folding or stability.
Why all the folds?
Think maximum surface area for the minimum amount of space.

13. Golgi Apparatus
The Golgi apparatus is an organelle that consists of closely layered stacks of membrane-enclosed spaces that process, sort, and deliver proteins.
The Golgi apparatus membranes contain enzymes that make additional changes to proteins.
The Golgi apparatus also packages proteins.

14. Golgi Apparatus (cont.)
After a protein is packaged in the Golgi apparatus, one of the following actions will occur:
The protein will be stored in the Golgi apparatus for later use.
The protein will be transported to other organelles within the cell.
The protein will be carried to the membrane and secreted outside the cell.

15. Vesicles
Vesicles are membrane-bound sacs that contain materials within the cytoplasm.
Vesicles transport material from place to place within the cell.
Vesicles are generally short lived.
Vesicles are formed and recycled as needed.

16. A protein’s trip in and around the cell.
It starts in the nucleolus of the nucleus.
Once the mRNA attaches to a ribosome, it is translated to a protein.
Once ribosomes are assembled in the nucleolus, they pass through the nuclear pore into the cytoplasm of the cell.
Ribosomes will be free or attached.
The proteins found in the free ribosomes are usually used for chemical reactions occurring in the cytoplasm.
The proteins found in the attached ribosomes on rough ER will be processed for use outside of the cell or incorporated into the cell membrane.

17. A protein’s trip (cont.)
After a protein has been made, part of the ER will pinch off and form a vesicle that surrounds the protein.
The vesicle will transport the protein to the Golgi apparatus.
Modifications to the protein will be made in the Golgi apparatus, and a new vesicle will be created for storage, transport, or secretion.

18. Different proteins will have different functions.
Some proteins serve as signaling factors, so when they are released from the cell, they will travel to another region and trigger a biochemical pathway.
Others proteins have certain enzymatic functions (e.g. pepsinogen is secreted into the stomach for digestive purposes).
Because proteins vary in structure and function, there are many different things that can happen, depending on the type of protein being released from the cell.

19. Embedded proteins on cell membranes have many functions.
Proteins that are embedded in the cell membrane serve as an "interface" between the outside environment of the cell and the inside of the cell.
So they tend to function in the following ways:
Cell signal reception: the embedded protein binds certain chemical signals and triggers a response inside the cell.
Inter-membrane transport: the protein acts as a channel, either allowing passive diffusion of nutrients (salt ions, glucose, etc.) or actively pumping chemicals in/out of the membrane.
External structure: for some cells, it is important to be able to cling to surfaces. The surface proteins can be specialized in shape to "grab" onto surfaces and stabilize a cell's position.