DNA's genetic code is the blueprint for life. It contains instructions for making proteins, the workhorses of our cells. This code is read and translated through a complex process involving transcription and translation, turning DNA's language into functional molecules.
Ribosomes play a starring role in this protein-making process. These cellular machines read the genetic instructions and assemble amino acids into proteins. It's like a molecular assembly line, churning out the building blocks that keep our bodies running.
Genetic Code and Protein Synthesis
DNA code for protein structure
- DNA contains genes which are nucleotide sequences coding for specific proteins
- Genes composed of exons (coding regions) and introns (non-coding regions)
- Genetic code is set of rules determining how nucleotide sequence in DNA translates into amino acid sequence in protein
- Genetic code based on codons which are nucleotide triplets
- Each codon specifies particular amino acid (Methionine, Proline) or stop signal (UAA, UAG, UGA)
- Codon sequence in gene determines amino acid sequence in resulting protein
- Amino acid order in protein determines its primary structure
- Protein's primary structure influences folding and final 3D shape which determines function (enzymes, structural proteins)
Components of transcription process
- Transcription is process of synthesizing RNA from DNA template
- Occurs in nucleus of eukaryotic cells (human, plant)
- Key steps of transcription: initiation, elongation, termination
- Initiation: RNA polymerase binds to promoter region on DNA and separates DNA strands
- Elongation: RNA polymerase moves along DNA template strand and synthesizes complementary RNA strand
- Termination: RNA polymerase reaches terminator sequence and releases newly synthesized RNA and DNA template
- Main components involved in transcription:
- DNA template strand provides genetic information
- RNA polymerase enzyme catalyzes RNA synthesis
- Ribonucleoside triphosphates (ATP, GTP, CTP, UTP) serve as building blocks for RNA (nucleotides)
- Resulting product of transcription is pre-mRNA molecule which undergoes further processing to become mature mRNA (splicing, capping, polyadenylation)
Translation and RNA roles
- Translation is process of synthesizing protein from mRNA template
- Occurs in cytoplasm of eukaryotic cells on ribosomes (rough ER)
- Translation stages: initiation, elongation, termination
- Initiation: Small ribosomal subunit binds to start codon (AUG) on mRNA with help of initiation factors and special initiator tRNA
- Elongation: Large ribosomal subunit joins complex, tRNA molecules bring amino acids to ribosome which are linked to form growing polypeptide chain
- Termination: Ribosome reaches stop codon (UAA, UAG, UGA), release factors cause ribosome to release completed polypeptide chain and dissociate from mRNA
- tRNA (transfer RNA) molecules crucial in translation
- Each tRNA has anticodon complementary to specific codon on mRNA
- tRNAs carry corresponding amino acid matching codon (tRNA-Met carries Methionine)
- tRNAs bring appropriate amino acids to ribosome based on mRNA codons
- mRNA (messenger RNA) is template for protein synthesis
- Carries genetic information from DNA to ribosomes
- Codon sequence in mRNA determines amino acid order in resulting protein
Ribosomes in protein synthesis
- Ribosomes are sites of protein synthesis in cells
- Composed of ribosomal RNA (rRNA) and proteins
- Eukaryotic ribosomes have large (60S) and small (40S) subunits
- Ribosomes facilitate protein synthesis by providing platform for amino acid assembly into polypeptide chains
- Ribosome has three sites: A (aminoacyl), P (peptidyl), E (exit)
- A site binds incoming tRNA carrying next amino acid
- P site holds tRNA carrying growing polypeptide chain
- E site holds empty tRNA before it dissociates from ribosome
- Ribosome has three sites: A (aminoacyl), P (peptidyl), E (exit)
- Ribosomes catalyze peptide bond formation between amino acids
- Peptidyl transferase center in large ribosomal subunit catalyzes peptide bond formation between amino acids in A and P sites
- Ribosomes move along mRNA 5' to 3', reading codons and adding amino acids to growing polypeptide chain
- Process continues until ribosome reaches stop codon, completed polypeptide chain released (insulin, collagen)
From Gene to Functional Protein
- Central dogma of molecular biology describes flow of genetic information: DNA → RNA → Protein
- Amino acids are building blocks of proteins, joined together to form polypeptide chains during translation
- After translation, proteins undergo post-translational modifications to achieve final functional form
- Protein folding occurs as newly synthesized polypeptide chain adopts its three-dimensional structure
- Folding is crucial for protein function and is influenced by amino acid sequence and cellular environment