Download Genetics

General Genetics
(Practical Session)
BIO221
Lecturer
Alshehri, Dokhnah Saeed
[email protected]
Alshehri, Dikhnah Saeed
THE
TH
9
LAB
The Structure of the DNA
and RNA
Alshehri, Dikhnah Saeed
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
Alshehri, Dikhnah Saeed
 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
 Both DNA and RNA are polynucleotides.
 They are made up of smaller molecules called nucleotides.
 DNA is made of two polynucleotide strands:
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
Nucleotide
 RNA is made of a single polynucleotide strand:
Nucleotide
Alshehri, Dikhnah Saeed
Nucleotide
Nucleotide
Nucleotide
Nucleotide
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.
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
Alshehri, Dikhnah Saeed
Pyramidines
Purines
Thymine - T
Adenine - A
Cytosine - C
Guanine - G
Uracil - U
Alshehri, Dikhnah Saeed
Alshehri, Dikhnah Saeed
Alshehri, Dikhnah Saeed
Alshehri, Dikhnah Saeed
 Nucleotides are
connected to each
other via the phosphate
on one nucleotide and
the sugar on the next
nucleotide
 A Polynucleotide
Alshehri, Dikhnah Saeed
Alshehri, Dikhnah Saeed
Alshehri, Dikhnah Saeed
 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.
Alshehri, Dikhnah Saeed
Alshehri, Dikhnah Saeed
Alshehri, Dikhnah Saeed
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 Acid
Nucleobases
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
Alshehri, Dikhnah Saeed
Base complement
Purines
Pyramidines
Adenine
Thymine
Adenine
Uracil
Guanine
Cytosine
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
Alshehri, Dikhnah Saeed
Alshehri, Dikhnah Saeed
Alshehri, Dikhnah Saeed
Alshehri, Dikhnah Saeed
Alshehri, Dikhnah Saeed
EXERCISE 1
 One strand of DNA has the base sequence:
CGATTGGCAGTCAT
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
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
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
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
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
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
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
Alshehri, Dikhnah Saeed