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THE HUMAN LIFE CYCLE and CELL DIVISION. BODY CELLS ARE DIPLOID- (2n) They contain two copies of each chromosome. One set from the dad’s sperm and one set from the mom’s egg.These replicate by MITOSIS.

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  1. THE HUMAN LIFE CYCLEand CELL DIVISION BODY CELLS ARE DIPLOID- (2n) They contain two copies of each chromosome. One set from the dad’s sperm and one set from the mom’s egg.These replicate by MITOSIS. GAMETES ARE HAPLOID- (n) They contain one copy of each chromosome randomly chosen (and mixed up) from the two that are available.They are haploid so that they can combine to form a diploid zygote.

  2. DNA- Deoxyribonucleic Acid GENOME- all the genes an organism has CHROMOSOMES- structures made of DNA and proteins CHROMATIDS- “half-chromosomes” CHROMATIN-DNA/protein complex that makes up chromosomes

  3. DNA double helix Histones “Beads on a string” Nucleosome Tight helical fiber Supercoil Sister chromatids Centromere • The DNA in a cell is packed into an elaborate, multilevel system of coiling and folding

  4. Unduplicated Chromosome Chromosome? Sister Chromatids? What’s in name? When the cell divides, the sister chromatids separate from each other and are called chromosomes again Chromosome duplication Duplicated Chromosome Sister chromatids Chromosome distribution to daughter cells Figure 8.5

  5. S phase (DNA synthesis; chromosome duplication) TWO PHASES OF THE CELL CYCLE Interphase (90% of time) Interphase • Cell growth and replication of DNA Mitosis • Cell divides G1 G2 Mitotic phase (M) (10% of time) Cytokinesis Mitosis Figure 8.6

  6. Centrioles Chromatin Nucleolus Nuclear envelope Plasma membrane Interphase • Interphase has three parts • G1- Organelle duplication • S - DNA replication • G2- Proteins needed for mitosis are produced • Cell spends most of its time in interphase and DNA stays loosely packed in the nucleus as chromatin

  7. Mitosis and Cytokinesis • Mitosis has 4 phases • Prophase • Metaphase • Anaphase • Telophase AND • Cytokinesis • We will go through each individually

  8. Prophase Metaphase Fragments of nuclear envelope Early mitotic spindle Centrosome Centromere Chromosome, consisting of two sister chromatids Spindle microtubules Spindle Figure 8.7.2

  9. Anaphase Telophase and Cytokinesis Nucleolus forming Cleavage furrow Nuclear envelope forming Daughter chromosomes Figure 8.7.3

  10. Cleavage furrow Cleavage furrow Contracting ring of microfilaments Daughter cells (a) Animal cell cytokinesis Figure 8.8a

  11. Cell undergoing Mitosis

  12. Cancer:Cells Growing Out of Control

  13. EXAM RESULTS • High Score = 82 • Scores were calculated using 82pts = 100% • So, a score of 68 would equal: 68/82 (100) = 82.9% • For those who turned in a study guide: • 5 pts was added to your exam score


  15. EXAM RESULTS 82.9% 24.4% 24.4%



  18. Haploid gametes (n = 23) Egg cell Sperm cell Meiosis Fertilization Diploid zygote (2n = 46) Multicellular diploid adults (2n = 46) Mitosis and development Figure 8.13 Gametes and the Life Cycle of a Sexual Organism • The life cycle of a multicellular organism is the sequence of stages leading from the adults of one generation to the adults of the next

  19. Pair of homologous chromosomes Centromere Sister chromatids Figure 8.12 Homologous Chromosomes A karyotype

  20. 1 2 Chromosomes duplicate Homologous chromosomes separate 3 Sister chromatids separate Homologous pair of chromosomes in diploid parent cell Homologous pair of duplicated chromosomes Sister chromatids Meiosis I Meiosis II Interphase before meiosis Figure 8.14 • The life cycles of sexual organisms involve an alternation of diploid and haploid stages

  21. Interphase Centrosomes (with centriole pairs) Nuclear envelope Chromatin Chromosomes duplicate The Process of Meiosis • Haploid gametes are produced in diploid organisms • Two consecutive divisions occur, meiosis I and meiosis II, preceded by interphase • Crossing over occurs

  22. Meiosis I Meiosis I: Homologous chromosomes separate Telophase I and Cytokinesis Prophase I Metaphase I Anaphase I • Meiosis I Sites of crossing over Microtubules attached to Chromosomes Sister chromatids remain attached Cleavage furrow Spindle Sister chromatids Tetrad Centromere Homologous chromosomes pair and exchange segments Tetrads line up Pairs of homologous chromosomes split up Two haploid cells form: chromosomes are still double

  23. Meiosis II: Sister chromatids separate • Meiosis II Telophase II and Cytokinesis Prophase II Anaphase II Metaphase II Sister chromatids separate Haploid daughter cells forming During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes

  24. Mitosis Meiosis Meiosis I Parent cell (2n) Parent cell (2n) Chromosome duplication Chromosome duplication Tetrad Crossing over Daughter cells 2n 2n Meiosis II n n n n Daughter cells

  25. Independent Assortment of Chromosomes Possibility 1 Possibility 2 Metaphase of meiosis I Metaphase of meiosis II Gametes Combination a Combination b Combination c Combination d Figure 8.17

  26. Random Fertilization • The human egg cell is fertilized randomly by one sperm, leading to genetic variety in the zygote

  27. Tetrad Prophase I of meiosis Chiasma, site of crossing over Metaphase I Spindle microtubules Metaphase II Gametes Recombinant chromosomes Crossing Over • Homologous chromosomes exchange genetic information • Genetic recombination occurs

  28. Down Syndrome: An Extra Chromosome 21 Figure 8.19

  29. The incidence of Down Syndrome increases with the age of the mother Figure 8.20

  30. Accidents During Meiosis Can Alter Chromosome Number • NONDISJUNCTION • The members of a chromosome pair fail to separate during anaphase • Gametes with an incorrect number of chromosomes are produced

  31. Meiosis I Nondisjunction Meiosis II Nondisjunction Gametes n n - 1 n - 1 n - 1 n + 1 n + 1 n + 1 n Number of chromosomes (a) Nondisjunction in meiosis I (b) Nondisjunction in meiosis II Figure 8.21

  32. Egg cell • The result of nondisjunction n + 1 Sperm cell Zygote 2n + 1 n (normal) Figure 8.22

  33. Other Chromosomal Abnormalities • Part of Chromosome #5 is missing • Cat-like cry (malformed larynx) • Deformed ears/eyelids • Severe retardation Fragile X Syndrome X chromosome is broken

  34. Abnormal Numbers of Sex Chromosomes • Nondisjunction • Also affects the sex chromosomes Table 8.1

  35. Web of skin Poor beard growth Breast development Constriction of aorta Poor breast development Under- developed testes Under-developed ovaries (A) A woman with Turner syndrome (XO) (B) A man with Klinefelter syndrome (XXY)

  36. Nucleic Acid Structure & Functions

  37. DNA- Deoxyribonucleic Acid • Stores genetic information • Is copied and passed from generation to generation • All living organisms have DNA and it is identical in structure and function in all organisms RNA-Ribonucleic Acid Is another nucleic acid molecule found in cells

  38. DNA and RNA: Polymers of Nucleotides • RNA is a nucleic acid very similar to DNA (it functions with DNA to make proteins) • They both consist of chemical sub-units (monomers) called nucleotides • The nucleotides are joined by a sugar-phosphate backbone

  39. Phosphate group Nitrogenous base Sugar Nitrogenous base (A,G,C, or T) Nucleotide Thymine (T) Phosphategroup Sugar (deoxyribose) DNA nucleotide Polynucleotide Sugar-phosphate backbone

  40. NUCLEOTIDES • There are five different nucleotides • Three are found in both DNA and RNA: • cytosine (C) • adenine (A) • guanine (G) • One is found only in DNA: • thymine (T) • RNA has uracil (U) in place of thymine

  41. Rosalind Franklin • She earned her doctorate in physical chemistry from Cambridge University in 1945 • Rosalind Franklin did the the X-ray crystallography work which elucidated the structure of DNA • Watson and Crick used her X-ray crystallography data to make a model of DNA • James Watson, Francis Crick, and Maurice Wilkins received a Nobel Prize for the double-helix model of DNA in 1962, four years after Franklin's death at age 37 from ovarian cancer.

  42. Watson and Crick’s Model of the Double Helix

  43. Hydrogen bond • Notice that the bases pair in a complementary fashion A=T or A=U (RNA), G=C • Hydrogen bonds hold bases together • Three for G-C, two for A-T

  44. FUNCTIONS of the NUCLEIC ACIDS • DNA has two functions: • Replication (for mitosis and meiosis) • Stores the codes for proteins in its sequence • RNA has one major function: • Plays THREE key roles in protein synthesis

  45. DNA Replication • When a cell or organism reproduces, a complete set of genetic instructions must pass from one generation to the next • This replication of DNA occurs during interphase (S) of the cell cycle.

  46. Parental (old) DNA molecule • DNA replicates by a template mechanism • This is call semi-conservative replication • A new strand is added to each old strand Daughter (new) strand Daughter DNA molecule (double helices)

  47. DNA REPLICATION Origin of replication Origin of replication • Begins at specific sites on a double helix • Proceeds in both directions Origin of replication Parental strand Daughter strand Bubble Two daughter DNA molecules

  48. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN • DNA functions as the inherited directions for a cell or organism • How are these directions carried out?

  49. How an Organism’s DNA Genotype Produces Its Phenotype • An organism’s genotype, its genetic makeup is the sequence of nucleotide bases in DNA • The phenotype is the organism’s specific traits • Traits are determined by the types of proteins an organism has in its cells • DNA and RNA function together to produce proteins

  50. Nucleus DNA DNA specifies the synthesis of proteins in two stages Transcription RNA Translation Protein Cytoplasm

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