Proteins are manufactured from the blueprints on DNA...help please?

Question

Proteins are manufactured from the "blueprints" found on DNA. After they are translated, they are moved through a system of internal membranes before being distributed throughout the rest of the cell. At some point in this process, they are modified to their functional form.

• Describe the movement of proteins from their manufacturing point through this internal membrane system.

• Discuss the role of each of the following structures in the whole process: cell membrane, vesicles (at two points in the process), ribosomes, Golgi apparatus, and endoplasmc reticulum. Be sure to identify the correct order in which the proteins move through each of these structures.

please hellpp..answers can be short just need a good explenation. :]

Answer 1

The "blueprint of life" in the DNA molecule exists as "Nucleotide Triplets" These triplets code for the amino acid sequence in polypetide chains, which make up the cells proteins. A sequences of nucleotides in the DNA which code for ONE polypeptide is called a "Gene."

During GENE EXPRESSION, the DNA sequences is translated to a short lived intermediate molecule called messenger RNA, or mRNA. mRNA is basically the "link" or "shuttle" between the DNA in the nucleus and the ribosomes in the cytoplasm, the organelles which synthesis the proteins based on the nucleotide sequence in the mRNA.

Many proteins have a so called "signal sequence" which determines its destination. After a protein has been synthesized on a ribosome, based on this "signal sequence" peptide, the protein may remain in the cytosol, enter the nucleus or go to the endoplasmic reticulum. Free ribosomes begins producing the polypeptide until a cytosolic signal recognition particle sequence is recognized and this causes attachment of the entire complex to the ER membrane. In there ER the proteins are modified and glycosylation, that is the protduction of glycoproteins takes place. The product "buds off" from the ER membrane and then goes to the golgi for further modification. The vessicle binds to the cis face of the golgi and starts to move through the golgi apparatus. Several chemical modification occurs as the product moves from the cis to the trans face. These include:

1. Further glycosylations (ie. ECM glycosaminoglycans)

2. Phosphorylation (using ATP imported into Golgi, ie LDL)

3. Sulfation of proteoglycans

4. Labeling of proteins for their final destination, weather the

    final product is required for a special organelle within the

    cell (ie. acid hydrolases in lysosomes) or for export (ie.

    hormones and neurotransmitters

The vesicles consists of a single phospholipid bilayer that functions as a "vehicle" using the microtubule network as a "free way" to move the products between individual organelles and the plasma membrane. These vesicles form "on demand" by budding of from the various organelles of the endomembrane system such as the ER and the Golgi as well as the cell membrane. The vessicles "fuse" with the lipid bilayer membranes of these organelles, hence intacellular membranes are VERY DYNAMIC but the rate of fusion and rate of  production is about the same so there is NO NET change in the membrane.

Due to the negative charge of the hydrophophilic "heads" of phospholipids, the binding of two membranes (the vesicle to the organelles or the cell membrane) requires a divalent cation, Ca++ and some 50 different proteins and this process is often highly regulated.

(ie. the calcium concentration in the cytosol is VERY LOW when exocytosis is to occur, then the conc rapidly shoots up due to a stimulus, ie an action potential, which causes the opening of calcium channels)

Well, hope that helps

Answer 2

Polypeptides are manufactured on the ribosomes, which are usually associated with the rough endoplasmic reticulum.  The polypeptide then makes its way through the ER where it is modified (e.g., some amino acids removed, maybe a sugar added, etc.).  The modified polypeptide then buds off the ER in a vesicle which travels to the Golgi where it is further modified (e.g., a couple polypeptides are put together to make a dipeptide, etc.) and packaged for use or secretion.  The protein now buds off of the Golgi and the vesicle containing it either heads to the membrane where it will exit through exocytosis or the protein is sent to it's needed location in the cell to do its job.