General Biology I LectureLab
General Biology I LectureLab BIOL 1110
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BIOL 1110 I bioll 1 107chemicalibonding REEDER CHEMICAL BONDING STABILITY A An atom with fewer than eight 8 valence electrons may react with another atom with the goal of achieving a B stable con guration Two ways by which a reaction can occur a One atom may lose valence electrons to g gain electrons from another atom process called ionic or electrovalent bonding b One atom may share valence electrons with one or more atoms to complete its outer shell process called covalent bonding 2 Stabilitv is achieved through CHEMICAL BONDING 3 Molecules and compounds are formed as a result of the binding force called a chemical bond 4 Two types of representative formulas a Structural indicates types and numbers of atoms as well as their arrangement in compounds type of bonds NEN covalent NaCl39ionic CaHClz39 b Molecular shows types and numbers of atoms in a compound HZO COZ N2 NaCl 5 Molecules can also become ionic by losing and gaining protons as well as electrons H ion proton Ionic Bonds 1 When two or more elements combine by losing and gaining valence electrons they are held together strongly by an electrostatic force called an ionic bond metal reacts with a nonmetal called a redox reaction 2 Atoms thereafter carrying a charge are called m a Positive charged ions cations derived from metals which bivalence electrons b Negative charged ions anions derived from nonmetals which gainvalence electrons 3 The opposite charges of the ions attract resulting in a bond 4 Ionic bonds are a representative of the weaker class of bonds that include the hydrogen bonds 5 Three types of inorganic compounds containing ionic bonds are acids bases and salts 6 Because of water s polarity charged nature 1HZO39 when inorganic compounds are placed in water the compounds ions dissociate in a process called ionization NAC139 HZO gt C139 1HZO39 Na a Electronegativitv measure of an atom s attraction for electrons in chemical bonds ON b Due to electronegative atom s larger mass when sharing electrons with an atom of lesser mass like H the electrons are pulled closer to the electronegative atom s nucleus 1 when attraction for electrons shared is unequal M as in the water molecule covalent 2 when attraction for electrons shared is equal nonpolar H2 02 N2 covalent 7 Compounds that separate into ions in water called electrolytes represent charged particles that can conduct electrical currents and are important in living systems nerve muscle energy transformations in cells Covalent Bonds 1 When two or more atoms combine by sharing valence electrons they are held very strongly together by a force called a covalent bond nonmetal reacts with a nonmetal 2 The number of electrons shared between two atoms is equal each atom involved contributes one electron to each m that is shared the atom s attraction for shared electrons can vary polar or nonpolar states described above 3 These electrons spend part of their time in the outer shell of each atom therefore they may be counted as belonging to M atoms When atoms of elements share equal numbers of electrons neither atom carries a charge 5 Covalent bonds are the most common bonds as well as the strongest that are found in the molecules of living organisms 6 These bonds may occur as single one pair of electrons shared double two pair andor ple three pair covalent bonds 7 Organic compounds are always characterized by covalent bonding 3 D Hydrogen Bonds 1 A hydrogen bond is a very weak chemical bond formed between an already bonded H atom and a strongly negative atom electronegative atom such as O or N 2 These bonds commonly form between one water molecule and another 6605 Page 1 of2 BIOL 11102230 REEDER Structures of Common Functional Groups Chemical Group Group Name Carboxyl organic acids R C OH RCOOH O Carbonyl Aldehyde R C H RCO Carbonyl O Ketones I I R C C C R RCOR R OH Hydroxyl ROH H Methyl I R 7 C 7 H CH3 I H H Amino amine I RNHZ R N I H R SH Sul iydryl RSH OH I ROPOH Phosphate I I O RPOAHZ O I I R 7 C Ester I O 7 R RCOOR Functional Groups Exam ple s Acids fatty am ino vinegar acetic Polysaccharides retinal form aldehyde pyridoxal Polysaccharides acetone corticosterone Alcohols glycerol methanol ethanol cholesterol vitam ins A amp E and carbohydrates Many organic molecules F ats oils waxes methane gas Proteins Nucleic Acids Cysteine amino acid proteins rubber DNA RNA ATP Lipids triglycerides phospholipids steroids Description Ionic H can dissociate as a H ion can act as an acid Polar Due to electronegative oxygen attracting covalent electrons C of group is bonded to at least one H atom aldehyde is positioned at mi of a carbon skeleton Polar C of group is bonded to two other carbons Ketone has an internal carbonyl group Polar Due to electronegative oxygen attracting covalent electrons Nonpolar hydrocarbon Ionic amino group acts as a base Help stabilize protein s internal structure maintaining its functional state Ionic Weakly acidic can release one or two hydrogen ions Ionic covalent bonding unites monomers of complex lipids 1 defined as specific arrangements of organic molecules that confer distinct properties including chemical reactivity to organic compounds polar or nonpolar qualities positively or negatively charged 2 have distinct chemical properties that they retain no matter Where they occur BIOI 1 102230 STRUCTURESCOMNIONFUNCTIONAL REEDER 2408 BIOL 1110 REEDER BIOCHEMISTRY I MATTER A Makeup 1 Element substances that cannot be broken down into simpler substances by ordinary chemical reactions 116 different elements of which 92 occur naturally on earth An element is a combination of atoms called isotopes all with the characteristic chemical properties atomic number of that element b Most elements in nature exist as mixtures of different isotopes 2 Atom the smallest discrete unit of a chemical element that retains the characteristic chemical properties of that element 3 Compound substance that typically breaks down into molecules containing two or more different atoms in a fixed ratio water is a chemical compound consisting of molecules produced when two atoms of hydrogen combine with one atom of oxygen not all compounds are made up ofmolecules ie NaCl because molecules are formed only via covalent bonding and NaCl is ionic 4 Molecule smallest quantity of a compound which has all the properties of that compound For example a given amount of water is made up of a number of exactly similar molecules each composed of two atoms of hydrogen and one of oxygen If the molecule of H20 were divided into its hydrogen and oxygen atoms it would no longer behave like the compound water Molecules may exist between different kinds of atoms H20 or between the same kinds of atoms 02 N2 H AtomSubatomic Particles l Proton positive charged39 contributes mass unit of one Alva atomic mass unit found in the atom39s nucleus each kind of element with its respective isotopes is uniquely identified by its number of protons atomic number 39 determines the number of electrons W 2 Neutron no charge39 contributes mass unit of one39 found in the atoms nucleus numbers may vary among the isotopes of a particular element 3 Electron negative charge39 insignificant mass found in clouds moving at great speeds around the atom39s nucleus no of electrons in the outer energy level valence shell determines the chemical properties of atoms most directly involved in chemical reactions C Properties 1 Electrons are the particles that participate in chemical reactions specifically those of the valence shell 2 Atom itself is electrically neutral because it has an equal number of protons and electrons 3 Atom39s nucleus is positively charged 4 Protons and neutrons are the only particles that contribute mass 5 Isotope characteristic atoms of the w element varying by their weights a Atoms with the same number of protons but varying numbers of neutrons therefore each atom has a different mass most elements are mixtures of isotopes of varying proportions b All isotopes of a given element have essentially the same chemical characteristics except for radioisotopes c Best known isotopes are of Carbon 13 in total 8C through 20C with three principal ones 1 All of these isotopes have six protons and six electrons but varying numbers of neutrons a over 99 of the carbon in nature is carbonl2 b most of the rest is carbonl3 c the rarest is carbonl4 which is unstable and radioactive its nucleus tends to break up into elements with lower atomic numbers in a process called radioactive decay Chlorine has two isotopes calcium has eight hydrogen has three etc a Isotopes of oxygen have seven eight nine or ten neutrons 15O 16O 17O 18O b Isotopes of hydrogen have zero hydrogen one deuterium or two neutrons tritium 1H 2H 3H c Radioactive isotopes radionuclide unstable isotopes whose nuclear breakup in the process of decay emits a significant amount of ener 1 some radioactive isotopes are more unstable than others and decay more readily 2 for any specific isotope the rate of decay is constant expressed as the halflife a the time it takes for one half of the atoms in a sample to deca b carbonl4 has a halflife of about 5730 years to become primarily N l4 via beta emission i by determining the ratios of the different isotopes of carbon nitrogen and other elements in biological samples and in rocks scientists are able to determine when these materials orme c potassium40 decays to form argon40 with halflife of 13 billion years N V Page 1 of3 9122005 6 3 energy released via spontaneous emission of one or more of three types of particles or rays gamma rays electromagnetic beta particles electrons and nucleus of another element and alpha particles positively charged helium nuclei stripped of their electrons a Radioactive examples C H3 tritium products of nuclear fission strontium 90 iodine 131 b Uses In medicine used for both diagnosis and treatment labeling a substance fat hormone drug with a radionuclide and following its course in the human body testing thyroid gland function treatment of cancer measure red blood cell production rate in the nuclear power industry 14C and potassiumargon dating attaching to an antibody to determine an antigen39s presence pacemakers irregular heartbeats are powered by energy emitted from 238 plutonium sealed in a case PET positronemission tomography provides diagnostic information about metabolic abnormalitiesthyroid i Commonly used radioisotopes for tracing movements of elements in plants and animals tritium 3H carbon 14 14C phosphorus 32 HP and 131I Atomic weight or mass indicates how heavy an atom of an element is compared with an atom of another element present system uses carbonl2 as the standard for comparison reflects the masses of the mixture of isotopes that occur in nature a b C All other elements are indicated as being so many times heavier or lighter than Cl2 Chloride is almost 3 times as heav Calculated as the ratio of its atomic mass compared with the atomic mass of carbonl2 l2 amu abundance of each isotope in nature is taken into account as well 1 Example more than 99 of hydrogen atoms in a naturally occurring sample have an atomic mass of l the atomic mass of hydrogen is 10079 reflecting the presence of isotopes deuterium with a mass of 2 even smaller amounts of tritium with a mass of 3 These different forms of the same element Isotopes II PERIODIC CHART USE A Atomic number Indicates the number of protons 2 Protons indicate the number of electrons equal numbers in a neutral atom B Number of neutrons working number Subtract the atomic number from the atomic weight rounded to the nearest whole number C Atomic weight mass D Atomic symbol 1 1 III ELECTRON DISTRIBUTION IN THE ATOM A Bohr Model of Atomic Structure not completely accurate today but is still a valuable teaching tool Protons and neutrons found in a centrally located nucleus contributes 999 of the atom39s mass Electrons move continuously around the nucleus at great speeds in shells represented as concentric circles up to 7 shells the electron distribution determines which atoms will combine with each other and how many will combine determines an atom39s chemical properties 1 2 a Between the electrons and nucleus there is nothing most of the atom39s volume consists of empty space Shells correspond to specific energies possessed by particular electrons energy level and can accommodate only a certain number of electrons a b The shell closest to the nucleus has the lowest energy level with each shell beyond having higher The first shell holds only two electrons the second holds up to eight and the third through sixth can hold more than eight no atom can have more than 8 electrons in its outermost shell 1 eight valence electrons results in the stable state for atoms with two or more shells 2 majority of element s atoms do not have eight in valence shell so are unstable and seek stability via bondin Inner shells are filled first and if there are not enough electrons to fill all the shells the outer shell is left incomplete It is possible for an electron to move from one shell its ground state to another within an atom When moving to a higher energy shell the electron must be excited by absorbing a discrete packet of energy known as quantum contains just the right amount of transition energy heating electrical charge sunlight quotquantLlIn leap 2 When moving to a lower energy shell the energy that provided its boost is released The biologically important elements typically have no more than four shells with never more than eight electrons in an outermost shell Page 2 of3 9l 22005 BIOL l l 10 REEDER GENETIC ABNORMALITIES I Mutations A Characteristics 1 Defined as changes in the DNA code that are passed on to subsequent generations chemical change most are a potential threat in which every population is subject to resulting in cell death can result in an altered phenotype 2 May arise spontaneously due to no known cause or may be induced by mutagens environmental agents that increase the rate of mutations a Chemical mutagens food additives hallucinogenic drugs industrial chemicals pesticides b Radiation radioactive minerals cosmic rays ultraviolet light of the sun 3 Two types of mutations a Chromosomal Involves portion of a chromosome entire gene or a number of genes with alterations in the structure or in the number of chromosomes b Gene Can arise by a single nucleotide change as in sickle cell hemoglobin most of the known inherited diseases are caused by defects in single genes and are autosomal recessive 4 Chromosomal Mutations leads to genetic imbalances resulting in multiple defects sEdrome result of aneuploids andor deletion translocation a Virtually all chromosome abnormalities result in a syndrome and because the nervous system is so complicated in its development it is quite sensitive to altered gene dosages and some form of mental retardation commonly occurs b In general chromosome abnormalities involving the autosomes are far more devastating than the abnormalities involving the sex pair c Changes in chromosome structure 1 Deletion segment of a chromosome is lost lethal when homozygous causes abnormalities when heterozygous cri du chat or cat39s cry syndrome in hum ans malformation of larynx resulting in the infant39s cry resembling that of a cat head and face deformities severe mental retardation IQ below 20 and typically devastating to health Chromosome 5 is abnormally short with a loss of some genes Causes include radiation various chemicals and viruses 2 Inversion segment of a chromosome is turned around 180 due to it breaking in two pieces being momentarily removed and flipped and rejoined reproductive problems when heterozygous as can lead to lethal chromosome disorganizations during crossing over in meiosis generally does not effect health unless a gene is physically disrupted 3 Translocations interchange of blocks of genes between two nonhomologous chromosomes reduced fertility in heterozygotes due to problems with pairing during meiosis form of Down Syndrome 1421 can cause deletions and duplications and be caused by certain viruses mumps drugs anticancer and radiation medical xrays or ultraviolet d Changes in Chromosome number 1 Polyploidy when organism has more than two sets of chromosomes common in plants and rare in animals when it occurs in all the body cells it is m in humans and many other animals most die as embryos or fetuses a Organisms are named according to the number of chromosome sets 1 Triploids 3N three of each kind of chromosome account for 17 of all spontaneous abortions and 3 of stillbirths and newborn deaths 2 Tetraploids 4N etc b In animals can result in formation of an abnormal gamete as sex determination is based on a single pair of chromosomes In plants typically reproductive process is not interfered with and certain types may be manipulated for their desired traits 2 Aneuploidy excess or deficiency of an individual chromosome in an otherwise normal diploid cell leads to genetic imbalances resulting in multiple defects syndrome which is often mental retardation individuals with more than one almost never survives birth generally arise as a result of an abnormal meiotic or mitotic division in which chromosomes fail to separate at anaphase nondisjunction trisomic individual with an extra in a pair monosomic lacking a pair member rare such as in 21 is usually lethal to an embryo or fetus a Generally extra genetic material is less dangerous than missing material C V BIOLl l lOGENETICABNORMALITIES 62402 11 7 V 5amp8 f g h Aneuploidy of the autosomes is generally more severe than aneuploidy of the sex chromosomes because the sex chromosomes do not contain as many genes needed for vital body functions as do the autosom es 50 of spontaneous abortions are caused by aneuploidies 1n mitotic aneuploidy if only a few cells are altered health may not be affected but if it occurs in the early embryo it may be serious Five types of autosomal aneuploids are known to survive birth Edward39s syndrome trisomy 18 and Patau39s syndrome trisomy 13 produce multiple defects and are lethal in infancy or earlier most common type is Down Syndrome trisomy 21 Down Syndrome usually have three trisomy number 21 chromosomes sparse hair folded eyes short stature stubby fingers large fissured tongue mental retardation the extra quotdosesquot of 21 bring about a genetic imbalance resulting in complex physical and mental abnormalities and variable in its expression some people with mild Down syndrome are chromosomal mosaics having some normal cells and some with trisomy 21 many patients often die young of complicating conditions with heart and kidney defects comm on may have suppressed immune systems and die from prolonged cold or in uenza individuals rarely live beyond age 40 l Nondisjunction a Results in a sperm or egg that has two copies of a particular chromosome or none rather than the normal one copy when it fuses in fertilization the resulting zygote has either 45 or 47 chromosomes b 1n Down Syndrome it typically results in an egg with two number 21 chromosomes instead of one of which either the chromosome pair or the chromatids failed to separate completely and instead went into the same daughter cell either in Meiosis 1 or 11 c Most apt to occur in the older female since children with syndrome are usually born to women over age forty egg cells have been arrested for an extremely long time on the brink of completing meiosis and may have a greater chance of being exposed to radiation or chemicals that can damage chromosomes 2 Translocation form of Down Syndrome 4 occurrence in a carrier individual either the mother or the father most of the genetic material from a chromosome 21 has become fused to a chromosome 14 creating a 1421 translocation chromosome on average such a carrier will produce four kinds of sperm so that when they fertilize four kinds of zygotes may result a 14 have only one 21 monosomy 21 which is lethal b 14 translocation form of Down s c 14 genotypically and phenotypically normal d 14 translocation carriers like father has 45 chromosomes one 14 one 21 and one 1421 e Can run in families and its incidence does not increase with maternal age Patau39s syndrome due to extra chromosome number 13 characterized by harelip and cleft palate Abnormal sex chromosomes 1 Turner39s syndrome nondisjunction of sex chromosomes during oogenesis may produce an egg that has either no X chromosome or two X39s 1f the first of these is fertilized by an Xbearing sperm a female with this syndrome is born Their genotype is E for sex Characteristics include nonfunctional ovaries fallopian tubes and uterus therefore no puberty or menstruation and no breast development stocky build webbed neck and subnormal intelligence sometimes 1f the egg having two X39s is fertilized by an Xbearing sperm a superfemale XXX results or triploX Characteristics include a tendency toward mental retardation in some cases no apparent physical abnormalities and many are fertile and have children with a normal chromosome count although may have menstrual irregularities 3 Klinefelter s syndrome When an egg with two X39s as produced above via nondisjunction is fertilized by a ybearing sperm a male with this syndrome results m Characteristics include nearly normal male general appearance underdeveloped testes and prostate breasts may be enlarged and female like sparse body hair usually tall with very long arms and legs and large hands and feet and may be mentally defective about half incidence 4 XYY Males due to nondisjunction during spermatogenesis in male parent Characteristics include taller than average persistent acne and tend to have lower than average intelligence and aggressive and antisocia N V Other Genetic Disorders Estimated 40005000 genetic diseases unable to cure any genetic diseases today but can treat the symptoms most are autosomal recessive BIOLll10GENETlCABNORMAL1TIES 62402 A Sickle Cill Anemiachromosome 11 Group of autosomal recessive or incomplete dominant traits due to gene defect resulting in red blood cell abnormalities caused by certain inappropriate amino acids at crucial locations in the hemoglobin molecule cell loses biconcave shape which is essential to its function and becomes sickleshaped or halfmooned results in slow blood flow blockage tissue damage and pain predominant in blacks 1 in 500 children lead short painful lives rarely living beyond age 40 B TaySachs Diseasechromosome 15 autosomal recessive condition characterized by abnormal accumulation of lipids due to the deficiency of an enzyme results in central nervous system destruction blindness and severe mental retardation in young children begins in the first year of life with death by the age of 5 prevalent in Jewish individuals of central or eastern European descent 1 in 600000 babies C Cystic Fibrosis chromosome 7 l autosomal recessive in white children 1 in 2000 white babies 2 kills more children than diabetes rheumatic fever and poliomyelitis combined 1 of every 20 persons in US is a heterozygous carrier kills 1 in 2000 children 3 Life expectancy l2 16 years some living to 3039s or 4039s 4 High level of sweat electrolytes pulmonary disease cirrhosis of the liver nonsecretion of digestive enzymes blockage of pancreatic and hepatic ducts by mucus resulting in an intestinal inability to absorb fats 5 Thick mucus interferes with lung clearance causing respiratory distress the mucus serves as a culture medium for bacteria and their toxins resulting in pneumonia 6 Child fails to gain weight with frequent respiratory and ear infections quot failure to thrivequot D Phenylketonuria PKU chromosome 12 l autosomal recessive homozygous results in enzyme deficiency that normally converts phenylalanine to tyros1ne 2 liver deficiency leads to a chain of events beginning with excessive phenylalanine levels in the blood which will be converted to toxic products that accumulate and damage the CNS severe mental retardation results 3 leads to a depression in the amino acid levels leading to excessive light coloration and mental deficiency 4 PKU infant is healthy at birth but through infancy and early childhood conditions worsen in US 1 in every 14000 white newborns rare in blacks 5 All newborns are required by law to be tested at birth for PKU by a blood sample taken from the heel 6 Diet treatment may be successful but is not a cure E Huntington39s Disease Chromosome 4 1 Rare autosomal dominant allele causing severe mental and physical deterioration uncontrollable muscle spasms personality changes ultimately insanity with no effective treatment onset late in life ages 35 and 50 Progressive nervous system deterioration F Other autosomal dominant genetic disease most autosomal dominant conditions do not produce symptoms until adulthood Achondroplasia form of dwarfism Chronic simple glaucoma some forms major cause of blindness in untreated Hypercholesterolemia high blood cholesterol propensity to heart disease Polydacgly extra fingers or toes Neurofibromatosis skin is covered with tumors some cancerous is often mild with as few as six light brown pigment spots on the skin or is grossly disfiguring quotElephant Manquot chromosome 17 111 Genetic Predispositions A Heart disease and schizophrenia B Manic depressive Chromosome 21 and Alzheimer39s disease 21 1V Genetic Counseling A Description 1 The genetic counselor is a new breed of medical professional who helps families understand their problem and evaluates pedigrees and test results to predict who in a family is likely to be affected by the condition in turn information is supplied to the family allowing the family to make a rational informed choice 2 The counselor helps patients put medical information in perspective calming panic as well as ensuring that patients adequately understand risks 3 Many counseling sessions deal with the disturbing issue of abortion since it may be an alternative in some lethal situations B Source of information utilized for diagnosis in counseling 1 Studying chromosomes and genes a Pedigree a chart compiling information on how family members are related and who among them have certain characteristics autosomal recessive autosomal dominant and sexlinked trait transmission may be traced V eP Nf BIOLll10GENETlCABNORMAL1T1ES 62402 BIOL 1110 REEDER PROTEIN SYNTHESIS 1 DNA and the Genetic Code Cellular Life A Functional Control of the Cell and its Activities Proteins are the strategic materials upon which all life functions of an organism depend 1 a Collagen of the skeleton hemoglobin of the blood actin and myosin that motorize muscles receptors by which neurotransmitters link and enzymes that all chemical reactions depend reactions including the manufacturing of nonprotein chemicals such as fats sugars and phospholipids are protein 2 Gene expression includes a complex series of events involving RNA molecule synthesis a b Synthesis of RNA molecules complementary to the DNA transcription Assembly of amino acids of a certain number type and arrangement translation 3 Human genes are a functional unit bioll 1 10 jroteinisynthesisdoc a Fquot up D quot1 0 96 Pquot F average consists of about 40000 bases 1 gene size can vary a largest human gene is dystrophin assoc with Duchenne muscular dystrophy consisting of 24 million bases almost all bases 991 are the same in all people only 15 ofthe genomic total codes for proteins 25000 genes the proteome total proteins produced is larger than the genome 1 the average human gene produces three different proteins alternative splicing while bacteria produces only one 2 each gene is divided into coding regions exons and noncoding regions introns a Introns 24 of total repeated sequences that do not code for proteins make up at least half of the human genome gene rich regions of the genome are predominantly composed of G and C bases while genepoor areas GM are predominantly A and T bases 1 under the microscope they appear as light coding and dark bands Qunk on chromosomes junk DNA is characterized by long stretches of repeated sequences that have no known function scientists use them to study evolutionary relationships repeats can be dated as to when they first appeared and their fates can be followed as they move from one species to another the human genome has a higher proportion of these repeats 50 as compared to other species in humans and other mammals genes are unevenly spread throughout the genome while in procaryotes and other eucaryotes fruit y roundworm genes are evenly spaced 1 genes appear to be concentrated in random areas of the genome with vast expanses of noncoding DNA in between chromosome 1 has the most genes about 3000 and the Y chromosome has the fewest about 230 genes code for RNA molecules mRNA tRNA rRNA they also code for the RNA component of the small nuclear ribonucleoprotein complexes used to modify complex RNA molecules mRNA in eucaryotes a gene includes a transcribed nucleotide sequence plus associated sequences regulating its transcription that yields a product with a specific cellular function 2 s V b c Page 1 of4 33109 4 V39 6 DNA s sequence of bases within the gene s nucleotide sequence will ultimately determine the amino acid sequence once it is transcribed into mRNA a RNA is required to serve as an intermediary between DNA and protein b DNA39s quotgenetic codequot nucleotide sequence is first transcribed into speci c RNA molecules mRNA tRNA rRNA c Only one of DNA39s two strands per proteincoding region gene is transcribed for a given gene called the template for the positive strand 1 within the structure of a doublestranded DNA molecule a particular strand may serve as the transcribed strand for some genes and the nontranscribed strand for others 2 also a given gene may sometimes be transcribed in more than one way and somewhat different forms of its protein product may be produced as a result 3 because there is a requirement for high levels of certain products multiple copies of the genes that encode them are present in the chromosome a genes of this type whose products are essential for all cells may occur as tandemly repeated gene sequences in all cells genes for rRNA and tRNA Genes are regulated in all life forms cells within multicellular life with a few exceptions contain all the same genetic information however m certain subsets of the total genetic information genome are expressed in any given cell a In bacterial cells energy efficiency and economical use of resources are usually the primary considerations most gene regulation is at the transcriptional level b in eucaryotes due to the greater cell complexity and need to control development there is greater emphasis on finetuning the control systems gene regulation occurs at many levels In cellular life genetic information always ows from DNA to RNA to protein In acellular life information may ow from RNA initially instead of DNA B The Genetic Code 1 2 E 4 96 V39 Twenty different amino acids found in proteins Because of the five different nitrogenous bases the genetic quotalphabetquot is represented by five different letters DNA contains four of the five A for adenosine I for thymine Q for guanine Q for cytosine with RNA39s four excluding thymine but replacing with uracil Q Secret of the code threeletter code words three nucleotides long are used Triplets Triplet code theog any four nucleotides arranged in triplets produce sixtyfour different code sequences words on the DNA more than enough to produce a unique code word for each amino acid called a codon in mRNA specifically codons specify amino acids a some of the amino acids in the codon assignments are specified by more than one codon called redundancy 1 only methionine and tryptophan have singletriplet codes all others are specified by two to six different codons The genetic code is nearly universal the same codons mRNA s nucleotide code words with a few minor exceptions are used for the same amino acids in all viruses bacteria plants animals and fungi 1 mRNA from one species can be translated in a cell of another species has made genetic engineering possibleRecombinant DNA Technology or rDNA II Protein Synthesis A The Process 1 bioll l 10 jroteinisynthesisdoc Transcription the synthesis of RNA occurs in the nucleus of eucaryotes and the cytoplasm of procaryotes a Information is transcribed from a single strand of DNA which acts as a template into complementa nucleotide sequences of mRNA tRNA and rRNA Page 2 of4 33109 Fquot RNA is synthesized on DNA dependent on RNA polymerases enzymes present in all cells 1 As RNA is synthesized it curls into it characteristic shapes or conformations that may be determined by complementary basepairing within the same RNA molecule tRNA Only one of the strands of DNA is transcribed into mRNA the positive or coding strand or quotsensequot in some viruses mitochondria and chloroplasts different parts of both strands code for proteins transcription occurs in the 53 direction of mRNA Speci c quotpromoterquot base sequences and terminator base sequences are required by the RNA polymerase I Promoters are speci c sites on the DNA where RNA polymerase recognize where to begin RNA synthesis are usually about 40 bases long and are positioned in the DNA just upstream of the point at which transcription will begin A length of the DNA uncoils assisted by unwinding enzymes correlates to the gene hydrogen bonds break RNA polymerase attaches to coding strand and begins attaching complementary RNA nucleotides to the template eventually until it reaches specific termination sites forming a strand of mRNA transcription 1 Eucaryotic mRNA must then be modi ed due to the presence of nonsense base sequences introns procaryotes lack introns Introns are edited out cleaved with the remaining sequences to be expressed exons spliced together as a functional mRNA strand 3 mRNA may consist of 5001000 nucleotides a mRNA has a noncoding leader sequence at its 539 end which contains recognition signals for ribosome rRNA binding b coding sequences containing the actual protein message follows the leader also it contains special termination signals specifying the protein s end c a noncoding 3 trailing sequence follows In eucaryotes mRNA leaves the nucleus and carries the information to the cytoplasm where ribosomes will attach and initiate translation in procaryotes ribosomal subunits attach to the mRNA as quickly as it is transcribed to initiate protein synthesis translation immediately procaryotic bacteria s mRNA may code for one or more proteins Translation conversion of the genetic information carried by an mRNA molecule to the amino acid sequence of a polypeptide occurs in the cytoplasm of eucaryotes a rRNA was initially transcribed on a DNA template composed of 100 to nearly 3000 long f quot quotJ is r J oftwo 39 J r J subunits one large 60s and the other smaller 40s each subunit is made of rRNA and protein when not involved in protein synthesis the two subunits are not bound together represents structural units required to present each codon of mRNA to the tRNA bacteria have smaller 50s amp 30s ribosome subunits 1 When protein synthesis begins rRNA s subunits are separate 2 A small subunit 40s binds to mRNA39s speci c bonding site and then in tRNA s compleX presence a larger subunit 60s joins to form a functioning mRNAribosome compleX a functional ribosome a number of proteins called initiation factors are also required a Proteins destined to become part of the cell s membrane g destined to be packaged for exportation from the cell are produced on attached ribosomes granular ER in eucaryotes b Proteins that are destined to function in a soluble form in the cytoplasm are usually produced on free ribosomes in eucaryotes no distinction in procaryotes bioll l leroteinisynthesisdoc Page 3 of4 33109 0 3 1 D 2 V quot1 N I J