10.4 Structure and Function of Cellular Genomes
3 min read•june 18, 2024
is the blueprint of life, containing instructions for every living organism. From genes to phenotypes, this genetic code shapes who we are and how we function. Understanding DNA's structure and organization is crucial for grasping the basics of life itself.
Prokaryotes and eukaryotes package their DNA differently, reflecting their unique cellular structures. , like and mitochondrial DNA, adds another layer of complexity to genetic organization. These elements play vital roles in cellular functions and evolution.
Genome Structure and Organization
Genes vs phenotypes
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- Genes are specific sequences of DNA that code for functional products like proteins or molecules and determine an organism's traits or characteristics
- Genotypes refer to the specific alleles or versions of genes an organism inherits from its parents, determined by the DNA sequence
- Phenotypes are the observable traits or characteristics of an organism that result from the expression of genes and their interaction with the environment (eye color, height, antibiotic resistance)
DNA packaging in cells
- DNA is tightly coiled and condensed to efficiently store and protect genetic material within the cell
- Prokaryotic involves a single circular attached to the cell membrane in the region, with ###-like_proteins_0### (, ) helping to condense and organize the DNA
- Eukaryotic DNA packaging involves multiple linear contained within a membrane-bound nucleus, with DNA wrapped around histone proteins to form
- exists in two states: loosely packed, transcriptionally active and tightly packed, transcriptionally inactive
- Chromosomes further condense during cell division processes like and
Genetic organization: prokaryotes vs eukaryotes
- Prokaryotic genomes typically consist of a single circular chromosome, lack membrane-bound organelles, have closely spaced genes with minimal non-coding DNA, and utilize (clusters of genes under the control of a single promoter)
- Eukaryotic genomes have multiple linear chromosomes within a membrane-bound nucleus, widely spaced genes with large amounts of non-coding DNA, introns (non-coding sequences removed during RNA splicing), exons (coding sequences remaining after RNA splicing), and regulatory sequences (promoters, enhancers) that control
Significance of extrachromosomal DNA
- Plasmids are small, circular DNA molecules separate from the main chromosome, commonly found in prokaryotes but also present in some eukaryotes, capable of autonomous , often carrying genes for specialized functions (antibiotic resistance, virulence factors), and facilitating horizontal transfer between cells
- Mitochondrial DNA () is circular DNA found in the mitochondria of eukaryotic cells that encodes proteins essential for cellular respiration and energy production and is maternally inherited in most species
- Chloroplast DNA () is circular DNA found in the chloroplasts of photosynthetic eukaryotes that encodes proteins involved in photosynthesis and is also maternally inherited in most species
DNA Structure and Function
- DNA is composed of nucleotides, which are the building blocks of genetic material
- The DNA double helix is held together by complementary base pairs (A-T and G-C)
- DNA is the process by which DNA is copied during cell division, ensuring genetic continuity
- involves the of DNA into RNA and of RNA into proteins
- Mutations are changes in the DNA sequence that can alter gene function and contribute to genetic diversity
Key Terms to Review (83)
Allele: An allele is one of two or more alternative forms of a gene that can occupy the same location on a chromosome. Alleles are responsible for the variations in inherited characteristics observed among individuals within a species.
Anthrax: Anthrax is a serious infectious disease caused by the bacterium Bacillus anthracis. It primarily affects livestock but can also infect humans through contact with contaminated animal products.
Bacillus anthracis: Bacillus anthracis is a gram-positive, rod-shaped bacterium that causes anthrax. It is known for its ability to form resilient spores that can survive in harsh environments.
Bacillus cereus: Bacillus cereus is a Gram-positive, rod-shaped bacterium found in soil and food. It is known for causing foodborne illnesses and can produce toxins leading to gastrointestinal infections.
Bacterial genomes: Bacterial genomes are the complete set of genetic material present within a bacterium, typically consisting of a single circular chromosome and sometimes plasmids. They encode all the information necessary for the bacterium's growth, reproduction, and function.
Base Pair: A base pair is a fundamental structural unit of nucleic acids, such as DNA and RNA, formed by the pairing of two complementary nitrogenous bases. These base pairs are essential for the double-helix structure and genetic information storage in cellular genomes.
Cholera: Cholera is an acute diarrheal illness caused by infection of the intestine with the bacterium Vibrio cholerae. It is primarily transmitted through contaminated water or food.
Chromatin: Chromatin is a complex of DNA and proteins found in the nucleus, which condenses to form chromosomes during cell division. It plays a critical role in regulating gene expression and DNA replication.
Chromatin: Chromatin is the complex of DNA and proteins that makes up the contents of the nucleus in eukaryotic cells. It is the physical form of genetic material within the cell and plays a crucial role in the structure and function of the cellular genome.
Chromatin remodeling: Chromatin remodeling involves the dynamic modification of chromatin architecture to allow access to condensed genomic DNA. This process is crucial for regulating gene expression, DNA replication, and repair.
Chromosome: A chromosome is a thread-like structure found in the nucleus of a cell that carries the genetic information, or genes, in the form of DNA. Chromosomes are essential for the proper storage, organization, and transmission of genetic material in both prokaryotic and eukaryotic cells.
Chromosomes: Chromosomes are DNA molecules that contain the genetic instructions for the development, functioning, growth, and reproduction of all known organisms. They are highly structured and organized within the nucleus of cells.
Colonization factor (CF): A colonization factor (CF) is a protein or molecule that enables bacteria to adhere to host cells, facilitating infection and colonization. These factors are critical for the establishment of bacterial infections and their persistence within the host.
Constitutive genes: Constitutive genes are genes that are continuously expressed at a constant level. They are essential for the basic functions and maintenance of cellular activity.
CpDNA: cpDNA, or chloroplast DNA, is the genetic material found within the chloroplasts of plant and algal cells. Chloroplasts are the organelles responsible for photosynthesis, and the cpDNA contains the genes necessary for the chloroplast to function and replicate independently within the cell.
Dental plaque: Dental plaque is a biofilm composed of bacteria and their byproducts that adhere to the surfaces within the mouth. It plays a significant role in oral diseases such as caries and periodontitis.
Diploid: A diploid cell contains two complete sets of chromosomes, one from each parent. It is the standard chromosome number in most eukaryotic organisms.
DNA: DNA (Deoxyribonucleic Acid) is the hereditary material in almost all living organisms, carrying genetic information essential for growth, development, and reproduction. It consists of two strands forming a double helix structure.
DNA gyrase: DNA gyrase is an enzyme that introduces negative supercoils into DNA, which is essential for DNA replication and transcription in bacteria. It is a type of topoisomerase that helps to relax positive supercoils formed ahead of the replication fork.
DNA packaging: DNA packaging is the process by which DNA molecules are compacted into a dense, organized structure within a cell. This allows the long DNA strands to fit inside the cell nucleus and protects them from damage.
DNA Polymerase: DNA polymerase is a critical enzyme responsible for the replication and repair of DNA, ensuring the accurate transmission of genetic information during cell division. It plays a central role in the structure and function of DNA, as well as the overall function of genetic material within cellular genomes.
Endosymbiotic theory: Endosymbiotic theory explains how eukaryotic cells evolved from prokaryotic organisms through a symbiotic relationship. It proposes that certain organelles, such as mitochondria and chloroplasts, originated as free-living bacteria that were engulfed by ancestral eukaryotic cells.
Epigenetics: Epigenetics is the study of heritable changes in gene expression that do not involve changes to the underlying DNA sequence. These modifications can affect how cells read genes and are influenced by environmental factors.
ETEC: Enterotoxigenic Escherichia coli (ETEC) is a type of E. coli bacteria that produces enterotoxins leading to diarrheal illness. It is commonly associated with traveler's diarrhea and affects the small intestine.
Euchromatin: Euchromatin is a lightly-stained, gene-rich region of chromatin in the nucleus of a eukaryotic cell. It is the more open and accessible form of chromatin that allows for active gene transcription and expression.
Exon: An exon is a sequence of DNA or RNA that codes for a portion of a protein or functional RNA molecule. Exons are the regions of a gene that are expressed, as opposed to the intervening sequences known as introns.
Extrachromosomal DNA: Extrachromosomal DNA is DNA that exists outside the chromosomal DNA within a cell. It is commonly found in plasmids and can replicate independently of chromosomal DNA.
Gel Electrophoresis: Gel electrophoresis is a laboratory technique used to separate and analyze macromolecules, such as DNA, RNA, and proteins, based on their size and electrical charge. It is a crucial tool in the study of cellular genomes and the visualization and characterization of these important biomolecules.
Gene: A gene is a segment of DNA that contains the instructions for making a specific protein or set of proteins. Genes are the basic physical and functional units of heredity.
Gene expression: Gene expression is the process by which information from a gene is used to synthesize functional gene products, primarily proteins. It involves transcription of DNA into mRNA and translation of mRNA into proteins.
Gene Expression: Gene expression is the process by which the genetic information encoded in DNA is converted into the functional products, such as proteins or RNA molecules, that carry out the biological activities of a cell. It is the fundamental mechanism by which cells use the information stored in genes to direct the synthesis of the gene products needed for their proper function and survival.
Genetics: Genetics is the branch of biology that studies genes, genetic variation, and heredity in organisms. It focuses on how traits are passed from parents to offspring through DNA.
Genome: A genome is the complete set of genetic material in an organism, including all of its genes and non-coding sequences. It contains the instructions needed for the growth, development, functioning, and reproduction of that organism.
Genome: A genome is the complete set of genetic information encoded in the DNA or RNA of an organism. It contains the instructions necessary for the development, function, and reproduction of that living being.
Genotype: A genotype is the genetic makeup of an organism, encompassing all of its genes. It determines specific characteristics and potential traits that can be expressed.
Genotype: Genotype refers to the specific genetic makeup or genetic constitution of an individual, which is determined by the combination of alleles inherited from their parents. It represents the complete set of genes present in a cell or organism and is the fundamental determinant of an organism's physical and functional characteristics.
Haploid: A haploid cell contains a single set of unpaired chromosomes, totaling half the number found in diploid cells. This is the typical chromosomal configuration of gametes (sperm and egg cells) in sexually reproducing organisms.
Heat-labile enterotoxin (LT): Heat-labile enterotoxin (LT) is a toxin produced by certain strains of Escherichia coli. It is sensitive to heat and can cause severe diarrhea by increasing cAMP levels in host cells.
Heat-stabile enterotoxin (ST): Heat-stabile enterotoxin (ST) is a type of exotoxin produced by certain bacteria, such as Escherichia coli. It is resistant to heat and can cause severe gastrointestinal disturbances.
Helicobacter pylori: Helicobacter pylori is a gram-negative, spiral-shaped bacterium that colonizes the human stomach lining. It is associated with various gastrointestinal diseases, including peptic ulcers and gastric cancer.
Herpesviruses: Herpesviruses are a large family of DNA viruses that cause diseases in animals and humans. They have double-stranded DNA genomes and exhibit latency, meaning they can remain dormant within the host cells before reactivating.
Heterochromatin: Heterochromatin is a tightly packed form of DNA and associated proteins within the nucleus of eukaryotic cells. It plays a crucial role in the structure and function of cellular genomes by regulating gene expression and maintaining chromosomal stability.
Histone: Histones are a group of small, basic proteins that associate with DNA in the nucleus of eukaryotic cells. They play a crucial role in the structure and function of cellular genomes by organizing and compacting DNA into a compact structure called chromatin.
Histone-like proteins: Histone-like proteins are structural proteins found in prokaryotes that play a crucial role in the organization and compaction of bacterial DNA. They function similarly to histones in eukaryotic cells by helping to regulate gene expression and maintain genome integrity.
Histones: Histones are proteins that package and order DNA into structural units called nucleosomes. They play a crucial role in gene regulation and DNA replication.
Horizontal gene transfer (HGT): Horizontal gene transfer (HGT) is the movement of genetic material between organisms other than through vertical inheritance (parent to offspring). This process contributes significantly to genetic diversity in prokaryotes.
Housekeeping genes: Housekeeping genes are genes that are constitutively expressed to maintain basic cellular functions necessary for the survival of a cell. They are typically involved in fundamental processes such as metabolism, cell structure maintenance, and DNA repair.
Housekeeping Genes: Housekeeping genes, also known as reference genes, are a class of genes that are essential for the maintenance of basic cellular functions. These genes are expressed constitutively in all cells, as they encode proteins involved in fundamental processes like cell growth, division, and survival.
HU: HU, or histone-like protein, is a small, basic protein found in the nucleoid of prokaryotic cells that plays a crucial role in the structure and function of cellular genomes. These proteins help compact and organize the genetic material within the limited space of the bacterial cell.
IHF: IHF, or Integration Host Factor, is a protein complex that plays a crucial role in the structure and function of cellular genomes. It is a global regulator of gene expression and DNA topology in many bacterial species, and it helps organize the bacterial chromosome by binding to specific DNA sequences.
Intergenic regions: Intergenic regions are non-coding sequences of DNA found between genes. They play roles in gene regulation and genome organization.
Intron: An intron is a non-coding sequence within a gene that is removed from the primary RNA transcript during the process of gene expression. Introns are found in the genes of most eukaryotic organisms and play a crucial role in the structure and function of cellular genomes.
Meiosis: Meiosis is a specialized type of cell division that occurs in sexually reproducing organisms, producing haploid gametes (such as sperm and eggs) from diploid parent cells. It is a fundamental process that ensures genetic diversity and enables the maintenance of a consistent chromosome count across generations.
Mitosis: Mitosis is the process of cell division in which a single parent cell divides into two or more genetically identical daughter cells. It is a fundamental process that ensures the accurate replication and distribution of genetic material during cell proliferation and growth in eukaryotic organisms.
MtDNA: mtDNA, or mitochondrial DNA, is the genetic material found within the mitochondria of eukaryotic cells. Mitochondria are organelles responsible for energy production through cellular respiration, and the mtDNA they contain encodes essential genes and proteins required for this process, making it a crucial component of cellular function and structure.
Mutation: Mutation is a permanent change in the DNA sequence of a gene or chromosome that can alter the genetic information and lead to changes in the structure or function of the organism. Mutations are a key driver of genetic diversity and evolution in both sexual and asexual organisms.
Noncoding DNA: Noncoding DNA consists of sequences in the genome that do not code for proteins. These regions have various regulatory and structural functions in the cell.
Nucleoid: The nucleoid is the irregularly-shaped region within a prokaryotic cell that contains most of the genetic material. Unlike a eukaryotic nucleus, it is not surrounded by a nuclear membrane.
Nucleoid: The nucleoid is a region within a prokaryotic cell that contains the cell's genetic material, usually in the form of a single, circular chromosome. It is the primary site of genetic information storage and replication in bacteria and archaea, serving as the functional equivalent of the nucleus in eukaryotic cells.
Nucleosome: A nucleosome is the fundamental unit of DNA packaging in the eukaryotic cell nucleus. It consists of approximately 147 base pairs of DNA wrapped around a histone protein octamer, forming the basic repeating subunit of chromatin.
Nucleotide: A nucleotide is the fundamental building block of nucleic acids, such as DNA and RNA. It consists of a nitrogenous base, a pentose sugar, and a phosphate group. Nucleotides play a crucial role in various biological processes, including energy production, cellular signaling, and the storage and transmission of genetic information.
Operons: Operons are genetic structures in prokaryotic organisms that contain a cluster of genes under the control of a single promoter. They allow for the coordinated expression of genes involved in related metabolic pathways or functions.
Parvoviruses: Parvoviruses are small, non-enveloped viruses with a linear single-stranded DNA genome. They primarily infect animals and are known for their ability to cause various diseases in different species.
PCR (Polymerase Chain Reaction): PCR, or Polymerase Chain Reaction, is a powerful molecular biology technique used to amplify specific DNA sequences exponentially. It is a fundamental tool employed across various fields, including microbiology, genetics, forensics, and diagnostics, to study and detect the presence of genetic material from a wide range of organisms, including prokaryotes, viruses, fungi, and protozoa.
Phenotype: Phenotype is the observable characteristics or traits of an organism resulting from the interaction of its genetic makeup (genotype) and environmental factors. These traits can include physical features, biochemical properties, and behavior.
Phenotype: Phenotype refers to the observable physical and biochemical characteristics of an organism, which are the result of the interaction between its genotype and the environment. It represents the expression of an organism's genetic makeup and is the foundation for understanding the relationship between genes and their observable effects.
Plasmid: A plasmid is a small, circular, double-stranded DNA molecule found in the cytoplasm of many prokaryotic cells, such as bacteria and archaea. Plasmids are distinct from the main chromosomal DNA and can replicate independently, allowing them to be passed on to daughter cells during cell division. Plasmids play crucial roles in the unique characteristics of prokaryotic cells, the habitats and relationships of prokaryotes, and the structure and function of cellular genomes.
Plasmids: Plasmids are small, circular, double-stranded DNA molecules that exist independently of the chromosomal DNA in bacteria. They often carry genes beneficial for survival, such as antibiotic resistance.
Poxviruses: Poxviruses are a family of large, complex viruses with double-stranded DNA genomes. They are known for causing diseases such as smallpox and cowpox.
Replication: Replication is the process by which a cell makes an exact copy of its DNA. It is a critical mechanism that ensures genetic information is accurately transmitted to daughter cells during cell division.
Replication: Replication is the process by which a cell or virus makes an identical copy of its genetic material, ensuring the faithful transmission of genetic information to its offspring. This fundamental biological process is essential for the propagation and evolution of all living organisms.
Rickettsia prowazekii: Rickettsia prowazekii is a gram-negative, obligate intracellular bacterium that causes epidemic typhus. It primarily infects endothelial cells lining blood vessels, leading to severe vascular inflammation.
RNA: RNA, or ribonucleic acid, is a crucial biological macromolecule that plays a vital role in various cellular processes, including the storage and expression of genetic information, protein synthesis, and gene regulation. As a nucleic acid, RNA is closely related to DNA, sharing many structural and functional similarities, yet also exhibiting distinct characteristics that make it a unique and essential component of living organisms.
Serratia marcescens: Serratia marcescens is a Gram-negative, rod-shaped bacterium known for producing a characteristic red pigment called prodigiosin. It can be an opportunistic pathogen involved in hospital-acquired infections and can affect the respiratory and urinary tracts.
Shigella flexneri: Shigella flexneri is a Gram-negative, rod-shaped bacterium that causes dysentery in humans. It is known for its ability to invade and multiply within the epithelial cells of the colon.
Streptococcus mutans: Streptococcus mutans is a Gram-positive bacterium primarily found in the human oral cavity. It plays a significant role in the development of dental caries (tooth decay).
Supercoiling: Supercoiling is the over-winding or under-winding of a DNA strand, and is an expression of the strain on that strand. It helps compact DNA to fit within cellular structures and plays a role in regulating gene expression.
Topoisomerases: Topoisomerases are enzymes that regulate the over-winding or under-winding of DNA during replication and transcription. They achieve this by making transient cuts in the DNA backbone to relax supercoils.
Transcription: Transcription is the process by which a segment of DNA is copied into RNA by the enzyme RNA polymerase. It is the first step in gene expression, allowing genetic information to be transcribed for protein synthesis.
Transcription: Transcription is the process by which the genetic information encoded in a DNA sequence is copied into a complementary RNA molecule, which then serves as a template for the synthesis of proteins. It is a fundamental step in the central dogma of molecular biology, where DNA is transcribed into RNA, which is then translated into proteins.
Translation: Translation is the process by which ribosomes synthesize proteins using mRNA as a template. It involves decoding the genetic information contained in mRNA to produce a specific polypeptide chain.
Translation: Translation is the process by which the genetic information encoded in messenger RNA (mRNA) is used to direct the synthesis of proteins, the fundamental macromolecules that carry out the majority of cellular functions. This process is a crucial step in gene expression, connecting the information stored in the genome to the functional molecules that enable life.
Viral genomes: Viral genomes are the genetic material of viruses, consisting of either DNA or RNA. They encode the necessary information for virus replication and propagation within host cells.