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PROTEIN SYNTHESIS

RNA Overview

• Definition: A single-stranded nucleic acid that carries out the instructions coded in DNA.

• Structure of RNA: Composed of nucleotides, each consisting of:

  • 5-carbon sugar (ribose)

  • Phosphate group

  • Nitrogenous base

Differences Between DNA and RNA

1. Sugar: RNA has ribose; DNA has deoxyribose.

2. Strand Structure: RNA is generally single-stranded; DNA is double-stranded.

3. Nitrogenous Base: RNA contains uracil (U) instead of thymine (T).

Types of RNA

• mRNA (messenger RNA): Carries genetic instructions from DNA in the nucleus to ribosomes in the cytoplasm, acting as a template for protein synthesis.

• tRNA (transfer RNA): Transports amino acids to the ribosome during translation, matching them to the mRNA sequence.

• rRNA (ribosomal RNA): Structural component of ribosomes, assisting in the assembly of amino acids into proteins.

Central Dogma of Molecular Biology

• Flow of Genetic Information: DNA → mRNA → Protein

  • Genes dictate the sequence of mRNA, which specifies the protein sequence.

Codons and Ribosome Structure

• Codons: Sequences of three nucleotides in mRNA that specify amino acids.

• Ribosome:

  • A Site: Where amino acids are brought in by tRNA; matches anticodon with mRNA codon.

  • P Site: Holds the growing polypeptide chain; peptide bonds are formed here.

  • E Site: Exit site for empty tRNA after the peptide bond formation.

Peptide Bond Formation

• Peptidyl Transferase: Enzyme facilitating the bond formation between amino acids during protein synthesis.

CHARGAFF'S RULE

• Complementary Base Pairing: Each base pairs specifically with another; A with T, C with G.

  • Purine-Pyrimidine Pairing: A purine (A, G) pairs with a pyrimidine (T, C).

• Hydrogen Bonds: A-T forms 2 bonds; C-G forms 3 bonds, stabilizing the DNA structure.

Types of Bases

• Purines: Adenine (A) and Guanine (G)

• Pyrimidines: Cytosine (C) and Thymine (T)

TRANSCRIPTION

• Definition: The process where a nucleotide sequence is copied from DNA to RNA.

• Location: In eukaryotes, occurs in the nucleus; in prokaryotes, occurs in the cytoplasm.

• Processing: Eukaryotic RNA undergoes modifications to become mature mRNA before leaving the nucleus.

TRANSLATION

• Definition: Decoding the mRNA sequence to form a polypeptide chain.

• Components of Translation:

  1. mRNA: Contains codon information crucial for protein synthesis.

  2. tRNA: Reads mRNA codons and carries specific amino acids.

  3. Ribosomes: Sites of protein synthesis; consist of rRNA and proteins.

  4. rRNA: Structural role in ribosome; facilitates binding sites for tRNA.

The Genetic Code

• Codons: Three-letter groups in mRNA that code for amino acids.

  • Start Codon: AUG (methionine)

  • Stop Codons: UAA, UAG, UGA

  • Total Codons: 61 codons encode for amino acids.

Steps of Translation

1. Activation: Amino acid attaches to its corresponding tRNA via enzyme (aminoacyl-tRNA synthetase).

2. Initiation: Charged tRNA binds to start codon (AUG) on the ribosome.

3. Elongation: tRNAs sequentially bring in amino acids, forming peptide bonds and extending the polypeptide chain.

4. Termination: Stop codons trigger release factors to release the completed polypeptide.

Protein After Translation

• Post-Translational Modifications: Proteins undergo modifications like folding and cleavage to become functional.

Importance of Proteins

• Functions: Include enzyme functions, structural roles (muscles, hair, nails), and regulation in cells.

GENETICS

• Definition: Study of heredity and variation in living organisms.

Key Terms

• Genotype: Genetic makeup of an organism.

• Phenotype: Observable physical traits derived from genotype.

• Genes: Segments of DNA instructing traits.

• Alleles: Different forms of a gene (e.g., dominant and recessive).

Mendelian Genetics

• Gregor Mendel: Father of Genetics; studied inheritance in pea plants.

• Dominance: Dominant traits conceal recessive traits in phenotype.

• Laws of Inheritance:

  • Law of Dominance: Only dominant traits express in phenotype when paired with recessive alleles.

  • Law of Segregation: Alleles segregate during gamete formation.

  • Monohybrid Cross: Involves one trait; Dihybrid Cross involves two traits.

Conclusion

• Genetic Variation: Results from the independent assortment of alleles, influencing traits and evolution.