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Eagle Zone-8 minutes
(write the question and complete the sentence with an answer from
the word bank)
1. Mitosis makes __new nuclei.
2. ______ coil and become condensed
3. Along the middle of the cell, called the _____, sister
________start to align.
4. When mitosis ends, _______ begins so cytoplasm can pinch in
half to make new cells called ________.
5. Mitosis allows chromosomes to ________ and divide on their
own.
Word Bank:
Reproduce chromosomes
chromatids
Cytokinesis
two
equator
daughters
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Why do we study DNA?
We study DNA for
many reasons,
e.g.,
• its central
importance to all
life on Earth,
• medical benefits
such as cures for
diseases,
• better food crops.
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Chromosomes and DNA
• Our genes are on
our chromosomes.
• Chromosomes are
made up of a
chemical called
DNA.
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The Shape of the Molecule
• DNA is a very long
polymer.
• The basic shape is
like a twisted ladder
or zipper.
• This is called a
double helix.
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The Double Helix Molecule
• The DNA
double helix
has two
strands
twisted
together.
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One Strand of DNA
• The backbone of
the molecule is
alternating
phosphates and
deoxyribose
sugar
• The teeth are
nitrogenous
bases.
phosphate
deoxyribose
bases
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Nucleotides
O
O -P O
O
O
O -P O
O
One deoxyribose together
with its phosphate and base
make a nucleotide.
O
O -P O
O
Phosphate
Nitrogenous
base
O
C
C
C
O Deoxyribose
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One Strand of DNA
nucleotide
• One strand of
DNA is a polymer
of nucleotides.
• One strand of
DNA has many
millions of
nucleotides.
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Four nitrogenous bases
DNA has four different bases:
C
• Thymine T
• Adenine A
• Guanine G
• Cytosine
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Two Kinds of Bases in DNA
• Pyrimidines are
single ring bases.
• Purines are
double ring
bases.
N
N C
O C
C
N C
N
N C
C
C
N
N C
N C
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Thymine and Cytosine are
pyrimidines
• Thymine and cytosine each have one
ring of carbon and nitrogen atoms.
N
O
C
C
O
C C
N
C
thymine
N
O
C
C
N
C
N
C
cytosine
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Adenine and Guanine are
purines
• Adenine and guanine each have two
rings of carbon and nitrogen atoms.
N
C
Adenine
N
C
C
N
O
N
C
N
N
C
N
C
C
C
N
Guanine
C
N
N
C
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Two Stranded DNA
• Remember, DNA
has two strands
that fit
together
something like a
zipper.
• The teeth are
the nitrogenous
bases but why
do they stick
together?
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C
N
N
C
N
C
C
C
C
N
N
N
C
C
C
O
• The bases attract each
other because of
hydrogen bonds.
• Hydrogen bonds are weak
but there are millions
and millions of them in a
single molecule of DNA.
• The bonds between
cytosine and guanine are
shown here with dotted
lines
N
Hydrogen Bonds
N
O
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Hydrogen Bonds, cont.
• When making
hydrogen bonds,
cytosine always
pairs up with
guanine
• Adenine always
pairs up with
thymine
• Adenine is bonded
to thymine here
N
O
C
C
O
C C
N
C
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Chargraff’s Rule:
• Adenine and Thymine
always join together
A
T
• Cytosine and Guanine
always join together
C
G
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DNA by the Numbers
• Each cell has about 2
m of DNA.
• The average human has
75 trillion cells.
• The average human has
enough DNA to go from
the earth to the sun
more than 400 times.
The earth is 150 billion m
• DNA has a diameter of or 93 million miles from
the sun.
only 0.000000002 m.
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DNA Replication Video
• http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=s
wf::535::535::/sites/dl/free/007243
7316/120076/micro04.swf::DNA%20
Replication%20Fork
Eagle Zone
Replication Practice
• On your paper, complete the missing
DNA strand by adding the
complementary bases.
• A T C G T T G C C A T C
• T A G C A A C G G T A G
Making Proteins
• The process of making proteins is
called PROTEIN SYNTHESIS
• There are several steps to make a
protein
– Replication (DNA only)
– Transcription (RNA)
– Translation (RNA)
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Replication
•
•
•
•
Copying of DNA
Makes a complementary strand
DNA CANNOT LEAVE THE NUCLEUS!
Write the complementary strand for the
DNA strand below using the base pairing
rules learned earlier (Chargaff’s Rule)
– GTA CCG ATC GGA
• Solution:
– CAT GGC TAG CCT
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TYPES OF RNA
• RNA CAN leave the nucleus!
• There are 3 main types of RNA
– Messenger RNA- (mRNA) carry copies of the
DNA instructions OUT of the nucleus
– Transfer RNA- (tRNA) transfers each amino
acid to the ribosome by coded messages from
mRNA
– Ribosomal RNA- (rRNA) assembles proteins
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Transcription
• RNA polymerase (an enzyme) binds to DNA
to separate the DNA strands
• The nitrogenous base thymine (T) now
becomes uracil (U) in an RNA strand
• Use the complementary DNA strand from
earlier (written below) to write the
transcribed RNA strand (mRNA)- don’t
forget the U’s!
– CAT GGC TAG CCT
• Solution
– GUA CCG AUC GGU
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Translation (protein synthesis)
pg. 304-305 in book
• The cell uses information from messenger RNA
(mRNA) to produce proteins
• What happens?
– mRNA comes out of nucleus into cytoplasm
– tRNA carries amino acids to create anticodon
(complimentary bases to mRNA)
– Ribosomes join with rRNA to break bonds to send tRNA
to work again
• Several amino acids in a chain make a protein
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