Transcript FORENSIC SCIENCE - Lamar County School District

DNA & RNA
The Nucleic Acids
Remember: Each chromosome is a very long DNA
molecule that contains many genes.
Gene: A segment of DNA that is part of a chromosome
that is responsible for inherited traits such as eye
color, hair color, skin color, etc.
It directs the protein production that controls the cell.
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DNA & RNA
The Nucleic Acids
DNA: (Deoxyribonucleic Acid):
•Is an organic molecule composed of nucleotides.
•Is a molecule that is common to all living things,
from bacteria to humans.
•It is the blueprint of an organism, containing the
genetic instructions for building proteins.
•A DNA molecule canNOT be viewed with a
compound light microscope.
The composition of DNA was first described correctly in
1953 by two scientists, Watson and Crick. They
discovered that it was formed from two long chains of
nucleotides shaped much like a spiraling ladder, and
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they
called it a double helix.
DNA & RNA
The Nucleic Acids
Structure of DNA: (DNA is composed of nucleotides.)
Nucleotides of DNA have three Parts:
1. Deoxyribose (a five carbon sugar)
2. Phosphate group
(these two bond together to make up the
of the ladder)
3. 1 of 4 Nitrogen Bases
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
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The Nucleic Acids
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The Nucleic Acids
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The nitrogen bases adenine and guanine are called
purines which have a double ring of carbon and
nitrogen.
The nitrogen bases cytosine and thymine are called
pyrmidines, which have a single ring of carbon and
nitrogen.
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DNA & RNA
The Nucleic Acids
•The 2 chains of nucleotides in a DNA molecule are held
together by hydrogen bonds between the nitrogen
bases.
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The Nucleic Acids
•The 2 chains of nucleotides in a DNA molecule are held
together by hydrogen bonds between the nitrogen
bases.
•The 2 bases on the same rung of the DNA ladder are
referred to as a base pair.
•In DNA
•Cytosine always bonds with guanine, and
•Thymine always bonds with adenine!
C=G
G=C
T=A
A=T
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DNA & RNA
The Nucleic Acids
•Base Pairing Rules. The strictness of base-pairing
results in 2 strands that are complementary, which
means the sequence of bases on one strand
determines the sequence of bases on the other strand.
Example:
1st strand of DNA has
T C GAAT T
The other strand must have A C T A
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DNA & RNA
The Nucleic Acids
•All organisms contain the same DNA (made up of
nucleotides with adenine, thymine, guanine, and
cytosine)
•The reason organisms can be different from each other
is because the order of nucleotides in two different
organisms are different (sequence of bases)
Example: A squirrel differs from a rosebush because the
order of nucleotides in its DNA is different.
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DNA & RNA
The Nucleic Acids
•Replication:
During mitosis and meiosis the cells divide. Each time
a cell divides it must make a copy of its DNA.
Replication is the process by which DNA is duplicated,
forming two identical copies from one original.
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DNA & RNA
The Nucleic Acids
These are the steps of replication:
1. The enzyme DNA helicase breaks the hydrogen
bonds between the nitrogen bases that hold the two
strands together, unzipping the DNA molecule.
2. As the DNA continues to unzip, free nucleotides from
the surroundings in the nucleus bond to the single
strands base pairing.
3. The enzyme DNA polymerase forms the sugar-tophosphate bonds that connect nucleotides on each
strand of DNA.
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DNA & RNA
The Nucleic Acids
Replication of DNA doesn’t begin at one end of the
molecule and end at the other, rather it occurs
simultaneously at many points on the molecule,
speeding up to process.
Replication is completed when the entire molecule has
been unzipped and replicated.
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DNA & RNA
The Nucleic Acids
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DNA & RNA
The Nucleic Acids
Each new DNA molecule has one nucleotide strand
from the original DNA molecule and one nucleotide
strand that has been newly synthesized from free
nucleotides in the cell.
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DNA & RNA
The Nucleic Acids
Gene Expression is the use of genetic information in
DNA to make proteins.
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DNA & RNA
The Nucleic Acids
Gene Expression is the use of genetic information in
DNA to make proteins.
Gene Expression takes place in 2 stages:
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DNA & RNA
The Nucleic Acids
Gene Expression is the use of genetic information in
DNA to make proteins.
Gene Expression takes place in 2 stages:
1. Transcription is when the RNA copy of a gene is
made.
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DNA & RNA
The Nucleic Acids
Gene Expression is the use of genetic information in
DNA to make proteins.
Gene Expression takes place in 2 stages:
1. Transcription is when the RNA copy of a gene is
made.
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DNA & RNA
The Nucleic Acids
Gene Expression is the use of genetic information in
DNA to make proteins.
Gene Expression takes place in 2 stages:
• Transcription is when the RNA copy of a gene is
made.
• Translation is the 2nd stage of gene expression
where 3 different kinds of RNA work together to
assemble amino acids into a protein molecule.
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DNA & RNA
The Nucleic Acids
Gene Expression is the use of genetic information in
DNA to make proteins.
Gene Expression takes place in 2 stages:
1. Transcription is when the RNA copy of a gene is
made.
2. Translation is the 2nd stage of gene expression
where 3 different kinds of RNA work together to
assemble amino acids into a protein molecule.
Those 3 different kinds of RNA that work together are
mRNA, tRNA, rRNA.
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The Nucleic Acids
Transcription
Transcription is the process of producing RNA
(Ribonucleic Acid) from DNA.
RNA is the form in which information moves from DNA
in the nucleus to the ribosomes in the cytoplasm.
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The Nucleic Acids
Transcription
The process of transcription is similar to the process of
replication, but RNA differs from DNA in 3 ways:
1. RNA is single stranded (DNA is double stranded)
2. RNA has ribose as the sugar (DNA has deoxyribose
as the sugar
3. RNA has four nitrogen bases, but Thymine is
replaced with Uracil
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There are 3 Types of RNA:
1. mRNA-messenger RNA:
It carries the information from DNA (in the nucleus)
out into the cytoplasm
2. tRNA-transfer RNA:
It brings amino acids to the ribosomes so they can
be assembled into proteins.
3. rRNA-ribosomal RNA:
It makes up the ribosomes, the site of protein
synthesis
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Cytosine
Cytosine
Guanine
Guanine
Adenine
Adenine
Uracil
Thymine
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The Nucleic Acids
The Genetic Code
Remember that DNA’s purpose is to provide a blueprint
for making proteins.
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The Nucleic Acids
The Genetic Code
Remember that DNA’s purpose is to provide a blueprint
for making proteins. Proteins are built from chains
of smaller molecules called amino acids, and there
are 20 of them.
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DNA & RNA
The Nucleic Acids
The Genetic Code
Remember that DNA’s purpose is to provide a blueprint
for making proteins. Proteins are built from chains
of smaller molecules called amino acids, and there
are 20 of them.
Recall that there are only four nitrogen bases. So how
can four bases code for 20 amino acids?
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The Genetic Code
The answer is that each strand of DNA is read in sets of
three nitrogen bases, called a codon.
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The Nucleic Acids
The Genetic Code
The answer is that each strand of DNA is read in sets of
three nitrogen bases, called a codon. By reading in
groups of three bases there are 64 combinations
possible.
Of these 61 code for amino acids, and there is a
START codon (AUG) and 2 STOP codons (UAA &
UAG)
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The Nucleic Acids
Protein Synthesis Equation:
DNA
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mRNA
Protein
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The Nucleic Acids
Protein Synthesis Equation:
DNA
mRNA
Protein
transcription
translation
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Translation
Translation (or protein synthesis, gene expression) is
the process of converting the information in a
sequence of nitrogen bases in mRNA into a
sequence of amino acids that make up a protein.
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Translation
The steps of translation are:
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Translation
The steps of translation are:
1. The first codon of the mRNA strand attaches to a
ribosome (rRNA).
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The Nucleic Acids
Translation
The steps of translation are:
1. The first codon of the mRNA strand attaches to a
ribosome (rRNA).
2. Then a tRNA molecule has a special section called
an anti codon that is complementary to the codon on
the mRNA molecule. The first codon is methionine.
AUG signals the start of protein synthesis.
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The Nucleic Acids
Translation
The steps of translation are:
3. Next the ribosome slides down the mRNA strand to
the next codon.
4. When the first and second amino acids are in place,
an enzyme joins them by a peptide bond.
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The Nucleic Acids
Translation
The steps of translation are:
5. This process continues until it reaches a stop
codon. The chain of amino acids are now
considered a protein.
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The Nucleic Acids
The order of events that leads to genetic expression:
Protein synthesis
•
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DNA to
RNA to amino acids to
protein
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The Nucleic Acids
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The Nucleic Acids
Mutations:
Mutation is any mistake or change in the DNA
sequence. Mutations in gametes can be passed on
to offspring of the affected individual, but mutations
in body cells affect only the individual in which they
occur.
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The Nucleic Acids
Mutations:
1. Chromosome mutation –involves a change in the
structure or number of chromosomes.
One example is nondisjunction (when one or more
pairs of homologous chromosomes fail to
separate during meiosis.)
Down Syndrome in humans is caused by
the presence of an extra 21st chromosome.
Other chromosome mutations may be caused by
deletion, translocation, inversion, and duplication
of parts of the whole chromosome.
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The
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Acids
Four Types of Mutations:
1. Deletion mutation- a piece of chromosome breaks off
completely.
The new cell will lack a certain set of genes. Often this
is fatal to the zygote.
2. Duplication mutation- a chromosome fragment attaches
to its homologous chromosome, which then carry two copies
of a certain set of genes.
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Deletion Mutation
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Duplication Mutation
3. Inversion mutation- the chromosome piece reattaches to
the original chromosome but in a reverse position.
4. If the piece reattaches to a nonhomologous chromosome
a translocation mutation results.
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Inverse Mutation
Translocation Mutation
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DNA & RNA
The Nucleic Acids
Mutations:
• Gene mutation—involves a change in the chemical
makeup of the DNA. This is where one or more DNA
nucleotides are deleted or substituted with others.
These are called point mutations.
Frame shift—are mutations that change one or just a
few nucleotides in a gene on a chromosome.
Example: sickle cell anemia and cystic fibrosis
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Occasionally random gene mutations produce
changes that make the individual better adapted
to the environment. Such mutated genes tend to
increase in frequency with in a population.
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DNA & RNA
The Nucleic Acids
Mutations:
3. Mutagens increase the incidence of mutation.
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DNA & RNA
The Nucleic Acids
Mutations:
1. Mutagen mutation increase the incidence of
mutation.
Examples of these:
Xrays
Ultraviolet rays
Radioactive substances
Chemicals
Nicotine
Alcohol
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