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Genes and How They Work

Computer Filename: genes1.ppt

Developed by Hugh B. Fackrell

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Overview

Genes are composed of DNA within the chromosome

Genes code for proteins DNA is transcripted into RNA RNA is translated into protein by

ribosomes Genes regulated by control of RNA

production

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Lecture Outline

Genetic Code Gene Expression transcription translation Protein Synthesis Gene Regulation Gene Architecture

Genes and How They WorkGenes and How They Work

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Concepts from OAC

Structure & Function of DNA & RNA Genetic code Transcription & translation Protein synthesis Gene Regulation: operators, promotors ,

repressors

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Background Terms & Concepts

Structure of DNA & RNA Ribosomes Enzymes Structure of Eukaryotic chromosomes

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The Genetic Code

Genetic information is stored in DNA sequences found in– Chromosomes– Mitochondria: 16 KB, 13 genes– Chloroplasts: 120-160 KB, 120 genes

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Structure of the Genetic Code

DNA : sequences of four nucleotides A,T,G,C CODONS : blueprint for the polypeptide Start & Stop Signals: Where to read the blueprint Regulatory Sequences: When to read the

blueprint– promotors– operators– enhancers

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CODONS

sequences of three adjacent nucleotides that code for one amino acid or polypeptide termination

64 codons encrypt of ~ 20 amino acids degenerate RNA: ACU, ACC,ACA, ACG

threonine degenerate DNA: TGA, TGG,TGT, TGC

threonine

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Start Codon

RNA: AUG

DNA: TAC also codes for methionine

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Stop Codon

Nonsense Codons RNA: UAA,UAG,UGA DNA: ATT, ATC, ACT

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Alternate Genetic Codes

Sequence Chromosome Mitochondrion

TGA Stop Trypt

ATA Isoleucine Methionine

AGA Arginine Stop

AGG Arginine Stop

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Interpreting the Genetic Code

Two step process :

– Transcription DNA --> RNA

– Translation RNA--> protein

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RNA

Ribosomal RNA Transfer RNA Messenger RNA

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Ribosomal RNA

called rRNA found in Ribosomes probably catalytic site provides site for protein assembly ribosomal structure different in

eukaryotes and prokaryotes

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Prokaryotic Ribosomal RNA

large subunit 5s(120), 23s (2900) Small subunit 16s (1540)

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Eukaryotic Ribosomal RNA

Large subunit 5s(120) 28s (4700) 5.8s (160) Small subunit 18s(1900)

18 S18 S 28 S28 S 5.8 S5.8 S

Transcribed Spacer RNATranscribed Spacer RNA

Ribosomal RNARibosomal RNA

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Ribosomal RNA

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Transfer RNA

called tRNA Smaller than mRNA or rRNA found in cytoplasm 40 different kinds of tRNA transports amino acids to ribosome positions amino acids on elongating

polypeptide

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tRNA

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Messenger RNA

called mRNA long single strand of RNA copy of the DNA to be decoded transfers information from the nucleus to

the cytoplasm for decoding

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Transcription

occurs in nucleus of eukaryotes

– cytoplasm of prokaryotes DNA unravels- single strand RNA Polymerase binds to Promotor site Reads from start sequence(TAC) assembles complementary single strand of RNA (primary

RNA) Disengages when reaches stop codon

Production of an RNA copy of the geneProduction of an RNA copy of the gene

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RNA being read from DNA

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Prokaryotic Transcription and Translation

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Antibody Structure

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Eukaryotic Transcription & Translation

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Intron Splicing

Regulated at DNA level by restriction endonucleases

Regulated at RNA level by SPLICEOSOMES

GU....AG sequences thalassemia syndromes

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Splicing of DNA

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Gene Rearrangement & Processing

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mRNA Splicing

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DNA Loops