chapter 12-2 chromosomes and dna replication notesnewburyparkhighschool.net/stillwagon/biocp/current...
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Chapter 12-2 Chromosomes
and DNA Replication Notes
I. The Review
A. Prokaryotic cells do not have a nucleus
1. DNA molecules are located in the cytoplasm
2. Usually a circular DNA molecule and it is
referred to as the cells chromosome
B. Eukaryotic cells have a nucleus
1. Can have 1000x more DNA than prokaryotic
cells
2. DNA is located in the form of a number of
chromosomes (in the nucleus)
a. Varies widely from species to species
Lots of DNA, but not all of it
codes for proteins!
C. DNA = Deoxyribonucleic acid (sugar =
deoxyribose)
1. Function: transmit and store hereditary, or
genetic information.
2. DNA molecules are LONG!
a. Ex: E. Coli (prokaryote that lives in human
colon) has 4,639,221 base pairs
b. This equals approximately 1.6mm
Chromatin (interphase)=
granular material
within the nucleus
Chromosome=
visible during
mitosis and can
be clearly seen
under the
microscope as an
“X” (two sister chromatids)
nucleosome
Let’sREVIEW...
histone
protein.
D. Nucleotide = Monomer of DNA
1. 3 parts: Phosphate group; deoxyribose
sugar; and one of the four Nitrogenous
bases –A, T, G, or C
Label Figure
E. Double Helix
1. Backbone = Deoxyribose & Phosphate Group
of each nucleotide (Held together by covalent
bonds)
2. “Steps of Ladder” = nitrogenous bases (Held to
complementary DNA strand by hydrogen bonds)
3. Any base sequence is possible following base
pairing rules:
a. A pairs with T
b. C pairs with G
F. How Does DNA Fit into your cells?
1. Forms a chromosome!
2. How? ….DNA coils
around proteins
called histones and
then this chromatin
supercoils around
itself to form
nucleosomes
a. Nucleosomes
bunch together to
form the visible
“X” chromosome
(prophase of
mitosis).
DNA is copied during a process
called1. replication.
2. translation.
3. transcription.
4. transformation.
replic
ation.
transla
tion.
transc
riptio
n.
transfo
rmatio
n.
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http://highered.mheducation.com/olcweb/cgi/plu
ginpop.cgi?it=swf::535::535::/sites/dl/free/007
2437316/120076/micro04.swf::DNA%20Repli
cation%20Fork
II. DNA Replication – duplicates DNA
A. Background Information
1. We must pass exact copies of DNA from one
cell to the next
2. Before a cell divides, it must copy its DNA so
that all cells have a copy of the genetic
instructions (remember cell cycle – S phase
of Interphase)
3. This process involves LOTS of enzymes!
An Intro to the
Enzymes!
4. Each half of the DNA double helix (parental
strands) can serve as a pattern (“template")
for the replication of complementary
(daughter) strands forming two double helix
molecules.
Semi-Conservative
Replication
B. The Process
1. An enzyme (DNA Helicase) unwinds &
"unzips" the DNA (separates the 2 DNA
strands) by breaking the Hydrogen bonds
between base pairs
a.Replication bubble-small area where
replication begins
b.Two forks of replication move in opposite
directions along the chromosome.
2. DNA polymerase (enzyme) bonds free
nucleotides to elongate the new daughter
strands using base pairing rules(A-T; C-G).
a. The sugar-phosphate groups of the new
nucleotide are covalently bonded to the
growing DNA chain (forming the new
"backbone")
3. The DNA Polymerase
will also "proofread" the
order of bases & make
corrections in the new
strand.
a. It finds a mistake…backs up; removes the incorrect
base then adds the correct base.
b. This maximizes the odds that each molecule is a
perfect copy of the original strand.
4. Remember the 2 DNA strands are
antiparallel, one strand runs up and the other
runs down
5. Polymerase can only add N-bases in the
direction of replication
a. Leading strand-new continuous
complementary DNA strand synthesized along
the template strand in the mandatory 5’ 3’
direction
b. Lagging strand-a discontinuous synthesized
DNA strand (fragments) that elongates in a
direction away from the replication fork. As
more of the parental strand is exposed more
nucleotides are laid down.
6. DNA Ligase (an enzyme) joins the
fragments of the lagging strand
In addition to carrying out the replication of
DNA, the enzyme DNA polymerase also
functions to1. unzip the DNA molecule.
2. regulate the time copying
occurs in the cell cycle.
3. “proofread” the new copies to
minimize the number of
mistakes.
4. wrap the new strands onto
histone proteins. unzip th
e DNA m
olecu
le.
regu
late
the ti
me co
pyin...
“pro
ofread” t
he new
cop...
wra
p the n
ew st
rands o
n..
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C. Each new DNA molecule has one
nucleotide strand from the original DNA
molecule and one strand that is newly made
(semiconservative replication)
Lagging Strand
Label Figure
Template Strands
Replication Fork
DNA Polymerase
DNA Polymerase
DNA Ligase
Leading Strand
Okazaki
Fragments
The first step in DNA replication is
1. producing two new strands.
2. separating the strands.
3. producing DNA
polymerase.
4. correctly pairing bases.
producin
g two n
ew st
rands.
separa
ting t
he stra
nds.
producin
g DNA p
olymera
se.
corr
ectly
pairi
ng base
s.
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DNA replication results in two DNA
molecules,
1. each with two new strands.
2. one with two new strands and the other with two original strands.
3. each with one new strand and one original strand.
4. each with two original strands.
each w
ith tw
o new
stra
nds.
one with
two n
ew st
rand...
each w
ith o
ne new
stra
n...
each w
ith tw
o orig
inal
st...
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DNA Vocab List
Nucleotide
Base pairing
Chromatin
Histone
Nucleosome
Chromosome
Replication
DNA polymerase
Helicase
Ligase
Replication fork
DNA Base Pairing Practice-NO PARTNERS YOU ALL HAVE A DIFFERENT MESSAGE
First Message Assigned:
Number of DNA Message Assigned:_____ (carefully copy below the DNA message assigned):
DNA: _________________________________________________________
Complementary Strand: _________________________________________________________
******See me in class for directions for this section******
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