1. CHAPTER 10: DNA,RNA & Protein Synthesis

2. 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

3. 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 )

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

5. 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)

6. C. How Chemical Bonds hold DNA together
Covalent bonds- between sugar & phosphates of 2 nucleotides
Hydrogen bonds- between complementary nitrogenous bases –

7. 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

8. 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

9. 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.

10. 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

11. 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)

12. 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

13. 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.

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

15. 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

16. 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

18. 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

19. 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.

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

22. 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 in textbook)

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