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DNA Replication
I. Terms:
• A. Genes- the
segments of DNA that
are the units of
inheritance.
Found on chromosomes.
•
• They control the development of traits.
(hair color, blood type. Etc.)
• B. DNA –
(Deoxyribonucleic acid)
chemical that codes for
proteins and controls
the development of
traits and cellular
activities.
• II. Watson and Crick proposed a model for the
DNA structure.
III. Structure of DNA:
•
A. very large
molecule
• B. Made of nucleotides. Each nucleotides consists
of:
• A phosphate group
• a five carbon sugar (deoxyribose)
• a nitrogen base
Nitrogen base
Phosphate group
5 carbon sugar
• C. The nucleotides are
joined together by bonds
between the phosphate
group of one nucleotide
and the sugar of the next
nucleotide. They form
chains called phosphate
sugar chains.
• D. The DNA molecule is composed of two
chains of nucleotides joined by weak
hydrogen bonds between the nitrogen bases.
• The chains of
nucleotides spiral
around a common
center, the shape is
called the double
helix or a twisted
ladder.
E. DNA Code
• E. The DNA code---The chains of nucleotides
in a DNA molecule connect together by bonds
according to a code called the DNA code.
• The code is determined by the order of the
nucleotides.
• The four bases are
A=adenine,
G=guanine,
C=cytosine,
T=thymine
• A joins to thymine,
G joins to cytosine
• The order of the
bases determine
the genetic make
up of the
individual.
F. DNA vs. RNA
•
DNA
• Double stranded
RNA
Single Stranded
• Contains deoxyribose
sugar
Contains ribose sugar
• Has A, G, C, T
• Original genetic
Code
Has A, G, C, U (uracil)
Copy of the genetic
code
IV. DNA replication- DNA makes a copy of
itself during interphase of the cell cycle.
• ***This occurs in
the nucleus of the
cell.
• Step 1- The
double helix
untwists and
looks like a
ladder.
• The hydrogen
bonds between
the bases.
• The two
nucleotide
chains begin
to break and
the chains
open like a
zipper.
• Step 2-Each chain
serves as a pattern
for the formation of
a new chain of DNA.
• Bases on the free
nucleotides found in
the nucleus, join
with the correct
bases according to
the DNA code.
• This type of
replication is known
as semi-conservitive.
• Step 3. -- bonds
form between the
phosphates and
the sugars.
• Step 4.--the two
new molecules of
DNA become
twisted again.
DNA Quiz: Copy the questions.
•
•
•
•
•
Describe the make up of DNA.
What is the bonding pattern of the bases?
What type of bond joins the bases?
What determines the genetic code?
Why does DNA go through replication?
V. DNA Transcription
The process of producing messenger
RNA (mRNA) in the nucleus.
• STEP 1: The DNA molecule carries the code to
make a specific protein.
• The portion of DNA that contains the code for
the specific protein untwists and unzips.
• Free RNA nucleotides found in the nucleus
pair with the exposed DNA strand.
http://www.johnkyrk.com/DNAreplication.html
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• The RNA code is as follows:
A – adenine joins with U – uracil
C – cytosine joins with G – guanine
•
• A sequence of three bases on a mRNA
molecule that codes for an amino acid is
called a codon.
•
• The mRNA molecule is completed by the of
formation of bonds between the RNA nucleotides.
The mRNA molecule separates from the DNA
molecule.
•The completed mRNA molecule leaves the
nucleus through the nuclear membrane and
moves to the ribosome in the cytoplasm.
DNA Transcription Quiz
1. What is being made in the process of
transcription?
2. Give 2 ways RNA is different from
DNA.
3. Where does transcription take place in
the cell?
4. Write the complimentary DNA strand
for the following: GTACCGGTAG
5. Write the RNA strand that would be
made from this DNA: TACGGACTT
VI. Translation: The assembly of a protein molecule according
to the code in a mRNA which occurs in the cytoplasm.
• Step 1: One end of a mRNA molecule
attaches to a ribosome.
• Step 2: Transfer RNA (tRNA) molecules in
the cytoplasm pick up the amino acids. They
are coded to correspond with a particular
mRNA.
tRNA
• Step 3: A tRNA
molecule with the
right anticodon
links to the
complimetary
codon on the
mRNA.
• Step 4: As the
mRNA moves along
the ribosome, the
next tRNA comes in
contact with the
ribosome.
• The next tRNA moves in position with its
amino acid which is linked together by peptide
bond.
• Step 5:
The first tRNA molecule is released and the next
codon comes into place . Then the next amino acid is
attached.
• ******Steps 3 – 5 Are repeated until the
entire message is translated. In this way
chains of amino acids are formed. A protein
molecule is built from one or more chains of
amino acids. There are 20 essential amino
acids in nature.
•
transcription
tranlation
• So: DNA ----→ mRNA ---- protein
DNA Technology
• Brought about a whole new science called
molecular genetics scientists study DNA
molecules and make changes in the DNA.
• Led to a new field
called genetic
engineering.
DNA extraction and Gel
Electrophoresis
• Technique used to separate the DNA from the
rest of the cell is called DNA extraction.
• Long molecules of DNA can be cut into smaller
pieces for study using special restriction
enzymes.
• Pieces of DNA are called fragments and can be
separated using gel electrophoresis.
• DNA fragment patterns can be used to
compare the DNA of different organisms, to
match the DNA of a specific organism, and to
identify one certain gene out of the thousands
of genes in the genome of one individual.
• Also called DNA fingerprinting
because each person’s DNA is
unique.
• This procedure can be used to
help prove or disprove a
criminal’s identity, and it can also
be used to show if two people
are related to each other.
Recombinant DNA
• DNA extraction also makes possible something
called recombinant DNA
• Takes short pieces of DNA from one organism
and joins it to the DNA of a completely
different organism.
• This can be placed back into a living cell by
transformation.
• This is currently being used in medicine because
scientists can transform bacteria so they will produce
hormones or other chemicals that the body needs.
Common example is insulin which some people do
not produce enough of and have the disease
diabetes.
• Scientists are working on methods to replace
defective genes with normal genes. If this is
perfected, it could assist in treating and
possibly eliminating genetic diseases such as
Huntington’s disease, cystic fibrosis, and sickle
cell anemia.
Transgenic Organisms:
• If an organism contains genes from a different
organism, they are called transgenic. Several
transgenic animals have been developed. Transgenic
animals have extra copies of growth hormone genes
which cause them to grow larger and faster.
• Transgenic plants have been produced that
are more resistant to diseases and pests so
that farmers can grow larger crops without
using as many chemicals and pesticides.
Disadvantages to transgenic organisms:
– Could pollinate wild
plants and produce
plants that could not
be controlled by
weed killers.
– Antibiotic resistant
genes could spread
into the environment
and cause bacteria to
become antibiotic
resistant.
– Genetic pollution
Reproductive Cloning:
• Involves transferring the genetic material of a donor
cell into an egg cell that has had its nucleus removed.
• The egg is stimulated by chemicals or electricity to
cause it to divide.
• Then it is implanted into the uterus of a female for
further development until birth.
• The cloned organism is genetically identical to the
original or parent organism.
Copy and complete:
1.
2.
3.
4.
5.
Who discovered the DNA structure?
How is DNA different from RNA?
What are the base pairs found in DNA?
List the three steps in transcription.
When in the cell cycle does DNA replication
occur?
6. Where does transcription occur?
7. What is the purpose of translation?
8. What is an organism that contains genes from
a different organism?
9. Cloning produces organisms that are--?
10. What is transformation?
11 .What is DNA fingerprinting?
12. What do scientists use to cut DNA in an
exact area?
13. What is it called when changes are made to
DNA?