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JaydenGibbs,United States,Teacher
Published Date:19-07-2017
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BASICS ON BASICS ON MOLECULAR BIOLOGY MOLECULAR BIOLOGY Cell – DNA – RNA – protein Sequencing methods arising questions for handling the data, making sense of it next two week lectures: sequence alignment and genome assemblyCells  Fundamental working units of every living system.  Every organism is composed of one of two radically different types of cells: – prokaryotic cells – eukaryotic cells which have DNA inside a nucleus.  Prokaryotes and Eukaryotes are descended from primitive cells and the results of 3.5 billion years of evolution. 2Prokaryotes and Eukaryotes  According to the most recent evidence, there are three main branches to the tree of life  Prokaryotes include Archaea (“ancient ones”) and bacteria  Eukaryotes are kingdom Eukarya and includes plants, animals, fungi and certain algae Lecture: Phylogenetic trees, this topic in more detail 3All Cells have common Cycles  Born, eat, replicate, and die 4Common features of organisms  Chemical energy is stored in ATP  Genetic information is encoded by DNA  Information is transcribed into RNA  There is a common triplet genetic code – some variations are known, however  Translation into proteins involves ribosomes  Shared metabolic pathways  Similar proteins among diverse groups of organisms 5All Life depends on 3 critical molecules  DNAs (Deoxyribonucleic acid) – Hold information on how cell works  RNAs (Ribonucleic acid) – Act to transfer short pieces of information to different parts of cell – Provide templates to synthesize into protein  Proteins – Form enzymes that send signals to other cells and regulate gene activity – Form body’s major components 6DNA structure  DNA has a double helix structure which is composed of – sugar molecule – phosphate group – and a base (A,C,G,T)  By convention, we read DNA strings in direction of transcription: from 5’ end to 3’ end 5’ ATTTAGGCC 3’ 3’ TAAATCCGG 5’ 7DNA is contained in chromosomes In eukaryotes, DNA is packed into linear chromosomes In prokaryotes, DNA is usually contained in a single, circular chromosome 8 chromosomes  Somatic cells (cells in all, except the germline, tissues) in humans have 2 pairs of 22 chromosomes + XX (female) or XY (male) = total of 46 chromosomes  Germline cells have 22 chromosomes + either X or Y = total of 23 chromosomes Karyogram of human male using Giemsa staining ( 9RNA  RNA is similar to DNA chemically. It is usually only a single strand. T(hyamine) is replaced by U(racil)  Several types of RNA exist for different functions in the cell. tRNA linear and 3D view: 10DNA, RNA, and the Flow of Information ”The central dogma” Replication Transcription Translation Is this true? Denis Noble: The principles of Systems Biology illustrated using the virtual heart 11  Proteins are polypeptides (strings of amino acid residues)  Represented using strings of letters from an alphabet of 20: AEGLV…WKKLAG  Typical length 50…1000 residues Urease enzyme from Helicobacter pylori 12 Amino acids 13How DNA/RNA codes for protein?  DNA alphabet contains four letters but must specify protein, or polypeptide sequence of 20 letters. 3  Trinucleotides (triplets) allow 4 = 64 possible trinucleotides  Triplets are also called codons 14Proteins  20 different amino acids – different chemical properties cause the protein chains to fold up into specific three-dimensional structures that define their particular functions in the cell.  Proteins do all essential work for the cell – build cellular structures – digest nutrients – execute metabolic functions – mediate information flow within a cell and among cellular communities.  Proteins work together with other proteins or nucleic acids as "molecular machines" – structures that fit together and function in highly specific, lock-and-key ways. 15Genes  “A gene is a union of genomic sequences encoding a coherent set of potentially overlapping functional products”  A DNA segment whose information is expressed either as an RNA molecule or protein (folding) (translation) MSG … (transcription) 5’ 3’ … a t g a g t g g a … … t a c t c a c c t … 3’ 5’ 16 http://fold.itGenes & alleles  A gene can have different variants  The variants of the same gene are called alleles MSG … MSR … 5’ 5’ … a t g a g t g g a … … a t g a g t c g a … … t a c t c a c c t … 3’ … t a c t c a g c t … 3’ 17Genes can be found on both strands 5’ 3’ 3’ 5’ 18Exons and introns & splicing Exons 5’ 3’ 3’ 5’ Introns are removed from RNA after transcription Exons are joined: This process is called splicing 19Alternative splicing Different splice variants may be generated 5’ 3’ A C B 3’ 5’ A C B C B A C … 20