Evolutionary significance of altered DNA Nucleotides The changes mutations are

Evolutionary significance of altered dna nucleotides

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Evolutionary significance of altered DNA Nucleotides - The changes (mutations) are the source of the genetic variation upon which natural selection operates and are ultimately responsible for the appearance of new species - Eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends called telomeres - Telomeres do not prevent the shortening of DNA molecules, but they do postpone the erosion of genes near the ends of DNA molecules - It has been proposed that the shortening of telomeres is connected to aging - The shortening of telomeres might protect cells from cancerous growth by limiting the number of cell divisions - There is evidence of telomerase activity in cancer cells, which may allow cancer cells to persist A chromosome consists of a DNA molecule packed together with proteins
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- The bacterial chromosome is a double stranded, circular DNA molecule associated with a small amount of protein - Eukaryotic chromosomes have linear DNA molecules associated with a large amount of protein - In a bacterium, the DNA is “supercoiled” and found in a region of the cell called the nucleoid Central Dogma: DNA RNA Proteins Important Processes - Replication: DNA RNA - Transcription: DNA to RNA (takes place in the nucleus - Messenger RNA: Carries genetic message of DNA to ribosomes in the cytoplasm - Translation: uses mRNA to produce proteins; occurs at ribosomes - RNA is the bridge between genes and the proteins for which they code Gene specify proteins - Gene expression: process by which DNA directs the synthesis of proteins (sometimes RNA) (1)transcription 2) translation - One gene- one polypeptide hypothesis: states that each gene codes for a polypeptide - triplet code: the instructions for what get translated into a protein Triplets of nucleotides - Determining the proteins from genes is based on a triplet code - Genes are transcribed into complementary nonoverlapping 3-nucleotide words of mRNA - These words are then translated into a chain of amino acids forming a polypeptide - During translation, the mRNA base triplets, called codons, are read in the 5’ 3’ direction Evolution of the genetic code - The genetic code is nearly universal, shared by the simplest bacteria and the most complex animals - Genes can be transcribed and translated after being transplanted from one species to another Transcription is the first stage of gene expression Elongation is where all the action happens - Nucleotides are added to the 3’ end of the growing RNA molecule Transcription termination -after RNA polymerase transcribes a terminator sequence in the DNA, the RNA - Enzymes in the eukaryotic nucleus modify pre-mRNA (RNA processing) before the genetic messages are dispatched to the cytoplasm -
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10/16/17 The structure and function of ribosomes, continued
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DNA DNA :replication DNA RNA :Transcription mRNA peptide bond formation Protein :Translation 3 STOP codons 1 START codons
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Termination of Translation - Elongation continues until a stop codon in the mRNA reaches the A site of the ribosome
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  • Spring '19
  • RON DORN

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