Introduction to Proteins and DNA

Introduction to Proteins

• Proteins orchestrate nearly every cell function and influence traits of multicellular organisms.
• DNA serves as a blueprint for protein synthesis, with each chromosome comprising a single DNA molecule wrapped around proteins.
• Genes are segments of DNA that code for amino acid sequences in proteins, crucial for life.

The Genetic Code

• DNA holds genes that dictate the unique sequence of amino acids for each protein.
• The order of amino acids influences the protein's chemistry, folding, shape, and function.
• The genetic information flow follows the Central Dogma: DNA → mRNA → Protein.

Central Dogma of Molecular Biology

• When a cell requires a protein, the corresponding gene is activated to produce a single-stranded mRNA through transcription.
• During translation, the mRNA is read to determine the sequence of amino acids in the protein.
• Each nucleotide in DNA corresponds to one in mRNA, while three mRNA nucleotides (codon) correspond to one amino acid.

Universal and Redundant Genetic Code

• mRNA is read in three-nucleotide segments called codons, with 64 possible combinations from four nucleotides (A, C, U, G).
• 61 codons specify one of 20 common amino acids; the remaining three are stop codons that do not code for amino acids.
• The genetic code is largely universal across species, indicating a common origin of life; e.g., mRNA from horses can produce horse globin in tulips.

Redundancy in the Genetic Code

• The redundancy allows multiple codons to specify the same amino acid, reducing the impact of mutations.
• Codons with related amino acids often differ by only one nucleotide; for example, ACU and ACG both code for threonine.
• Cysteine and serine are encoded by similar codons, reflecting their chemically similar properties.

Stop Codons and Start Codon

• Out of 64 codons, three are stop codons that terminate protein synthesis, while the AUG codon serves dual purposes as a start codon for translation and codes for methionine.
• The reading frame for protein synthesis begins at the AUG codon located near the mRNA's 5' end.

Experimental Confirmation of Genetic Code

• The encoding of amino acids by nucleotide triplets was validated experimentally, establishing that two-nucleotide combinations (only 16 possible) are insufficient for all amino acids.
• The experimental design confirmed that nucleotide triplets are essential for specifying amino acids due to the 64 possible combinations available.

This quiz explores the fundamental role of proteins in cellular functions and how DNA serves as the blueprint for protein synthesis. It covers the relationship between genes and the production of various proteins essential for multicellular organisms. Test your understanding of these critical biological concepts.