Biology 9 Lesson 15: DNA
1. Theoretical Summary
1.1. The chemical structure of DNA
– The monomer of DNA – Nucleotide
+ Composed of elements: C, H, O, N, P
+ Belonging to the organic macromolecule, which is structured according to the principle of polymerism, the monomers are 4 types of nucleotides.
The structure of a nucleotide consists of three components:
- Phosphate group: H3PO4
- Pentose sugar: C5HtenO4
- Nitrogen bases: A, T, G, X
+ Types of nucleotides: There are 4 types called by the names of nitrogenous bases: A = Adenine, G = Guanine, T = Timin, X = Citozin
+ Nucleotides are linked together by phosphodiester bonds to form polynucleotide chains.
Each DNA molecule consists of 2 polynucleotide chains linked together by hydrogen bonds (additional bonds) between the nitrogenous bases of the nucleotides.
- A – T = 2 hydrogen bonds
- G – X = 3 hydrogen bonds
+ The DNA molecule of each organism is characterized by the number, composition and arrangement sequence of nucleotides. The different arrangements of the four types of nucleotides make up the diversity of DNA.
+ The diversity and specificity of DNA is the basis for the development of diversity and specificity of organisms.
1.2. Space structure
– In addition to the DNA structure discovered by Watson and Crick, there are many other types of models of DNA. But this is the structure that won the Nobel Prize and is recognized by many scientists, so it should be considered the main structure.
According to the Wat-son and Crick model:
The DNA molecule is a double helix consisting of two polynucleotide chains twisted around an imaginary axis. – Twist to the right. To form a torsion cycle, there are 1 large groove and 1 small groove.
– The ladders are nitrogenous bases and the walls and handrails are sugar molecules and phosphate groups.
+ Helix diameter 2 nm (20 Ao), 1 high period 3.4 nm (34 Ao) including 10 nucleotide pairs.
- In eukaryotic cells, DNA is linear
- In prokaryotic cells, DNA is circular.
Consequences of the principle of complementarity:
– Due to the complementary nature of the two chains, knowing the monomer sequence of one circuit can infer the monomer sequence of the other.
The ratio of the different types of DNA monomers:
- A = T; G = X
- A+ G = T + X
- (A+G): (T+X) = 1.
- N= A + T + G + X = 2X + 2T = 2G + 2A
- L = N/2 x 3.4 (A0)
2. Illustrated exercise
– Suppose on strand 1 of DNA, the number of nucleotides is: A1 = 150; G1 = 300. On circuit 2 there is A2 = 300; G2 = 600.
+ Based on the principle of complementarity, find the number of nucleotides of the remaining types on each single strand and the number of each type of nucleotide for the whole DNA segment, the length of the DNA.
According to NTBS:
A1 = T2 = 150 ; G1 = X2 = 300; A2 = T1 = 300; G2 = X1 = 600
=> A1 + A2 = T1 + T2 = A = T = 450; G = X = 900.
The total number of nucleotides is: A+ G + T+ X = N
The length of DNA is: N/2 x 3.4
3.1. Essay exercises
Question 1: Describe the chemical structure of DNA
Verse 2: Why does DNA have a very diverse and specific structure?
Question 3: Describe the spatial structure of DNA. What are the consequences of the principle of complementarity?
Question 4: A single strand of a DNA molecule has the following arrangement:
A – T – G – X – T – A – G – T – X
Write an additional single circuit with it
3.2. Multiple choice exercises
Question 1: One gene has a length of 2193 A0, the gene duplication process has created 64 single strands in the subgenes, which contain 8256 T-type nucleotides. The number of nucleotides of each type in the above gene is:
A. A = T = 258; G = X = 387
B. A = G = 258; T = X = 387
C. A = T = 387; G = X = 258
D. A = T = 129; G = X = 516
Verse 2: One gene has 480 adenine and 3120 hydrogen bonds. That gene has a nucleotide count of
A. 1200 nucleotides
B. 2400 nucleotides
C. 3600 nucleotides
D. 3120 nucleotides
Question 3: A DNA molecule in eukaryotes has an X-type nucleotide that makes up 15% of the total nucleotides. Calculate the ratio of the number of T-type nucleotides in this DNA molecule.
Question 4: The function of DNA is:
A. Carries genetic information
B. Helps exchange substances between the body and the environment
C. Transmission of genetic information
D. Carrying and transmitting genetic information
Question 5: In gene duplication, the free G-type nucleotide on the template binds to:
A. T of the environment
B.A of the environment
C. G of the environment
D. X of the environment
After completing this lesson, you should:
- Students analyze the chemical composition of DNA, especially its specificity and shape.
- Describe the spatial structure of DNA according to the model of J. Oatson, F. Crick.