1. 7.2 Transcription and gene expression
Understanding:
Gene expression is regulated by proteins that bind to specific base sequences in DNA
The environment of a cell and of an organism has an impact on gene expression
Nucleosomes help to regulate transcription in eukaryotes
Transcription occurs in a 5’ to 3’ direction
Eukaryotic cells modify mRNA after transcription
Splicing of mRNA increases the number of different proteins an organism can produce
Applications:
The promoter as an example of non-coding DNA with a function
Skills:
Analysis of changes in DNA methylation patterns
Nature of science:
Looking for patterns, trends and discrepancies: there is mounting evidence that the environment can trigger heritable changes in epigenetic factors

2. Non coding DNA
Coding
Not all DNA codes for a polypeptide to be made May have another useful function Non-coding sequences of DNA Example: Promotor
Non Coding
Applications:
The promoter as an example of non-coding DNA with a function

3. Promotors
Located near a gene Binding site of RNA polymerase Initiates transcription Promoters are not transcribed into RNA Same sequence for most genes (general RNA polymerase binding)
Applications:
The promoter as an example of non-coding DNA with a function

4. Gene Expression
Some proteins not regulated (essential for survival so are expressed all the time) Some produced at certain times, in certain amounts Different causes: Variation in environmental conditions Cellular differentiation
Understanding:
Gene expression is regulated by proteins that bind to specific base sequences in DNA

5. Different proteins used to regulate transcription
Gene Expression
Different proteins used to regulate transcription
Different sections of DNA bases where these proteins bind
Unique to the specific gene they are regulating
Enhancers
Silencers
Promoter-proximal elements
Understanding:
Gene expression is regulated by proteins that bind to specific base sequences in DNA

6. Promoter-proximal elements
Promoters
Promoter-proximal elements
Enhancers
Silencers

7. Promoter proximal elements
Near to promoter
Specific sequence for each gene
Contains other regulatory elements
Understanding:
Gene expression is regulated by proteins that bind to specific base sequences in DNA

8. Enhancers
Silencers
Increase the rate of transcription Does not need to be near promoter
Decrease the rate of transcription
Does not need to be near promoter
Understanding:
Gene expression is regulated by proteins that bind to specific base sequences in DNA

9. Promotors
Located near a gene Binding site of RNA polymerase Initiates transcription Promoters are not transcribed into RNA Same sequence for most genes (general RNA polymerase binding)
Applications:
The promoter as an example of non-coding DNA with a function

10. Nature vs Nurture EYE COLOUR SCARS TATTOOS
Your characteristics are due to your environment, your genes, or a bit of both. Put the characteristics on the scale
ACCENT
WEIGHT
SUN TAN
HAIR COLOUR
INTELLIGENCE
Environmental
Inherited
Understanding:
The environment of a cell and of an organism has an impact on gene expression

11. Gene Regulation
Production of skin pigmentation during exposure to sunlight Melanin produced to protect against UV rays from the sun Gene regulation in response to environment
Understanding:
The environment of a cell and of an organism has an impact on gene expression

13. Gene Expression
Many studies on identical and non identical twins raised together or apart More evidence for intelligence is inherited Mr. Burford: THE JIM TWINS
Understanding:
The environment of a cell and of an organism has an impact on gene expression

14. Prior Learning
DNA molecules are paired with a protein called histone Histones help to package DNA 8 histones make up a nucleosome Essential as DNA can be 4cm long, it must fit into a microscopic nucleus
Understanding:
Nucleosomes help to regulate transcription in eukaryotes

15. Impact the visible characteristics of an individual
Nucleosomes
Chemical modification of histones is important in whether a gene is expressed or not.
Add:
Acetyl group (COCH3)
Methyl group (CH3)
Phosphate group (PO4)
Increase or decrease the accessibility of the gene to transcription factors
Impact the visible characteristics of an individual
Epigenetic tags
Understanding:
Nucleosomes help to regulate transcription in eukaryotes

16. Methylation
Direct methylation of DNA decreases gene expression Methylation of histones can increase or decrease gene expression
Skills:
Analysis of changes in DNA methylation patterns

17. Epigenetic Tags
Evidence that chemical modifications that occur to DNA in one generation may be passed onto the next Sum of epigenetic tags in an organism = epigenome
Nature of science:
Looking for patterns, trends and discrepancies: there is mounting evidence that the environment can trigger heritable changes in epigenetic factors

18. Transcription starts at a promoter
Initiation (start at promoter)
Elongation (build)
Termination (RNA completed and breaks off at terminator) 5’ 3’ 3’ 5’
Transcription starts at a promoter
5’ to 3’ direction
Understanding:
Transcription occurs in a 5’ to 3’ direction

19. Initiation RNA polymerase binds to promoter DNA unwinds H bonds break
Strands separate
Adds the 5’ end of a free nucleotide to the 3’ end of the growing mRNA molecule
Understanding:
Transcription occurs in a 5’ to 3’ direction

20. Elongation Enhancers speed up rate of transcription
Silencers slow down rate of transcription
Free RNA nucleotides attracted to complementary base pairs (AU, CG)
Nucleotides joined by RNA polymerase in 5’ to 3’ direction
Understanding:
Transcription occurs in a 5’ to 3’ direction

21. Termination RNA reaches terminator and detaches H bonds break
RNA molecule detaches from DNA
DNA forms double helix again (H bonds form)
Many RNA polymerases can follow one another
Understanding:
Transcription occurs in a 5’ to 3’ direction

22. Intiation
Elongation
Termination

23. Post Transcriptional Modification
Prokaryotes: No nuclear membrane: transcription and translation coupled Eukaryotes: can carry out modification before mRNA leaves nucleus
Understanding:
Eukaryotic cells modify mRNA after transcription

24. Post Transcriptional Modification
Pre-mRNA  mature mRNA RNA splicing (Introns removed and exons joined together)
Understanding:
Eukaryotic cells modify mRNA after transcription

25. Post Transcriptional Modification
Allows one gene to code for multiple proteins Must have multiple exons Exons may or may not be included in mRNA
Understanding:
Splicing of mRNA increases the number of different proteins an organism can produce

26. Exam Question
Explain the process of DNA transcription leading to the formation of mRNA (8 marks)

27. Mark Scheme RNA polymerase; (polymerase number is not required)
binds to a promoter on the DNA;
unwinding the DNA strands;
binding nucleotides to the DNA;
it moves along in a 5′→3′ direction;
using complementary pairing/Adenine-Uracil and Cytosine-Guanine;
until a terminator signal is reached;
RNA detaches from the template and DNA rewinds;
RNA polymerase detaches from the DNA;
many RNA polymerases can follow each other;
introns have to be removed in eukaryotes to form mature mRNA;
8 max