Biology 9 Lesson 16: DNA and the Nature of Genes
1. Theoretical Summary
1.1. How does DNA replicate itself?
– DNA replication takes place in the nucleus of the cell, at interphase chromosomes.
DNA replicates itself according to the original pattern.
– Duplication process:
- The two strands of DNA gradually separate vertically.
- Nucleotides on 2 strands of DNA are associated with free nucleotides in the intracellular environment according to NTBS.
- 2 new strands of 2 DNA are gradually formed based on the template strand of the parent DNA and in opposite directions.
– Result: 2 daughter DNA is formed similar and similar to mother DNA, in which each daughter DNA has 1 strand from mother, 1 new strand synthesized from intracellular material. (This is the basis of the development of the genetic phenomenon.)
The process of self-replication of a DNA molecule follows the following principles:
- Complementary Principle: The new strand of the daughter DNA is synthesized based on the template strand of the parent DNA.
- Principle of half-retention (semi-conservative): In each daughter DNA, there is a new strand synthesized from free nucleotides in the intracellular environment and a template strand of the parent DNA.
1.2. The nature of genes
- A gene is a segment of a DNA molecule that has a definite genetic function.
- The chemical nature of genes is DNA – Each structural gene is a segment of the DNA molecule, which stores the regulation of the structure of a protein.
- Function: A gene is a structure that carries the information that determines the structure of a protein.
1.3. What is the function of DNA?
- Carrying genetic information is the number, composition, and sequence of nucleotides on DNA.
- Preservation of genetic information is that all errors in the DNA molecule are mostly corrected by enzyme systems in the cell.
- Transfer of genetic information (via DNA replication) from one cell to another.
2. Illustrated exercise
A segment of DNA molecule with A = 1600 nu, has X = 2A
a. Find the number of Nu type T, G, X.
b. How many helices does a DNA molecule have?
c. Calculate the length of the above DNA molecule.
d. When the above DNA molecule duplicates itself to produce 2 new daughter DNA molecules, how many nucleotides of each type must be supplied by the intracellular environment?
a. T = A = 1600 (Nu); G = X = 2 A = 1600 x 2 = 3200 (Nu)
b. Number of turns:
N = 2A + 2G = 2 x 1600 + 2 x 3200 = 9600 (Nu)
⇒ Number of turns: C = N : 20 = 480 (turns)
c. Calculate the length (L):
L = (N/2) x 3.4 = (9600: 2) 3.4 = 16320 (A0)
d. When the above DNA segment duplicates itself, the number of nucleotides required by the intracellular environment is equal to the number of nucleotides present in the parent DNA molecule.
⇒ Amt = Tmt = 1600 Nu; Gmt = Xmt = 3200 Nu
3.1. Essay exercises
Question 1: Briefly describe the process of DNA replication
Verse 2: Explain why the two daughter DNA produced by replication are the same as the parent DNA
Question 3: State the chemistry and function of genes.
Question 4: A piece of DNA has the following structure:
Circuit 1: AGTXXT
Circuit 2: TXAGGA
Write the structure of the two daughter DNA fragments that are formed after the above-mentioned parent DNA strand finishes the process of self-replication.
3.2. Multiple choice exercises
Question 1: In each daughter DNA molecule produced by duplication:
A. Both strands are derived from the parent DNA
B. Both chains are synthesized from environmental nucleotides
C. Has 1 strand received from the parent DNA
D. There are half-chains synthesized from environmental nucleotides
Verse 2: In DNA replication, a free T-type nucleotide from the medium is bound to:
A. T circuit mold
B. G circuit mold
C. A circuit mold
D. X mold circuit
Question 3: 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
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: One gene has a length of 3570 Å. Calculate the number of helices of the gene.
Question 6: 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.
After completing this lesson, you should:
- State the mechanism of replication of DNA according to the principle: complementarity, semi-conservative.
- Understand the nature of genes.
- State the function of DNA.