Protein Metabolism

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  • Topic: DNA, RNA, Protein
  • Pages : 5 (1463 words )
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  • Published : February 22, 2013
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Proteins play an important role in the human body. The DNA molecule controls the synthesis of proteins. The DNA contains genes which are sequences of nucleotides and bases. Proteins are used for growth and repair. Proteins are made up of amino acids linked together by peptide bonds. Firstly 'amino acid synthesis' is the set of biochemical processes by which the various amino acids are produced from other compounds. The substrates for these processes are various compounds in the organism's diet, not all organisms are able to synthesise all amino acids.

Proteins are made in the ribosome's organelles in the cytoplasm. So to start the process of protein synthesis DNA’s code must be copied and taken to the cytosol. In the cytoplasm the code must be read so that the amino acids can be assembled to make proteins. This is the start of protein synthesis. There are 3 different types of RNA:

* mRNA (messenger RNA) (Applin, D (1997)) states, “DNA employs a message to take instructions to where they are needed. This messenger is a substance called messenger RNA (mRNA) * rRNA (Ribosomal RNA) along with protein makes up the ribosome * tRNA (Transfer RNA) transfers amino acids to the ribosome’s where proteins are synthesised Since DNA is part of a larger molecule which contains chromosomes that are unable to move from the nucleus it needs something else to send a “coded message”. These are messenger RNA molecules. (Baker, M (2004)) states, “In the process of transcription, DNA is used as a template to produce a molecule of mRNA. This occurs in the nucleus.” RNA synthesis transcription is the first step of gene expression, in which a particular segment of DNA is copied into RNA by the enzyme RNA polymerase. During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallel RNA strand, also unlike DNA replication where DNA is synthesised, transcription does not involve an RNA primer to initiate RNA synthesis.

Fig.1 to show the structure of RNA. This is a single stranded molecule which contains the base Uracil (U)

DNA consists of four nucleotide bases [adenine (A), guanine (G), cytosine (C) and thymine (T)] that are paired together (A-T and C-G) to give DNA its double helix shape. There are three main steps to the process of DNA transcription. Transcription requires the enzyme RNA polymerase. RNA Polymerase Binds to DNA. DNA is transcribed by an enzyme called RNA polymerase. Specific nucleotide sequences tell RNA polymerase where to begin and where to end. RNA polymerase attaches to the DNA at a specific area called the promoter region. This process uses mRNA to copy a template strand of DNA. In order for this to happen the DNA double helix must be ‘unzipped’ (Pickering, W (1996)) states, “Original ‘parent’ DNA is unwound exposing each single chain of bases”. The DNA strand is read from the 3’ to the 5’ end. And the mRNA is made from the 5’ to the 3’ end. During transcription only the exons (coding parts of DNA) are copied and introns (non coding) are ignored. The mRNA strand, once complete detatches itself from the DNA strand and exits the nucleus via the nucleus pores and enters the cytoplasm.

During transcription RNA polymerase binds to the DNA to unwind the DNA strand and allow RNA polymerase to transcribe only a single strand of DNA into a single stranded RNA polymer called messenger RNA (mRNA). (Baker, M (2004)) states, “In the process of transcription, DNA is used as a template to produce a molecule of mRNA. This occurs in the nucleus.” The strand that serves as the template is called the antisense strand. The strand that is not transcribed is called the sense strand. Like DNA, RNA is composed of nucleotide bases. RNA however, contains the nucleotides adenine, guanine, cytosine and uracil (U). When RNA polymerase transcribes the DNA, guanine pairs with cytosine and adenine pairs with uracil.

Promotors are regions on DNA that show where RNA polymerase must bind to...
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