Honors Biology Ch. 8 Notes

Honors Biology, Period 5 Chapter 8 Notes Section 8.4: Chromosomes Replicate Before Each Cell Division I. General Terms 1. DNA (Deoxyribonucleic acid) – nucleic acid that stores hereditary information -forms of DNA: A. nucleotide smallest B. gene C. chromosome D. chromatin broadest E. genome – total collection of genetic information 2. Gene – A sequence of nucleotides that encodes traits (trait = physical) **Approximately 30,000 different genes in the human genome How many total genes in the nucleus of a somatic cell? 60,000 somatic cells are diploid

GACT science

3. Chromosome – A linear structure composed of a set of genes. **A single chromosome may contain anywhere from several hundred to several thousand genes except the y chromosome, which only has about 5 genes. 4. Chromatin – storage form of DNA, where the chromosomes are packaged with storage proteins called HISTONES. -When in chromatin form, individual chromosomes are not visible, but appear as a dark mass under the microscope. 5. Genome – A complete set of genetic information *individual genome *species genome (i.e. the human genome) 6. nucleotide – monomers that make up DNA -small organic molecule consisting of a phosphate group, a ribosugar and a nitrogenous base 7. Gene and Allele Gene – information of a trait Example: -gene for eye color -gene for hair color -gene for cholesterol receptors

Allele – different versions of a gene -blue eye color -brown hair II. Chromosome Replication -Before a cell can divide into two daughter cells, it must first make a complete copy of its chromosomes to pass onto new cells Section 8.8: The Cell Cycle The Cell Cycle: An ordered sequence of events from the time a cell is first formed until its division into two new cells Stages of the Cell Cycle The Cell Cycle consists of two general phases 1. Interphase (90%) 2. Mitotic Phase (10%) INTERPHASE -growth phase -characterized by high metabolic activity -the cell is performing its normal function -interphase is divided into 3 sub categories: 1. G1 (first gap) – cell growth 2. S Phase – DNA synthesis (DNA is copied) 3. G2 (second gap) – growth/ preparation *G0 and the restriction point - G0 – resting phase -restriction point – stage in the cell cycle when the cell evaluates the environment -By the end of G2, the cell has: 1. doubled its size 2. doubled all of its contents 3. DNA appears as chromatin (chromosomes NOT visible) 4. centrosomes become visible (centrioles that display radiating microtubule fibers)

Before S Phase:

After S Phase:

sister chromatids

Eye color HT

IQ Maternal #1

Paternal #1

chromosome

chromosome

Homologous pair MITOTIC PHASE -This is the period where the cell actually divides The effect: A single diploid cell is split into two genetically and structurally identical diploid somatic cells 5 stages: 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase **See figure 8.6 PROPHASE -the nucleus disappears -chromatin condenses and chromosomes become visible *each chromosome consists of two sister chromatids joined a centromere -the mitotic spindle begins to develop -centrosomes move towards the poles of the cell PROMETAPHASE -the nuclear envelope breaks into fragments and disappears -centrosomes reach the poles of the cell -kinetochore fibers develop along the centomere of each chromosome -some of the microtubules of the spindle connect with the kinetochore fibers

METAPHASE -mitotic spindle is completely assembled -chromosomes align along the metaphase plate (equator) *the equator is a fictitious line that bisects the cell -sister chromatids straddle the equator ANAPHASE -the mitotic spindle pulls the sister chromatids apart -the newly liberated sister chromatids move towards opposite poles TELOPHASE & CYTOKINESIS *these two events occur simultaneously, but are separate events Telophase -nucleolus reappear -nuclear envelope reforms -chromosomes revert to chromatin -mitotic spindle disappears Cytokinesis -involves the division of cytoplasm -this physically divides one cell into two cells -this process is different for plants and animals *animal cells – cleavage furrow + contractile ring *plant cells – cell plate Affecting Cell Division Anchorage dependence: -cells must be in contact with a solid surface in order to divide. *extra-cellular matrix -density-dependent inhibition *normal cells stop dividing upon contact with other cells. *crowded cells stop dividing -growth factors *proteins secreted by certain somatic cells the stimulate other cells to divide Section 8.9: Growth Factors Signal The Cell Cycle Control System Growth factors – enter the cell via receptor-mediated endocytosis. *Figure 8.9 A – illustrates 3 checkpoints (G1, G2, M) *M checkpoint is the checkpoint at the end of mitosis at the end of metaphase

Section 8.10: Cancer Cells -cancer is a disease of the cell cycle -it affects 1 out of every 5 people How it works: 1. A single healthy cell undergoes transformation to a cancer cell. 2. The cancer cell will then form a tumor. *tumor – abnormally growing mass of cells *Benign tumor – If the abnormal cells remain localized *Malignant tumor – spreads to other tissue of the body (metastasize) Why? 1. Cells do not heed density-dependent inhibition 2. They proceed past checkpoints without growth factors 3. Some cancer cells secrete their own growth factors Naming Cancers: 1. carcinomas – cancers that originate in external or internal coverings of the body (i.e. skin) 2. sarcomas – cancers that originate in tissues that support the body (i.e. bone and muscle) 3. leukemias and lymphomas – cancers of the blood forming tissue (i.e. bone marrow, spleen and lymph nodes) Treatments: Benign Tumors 1. surgery 2. radiation treatment Malignant Tumors 1. Chemotherapy (drugs) a. Paclitaxel (taxol) – freezes the mitotic spindle arresting a cell in metaphase (from the Pacific Yew Tree grown in Oregon) b. Vinblastin – inhibits spindle formation in prophase (from the Periwinkle Plant on Madagascar) Section 8.11: Review of Functions of Mitosis 1. 2. 3. 4.

replace dead/lost cells repair damaged tissue asexual reproduction (budding) growth

Section 8.12: About Chromosomes There are two types of chromosomes: 1. autosomes – chromosomes that do not influence gender (44)

2. sex chromosomes – chromosomes that influence gender (2) How many homologous pairs of chromosomes do you have? 22  in males the ‘XY’ are not the same 23  in females the ‘XX’ are homologous Section 8.13: Gametes Compare somatic cells and gametes in humans Somatic cells: A. diploid B. diploid number (2n) = 46 **44 autosomes and 2 sex chromosomes C. most chromosomes exist in pairs D. are all genetically identical E. are produced by mitosis Gametes: A. haploid B. hapoid number (n) = 23 C. chromosomes are not in pairs D. are all genetically unique E. are produced by meiosis Ferlitization: 2 haploid gametes fuse to create a diploid zygote Growth: Zygote divides into trillions of cells by meiosis Section 8.14: About Meiosis What is meiosis: -meiosis is a type of cell division that produces gametes -single diploid somatic cell divides into 4 haploid gametes Males: spermatocyte  4 sperm cells Female: oocyte  1 (functional) egg cell Meiosis occurs only in the gonads. Mitosis occurs Male: testes everywhere else Female: ovaries *meiosis does not occur in gametes, it produces them. -the process is triggered by hormones released during puberty. Section 8.18: Crossing-Over -refers to the exchange of DNA between non-sister chromatids of the homologous pair during prophase I of meiosis.

-is an example of Genetic Recombination Defined – the production of gene combinations differ from those carried by the original chromosome Key events: 1. synapsis – the coming together of homologous (tetrads) 2. formation of chiasmata (chiasma) – these are regions where the non-sister chromatids of a homologous pair attach. 3. Crossing-over – the physical exchange of DNA between chromosomes ** crossing-over only occurs between maternal and paternal copies of the same homologous pair. ** crossing-over can occur at 1 or more locations along the chromosome. **see figure 8.18 B Question: Why does it not occur between non-homologues? What accounts for the Genetic Diversity of Gametes? 1. Independent assortment 2. crossing-over Section 8.16: Independent Assortment -refers to the arrangement of homologous pairs of chromosomes during metaphase I of meiosis. **see figure 8.16 -how many different combinations of chromosomes can be created through independent assortment? -possible combinations of chromosomes = 2n -an adult can produce 223 genetically unique gametes. How many different zygotes can be created through the random fertilization of a sperm and an egg cell? -number of genetically unique zygotes = 64 trillion NONDISJUNCTION *autosomes – all non-sex chromosomes (#1-22) *sex chromosomes – X and Y *note: chromosomes #1-44 are homologous pairs of chromosomes. 45 and 46 are homologous in females only. Key Terms: Nondisjunction – the failure of homologues or sister chromatids to separate during cell division Aneuploidy – abnormal number of chromosomes (chromosomal aberration) Trisomy – 3 copies of a chromosome Monosomy – 1 copy of a chromosome Karyotype – standard picture of grouped chromosomes in a cell Amniocentesis – the process of collecting fetal cells from the amniotic sac

DISORDERS ASSOCIATED WITH NONDISJUNCTION OF AUTOSOMES Chromosome

Common Name

Clinical Description

Trisomy 13

Patau Syndrome (1/5000)

Serious eye, brain, and circulatory defects Death within one year.

Trisomy 18

Edwards Syndrome (1/10000)

Every organ is faulty. Death within one year.

Trisomy 21

Down Syndrome (1/700) (Increases with the age of The female)

Mental retardation, short stature, heart problems, increased risk of leukemia & Alzheimer’s, sterile

Trisomy 22

Down Syndrome2

Same as above + increased skeletal deformities

DISORDERS ASSOCIATED WITH NONDISJUNCTION OF SEX CHROMOSOMES Chromosome

Common Name

Clinical Description

XO

Turner Syndrome

short stature, webbed neck, female, not fully developed sexually, sterile

XXY

Klinefelter Syndrome (1/2000)

sterile male, underdeveloped testes, secondary female characteristics

XYY

None/ supermale

tall male, heavy acne, slight Retardation, fertile (criminals?)

XXX

metafemale/ superfemale

fertile female, normal Intelligence

*CANNOT SURVIVE WITHOUT AN X CHROMOSOME.

OTHER DISORDERS IN MEIOSIS 1. Deletion – part of a chromosome is broken off and the fragment is lost during meiosis Example: Cri-du-chat syndrome cause: part of chromosome 5 breaks off symptoms: small head, moon face, severe retardation, cries like a kitten 2. Duplication – when a chromosome fragment attaches to a sister chromatid 3. Inversion – when the chromosome fragment reattaches to the original chromosome but in the reverse direction 4. Translocation – attachment of a fragment of a chromosome to a nonhomologue Example: CML (Chronic Myelogenous Leukemia) cause: part of chromosome #22 has crossed over with #9 (The Philadelphia Chromosome) symptoms: large spleen, anemia, skin bruises or lethargy. - it often advances to more serious stages that includes acute myeloid leukemia - most patients with CML are adults - children may develop the disease, but only rarely - previous radiation exposure can predispose to this leukemia