Cell Structure and Function

A. Contain 2 taxa (Domains) Archaea and Bacteria (both lack nuclei)

1. No nuclear membrane - able to simultaneously read their DNA and produce protein

2. No internal membrane bound organelles.

 

Eukaryotic Cells

A Nucleus - membrane bound internal area of the cell.   Houses the DNA (Deoxyribonucleic acid)   which codes for and controls all cellular functions - THE CONTROL CENTER OF A CELL.  

                      1. the DNA of eukaryotic chromosomes is slightly different than that of their prokaryotic counterparts.   Eukaryotic DNA is linked to basic (alkaline) proteins known as histones

                      2. prokaryotic chromosomes are much smaller and have no histones.   They are said to be composed of "naked DNA"

 

 

C. Cell Envelope

 1. Glycocalyx

2. Cell Membrane - A membrane that surrounds the cytoplasm and regulates the passage of material into and out of the cell

 3. Cell Wall - A protective barrier outside the cell membrane of plant, fungal, alga, or bacterial cells.   This structure provides rigid support and protects from osmotic lysis.

 

  D   . The Endomembrane system - an internal network of membranes that includes:

     1. The nuclear membrane

     2. Endoplasmic reticulum

a. rough endoplasmic reticulum (RER) -   a complex series of membranes that is dotted with ribosomes.   These function in protein synthesis and/or the modification of protein

1) Ribosomes - Small grainy looking particles that function as the "workbench of protein synthesis".   May exist bound to endoplasmic reticulum (RER) or free in the cytoplasm (polysomes)

b. smooth endoplasmic reticulum (SER) - ER without ribosomes - the functions varies depending upon the cell's needs or function.   Commonly SER is thought to be involved in lipid synthesis and storage or storage of certain ions

 

 

 

 

  3. Golgi apparatus - Flattened membranous sacks with vesicles at the edges.   Modification and secretion of cell products.   Vesicles may fuse with the cell membrane to internalize substances or dump cell products to the exterior.

 

4.   Membrane bound vesicles: -derived from the Golgi- the only way to really identify these vesicles is to know the chemical composition on the substances contained within them

   a. peroxisomes - contain enzymes that oxidize and detoxify substances

   b. lysosomes - contain hydrolytic enzymes that break down internalized materials

he RER linked to the Golgi Body represents a method for a cell to produce proteins for export. DNA from the nucleus is transcribed to RNA. The RNA exits the nucleus through nuclear pores and binds to ribosomes on the RER. As Translation takes place the newly synthesized protein is threaded to the inner compartments of the RER known as cisternae. Ribosomes released, transport vesicles can then fuse with the Golgi. Protein modification can continue. Condensing vesicles can then fuse with the cell membrane and dump their products to the outside. This process is known exocytosis. Particles or chemicals may be internalizes through the system as well by endocytosi                                                                                         

 

 

II. Other Cellular Organelles

A. Mitochondria - Energy powerhouse of the cell - site of most of the synthesis of Adenosine Triphosphate (ATP). The Mitochondria is the site of ATP production by the process of cellular respiration. The coenzymes of cellular respiration are found on the inner membrane of the mitochondria known as the cristae.

 

 

 

 

B. Chloroplasts - found in higher plant cells - site of photosynthesis Please note that plants do both photosynthesis and respiration and have both mitochondria and chloroplasts. Like mitochondria, chloroplasts are a double membraned organelle. The inner membranes are called the thylakoids arranged in stacks called grana (granum is singular).

C. Endosymbiosis. Mitochondria and chloroplasts perhaps represent a prime example of endosymbiosis. Endosymbiosis is the idea that some eukaryotic organelles have evolved from prokaryotic cells. (Page 124 of your text) Mitochondria and cloroplasts have a double membrane similar to that of some prokaryotes. Further, mitochondria and chloroplasts have their own DNA, without histones, and replicate independently of the cell. Both organelles have their own protein synthesis machinery (70s ribosomes). All of these are more similar to prokaryotic cells.

D. Cytoskeletal elements - provide cellular support and movement

1. microfilament - long fibers composed of actin - contractile -

2. Microtubules   - larger cylinders - *provide internal cell support- more commonly associated with animal cells

 3. Centrioles - specialized microtubules that form during cell division - described as an attachment site for spindle fibers

 

E. Organelles of Motility

        1. cilia - described as short and hair-like cilia provide motility for the whole organism and can additionally move substances along the surface of cells and/or structures.   Cilia first appear in the protozoa and are found in human tissues as well.   Where?

        2. flagella- Longer and more whip like.   Eukaryotic flagella move back and forth in a whip-like motion. Structurally they are very different from prokaryotic flagella. Both cilia and flagella have a 9 + 2 arrangement as seen below in eukaryotic cells

 

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