Higher Biology Unit 1: 1.3 Transcription

Revision What is an organism’s genotype? The genetic code that control its characteristics What is an organism’s phenotype? The characteristics possessed by that organism as a result of its genotype

Learning Intentions To be able to describe the stages involved in transcription

Success Criteria I can describe the stages involved in transcription I can explain the importance of the following terms: RNA Polymerase, intron, exon, splicing, primary transcript, mature transcript

Genes A gene is a small section of DNA that carries the code for a particular protein Taking the code from a gene and using it to make a protein is a process known as gene expression Gene expression is a 2 staged process The processes are transcription and translation

Proteins The genotype (order of bases in an organism’s DNA) carries the code to make proteins from long chains of amino acids The proteins synthesised are what controls the phenotype of the organism Synthesis of proteins can be affected by intra and extra cellular factors

Protein Synthesis From Nat 5 what molecules/structures are involved in protein synthesis? DNA, mRNA, nucleotides, nucleus, ribosome Where does protein synthesis start? Nucleus Where does protein synthesis finish? Ribosome

Overview of gene expression Nucleus A G A G G T T G A C G A A T C T C C A A C T G C T T DNA Transcription Overview of gene expression mRNA U C U C C A A C U G C U U codon ser pro thr ala Ribosome Translation Protein

Transcription Transcription is the synthesis of a molecule of mRNA from a stand of DNA mRNA carries the code for proteins from the nucleus to the ribosomes

DNA/RNA comparison DNA (deoxyribonucleic acid) RNA (ribonucleic acid) Double Stranded Single Stranded Bases are: Adenine, Thymine, Guanine, Cytosine Bases are: Adenine, Uracil, Guanine, Cytosine Base pairing rule Adenine : Thymine Guanine : Cytosine Base Pairing Rule Adenine : Uracil Made of deoxyribose sugar, phosphate and base Made of ribose sugar, phosphate and base

Transcription Transcription of a gene starts at a region of DNA known as the promoter Transcription finishes at a sequence of DNA known as the terminator sequence RNA polymerase is the enzyme responsible for transcription

RNA Polymerase RNA polymerase moves along the DNA start from the promoter sequence to the terminator sequence As it moves along it unwinds the DNA strand This allows free nucleotides to join with their complementary partners The complementary bases form the primary mRNA transcript molecule Nucleotides are added at the 3’ end of the mRNA molecule

Primary Transcript The mRNA molecule formed is known as the primary transcript It is made up of regions called introns and exons Exons are regions of the mRNA molecule that will code for the final protein Introns are non coding regions

Splicing

Splicing The removal of introns and joining together of the remaining exons is known as splicing This results in a mature mRNA transcript being formed which passes out of the nucleus and into the cytoplasm