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Nucleotide Structure Genes and Heredity O Gene = Short segment of a chromosome (usually hundreds to many thousands of nucleotides long) that encodes amino acid sequence of a functional product (an RNA or protein) H HO P O O C5’ H H HO Phosphate HO H Deoxyribose P A 3’ Chromosome Free 3’ 5’ 5’ 3’ T 5’ 3’ G C A DNA molecule is made up of two strands. These strands are antiparallel (they run in opposite directions). The sequence of one strand is complementary to the sequence of the other strand (A pairs with T; G pairs with C). 5’ 3’ T A P P 5’ 3’ T A RNA primers create short (a few nucleotides) double-stranded regions to which DNA Polymerase can bind. 3’ 5’ C 3’ G P 3’ P Cytosine DNA Helicase unwinds the double strand to begin the process of DNA Replication Leading Strand P P Guanine Lagging Strand P P 5’ 3’ DNA Replication A strand of DNA is a string of nucleotides hooked together by sugarphosphate bonds. P A Thymine C 5’ 3’ 5’ G Attached DNA Structure P P T Adenine 3’ 5’ P Phenotype = type of proteins an organism produces AND the observable characteristics that result from these proteins P Genotype = type of gene(s) an individual possesses One molecule of DNA Nitrogenous NitrogenousBase Base O 4’ C C C1’ HH H C C C2’ H 3’ C 5’ DNA Polymerase reads old DNA strand (3 ’!5 ’) and synthesizes a complementary strand. 5’ Bacterial DNA Replication (Rolling Circle Model) DNA Replication (continued) After completion of initial DNA synthesis, two “identical ” DNA molecules result (here shown as blue and red). DNA Ligase DNA Helicase DNA Polymerase returns and replaces the RNA primers with DNA. The new strand of one molecule has identical sequence to the old strand of the other molecule. DNA Ligase Old Strand New Strand The enzyme, DNA Ligase , glues together the sugar-phosphate backbones of DNA fragments. New Strand Old Strand DNA Polymerase reads old DNA strand (3 ’!5 ’) and synthesizes a complementary strand. Transcription DNA RNA Similar to DNA Replication except: (1) RNA Polymerase synthesizes RNA and (2) RNA is produced (not DNA). O H HO P O C H HO Phosphate O C HH C H C C H U Nitrogenous Base Characteristic Name Size Function Structure Number of different types HO OH H Deoxyribose Ribose Characteristic Sugar Nucleotides Complementary Base Pairing Structure of DNA strands Types of RNA Information Storage DNA Deoxyribose (2’ carbon has Hydrogen) A, G, C, Thymine (T) G:::C, A::T Sugar-Phosphate Backbone presenting nucleotides in sequence Nucleotide sequence read 5’! 3’ RNA Ribose (2’ carbon has hydroxyl -OH) A, G, C, Uracil (U) G:::C, A::U Sugar-Phosphate Backbone presenting nucleotides in sequence Nucleotide sequence read 5’! 3’ Number of strands in typical molecule Stability Double-stranded Very Stable (long-lasting) Single-stranded Somewhat unstable (short-term) mRNA Messenger RNA Variable Encodes amino acid sequence of specific protein Single-stranded, linear tRNA Transfer RNA Short (~75 nucleotides) Decodes mRNA sequence, carries a specific amino acid Single-stranded but twisted into characteristic clover-leaf shape As many as there are proteins to be made (~5000 in E. coli; ~100,000 in humans) 20 to 64 rRNA Ribosomal RNA 3 different sizes Forms functional part of ribosome Single-stranded but packaged together with other rRNAs and with ribosomal proteins 3 AA Anticodon tRNA Ribosome Translation 1. Small ribosomal subunit binds to mRNA and moves 5 ’ ! 3’ until it reaches a START CODON. The Universal Genetic Code 3. Large ribosomal subunit binds such that tRNA -Met fits into one the two pockets. 5’G C G A C U U G A U G C C C U U U U C A U G A 3’ mRNA 2. tRNA binds to start codon . This tRNA has ANTICODON with complementary sequence to start codon . This tRNA also carries the specific amino acid Methionine . Pro 5. The amino acids bind to one another. The first tRNA , without its amino acid, becomes destabilized and falls out of the ribosome. The ribosome then moves down one codon . Met 4. A second tRNA , whose anticodon is complementary to the exposed codon , fits into the second pocket of the large ribosomal subunit. Prokaryotes vs Eukaryotes: Chromosome Structure Characteristic Prokaryotes Number of Chromosomes Chromosome Shape Plasmids Direction of Replication Introns Gene Arrangement RNA Editing Timing of Transcrption /Translation Eukaryotes Prokaryotic Gene Expression Plasmid Small, circular molecule of DNA. May contain useful genes such as those for antibiotic resistance, bacteriocins ,and genes that cause increased genetic recombination. Chromosome One. Circular. No histones . Contains all genes essential for fundamental processes 5’!3 ’, bidirectional RNA Polymerase binds to operator, reads the DNA and transcribes the structural genes (Z, Y, and A). I gene Typical Procaryotic Cell lac Operon Promotor Operator (RNA (Repressor Polymerase binding site) binding site) Lactose Repressor Protein Z Y A Mutations: Genotypic Effects DNA 5’C G G T A C G G A C C C A C G T C G A C T T T T T A 3’G C C A T G C C T G G G T G C A G C T G A A A A A T Mutations: Phenotypic Effects 3’ 5’C G G T A C G G A C C C A C G T C G A C T T T T T A 3’G C C A T G C C T G G G T G C A G C T G A A A A A T 5’ mRNA What is the nucleotide sequence of the other DNA strand? 1. Amino Acid Sequence? What is a mutation? 2. If nucleotide 12 mutates from C to T what is the amino acid sequence? What is a BASE SUBSTITUTUION mutation ? What is a DELETION mutation? 3. If nucleotide 11 mutates from C to T, what is the amino acid sequence? What is a ADDITION mutation ? 4. If nucleotides 14 and 15 are deleted, what is the amino acid sequence? 3’ 5’