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

Double Helix

Nitrogen Bases In DNA 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 1.Very Complex 2.Extremely rapid 3.Very accurate (only one in a billion nitrogen bases are paired incorrectly). 4.Process requires enzymes DNA

DNA Replication Process 4 Steps 1. DNA unwinds (like a twisted ladder) 2.The double helix is unzipped by the enzyme- DNA 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

Example: 1.DNA Strand: TCGTATTAA 2.Give the complementary strand 1.TCGTATTAA 2.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 What are they made of? Amino acids Where are they made? Ribosomes Uses of proteins in body? Enzymes, collagen- structure, hemoglobin- carries 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