Cell Cycle and DNA

Why are cells small? Diffusion DNA Surface area-to-volume ratio Fast and efficient over small distances Slow and inefficient over large distances DNA Blueprint for proteins More cytoplasm needs more proteins therefore we would need more DNA Surface area-to-volume ratio A cell’s volume increases much faster than its surface area Plasma membrane does not have enough area to allow all the oxygen, waste and nutrients to diffuse

                                                       Parameters Case I Case II Case III Case IV Length (L) 1 2 3 4 Face Area (L2) 9 16 Volume (L3) 8 27 64 Surface Area(L2 x 6 faces) 6 24 54 96 Area/Volume ratio 1.5

G1 S First stage of interphase Rapid growth and metabolic activity -DNA synthesis – DNA copies itself -Middle of Interphase First stage of interphase Rapid growth and metabolic activity

G2 Cell prepares for mitosis (cell division) In animal cells, centrioles begin to form spindle fibers which aid during cell division End of Interphase

M Cell divides into 2 identical daughter cells over 4 stages (PMAT) Cells are identical to each other and to the parent cells

MITOSIS YouTube: Click

Review of Mitosis Prophase Metaphase Anaphase Telophase

DNA Deoxyribose nucleic acid Holds genetic information Found in the nucleus Chromosomes are made up of long strands of DNA Genes are found on the chromosomes

CHROMATIN

In the nucleus, the DNA double helix is packaged by special proteins (histones) to form a complex called chromatin. The chromatin undergoes further condensation to form the chromosome. So while the chromatin is a lower order of DNA organization, chromosomes are the higher order of DNA organization. An organism’s genetic content is counted in terms of the chromosome pairs present. e.g. humans have 23 pairs (so 46 total) of chromosomes. http://www.diffen.com/difference/Chromatin_vs_Chromosome

DNA Structure DNA is a polymer of nucleotides 3 Parts of a nucleotide (1) Simple Sugar – deoxyribose (2) Phosphate group (3) Nitrogen Base (4 Kinds)

The 4 Kinds of Bases Adenine (A) always pairs with Thymine (T) Guanine (G) always pairs with Cytosine (C)

DNA in the Cell Cycle

Bonding in DNA Covalent Bond Covalent Bond holds the phosphate of one nucleotide to the sugar of another nucleotide Making the outside of the DNA ladder Covalent Bond

Bonding in DNA Hydrogen Bond Hold the nitrogen bases together Making the rungs of the ladder Together the Covalent and Hydrogen bonds create the double helix (twisted ladder)

Scientists James Watson and Francis Crick Won a Nobel Prize in 1953 for discovering the double helix shape of DNA

Scientists (continued) Rosalind Franklin Had information that Watson and Crick “borrowed” to piece together the shape of DNA (was given no credit) VIDEO

DNA Replication Making a copy of DNA 3 Steps (1) DNA unwinds – helicase unzips the DNA (2) Free nucleotides in the nucleus pair up with exposed bases from the unzipped DNA (3) Phosphates and sugars pair up forming a backbone for the free nucleotides