Arrangement of Genes PDF

Arrangement of Genes Icolyn Amarakoon, MPhil, PhD Email: [email protected]  OBJECTIVES Explain in molecular terms what is meant by a gene and the variations of the standard gene Discuss the importance and relationship between genome size and organism complexit...

Arrangement of Genes Icolyn Amarakoon, MPhil, PhD Email: [email protected]  OBJECTIVES Explain in molecular terms what is meant by a gene and the variations of the standard gene Discuss the importance and relationship between genome size and organism complexity Describe the arrangement (and expression) of prokaryotic and eukaryotic genes Describe the types and functions of gene sequences in genomes First things first…FRIENDLY ADVICE  4 Structure and Function of DNA & RNA  5 The Central Dogma of Molecular biology  The flow of genetic information: DNA → RNA → Protein DNA REPLICATION TRANSCRIPTION TRANSLATION A gene is expressed in two steps: ▫ DNA is transcribed to RNA ▫ RNA is translated into protein  6 Significance Life depends on the ability of cells: ▫ to store, retrieve and translate the genetic instructions required to make and maintain a living organism. This hereditary information is passed on ▫ from a cell to its daughter cells at cell division, ▫ from one generation of an organism to the next through the organism's reproductive cells.  7 Relevance These instructions are stored within every living cell as its genes, the information- containing elements that determine the characteristics of a species as a whole and of the individuals within it.  8 Components of Nucleic acids Ribonucleic Acid: Deoxyribonucleic Acid: DNA RNA is the genetic material that is the hereditary material transcribes DNA's in humans instructions and translates these instructions to proteins DNA and RNA are polymers [polynucleotides] Monomer unit is a nucleotide.  9 Nucleotide A nucleotide consists of: ▫ a 5-carbon sugar (pentose) – deoxyribose for DNA and ribose for RNA ▫ a purine or a pyrimidine base containing nitrogen attached to the sugar ▫ and a phosphate group.  10 5-carbon sugar (Pentose)  11 Nitrogen bases  12 Nitrogen bases  13 Nucleotide Pentose ring  14 RNA: Ribonucleic Acid Chemically, RNA is very similar to DNA. There are some main differences: ▫ – RNA uses ribose instead of deoxyribose in its backbone. ▫ – RNA uses the base Uracil (U) instead of Thymine (T). U is also complementary to A. ▫ – RNA tends to be single-stranded. Functional differences between RNA and DNA ▫ – DNA single function, RNA many functions Example of types of RNA: mRNA, tRNA, rRNA  15 Components of Nucleic Acids  16 DNA & RNA backbone DNA/RNA backbone a polymer with an alternating sugar-phosphate sequence. The deoxyribose sugars are joined at both the 3'-hydroxyl and 5'-hydroxyl groups to phosphate groups in ester links, also known as "phosphodiester" bonds  17 Discovery of DNA Structure One of the most important discoveries in biology Good illustration of science in action: ▫ Missteps in the path to a discovery ▫ Value of knowledge ▫ Value of collaboration ▫ Cost of sharing your data too early  18 Watson and Crick  19 Franklin and Wilkins  20 DNA Helix Axis DNA is a double stranded macromolecule. Two polynucleotide chains, held together by weak bonds, form a DNA molecule  21 Features of the DNA Double Helix Two DNA strands form a helical spiral, winding around a helix axis in a right-handed spiral The two polynucleotide chains run in opposite directions  22 Features of the DNA Double Helix The sugar-phosphate backbones of the two DNA strands wind around the helix axis The bases are on the inside of the helix, stacked like the steps of a spiral staircase.  23 BASE PAIRS RULES Adenine always base pairs with Thymine (or Uracil if RNA) ▫ A’ forms 2 hydrogen bonds with T on the opposite strand Cytosine always base pairs with Guanine. ▫ G’ forms 3 hydrogen bonds with C on the opposite strand There is exactly enough room for one purine and one pyrimidine base between the two polynucleotide strands of DNA.  24 The standard A=T and G≡C base pairs have very similar geometries and there is exactly enough room for one purine and one pyrimidine base between the strands of DNA. Incorrectly paired bases can exclude them from the active site (Blue shade)  25 Genetic code The nucleotide sequence of the mRNA is composed of four different nucleotides whereas a protein is built up from 20 amino acids. To allow the four nucleotides to specify 20 different amino acids, the nucleotide sequence is interpreted in codons, groups of three nucleotides. These codons have their corresponding anticodon in the tRNA. each anticodon is linked to one particular amino acid. each codon specifies one amino acid. This is referred to as the genetic code  26 THE GENETIC CODE  27 The Central Dogma of Molecular biology  The flow of genetic information : DNA → RNA → Protein DNA REPLICATION TRANSCRIPTION TRANSLATION A gene is expressed in two steps: ▫ DNA is transcribed to RNA ▫ RNA is translated into protein How genes and chromosomes relate  29 What is a chromosome? In the nucleus the DNA molecule is packaged into thread-like structures called chromosomes. Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing. Chromatin- unwound DNA Identical chromatids short p arm centromere long q arm telomere  chromosomes contain DNA, histones and other proteins that affect gene expression (which proteins and how many proteins are synthesized from a given gene).  Chromosome Pairing nucleus of every human cell contains 23 pairs of chromosomes, [total 46 chromosomes] 22 pairs of non-sex (autosomal) chromosomes and one pair of sex chromosomes ▫ each pair consists of one chromosome from mother and one from father  Mitochondrial chromosome each mitochondrion contains its own circular chromosome ▫ chromosome contains DNA (mitochondrial DNA) that codes for some, of the proteins that make up that mitochondrion. ▫ Mitochondrial DNA usually comes only from the mother  Chloroplast DNA Chloroplasts have their own DNA, (ctDNA or cpDNA). It is also known as the plastome. chloroplasts have their entire chloroplast genome combined into a single large circular or linear DNA molecule, [120,000–170,000 bp]  Chloroplast DNA chloroplast DNAs contain two inverted repeats, separate a long single copy section (LSC) from a short single copy section (SSC). The inverted repeats vary wildly in length, ranging from 4,000 to 25,000 base pairs long The inverted repeat regions are highly conserved among land plants,  Prokaryotes {Greek for 'before nucleus‘} lack a discrete nucleus , thus chromosomes not enclosed by a separate membrane. ▫ chromosome is located in a region of the cell cytoplasm known as the nucleoid.  Prokaryotic chromosomes In addition to the main chromosome, bacteria are also have extra- chromosomal genetic elements called plasmids. ▫ small circular DNA molecules contain genes that are not essential to growth or reproduction What is Genome ? Genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA. Comparative genome sizes of organisms Genome Size Discrepancy between genome size (DNA content) and genetic complexity (coding potential) ‘Excess’ DNA compared to coding potential Due to presence of non-coding regions, genome size not equated to complexity Increased amount of non-coding in larger genomes Characterizing Genomes In general, eukaryotic genomes are larger and have more genes than those of prokaryotes ▫ However, the complexity of an organism is not necessarily related to its gene number The Human Genome Project found fewer genes than expected -Initial estimate was 100,000 genes -Number now appears to be about 19,000-25,000 Genome size of Eukaryotes  C-Value: Eukaryotic genome sizes vary The haploid genome size of eukaryotes, called the C-value, varies enormously: Small genomes include: ▫ Encephalotiozoon cuniculi (2.9 Mb) : variety of fungi (10-40 Mb) ▫ Takifugu rubripes (pufferfish)(365 Mb):same number of genes as other fish or as the human genome, but 1/10th the size Large genomes include: ▫ Pinus resinosa (Canadian red pine)(68 Gb) ▫ Protopterus aethiopicus (Marbled lungfish)(140 Gb) ▫ Amoeba dubia (amoeba)(690 Gb)  C-Value Paradox The range in C-values does not correlate well with the complexity of the organism. This phenomenon is called the C-value paradox. We would expect that the more complex the organism, the larger the genome size. Thus, a linear relationship between genome size and organism complexity. This idea appears to make sense: ▫ the more complex the organism is, the more genetic information it needs (larger C value) ▫ In smaller organisms (viruses, bacteria) there is no room for excess DNA (smaller C value) Species and Common Name Estimated Total Size of Genome Estimated Number of (bp)* Protein-Encoding Genes* Saccharomyces cerevisiae (unicellular 12 million 6,000 budding yeast) Trichomonas vaginalis 160 million 60,000 Plasmodium falciparum (unicellular 23 million 5,000 malaria parasite) Caenorhabditis elegans (nematode) 95.5 million 18,000 Drosophila melanogaster (fruit fly) 170 million 14,000 Arabidopsis thaliana (mustard; thale 125 million 25,000 cress) Oryza sativa (rice) 470 million 51,000 Gallus gallus (chicken) 1 billion 20,000-23,000 Canis familiaris (domestic dog) 2.4 billion 19,000 Mus musculus (laboratory mouse) 2.5 billion 30,000 Homo sapiens (human) 2.9 billion 20,000-25,000 C-value Paradox Sequence complexity is not the same as length. ▫ Complexity is the number of base pairs of unique, i.e. nonrepeating, DNA. This is the C-value Paradox, that in the most complex organisms, there doesn’t appear to be the expected relationship between complexity and genome size  Prokaryotic genomes compact compared with eukaryotes, they lack introns genes are expressed in groups known as operons.  General structure of an operon An operon is made up of 4 basic DNA components: Promoter – nucleotide seq. enables a gene to be transcribed Regulator- genes control the operator gene Operator- segment of DNA that a repressor binds to Structural genes- genes co-regulated by the operon Eukaryotic genome structure General Structure of a Gene  General structure of a gene Start site: start site for transcription. Promoter: 'upstream' of the gene (toward the 5' end). Not transcribed into mRNA, transcription factors bind to the promoter region and assist in the binding of RNA polymerases. Enhancers: Some transcription factors (called activators) bind to regions called 'enhancers' that increase the rate of transcription. Silencers: Some transcription factors (called repressors) bind to regions called 'silencers' that depress the rate of transcription.  Genomes Prokaryotic Genomes Eukaryotic Genomes The genome sizes are variable, The genomes are compact; their entire DNA is functional. divided into multiple linear chromosomes; each The sizes ranges from about 1 million to 10 contains a DNA million base pairs of DNA not organized into operons; one mRNA makes one usually in a single, circular chromosome protein. Genes are clustered together and arranged Many genes (most human genes) are split; introns into operons, where they are transcribed as removed and the exons spliced to make a mature a single mRNA that is translated to make all mRNA. the proteins in the operon. The multiple exons can be spliced in different The size of prokaryotic genomes is directly ways to make multiple mRNAs and multiple related to their metabolic capabilities – the proteins from a single gene (alternative splicing). more genes, the more proteins and enzymes The majority of human genes can be spliced in two they make. or more different ways. Therefore, the actual number of human proteins far exceeds the number of protein-coding genes.  55 What is a Gene? A gene is the basic physical and functional unit of heredity. ▫ It is a sequence of nucleotides along a DNA strand - with 'start' and 'stop' codons and other regulatory elements - that specifies a sequence of amino acids that are linked together to form a protein Every person has two copies of each gene, one inherited from each parent Finding Genes Genes are identified by open reading frames (ORFs) ▫ An ORF begins with a start codon and contains no stop codon for a distance long enough to encode a protein Sequence annotation ▫ The addition of information, such as ORFs, to the basic sequence information Open Reading Frames (ORFs) Sample sequence showing three different possible reading frames. Start codons are highlighted in purple, and stop codons are highlighted in red. Sequence annotation  GENE The length of the gene determines the length of the protein the gene codes for Humans have about 20,000 to 23,000 genes. Protein synthesis is controlled by genes, which are contained on chromosomes.  Arrangement of Genes Genes are arranged linearly along the DNA of chromosomes. ▫ genotype is a person’s unique combination of genes. ▫ karyotype is the full set of chromosomes in a person’s cells ▫ phenotype is the entire physical, biochemical, and physiological makeup of a person—ie, how the cell (and thus the body) functions Arrangement of Genes Each gene has a specific location (locus) ▫ the same on each of the 2 homologous chromosomes genes that occupy the same locus on each chromosome of a pair (one inherited from the mother and one from the father) are called alleles. identical alleles for gene is homozygosity; non-identical alleles is heterozygosity  Gene Components Genes consist of exons and introns. ▫ Exons code for amino acid components of the final protein. ▫ Introns contain other information that affects control and speed of protein production.  Gene Structure: Gene Family Gene family: set of genes in a genome that encode related or identical proteins or RNAs ▫ genes that are involved in a particular structure or function can be deemed as a family of genes, eg DNA pol and RNA pol involved in DNA replication and transcription. How are gene families organized? ▫ In many genomes gene families either dispersed or organized as gene clusters Gene organization in the alpha and beta globin gene families  Globin Gene Families Globin genes expressed in 3 different stages: embryonic, foetal and adult stages of development  Gene Structure: Gene Family Gene superfamily: A group of distantly related genes, often sharing similarities across only part of their sequences Eg: Immunoglobulin (Ig) superfamily -IgG, IgA, IgE, IgD, IgI  Immunoglobulin (Ig)gene superfamily T-cell receptors (TCR) and the class I and class II MHC molecules (1) are basically similar genes are located on different chromosomes, the gene products form functional complexes with each other. Others, such as the V, D, and J gene segments of all antigen receptors and their genes for the C domain lie close together in gene clusters  Gene Structure: SuperGene Family Excisions are made depending on which Ig protein is needed from the mRNA  Gene Structure: Gene Clusters arise from tandem duplications ▫ during DNA replication ▫ meiotic recombination (result in copies of a given DNA region), duplicates can moved from a cluster onto another chromosome via translocations between two chromosomes; thus dispersing a gene family throughout the genome How are gene clusters formed? Unequal crossing-over during meiosis ▫ mispairing of chromosomes ▫ rearranges gene clusters ▫ at sites where genes exist as clusters and the end result is accumulation of duplications and deletions eg. deletion of various globin genes Beta Globin Gene Cluster  Gene Structure: Tandem Clusters identical copies of the same gene that occur near each other. ▫ transcribed near each other. ▫ transcribed simultaneously, [increasing the amount of mRNA available for protein synthesis] Tandem clusters also include genes that do not encode proteins, such as clusters of rRNA genes. Short Tandem Repeats [STR]  Non-coding DNA in humans Segmental duplications (5% of genome) ▫ long nucleotide sequences that have been duplicated and moved either within a chromosome, or to a non- homologous chromosome.  Non-coding DNA in humans Introns (24% of genome) ▫ non-coding regions that make up most of each human gene. the DNA sequence in a Eukaryotic gene has both: ▫ exons : the sequences in the DNA molecule that code for the amino acid sequences of corresponding proteins. ▫ intron: that is not translated into a protein. Transcription: DNA – preRNA - mRNA  Splicing Outline Introns are transcribed along with exons in the primary transcript Introns are removed as the exons are spliced together  Alternative Splicing But how can 25,000 human genes encode three to four times as many proteins? Alternative splicing - yields different proteins with different functions  Alternative Splicing Patterns Alternative splicing of the same pre-mRNA gives rise to very different products ▫ Alternative splicing patterns occur in over half of human genes ▫ Many genes have more than 2 splicing patterns, some have thousands  Non-coding DNA in humans Pseudogenes (2% of genome) ▫ normal protein-coding genes that may have lost their function due to mutations. The DNA sequence is nearly identical to that of a functional gene, but contains one or more mutations, making it non-functional.  81 Pseudogenes and Vitamin C GULO In most mammals Gene 1 Gene 2 gene3 Gene Enzyme 1 Not so in primates… Enzyme 2 Enzyme Gulo Enz3 A B C Vitamin C D Vitamin C Portion of Working GULO Gene in Rat: Matching GULO Pseudogenes in 4 Primates Note Deletion  Non-coding DNA in humans Structural DNA (20% of genome) ▫ remains tightly coiled throughout the cell cycle and tends to be localized near the centromeres and telomeres.  Non-coding DNA in humans Simple sequence repeats (3% of genome) ▫ composed of a short sequence of nucleotides that is repeated thousands of times. Eg AAA, ATATATAT, CGTCGTCGT etc.. ▫ Scattered throughout genome. ▫ Different people may have different numbers of these repeats at different loci (think of different copy numbers as alleles). ▫ Microsatellite Markers: Tandem repeats of a 2 bp sequence such as CA. ▫ Minisatellite Markers (aka Variable Number Tandem Repeats- VNTRs):Tandem repeating units of 15-100 bp.  Microsatellites as molecular markers Use PCR primers that are complementary to single copy sequences flanking microsatellites to amplify microsatellite-containing region. Depending on number of microsatellite repeats, will get different lengths PCR products (many different possible alleles, not just two)  VNTRs used to generate DNA fingerprints Since some repeated sequences are present at multiple places in genome, a single probe can detect multiple VNTRs on one genomic Southern blot. 3 VNTR loci DNA fingerprint VNTR fragments from an individual’s genome.  Non-coding DNA in humans Transposable elements or transposons (45% of genome) ▫ segments of DNA that move around from one location to another within the genome.  the transposon is duplicated and the copy moves to a new location or the transposon is removed from its original location and is then inserted in a new location.  Transposons:interspersed repeats Main types: ▫ long interspersed elements (LINEs) ▫ short interspersed elements (SINES) eg Alu family ▫ Long Terminal Repeats (LTRs) :Repeats on the same orientation on both sides of element e.g. ATATATNNNNNNNATATAT ▫ DNA transposons: Inverted repeats on both sides of element e.g. ATGCNNNNNNNNNNNCGTA  Mendel’s Laws: Chromosomes Locus : physical location of a gene on a chromosome Alleles: Homologous pairs of chromosomes often contain alternative forms of a given gene. Different alleles of the same gene segregate at meiosis I Alleles of different genes assort independently in gametes Genes on the same chromosome exhibit linkage- inherited together  Types of Gene Mapping Genetic Mapping: a genetic map must show the positions of distinctive features. In a geographic map these markers are recognizable components of the landscape, such as rivers, roads and buildings. It is based on the use of genetic techniques to construct maps showing the positions of genes and other sequence features on a genome. ▫ Genetic techniques include cross-breeding experiments or, in the case of humans, the examination of family histories (pedigrees)  Types of Gene Mapping Physical Mapping: A physical map is a representation of the physical distance, in nucleotides, between genes or genetic markers. It present the intimate details of smaller regions of the chromosomes (similar to a detailed road map)  Genetic Maps A genetic map is simply a representation of the distribution of a set of loci within the genome. ▫ describes the order of markers along the chromosomes of a genome. Gene Mapping Gene mapping determines the order of genes and the relative distances between them in map units using genetic markers ▫ 1 map unit = 1 cM (centimorgan) Genetic Mapping- Genetic Markers A genetic marker is a gene or sequence on a chromosome that co- segregates (shows genetic linkage) with a specific trait. ▫ The generation of genetic maps requires markers, just as a road map requires landmarks (such as rivers and mountains). good genetic marker is a region on the chromosome that shows variability or polymorphism (multiple forms) in the population. Genetic Mapping- Genetic Markers Genetic markers used in generating genetic maps ▫ restriction fragment length polymorphisms (RFLP), ▫ variable number of tandem repeats (VNTRs), ▫ microsatellite polymorphisms ▫ single nucleotide polymorphisms (SNPs) DNA of every individual give a unique pattern of bands when cut with a particular set of restriction endonucleases (individual’s DNA “fingerprint.”) Uses of Gene Mapping Identify genes responsible for diseases. ▫ Heritable diseases ▫ Cancer Identify genes responsible for traits. ▫ Plants or Animals ▫ Disease resistance ▫ Meat or Milk Production Gene Mapping genes that are closer together are more likely to be inherited together looking at the patterns of inheritance one can figure out the genetic distance between different genes Modern genetic maps use smaller markers, often changes in a single nucleotide (say an A turning into T or a C turning into a G) called a single nucleotide polymorphism (or SNP) between different individuals of the same species  Gene Mapping Recombination results from crossing-over between linked alleles. Recombination changes the allelic arrangement on homologous chromosomes  Genetic-linkage mapping Genetic-linkage maps illustrate the order of genes on a chromosome and the relative distances between those genes. ▫ by tracing the inheritance of multiple traits, such as hair color and eye color, through several generations. Genetic map of chr.9 of the corn plant (Zea mays) with distances in centimorgans(cM) Physical Maps uses molecular biology techniques to examine DNA molecules directly in order to construct maps showing the positions of sequence features, including genes. provides detail of the actual physical distance between genetic markers including the number of nucleotides Physical Maps Three methods used to create a physical map: Cytogenetic mapping, ▫ Direct binding of probes to chromosome ▫ Breakpoints in disease Radiation hybrid mapping, ▫ chromosomes are broken into several segments with X-rays Nucleotide sequence mapping. ▫ complete or partially sequenced organisms  Cytogenetic Mapping uses information obtained by microscopic analysis of stained sections of the chromosome. ▫ It shows banding pattern observed under light microscopy of stained chromosomes. It is possible to determine the approximate distance between genetic markers using cytogenetic mapping, but not the exact distance (number of base pairs)  Cytogenetic Mapping: Philadelphia Chromosome Chronic myelogenous leukemia (CML) is characterized by a reciprocal translocation between chromosomes 9 and 22 that produces the Philadelphia chromosome. Invariably there is disease progression, with loss of the capacity for terminal differentiation by the hematopoietic stem cell, resulting in an acute leukemia  Nucleotide sequence mapping Physical maps give the physical, DNA-base-pair distances from one landmark to another. ▫ maps are based on the direct analysis of DNA. ▫ Physical distances between and within loci are measured in basepairs (bp), kilo-basepairs (kb) or megabasepairs (mb). GENOME MAPPING Both genetic linkage maps and physical maps are required to build a complete picture of the genome. Having a complete map of the genome makes it easier for researchers to study individual genes. ▫ Genetic maps provide the outline ▫ physical maps provide the details. It is easy to understand why both types of genome mapping techniques are important to show the big picture. ▫ Information obtained from each technique is used in combination to study the genome. Gene Expression and Regulation Gene expression is the process by which the genetic code - the nucleotide sequence - of a gene is used to direct protein synthesis and produce the structures of the cell.  Activation of Gene External signals can activate genes. Gene expression are controlled by external signals such as steroid hormone (that can enter the cell) and protein growth factors. Steroid hormones are lipid soluble and bind receptor proteins inside the cell. ▫ Steroid/receptor complexes can act as transcription factors binding steroid response elements in the DNA.  Activation of Gene Protein growth factors: interact with cell surface receptors to generate an intracellular signal. ▫ Peptide/proteins bind receptors in the cell membrane and signal transduction mechanisms cause the activation or inactivation of transcription factors (by phosphorylation of a transcription factor or release from a cytoplasmic complex).  Gene expression depends on multiple factors: Epigenetic factors: Factors that affect gene expression without changing the genome sequence. ▫ DNA methylation tends to silence a gene. ▫ Histones resemble spools around which DNA winds. Histone modifications such as methylation  Gene expression Gene expression involves two main stages ▫ Transcription: the production of messenger RNA (mRNA) by the enzyme RNA polymerase, and the processing of the resulting mRNA molecule. ▫ Translation: the use of mRNA to direct protein synthesis, and the subsequent post-translational processing of the protein molecule. Structural Gene Exons: Exons code for amino acids which determine the amino acid sequence of the protein. Introns: Introns are portions of the gene that do not code for amino acids, and are removed (spliced) from the mRNA molecule before translation. Gene Control Regions Start site: start site for transcription. Promoter: 'upstream' of the gene (toward the 5' end). Not transcribed into mRNA. Transcription factors bind to the promoter region and assist in the binding of RNA polymerases. Enhancers:. Some transcription factors (called activators) bind to regions called 'enhancers' that increase the rate of transcription. Silencers: Some transcription factors (called repressors) bind to regions called 'silencers' that depress the rate of transcription. Gene Control Regions: Promoter There are two types of promoters which are: Basal promoter or core promoter -These promoters reside within 40bp upstream of the start site. These promoters are seen in all protein coding genes. Gene Control Regions: Promoter Upstream promoters - These promoters may lie up to 200bp upstream of the transcriptional initiation site. The structure of this promoter and the associated binding factors keeps varying from gene to gene. Gene Control Regions: Enhancer Enhancers can be located: ▫ upstream, ▫ downstream ▫ within the gene that is transcribed. The binding of these enhancers with enhancer binding proteins (transcription factors) increases the rate of transcription of that gene to a greater extent. Gene Control Regions: Enhancer Gene Control Regions: Enhancer Enhancers are responsible for the cell or tissue specific transcription. Each enhancer has its own transcription factor that it binds to.  Transcription Transcription is the process of RNA synthesis, controlled by the interaction of promoters and enhancers. After transcription the RNA molecule is processed in a number of ways Translation the mature mRNA molecule is used as a template to assemble a series of amino acids to produce a polypeptide with a specific amino acid sequence. The complex in the cytoplasm at which this occurs is called a ribosome Post-translation processing of the protein Mechanisms of gene regulation Cellular processes that control the rate and manner of gene expression. Regulating the rate of transcription. Regulating the processing of RNA molecules, Regulating the stability of mRNA molecules. Regulating the rate of translation.  Difference Between Prokaryotic and Eukaryotic Gene Expression Prokaryotic Eukaryotic lack nuclei and other organelles the genome is located in the nucleus three promoter elements: One upstream have larger set of promoter elements, the of the gene being transcribed, one that primary one the TATA box is 10 nucleotides downstream of it and transcription initiation factors assemble one that is 35 nucleotides downstream. an initiation complex transcription initiation factors do not have 80S ribosomes (a 40S subunit and a assemble an initiation complex. 60S subunit ) have 70S ribosomes (30S subunit and a 50S subunit)  Difference Between Prokaryotic and Eukaryotic Gene Expression Prokaryotic Eukaryotic regulate entire metabolic pathways regulation is much more rather than regulating each enzyme complex and often relies on separately various feedback mechanisms, Bacterial enzymes for a given developmental processes and pathway are adjacent to each other environmental factors. on a cell's DNA and are transcribed co-regulated tend to have the into one mRNA called same DNA regulatory element polycistronic mRNA sequence associated with each co-regulated genes are often gene organized into an operon Difference Between Prokaryotic and Eukaryotic Gene Expression