1. Higher Biology
Unit 1:
1.3 Transcription

2. 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

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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

14. 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

15. Splicing

16. 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