Presentation on theme: "Transcription Transcription is the synthesis of mRNA from a section of DNA. Transcription of a gene starts from a region of DNA known as the promoter."— Presentation transcript:
1 TranscriptionTranscription is the synthesis of mRNA from a section of DNA.Transcription of a gene starts from a region of DNA known as the promoter.
2 Promoter: Start of a gene Terminator: End of a gene
3 RNA polymeraseThis enzyme is responsible for transcription. RNA polymerase binds at the promoter and unwinds the DNA.
4 RNA polymerase adds nucleotides onto the 3’ end of the growing mRNA molecule. Due to the base-pairing rules the mRNA produced will be complementary to the DNA. The molecule elongates until it reaches the terminator sequence. The molecule produced is called the primary transcript.
6 Modification of the primary transcript Not all the regions in a eukaryotic gene are required to produce the final protein. These non-coding regions are called introns. The coding regions are called exons.
8 RNA splicingAfter the mRNA has been transcribed the introns are removed. The remaining exons are spliced together to form a continuous sequence. This is called the mature transcript. The mature transcript then leaves the nucleus to travel to the cytoplasm.
10 Genetic codeTranslation is the synthesis of protein following the code with in the mature mRNA transcript. The mRNA is made of sequences of three nucleotides (a triplet of bases) called codons. Each codon is code for one amino acid.
12 tRNAA further type of RNA is found in the cell’s cytoplasm. This is called tRNA (transfer RNA) and is made of a single chain of nucleotides. It is folded into a 3D structure, held together by hydrogen bonds.
18 Ribosomes are small, roughly spherical structures found in all cells Ribosomes are small, roughly spherical structures found in all cells. They contain the enzymes essential for protein synthesis. The ribosome’s function is to bring the tRNA molecules bearing amino acids in contact with the mRNA.
19 Site P – holds the tRNA carrying the growing polypeptide chain Site P – holds the tRNA carrying the growing polypeptide chain. Site A – holds the tRNA carrying the next amino acid to be joined to the chain.Site E – releases the empty tRNA once it has dropped off its amino acid.
20 The translation process 1. The ribosome binds to the 5’ end of the mRNA so that the start codon (AUG) is in site P. 2. Next a tRNA carrying the amino acid methionine becomes attached to site P.
21 3. The mRNA codon at site A bonds complementary anticodon on the appropriate tRNA bearing the correct amino acid.4. A peptide bond then forms between these two amino acids.5. The ribosome then moves along one codon.6. The tRNA from Site P is move to Site E and released.7. Steps 3-6 then repeat until it reaches a stop codon.