Chapter 12
Background information
• Chromosomes are made of DNA and
proteins.
• Until the 1940’s there was a debate
about which was the genetic material
because proteins are more complex
than DNA.
• Finally in 1952 DNA was proven to
be the genetic material.
What is DNA?
• Deoxyribonucleic Acid
• Double stranded
• An organisms genetic code………..what it looks
like, what genetic diseases you may have, how
that organism acts. DNA controls everything
about an organism
• The sequence of nitrogen bases determines
what the organism will be.
DNA Composition
Composed of repeating nucleotides.
Nucleotides have three parts:
1. Sugar (deoxyribose)
2. Phosphate group
3. Nitrogen base
Nucleotide
Nucleotide
Double Helix
Nitrogen Bases In DNA
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•
•
•
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
• Adenine always pairs with Thymine (A-T)
• Cytosine always pairs with Guanine (C-G)
Pyrimidines
• Are single ringed: Cytosine and thymine
Purines
• Are Double ringed: Adenine and Guanine
Discovery of DNA
• Once DNA was proven to be the
genetic material there was a race
to determine the structure of
DNA.
Discovery of DNA
• James Watson (American) and Francis Crick
(British) discovered the 3D structure of DNA.
Won noble prize in 1962 (Watson and Crick)
• DNA structure is referred to a double helix
• Two strand of DNA held together by weak
hydrogen bonds. Adenine always pairing with
Thymine and Cytosine always pairing with
Guanine
Other DNA Scientist
• Martha Chase and Alfred Hershey• Extracted DNA from the protein coats of a
simple viruses called, bacteriophages, using a
simple kitchen blender. (1952) Won Noble
prize in 1969.
Other DNA Scientist
• Erwin Chargaff discovered
base pairing rules
•A always pairs with T
•C always pairs with G
Noticed that for all organisms the amount of guanine was
equal to the amount of cytosine, the amount of adenine
was equal to the amount of thymine.
• Maurice Wilkins & Rosalind Franklin
determined the general structure of DNA
using X-ray diffraction.
Replication
• Process of making a copy of DNA
• DNA
DNA
1. Very Complex
2. Extremely rapid
3. Very accurate (only one in a billion nitrogen
bases are paired incorrectly).
4. Process requires enzymes
DNA Replication Process
4 Steps
1. DNA unwinds (like a twisted ladder)
2. The double helix is unzipped by the enzymeDNA helicase
3. The complementary bases will be paired to
each side of the original strand
4. The DNA will rewind or twist
*Each of the new DNA molecules will contain ½
of the original DNA sequence
DNA Replication
DNA Replication
• Example:
1. DNA Strand: TCGTATTAA
2. Give the complementary strand
1.
2.
TCGTATTAA
AGCATAATT
Protein Synthesis
• DNA is the blueprint for protein synthesis.
• Proteins are made on the ribosome's in the
cytoplasm.
• DNA is too large to leave the nucleus.
• Therefore the cell must make a copy to get the
DNA out. This copy is RNA.
• Here is how we get from genes (DNA) to traits
(proteins).
DNA
transcription
RNA
translation
Protein
Protein Recall
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•
•
•
•
•
What are they made of?
Amino acids
Where are they made?
Ribosomes
Uses of proteins in body?
Enzymes, collagen- structure, hemoglobincarries O2 in blood, antibodies
RNA –vs- DNA
• RNA- Ribonucleic acid
Single stranded
Composed Of:
1. Sugar (Ribose)
2. Phosphate group
3. Nitrogen base URACIL instead of
THYMINE (A, U,C,G)
Types of RNA
1. Messenger RNA (mRNA) – carries the
nucleotides that code for the protein from
the nucleus to the ribosomes.
2. Transfer RNA (tRNA)-picks up individual
amino acids in the cytoplasm and carries
them to the ribosomes to pair with the
mRNA.
3. Ribosomal RNA (rRNA)-binds the mRNA to
the tRNA.
Transcription (occurs in the nucleus)
• Process of making RNA off of DNA
Example:
Base sequence of DNA:
AGCTGA
Complementary mRNA:
UCGACU
Reading the Genetic Code
• Three nitrogen bases code for an amino acid.
• This three nitrogen base group is referred to
as a CODON.
• You must break the mRNA down into
multiples of three. Then read chart.
Translation
• Process of converting mRNA into amino acids
(reading the chart) which codes for proteins.
Amino Acid Codon Chart
Genetic Changes
• Mutations: changes in the genetic code
• Some may be good. Most are bad
• Examples:
Good Mutation- Animals stronger or faster.
Bad Mutation-Does not code for needed
proteins . Mutations in body cells are not
passed to offspring only those in sex cells
Causes of Mutations
• Radiation
• High temperatures
• Chemicals (drugs, asbestos,formaldehyde,
agent orange)
• Ultraviolet light
• Nuclear radiation
Types of Mutations
• Deletions:
When part of the chromosome is left out
Insertion
• When part of the chromosome breaks off and
attaches someplace else
Inversion
• Part breaks off and attaches backwards
Translocation
• Part breaks off and is added to a different
chromosome
Mutations