CHAPTER 10: DNA,RNA & Protein Synthesis

I. Discovery of DNA Scientist originally believed PROTEINS would be the molecules which contained hereditary information. Some scientists who did experiments that proved DNA had genetic information: 1. Fredrick Griffith 2. Oswald Avery 3. Hershey & Chase

James Watson & Francis Crick In 1953 DNA structure discovered Double Helix model. (2 chains of DNA) Showed how DNA could replicate. Relied on work of other scientists: Rosalind Franklin & Maurice Wilkins took X-ray photos of DNA structure ( Franklin died 1958 before Watson & Crick received Nobel Prize. 1962.)

II. DNA structure Double Helix shape is formed by base pairs attached to a sugar-phosphate backbone. -

B. Parts of Nucleotides 1. 5 carbon sugar in DNA- deoxyribose (in RNA= ribose) 2. phosphate group 3. nitrogenous bases ( there are 4 different ones) Adenine Guanine Cytosine Thymine (in RNA- no thymine- Uracil is the base)

C. How Chemical Bonds hold DNA together Covalent bonds- between sugar & phosphates of 2 nucleotides Hydrogen bonds- between complementary nitrogenous bases – www.molecularstation.com/dna/dna-structure/

D. Base Pairing Rules Adenine always bonds with Thymine (AT) Guanine always bonds with Cytosine (GC) Note: 3 hydrogen bonds: GC 2 Hydrogen bonds: AT

Must have 1 purine (a 2 ring shape) plus 1 pyriomidine (1 ring shape) in each pair or the would not “fit” inside ladder of DNA 2. Purines (A, G) double C ring 3. Pyrimidines (T, C) single C ring

III. DNA Replication A. Is the process by which DNA is copied in a cell before a cell divides by mitosis, meiosis or binary fission.

B. Steps in Replication 1. Helicase enzymes -separate hydrogen bonds in strands – create replication fork 2. Attach- DNA polymerase enzyme -adds nucleotides 3. Release –DNA polymerase enzyme – now have 2 identical DNA strands oak.cats.ohiou.edu/.../Heredity/Heredity.htm

Mutation- a change in the nucleotide sequence of a DNA molecule. C. Errors DNA replication is very accurate. Errors occur ~ 1 in 1 billion paired nucleotides. “Proofreading” enzyme checks for “spelling” errors. *If a mistake does occur- new DNA is different: Mutation- a change in the nucleotide sequence of a DNA molecule. Caused by chemicals, radiation,UV rays. Mutations can be favorable - or harmful. (example- cancer)

IV Protein Synthesis Flow of Information (DNA – RNA - Proteins) Before protein can be synthesized, the instructions in DNA must first be copied to another type of nucleic acid called messenger RNA. Then -a group of 3 nucleic acids codes for an amino acid & it is built at the ribosomal RNA with help from the transfer RNA

RNA differs from DNA in the following ways: RNA is single stranded while DNA is double stranded. RNA has a sugar called ribose while DNA has a sugar called deoxyribose. RNA has the nitrogenous base uracil while DNA has the base thymine.

B. 3 types RNA: 1. messenger RNA(mRNA) 2. transfer RNA (tRNA) 3. ribosomal RNA (rRNA)

Messenger RNA, or mRNA. Transfer RNA or tRNA. Ribosomal RNA or rRNA carries the code for building a protein from the nucleus to the ribosomes in the cytoplasm. It acts as a messenger. Transfer RNA or tRNA. picks up specific amino acids in the cytoplasm & brings them into position on ribosome where they are joined together in specific order to make a specific protein. Ribosomal RNA or rRNA place for protein synthesis

C. Steps in Transcription-making RNA 1. RNA polymerase (enzyme)– binds to promoter area on DNA 2. Nucleotides added & joined by the enzyme (RNA polymerase) Termination signal- stop- RNA polymerase releases both DNA & new RNA molecules

www.smartdraw.com/.../dna_transcription.htm

D. Proteins Review of protein structure -recall that proteins are made of amino acids joined together with peptide bonds -there are 20 different amino acids, the order they are joined determines the structure & function of the proteins. -proteins can be very large, complicated molecules

mRNA codons for specific amino acids Each 3 nucleotide sequence (letters) in mRNA encodes for 1 specific amino acid, or a “start” or “stop” signal. Each 3 nucleotide group is called a codon. The genetic code- means the rules that relate how a particular sequence of nitrogenous bases corresponds to a particular amino acid.

teachline.ls.huji.ac.il/72693/weekly2.html

E. Steps in Translation Initiation- tRNA & mRNA join together. (The codon is on the mRNA, the “anticodon” is on tRNA) The tRNA has an amino acid attached to it) Elongation- continued as ribosome moves the distance of 1 codon on mRNA Elongation is built with new tRNAs attaching each amino acid as it reads the codons on the mRNA. Termination- ribosome reaches “stop” codon on the mRNA Disassembly – each piece is free. (see sequence page 208-209 in textbook)

Remember: Replication- copying DNA from DNA Transcription- making RNA from DNA Translation- making proteins