AP Bio DNA and Mitosis

Name: ______Period: ___ Date:______

The Structure of DNA

Chargaffanalyzed the amounts of the four nucleotides found in DNA (Adenine, Thymine, Guanine, Cytosine) and noticed a pattern.

1. The amount of A, T, G, C varies from species to species
2. In each species, the amount of A = T, and the amount of G = C ---- Base Pair Rule
Bases come in two types:pyrimidines(cytosine and thymine) andpurines(guanine and adenine)

RosalindFranklinand Wilkins spent time takingX-ray diffractionpictures of the DNA molecule in an attempt to determine the shape of the DNA molecule. 

Watson and Crickare credited with finally piecing together all the information previously gathered on the molecule of DNA. They established the structure as adouble helix- like a ladder that is twisted. The two sides of the ladder are held together by hydrogen bonds.

Watson & Crick Model of DNA:

  • The sugar (deoxyribose) and phosphates make up the "backbone" of the DNA molecule.
  • The phosphate is attached to the 5' carbon (the 5 is a number given to sugar molecules).
  • The DNA strand has a free phosphate on th 5' end, and a free sugar on the 3' end - these numbers will become important later.

Adenine always pairs with Thymine | Guanine always pairs with Cytosine

Side1:: A A T T G G C C A G A T A C
Side2:: T T A A C C G G T C T A T G

DNA is composed of subunits callednucleotides, strung together in a long chain -- Each nucleotide consists of: a phosphate, a sugar (deoxyribose), and a base

More Images:

Here the 5' end and the 3' end are seen again, each side of the ladder has an opposite orientation. One side of the ladder as a free sugar (the 3'end) the other side has a free phosphate (the 5'end). This arrangement is called:ANTI-PARALLEL

The Cell Cycle

**Orderly set of steps between eukaryotic cell divisions

Why do Cells Divide?

  • Growth
  • Reproduction (in single celled organisms)
  • Repair

Some Cells never divide, others divide frequently.

Control of the Cell Cycle

  • G1 Checkpoint - Check to see if DNA is damaged
  • G2 Checkpoint - Check to see if DNA is replicated properly
  • M Checkpoint - spindle assembly checkpoint, check for alignment of chromosomes

Apoptosis- programmed cell death, if any of the checks fail

Mitosis & Cytokinesis

Mitosis - The division of the nucleus that results in identical complete copies of chromosmes packaged into two new nuclei
Cytokinesis - The division of the cytoplasm that results in two daughter cells

**In plant cells, cytokinesis begins when a new cell wall forms between the two new cells.
**In animal cells, the two new cells pinch and pull apart

Mitosis produces:

  • 2 daughter cells
  • The two daughter cells containt the exact same number of chromosomes as the original parent cell
  • Daughter cells are DIPLOID

The Cell Cycle and Cancer

neoplasm: abnormal growth of cells
benign: non-cancerous
malignant: cancerous

Cancer: cellular growth disorder that results from the mutation of genes that regulate the cell cycle

Cancer cells

  • lack differentiation
  • have abnormal nuclei
  • form tumors
  • undergo metastasis & angiogenesis

MITOSIS Practice

10. In humans, each cell (except sex cells) has how many chromosomes? ______
11. After mitosis, how many daughter cells are produced? ______
12. After mitosis (in a human cell), each daughter cell has how many chromosomes? _____
13. How many phases are in MITOSIS? ______
14. Which phase of the cell cycle is the longest? ______
15. During which phase does cytokinesis begin? ______