ONE GENE ONE POLYPEPTIDE Gene sequence of nucleotides

ONE GENE – ONE POLYPEPTIDE Gene: sequence of nucleotides in DNA that performs a specific function, ex. coding for a protein. Proteins: phenotypic characteristics, antibodies, hormones, drive cellular processes (metabolism), their absence or presence in an altered form can result in genetic disorders. Each gene in our DNA codes for one particular protein. Evidence: Archibald Garrod (British physician, early 20 th century): Studied patients with alkaptonuria, they lack the enzyme to break down alkapton, which leads to black urine and noticed the illnesses recurs in some families. Concluded error in hereditary material results in error of enzyme. Beadle and Tatum (23 years later) demonstrated the hypothesis. Using mutant strains of red bread mould and the synthesis of amino acids they were able to show that the lack of a particular enzyme to produce an amino acid corresponded to a mutation in a specific gene.

Evidence continued: Hemoglobin is made of 2 alpha polypeptides and 2 beta polypeptides Each chain is controlled by a different gene. Ingram found that in sickle cell anemia red blood cells, the 6 th amino acid of the beta-chain, normally glutamic acid, is substituted with valine Significance: linked a hereditary abnormality to a single alteration in the amino acid of a protein – ultimately controlled by a single gene Hemophilia, cystic fibrosis also caused by single gene alterations.

PROTEIN SYNTHESIS Occurs in the cytoplasm on ribosomes. But DNA (code) is not able to exit the nucleus (could be damaged). Messenger RNA (m. RNA): copies and transports the code to the ribosome. Transcription: the copying of the DNA info into m. RNA Transcribe (one form to another) Translation: ribosomes use the m. RNA blueprint to synthesize proteins. Translate (one language to another)

RIBONUCLEIC ACID - RNA Ribose sugar (one more O than deoxyribose – an OH at C 2) Uracil base instead of thymine (H on C 1 instead of CH 3), pairs with adenine Single stranded 3 major classes: m. RNA: copy of a gene – template for protein building at the ribosome Transfer RNA (t. RNA): transfers amino acids to the ribosome to build a protein Ribosomal (r. RNA): structural component of the ribosome along with proteins next. . . Transcription

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GENETIC CODE There are 20 amino acids found in proteins, only 4 bases in m. RNA (U C A G) Codons: sequences of three bases used to code for an a. a. 43=64 possible codons (some amino acids have more than one codon) Ex. UUU UUC, UCU, UCC all code for phenylalanine (a. a. ) This redundancy helps to reduce errors AUG: start codon (Methionine) used 99% of the time UAA, UAG, UGA: stop codons The m. RNA transcript is read in sets of 3 nucleotides (one codon) to determine which a. a. is next.

TRANSCRIPTION OVERVIEW 3 processes: initiation, elongation and termination. Initiation: RNA polymerase binds to DNA at a promoter site near the beginning of the gene. Elongation: RNA polymerase uses the appropriate ribonucleotides to build the m. RNA transcript. Termination: RNA polymerase passes the end of the gene, recognizes a stop signal. m. RNA transcript is then completely released from the DNA.

TRANSLATION OVERVIEW Also initiation, elongation and termination Initiation: Ribosome binds to a specific sequence on the m. RNA Elongation: the ribosome moves along the m. RNA and t. RNA delivers the appropriate amino acid and the polypeptide is elongated. Termination: the ribosome reaches a stop signal, the ribosome falls of the m. RNA and the polypeptide chain is released.