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Which list best describes the path taken by newly synthesized proteins, beginning with the synthesis of the protein and ending with sorting to intracellular or extracellular destinations?

Question
Which list best describes the path taken by newly synthesized proteins, beginning with the synthesis of the protein and ending with sorting to intracellular or extracellular destinations?
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Step 1

Proteins are the building blocks of the body and its functional unit. It is made up of a long chain of amino acids. Bonding between amino acid formed polypeptide chain which is a functional unit of protein.

 

Protein formation occurs by two main processes

1) Transcription

2) Translation

Step 2

Transcription process occur in further three steps

  1. a) Initiation
  2. b) Elongation
  3. c) Termination

 

Initiation

Initiation occurs in the nucleus of a cell. Here unwind the DNA which has double helix formation in the region of a gene.

 

Gene

A gene is a segment of DNA molecules that contain information or direction of how to build a protein.

 

Next

An enzyme RNA polymerase attaches to DNA strand and move to the promoter or start origin of the gene.

The hydrogen bond between the DNA strands is broken and the result is bubbling out of the region. This allows nitrogen bases is to expose.

 

Elongation 

In the elongation phase, free RNA nucleotide comes in the pair of exposed bases of template strand of DNA.

 

There are four different bases in DNA each of these pair up with one type of base in developing a strand of RNA.

 

DNA bases           RNA bases

Thymine pair with adenine

Adenine pair with uracil

Cytosine pair with guanine

Guanine pair with cytosine

 

DNA, RNA bases differ and RNA contains uracil and DNA contain thymine. This base-pairing did by a hydrogen bond. This process continues as RNA polymerase moves down and continue until the entire genes transcribed. Once it is completed a new pre-messenger RNA (pre-mRNA) has been formed.

 

The hydrogen bonds between the DNA and the mRNA are broken. The RNA polymerase is released. The DNA return to double helix formation and newly formed pre-m-RNA strand ready to synthesis protein.

 

Pre mRNA modification

Pre mRNA have intron and exon. Introns are non-coding region remove by a structure called spliceosome.

Then, the enzyme comes and places together with the exon section.

Two other modification also made in m-RNA.

1)     Capping

Capping which increases the stability of strand. And on the other end poly-A tail is added which help in translation of strand.

Now the final version m-RNA created and it releases from the nucleus to nuclear pores into the cytoplasm travels to the ribosome.

Second major state of protein synthesis.

Translation

Translation occurs in complexes form that comprises the largest small subunits of ribosomes.

The m-RNA and t-RNA

The m-RNA is read by three bases section at a time. These three bases are called codon and way to terminate amino acid required t-RNA has binding site refers to anti-codon that contain three bases. The pair of bases of m-RNA codon now the ribosome move along to m-RNA and until it reaches start codon.

A t-RNA picked up required amino acid to free-floating amino acid in the cytoplasm and bring to the ribosome. Here anticodon comes and attaches put amino acid into the place.

Next

The ribosome moves along with mRNA moves down the mRNA strand. t-RNA bring required amino acid and two amino acid formed a peptide form. This process keeps happening form long chain of amino acids. A release factor binds to complex and releases the signal end of the process and the two subunits of ribosomes separated from m=RNA and newly synthesis protein polypeptide chains released

The final step

m-RNA can be read more than one ribosome a time. So many copies of a protein can be produced very quick.

 

Step 3

Post translation modification

When nascent protein formed it is not fully active need more modification.

 

1) Trimming

When newly protein formed all amino acid is not active so their need to remove some amino acid with the help of endoprotease enzyme. This process occurs in the endoplasmic reticulum or maybe in Golgi apparatus depend on where its need.

 

2) Covalent attachments

Newly proteins are not fully active there is need of phosphorylation which is the addition of phosphate group with the help of kinase enzyme to make active proteins.

 

3) Glycosylation

Addition of glucose to make active proteins.

 

4) Hydroxylation

Addition of hydroxyl group to make protein active.

So these post-translation modifications occur to make protein fully active.

...

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