Chapter 4 Genetics and Cellular Function- DNA & RNA- Nucleic Acidso Nucleus center of hereditary and cellular controlo DNA structure & function DNA is a polymer of nucleotides consisting of a sugar, phosphate group, & single or double ringed nitrogenous bases Pyrimidine: single carbon-nitrogen ring- Cytosine & thymine Purine: double ringed- Adenine & guanine Double helix- Backbone of deoxyribose alternating with a phosphate group- Steps are the nitrogenous baseso Base pairs A&T form two hydrogen bonds with each other C&G form three hydrogen bonds with each other Law of Complementary Base Pairing: one strand governs the next Function: to carry genes for the synthesis of proteins- 20,000 genes = 2% proteins and 98% protein is non codingo Chromatin & Chromosomes Chromatin: fine, filamentous version of DNA that form chromosomes Non-dividing cells: chromatin looks like beads on a string- Each bead is a histoneo Cluster of 8 proteinso DNA winds around histone 1.5 timeso Nucleosomes: a core particle and a short segment of DNA linker- Nucleosomes are arranged in a zigzag pattern allowing chromatin to fold - 30nm strand is thrown into complex irregular loops, and coils that make chromosomes 300nm thick & 1000x shorterthan DNA molecules - Each chromosome is packed into its own spheroidal region of the nucleus called chromosome territory Dividing cells- DNA is replicated- Each chromosome has 2 sister chromatids o Pinched together by a centromereo Each side of centromere is a kinetochore o RNA Structure & Function (Big-small) mRNA, rRNA, tRNA Only a one nucleotide chain Ribose sugar Uracil instead of thymine Disposable molecule that works in the cytoplasm- Genes & Their Actionso What is a gene? “unit of heredity” Don’t always code for protein Overlap sometimes- Short ones embedded in bigger ones Gene: an information containing segment of DNA that codes for RNA which then usually codes for a protein o The Genome 46 Chromosomes; 23 pairs Genome: all DNA in 46 chromosomes Geonomics: study of the whole genome and how its genes & noncoding DNA interact to affect the structure & function of whole organism- Humans have fewer than 100,000 genes - Genes generate million of proteins- Genes average 3,000 bases long, but range up to 2.4 million- All humans are 99.99% identicalo Single nucleotide polymorphism account for all human variation- Gene rich & gene poor chromosomes- Geonomic Medicineo Genetic Code: a system that enables these 4 nucleotides ro code for the amino acid sequence of all proteins A sequence of 3 DNA nucleotides stand for one amino acid: base triplets- Called a codon in RNA 61/64 code for amino acids- UAG, UGA, UAA are stop codons- AUG start codono Protein synthesis Different genes are activated in different cells mRNA is made when a gene is activated - nucleus  cytoplasm- DNA  RNA(transcription)  protein(translation) Transcription: copy genetics from DNA to RNA- DNA too large to leave nucleus- RNA polymerase binds to DNA sequence & assembles mRNAo Opens 17 base pairs at one time - Pre-mRNAo Exons be translated into proteinso Introns must be removed before translation  Enzymes remove and degrade them- Alternative Splicing: one gene can code for more than one protein Translation: converts language of nucleotides into language of amino acids- mRNA carries code from nucleus to cytoplasmo Protein cap acts like passport & recognition site to tell ribosomes where to begin- tRNA: bind free amino acids in the cytosol & deliver it to the ribosome to be added to a growing protein chaino Turns back and coils on itself to form an “L” o One loop is anticodon-complement to mRNAo First tRNA to bind to a ribosome is called initiator tRNA - Ribosomes: “reading machines” o Large & small subunits o Only come together when translating mRNAo 3 pocket for tRNA A-siteP-site  E-site- Three Stepso Initiation: mRNA through nuclear pore into cytosol to form a loop Leader sequence and small subunit bind on mRNA and slide until it finds start codon Anticodon binds with start codon and slides into P-site Large subunit joinso Elongation: tRNA arrives with another amino acide; binds to A-site and anticodon pairs with second codon of mRNA  Every time tRNA leaves E-site it goes to pick up another amino acid- Uses 1 ATP Not super preciseo Termination: reaches stop codon A-site binds a protein called a release factor Causes break away into cytosolo Making proteins for packing or export ER modifies and packages it One single mRNA is translated by 10-20 ribosomes at a time- Polyribosomeso Protein Processing & Secretion After sequencing often bound by an older protein called a chaperone- Guides it to fold in proper shape - Stress proteins or heat-shock protein Used in cytosol on a free ribosome Packaged in lysosome or secreted its docked to RER- Then send it to Golgi apparatus  Post-Translational modifications: chain folds back and 3 disulfide bridges are formed  RER then transport vesicles coated with clathrin Protein unloads into Golgi Complex  Addition modifications in GC Golgin Complex cisternae furthest from the RER binds a Gogli Vesicle containing final protein Some vesicles become lysosomes or secretory vesicleso Gene regulation- DNA Replication & The Cell Cycleo DNA Replication Double helix unwinds from histones Like a zipper DNA helicase opens one short segment of the helix at a time - Point where opened is replication fork  DNA Polymerase reads exposed bases and matches with complementary base pair - Each strand is copied by a different polymerase in opposite directions- Segments are joined by DNA Ligase- Semiconservative replication During replication new histones are made in cytoplasm, then transported into nucleuso Errors and Mutations Prevention of errors- Polymerase double checks  Mutations: change in DNA structure - Replication errors, environmental errors - Can be passed on- Doesn’t always cause noticeable changeo Cell Cycle: G1, S, G2, M G1: First gap phase- Between cell division and DNA replication- Synthesizes proteins, grows, accumulates material needed to replicate DNA- 8-10 hours S phase: Synthesis phase - Make duplicates of centrioles and all nuclear DNA - -6-8 hours G2: Second gap phase- Further growth, makes more organelles and synthesizes enzymes needed for cell division- Repairs errors in DNA