Unit 1 Notes
Unit 1 Notes Biosc0160
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Date Created: 02/09/15
Biology 2 Notes Chapter 12 The Cell Cycle Cell Theory all organisms are made of cells and all cells come from preexisting cells 0 Cell division new cells come by splitting old cells Single cell embryos grow into multicellular organisms o 2 Types of Cell Divisions 0 meiosis results in daughter cells that are genetically from each other and have 12 parents genes Production of sperm and egg gametes o mitosis genetic material is replicated Production of somatic cells Similarities of Mitosis and Meiosis o Cytokinesis division of cytoplasm o Reproduction 15 of life attributions How do Cells Replicate 0 Copy DNA 0 Separate copies 0 Divide cytoplasm Eukaryotic Cell Replication is Responsible for 0 Growth 0 Wound repair 0 Reproduction Asexual reproduction produces offspring genetically identical to parent Chromosome Info 0 Chromosome single long DNA wrapped around proteins called histones DNA encodes hereditary info Gene length of DNA that codes a particular protein or RNA 0 Chromatid each DNA copy in a replicated chromosome 2 chromatids are attached all the way down by cohesions When mitosis begins it is only attached at a centromere Called sister chromatids Chromatin DNA in quotloose statequot 0 Cell Cycle Phases 0 M Phase Dividing phase 0 lnterphase between phase no dramatic changes but it is when it grows prepares to divide and develops specialized funcUons o S phase part of interphase where replication of genetic material happens discovered with autoradiography OO Biology 2 Notes Gap Phases Discovery 0 Gap when DNA was not being copied cells divide organelles and increase size quot3939 r v J The cell double chemacquot the r clluplicated chromosomes for I V W airman making enyr ieeded 5 If quot remain quot 39 E 39itquot35395 if i n y in 5 a r g i 7 ERE ii s G Ha lEEIclh nFtherel chmmeecimes 39 i 19 duplicated by the Calluiar cements I quot E tluding the chromosomes are duplicated Gl i i e a Cell cycle arrest o 61 phase end of M and start of S o 62 phase end of S and start of M o Mitosis o interphase o prophase when chromosomes condense into compact structures formation of spindle apparatus structure that makes forces that 1 move replicated chromosomes during early mitosis and 2 pulls chromatids apart in late mitosis made up of microtubules polar microtubules extend from each spindle pole and overlap MTOC is a centrosome contains a pair of centrioles o prometaphase nuclear envelopes disintegrates microtubules attach to chromosomes at kinetochores microtubules that attach to them kinetochore microtubules kinesin and dynein walk chromosomes up microtubules o metaphase all chromosomes line up in middle of spindle metaphase plate held in place by astral microtubules that come from MTOCs and interact with proteins on cell membrane Biology 2 Notes 0 anaphase chromatids split into 2 daughter chromosomes and are pulled to opposite poles doubles of chromosomes 0 telophase nuclear envelope reforms around new chromosomes 0 cytokinesis How do Chromosomes Move in Anaphase o Spindle apparatus is made of microtubules which attach to kinetochores with positive ends 0 Kinetochore microtubules remain stationary during anaphase but shorten because tubulin subunits are lost from their plus ends As microtubules ends shrink back the chromosomes are pulled along Cytokinesis 0 Cell plate where the mid spindle was the vesicles fuse to form a attened saclike structure 0 Cleavage furrows ring of actin laments are bound to by myosin which uses ATP to slide the actin down 0 Bacterial Cell Replication o Binary fission basically same thing as M phase 0 Cell Cycle Variability 0 Different cells differ in length of 61 phase ln rapidly dividing cells g1 is eliminated Nondividing cells stuck in 61 g zero 0 Can differ because of environment Ex liver cells can start replicating slower once there is damage 0 Cell cycle regulatory molecules 0 MPF M phase promoting factor induces M phase 0 Made up of protein kinase catalyzes transfer of phosphate from ATP which can activate or deactivate cyclins protein kinase is only functional when bound to it 0 Result in cyclindependent kinase Cdk protein kinase subun o How is it turned on One spot on one side of Cdk activates and the other deactivates o How is it turned off Negative feedback Destroying speci c proteins 0 Cell Cycle Checkpoints 0 Critical point when cell cycle is regulated 0 Tumor without checkpoints the cells keep dividing and make a mass Passif o 61 Checkpoints Biology 2 Notes Cell size is good Nutrients are sufficient Social signals are present DNA is undamaged If it is p53 protein stops cycle until repaired which is known as apoptosis 0 Proteins like these are called tumor suopressors o 62 checkpoints Chromosomes have replicated successfully DNA is undamaged Activated MPF is present 0 M phase checkpoint Chromosomes have attached to spindle Chromosomes have segregated and MPF is present 0 Cancer disease caused by cells that cant stop dividing bad because they steal nutrients and space 0 2 types of defects make protein active that should be Ras prevent tumor suppressor genes p53 0 Tumors Wcancerous Metastasis gain ability to attach from original tumor and invade other tissues Benign not cancerous 0 Where does Cancer Start Gl checkpoint defects Prokaryotes go through 61 based on size Multicellular social control communicate as to bene t whole organisms Social Control 0 Based on growth factors small proteins that stimulate cell division In experiment cells only grew after serum liquid portion of blood that s not blood or remnants Cancerous cells don t need growth factors 0 How does 61 Checkpoint Work 0 E2F regulatory protein that triggers genes needed for S phase 0 Rb regulates E2F When bound together E2F doesn t work 0 How do Social Controls and Cell Cycle Checkpoints Fail 0 When cells divide without go ahead signal from growth factors Biology 2 Notes Gi cyclin is over produced 0 Excessive amounts of growth factors Cyclin production in absence of growth signals 0 Rb is defective Doesn t bind normally to E2F or doesn t exist Chapter 13 Meiosis Why Sex Why Meiosis o Sperm male g female GAMETES Combine in fertilization 0 Question how can the chromosomes of egg and sperm combine but in the end have the same as sperm egg Meiosis is nuclear division that leads to halving chromosomes number and produce egg sperm Chromosomes o 2 types sex chromosomes XY determine sex autosomes not sex chromosomes 0 homologous chromosomes same size and shape and carry same genes can be different versions of genes called alleles o karyotype and types of chromosomes present 0 ploidy can have more than 1 of each type of chromosome diploid 2 versions of each chromosome haploid 1 copy of each chromosomes 1 allele of each gene 0 Notation Haploid n of distinct types of chromosomes Ploidy n of complete chromosome sets Diploid 2n 2 chromosomes of each type moms and dads At beginning of meiosis there are 2 replicated chromosomes each with 2 sister chromatids in it 0 Overview of Meiosis o Meiosis 1 homologs in each chromosomes pair separate At end one of each type of chromosome Diploid 2n parent cell produces 2 haploid n cells still has two sister chromatids Reduction division reduction in chromosome number 0 Meiosis 2 sister chromatids from each chromosome separate At the end cells have 1 of each type of chromosome not replicated anymore Biology 2 Notes Gametogenesis formation of eggsperm cells Life cycle sequence of events from fertilization to product offspring Meiosis 1 o lnterphase uncondensed chromosomes replicate 0 Early Prophase 1 chromosomes condense spindle apparatus forms nuclear envelope begins to break down synapsis pairing of homologous chromosomes Synapsis homologous pairs come together by breaking then connecting DNA of 2 homologs at 1 or more spots M Tetrad 0 Late Prophase 1 chiasmata crossover points visible nuclear envelope broken down Often multiple chiasmata between nonsister chromatids Crossing over reciprocal exchanges between different homologs create nonsister chromatids that have both parental and maternal segments 0 Metaphase 1 migration of bivalents to metaphase plate is complete 0 Anaphase 1 homologs separate and begin moving to opposite poles of the spindle apparatus 0 Telophase 1 Cytokinesis chromosomes move to opposite poles of the spindle apparatus spindle apparatus dissembles Result chromosomes are mixed up because Crossing Over 0 Random Distribution during metaphase Metaphase 2 same as mitosis 0 Difference between Meiosis Mitosis o Homologs pairs don t pair in mitosis see pgs 24445 Crossing Over 0 Sister chromatids are held together full length by cohesions At prophase 1 chromosomes begin to condense o Homologs pair initiated by a break in the DNA which causes crossover o A network of proteins forms the synaptonemal complex which holds the 2 homologs tightly together 0 SC dissociates and homologs partially separate only held together at chiasmata Eventually broken but info has been exchanged Asexual vs Sexual Biology 2 Notes 0 Asexual doesn t involve gametes mitosis and offspring are clones 0 Sexual involves production and fusion of gametes How Meiosis Promotes Genetic Variation 0 Independent assortment when pairs of homologs line up during meiosis 1 and they separate a variety of results can happen Genetic recombination new combos of alleles o Crossing over new combos of alleles within a chromosome Genetic recombination o Fertilization and Genetic Variation 0 Even if you self fertilize there will still be differences hermaphrodites 0 Never really selffertilization its usually outcrossing another person which adds to variation 0 When Meiosis Goes Wrong 0 Ex miscarriage down syndrome trisomy extra copy 0 How do mistakes occur Nondisiunction Both homologs in meiosis 1 or both sister chromatids in meiosis 2 move to the same pole of the parent cell 0 Possible problems Trisomy n1 Monosomy n1 Triploidy 3 copies of every chromosome 0 Why do mistakes occur Problems attaching microtubules to kinetochores early in meiosis 1 Separating chromosomes that have a chiasma Patterns Smaller chromosomes sex 0 Formation of eggs Maternal eggs 0 Why Does Meiosis Exist o Asexual reproduction is more efficient because it doesn t produce males 0 Purifying selection hypothesis sexual individuals are likely to have some offspring that lack the deleterious alleles 0 Changing environment hypothesis If a new diseases came asexual beings would all be susceptible but if there is some variability some will be able to ght it off and continue the population Chapter 14 Mendel and the Gene Biology 2 Notes Chromosome theory meiosis causes the pattern of inheritance the hereditary factors called genes are located on chromosomes 0 Launched genetics branch of bio that focuses on the inheritance of traits Hereditary transmission of traits from parent to offspring Trait any characteristic of an individual height to membrane protein 0 Mendel s Experiment Background 0 Question what are the basic patterns in the transmission of traits from parent to offspring o Hypothesis At the Time Blending lnheritance moms and dads traits blend together to form offspring BLACK WHITE GREY Inheritance of Acquired Characters traits in parents are modi ed through use and past down Giraffes strain their next 0 Experiment Garden pea model organism used for research because it is practical and results will apply to others 0 Usually peas self fertilize has both male and female parts Mendel ddled with them to do cross fertilization so he could control them Mendel studied 7 different phenotypes observable traits First created a pure line creating identical offspring so he could later compare results with hybrids offspring that differ in 1 or more traits Mendel s Experiment with 1 Trait o Went against former hypothesis 0 Monohybrid cross mating between parents that carry 2 different determinants for the same trait o Explanation Wrinkled gene is recessive can be hidden Round gene is dominant phenotype is observed Biology 2 Notes 0 Reciprocal Cross set of mating s where moms and dads phenotype in initial cross are switched It is a check and if it shows the same results it doesn t matter where genes come from oNew hypothesis particularate inheritance o Hereditary determinants maintain their integrity from generation to generation Don t blend are all just there 0 Gene hereditary determinant for a traits Allele different versions of genes Genotype alleles found in an individual 0 Affects phenotype dominance and recessive affects this Principle of Sedredation o Explains 31 ratio 0 Gene pair must separate and go into different gametes each gamete contains 1 allele Homozvgous 2 copies of the same allele Heterozvgous 2 different alleles for genes in an individual 0 Mendel s Experiment with 2 Traits o Dihybrid cross mating between 2 individuals that are both heterozygous for 2 traits o Hypothesis Independent assortment alleles for color and shape would be transmitted independently CORRECT Dependent assortment alleles for color and shape would be transmitted together INCORRECT 0 Test Crosses Used to conform data by using a parent that contributes only recessive alleles to offspring to help determine the unknown genotype Mendel s Experiments Provided Framework based on o Segregation of paired genes into separate gametes 0 Independent assortment of genes that affect different traits Chromosome Theory of lnheritance Mendel s rules can be explained by meiosis Biology 2 Notes 0 Meiosis explains Principle of segregation the separation of alleles during anaphase of meiosis 1 is responsible Independent assortment if the alleles for genes are located on different chromosomes they assort independently of each other 0 Testing Chromosome Theory 0 Studied fruit ies Wild type most common phenotype red eyes Mutation heritable change from genes white eyes 0 Performed a reciprocal cross Found all female offspring had red eyes and males had white eyes l proved this mutation had to do with a sex chromosome 0 X linked inheritance and v linked inheritance sex linked inher ance o Autosomal inheritance genes on non sex chromosomes 0 Questions 0 What happens when genes are located on the same chromosome Linkage the tendency of some alleles of different genes to be inherited together when genes are on same chromosome Linked genes don t assort independently Crossing over helps make alleles on same chromosome not always stay together the further away the genes are from each other crossing over is more likely Forms a recombinant combination is different from their parents Genetic map diagram showing relative positions of genes on a chromosome 0 How many alleles can a gene have Multiple allelism existence of over 2 alleles for the same gene 0 Example ABO blood type 0 Creates over 2 distinct phenotypes polymorphic trait o Are alleles always dominant recessive Codominance simultaneous expression of phenotype associated with each allele of heterozygous Example AB blood type Incomplete dominance a phenotype that is in between 2 homozygous parents Biology 2 Notes 0 Example pink owers from red and white 0 Does each gene affect just one trait No pleiotropic a gene that in uences many traits Example FBNI affects height heart and chest shape in Marfan Syndrome o Is there more to phenotype than genotype Yes Environment temp moms womb Interactions between genes sometimes different genes work together to control a single trait Gene by gene interactions 1 trait in uenced by 2 allele from different genes 0 Can Mendel s principles explain traits that don t fall in distinct categories Discrete traits traits that are clearly different from each other Quantitative traits height continuously varying traits that don t fall in distinct categories 0 If many genes each contribute a small amount to the value of a quantitative trait than a normal distribution results for population Polygenic inheritance the transmission of quantitative traits each gene adds a small amount to value of phenotype 0 Human inheritance 0 Mode of transmission describes a trait as autosomal or sexlinked gives the type of dominance of the allele To learn they use a pedigree family tree Recessive vs Dominant o Recessive Individuals must be homozygous l if parents don t have trait they are heterozygous for that trait carrier 0 2 carriers 14 of offspring o dominant high chance of having it even if parents are homozygous and heterozygous Autosomal vs Sexlinked o Autosomal if equally found in men and women 0 X linked Recessive males often have it more than females 0 Usually skips a generation 0 most are recessive o ylinked not common Biology 2 Notes Chapter 15 DNA and Gene Synthesis and Repair 0 What are Genes Made of DNA or Protein 0 HersheyChase Experiment Studied a virus T2 which is made up of DNA and protein and watched it affect a cell During the infection the capsid exterior protein coat was left outside the cell Based experiment on the fact that proteins contain sulfur but no phosphorous and DNA contains phosphorous but no sulfur Saw what element was in the cells Answer DNA is hereditary material 0 Structure of DNA 0 Primary Deoxyribonucleotide contains deoxyribose sugar phosphate group nitrogenous base bonded by phosphodiester bonds Backbone made of sugar and phosphate groups Bases that project from backbone with directionality 0 Secondary Antiparallel strands twist Stabilized by AT GC complementary base pairing Hypotheses about DNA synthesis 0 Semiconservative replication parental strands of DNA separate and each could be used as a template for a daughter strand each daughter DNA would consist of one old and one new strand 0 Conservative replication bases temporarily turn outward so complementary strands could serve for an entirely new helix all at once result in an intact parental molecule and a brand new DNA molecule 0 Dispersive replication parental double helix were cut wherever 1 strand crossed over another and DNA was synthesized in short sections stretches of old DNA would be interspersed with new DNA down the length of each daughter strand Meselson Stahl Expeiment o Proved that replication was semiconservative DNA synthesis 0 DNA bolvmerase an enzyme there are several types that can only work in on direction by adding deoxyribonucleotides to only the 3 end of a growing DNA chain DNA synthesis proceeds in 5 3 direction Biology 2 Notes 0 DNA synthesis is an exergonic reaction because the monomers that are used are dNTPs and have high potential energy 0 Bidirectional occurs in 2 directions at the same time 0 Stages of Replication 0 Origin of replication a speci c sequence of bases where the replication bubble occurs Bacterial chromosomes one Eukaryotic multiple origins of replication 0 Helix Opening DNA helicase breaks the hydrogen bonds between the base pairs Single strand DNAbinding proteins SSBPs attach to the separated strands and prevent them from snapping back into the double helix Topoisomerase enzyme that cuts DNA allows it to unwind and rejoins it ahead of the advancing replication fork 0 Leading Strands o Lagging Strand Biology 2 Notes 0 The End Replication Problem 0 Telomere the region at the end of a eukaryotic chromosome 0 Problems arise because the lagging end is to short no DNA synthesis occurs after primer is removed This eventually results in the shortening of the chromosome so your losing deoxyribonucleotides every time o The End Replication Solution 0 Telomeres done contain genes they are made of stretches of bases Telomerase enzyme that catalyzes the synthesis of DNA from an RNA template adds DNA onto the end of the chromosome to keep it from getting shorter 0 Process End is unreplicated when the RNA primer is removed from the 5 end of the lagging strand a strand of parent DNA remains unreplicated Telomerase extends unreplicated end telomerase binds to the overhanging section of singlestranded DNA Telomerase adds deoxyribonucleotides to the end of the parent DNA extending it Again telomerase extends unreplicated end telomerase moves down the DNA strand and adds additional repeats Lagging strand is completed primase DNA polymerase and ligase then synthesize the lagging strand in the 5 3 direction which prevents the chromosome form shortening Biology 2 Notes 0 Telomerase Regulation Only active in a limited number of cell types Not really found in somatic cells only really cells that produce gametes Cancer cells have telomerase which helps them unlimitedly divide o Repairing Mistakes in DNA Synthesis 0 DNA polymerases are selective about the bases they add to a growing strand because Correct base pairings are energetically the most favorable These correct pairings have a distinct shape 0 DNA polymerase proofreads If the wrong base is added during DNA synthesis the enzyme pauses removes the mismatched deoxyribonucleotides then procedes o Mismatch repair Mismatch repair occurs when mismatched bases are corrected after DNA synthesis is complete 0 Nucleotide Excision Repair To x problems caused by chemical attack radiation or other events lt xes thymine dimers and many other types of damage that distort the DNA helix caused by UV Process 0 Error detection enzymes detect an irregularity in DNA structure and cut the damaged strand 0 Nucleotide excision an enzyme excises a stretch of nucleotides that includes the damage 0 Nucleotide repacement DNA polymerase lls in the gap in the 5 3 direction 0 Nucleotide linkage DNA ligase links the new and old nucleotides into a continuous strand Xeroderma Pigmentosum disease that makes you sensitive to UV rays Chapter 16 How Genes Work 0 gene expression the process of converting archieved info into molecule that do things in cells Beadle and Tatum o How to discover genes Knock out a gene by damaging it and then infer what the gene does by observing the phenotype Biology 2 Notes 0 Knockout loss of function null alleles alleles that don t function 0 One Gene One Enzvme Hvoothesis Each gene contains the info needed to make an enzyme Experiment 0 Exposed cells to radiation denatures DNA 0 Couldn t make enzyme to make pyridoxine there was no pyridoxine 0 N crassa cells can make their own arginine in a metabolic pathway 0 Genetic screen technique for picking certain types of mutants out of other mutants Found mutant that lacked arginine 0 Put them in different conditions growth showed lack in some conditions PROVED HYPOTHESIS CORRECT see gure 162 0 Follow up showed genes contain info for constructing all proteins 0 Basic DNA lnfo Pyrimidines Purines Thymine T Adenine A Cytosine C Guanine G Genetic Code Hypothesis DNA is only an information storage molecule and has to be read before being translated to proteins 0 Different combos of bases different amino acids 0 Indirect Path 0 How we knew cell structure 0 RNA acts as a link mRNA carries info from nucleus from DNA to site of protein synthesis RNA polymerase enzyme that synthesizes RNA according to sequence of bases on DNA 0 Central Doqma o Summarizes the ow of info in cells DNA RNA Proteins Sequencel sequence sequence 0 Transcription DNA mRNA copying hereditary information 0 Translation mRNA proteins using info in nucleic acids to synthesize proteins Genotypes Phenotypes see Fig 164 o Genotype sequence of bases in DNA Biology 2 Notes 0 Phenotype product of proteins produced 0 When alleles differ in DNA sequence proteins produced may differ Exceptions to the Central Dogma 0 Many genes code for RNA molecules that do not function as mRNAs not translated into proteins Some form parts of ribosome regulate which genes are expressed Info ows from RNA to DNA sometimes 0 Reverse transcriptase viral polymerase that synthesizes a DNA version of RNA genes Genetic Code the rules that specify the relationship between a sequence of nucleotides in DNA and RNA and the sequence of amino acids in a protein 0 Genetic quotwordquot Triplet code a 3 base code provides more than enough words for all 20 amino acids 0 Redundancy more than 1 triplet bases might speci c for the same amino acids 0 Codon a group of 3 bases that specify a particular amino acids 64 codons Messing Up Code 0 A single addition or deletion mutation throws the sequence of codons reading frame out of register 0 The only time functional proteins can be produced is when 3 bases were added or removed Start codon AUG signals protein synthesis should be at that point on the mRNA molecule Stop codon UAA UAGUGA signals protein is complete doesn t code for an amino acid Properties of the Code 0 Code is redundant all AA s except methionine and tryptophan are coded by more than 1 codon o Unambiguous a single codon never codes for more than 1 AA 0 Nonoverlapping once the ribosome locks into the rst codon it reads each separate codon one after another 0 Nearly universal with a few exceptions all codons specify the same AA in all organisms o Conservative when several codons specify the same AA the rst 2 bases in those in those codons are almost always identical Genetic code is NOT RANDOM Using the Code Biology 2 Notes 0 Predict the codons AA sequence encoded by a particular DNA sequence 0 Determine the set of mRNA and DNA sequences that would code for a particular sequence of AA 0 Mutation any permanent change in an organism s DNA create new alleles 0 Point mutation a single base change Missense mutation changes in nucleotide sequence that changes amino acid Silent change in nucleotide sequencer that doesn t change the amino acid Nonsense change in nucleotide sequence the results in an early stop codon Frameshift addition or deletion of a nucleotide o Chromosome Mutation Polyploidy anaploidy or mistakes in Chromosome segment can detach and lnversion segments are ipped Translocation attach to different chromosome Deletion segment of chromosome is lost Duplication additional copies are present 0 Mutations can be Bene cial Neutral Deleterious Chapter 17 Transcription RNA Processing and Translation 0 Transcription 0 RNA polymerase is the enzyme that starts translation Once an NTP matches a base on the DNA template is in place RNA polymerase forms a phosphodiester linkage from the mRNA and the new ribonucleoside monophosphate Template strand strand that is read by the enzyme Nontemplate coding strand matches the sequence of the RNA that is transcribed from the template strand RNA polymerase works in 5 3 direction but doesn t require a primer Phases of Transcription o Initiation Sigma must bind to RNA polymerase for it to work Sigma RNA polymerase core enzyme holoenzyme Biology 2 Notes When holoenzyme binds to DNA at promoters that can start transcription Differences can account for environmental changes 10 box the place that is centered about 10 bases from the point where bacterial RNA polymerase starts transcription 0 Downstream DNA that is in the direction RNA polymerase moves during transcription Upstream other direction 0 1 site places where transcription begins Initiation is complete when RNA polymerase extends the mRNA from the 1 site 0 Elongation All prominent channels and grooves of the enzyme are lled and ribonucleoside triphosphates enter and RNA exits 0 Termination Transcription stops when RNA polymerase transcribes a DNA sequence that functions as a transcription termination signal 0 Differences in Transcription in Eukaryotes o Eukaryotes have three polymerases RNA polymerase llllll o Promoters in eukaryotic DNA are more diverse TATA box 0 No Sigma Protein instead there is a basal transcription factors 0 Termination eukaryotic proteincoding genes involves a polylA signal 0 RNA Processing 0 The initial product of transcription is the primary transcript still not functional Called premRNA o lntrons v Exons lntrons sections of the primary transcript that aren t represented in nal product Biology 2 Notes script Exons expressed 3 o Splicing When introns are removed from growing RNA strand 0 Caps and Tails 0 Cap 5 cap added at the 5 end 0 Tail 3 end a polylAl tail 0 Product is a mature mRNA 0 Helps efficiency of translation and keeps RNA from getting hurt 0 RNA processing any modi cation splicing or captail needed to convert a primary transcript into m SplicedmRNA W a mature RNA Exon Exon Ribosomes spliced tran PROCESS anNPs SPL39CE L Exon 3 1 snRNPs bind to start of intron and an A base within the intron 2 snRNPS assemblle to form the spliceosome 3 Intron is cut loop forms Excised intron I 4 Intron Is release as a lariat exons ar ioined together criPt39 FIGURE 176 lntrons Are Splice d Out of the Primary Trans 0 Strong correlation between number of ribosomes and i rate of protein synthesis 0 Translation in Bacteria v Eukaryotes o Bacteria Translation starts before transcription ends Multiple ribosomes attach to each mRNA forming a polyribosome because there is no nuclear envelope 0 Eukaryotes Transcription and translation are separated o tRNA 0 Watson discovered this bridge between the amino acid and the mRNA 0 Structure CCA sequence at 3 end of each tRNA molecule offered a site for amino acid attachment Triplet anticodon set of ribonucleotides that forms base pairs with mRNA codon Lshaped maintains precise physical distance between anticodon and amino acid 0 How do amino acids attach to tRNA 3 Requirements 0 input of energy enzymes called aminoacyltRNA synthetases for each of 20 major amino acid there is different aminoacyltRNA synthetases he 51131 Splicil lg The P boar e ine 1 Once to for ceOSC prote mole 3 Thei with 4 The exon quen Splicing graded t As yc be splicr differen Curr actions molecul Catalyu bOZYme hyPOthl tant cat Biology 2 Notes 0 combo of tRNA molecule covalently linked to an amino acid is called an aminoacyl tRNA 20 amino acids 61 mRNA 4O tRNA because wobble hvpothesis many amino acids are speci ed by more than one codon codons for the same amino tend to have the same nucleotides for 12 but different for 3 0 Structure and Function of Ribosome 0 Translation begins when the anticodon of an aminoacyl tRNA binds to the codon Translation is complete when peptide bond forms 0 Ribosomes have 2 major parts Large subunit Small subunit 0 Ribosomes are many of up rRNA and proteins 0 3 slots in RNA A carries the amino acid P holds the growing polypeptide chain E when amino acid is about to leave the ribosome Stages 0 Initiation mRNA binding to small subunit The ribosome binding site Shine Daldarno Seduence binds to a complementary sequence in an RNA molecule in the small subunit of the ribosome helped by initiation factors Initiator aminoacyl tRNA binds to start codon Large subunit of ribosome binds completing ribosome assembly Translation can begin now 0 Elongation Incoming aminoacyl tRNA new tRNA moves into A site where its anticodon base pairs with the mRNA codon Peptidebond formation the amino acid attached to the tRNA in the P site is transferred to the amino acid of the tRNA in the A site Translocation the ribosome moves one codon down the mRNA with the help of elongation factors The tRNA attached to the polypeptide chain moves into the P site The A site is empty 0 Termination Biology 2 Notes Release factor binds to stop codon when the translocating ribosome reaches a stop codon a protein release factor lls the A site The release factor breaks the bond linking the tRNA in the P site to the polypeptide chain Polypeptide and uncharged tRNAs are released Ribosome subunits separate The subunits are ready to attach to the start codon of another message 0 Post Translational Modi cations 0 Folding Facilitated by molecular chaperones Chemical modi cations Ribosome and Enzyme or a Ribozyme o Ribozyme Biology 2 Notes
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