DNA & Cell Reproduction

1. DNA & Cell Reproduction MODERN BIOLOGY Chapters 10-1 & 8

2. DNA What is DNA? Deoxyribonucleic acid or DNA is a long thin molecule (nucleic acid) that stores genetic information. Main Function: Store and transmit the genetic information that tells cells which proteins to make and when to make them. l

3. Structure of DNA DNA -The Double Helix Scientists James D. Watson and Francis Crick determined the structure of DNA in 1953, using the X-ray crystallography work of Rosalind Franklin and Maurice Wilkins that indicated DNA had a helical structure (shaped like a twisted ladder).

4. Structure of DNA Made of smaller, repeating subunits called NUCLEOTIDES. Each nucleotide is made of 3 parts: 1. Sugar (deoxyribose) 2. Phosphate 3. 4 different Nitrogenous Bases (A, G, C, T)

5. Structure of DNA *Sugar and phosphate group - same in all nucleotides . *4 different Nitrogen bases: Adenine, thymine, guanine and cytosine

6. Structure of DNA The bases, adenine, thymine, guanine, and cytosine, are often labeled A, T, G and C. Each base always pairs with its ‘partner’ base; referred to as complementary base pairing’.

7. Structure of DNA Complementary Base Pairing Adenine always bonds with thymine to form a step Cytosine always bonds with guanine to form a step Deoxyribose sugar and phosphate are the backbone or sides of the ladder

8. Structure of DNA

9. ~FYI~ A DNA molecule can have billions of ‘steps’. Approx. six billion in the human cell !! These steps are made up of different combinations of the base pairs, A, G, T, C. The number and pattern of pairs form a genetic "code" that makes up genes-the genetic code that controls growth, development and characteristics of an organism. Using just these four bases, nature can create an almost unlimited variety of genetic messages. http://www.pbs.org/wgbh/nova/genome/media/2809_q_02.htm

10. DNA Replication Cells that divide must pass exact copies of their DNA to their offspring cells. REPLICATION-the process of duplicating a DNA molecule. During replication , the double helix unwinds & separates. Each chain serves as a template for a new chain, or strand of DNA.

11. DNA Replication The Steps of DNA Replication: 1. To begin the process, the double helix unwinds. As with all metabolic activities, an enzyme (DNA helicase) is needed for this process. 2. DNA helicase unzips the 2 strands of nucleotides in between the bases – point called the replication fork. Now the bases are exposed. http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter14/dna_replication_fork.html

12. DNA Replication • The Steps: • 3. Complementary nucleotides floating in the nucleus pair with the exposed bases. • DNA polymerase (another enzyme!) assists in the addition and bonding of the complimentary nucleotide. • Result: 2 new strands of DNA - each consisting of ½ new DNA and ½ old DNA. (identical to the original) • http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter14/how_nucleotides_are_added_in_dna_replication.html

13. DNA Replication

14. http://www.youtube.com/watch?v=hfZ8o9D1tus DNA REPLICATION WORKSHOP ACTIVITY http://www.pbs.org/wgbh/aso/tryit/dna/# http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter3/animation__dna_replication__quiz_1_.html

15. Accuracy & Repair of DNA • DNA replication is accurate - usually only 1 error in every 10,000 paired nucleotides • But any error, called a mutation, can have serious effects • Radiation, chemicals , heat can damage DNA (mutation) • Cell has proofreading techniques – like spell check • Over 20 or more repair enzymes fix errors

16. http://learn.genetics.utah.edu/content/begin/dna/tour_dna.htmlhttp://learn.genetics.utah.edu/content/begin/dna/tour_dna.html

18. Cell Reproduction All cells come from the division of pre-existing cells. Cell division or Cell Reproduction allows for growth and repair, carries on life and passes genetic information to future generations.

19. Cell Reproduction 1. Before a cell can divide, the loosely packed genetic material (DNA) in the nucleus of the eukaryotic cell must make exact copies of itself. This loosely packed genetic material (DNA) is referred to as chromatin. 2. Chromatin then coils into very compact structures called chromosomes. Each chromosomes consists of two identical strands of DNA tightly wrapped around proteins called histones.

20. Cell Reproduction

21. Chromosomes 3. These two identical halves are referred to as chromatids (or ‘sister chromatids’) Centromere - Holds the two chromatids together. 4. During division, sister chromatids from each chromosome separate and each new cell will get one.

22. Cell Reproduction

23. Chromosome Numbers Every Species has a different number of chromosomes Humans have 46 chromosomes (23 pairs) Human and animal chromosomes are either: • Autosomes • sex chromosomes 44 autosomes(do not determine the sex) 2 sex chromosomes (determine the sex) Females have 2 X chromosomes Males have an X and a Y chromosome

25. Chromosome Numbers Every cell of an organism produced by sexual reproduction has two copies of each autosome Autosomal Homologous chromosomes (sometimes called homologues) are the same size and shape and carry genes for the same traits.

26. Chromosome Numbers KARYOTYPE: *An arranged photomicrograph of chromosomes. *Shows the number of chromosomes, and what they look like under a microscope. *Helps determine problems in chromosomes. **Attention is paid to: chromosome number & length position of the centromeres banding pattern sex chromosomes

30. Chromosome Numbers Trisomy 21 – Down Syndrome • 3 copies of chromosome 21 instead of 2 • 1 in 900 births • More common with older mothers • Some impairment of cognitive ability and physical growth • A particular set of facial characteristics

31. Chromosome Numbers Cells having two sets of chromosomes are said to be diploid (2n). Diploid - having both chromosome for each homologous pair. All human cells (somatic), except reproductive cells (sperm & egg) are diploid cells. 46 - 22 pairs homologous chromosomes & 2 sex chromosomes.

32. Chromosome Numbers Cells with only one of the two chromosomes is considered haploid (1n) Sperm and egg cells are haploid. Haploid cells have half the number of chromosomes that are present in diploid cells. When two haploid cells combine, each new cell will be diploid.

33. Chromosomes: Eukaryote vs. Prokaryote

34. Cell Division Every Cell has a life of its own! Every Cell comes from pre-existing cells! • single-celled organisms • billion of cells that make up the bodies of plants and animals. Each cell has: • A beginning (growth) • A middle (genetic material replicates and cell prepares for cell division) • And an end (Mitosis & Cytokinesis ) Voila - TWO NEW CELLS!!

35. Cell Division: Eukaryote vs. Prokaryote Cell division - the process by which cells produce offspring cells It is very different for prokaryotes and eukaryotes

36. Cell Division: Eukaryote vs. Prokaryote • Cell Division in Prokaryotes: • Binary fission – division of a prokaryotic cell into two offspring • Single chromosome copies itself • Cell grows to 2X its size • Cell wall forms between the 2 chromosomes • Each new cell is identical

37. Cell Division: Eukaryote vs. Prokaryote • Cell division in eukaryotes • Mitosis – • Division of a cell’s nucleus that produces a genetically identical cell • It does not change the amount of DNA in a cell • Mitosis occurs in the reproduction of unicellular organisms and in the addition of cells to a tissue or organ of a multicellular organism.

38. Cell Division: The Cell Cycle The Cell Cycle is the process or stages cells go through to grow, copy their DNA, and divide to make new cells. The cycle starts when a cell is formed and ends when a cell divides to make new cells. http://www.cellsalive.com/cell_cycle.htm

39. Cell Division: The Cell Cycle The Cycle consists of: Interphase – time between cell division Mitosis – nucleus of cell divides Cytokinesis – division of cytoplasm = 2 new cells!

40. Cell Division: The Cell Cycle • Interphase • Takes up 80-90% of a cells lifespan • Three distinct parts: • G1 (Growth Phase) – cell doubles in size, organelles double in number • S (Synthesis Phase) – chromatin (DNA) replicates • G2 (Growth Phase) - rapid growth phase & cell check *prepare for next division • G0 (resting phase) – muscles cells, retina cells, nerve cells – those you don’t need a lot of go into a resting phase

41. Cell Division: The Cell Cycle Mitosis • Chromosomes separate • Nucleus divides There are four important stages of Mitosis: • Prophase • Metaphase • Anaphase • Telophase

42. The Four Stages of Mitosis Mnemonic “(P)LEASE” - Prophase “(M)AKE” - Metaphase “(A)NOTHER” - Anaphase “(T)WIN” - Telophase

43. Cell Division: Mitosis • Prophase • Chromatin coils and forms chromosomes • nucleolus and nuclear membrane disappear • centrosomes and spindle fibers appear. • Chromosomes can be seen under a microscope.

44. Cell Division: Mitosis • Metaphase spindle fibers assist in aligning all chromosomes at the center of the cell.

45. Cell Division: Mitosis • Anaphase Spindle fibers pull chromosomes apart. One set of chromosomes is pull toward one pole of the new cell and the other set toward the other.

46. Cell Division: Mitosis • Telophase • Centrioles and spindle fibers disappear. • Middle of an animal cell pinches together. • A nuclear membrane forms around each new set of chromosomes. • In plant cells, a new cell wall and a new cell membrane form down the middle of the cell.

47. Mitosis in Plant Cells

48. Cell Division: Mitosis • Cytokinesis • Cytoplasm and organelles split and form two daughter cells – exactly like the parent cell • Each cell receives an identical copy of the original cell’s chromosomes and half of the cytoplasm and organelles

49. Now Take the Mitosis Quiz Record your resultsSpecial thanks to Cell Division: Mitosis Please watch this video