Living bacteria and dead bacteria killed mouse Harmless bacteria picked up DNA from harmful...
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Transcript of Living bacteria and dead bacteria killed mouse Harmless bacteria picked up DNA from harmful...
Proof that DNA Controls Traits
Living bacteria and dead bacteria killed mouse
Harmless bacteria picked up DNA from harmful bacteria – changed into harmful bacteria
Solving the Structure of DNA Chargaff’s Rule – Percentages of adenine =
thymine, percentages of guanine = cytosine. Rosalind Franklin – used X-ray diffraction
› X-shaped pattern showed shape› 1952
Watson and Crick› James Watson – American biologist› Francis Crick – British physicist› The clues in Franklin’s X-ray pattern enabled
Watson and Crick to build a model that explained the specific structures and properties of DNA – 1953
› http://www.youtube.com/watch?v=JiME-W58KpU
DNA Structure DNA = Deoxyribonucleic acid – a
nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds.
Nucleotides – three basic components: a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base.› Nitrogenous bases – Adenine,
Guanine, Cytosine, Thymine
Features:1. Two main sides – ladder2. Double-helix structure3. Four nitrogen bases – A,T,C,G
A always pairs with T C always pairs with G
4. DNA polymerase – an enzyme that joins individual nucleotides to produce a new strand of DNA.
How DNA Works
The order of nitrogen bases, A, T, C, and G, is the coded message› A – T› C - G› The order of the bases can be slightly different
and cause traits to be very different Sickle cell anemia
› Nitrogen bases make new messages – similar to the alphabet Letters w, o, and l form the word owl. They also
form the word low.
How DNA Copies Itself
1. DNA ready to make a copy of itself2. Molecule opens up in middle3. DNA polymerase molecule runs along original
DNA strand. Loose nitrogen bases are present in nucleus. DNA polymerase joins bases on the open rungs. A pairs with T and C pairs with G.
4. Two DNA molecules form. They are exactly alike.http://www.youtube.com/watch?v=z685FFqmrpo&feature=relatedhttp://www.youtube.com/watch?v=hfZ8o9D1tus&feature=related
Comparing RNA and DNA
Three important differences:1. The sugar in RNA is ribose instead of
deoxyribose.2. RNA is single-stranded.3. RNA contains uracil in place of thymine.
Functions of RNA
Messenger RNA (mRNA) – carry information from DNA to other parts of the cell.
Ribosomal RNA (rRNA) – Make up ribosomes, where proteins are made.
Transfer RNA (tRNA) – transfers each amino acid to the ribosome as it is specified by the coded messages in mRNA.
Making Proteins Where are proteins made?
› Ribosomes How can DNA in the nucleus control what
happens at the ribosomes?› RNA – ribonucleic acid – a chemical that acts as
a messenger for DNA Carries coded DNA message from nucleus to
ribosomes› Transcription – the process of making RNA
from a DNA template
Making Proteins RNA arrives at ribosomes, and must be
decoded.› Translation – the synthesis of a protein
from an mRNA template Once message is translated, protein is
made. Kinds of proteins determine traits you
have.
The Genetic Code
Polypeptides – proteins are made by joining amino acids together into long chains.
The genetic code is read three “letters” at a time, so that each “word” is three bases long and corresponds to a single amino acid.› Codon – each three-letter “word” in mRNA.› Anticodon – each tRNA molecule has three
unpaired bases. Complementary to one mRNA codon.
Mutations Any change in copying the DNA message
› Bases A, T, C, and G may join incorrectly Point mutations – occur at a single point
in the DNA sequence.› Substitutions – one base changed to a
different base.› Insertions and Deletions – one base inserted
or removed. Also called frameshift mutations – shift the
“reading frame” of the genetic message. Change every amino acid that follows the point of the mutation.
Effects of Mutations
Mutagens – chemical and physical agents in the environment.› Pesticides, tobacco smoke, X-rays, UV light
Harmful and Helpful Mutations – › Sickle cell disease – disorder associated
with changes in the shape of red blood cells.
› Beneficial – mosquitoes becoming pesticide resistant.