EasyBiologyHigh School (11–12)Heredity and Evolution › Molecular Basis of InheritanceNumericalAPA-LevelIB
The template strand of a short gene reads 3′-TACGGATTCAGC-5′…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
The template strand of a short gene reads 3′-TACGGATTCAGC-5′.
- Write the mRNA from its 5′ end to its 3′ end.
- How many uracil bases does the mRNA have?
- How many G and C bases does the mRNA have together?
- Write the coding strand from its 5′ end to its 3′ end.
Need a reminder? The key ideaShow
The RNA polymerase reads the template strand from 3′ to 5′ and builds the RNA from 5′ to 3′, with U in the place of T. The RNA has the sequence of the coding strand. A hnRNA loses its introns by splicing, gets a cap at the 5′ end and gets a tail of 200 to 300 adenylate residues at the 3′ end.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Template 3′-TACGGATTCAGC-5′.
Plan. Pair the bases to make the RNA. The RNA runs from 5′ to 3′ as the template is read from 3′ to 5′.
Step 1. (a) Pair the bases one by one. T gives A, A gives U, C gives G, G gives C, G gives C, A gives U. Then T gives A, T gives A, C gives G, A gives U, G gives C, C gives G. The mRNA is 5′-AUGCCUAAGUCG-3′.
Step 2. (b) The U bases are at positions 2, 6 and 10, so there are .
Step 3. (c) G: positions 3, 9 and 12, which is 3. C: positions 4, 5 and 11, which is 3. Together .
Step 4. (d) Replace U with T: 5′-ATGCCTAAGTCG-3′.
Answer: 5′-AUGCCUAAGUCG-3′; ; ; 5′-ATGCCTAAGTCG-3′.
Check. The mRNA begins with AUG, the start codon.
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