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Biology

RNA and protein synthesis

Protein synthesis

The following factors must be present for DNA replication [replication: Production of an identical copy. and transcription:

  • gene (DNA) to act as a template
  • supply of free RNA nucleotides
  • enzymes
  • ATP

The base sequence in a DNA molecule, represented by the letters A T C G, make up the genetic code.

The bases hydrogen bond together in a complementary manner between strands. A will always go with T (U in RNA) and G will always go with C.

This code determines the type of amino acids and the order in which they are joined together to make a specific protein. The sequence of amino acids in a protein determines its structure and function.

The DNA code is a triplet code [triplet code: the genetic code made by a triplet of bases in the DNA chains: AAA; GCT; CAT etc. Each triplet, a group of three bases, codes for a specific amino acid:

  • the triplet of bases on the DNA and mRNA is known as a codon
  • the triplet of bases on the tRNA is known as an anti-codon

The main stages of protein synthesis are transcription and translation.

The process of transcription

Process of transcription - free RNA nucleotides form complementary base pairs with one strand of DNA bases. mRNA strand is synthesized. mRNA peels off the DNA and moves out of the nucleus into the cytoplasm.

Transcription takes place in the nucleus:

  • the gene coding for the protein required untwists then unzips, the H-bonds between the strands break
  • free RNA nucleotides form complementary base pairs [base pair: The pair of nitrogenous bases that connects the complementary strands of DNA. with one strand of DNA bases
  • weak hydrogen bonds form between base pairs
  • sugar phosphate bonds form between RNA nucleotides
  • mRNA strand is synthesized
  • mRNA peels off the DNA and moves out of the nucleus into the cytoplasm

The process of translation

The process of translation.

Translation takes place on the ribosomes in the cytoplasm, or found on the rough Endoplasmic Reticulum (ER):

  • the ribosomes are the sites of protein synthesis
  • the mRNA strand attaches to a ribosome
  • tRNA molecules [molecules: a collection of two or more atoms held together by chemical bonds. The fundamental unit of compounds transport specific amino acids to the ribosome
  • each mRNA codon codes for a specific amino acid
  • the anti-codons and codons match up and form complementary base pairs
  • peptide bonds form between the adjacent amino acids to form the polypeptide (protein)

It is important to note that the tRNA is reused and collects another specific amino acid. Once the protein has been synthesised [synthesised: made or put together mRNA may move to another ribosome to make a further protein or it can be broken down into free nucleotides to be reused.

Processing the proteins

Processing the proteins - After translation, the protein passes into the channels of the rough endoplasmic reticulum (ER) for transportation. The protein is then passed from the rough ER to the Golgi apparatus inside tiny fluid-filled sacs, called vesicles. The Golgi apparatus packages the protein enzyme in a secretory vesicle, which fuses with the cell membrane and releases the protein from the cell.

After translation, the protein passes into the channels of the rough endoplasmic reticulum (ER) for transportation. The protein is then passed from the rough ER to the Golgi apparatus inside tiny fluid-filled sacs, called vesicles. The Golgi apparatus is a system of membranes [membrane: a very thin layer of tissue, which are responsible for the modification, processing, and packaging of the proteins. The protein may have a carbohydrate added, to form a glycoprotein. The Golgi apparatus packages the protein in a secretory vesicle, which fuses with the cell membrane and releases the protein from the cell.

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