MCB EXAM 2 Lecture 11 Ch 8 Objectives Define genetics genome chromosome gene genetic code genotype phenotype and genomics the science of heredity it includes the study of what genes are how they carry information how they are replicated and passed to subsequent generations of cells or passed between organisms and how their expression of their information within an organism determines the particular characteristics of that organism the genetic information in a cell includes chromosomes and plasmids structures containing DNA that physically carry hereditary information the chromosomes contain Genetics genome chromosome the genes gene segments of DNA except in some viruses in which they are made of RNA that code for functional products genetic code sequence of a protein genotype the set of rules that determines how a nucleotide sequence is converted into the amino acid an organism s genetic make up the information that codes for all the particular characteristics of an organism Represents potential properties but not the properties themselves refers to the actual expressed properties such as an organisms ability to perform a particular chemical reaction Is the manifestation of genotype phenotype genomics the sequencing and molecular characterization if genomes Describe how DNA serves as genetic information DNA replication makes it possible the flow of genetic information from one generation to the next The DNA of a cell replicates before cell division so that each offspring cell receives a chromosome Describe DNA replication RNA transcription and protein translation In DNA replication one parental double stranded DNA molecule is converted to two identical identical to the parents daughter molecules Because the bases along the two strands of double helical DNA are complementary one strand can act as a template for the production of the other strand DNA rep requires the presence of several cellular proteins that direct a particular sequence of events 1 enzymes unwind the parental double helix 2 proteins stabilize the unwound parental DNA 3 the leading strand is synthesized continuously by DNA polymerase 4 the lagging strand is synthesized discontinuously RNA polymerase synthesizes a short RNA primer which is then extended by DNA polymerase 5 DNA polymerase digests RNA primer and replaces it with DNA 6 DNA ligase joins the discontinuous fragments of the lagging strand energy for DNA rep is supplied from the nucleotides which are actually nucleoside triphosphates genetic information in DNA is copied or transcribed into a complementary base sequence of RNA transcription RNA is the synthesis of a complementary strand of RNA from a DNA template 1 RNA polymerase binds to the promoter and DNA unwinds at the beginning of a gene 2 RNA is synthesized by complementary base pairing of free nucleotides with the nucleotide bases on the template strand of DNA 3 the site of synthesis moves along DNA DNA that has been transcribed rewinds 4 transcription reaches the terminator 5 RNA and RNA polymerase are released and the DNA helix re forms the process allows the cell to produce short term copies of genes that can be used as the direct source of information for protein synthesis Translation takes place in the nucleus in eukaryotes 1 components needed to begin translation come together 2 on the assembled ribosome a tRNA carrying the first amino acid is paired with the start codon on the mRNA The place where this first tRNA sits is called the P site A tRNA carrying the second amino acid approaches 3 the second codon of the mRNA pairs with a tRBA carrying the second amino acid at the A site The first amino acid joins to the second by a peptide bond This attaches the polypeptide to the tRNA in the P site 4 the ribosome moves along the mNA until the second tRNA is in the P site The next codon to be translated is brought into the A site The first tRNA now occupies the E site 5 the second amino acid joins to the third by another peptide bond and the first tRNA is released from the E site polypeptide 6 the ribosome continues to move along the mRNA and new amino acids are added to the 7 when the ribosome reaches a stop codon the polypeptide is released 8 Finally the last tRNA is released and the ribosome comes apart The released polypeptide carries the coded information making specific proteins from DNA to ribosomes where proteins are forms a new protein Describe functions of mRNA rRNA and tRNA mRNA synthesized rRNA tRNA the central component of the ribosome it make up the ribosome along with other proteins and provides a mechanism to decode mRNA and interact with tRNA during translation recognize specific codons and transports the required amino acids based on the triplet codon Explain the regulation of gene expression in bacteria by operon lactose into the cell Francois Jacob and Jacques Monod formulated this general model in 1961 to account for the regulation of protein synthesis based their models on studies of the induction of enzymes of lactose catabolism in E coli B galactoside splits the substrate lactose into glucose and galactose lac permease involved in the transport of lactose into the cell transacetylase metabolizes certain disaccharides other than lactose the genes for the three enzymes in lactose uptake and utilization are next to each other on the bacterial chromosome and are regulated together these genes which determine the structure of proteins are called structural genes to distinguish them from an adjoining control region on the DNA when lactose is introduced into the culture medium the lac structural genes are all transcribed and translated rapidly and simultaneously how regulation occurs in the control region off the lac operon are 2 relatively short segments of DNA the promoter is the region of DNA where RNA polymerase initiates transcription the operator acts as a stop or go signal for transcription of the structural genes a set of operator and promoter sites and the structural genes they control define an operon thus the combo of the 3 lac structural genes and the adjoining control regions is called the lac operon A regulatory gene called the I gene encodes a repressor inhibits gene expression and decreases the synthesis of enzymes protein that switches inducible and repressible operons on or off The lac operon is an inducible operon In the absence of lactose the repressor binds to the operator site thus preventing transcription if lactose is present the repressor binds to a
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