DNA In Protein Synthesis -The Genetic Code

In stage one of the process by which the information of the gene is used to determine how the protein molecule is constructed, a copy of the code is made by building a molecule of mRNA which is catalysed by RNA polymerase, involving complementary base paring with the antisense strand as a template. The mRNA strand then leaves the nucleus through pores in the nuclear membrane and passes to the ribosomes in the cytoplasm to be 'read'.

The second stage of protein synthesis occurs in the ribosomes in the cytoplasm, and AAs are activated for protein synthesis by combining with short lengths of tRNA, with a different tRNA for each of the 20 AAs. One end of each tRNA molecule is a site where a particular AA can attach and at the other end there is an anticodon.

Anticodons are made up of a sequence of 3 bases which are complementary to the the codon of mRNA that codes for the specific AA.

Translation is stage 3 and occurs in the ribosomes in the cytoplasm, where a protein is assembled one AA residue at a time as a ribosome moves along the mRNA reading the codons.

Complementary anticodons of the AA-tRNA slot into place and are temporarily held in position by hydrogen bonds. While there the AAs of neighbour AA-tRNAs are joined by peptide linkages.

Genes function (are expressed) only in cells they relate to, when they are needed.

In eukaryotes, genes are only transcribed if an RNA polymerase enzyme binds to a region of DNA situated close to the gene known as a ___ .

What are the special features of promoters in eukaryotic chromosomes?

The steps of the expression of a gene begin when the genetic informaiton in DNA is transcribed into a molecule of mRNA by complementary base paring. The RNA polymerase binds to a promoter region (the 'start' signal for transcription) located immediately before the gene.

Highlight the characteristics that apply to the sense strand and leave the once that apply to the antisense strand blank.

RNA polymerase draws on a pool of free nucleotides.

As the RNA trand is formed, it falls away from the antisense strand and hydrogen bonds re-form between the two DNA strands. The process continues until a base sequence known as the inhibitor is reached, causing both RNA polymerase and the completed mRNA strand to be freed from the site of the gene.

The sections of DNA that carry meaningful information are called introns and the intervening lengths f DNA are called exons.

When a split gene is transcribed into mRNA, the sequence of introns continues to exist exactly as it occurred in the DNA, and so an enzyme catalysed reaction known as ___ removes the introns to shorten the length of mRNA which is now described as mature before it moves out into the cytoplasm.

The AA activation process by ehich AA are combined with tRNA occurs in the cytoplasm and requires ATP.

It is this tRNA, once attached to its AA, which facilitates the translation of the three-base sequences of each codon of mRNA into a sequence of AAs in a protein.

The codon located on one end of the tRNA is complementary to the codon of mRNA that codes for that specific AA.

An AA is attached to its tRNA by enzyme action specific to that AA, which allows recognition by a specific tRNA activating enzyme which attaches a specific AA to the tRNA and ensure they'r ein the right sequence.

Translation occurs in the ribosomes which are organelles made up of a large and small subunit which are both composed of ___ and protein. During translation, the mRNAs bind with the ___ subunit where also occur the three sites where the tRNA's interact.

At the 1st site, codons of the incoming tRNA bind to specific tRNA AAs through their anticodons by complementary base paring.

At the 2nd site, the tRNA leaves the ribosome following transfer of its AA to the growing protein chain.

At the 3rd site, the AA attached to its tRNA is condensed with the growing polypeptide chain by formation of a peptide linkage.

The structure of mRNA, ribosomes and their growing protein chain, is called a polyphosphome.

Other ribosomes that synthesis proteins to be excreted from the cell or packages in lysosomes are located where?

post-transcriptional modifications refer to processing steps that some proteins (inactive precursors) needs to go through in order to be activated.

post-transcriptional modifications refer to processing steps that some proteins (inactive precursors) needs to go through in order to be activated.

The central dogma of molecular biology refers to the one-way flow of coded information from the nucleus to the cytoplasm.

An exception to the central dogma of molecular biology is the enzyme secreted by the HIV nucleic acid -reverse transcriptase, which catalyses the copying of the RNA strand to form a DNA double helix which enters the host nucleus and becomes attached to a hsot chromosome.

Reverse-transcriptase can be extracted from retroviruses and used in genetic modification for the synthesis of a DNA strand, complementary to an existing RNA strand.

DNA ligase occurs with nucleic acid in the nucleus of all organisms and is used for..

Polymerase occurs in the same place as ligase and is used for..

Restriction enzymes found in the cytoplasm of bacteria can be used for breaking DNA molecules into shorter lengths at specific nucleotide sequences.