DNA and Mitosis Notes LISA Pre-AP Biology

DNA � Stands for deoxyribonucleic acid

�  DNA is an example of what kind of macromolecule? � Nucleic acids!

� Function �  Contains the “code” for life �  Is the pattern for making proteins

� **more on this next semester!

� Found in the nucleus � Characteristics

�  Double stranded helix � Twisted ladder

�  Can take on a few different forms � Chromatin: an

uncondensed form of DNA �  The DNA is loose, like an

unraveled extension cord

� Chromosome: a condensed form of DNA �  The DNA is organized, like

an extension cord that is all wound up

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� DNA is an example of a nucleic acid polymer What is the monomer called?

� Nucleotide �  Nucleotide = base unit

of DNA �  Consists of sugar,

phosphate, and a nitrogen base

Nitrogen Base � There are four

�  Adenine (A) �  Cytosine (C) �  Thymine (T) �  Guanine (G)

Nitrogen Bases � These bases bond in

very specific ways � Adenine always binds

with Thymine � Cytosine always bonds

with Guanine

� Example: �  Given that DNA is a double strand, what is

the code on the mystery strand?

Strand 1: A C T C G A C T G A T C

� Example: �  Given that DNA is a double strand, what is

the code on the mystery strand?

Strand 1: A C T C G A C T G A T C

Strand 2: T G A G C T G A C T A G

� When a cell divides, it must be copied. �  Known as replication �  This is going to make a new copy of DNA for

the new cell

� Next, we are going to talk about how the cell divides and what happens to the DNA

Cell Division � Cell division is necessary for the

reproduction of both somatic (body) and sex cells (gametes) �  Division of somatic cells: mitosis �  Division of gametes: meiosis

�  Involves the distribution of identical genetic material (DNA) to two daughter cells

The Cell Cycle

�  Interphase �  G1 �  S �  G2

� Cell Division �  Mitosis �  Cytokinesis

Cell  Division  

Cytokinesis  

M  phase  

G1  phase  (Cell  Growth)  

S  Phase  (DNA  Copied)  

G2  Phase  (Growth  and  prepara>on  

for  division)  

Interphase  

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Interphase �  Most of the time spent in this

phase �  Cell grows and copies its

chromosomes in preparation for cell division

�  G1 = Growth �  S = DNA Synthesis

�  DNA is copied �  G2 = Cell prepares for division

�  Sometimes cells exit cycle from G1 and enter G0 where they simply exist and never divide.

Interphase � G1 Phase; “first gap”

�  Cell grows by producing proteins and organelles

� S Phase; “synthesis” �  Chromosomes are duplicated

� G2 Phase; “second gap” �  Cell continues to grow and prepares for

division

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Mitosis � Division of the nucleus � 4 phases of Mitosis

�  Prophase �  Metaphase �  Anaphase �  Telophase

Prophase � Chromatin condenses to become chromosomes

�  Chromosomes appear as sister chromatids � They are identical!

� Nuclear membrane disappears � Centrioles (an organelle) move to opposite sides

of the cell �  creates spindle fibers

� Microtubules

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Metaphase � Chromosomes line up along center of cell

�  The “metaphase plate” �  Spindle fibers attach to centromere to move them

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Anaphase � Sister chromatids

separate at the centromere �  Chromatid: half

of a chromosome

� Slowly pulled to opposite sides of the cell

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Telophase � Two daughter nuclei begin to form � Spindle fibers disassemble � Chromosomes return to chromatin � Nuclear membrane forms � Mitosis is complete

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Cytokinesis � Division of the cytoplasm � Animal cells pinch in creating cleavage furrow � Plant cells develop a cell plate

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