Download - Genes and Proteins Combined
Genes and Proteins
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
The Structure of DNA
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
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
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
Transcription and Translation
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
Transcription
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
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
Triplet Codon
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
Translation
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
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
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
Mutations: Substitution
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
Mutations: Deletions
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