DNA

Experiments: 

Griffith’s Experiment: Gave mice pneumonia, discovered a “transformation” factor

• S Strain - Deadly

• R strain - Not deadly

Avery et al. Experiment

• Demonstrated that DNA is the transformation factor, not protein

Hershey and Chase

• Evidence that DNA, not protein, carries the genetic information

Structure of DNA

• Franklin - did an X ray of DNA

• Watson and Crick - double helix + base discovery

Nucleotides - building blocks of DNA

• Made of Phosphate Sugar Nitrogenous Base

4 types of Nitrogenous Bases

• Adenine (purine)

• Guanine (purine

• Cytosine (pyridimine)

• Thymine (pyridimine)

(A and T will always go together, as well as C and G)

Replication of DNA

• Enzymes separate the DNA strands

• DNA helicase

• Complementary Bases Pair

Replication Forks

• Only part of the strand separates as replication begins. DNA polymerase works in only one direction along the strand

• LEading strand - replication is continuous

• Lagging strand - DNA polymerase makes small Okazaki fragments

What is the Secret of Life?

• “The sequence of bases in DNA codes for the sequence of amino acids in proteins”

Why do cells need to divide?

• Allows for differentiation

Limits to cell growth : 

•  as diameter increases, surface area to volume ratio decreases

Diffusion / osmosis occurs at a set rate, therefore a larger cell has difficulty obtaining all the nutrients and gas it needs and has trouble getting rid of waste. 

Solution…

• The cell makes copies of its DNA and divides into 2 daughter cells

The Cell cycle

• G1 - cell growth, normal cell function

  • S - DNA replication (synthesis)

    • G2 - preparation for division

      • Mitosis - division and separation of the chromosomes

        • Cytokinesis - division of the cytoplasm

G0 phase - cell stays in G1 type of phase forever

Chromosomes

• Chromatin = DNA and proteins

  • DNA is wound around histone proteins to make a nucleosome

    • Nucleosomes are wound around each other to make a coiled strand

      • The coiled strand is super coiled to make a chromosome

Facts about chromosomes

• Most organisms have pairs of homologous chromosomes

• Homologous means they have genes that code for variations of the same thing

• For example, one gene may code for hair color, but one can code for red and one can code for brown

• Humans have 23 pairs of chromosomes, thus, we have 46 chromosomes

More

• When a chromosome doubles, it is still one chromosome until it divides

• The 2 parts of a doubled chromosome are called chromatids

• Chromatids are connected by a centromere

• Once the chromatids separate each is called a chromosome

Mitosis

• Chromatin must condense into chromosomes,

  • Chromosomes line-up in the center of the cell

    • Sister chromatids move to opposite sides of the cell and 2 new nuclei form

(I)nterphase (P)rophase on a (M)etaphase (A)naphase (T)elophase

I P on a MAT

Interphase (1st)

• All of the cell cycle except mitosis and cytokinesis

  • Includes normal cell growth and activity, DNA synthesis, and preparation for division

Prophase

• Longest phase of mitosis

  • Chromosomes condense and become visible

    • Spindle forms

      • Nuclear envelope and nucleolus disappear

Metaphase

• Chromosomes line up on the equator of the cell

  • Microtubules connect to the centromeres

Anaphase

• Centromeres separate

  • Chromatids get pulled to opposite sides of the cell, becoming chromosomes

Telophase

• Chromosomes begin to unwind

  • Nuclear envelope and nucleolus reform

    • Spindle falls apart

Cytokinesis

• Animal cell

  • Membrane moves inward and the cytoplasm is pinched in 2

• Plant cell

  • A cell plate forms, becomes a new cell wall