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Transcript Processing Protein Folding RNAi Gene Repair

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Transcription factor recognizes TATA Box and binds to DNA RNA polymerase bonds to DNA RNA polymerase separates strands and strings together complementary nucleotides (using U instead of T) Primary transcript has been created when terminator region is reached

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Transcription: Creates molecule to carry protein instructions from DNA Creates exact replica complementary to DNA

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Alteration of ends of transcript: 5 end capped with modified guanine Keeps RNA from degrading in the cytoplasm Cleavage factors and stabilizing factors bind to 3 end Poly A polymerase binds and cleaves 3 end and adds poly A tail made of adenine

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RNA splicing: Nucleotides removed Introns = non-coding regions Exons = coding regions to be expressed Small nuclear ribonucleoproteins (snRNPs) = proteins that detect adenine at branching site Spliceosomes remove the intron and bind the two exons

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The sequence of amino acids defines a proteins primary structure.

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Blueprint for each amino acid is characterized by base triplets Found in the coding region of genes Ribosomes recognize triplets and create proteins

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Covalent bonds between amino acids help stabilize the protein Shape and stability also maintained by chemical forces

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Chaperone proteins: Prevent nearby proteins from inappropriately associating and interfering with proper folding Surround protein in protective chamber during folding Ex) bacteria: GroEL and GroES Use ATP Also assist in refolding proteins

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Chaperone proteins protecting folding proteins

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Models of protein folding: Diffusion Collision Model: Nucleus is formed Secondary structures collide and pack together Nuclear Condensation Model: Secondary and tertiary structures are made simultaneously

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RNAi = RNA Interference RNAi is used to: Silence specific genes Fix gene expression problems in mammals Also known as: Cosuppression Post Transcriptional Gene Silencing Quelling

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Types of small silencing RNA: Small interfering RNA (siRNA) Endogeneous: derived from cell Exogeneous: delivered by humans Micro RNAs (miRNA) PIWI-interacting RNAs (piRNA) RNAi breaks up mRNA before it is synthesized.

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Allows singling out of genes to determine function.

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Could halt progression of: Cancer HIV Arthritis All other diseases

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DNA can be damaged by: Radiation (gamma, x-ray, and ultraviolet) Oxygen radicals from cellular respiration Environmental chemicals (hydrocarbons) Chemicals used in chemotherapy

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Four major types of DNA damage: Deamination: amino acid group lost Mismatched base Backbone break Covalent cross-linkage between bases Deamination in DNA

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Repairing damaged bases: Direct chemical reversal Excision repair mechanisms: Base excision repair (BER) Nucleotide excision repair (NER) Mismatch repair (MMR)

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Chemical Reversal Ex) glycosylase enzymes remove mismatched T and restore correct C

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Excision repair mechanisms: Base excision repair: DNA glycosylases identify damaged bases DNA glycosylases remove damaged bases Deoxyribose phosphate backbone component removed, creating gap Gap filled with correct nucleotide Break in strand ligated

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Excision repair mechanisms: Nucleotide excision repair: Protein factors identify damage DNA is unwound Faulty area is cut out and the bases are removed DNA is synthesized to match that of the opposite, correct strand DNA ligase adds synthesized DNA

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Excision repair mechanisms: Mismatch repair Corrects mismatches of normal bases (A&T, C&G) by: Identifying mismatched bases Cutting mismatched bases

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Any Questions?