Microbial Genetics Structure and Function of Genetic Material The Regulation of Bacterial Gene Expression Mutation: Change in Genetic Material Genetic Transfer

Structure and Function of Genetic Material

To define Genotype and phenotype To describe the process of DNA replication To describe the process of Transcription and Translation

Genetics is the study of.. what genes are how genes carry information how their information is expressed how genes are replicated and passed to subsequent generations and other organisms Genetic is the science of heredity

Genes are make of DNA (except for some virus) DNA- deoxyribonucleic acid DNA is make up of nucleotides Nucleotide is composed ;

nitrogenous base sugars 2-deoxyribose (DNA) ribose (RNA) phosphate group

Nitrogenous bases- 4 different nucleic acid base Adenine (A) Guanine (G) Cytosine (C) Thymine (T) --Uracil (U) in RNA Genetic information is coded in the sequence of bases

Purine Pyrimidine

DNA double stranded helix each strand has a sugar-phosphate backbone; nitrogeneous base attaches to each sugar two strands are held together by hydrogen bonds between specific nitrogen bases A T - 2 hydrogen bonds G C - 3 hydrogen bonds bacterial DNA: 4 million bases; circular eukaryotic DNA: more condensed and associated with proteins and histones

Functions of DNA 1. Storage of genetic information 2. Self-duplication and inheritance 3. Expression of genetic message

Functions of DNA 1. Storage of genetic information Contain a stored record of instruction that determined all the heritable characteristics that an organism exhibits Contain the information for the specific order of amino acids in all protein that is synthesized by an organism

2.Self-duplication and inheritance contain information for its own replication DNA replication—allows genetic information to be transmitted from one cell to its daughter cells and from one individual to its offspring

3. Expression of genetic message Direct cellular activity The information in DNA must be used to direct the order by which specific amino acids are incorporated into a polypeptide chain

RNA RNA- ribonucleic acid different from DNA; DNA is double stranded, RNA is usually single stranded the 5 carbon sugar is ribose Uracil base instead of tymine

RNA in bacterial cells Messenger RNA (mRNA) - an RNA molecule that contains the genetic information necessary to encode a particular protein, from DNA to ribosomes, where proteins are synthesized. Messenger RNA (mRNA) - an RNA molecule that contains the genetic information necessary to encode a particular protein, from DNA to ribosomes, where proteins are synthesized. Ribosomal RNA (rRNA) -formed an integral part of ribosomes, the cellular machinery for protein synthesis Ribosomal RNA (rRNA) -formed an integral part of ribosomes, the cellular machinery for protein synthesis Transfer RNA (tRNA)- an adaptor molecule used in translation that have a specificity for both a particular amino acid and for one or more codon Transfer RNA (tRNA)- an adaptor molecule used in translation that have a specificity for both a particular amino acid and for one or more codon

Genotype and Phenotype Gene: sequence of nucleotides that codes for a functional product, usually a protein Genotype: genetic composition of an organism; information that codes for all the characteristics collection of genes, entire DNA Phenotype: actual expressed properties of an organism observable characteristic manifestation of genotype

Central Dogma of Genetics - one way transfer of genetic information from nucleic acid to protein (Replication) DNA RNAprotein translation reverse transcription DNA is copied (transcribed) to mRNA which is then translated to a sequence of amino acids to form proteins DNA is copied (transcribed) to mRNA which is then translated to a sequence of amino acids to form proteins transcription

Replication- synthesis of DNA using DNA as template Replication- synthesis of DNA using DNA as template DNA duplicate DNA duplicate product are 2 double helices, the two strand becoming 4 strands product are 2 double helices, the two strand becoming 4 strands Transcription-the synthesis of RNA using a DNA template (the transfer of information to mRNA) Transcription-the synthesis of RNA using a DNA template (the transfer of information to mRNA) Translations - the synthesis of protein using the genetics information in mRNA as a template. Translations - the synthesis of protein using the genetics information in mRNA as a template.

Information present as genetic code 3 (triplet) bases encoded a single amino acid triplet bases--- codon tRNA has anticodon which is complementary to the codon of mRNA

Prokaryotic and Eukaryotic genetics * In prokaryotes: no membrane separating chromosome from cytoplasm; translation can begin before transcription is complete * In prokaryotes: no membrane separating chromosome from cytoplasm; translation can begin before transcription is complete

In eukaryotes: chromosome in nucleus and ribosome in cytoplasm; transcription and translation are spatially separated Transcription occurs in nucleus, translation begins when mRNA enters cytoplasm genes split into 2 or more coding region (exons) noncoding region (introns) separating coding region exon and intron regions--primary transcript (pre- mRNA) remove introns functional mRNA

RNA processing in eukaryotic cells Exon Intron Exon Intron Exon DNA transcription by RNA polymerase Primary RNA transcript introns are removed (by ribozymes); exons are spliced mRNA transfer into the cytoplasm

Primary

DNA replication Two stand of DNA complementary- one strand can be the template of replication in bacteria, there is a single location in the chromosome where DNA synthesis is initiated-- origin of replication at the origin, DNA double helix opened up and the initiation of replication occurs on the 2 single strand

As replication proceed, the site of replication (replication fork), moves down the parental DNA. Called semiconservative replication-- each new DNA contains one original conserved strand and one new strand

DNA replication always proceed from 5’ phosphate to 3’ hydroxyl (always adding new nucleotide to the 3’-OH of the growing chain) The two DNA strand grow in different direction by forming 2 new strand 1.leading strand, synthesized continuously as DNA polymerase moves toward the replication fork. (DNA polymerase- an enzyme that synthesized a new strand of DNA)

2. lagging strand- DNA synthesis occurs discontinuously- about 1000 nucleotides as DNA polymerase moves away from the replication fork. -each short stretch of DNA--Okazaki fragment RNA primers (synthesized by RNA polymerase to provides a 3’ OH), needed to start synthesis of lagging strand DNA polymerase removes the RNA primers DNA ligase joins the newly made DNA fragment with the previous one.

DNA replication contd... DNA replication -accurate process DNA replication -accurate process Proofreading by DNA polymerase Proofreading by DNA polymerase In E. coli: synthesis is at 1000 nucleotides /sec at 37°C In E. coli: synthesis is at 1000 nucleotides /sec at 37°C

Transcription Synthesis of a complementary strand of RNA from a DNA template Synthesis of a complementary strand of RNA from a DNA template a strand of mRNA is synthesized using a specific gene-- a portion of DNA as template a strand of mRNA is synthesized using a specific gene-- a portion of DNA as template complementary RNA is synthesized from A,C,G,U which pair with the sense strand of DNA complementary RNA is synthesized from A,C,G,U which pair with the sense strand of DNA example, template DNA A T G C A T example, template DNA A T G C A T newly synthesized mRNA U A C G U A newly synthesized mRNA U A C G U A needs RNA polymerase and supply of DNA nucleotides needs RNA polymerase and supply of DNA nucleotides

Transcription process Only one of two DNA strands as template Only one of two DNA strands as template RNA polymerase binds at the promoter site RNA polymerase binds at the promoter site promoter- a site in DNA to which RNA polymerase can bind and begin transcriptionpromoter- a site in DNA to which RNA polymerase can bind and begin transcription assembled free RNA nucleotide into new chain- complementary base pair as a guide assembled free RNA nucleotide into new chain- complementary base pair as a guide

new RNA chain grows, RNA polymerase moves along the DNA RNA synthesis continues until reaches end-point of transcription which is the termination site (terminator) RNA polymerase and newly formed mRNA release from the DNA synthesis is from 5’--> 3’

Translation Process in which information in the mRNA is used to dictate the amino acid sequence of a protein Process in which information in the mRNA is used to dictate the amino acid sequence of a protein occurs at the ribosomes occurs at the ribosomes mRNA is read from 5’-->3’ direction mRNA is read from 5’-->3’ direction mRNA- codon (group of 3 nucleotide) mRNA- codon (group of 3 nucleotide)

specific amino acid attached to tRNA which carry the anticodon base-pairing between codon-anticodon results in specific amino acid being brought to the site for protein synthesis ribosomes moves along the mRNA strand as amino acid are attached to the growing strand (first amino acid joins to the seconds by a peptide bonds )

P-side (Peptide site) A- site (Acceptor site)

Genetic code Refers to the relationship among the base sequence of DNA, the corresponding codons of mRNA and the amino acid for which the codons code Refers to the relationship among the base sequence of DNA, the corresponding codons of mRNA and the amino acid for which the codons code Code is degenerate- amino acid are signaled by several alternative codon (20 amino acid, 64 possible codon, e.g. leu have 6 codon) Code is degenerate- amino acid are signaled by several alternative codon (20 amino acid, 64 possible codon, e.g. leu have 6 codon)

sense codon code for amino acid nonsense codon -do not code for amino acid, signal the end of protein molecule synthesis 64 codons; 61 sense; 3 nonsense/stop codon start codon is AUG (met) stop codon -UAA, UAG, UGA