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The Central Dogma of Biology
Central Dogma: Describes the flow of genetic information within a biological system: DNA → mRNA → Protein
Gene: Region of DNA that holds instructions for making proteins.
mRNA: Intermediate copy that carries genetic information from DNA to ribosomes for protein synthesis.
Protein: Final functional product of gene expression.
Organization of Genetic Information in DNA
Protein Coding Regions: These segments of DNA are called genes and are copied into mRNA to create proteins.
Non-Coding DNA:
Some non-coding DNA produces functional RNA.
Others serve regulatory purposes to control gene expression.
DNA vs RNA Differences:
DNA: Double-stranded, contains thymine (T).
RNA: Single-stranded, contains uracil (U) instead of thymine.
Transcription
Process of Transcription: Involves the synthesis of mRNA using DNA as a template by the enzyme RNA Polymerase through three key steps:
Initiation: RNA Polymerase binds to the control region of DNA.
Elongation: RNA Polymerase moves along the DNA template strand in 3' to 5' direction and builds mRNA in 5' to 3' direction.
Termination: RNA Polymerase encounters a terminator sequence and stops transcription.
Chromatin Types:
Euchromatin: Loosely coiled, actively copied or used.
Heterochromatin: Tightly coiled, not actively copied.
RNA Polymerase Properties:
Does not proofread or fix errors.
Role of Histones: Proteins that help package DNA, regulate access to genes.
Transcription Factors: Proteins that bind to regulatory DNA sequences to influence gene expression.
Gene-specific transcription factors can either activate or silence gene expression.
General transcription factors are required for all genes.
mRNA Processing
Introns: Non-coding regions that are removed during mRNA processing.
Exons: Coding regions that are spliced together to form mature mRNA, which exits the nucleus and is translated into protein.
5' Cap: Protective structure that also facilitates ribosome attachment.
3' Poly-A Tail: Stabilizes mRNA and aids in its export from the nucleus.
Translation
Process of Translation: Converts mRNA sequences into amino acid sequences to form proteins. Occurs in the cytoplasm or rough ER.
Roles of RNA in Translation
mRNA: Carries the genetic code from DNA to ribosomes.
tRNA: Transfers specific amino acids to the growing polypeptide chain by matching its anticodon with the codon on mRNA.
rRNA: Combines with proteins to form ribosomes, helping in the assembly of polypeptides.
Steps in Translation
Initiation: Ribosome assembles at start codon (AUG), and the first tRNA brings methionine.
Elongation: tRNAs sequentially bring amino acids, which are linked by peptide bonds.
Termination: Translation stops upon reaching a stop codon, and the completed polypeptide is released.
Genetic Code Properties
Triplet: Three nucleotide bases encode one amino acid.
Non-overlapping: Each nucleotide is part of only one codon.
Degenerate: Multiple codons can encode the same amino acid.
Unambiguous: Each codon specifies only one amino acid.
Punctuated: Includes start and stop codons.
Universal: The same codons specify the same amino acids across all organisms.
RNA Types and Their Functions
mRNA: Carries the code for proteins from DNA in the nucleus to ribosomes.
tRNA: Brings amino acids to the ribosome during translation; recognizes codons through complementary base pairing.
rRNA: Structural component of ribosomes; facilitates translation.
Conclusion on Mutations and Protein Function
Mutations: Changes in DNA sequence can lead to altered protein function, affecting health and development.
Point Mutations: Include silent, missense, and nonsense mutations, affecting amino acid sequences differently.
Frameshift Mutations: Insertions or deletions that alter downstream amino acid sequences leading to functional consequences.