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LESSON X:
GENE EXPRESSION AND MUTATIONS
To Address NYS Standards:
2 (Organisms inherit genetic information in a variety of ways that result in continuity of
structure and function between parents and offspring) and 4 (The continuity of life is
sustained through reproduction and development).
Behavioural Objective:
The students will be able to completely understand the ways in which prokaryotic and
eukaryotic genes are controlled. The students will also become acquainted with the
numerous ways in which a mutation can occur, and what the effects may be.
Explanation of Lesson Plan:
This lesson will allow students the chance to tie together DNA structure, transcription,
translation, and some modern genetics. By examining how these processes can go awry,
the students will gain a deeper understanding of their workings.
Hook: (5 minutes)
“We all now know how DNA is transcribed into RNA. We also know how that RNA is
made into a protein. What we need to find out today is what controls all that. How do
we ensure that we produce only the RNA (and thus proteins) that we need, and only when
we need them?”
Test of Prior Learning: (2 minutes)
1. Remind me how RNA is made.
2. What tells RNA polymerase to start or stop?
3. What tells DNA polymerase to start or stop?
New Learning: (30 minutes)
1. What we need to find out is how genes are controlled. We don’t want them on all the
time, but we don’t want them off all the time, either.
2. In prokaryotes, things called operons control the process.
3. There is an operator gene that must be active in order for anything to happen.
4. There is protein called a repressor that is produced by the regulator gene.
5. When the repressor protein is bound, transcription can’t happen.
6. However, if another molecule binds to the repressor protein, it changes shape and can
no longer bind to the operator.
- Demonstration with boxes.
7. This frees up the operator, and the gene can be transcribed!
8. This is in prokaryotes. In eukaryotes, the system is much more complicated, of
course.
9. Recall that chromatin is just lying around the nucleus. Some of it is tightly packed,
some of it is uncoiled.
10. The uncoiled bits are easy to transcribe, while the still-coiled bits are hard. There are
genes that control which bit of DNA is transcribed or not, and these genes are usually
very far away.
11. Environment can control genes, as well. Himalayan rabbits get black fur if the
temperature is below 33 degrees.
12. Remember Crepidula fornicata? It turns on an entire other set of genes to switch
sexes!
13. In fruit flies, higher temperatures have increased homosexual behaviour, while
normal room temperatures promote heterosexual behaviour.
14. How much food you eat or how much exercise you get can affect your metabolism –
controlled ultimately by enzymes and genes!
15. Oncogenes are worth mentioning – they are genes that, when activated or turned off
cause cancer.
16. There are several things that can go wrong. If a chromosome is disrupted, you get a
chromosomal mutation.
17. If a gene is changed, it is called a gene mutation. Point mutations are just one base
changed, while frameshift mutations change the entire code from that point on.
- make chart with frameshift vs. point mutations.
18. Additions, deletions, insertions, inversions (bit of DNA rotated)
19. Nondisjunction is when chromosomes stick together, causing polyploid individuals,
ex: strawberries.
20. Mutagens or things that look a lot like nucleotides can get wedged into DNA and
disrupt it.
21. Gene expression can be controlled at translation, transcription, or many other points.
- pictures in Pierce
22. Antisense RNA is complimentary to some RNA, so can bind to it and turn it off.
23. Alternative splicing can control what genes are produced.
Test of New Learning: (3 minutes)
1. What causes mutations?
2. How are genes controlled in eukaryotes and prokaryotes?