Genes and Proteins Combined
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Transcript of Genes and Proteins Combined
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Genes and Proteins
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DNA• Hershey and Chase Experiments– Showed that viruses inject their DNA into bacteria
and direct bacteria to replicate it for them• DNA not protein is genetic material
• DNA– Double helix– Made of EQUAL amounts of nucleotides: Adenine,
Guanine, Cytosine, Thymine– Each part of helix is complementary to other, run
in opposite directions– 3 prime and 5 prime ends
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The Structure of DNA
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DNA vs. RNA
DNA• Double helix• Backbone -
Deoxyribose• Thymine binds with
adenine• Stores code for making
RNA and proteins
RNA• Single helix• Backbone - Ribose• Uracil pairs with adenine• Types of RNA
– Messenger RNA (mRNA) – carries info. For a specific protein. Segment is codon
– Ribosomal RNA (rRNA) – combines with proteins to form ribosome
– Transfer RNA (tRNA) – connectors to bind an mRNA codon to a specific RNA
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The Genetic Code• Genome – All the genetic material in cells– All different sizes depending on complexity of
organisms• Chromosome – Package of DNA and associated
proteins– You have 23 pairs or 46 total chromosomes
• Gene – sequence of DNA on a chromosome that codes for a specific protein or RNA molecule
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Protein Synthesis• Transcription – Copying a gene’s DNA to a
complementary RNA molecule, occurs in nucleus
• Translation – Copying translating an mRNA strand into the language of amino acids
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Transcription and Translation
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Transcription• Transcription – Copying a gene’s DNA to a
complementary RNA molecule, occurs in nucleus– Just copying the “words”
• Occurs in 3 Steps– Initiation – Enzymes unzip DNA double helix, RNA
polymerase binds to promoter• Promoter – DNA sequence at the beginning of a gene
– Elongation – RNA polymerase, adds nucleotides from 3’ to 5’ end making RNA molecule
– Termination – RNA polymerase gets to termination sequence at end of gene, separates and releases new RNA molecule
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Transcription
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Preparation for Translation
• Prokaryotic Cells - begin translation as RNA molecule is being transcribed
• Eukaryotic Cells – mRNA can’t cross nuclear membrane– Add nucleotide cap to end of 5’ end of mRNA– Add 100-200 adenines – “poly a-tail”– Helps ribosomes attach to 5’ end of mRNA– Helps prevent degradation of mRNA– Introns removed from RNA, exons spliced together
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Translation• Translate DNA/RNA language into a amino acid
language to make protein• Occurs at ribosome– Made of rRNA
• Uses– mRNA – carries codon information– tRNA – binds to mRNA and amino acid
• Functional Unit = Codon – 3 base pair “word” that coincides with an amino acid– Genetic Code
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Triplet Codon
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Translation
• Occurs in 3 Steps– Initiation – at 5’ end “start” codon (AUG) codes for
methionine, calls large subunit, start polypeptide– Elongation – tRNA brings 2nd amino acid, covalently
bonds with 1st amino acid, release 1st tRNA, get another tRNA and so on to make poly peptide chain
– Termination – “Stop” codon (UGA, UAG, or UAA). NO amino acid corresponds to “stop”, release factors, release last tRNA, ribosomal units separate, polypeptide chain released
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Translation
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Polypeptide to Protein• Polypeptide chain is NOT a protein• Folding/packaging occurs in endoplasmic reticulum
and/or Golgi apparatus• Chain folds in cytoplasm to get 3-D structure• Errors can occur– Wrong amino acid sequence “messes” up folding
• Cystic fibrosis– Error in folding with correct sequence
• Alzheimer Disease – incorrect folding of amyloid, forms mass in brain
– Error in joining polypeptide chains• Misfire in types or how joined. Hemoglobin
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Expressing Proteins
Prokaryotic• No transcription factors• Expresses whole
genome at once• No introns – no splicing
needed
Eukaryotic• Uses transcription
factors• Expresses only certain
needed genes• Must splice to get rid of
introns
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Mutations
• Mutation – Change in cell’s DNA sequence• Not always harmful, can lead to genetic variability• Point Mutation – changes 1 or a few base pairs in
a gene– Silent – mutation codes for same protein– Missense – mutation codes for different amino acid,
changing proteins shape (ex. Sickle cell anemia)– Nonsense – mutation codes for “stop” codon instead
of amino acid – makes shorter peptide chain
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Mutations: Substitution
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Mutations• Frameshift Mutation
– One or more nucleotides are added or subtracted from gene• Adds or deletes nucleotides in number other than multiple of 3
– Disrupts codon reading, alters amino acid sequence
– Insertions – Deletions– Diseases – colorectal cancer, Crohn’s, Cystic Fibrosis
• Expanding Repeats– Number of a 2 or 4 nucleotide sequence increases over several
generations• Symptoms get more and more severe• Huntington’s Disease – makes extra glutamines, makes fibrous clumps in
brain
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Mutations: Deletions
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Mutations
• Causes– Spontaneous – DNA replication error– Mutagens – external agent that induces mutations
• UV Radiation, x-rays, chemical weapons, nuclear energy, tobacco– During Meiosis– Transposons – jumping pieces of DNA
• Types– Germline – occurs in cells that give rise to sperms and eggs
• Things that run in families– Somatic – occurs in non-sex cells
• DOES NOT get passed on