Living bacteria and dead bacteria killed mouse Harmless bacteria picked up DNA from harmful...

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Chapter 12 – DNA Chapter 13 – RNA and Protein Synthesis

Transcript of Living bacteria and dead bacteria killed mouse Harmless bacteria picked up DNA from harmful...

Chapter 12 – DNAChapter 13 – RNA and Protein

Synthesis

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.

DNA and Chromosomes

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.