DNA & Cell Division

http://buffonescience9.wikispaces.com/UNIT+3+-+Cell+Reproduction

  • VOCAB: Cell cycle, DNA, centromere, chromatid, chromosome, gene, mitosis, spindle fibers, microtubules, asters
meiosis, diploid, haploid, centriole, cytokinesis, synapsis, trisomy, crossing over, telomere,





Meiosis

http://www.youtube.com/watch?v=kVMb4Js99tA
http://www.pbs.org/wgbh/nova/baby/divide.html
    • only occurs in organisms that utilize sexual reproduction
    • occurs from stem cells to make sex cells ( sperm & ovum)
    • starts with a diploid stem cell, ends with 4 DIFFERENT haploid sex cells
    • PMAT1PMAT2
    • spermatogenesis or oogenesis depending on the sex of the individual

meiosis.jpg



Interphase G1, S, G2 (just as in mitosis)



(MEIOSIS I)

Prophase I
1) chromatin winds into chromosomes
2) chromosomes find their homologue in a process call synapsis
3) homologues form tetrads and touch
4) chromosomes trade pieces of their telomeres in a process called CROSSING OVER
5) this particular stem cell has a diploid number of 4


Metaphase I
1)homologues line up in PAIRS along the center of the cell
2)INDEPENDENT ASSORTMENT occurs



Anaphase I
1) homologous chromosomes separate, moving one to each side of the cell
in a process called segregation
2) the process will effectively reduce the chromosome number from (in humans) 46 doubles to 23 double chromosomes


Telophase I
cell pinches

Cytokinesis I
-pinch off
-notice the 2 new cells are now double haploid (2 double chromosomes instead of 4)

(MEIOSIS II)

Prophase II
(like mitosis)



Metaphase II
(like mitosis)



Anaphase II
(like mitosis)





Telophase II
like mitosis except the ovum in females produces one huge egg and three discarded "polar bodies" by unevenly distributing cytoplasm. Spermatogenesis make 4 viable sperm, however.

Cytokinesis II
creates 4 DIFFERENT haploid cells for sexual reproduction

Excellent HELP!!!!!!!!!!!!!!!!!! (courtesy of Noah Smith)
http://www.sumanasinc.com/webcontent/animations/content/meiosis.html

PRACTICE MITOSIS VS MEIOSIS
http://www.biologyinmotion.com/cell_division/



DNA: Its structure and Function

dna_structure.gif

-1952 Roselin Franklin xrayed DNA

-1953 Watson & Crick proved DNA to be inheritable & discovered its stucture

-DNA is found in every cell with a nucleus & is the BLUEPRINTS or recipe for who you are

-the secret code of DNA is found within the sequence of the nitrogen bases (rungs)

-DNA is comprised of rungs made of pairs of bonded nitrogen bases (A-T & T-A ; G-C & C-G)

-Its shape is considered a double helix and was discovered to be such by Watson & Crick in 1953 (Nobel prize for this work on x-raying DNA)

-Nitrogen bases attach to a deoxyribose (sugar) on the rails or backbone of the strand

-Phosphate molecules connect deoxyriboses together along the rails












http://www.youtube.com/watch?v=oNW_ykH3AvA&feature=more_related

WATCH THIS CLIP WITHOUT THE SOUND FOR AN EXCELLENT ANIMATION OF REPLICATION SHOWING THE LAGGING STRAND vs. THE LEADING STRAND AND FORMATION OF OKAZAKI FRAGMENTS: http://www.youtube.com/watch?v=d1A4bJqmINU&feature=related

CHECK YOURSELF QUESTIONS ON DNA STRUCTURE AND REPLICATION
1) What 4 base pairs make up the nitrogen bases (rungs) of the DNA double helix and which nitrogenous base bonds with which?
2) What distinguishes the the way A bonds to T vs. C bonds to G (hint: H-bond numbers)?
3) When DNA is synthesized, it must snap itself together in the direction of moving from what prime to what prime?
4)What enzyme unzips the original DNA from the parent cell in order to begin the process of copying it?
5)Free floating snapped-together DNA parts for replication consisting of a nitrogenous base, deoxyribose, & phosphate are called what?
6)The backbone of DNA is made alternating molecules of what in BETWEEN the rungs and what attached to the rungs?
7)Which strand of new DNA moves easily in the direction of the helicase because of the 5-->3 synthesis rule?
8)Which strand has to work opposite of the helicase direction and thus has to make fragments and later "glue" them together?
9)What purpose does starter RNA Primase serve?
10)What are Okazaki fragments?
11)What does semi-conservative mean in terms of DNA synthesis?
12)The copied DNA in Interphase (S) is now coiled into what?
13) The 46 double chromosomes are made of two sister chromatids, one side from the first daughter copy and the other side the identical corresponding daughter copy...what are these two identical coils held together at?
14) A full copy of your DNA is found in nearly every nucleated cell in your body. Two cells in the human body that do not have a full set of your DNA are a) eggs or sperm and b) red blood cells. What is the reason for this in each case? (hint: the reason is very different for "a" vs "b")


dna_replicating.gif