: Life

•• : (cell)• Prokaryote cell • Eukaryote cell ••

Biochemistry-Chpater1: Life

? ?Biochemistry is the study of the chemical reactions on the molecular level that occur in living organism.

?to interpret the biological functions of living organisms in the language of chemistry.

- ?:

Norman Horowitz :• All living things grow, reproduce (replication)• Obtain energy from their surroundings, build new moleculesfrom basic organic molecules (catalysis)• Repair themselves, and respond to external stimuli (mutability)

All living things are composed of one or more cells and that cells are more or less alike and carry out similar functions to keep themselves alive.

Matthias Schleiden & Theodor Schwann

1839(true cell theory)

examined a cut section of cork and gave the cavities he saw the name cell, meaning "little rooms".

Robert Hooke1665

used magnifying lenses to study living world invisible to the naked eye.

Anton van Leeuwenkoek1660

The development of cell theory

( )

: eukaryotes( ) prokaryotes( ),( )

eukaryotes

General concepts about cells1. What do cells look like?There is no general common shape, cell can come in shapes such as cubes (cells lining sweat ducts), spheres (white blood cells of the immune system), bismarck doughnuts (red blood cells), columns (cells lining the gut), balloons (cells lining the urinary bladder), ellipsoids or rods (some bacteria), and pancakes (cells on the surface of the skin) . Bacterial cells are usually spherical, rod-shaped, comma-shaped, or corkscrew shaped.2. The cell size?Cells are microscopic in size. Human red blood cells are about 7.5 micrometers wide, and are about 5-100 times as large as a bacterial cell. The diameter of a typical spherical bacterial cell is about 1 �m, while the human liver cell (hepatocyte) is roughly 25 �m. A micrometer, or micron, ( - 1000

), is one millionth of a meter in length.

Streptococcus Pneumoniae(bacterium that causes lobar pneumonia.)

Clostridium tetani(bacterium that causes tetanus infections.)

Mycobacterium tuberculosis(bacterium that causes TB)

Proteus mirabilis(bacterium that causes urinary tract and wounds infection.)

Escherichia ColiHuman nerve cells, located in the spinal cord where they send electrical signals to muscle cells.

The biochemical processes must be viewed in the context of cell structures. The cells can be divided into two broad categories, eukaryotes and prokaryotes depending on whether or not their DNA is surrounded by membrane. In eukaryotes, a membrane surrounds the DNA to form a intracellular compartment called the nucleus. Prokaryotes do not have a defined nucleus. Intracellular membrane-enclosed compartments (called organelles) are the major characteristic intracellular structure in eukaryotes which ensure biological processes to function properly.

Prokaryotes

Procaryotic cells have three architectural regions :1. appendages (proteins attached to the cell surface) in the form of flagella and pili.2. a cell envelope consisting of a capsule, cell wall (30~250 Å thick) and plasma

membrane (~70 Å thick).3. a cytoplasmic region that contains the cell genome (DNA) and ribosomes and

various sorts of inclusions.

Prokaryote

DNAExtrachromosomal genetic material *Plasmid

DNAGenetic material of cell Chromosome

RNA and protein Sites of translation (protein synthesis) (250 Å diameter)

Ribosomes

Phospholipid and protein Permeability barrier; transport of solutes; energy generation; location of numerous enzyme systems

Plasmamembrane

Protein against phagotrophicengulfment

Attachment to surfaces; protection Common pili or fimbriae

ProteinMediates DNA transfer during conjugation *

Sex pilus

Pili

ProteinSwimming movement Flagella

Predominant chemical composition

Function(s)Structure

Prokaryotes

ProkaryoteCell envelope:

The cell protoplasm (cytoplasm) is surrounded by the plasma membrane (~70 Å thick), a cellwall (30-250 Å thick) and a capsule. All cells have a membrane, which is the essential and definitive characteristic of a "cell". Almost all prokaryotes have a cell wall to prevent damage to the underlying protoplast. Outside the cell wall, foremost as a surface structure, may be a polysaccharide capsule.

Most prokaryotes contain some sort of a polysaccharide layer outside of the cell wall polymer. In a general sense, this layer is called a capsule. A true capsule is a discrete detectable layer of polysaccharides deposited outside the cell wall. A less discrete structure or matrix which embeds the cells is a called a slime layer.

Bacterial capsules outlined by India ink viewed by light microscopy. This is a true capsule, a discrete layer of polysaccharide surrounding the cells.

A bacterial structure sometimes observed as an inclusion is actually a type of dormant cell called an endospore. Endospores exhibit no signs of life, being described ascryptobiotic. They are highly resistant to environmental stresses such as high temperature (some endospores can be boiled for hours and retain their viability), irradiation, strong acids, disinfectants, etc. They are probably the most durable cell produced in nature. Although cryptobiotic, they retain viability indefinitely such that under appropriate environmental conditions, they germinate back into vegetative cells.

Spores

Bacterial endospores. Phase microscopy of sporulating bacteria demonstrates the refractivity of endospores, as well as characteristic spore shapes and locations within the mother cell. *

Prokaryote Cell WallsFunctions of the Bacteria cell walls:• They are an essential structure for viability.• They are composed of unique components found nowhere else in

nature.• They are one of the most important sites for attack by antibiotics.• They provide ligands for adherence and receptor sites for drugs or

viruses.• They cause symptoms of disease in animals.• They provide for immunological distinction and immunological

variation among strains of bacteria.

Profiles of Cell Walls

Gram-positive Bacteria (those that retain the purple crystal violet dye when subjected to the Gram-staining procedure) the cell wall is thick (15-80 nanometers), consisting of several layers of peptidoglycan.Gram negative Bacteria (which do not retain the crystal violet) the cell wall is relatively thin (10 nanometers) and is composed of a single layer of peptidoglycan surrounded by a membranous structure called the outer membrane. The outer membrane of Gram-negative bacteria invariably contains a unique component, lipopolysaccharide (LPS or endotoxin), which is toxic to animals. The Gram-negative wall appears thin and multilayered. It consists a relatively thin peptidoglycan sheet between the plasma membrane and a phospholipid-lipopolysaccharide outer membrane. The space between the inner (plasma) and outer membranes (wherein the peptidoglycan resides) is called the periplasm.

Gram StainingA staining procedure devised more than a century ago would still serve as one of

the most widespread methods of bacterial classification?1. smears a sample of bacteria on a slide.2. soaks it in a violet dye and then treats it with iodine.3. The slide is then rinsed with alcohol and counterstained with a pink dye

called safranine.

the gram-negative bacteria appear bright pink to red. Gram-positive cell appear dark purple to brown. The difference between the two cell types appears to be in the amount of peptidoglycan in the cell wall. ( )

http://fig.cox.miami.edu

ProkaryotesInclusions

Inclusions are distinct granules that may occupy a substantial part of the cytoplasm. Inclusion granules are usually reserve materials of some sort. For example, carbon and energy reserves may be stored as glycogen (a polymer of glucose) or as polybetahydroxybutyric acid (a type of fat) granules. Polyphosphate inclusions are reserves of PO4 and possibly energy; elemental sulfur (sulfur globules) are stored by some phototrophic and some lithotrophic procaryotes as reserves of energy or electrons. Some inclusion bodies are actually membranous vesicles or intrusions into the cytoplasm which contain photosynthetic pigments or enzymes.MesosomesThe plasma membrane of prokaryotes may invaginate into the cytoplasm or form stacks or vesicles attached to the inner membrane surface. These structures are sometimes referred to as mesosomesSuch internal membrane systems may be analogous to the cristae of mitochondria or the thylakoidsof chloroplasts which increase the surface area of membranes to which enzymes are bound for specific enzymatic functions. The photosynthetic apparatus (light harvesting pigments and ATPase) of photosynthetic prokaryotes is contained in these types of membranous structures. Mesosomesmay also represent specialized membrane regions involved in DNA replication and segregation, cell wall synthesis, or increased enzymatic activity.

Energy Sources of Prokaryotes• Organisms that use radiant energy (light) are called phototrophs.• Organisms that use (oxidize) an organic form of carbon are called heterotrophs or

chemo(hetero)trophs.• Organisms that oxidize inorganic compounds are called lithotrophs.• The carbon requirements of organisms must be met by organic carbon (a chemical compound

with a carbon-hydrogen bond) or by CO2. Organisms that use organic carbon are heterotrophsand organisms that use CO2 as a sole source of carbon for growth are called autotrophs.

Most Bacteria, some Archaeaorganic compoundsOrganic compounds Chemoheterotrophs or Heterotrophs

A few Bacteria and many Archaea

CO2Inorganic compounds, e.g. H2, NH3, NO2, H2S

Chemoautotrophs or Lithotrophs(Lithoautotrophs)

Some Purple and Green Bacteria

organic compoundsLightPhotoheterotrophs

Cyanobacteria, some Purple and Green Bacteria

CO2Light ( )Photoautotrophs

ExamplesCarbon SourceEnergy SourceNutritional Type

Environmental Requirements for Microbial Growth : OxygenOxygen is a universal component of cells and is always provided in large amounts by H2O. However, procaryotes display a wide range of responses to molecular oxygen O2.• Obligate aerobes require O2 for growth; they use O2 as a final electron acceptor in aerobic respiration.• Obligate anaerobes (occasionally called aerophobes) do not need or use O2 as a nutrient. In fact, O2 is a toxic substance, which either kills or inhibits their growth. Obligate anaerobic procaryotes may live by fermentation, anaerobic respiration, bacterial photosynthesis, or the novel process of methanogenesis.• Facultative anaerobes (or facultative aerobes) are organisms that can switch between aerobic and anaerobic types of metabolism. Under anaerobic conditions (no O2) they grow by fermentation or anaerobic respiration, but in the presence of O2 they switch to aerobic respiration.• Aerotolerant anaerobes are bacteria with an exclusively anaerobic (fermentative)type of metabolism but they are insensitive to the presence of O2. They live by fermentation alone whether or not O2 is present in their environment.

Fermentation: an intramolecular oxidation-reduction processes to metabolize various organic compounds.

Effect of Oxygen on the growth of prokaryotes

Growth

Growth

Growth

No growth

No growth

Anaerobic

Not required and not utilized GrowthAerotolerantAnaerobe

Not required for growth but utilized when available

GrowthFacultativeAnaerobe(Facultative Aerobe)

ToxicNo growth Obligate Anaerobe

Required but at levels below 0.2 atm

Growth if level not too high

Microaerophile

Required (utilized for aerobic respiration)

GrowthObligate Aerobe

O2 EffectAerobicGroup

Other environmental factors are pH, temperature, water, etc..

Prokaryotic classification In Determinative Microbiology, some of the features that have been used to classify prokaryotes include:Gram stain (cell wall structure), Mole percent G+C in the genome, Growth temperature, Ability to form heat stable spores, Electron acceptors for respiration (if any), Photosynthetic ability, Motility, Cell shape, Ability to use various carbon and nitrogen sources, Special nutritional requirements (e.g., vitamins)

:(1) From the standpoint of many areas of microbiology:A determinative classification is sufficient. For example, in clinical microbiology the identification of organisms permits the physician to assess pathogenicity, and to select a treatment. In this context, the purely determinative nature of a classification was not crucial. If the organism has previously been described, and hence is already in the classification, then it can be identified and treated.(2) From a biological point of view:The lack of a natural system was an unsatisfactory state of affairs. It does not permit the projection of properties of previously described organisms onto new ones that might be closely related, but not identical, to those known before. In addition, it does not help us understand an organism that we have been unable to cultivate in the laboratory. Finally, it does not permit studies of the origin and evolution of cellular functions (e.g., drug resistance, aerobiosis or photosynthesis), because there is no evolutionary (historical) framework.

MOLECULAR PHYLOGENY (1)

Method 1: DNA-DNA HybridizationOne important technique for comparing prokaryotes at the molecular level is DNA-DNA hybridization. In this test, the genomic DNA from one species is mixed with the DNA from a second species and the similarity of the DNAs is reflected in the extent to which strands of DNA from one organism anneal with strands of DNA from the other organism. The sensitivity of DNA DNA hybridization declines rapidly as the organisms become more diverged, limiting the method to characterization of closely related strains, species and genera. *** DNA-DNA Hybridization :

(1) The gene must be present in all organisms of interest. Thus, to infer relationships that span the diversity of prokaryotes (or life), we must look at the central (universal) cellular functions. Examples include genes whose products function in replication, transcription, or translation—the processes constituting the "Central Dogma" of molecular biology.

(2) The gene cannot be subject to transfer between species (lateral transfer). (3) The gene must display an appropriate level of sequence conservation for the divergences of interest.(4) The gene must be sufficiently large to contain a record of the historical information. Thus, although

transfer RNA (tRNA) genes are present in all species, they are too small (about 75 nucleotides) to provide an accurate sample of evolutionary history.

Although the morphologies and physiologies of prokaryotes are much simpler than those of eukaryotes, there is a large amount of information in the molecular sequences of their DNA, RNAs and proteins. Thus, it is possible to use molecular similarities to infer the relationships of genes, and, by extension, to learn the relationships of the organisms themselves.

MOLECULAR PHYLOGENY (2)Method 2: Ribosomal RNA Genes and Their Sequences Most prokaryotes have three rRNAs, called the 5S, 16S and 23S rRNA. If relationships were analyzed by comparing sequence data, rather than hybridizing the molecules, one could infer relationships without having all of the molecules in hand (only the sequence data from previous studies are necessary). This was already being done with protein sequences.Carl Woese recognized the full potential of rRNA sequences as a measure of phylogenetic relatedness. He initially used an RNA sequencing method that determined about 1/4 of the nucleotides in the 16S rRNA (the best technology available at the time). This amount of data greatly exceeded anything else then available. Usingnewer methods, it is now routine to determine the sequence of the entire 16S rRNA molecule. Today, the accumulated 16S rRNA sequences (about 10,000) constitute the largest body of data available for inferring relationships among organisms.

The name is based on the rate that the molecule sediments (sinks) in water. Bigger molecules sediment faster than small ones.

Large subunit of ribosome290423SSmall subunit of ribosome154216SLarge subunit of ribosome1205S

LocationSize (nucleotides)NameRibosomal RNAs in Prokaryotes

The 5S has been extensively studied, but it is usually too small for reliable phylogenetic inference. The 16S and 23S rRNAs are sufficiently large to be quite useful.

S Svedberg unit It is a unit of time amounting to 10-13 s or 100 fs.Bigger particles have higher svedberg values.

S Svedberg unit It is a unit of time amounting to 10-13 s or 100 fs.Bigger particles have higher svedberg values.

ExamplesComparison of small subunit rRNA gene sequences from organisms spanning the known diversity of life

...GTGTCAGCCGCCGCGGTAATACCAGCTCCGCGAGTGGTCGGGGTGATTACTGGGCCTAAAGCG... Sulfolobussulfotaricus

...GTGGCAGCCGCCGCGGTAATACCGGCGGCCCGAGTGGTGGCCGCTATTATTGGGCCTAAAGCG... Thermococcus celer

...GTGCCAGCAGCCGCGGTAATACCGACGGCCCGAGTGGTAGCCACTCTTATTGGGCCTAAAGCG... Methanococcusvannielii

...GTGCCAGCAGCCGCGGTAATACGTAGGGGGCAAGCGTTACCCGGATTTACTGGGCGTAAAGGG... Thermotogamaratima

...GTGCCAGCAGCCGCGGTAATACGGGAGAGGCAAGCGTTATCCGGAATTATTGGGCGTAAAGCG... Anacystis nidulans

...GTGCCAGCAGCCGCGGTAATACGGAGGGTGCAAGCGTTAATCGGAATTACTGGGCGTAAAGCG... Escherichia coli

...GTGCCAGCAGCCGCGGTAATTCCAGCTCCAATAGCGTATATTTAAGTTGTTGCAGTTAAAAAG... corn

...GTGCCAGCAGCCGCGGTAATTCCAGCTCCAATAGCGTATATTAAAGTTGTTGCAGTTAAAAAG... yeast

...GTGCCAGCAGCCGCGGTAATTCCAGCTCCAATAGCGTATATTAAAGTTGCTGCAGTTAAAAAG... human

Prokaryote descentAn analysis of 16S rRNA-based phylogenetic tree showing the three (identified) Domains of life—Bacteria, Archaea and Eucarya.Archaea consists of three different kinds of organisms:(1) methanogens: produce methane (reduce CO2 with H2)(2) halobacteria: live in environment with >2M NaCL)(3) thermoacidophiles:live in acidic hot spring (~90 ºC and pH <2)

EukaryotesEukaryotic cells 10-100 �m

prokaryote Eukaryotic cells

organelleCells are surrounded by a bordering membrane called the cytolemma, plasmalemma, cellmembrane, or plasma membrane.

The nucleus is the central region of the cell containing the cell's DNA (genetic code, or genome). The nuclear membrane is biochemicallysimilar to, and often anatomically continuous with, the cell membrane.The prominent structure in the nucleus is the nucleolus. The nucleolus produces ribosomes, which move out of the nucleus to positions on the rough endoplasmic reticulum where they are critical in protein synthesis.

Eukaryotes architecture- , ribosome, ERNucleic Acids (DNA, RNA) are the genetic code molecules of cells. All cells use DNA as the genetic code molecule, and in eukaryotes the DNA is packaged in a nuclear region inside of a spherical nuclear membrane that contains pores. A gene is a length of DNA coding for a cell protein (enzyme or structural protein). The photo shows a piece of cellular DNA. It is highly coiled and is called a chromosome.

Ribosomes are small snowmen-shaped structures floating free in the cytoplasm or attached to endoplasmic reticulum. They are made of proteins and also of ribonucleic acid (rRNA). Ribosomes are the site where amino acids are assembled into proteins, under the guidance of the genetic code molecule "messenger RNA" (mRNA). mRNA is a mirror image copy of a DNA gene segment. Transfer RNA (tRNA) is a special type of RNA that carries specific amino acids to the ribosome. Endoplasmic Reticulum, or ER for short, is a membranous tubule system throughout a cell that serves several functions: Smooth ER (SER), devoid of ribosomes, detoxifies cell poisons and also is the site of steroid synthesis; Rough ER (RER), studded with ribosomes, modifies proteins synthesized on ribosomes, sometimes glycosylating (adding sugars to) proteins to create glycoproteins (such as the ABO proteins of infamous blood type notoriety).

Eukaryotes architecture-Golgi, centrioles, mitochondriaGolgi material looks like a stack of flattened pancakes with vesiclesat the edges. It functions for packaging material into vesicles for transport to other parts of the cell or for cell export (for example packaging of synthesized antibody proteins for export in the case of an immune system plasma cell)..

Mitochondria are submarine-shaped structures with membranous infoldings called cristae. The mitochondrion is the powerhouse of the cell, where most of a cell's ATP energy is made during cell metabolism using oxygen (aerobic metabolism).Mitochondria contain DNA (called m-DNA) and ribosomes. The bacteria-like functions of mitochondria leads to the hypothesis that mitochondria evolved from originally aerobic bacteria, which formd a symbiotic relationship with a primordial anaerobic eukaryote.(the origin of endosymbiotic).

Centrioles are short arrays of microtubules, appearing like a piece of cut licorice candy, located near a cell's nucleus. Centrioles function analogous to fishing rod and reels with hooks. During cell division, centrioles elongate, seeking out cell chromosomes (supercoiled DNA and histone protein molecules) to attach to and "reel" (move) to ends of the cell for orderly cell division following DNA replication.

Eukaryotes architectureInclusion bodies are chunks of miscellaneous material inside of cells, such as starch or fat granules, and so on.Lysosomes are membranous sacs that store powerful destructive enzymes, used to destroy other cell organelles, to destroy the cell at some point, or to destroy engulfed microbes or debris in the case of certain immune system cells. Cell such as certain white blood cells have numerous lysosomes to help destroy foreign engulfed particles or bacteria. Lysosomes are produced by the Golgi apparatus.Peroxisomes(microbodies) are membrane-enclosed organelles which contain oxidative enzymes. Some peroxisomal reactions generate hydrogen peroxide (H2O2), a reactive substance used in the enzymatic oxidation of other substances or degraded through a disproportionation reaction by enzyme catalyse.

The proper functioning of the cell requires careful control of the levels of important structural proteins, enzymes, and regulatory proteins. The only way that cells can reduce the steady state level of a particular protein is by proteolytic degradation. Thus, complex and highly-regulated mechanisms have been evolved to accomplish this degradation. An additional role of intracellular proteolysis is in the stress-response. Cells which are subject to stress such as starvation, heat-shock, chemical insult or mutation respond by increasing the rates of proteolysis. One function of this enhanced proteolysis is to salvage amino acids from non-essential proteins. These amino acids can then be reutilized in the synthesis of essential proteins or metabolized directly to provide energy.Another function is in the repair of damage caused by the stress. For example, oxidative stress has been shown to damage a variety of proteins and cause them to be rapidly degraded.

Eukaryotes architecture

(a) Microtubules and Microfilaments (~250 Å) are linear protein (tubulins) arrays that function in the cell for transport of cell materials within the cell, for movement of cell DNA during cell division, for creation of the cell cytoskeleton (cell skeleton), and for creation of cilia and flagella. Very long cilia, such as sperm tails, are termed flagella

(b) Microfilaments (~ 90Å) consist of the protein actin. Both microtubules and microfilaments have mechanically supportive function. When interacting with myosin, the contractile assemblies are responsible for intracellular movements.

(c) Intermediate filaments (100-150 Å in diameter)have load bearing function to endure mechanical stress. : keratin

The cytoskeleton maintains the cell's shape, anchors organelles in place, and moves parts of the cell in processes of growth and motility.

Mitosis is the process by which cells divide. The parent cell has already duplicated its chromosomes , providing both daughter cells with a complete copy of genetic information.

Eukaryotic animal cellThis is a transmission electron micrograph of tissue removed from the small intestine of a mouse and magnified approximately 26,000 times.

organellecell ?

cells?

Eukaryotes architectureVacuoles are membranous sacs that store nutrients, wastes, or water. They are more prominent in plant cells (90% cell volume).

Chloroplast are the organelles within which the biochemical reactions of photosynthesis occur. The outer covering of chloroplasts is composed of two membranes. The interior of chlroplasts is traversed by a series of double membranes called thylakoids which are surrounded by a fluid called the stroma. In addition to enzymes, the stroma contains DNA, and ribosomes. The pigments (e.g., the green chlorophylls and orange carotenoids), responsible for absorbing the light energy, are embedded within the thylakoidmembranes. Stacks of these thylkoidmembranes are called grana (singular = granum).

The Aims of Biochemistry(a) To study the biological organisms in molecular structural details.

Multi-cellularorganisms

Organelles(such as mitochondrials,

nucleus etc)

CellsOrgans

Supramolecularassembles

MacromoleculesProtein

Nucleic acidsPolysaccharides

lipids

Building Blocks of Bio-macromolecules

Lipids are small to be classified as macromolecules.It may look simple of these monomeric units, but the enormous number of ways these monomeric units can be arranges to create diverse properties of these molecules.

The Aims of BiochemistryTo understand metabolic pathway which is a series of biological reactions that produce one or more specific products.Each reaction step in metabolic process is so efficient that there is no redundant products generated or insufficient requirement for a reactant.

Metabolism

CatabolismBreak down nutrient to

generate energy

AnabolismBiomolecule synthesis From simple component

Provide ATP

The Aims of Biochemistry

To understand the expression and transmission of genetic information.

Genetics: a review ( )Chromosome:A linear end-to-end arrangement of genes and other DNA, sometimes with associated protein and RNA. The form of the genetic material in viruses and cells. A circle of DNA in prokaryotes; a DNA or an RNA molecule in viruses; a linear nucleoprotein complex in eukaryotes.The number of unique chromosome (N) in each cell is known as its haploid number, and the total number of chromosome (2N) is its diploid number.Gamete:A germ cell having a haploid chromosome complement (23 for humans). Gametes from parents of opposite sexes fuse to form zygotes. A specialized haploid cell that fuses with a gamete from the opposite sex or mating type to form a diploid zygote; in mammals, an egg or a sperm. Zygote:The unique diploid cell formed by the fusion of two haploid cells (often an egg and a sperm) that will divide mitotically to create a differentiated diploid organism. Somatic cell:A cell that is not destined to become a gamete; a cell whose genes cannot be passed on to future generations. Two copies of each chromosome (homologous pairs) present in every somtic cell.Mitosis: (divided by somatic cells)The nuclear division producing two daughter nuclei identical to the original nucleus. A type of nuclear division that produces two daughter nuclei identical to the parent nucleus normally just prior to cell division.( 2N chrmosome)

Genetics: a review ( )Meiosis: (divided by germ cells)Two successive nuclear divisions (with corresponding cell divisions) that produce haploid gametes (in animals) or haploid sexual spores (in plants and fungi) having one-half of the genetic material of the original cell. The nuclear and cell division process in diploid eukaryotes that results in four haploid gametes or spores having one member of each original pair of homologous chromosomes only per nucleus.

function:Genotype:The specific allelic composition of a cell, either of the entire cell or more commonly for a certain gene or a set of genes. The genes that an organism possesses.Phenotype:(1)The detectable outward manifestations of a specific genotype.(2)The observable attributes of an organism. Permissive condition:Environmental condition under which a conditional mutation shows the wild-type phenotype. Under restrictive condition, a conditional mutation is unviable.Allele:Alternative form of a gene. One of the different forms of a gene that can exist at a single locus. Every species contains a pair of genes governing a particular trait, one inherited from each of its parents.Gene locus:The specific place on a chromosome where a gene is located.

Genetics: a review ( )Homozygous gene pair:A diploid gene pair having identical alleles in both copies for example, AA or, aa. Heterozygous:A gene pair having different alleles in the two chromosome sets of the diploid individual for example, Aaor, A1A2. Wild-type:The genotype or phenotype that is found in nature or in the standard laboratory stock for a given organism. The phenotype of a particular organism when first seen in nature. RecessiveAn allele that is not expressed in the heterozygous condition. Also the phenotype of the homozygote of a recessive allele.

genetic :(1) zebra fish ( )(2) (Drosophila): 14(3) Bacteria: 20(4) Yeast: 90(5) Bacteriophage:

Electron micrograph of a bacterial endospore

The spore has a core wall of unique peptidoglycan surrounded by several layers, including the cortex, the spore coat and the exosporium. The dehydrated core contains the bacterial chromosome and a few ribosomes and enzymes to jump-start protein synthesis and metabolism during germination