KEGS Biology Blog


YEAR 13 Friday 30th November Section 2
December 1, 2012, 10:23 pm
Filed under: Uncategorized

Transcription, translation and mutations

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Translation

Translation is the second stage of protein synthesis, when the amino acids are assembled into a polypeptide in a sequence dictated by the sequence of codons on the mRNA. The genetic code, copied from DNA into mRNA, is now translated into a sequence of amino acids. This chain of amino acids is the polypeptide. It happens at ribosomes, which may be free in the cytoplasm but many are bound to the rough endoplasmic reticulum.

Ribosomes are assembled in the nucleolus of eukaryote cells. Each is made of two subunits and there is a groove into which the length of mRNA, with the code for the sequence of amino acids, can fit. The ribosomes can then move along the mRNA, which can slide through the ribosomal groove almost like the workings of an audio cassette tape. The code is read and the amino acids can be assembled in the correct order to make a functioning protein.

It is important to create the correct sequence of amino acids in a protein because:
– It forms the primary structure of a protein
– The primary structure determines the tertiary structure
– The tertiary structure is what allows a protein to function
– If the tertiary structure is altered, the protein can no longer function so effectively, if at all

Transfer RNA is made in the nucleus and then passes into the cytoplasm. They are lengths of RNA that are shaped almost like lower case Ts and have exposed bases at one end where a specific amino acid can bind. At the other end it has three exposed bases (anticodon) which are complimentary to the complementary codon on the mRNA strand.

Mutations

Mutations are a change in the amount of, or arrangement of, the genetic material in a cell. Mutations occur randomly and spontaneously. A mutation is detected as a marked difference in characteristics of an organism that arises from normal parents. Somatic mutations occur in cells in the body other than the sex cells. Mutations of this kind are not transmitted to the next generation, but they may be significant in the life of an organism if they contribute to the malfunctioning of the body. Sex cell mutations, on the other hand, occur in the reproductive tissue and result in changes to the genome of the gamete. These mutations may be passed onto offspring.

The two main classes of mutation are:
– Point mutations (substitutions) where one base pair replaces another
– Insertion/deletion mutations in which one or more nucleotide pairs are inserted or deleted from a length of DNA causing a frameshift

Many genetic diseases are the result of DNA mutations. Sickle-cell anaemia is an example of one of these diseases. There is a difference between sickle-cell haemoglobin and normal haemoglobin and it lies in a single base pair controlling the beta chain. The mutation on codon 6 causes valine to be inserted in place of glutamic acid. Sickle-cell haemoglobin consequently crystallises at low oxygen concentration and carries less oxygen. Other genetic diseases that occur as a result of DNA mutations include Huntington’s and cystic fibrosis.

Comment by ebelen

Transcription

Transcription is the first stage of protein synthesis in which an mRNA molecule is made using a length of DNA as a template.

– A gene to be transcribed unwinds and unzips. Hydrogen bonds between complementary bases are broken
– Free nucleotides bind to their exposed complementary bases (catalysed by RNA polymerase)
– The two extra phosphoryl groups are released
– The mRNA strand produced is complementary to the nucleotide base sequence on the template and is consequently a copy of the base sequence on the coding strand of DNA
– Our brand new mRNA molecule is released from the DNA, passes out of the nucleus through a pore in the nuclear envelope and is ready to partake in the next stage of coding for the amino sequence in a polypeptide

Translation

Translation is the second stage of protein synthesis, when the amino acids are assembled into a polypeptide in a sequence dictated by the sequence of codons on the mRNA. The genetic code, copied from DNA into mRNA, is now translated into a sequence of amino acids. This chain of amino acids is the polypeptide. It happens at ribosomes, which may be free in the cytoplasm but many are bound to the rough endoplasmic reticulum.

Ribosomes are assembled in the nucleolus of eukaryote cells. Each is made of two subunits and there is a groove into which the length of mRNA, with the code for the sequence of amino acids, can fit. The ribosomes can then move along the mRNA, which can slide through the ribosomal groove almost like the workings of an audio cassette tape. The code is read and the amino acids can be assembled in the correct order to make a functioning protein.

It is important to create the correct sequence of amino acids in a protein because:
– It forms the primary structure of a protein
– The primary structure determines the tertiary structure
– The tertiary structure is what allows a protein to function
– If the tertiary structure is altered, the protein can no longer function so effectively, if at all

Transfer RNA is made in the nucleus and then passes into the cytoplasm. They are lengths of RNA that are shaped almost like lower case Ts and have exposed bases at one end where a specific amino acid can bind. At the other end it has three exposed bases (anticodon) which are complimentary to the complementary codon on the mRNA strand.

Mutations

Mutations are a change in the amount of, or arrangement of, the genetic material in a cell. Mutations occur randomly and spontaneously. A mutation is detected as a marked difference in characteristics of an organism that arises from normal parents. Somatic mutations occur in cells in the body other than the sex cells. Mutations of this kind are not transmitted to the next generation, but they may be significant in the life of an organism if they contribute to the malfunctioning of the body. Sex cell mutations, on the other hand, occur in the reproductive tissue and result in changes to the genome of the gamete. These mutations may be passed onto offspring.

The two main classes of mutation are:
– Point mutations (substitutions) where one base pair replaces another
– Insertion/deletion mutations in which one or more nucleotide pairs are inserted or deleted from a length of DNA causing a frameshift

Many genetic diseases are the result of DNA mutations. Sickle-cell anaemia is an example of one of these diseases. There is a difference between sickle-cell haemoglobin and normal haemoglobin and it lies in a single base pair controlling the beta chain. The mutation on codon 6 causes valine to be inserted in place of glutamic acid. Sickle-cell haemoglobin consequently crystallises at low oxygen concentration and carries less oxygen. Other genetic diseases that occur as a result of DNA mutations include Huntington’s and cystic fibrosis.

Comment by ebelen




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