Protein synthesis

[Smiley_]

Hi could I please get a symplified version of protien synthesis.
I dont understand the definition in my text book
?

thanks


with organelles if possible?

[pi]

Quite a large diagram, but simple to understand:

http://dr282zn36sxxg.cloudfront.net/datastreams/f-d%3A8ecf723b6d7a84632d884e353e3b327298974c72bde96449cf227304%2BIMAGE%2BIMAGE.1

You go into more depth in Unit 4, so I wouldn't stress much at all right now.

[alondouek]

Difficult thing to simplify, but here we go (I'll do this based on Unit 3 theory, it gets a little more complex and detailed in Unit 4):

So you have two major processes in protein synthesis; transcription and translation.

Firstly, you have a DNA template strand. This contains the coded information (or the 'instructions') for the protein that we're building. As you would know by now, the DNA strand is made up of triplet sequences consisting of the nucleotide bases A, C, T and G. These DNA triplets each code for a specific amino acid (or a STOP signal) via RNA.

Before we discuss the actual processes of transcription and translation, let's just look at this (very) basic 'flowchart':



Because we know that proteins are effectively folded polypeptide sequences, we can say that the above 'flowchart' occurs to produce this sequence.

So, transcription:

The enzyme RNA polymerase attaches complementary RNA nucleotides (A-T, C-G, G-C, U-A) to the DNA template strand. (At this point, a massive number of things happen involving pre-mRNA, caps and tails that you'll learn in Unit 4. At this point, we have our mRNA strand - remember that its codons are complementary to the DNA triplets of the template strand.

Now for translation:

The mRNA strand moves to the ribosome, which consists primarily of rRNA. The ribosome (a small ribosomal subunit) moves along the mRNA strand until it reaches a START codon (which codes for the amino acid Methionine (Met)). When the ribosome reaches here, a tRNA molecule with an anticodon that is complementary to the mRNA codon attaches to the mRNA strand (note that it carries the Met amino acid). Other complementary tRNA molecules move into place, with each new one adding a coded-for amino acid to the polypeptide chain being formed. Eventually, the ribosome will reach a STOP codon (which does not code for any amino acid); this terminates the construction of the polypeptide sequence.

When this occurs, the polypeptide sequence is released and begins the folding processes it requires to become a final protein product.

[Yacoubb]

Protein Synthesis and secretion takes place in two stages:
(1) Transcription
(2) Translation

Transcription:
* Transcription is the process by which the DNA molecule (genetic material and hereditary information) is copied to form a single stranded molecule messenger RNA (mRNA).
* Transcription takes place in the nucleus of eukaryotic cells.
* The transcribed RNA molecule is called pre-mRNA, and it leaves the nucleoplasm and enters the cytoplasm via the nuclear membrane.
* pre-mRNA molecule contains both introns and exons.
* Exons are three concurrent nucleotides that form a codon, that of which codes for an amino acid.
* Introns are junk codons that do not code for any amino acids and are removed by splicing.
* The mRNA molecule now becomes shortened and all the codons code for amino acids.

Translation:
*The mRNA molecule is now in the cytoplasm.
* tRNA molecules (transfer RNA) carries amino acids from mRNA to the ribosomes by carrying anti-codons complementary to the amino acid codons.
* These amino acids are sythesised and joined together to form a polypeptide (protein); here, the condensation reaction occurs and the amino acids are joined by strong peptide covalent bonds.
* A protein has been formed.

Now this is the important bit to consider:
* If a cell synthesises a protein that is going to function within the intracellular aqueous environment of the cell, the protein is synthesised within free ribosomes. These are ribosome organelles that are found suspended in the cytosol.
* If a cell synthesises a protein that will act outside the intracellular environment, and function in the extracellular matrix, the protein is synthesised within ribosomes attached to the rough endoplasmic reticulum, or simply stated, synthesised in the rough endoplasmic reticulum.

The protein molecule is transported within a cell through the endoplasmic reticulum, an organelle made up of a network of folded membranes that transport substances within a cell.

If the cell is to be secreted in order to function in the extracellular matrix...
The protein molecules are transported by the rough endoplasmic reticulum to the Golgi Complex, an organelle containing a series of flattened, membranous sacs that package, modify and prepare the protein for exportation out of a cell.

The protein is packaged into vesicles which bud off from the main Golgi Complex organelle and fuse with the plasma membrane, leaving the cell by exocytosis.

[Smiley_]

Protein Synthesis and secretion takes place in two stages:
(1) Transcription
(2) Translation

Transcription:
* Transcription is the process by which the DNA molecule (genetic material and hereditary information) is copied to form a single stranded molecule messenger RNA (mRNA).
* Transcription takes place in the nucleus of eukaryotic cells.
* The transcribed RNA molecule is called pre-mRNA, and it leaves the nucleoplasm and enters the cytoplasm via the nuclear membrane.
* pre-mRNA molecule contains both introns and exons.
* Exons are three concurrent nucleotides that form a codon, that of which codes for an amino acid.
* Introns are junk codons that do not code for any amino acids and are removed by splicing.
* The mRNA molecule now becomes shortened and all the codons code for amino acids.

Translation:
*The mRNA molecule is now in the cytoplasm.
* tRNA molecules (transfer RNA) carries amino acids from mRNA to the ribosomes by carrying anti-codons complementary to the amino acid codons.
* These amino acids are sythesised and joined together to form a polypeptide (protein); here, the condensation reaction occurs and the amino acids are joined by strong peptide covalent bonds.
* A protein has been formed.

Now this is the important bit to consider:
* If a cell synthesises a protein that is going to function within the intracellular aqueous environment of the cell, the protein is synthesised within free ribosomes. These are ribosome organelles that are found suspended in the cytosol.
* If a cell synthesises a protein that will act outside the intracellular environment, and function in the extracellular matrix, the protein is synthesised within ribosomes attached to the rough endoplasmic reticulum, or simply stated, synthesised in the rough endoplasmic reticulum.

The protein molecule is transported within a cell through the endoplasmic reticulum, an organelle made up of a network of folded membranes that transport substances within a cell.

If the cell is to be secreted in order to function in the extracellular matrix...
The protein molecules are transported by the rough endoplasmic reticulum to the Golgi Complex, an organelle containing a series of flattened, membranous sacs that package, modify and prepare the protein for exportation out of a cell.

The protein is packaged into vesicles which bud off from the main Golgi Complex organelle and fuse with the plasma membrane, leaving the cell by exocytosis.

'

thanks