DNA replication
BIG IDEA
• Living systems store, retrieve, transmit and
respond to information essential to life
processes.
Enduring understanding
• Heritable information provides for continuity
of life.
• Essential Knowledge:
– DNA is the primary source of inheritable info
– In eukaryotes, heritable info is passed on the next
generation via processes that include the cell cycle
and mitosis and meiosis plus fertilization.
– The chromosomal basis of inheritance provides an
understanding of the pattern of passage
(transmission) of genes from parent to offspring.
1. How was the structure of DNA
identified?
2. Erwin Chargoff:
*Chargoff’s rule : The proportion of adenine
equals that of thymine, and guanine equals
that of cytosine -- therefore, purines are
proportionate to pyrimidines
Homework
• Read p. 241- 243…be prepared to write out
the answers to questions 1-4 on p. 243 in class
tomorrow.
• Take notes for a quiz on p. 295-299.
1. Why do cells divide?
2. Surface area to volume ratio is not large
enough
* cells cannot move molecules in/out effectively
2.Cells are used to repair tissue damage
2. DNA overload if it gets too big
2. Organisms develop and grow
1. Why & how does DNA replicate
prior to cell division?
2. Cells need to transmit their DNA to cells
* body cells (somatic cells) need to be identical
to parent cell
* sex cells (gametes) need to pass
1/2 genetic material to offspring
2. DNA is the genetic code within chromosomes
* DNA is wrapped tightly around proteins
(histones) = nucleosome
* Nucleosomes are looped and coiled to make
chromosomes compact
* Chromatin is the “substance” of DNA &
histones
Refer to page 297 of textbook
2.Cells replicate their DNA
* Occurs during the S (synthesis) phase of
the Cell Cycle
2. Steps to DNA semi-conservative replication
* DNA unzips (helicase)
* DNA polymerase joins new
nucleotides to form new
strand
* Replication goes in
both directions
Practice replication
3’
A T G C A G
5’
5’
T A C G
3’
T C
2. Other jobs of DNA polymerase
* connects sugars to phosphates
* proofreads DNA.
DNA replication video animation
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/007243
7316/120076/micro04.swf::DNA Replication Fork
• 2. cell must copy lots of DNA quickly
3. solution: multiple origins
2. telomeres shorten with cell divisions....adult
cells stop using telomerase.....cancer cells
keep telomerase working......FOUNTAIN OF
YOUTH?
Think about this.
• Why do cells divide?
• When do cells replicate their DNA?
• Do organisms grow by getting bigger cells? Or
more cells?
• How does a lizard regrow a tail?
Romanovs mDNA
http://www.dnai.org/d/index.html?m=2,1
PCR- a technique used to copy DNA
• http://www.dnalc.org/resources/animations/
pcr.html
Refer to iPad- tutorial w/shoelaces
reflection p. 485
• PREVIEW OF MITOSIS/
– Listen to vocabulary
1. What is the cell cycle of a cell?
2.
Interphase: stage 1
G1 - growth,
protein synthesis,
general cell functioning
S - DNA is replicated
G2 - cell prepares for division
2.Mitosis (nuclear division)
a. Prophase –
chromosomes condense chromatids visible -nuclear
membrane dissolves
•
• b. Metaphase - chromatids line up along
middle of cell (equator)
c. Anaphase - chromatids pull apart to
opposite poles of cell (spindle fibers
made in G2 pull chromatids apart)
d. Telophase - nuclear membranes reappear,
cell pinches in to divide in plants the cell plate
(wall) forms
Cytokinesis
• Cell continues to pinch in & cytoplasm divides
out—2 new daughter cells are made… both
have identical copies of the chromosomes
Review of cell cycle
Tutorial
http://sciencenetlinks.com/interactives/dna.html
Online tutorials
• http://district.bluegrass.kctcs.edu/rmccane00
01/shared_files/bio137website/BIO137/137La
b2/Lab2MitosisSlides.html
Create a table
• Create a two column chart.
• Column one- describe what is happening
• Column two- sketch the image…
1.How do cells regulate the cell
cycle?
• 2. Cells stop growth when they come in
contact with one another
• 2. Regulatory proteins (cyclins)
* Check to see that DNA is replicated
*Check to make sure spindle fibers are attached
2. Growth factors stimulate/stop cell division
Analyze Rise & Fall of Cyclins
• iPad p. 491 parrot book
• 2. Apoptosis- programmed cell death
– * forms body parts- foot, hand…
– * cells die if there is a problem (usually)
– * too much cell death- Parkinson’s disease
• 2. Cancer is uncontrolled cell growth
– *cells don’t respond to regulators
– * p53 gene is often defective (pro-oncogene)
Cancer knows no bounds
Timeline
• 1. notes: why do cells divide? & how does
DNA replicate?
• mtDNA/Romanovs & PCR computer lab.
• Notes: cell cycle/color code sheet…
• Online mitosis (full period)
• Notes: cancer/stem cells & cell regulation
• 1. Give 2 reasons why cells divide.
• 2. As a cell increases in size, which increases
more rapidly, its surface area or volume?
• 3. Calculate the surface area to volume of a
cube 2 x 2 x 2.
• 4. Do prokaryotic cells have a nucleus?
• 5. What are the proteins that DNA is tightly
coiled around?
• 6. What is chromatin?
• 7. The process of DNA copying is called:
• 8. The enzyme responsible for copying DNA is
called: