1. General Genetics (Practical Session) BIO221 Lecturer Alshehri, Dokhnah Saeed dalshehri@ut.edu.sa Alshehri, Dikhnah Saeed

2. THE 9 TH LAB The Structure of the DNA and RNA Alshehri, Dikhnah Saeed

3. OUTLINES:  The structure of DNA and RNA.  DNA and RNA are polynucleotides.  The rule of getting complementary base pairing  Some practical exercise And class activates. Alshehri, Dikhnah Saeed

5.  Genetic material of living organisms is either DNA or RNA.  DNA – Deoxyribonucleic acid  RNA – Ribonucleic acid  Genes are lengths of DNA that code for particular proteins. Alshehri, Dikhnah Saeed

6.  Both DNA and RNA are polynucleotides.  They are made up of smaller molecules called nucleotides.  DNA is made of two polynucleotide strands:  RNA is made of a single polynucleotide strand: Alshehri, Dikhnah Saeed Nucleotide

7. Alshehri, Dikhnah Saeed A nucleotide is made of 3 components:  A Pentose sugar  This is a 5 carbon sugar  The sugar in DNA is deoxyribose.  The sugar in RNA is ribose.

8. Alshehri, Dikhnah Saeed  A Nitogenous base  In DNA the four bases are:  Thymine  Adenine  Cytosine  Guanine  In RNA the four bases are:  Uracil  Adenine  Cytosine  Guanine

9. Alshehri, Dikhnah Saeed Pyramidines Thymine - T Cytosine - C Uracil - U Purines Adenine - A Guanine - G

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13.  Nucleotides are connected to each other via the phosphate on one nucleotide and the sugar on the next nucleotide  A Polynucleotide

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16.  The Nitrogenous Bases pair up with other bases. For example the bases of one strand of DNA base pair with the bases on the opposite strand of the DNA.

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19. THE RULE:  Adenine always base pairs with Thymine (or Uracil if RNA)  Cytosine always base pairs with Guanine.  This is beacuse there is exactly enough room for one purine and one pyramide base between the two polynucleotide strands of DNA. Nucleic AcidNucleobasesBase complement DNA adenine(A), thymine(T), guanine(G), cytosine(C) A=T, G ≡ C RNA adenine(A), uracil(U), guanine(G), cytosine(C) A=U, G ≡ C

20. Alshehri, Dikhnah Saeed PurinesPyramidines Adenine Thymine AdenineUracil GuanineCytosine

21. Alshehri, Dikhnah Saeed  Property 1 - it must contain, in a stable form, information encoding the organism’s structure, function, development and reproduction  Property 2 - it must replicate accurately so progeny cells have the same genetic makeup  Property 3 - it must be capable of some variation (mutation) to permit evolution

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26. EXERCISE 1  One strand of DNA has the base sequence: C G A T T G G C A G T C A T Determine the sequence of bases in the complementary strand of mRNA that would form next to this DNA strand. Write the sequence of bases in the complementary mRNA strand. Alshehri, Dikhnah Saeed

27. THE ANSWER:  C always pairs with G, and A always pairs with T. However since this is mRNA and all RNA uses Uracil instead of Thymine. A will pair with U. GCUAACCGUCAGUA Alshehri, Dikhnah Saeed

28. EXERCISE 2  Write the complementary strand of DNA to the following sequence. 5 ′ A-C-T-C-G-G-T-A-A 3 ′ Alshehri, Dikhnah Saeed

29. THE ANSWER:  Remember, A pairs with T and G pairs with C. Go through the original 5 ′  to 3 ′ sequence pairing each A with T and each C with G. Keep in mind that  the complementary strand will read from left to right in the 3 ′ to 5 ′  direction. Therefore, the complementary strand starts with 3’ and ends with 5’. Original strand 5 ′ A-C-T-C-G-G-T-A-A 3 ′ The Complementary 3 ′ T-G-A-G-C-C-A-T-T 5 ′ Alshehri, Dikhnah Saeed

30. EXERCISE 3  What is the DNA template that codes for the mRNA segment with the nucleotide sequence of sequence of 5 ′ G-C-U-A-G-U 3 ′ ? Alshehri, Dikhnah Saeed

31. THE ANSWER:  Again, there are two ways to approach this problem:  Memorizing base-pair rules:  Complementary bases in mRNA 5 ′ G-C-U-A-G-U 3 ′  Portion of DNA template 3 ′ C-G-A-T-C-A 5 ′  Associate with DNA synthesis:  Complementary bases in mRNA 5 ′ G-C-U-A-G-U 3 ′  Change all U’s to T (no U in DNA) 5’ G-C-T-A-G-T 3’  Follow normal base-pairing rules: 3 ′ C-G-A-T-C-A 5 ′ Alshehri, Dikhnah Saeed

32. EXERCISE 4  Answer the following:  a) What codons specify tyrosine?  b) What amino acid is coded by CCG?  The ANSWER:  a) Table (1) UAC and UAU.  b) Table (2) Pro (proline). Alshehri, Dikhnah Saeed