Bio Unit 3 PDF - Cell Biology

Unit 3: The Cell Cycle: The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene Genes are made of DNA, a nucleic acid made of monomers called nucleotides The roles of nucleic acids: Two types: Deoxyribonucleic acid(DNA) Rib...

Unit 3: The Cell Cycle: The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene Genes are made of DNA, a nucleic acid made of monomers called nucleotides The roles of nucleic acids: Two types: Deoxyribonucleic acid(DNA) Ribonucleic acid(RNA) DNA provides directions for its replication The components of Nucelic Acid: Nucleic acids are called polymers called polynucleotides Each polynucleotide is made of monomers called nucleotides Each nucleotide consists of a nitrogenous base, a pentose sugar, and one or more phosphate groups There are two families of nitrogenous bases: Pyrimidines have a single ring and include cytosine, Thymine, and uracil Purines have a double ring and include adenine and guanine Thymine is found only in DNA and Uracil only in RNA DNA vs RNA: The sugar in DNA is deoxyribose, in RNA it is ribose DNA has the base thymine, RNA has Uracil Nucleotide Polymers: Adjacent nucleotides are joined by a phosphodiester linkage, formed in a dehydration reaction. These links create a backbone of sugar-phosphate units with nitrogenous bases as appendages. The ends of a DNA polymer have directionality The sequence of bases along a DNA or mRNA polymer is unique for each gene The structure of DNA and RNA molecules: DNA molecules have two polynucleotides spiraling around the imaginary axis, forming a double helix In the DNA double helix, the two backbones run in opposite directions from each other, an arrangement referred to as antiparallel Most DNA molecules are very long with thousands or millions of base pairs Adenine always with thymine Guanine always with cytosine Somatic cells vs Gamete cells: Gamete cells: reproductive cells Somatic cells: any cell of a living organism other than the reproductive cells Cell Divison: The ability of organisms to produce more of their kind best distinguishes living things from nonliving matter In unicellular organisms, the division of one cell reproduces the entire organism. Cell division enables multicellular eukaryotes to develop from a single cell and once fully grown to renew, repair, or replace cells as needed. Most cell division results in the distribution of identical genetic material in two daughter cells DNA is passed from one generation of cells to the next with remarkable fidelity Cell Cycle summary: Interphase(copying of chromosomes) -G1 phase(first gap) -S phase(synthesis) -G2 phase(second gap) Mitosis(division of chromosomes) Cytokinesis(division of the cell) Phases of Mitosis: Mitosis is conventionally divided into five phases: Prophase Prometaphase Metaphase Anaphase Telophase P-P-M-A-T Phases of the cell cycle: The cell consists of: Interphase, including cell growth and copying of chromosomes in preparation for cell division Mitotic(M) Phase, including mitosis and cytokinesis The Mitotic Spindle: Structure made of microtubules and associated proteins It controls chromosome movement during mitosis In animal cells, the assembly of spindle microtubules begins in the centrosome, a type of microtubule organizing center. The centrosome duplicates during interphase, forming two centrosomes that migrate to opposite cell ends during prophase and prometaphase. Spindle microtubules grow out from the centrosomes during their migration During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes Kinetochores are protein complexes that assemble on sections of DNA at centromeres At metaphase, the centromeres of all the chromosomes are at the metaphase plate, an imaginary structure at the midway point between the spindle's two poles  At metaphase, the centromeres of all the chromosomes are at the metaphase plate, an imaginary structure at the midway point between the spindle's two poles In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell The microtubules shorten by depolymerizing at their kinetochore ends Chromosomes are also reeled in by motor proteins at spindle pores, and microtubules depolymerize after they pass by the motor proteins Cytokinesis: In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow, a shallow groove in the cell surface. In plant cells, a cell plate forms during cytokinesis Binary Fission in Bacteria: Prokaryotes reproduce by a type of cell division called binary fission In bacteria, the single chromosome replicates, beginning at the origin of replication The two daughter chromosomes actively move apart while the cell elongates The plasma membrane pinches inward dividing the cell into two Comparison of Asexual and Sexual Reproduction: In asexual reproduction, a single individual passes genes to its offspring without the fusion of gametes A clone is a group of genetically identical individuals from the same parent, produced asexually In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism Sets of chromosomes in human cells: Human somatic cells have 23 pairs of chromosomes A karyotype is an ordered display of the pairs of chromosomes from a cell The two chromosomes in each pair are called homologous chromosomes, or homologs Chromosomes in a homologous pair are the same length and shape and carry genes controlling the same inherited characters. The sex chromosomes which determine the sex of the individual are called X and Y. Human females have a homologous pair of X chromosomes(XX) Human females have a homologous pair of one x and one y chromosome(XY) The remaining 22 pairs of chromosomes are called autosomes Each pair of homologous chromosomes includes one chromosome from each parent The 46 chromosomes in a human somatic cell are two sets of 23: one from the mother and one from the father A diploid cell(2n) has two sets of chromosomes For humans, the diploid number is 46(2n=46) Each chromosome is replicated in a cell in which DNA synthesis has occurred. Each replicated chromosome consists of two identical sister chromatids A gamete contains a single set of chromosomes and is haploid For humans, the haploid number is 23(n=23)  Each set of 23 consists of 22 autosomes and a single sex chromosome In an unfertilized egg(ovum), the sex chromosome is X In a sperm cell, the sex chromosome may be either X or Y The behavior of Chromosome sets in the human life cycle: Fertilization is the union of gametes The fertilized egg, called a zygote, has one set of chromosomes from each parent and so is diploid. The zygote produces somatic cells by mitosis and develops into an adult At sexual maturity, the ovaries and testes produce haploid gametes Gametes are the only types of human cells produced by meiosis rather than mitosis Meiosis results in one set of chromosomes in each gamete Fertilization and meiosis alternate in sexual life cycles to maintain chromosome number The variety of sexual life cycles: Gametes are the only haploid cells in animals They are produced by meiosis and undergo no further cell division before fertilization Gametes fuse to form a diploid zygote that divides by mitosis to develop into a multicellular organism The Human Life Cycle: The alternation of meiosis and fertilization is common to all organisms that reproduce sexually The three main types of sexual life cycles differ in the timing of meiosis and fertilization Three types of sexual life cycles: In the diploid-dominant cycle, the multicellular diploid stage is the most obvious life stage; the only haploid cells produced by the organism are the gametes. This is demonstrated in the human example. Most fungi and algae employ a haploid-dominant life cycle type in which the body of the organism is haploid; specialized haploid cells from two individuals join to form a diploid zygote. Observed in all plants and some algae, species with alternation of generations have both haploid and diploid multicellular organisms as part of their life cycle. Haploid dominant: In most fungi and some protists, the only diploid stage is the single-celled zygote; there is no multi-cellular diploid stage The zygote produces haploid cells by meiosis Each haploid cell grows by mitosis into a haploid multicellular organism The haploid adult produces gametes by mitosis Alternation of generations: Plants and some algae exhibit an alternation of generations This life cycle includes both a diploid and haploid multicellular The diploid organism called the sporophyte, makes haploid spores by meiosis  Each spore grows by mitosis into a haploid organism called a gametophyte A gametophyte makes haploid gametes by mitosis Fertilization of gametes results in a diploid sporophyte Depending on the type of life cycle, either haploid or diploid cells can divide by mitosis However, only diploid cells can undergo meiosis In all three life cycles, the halving and doubling of chromosomes contribute to genetic variation in offspring How meiosis reduces chromosome number: Meiosis halves the total number of chromosome sets from two to one, with each daughter cell receiving one set of chromosomes The stages of Meiosis: Meiosis 1: Chromosomes condense progressively throughout prophase 1 Homologous chromosomes pair up, aligned gene by gene In crossing over, non-sister chromatids exchange DNA segments at points called chiasmata Events proceed much as in mitosis: Metaphase 1, Anaphase, Telophase 1 Meiosis 2: Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 and cytokinesis Meiosis 2 is very similar to mitosis. The only real difference is that the cells are haploid at the start The big, important differences between meiosis 2 and mitosis: There is no DNA replication between Meiosis 1 and 2, so we have only one homologous chromosome Crossing over and synapsis during prophase 1: During prophase 1, two members of a homologous pair associate along their length DNA molecules of the maternal; and paternal chromatid are broken at matching points The DNA breaks are closed so that a paternal chromatid is joined to a piece of a maternal chromatid, and vice versa Because homologous chromosomes all have their genes in the same order and position, one gene only exchanges with its equivalent on the other chromosome Genetic variation produced in sexual life cycles contributes to evolution: Mutations(changes in an organism’s DNA) are the source of genetic diversity Mutations create different versions of genes called alleles Reshuffling of alleles during sexual reproduction produces genetic variation Origins of genetic variation among offspring: The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises in each generation Three mechanisms contribute to genetic variation: Independent assortment of chromosomes Crossing over Random fertilization The evolutionary significance of genetic variation within populations: Natural selection results in the accumulation of genetic variations favored by the environment Sexual reproduction contributes to the genetic variation in a population, which originates from mutations Cellular organization of the genetic material: All the DNA in a cell constitutes the cell’s genome A genome can consist of a single DNA molecule (common in prokaryotic cells) or several DNA molecules(common in eukaryotic cells) DNA molecules in a cell are packaged into chromosomes Drawing the deck of genes: The “blending” hypothesis is the idea that genetic material from two parents blends(the way blue and yellow paint blend to make green) The “particulate” hypothesis is the idea that parents pass on discrete heritable units(genes) Mendel documented a particulate mechanism through his experiments with garden peas Mendel’s experimental, Quantitative approach: Mendel probably chose to work with peas because: There are many varieties with distinct heritable features or characters; character variants are called traits He could strictly control mating between plants In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization The true-breeding parents are the P generation The hybrid offspring of the P generation are called the F1 generation When F1 individuals self-pollinate or cross-pollinate with other F1 hybrids, the F2 generation is produced The law of segregation: When Mendel crossed contrasting, true-breeding white and purple flowered pea plants, all of the F1 hybrids were purple When Mendel crossed the F1 hybrids, many of the F2 plants had purp;e flowers, but some had white Mendel discovered a ratio of about three to one, purple to white flowers, in the F2 generation  Mendel observed the same pattern of inheritance in six other pea plant characters, each represented by two traits What Mendel called “heritable factor” is what we now call a gene Mendel’s model: First, alternative versions of genes account for variations in inherited characters These alternative versions of a gene are now called alleles Each gene resides at a specific locus on a specific chromosome Second, for each character, an organism inherits two alleles, one from each parent Third, if the two alleles at a locus differ, then one dominant allele determines the appearance of the organism, and the other(the recessive allele) has no noticeable effect on appearance. Fourth(the law of segregation), the two alleles for a heritable character separate during gamete formation and end up in different gametes Mendel’s segregation model accounts for the 3:1 ratio he observed in the F2 generation of his crosses. Possible combinations of sperm and egg can be shown using a Punnett square to predict the results of a genetic cross between individuals of known genetic makeup. A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele. For example, P is the purple-flower allele and p is the white-flower allele. Genetic vocabulary: An organism with two identical alleles for a character is said to be homozygous for the gene controlling that character An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that character Unlike homozygotes, heterozygotes are not true-breeding Because of the effects of dominant and recessive alleles, an organism’s traits do not always reveal its genetic composition. Therefore, we distinguish between an organism’s phenotype, or physical appearance, and its genotype, or genetic makeup. Rules of probability: We can apply the rules of probability to predict the outcome of crosses involving multiple characters A dihybrid or other multicharacter cross is equivalent to two or more independent monohybrid crosses occurring simultaneously. In calculating the chances for various genotypes, each character is considered separately, and the individual probabilities are multiplied. Inheritance patterns are often more complex than predicted by simple Mendelian genetics: Few heritable characters are determined as simply as the traits Mendel studied However, the basic principles of segregation and independent assortment apply even to more complex patterns of inheritance Genetics Glossary: Complete dominance: one allele hides the other where present Incomplete dominance: heterozygotes are between homozygotes on a spectrum Codominance: 2 dominant alleles affect alleles affect phenotype in different ways Multiple alleles: more than 2 alleles for a given gene Pieiotropy: alleles have more than one phenotype Polygenic: more than one gene gives a phenotype Epistasis: where one gene affects another's action in the generation of a phenotype Nature and nurture: environmental impact on phenotype: Another departure from Mendelian genetics arises when the phenotype for a character depends on environment as well as genotype Genotype is generally associated with a range of phenotype possibilities due to environmental influences By convention: Circles=females, squares=males Shaded symbols mean an individual is affected by a condition, while an unshaded symbol means they are unaffected A horizontal line between man and woman represents mating and resulting children are shown as offshoots to this line Shaded symbols mean an individual is affected by a condition, while an unshaded symbol means they are unaffected A horizontal line between man and woman represents mating and resulting children are shown as offshoots to this line Recessively inherited disorders: Many genetic disorders are inherited in a recessive manner These range from relatively mild to life-threatening The behavior of recessive alleles: Recessively inherited disorders show up only in individuals homozygous for the allele carriers are heterozygous for the allele Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal Most people who have recessive disorders are born to parents who are carriers of the disorder Pedigree: A pedigree is a family tree that contains a family history for a particular trait It describes the traits of parents and family across a generation Pedigrees can also be used to make predictions Typically, questions involving pedigree analysis won’t involve making punnett squares for each cross, and they involve a single gene It’s important to remember that the rules of multiplication and addition still apply Sex-linked characters(next week) bring a new flavor to pedigree analysis Treatments for genetic diseases: Treatment aims to introduce healthy versions of genes into the stem cells of patients  The introduced gene does not affect the germ cells, so it does not pass down to the next generation Cystic Fibrosis: Sickle-Cell Disease The chromosomal basis of Mendel's laws: Mitosis and Meiosis were first described in the late 1800s The chromosome theory of inheritance states: Mendelian genes have specific loci(positions) on chromosomes Chromosomes undergo segregation and independent assortment The behavior of chromosomes during meiosis can account for Mendel’s laws of segregation and independent assortment Morgan’s choice of experimental organism: Morgan noted wild-type or normal phenotypes that were common in the fly populations Traits alternative to the wild type are called mutant phenotypes The first mutant phenotype he discovered was a fly with white eyes instead of the wild-type red The chromosomal basis of sex: Humans and other mammals have two types of sex chromosomes: a larger X chromosome and a smaller Y chromosome Individuals who inherit two X chromosomes develop anatomy we associate with the female sex Properties considered male are associated with the inheritance of one X and Y chromosome Only the ends of the Y chromosome have regions that are homologous with corresponding regions of the X chromosome These regions allow the X and Y chromosomes to pair and behave like homologs during meiosis in males Each ovum contains an X chromosome, while a sperm may contain either an X or a Y chromosome Other animals have different methods of sex determination A gene that is located on either sex chromosome is called a sex-linked gene Genes on the X chromosome are called X-linked genes Genes on the Y chromosome are called Y-linked genes; there are a few of these Inheritance of X-linked Genes: X-linked genes follow specific patterns of inheritance: For a recessive X-linked trait to be expressed: A female needs two copies of the allele(homozygous) A male needs only one copy Some disorders: Color blond Duchene muscular dystrophy X inactivation in female mammals: In mammals females, one of the two chromosomes in each cell is randomly inactivated during embryonic development The inactive X condenses into a Barr body If the female is heterozygous for a particular gene located on the X chromosome, she will be a mosaic for that character Mapping the distance between genes using recombination data: Scientific inquiry: Genes that are far apart on the same chromosome can have a recombination frequency near 50% Such genes are physically connected but genetically unlinked Locating genes along chromosomes: Mendel’s hereditary factors were genes; segments of DNA located along chromosomes The location of a particular gene can be seen by tagging isolated chromosomes with a fluorescent dye that highlights the gene Sex-linked punnett squares: By convention, we use an X or Y to indicate the chromosome on which the allele is carried The allele is designated by a superscript letter, often capitalized or not Alterations of chromosome number or structure cause some genetic disorders Large-scale chromosomal alterations in humans and other mammals often lead to spontaneous abortions or cause a variety of developmental disorders Plants tolerate genetic changes better than animals do 1. Nondisjunction leading to aneuploidy 2. Breakage of chromosomes leading to: -Deletion -Duplication -Inversion -Translocation Abnormal chromosome number: In nondisjunction, pairs of homologous chromosomes do not separate normally during meiosis I or sister chromatids do not separate during meiosis II As a result, one gamete receives two of the same type of chromosome, and another gamete receives no copy Aneuploidy results from fertilization involving gametes in which nondisjunction occurred Offspring with this condition have an abnormal number of a particular chromosome A monosomic zygote has only one copy of a particular chromosome A trisomic zygote has three copies of a particular chromosome Polyploidy is a condition in which an organism has more than two complete sets of chromosomes -Triploidy(3n) is three sets of chromosomes  -Tetraploidy(4n) is four sets of chromosomes Polyploidy is common in plants but not in animals Spontaneous origin of polyploid individuals plays an important role in the evolution of plants Alterations of chromosome structure: Breakage of a chromosome can lead to four types of changes in chromosome structure: Deletion removes a chromosomal segment Duplication repeats a segment Inversion reverses the orientation of a segment within a chromosome A diploid embryo that is homozygous for a large deletion is likely missing a number of essential genes; such a condition is generally lethal Duplications and translocations also tend to be harmful In inversions the balance of genes is normal, but phenotype may be influenced if the expression of genes is altered Human disorders due to chromosomal alterations: Alterations of chromosome number and structure are associated with some serious disorders Some types of aneuploidy upset the genetic balance less than others, resulting in individuals surviving to birth and beyond These surviving individuals have a set of symptoms, or syndrome, characteristic of the type of aneuploidy Down syndrome: Down syndrome is an aneuploid condition that results from three copies of chromosome 21 It affects about one out of every 380 children born in the united states The frequency of Down syndrome increases with the age of the mother, a correlation that has not been explained Some research points to an age-dependent abnormality in meiosis Aneuploidy of sex chromosomes: Aneuploid conditions involving sex chromosomes appear to upset the genetic balance less than those involving autosomes Monosomy X, called Turner syndrome, produces X0 females, who are sterile It is the only known viable monosomy in humans Disorders caused by structurally altered chromosomes: The syndrome cri du chat results from a specific deletion in chromosome 5 A child born with this syndrome is severely intellectually disabled and has a catlike cry; individuals usually die in infancy or early childhood Certain cancers, including chronic myelogenous leukemia are caused by translocations of chromosomes Causes: There is an inbuilt error rate to meiosis Some genetic conditions can make errors more likely  Some environmental conditions also impact chances of chromosomal conditions