Students can go through AP Inter 2nd Year Botany Notes 3rd Lesson Molecular Basis of Inheritance will help students in revising the entire concepts quickly.
AP Inter 2nd Year Botany 3rd Lesson Molecular Basis of Inheritance Notes
→ DNA (deoxyribonucleic acid) is the genetic material for the majority of organisms.
→ DNA is a long polymer of deoxyribonucleotides, and its length is defined by the number of nucleotides or base pairs.
→ A nucleotide consists of three components: a nitrogenous base, a pentose sugar, and a phosphate group.
→ Nitrogenous bases are categorized as Purines (Adenine, Guanine) and Pyrimidines (Cytosine, Thymine, Uracil).
→ Nucleotides link through 3′-5′ phosphodiester linkages to form a polynucleotide chain.
→ RNA differs from DNA by having an additional 2′-OH group on its ribose sugar.
→ In 1953, Watson and Crick proposed the Double Helix model of DNA based on X-ray diffraction data.
→ Chargaff’s rule states that for double-stranded DNA, the ratios of A:T and G:C are constant and equal to one.
→ The two chains of the double helix have anti-parallel polarity (one 5′ → 3′, the other 3′ → 5′).
→ Chromatin consists of repeating nucleosome units, appearing as ‘beads-on-string’ under an electron microscope.
→ Euchromatin is loosely packed and transcriptionally active, while Heterochromatin is densely packed and inactive.
→ Frederick Griffith (1928) discovered the Transforming Principle using Streptococcus pneumoniae.
→ Avery, MacLeod, and McCarty proved that DNA alone was the biochemical responsible for this transformation.
→ Genetic material must fulfill four criteria: replication, stability, mutability, and expression of characters.
→ DNA is chemically more stable than RNA because it lacks the reactive 2′-OH group.
→ The RNA World theory suggests RNA was the first genetic material and essential life processes evolved around it.
→ DNA ligase joins the discontinuously synthesized fragments.
→ A transcription unit includes a Promoter, a Structural gene, and a Terminator.
→ Exons are coding sequences that appear in mature RNA; introns are non-coding and are removed during splicing.
→ The Genetic Code is a triplet system; 61 codons code for 20 amino acids, while 3 are stop codons.
→ The code is degenerate (one amino acid coded by multiple codons) and nearly universal.
→ Frameshift mutations occur when the insertion or deletion of bases changes the reading frame of the genetic code.
→ The Lae Operon is a regulated system in bacteria where genes for lactose metabolism are switched on by the inducer, lactose.
→ The movement of a gene from one linkage group to another is called translocation.
→ The equivalent of a structural gene is cistron.
→ A complex of ribosomes attached to a single strand of RNA is known as polysome.
→ AUG is the starter codon.
→ Spliceosomes are not found in cells of bacteria.
→ The association of histone H with a nucleosome indicates that the DNA is condensed into a chromatin fibre.
→ The final proof for DNA as the genetic material came from the experiments of Hershey and Chase.
→ The first phase of translation is aminocylation of tRNA.
→ Transposons can be used in Gene silencing.
→ DNA polymorphism forms the basis of both genetic mapping & DNA fingerprinting.
→ The role of RNA polymerase III in the process of transcription in Eukaryotes in Transcription of TrNA , 5 sr RNA & sn RNA.
→ The salient features of genetic code are code is unambiguous, specific & is nearly universal.
→ Lactose acts as an induces for lacoperon.
→ Chromosome I is the last chromosome sequenced in Human Genome Project.
→ The lactose present in the growth medium of bacteria is transported to the cell by the action of Permease.
→ The rho (ρ) factor is important for the termination of transcription.
Molecular basis of inheritance is the mechanism by which genetic information is stored, replicated, and expressed in living organisms. This process is governed primarily by Deoxyribonucleic acid (DNA), which acts as the blueprint for life and dictates the structure and function of every cell.
1. The Structure of DNA:
DNA is a double-helix polymer consisting of two anti-parallel polynucleotide strands. Each nucleotide is composed of three parts:
- Deoxyribose sugar
- Phosphate group
- Nitrogenous base: Adenine (A), Thymine (T), Guanine (G), or Cytosine (C).
The two strands are connected by weak hydrogen bonds: A = T, G = C
2. DNA Replication:
Replication is semi-conservative, meaning each new DNA molecule consists of one original parental strand and one newly synthesized strand. Enzymes like DNA polymerase work to unzip the double helix and add complementary nucleotides to each exposed strand.
3. The Central Dogma:
Genetic information flows in one primary direction from DNA to RNA to Protein.
- Transcription: The process in the cell nucleus where a specific segment of DNA (a gene) is copied into messenger RNA (mRNA).
- Translation: The process in the cytoplasm where ribosomes decode the mRNA sequence to build a specific chain of amino acids, forming a functional protein.
4. Gene Expression & The Genetic Code:
- The information in mRNA is read in sets of three nucleotides, known as codons.
- Each codon dictates a specific amino acid.
- The genetic code is universal, non-overlapping, and degenerate.