Summary of "مراجعة ليلة الامتحان biology تالتة ثانوي ا شرح المنهج كامل | final revision biology 3rd secondary"

Summary of Main Ideas and Concepts

Genetic material confusion: Initially, scientists debated whether proteins or DNA were the genetic material.
DNA structure basics: DNA is a polymer made of repeating units called nucleotides (four types).
Protein complexity: Proteins are made of 20 amino acids, making them more diverse than DNA.
Genetics definition: The study of inheritance and genetic material.

Two strains of bacteria:
- S strain (smooth): Virulent, encapsulated, no immune response.
- R strain (rough): Non-virulent, non-encapsulated, immune system can fight it.
Heat-killed S strain + live R strain injected into mice caused death, showing transformation.
Conclusion: Something from dead S strain transformed R strain into virulent bacteria.

Isolated components from dead S strain to identify the transforming factor.
Found DNA was responsible for transformation, not protein.
Used enzymes like protease (breaks protein) and DNase (breaks DNA) to confirm DNA is genetic material.

Bacteriophage structure: protein coat outside, DNA inside.
Used radioactive labeling of protein (sulfur) and DNA (phosphorus).
Found DNA entered bacteria, protein did not, confirming DNA as genetic material.

Rosalind Franklin’s X-ray diffraction revealed DNA is a helix with sugar-phosphate backbone outside and bases inside.
Watson and Crick proposed the double helix model.
Base pairing rules: Purines (A, G) pair with Pyrimidines (T, C)
- A pairs with T (2 hydrogen bonds)
- G pairs with C (3 hydrogen bonds)
DNA strands are antiparallel (5’ to 3’ and 3’ to 5’).

DNA replication is semi-conservative, producing two identical DNA molecules.
Key enzymes:
- Helicase: Unwinds DNA.
- DNA Polymerase: Synthesizes new DNA strand from 5’ to 3’.
- Ligase: Joins Okazaki fragments on lagging strand.
Leading strand synthesized continuously; lagging strand synthesized in fragments.
Proofreading and repair mechanisms correct errors.

Mutations: Changes in nucleotide sequence; can be gene mutations or chromosomal mutations.
Causes: environmental factors like radiation, chemicals, errors during replication.
Repair enzymes recognize and fix mismatches.
Some mutations are hereditary (germline), others somatic.

Prokaryotes: Circular DNA, no nucleus, DNA attached to plasma membrane, plasmids present.
Eukaryotes: Linear DNA in nucleus, associated with histone and non-histone proteins forming chromatin.
Chromatin structure: DNA wrapped around histones forming nucleosomes, further condensed into chromosomes.

Types of RNA:
- mRNA (Messenger RNA): Carries genetic code from DNA to ribosome.
- rRNA (Ribosomal RNA): Structural and catalytic component of ribosomes.
- tRNA (Transfer RNA): Delivers amino acids to ribosome during translation.
Transcription: Copying DNA to mRNA.
Translation: Ribosome reads mRNA codons, tRNA brings amino acids, forming polypeptides.
Genetic code: Triplet codons (64 total, 61 code for amino acids, 3 stop codons).
Start codon: AUG (methionine).
Peptide bonds form between amino acids catalyzed by peptidyl transferase.

Restriction enzymes cut DNA at specific sequences, producing sticky or blunt ends.
DNA fragments can be inserted into plasmids, which are introduced into bacteria for cloning.
PCR (Polymerase Chain Reaction) amplifies DNA using heat-stable Taq polymerase.
Applications: production of human insulin, growth hormones, genetically modified organisms (GMOs), gene therapy.