Understanding Chromosomes: Structure and Function

1. Lesson 8.1 CHROMOSOMES

2. Chromosome • One DNA strand & attached proteins • Condensed version of chromatin (long DNA strand) • Duplicated in preparation for mitosis one chromosome (unduplicated) one chromosome (duplicated)

3. How much do you think a chromosome is made up of DNA/proteins? • 40% DNA, 60% protein

4. Don’t forget what DNA looks like! twisted ladder double helix Watson + Crick

9. Each chromosome consists of 2 identical parts called sister chromatids. The point at which the sister chromatids are connected is called the centromere The kinetochore is the part of the centromere that attaches to the spindle fiber.

11. 2 Types of chromosomes • Autosomes –body chromosomes • Sex chromosomes – determine the sex X or Y females XX Males XY

12. What are 3 similarities between Homologues? shape size genes

13. Hmm.. Is a chromosome in a DNA? Or is DNA in a chromosome? • DNA is in a chromosome

15. FOUND? LOOKS LIKE? FOUND? LOOKS LIKE? EUKARYOTIC PROKARYOTIC attached to cell membrane in nucleus X circular <<LINK>>

17. Chromosome Structure DNA one 1 strand of double helix Supercoil =chromatin histone

18. Histones: proteins that are entwined in regularly arranged bead-like groups along the DNA • Keeps DNA strong so it gives shape to chromosomes

19. nucleosome - DNA wrapped around 1 histone WHERE IS THE NUCLEOSOME?!

20. Nonhistones: other proteins that control certain parts of the DNA Ex. DNA helicase – Unzips 2 strands of DNA in replication

21. C. Chromatin: • DNA strands are very tightly wound into a supercoiled string, which is coiled again, forming chromatin. • This allows for a great deal of genetic information to be compacted into a small area. increases SURFACE AREA!

22. One, loooong strand of DNA

23. D.Genes: • Segment of DNA that holds instructions to make a that will show a TRAIT protein

24. For example… trait • The color of your hair is a: • The building blocks that make up the pigmentation of your hair are: • The instructions on how to assemble these proteins is found on a: proteins gene

25. GENE 1. Codes for a trait or protein 2. Thousands of different ones 3. Has many nucleotides 4. Made of codons 5. Found in DNA CODON 1. Codes for amino acids 2. 64 possible codons 3. 3 nucleotide sequence 4. Codon is part of a gene 5. Found in mRNA Comparison of Gene and Codon holds instructions makes proteins

26. ~23,000 genes have been identified in the HUMAN GENOME PROJECT • Less on smaller x’s • More on larger X’s • SHOWS CHROMOSOMES PRESENT IN A CELL

27. Epigenetics – altering genes by messing with OUTSIDE DNA stuff like RNA or HISTONES!

28. Lots of DNA ! • Stretched out, the DNA from one human body cell would be more than _______ !!!!! There are over 6 billion nucleotides • A single line of DNA from a salamander cell would extend for ten meters 20m long

29. 3 nucleotides =CODON =1 amino acid

30. DIPLOID 2n Body cells Humans 46 Two of each type of chromosome – (homologous pairs) HAPLOID n Gametes (sperm or egg cells) One of each chromosome type Humans 23 II. Chromosome Number

31. Is an organism MORE complex if it has MORE chromosomes??? • Nope!

32. EVERY SPECIES HAS A SPECIFIC # OF CHROMOSOMES

33. in this example... least most closest

34. What is the animal that has the highest # of GENES ?

35. Microscopic WATER FLEA (DAPHNIA) has 8000 more genes than humans!

36. III. Human Chromosome Number 46 • Diploid chromosome number (2n) = • Two sets of 23 chromosomes each • One set from father • One set from mother • Mitosis produces cells with 46 chromosomes--two of each type • Meiosis produces cells with 23 chromosomes – one of each type

37. Understanding Cell Division • What instructions are necessary for inheritance? • When you grow, how do you stay “you”? • How is DNA passed into new cells made? • How do you make “half” of a cell ready to make a baby? • How is DNA cut in half in a sex cell? DNA mitosis meiosis

38. homologous pairs 1 X, 1Y 2 X's

39. organized pic of our 46 chromosomes autosomes sex chromosomes

40. Roles of Mitosis • Multicellular organisms • Grow • Replace Cells • Unicellular organisms • Asexual reproduction

41. cell that has just finished mitosis

42. Division Mechanisms Eukaryotic organisms • Mitosis • Meiosis Prokaryotic organisms • _____________________________ (= mitosis) binary fission

43. 2 new bacteria! Binary fission

44. 3 easy steps to divide a bacteria…err.. BINARY FISSION: • 1. chromosomes make copies • 2. cell grows til about 2x its size! • 3. cell wall forms in between the copied chromosomes and the cell SPLiTS!

45. IV. Cell Cycle • Cycle starts when a new cell forms • During cycle, cell increases in mass and duplicates its chromosomes • Cycle ends when the new cell divides <<LINK>>

46. A. Stages of Interphase • G1 (GAP 1) • Interval or gap after cell division – cell grows • S (DNA SYNTHESIS) • Time of DNA synthesis (replication) • G2 (GAP 2) • Interval or gap after DNA replication- prepares for cell division

47. Go stops growth S synthesizes copy of DNA The Cell Cycle G1 cell GROWS cytokinesis G2 prepares to divide mitosis Fig. 8.4, p. 130

48. 1. G1 Phase • after cell division, daughter cells are small and ATP is low • rapid cell growth occurs • certain enzymes used in DNA synthesis are made • cell carries out routine functions • chromosomes are not visible – long thin strands – chromatin

49. GDF 11 protein (growth differentiation factor) might be key to YOUTH bc it freezes cells at the G0 stage!

50. 2. S Phase • DNA replication; chromosomes – sister chromatids form 3. G2 Phase • preparation for mitosis • energy level restored (ATP) • Materials needed to manufacture mitotic structures are made and stockpiled • Increase in protein synthesis (enzymes) 4. Go Phase– (after G1) some cells do not divide again (nerve cells)