Gene Expression: Process of using DNA instructions to synthesize functional products, typically proteins.
Two major steps:
Transcription: DNA is converted to mRNA (messenger RNA).
Translation: mRNA is used to synthesize proteins.
Translation involves the ribosome reading the genetic code carried by mRNA to build a polypeptide chain, which folds into a protein.
This process is critical for cell functions like growth, division, signaling, transport, and catalysis.
Translation Overview (From Your Course Material)
Translation: The biological process of building proteins from mRNA using ribosomes, tRNA, rRNA, and amino acids.
Occurs in three main stages:
Initiation: Assembling the components.
Elongation: Sequential addition of amino acids.
Termination: Process ends upon reaching a stop codon.
Molecules Involved in Translation
1. mRNA (messenger RNA)
Role: Carries genetic instructions from DNA to the ribosome.
Connection: Acts as the translation template; each codon (3 nucleotides) corresponds to an amino acid.
2. tRNA (transfer RNA)
Structure: Cloverleaf shaped; includes:
Anticodon: Base-pairs with mRNA codons.
Amino Acid Attachment Site
Connection: Delivers correct amino acids to ribosome via anticodon-codon matching.
3. Amino Acids
Role: Building blocks of proteins.
Connection: Delivered by tRNA to be added to the polypeptide chain.
4. Ribosomes
Structure: Two subunits (large and small), made of rRNA and proteins.
Connection: Machinery reading mRNA to connect amino acids. Has three sites:
A (Aminoacyl site): Entry for new tRNA.
P (Peptidyl site): Holds the growing chain.
E (Exit site): Used tRNA exits.
5. rRNA (ribosomal RNA)
Role: Structural and catalytic component of ribosomes.
Connection: Forms peptide bonds and aligns tRNA/mRNA during translation.
6. Initiation Factors
Role: Assist in ribosome assembly and mRNA binding.
Connection: Ensure correct start of translation at AUG start codon by recognizing specific sequences (e.g., Shine-Dalgarno in prokaryotes).
7. Elongation Factors
Role: Aid in tRNA delivery and ribosome movement.
Connection: Use GTP energy for elongation.
8. Release Factors
Role: Recognize stop codons and release finished protein.
Connection: Terminate translation and disassemble the machinery.
Summary
Translation: Assembly of proteins using mRNA as instructions, tRNA as amino acid carriers, ribosomes as builders, and rRNA along with various protein factors to coordinate the process.