BIOL 1710 CH15 & CH16

Translation and transcription are fundamental processes in molecular biology, governing the synthesis of proteins from genetic information embedded in DNA.

Process of Transcription: Involves converting DNA into RNA, specifically mRNA (messenger RNA).
- Initial step in gene expression.
- Recognized significance of RNA's role in protein synthesis.

Codons: Sequence of three nucleotides that code for specific amino acids.
- Nucleotides include adenine (A), guanine (G), cytosine (C), and uracil (U) in RNA (thymine (T) is found in DNA).
- Example: Codon for Methionine is AUG.

Initiation: Begins with RNA polymerase binding to the promoter region of the gene.
- Promoter Regions: Specific DNA sequences necessary for RNA polymerase attachment.
  - Prokaryotes: The promoter has a -10 and -35 consensus sequence.
- Eukaryotes: Involves multiple transcription factors and a more complex initiation process.
Elongation: RNA polymerase synthesizes mRNA by adding complementary RNA bases to the growing strand.
- DNA template read in a 3’ to 5’ direction, while RNA synthesis occurs in a 5’ to 3’ direction.
- RNA contains Uracil (U) instead of Thymine (T).
Termination: Occurs once RNA polymerase reaches a termination signal.
- Can involve formation of a hairpin loop in prokaryotes or a sequence-specific signal in eukaryotes leading to dissociation of the RNA polymerase.

Key Differences:
- Prokaryotes transcribe and translate simultaneously without compartmentalization, whereas eukaryotes perform these processes in distinct cellular locations.

Eukaryotes:
- Transcription occurs in the nucleus.
- Involves splicing (removal of introns) post-transcriptional modifications (capping and polyadenylation).
- Requires several transcription factors to assist RNA polymerase.
Prokaryotes:
- Simpler structure, transcription occurs in the cytoplasm.
- Transcriptional machinery directly interacts with the DNA, hence much faster than in eukaryotes.

Splicing: Removal of introns and joining of exons by spliceosomes.
- Exons: Coding sequences that will remain in mRNA.
- Introns: Non-coding sequences that are removed and typically not used for protein coding.
Capping and Polyadenylation: Addition of a methyl cap at the 5’ end and a poly-A tail at the 3’ end for stability and export from the nucleus.
- Protects mRNA from degradation in the cytoplasm.

Introns, while often considered non-coding, may play a role in genetic recombination and regulatory processes influencing gene expression and phenotype variation.

Process of Translation: The decoding of mRNA to synthesize proteins.
- Occurs in the cytoplasm at the ribosome.

Initiation: mRNA binds to the ribosome, and the first tRNA carrying methionine (from the start codon AUG) attaches at the P-site.
Elongation: tRNAs bring amino acids to the ribosome based on codon sequence on the mRNA.
- Each tRNA has an anticodon that pairs with the mRNA codon.
- Peptide bonds form between adjacent amino acids creating a polypeptide chain.
Termination: Occurs when a stop codon is reached, leading to the release of the completed polypeptide.

Gene Expression: The process where specific genes are activated or silenced to produce the desired proteins, regulated at transcriptional and translational levels.
- Regulation is influenced by environmental factors, hormonal signaling, and the availability of transcription factors.

Operons: Groups of genes regulated together, common in prokaryotes, simplifying the coordination of gene expression.
- Repressors: Molecules that bind operators to prevent transcription; triggered by the presence of specific substrates (e.g., tryptophan).
- Activators: Molecules that enhance transcription, often activated by certain stimuli (e.g., lactose removing repressor from the lactose operon).

Central Dogma: Genetic information flows from DNA to RNA (transcription) and then from RNA to protein (translation).
This flow of information is vital for producing proteins that perform essential functions within organisms.

Importance of codon charts to determine which amino acids correspond to specific mRNA codons and their roles in protein synthesis.
The multifunctional nature of proteins: structural, enzymatic, signaling, and cellular transport roles critical to an organism's survival and functionality.