Download DNA structure and replication

DNA structure and
replication
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Where is DNA located in the Cell?
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What do we know about DNA?
Inside the nucleus of every human cell
is nearly 6 feet of DNA!
It can't be crammed into the nucleus
like a ball of string.
Instead, it is combined with proteins
and organized into a precise, compact
structure, a dense string-like fiber
called chromatin
•Each DNA strand wraps around groups of small protein
molecules called histones forming a series of bead-like
structures, called nucleosomes,
•Under the microscope, uncondensed chromatin has a "beads
on a string" appearance.
•This compression and structuring of DNA serves several
functions. The allows the DNA takes up much less space, and
inactive DNA can be folded into inaccessible locations until it
is needed.
DNA before Replication
DNA structure
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DNA is made up of many
nucleotides connected
together
 A nucleotide is made of:
– Sugar (deoxyribose)
– Phosphate
– Base
• Adenine, Guanine, Thymine
or Cytosine
Phosphate
BASE
SUGAR
DNA structure
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The same bases always
connect together
 A — T and C — G
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The order of the bases
give the DNA its
information or code
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DNA always comes in
two strands, like a
ladder— it is called
double stranded
DNA structure
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In 3-D
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DNA winds
up in a
double
helix
How could you get DNA out of a
nucleus?
How much DNA material could you
retrieve from a strawberry?
What would the DNA look like?
What would you be able to see?
Purpose:
 Procedure: See Hand out
 Data:Observations
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Copying DNA: DNA replication
Before the cell divides in Mitosis and
Meiosis all of the DNA must be copied.
 How?
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Do you remember the basic form
of DNA?
DNA Replication
DNA
needs to replicate
itself to create more cells.
Both body cells and sex
cells
Steps to DNA replication

DNA is unwound and unzipped by enzymes
 The DNA code is read by DNA polymerase
(an enzyme) which adds the corresponding
nucleotide (Nitrogenous base, sugar and
phosphate)
 Example Adenine is added to Thymine and
Cytosine is added to Guanine
DNA before Replication
Both DNA Strands are read and a
new identical DNA strand is created.
If the original DNA strand was
ATCGCCGTTA The corresponding strand
created would be TAGCGGCAAT
 What strand would be created if the original
strand was AAAACCGGATTT?
 The strand would be TTTTGGCCTAAA
 You are so SMART!!!!!!!!!!!

Lets try a few more What DNA
strand would be created from the
following DNA strand?
AATTACGCGGCCC
Did you say TTAATGCGCCGGG
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How about TATATACCGATTTA
Did you say ATATATGGCTAAAT
Great!!!
The DNA Polymerase
T  serves as a proof reader to correct any
mistakes that could occur
 Mistakes occur in 1/10,000
nucleotides added. An error creating a
DNA could cause a disease to occur or
the wrong directions given in another
part of the cell.
 Fun Fact… some people lack DNA
polymerase.
 They are more succeptable to getting
cancer when DNA is damaged from
exposure to UV rays.
How is the code read in the DNA
to create proteins and give
directions other places in the cell?
Transcription
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The code to create proteins which lies in the
DNA must be carried to a place where there
are materials for the proteins to be created.
Where are proteins created?
There is a Problem!!!!
DNA is copied to mRNA because DNA is too
big to leave through the nuclear pores.
It must be changed to something that can fit
through the nuclear membrane
mRNA can do the job!!!!
mRNA is created

RNA Polymerase opens the DNA molecule
 RNA polymerase looks for a specific code that
tells it when to start creating mRNA called a
promoter
 mRNA is created similarly to how DNA is
replicated except mRNA does not have
Thymine.mRNA Polymerase adds uracil to the
mRNA strand instead of thymine to an
adenine
The corresponding Nitrogenous bases are
added as well as the sugar and phosphate
attached.
Can you break the DNA code?
If the DNA sequence was
ATTCGGCCATT what would the mRNA
sequence be that was created?
 ___________________________
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Did you say UAAGCCGGUAA
 Yeah!!

Lets try a few more
If the DNA sequence was
ATTCCGCCGG
What would the mRNA sequence be?
 Did you say UAAGGCGGCC?
 How about TTCCGCGCGCCGAA?
 Did you say AAGGCGCGCGGCUU
 Great!!!
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Translation: when proteins are
made from the mRNA
code

The mRNA travels to the ribosome where the building
materials are
 TrNA (Transfer RNA) is great at breaking codes in
the mRNA to make proteins
 Proteins are made of Amino Acids
 There is a specific code for every three letter
nitrogenous base sequence in mRNA
 These three letter sequences are called codons.
 Each codon tells which amino acid to add to the
protein.
Three letter Codes are Codons.
For example….

GUU on mRNA signals a transfer rNA
molecule to bring Valine a specific type of
amino acid.
 If the three letters were GCC the tRNA would
bring Alanine and add it to the protein.
 Just like building blocks make a wall,Different
amino acids create a unique protein
 This occurs at the ribosome
If I gave you the RNA sequence of
CGGGUAUUAUGUGAAUGA what series of Amino Acids would
be created into a protein?
Did you say Arginine,Valine,Leucine, Cytosine and Glutamine?
YOU ROCK!!!!!
Lets try one more….. If I gave you the MrNA strand of
CGUAGUAGAAGGGCGUGA what Amino Acids would you
bring together?
Arganine, Serine, Argenine, Argenine,Alanine
FABULOSO!!!!!
Amino Acids connect to make
proteins
Here is a great picture of the
whole process….
To review, I will give you the
player…. You will tell me what is
does in the process and where it
hangs out. First for DNA
replication
DNA strand
 DNA polymerase

Now for transcription and
translation
DNA strand
 Nuclear Membrane
 RNA polymerase
 MrNA
 TrNA
 Amino Acid
 Ribosome
 Codon
 Protein
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Your Job…….
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Create 2 comic strips:
1 comic must illustrate how DNA is created
for creating new cells
It must include all major players involved
They must talk about their role in the process
in your own words
They must be pictured in the location they do
their job.
The other comic….
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Illustrates transcription (Creation of mRNA)
and translation (Creation of a protein)
(How mRNA is created and the code from a
DNA molecule allows a unique protein to be
made)
 This comic must represent each player
involved….
 Each player must talk about their individual
role in the process
 Each player must be located in the
environment they do their job.
This will be due….
Next Friday
 You will have Friday as a work day and
some of Monday/Tuesday
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Making Copies: DNA Replication
1.
When DNA is copied, the
rungs of the ladder break
right down the middle, and
pulls apart.
2. A protein: DNA polymerase,
grabs onto new nucleotides
and attaches them using the
old DNA as a template
3. New bases are matched to the
exposed bases on each
strand, and the original DNA
molecule becomes two new
identical DNA
4. The result is two identical DNA
molecules!!