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DNA, PROTEIN SYNTHESIS, & Mutations Chapters 12 Pages 287-308
Chapter 12:Section 1 I.History A. Frederick Griffith- 1928 - Tried to figure out how bacteria made people sick. - Heat killed, disease-causing bacteria passed “something” along to harmless bacteria. - He called this process “Transformation.”
B. Oswald Avery- 1944 - Determined DNA is the molecule of inheritance and not proteins. –Did this by destroying other cell parts piece by piece.
C.Alfred Hershey & Martha Chase- 1952 Hershey & Chase – determined that DNA transmits genetic information from parent to offspring, & not any other molecule Worked with bacteriophages – viruses that invade bacterial cells Used bacteriophages with radioactive markers (1952)
Structure of Bacteriophage Protein coat – outer covering DNA – inner core
Hershey & Chase One bacteriophage had radioactive phosphorus-32 in its DNA & was used to infect a bacterial cell The other had radioactive sulfur-35 in its protein coat & was used to infect a bacterial cell Both bacterial cells were examined Only the bacteriophage with P-32 was inside the bacterial cell, proving that DNA is the material that transmits genetic info
Hershey and Chase
D. Erwin Chargaff- Late 1940’s Found there are 4 bases in a DNA molecule –Adenine, Guanine, Cytosine and Thymine Found that the amount of A = T and G = C
E. Rosalind Franklin (1952) Franklin used X-ray diffraction to get information about the structure of DNA Was able to tell that DNA had an “X” like structure where the strands are twisted around each other All of these discoveries led to the following….
F. Watson and Crick - The discovery of the structure of DNA was made in 1953 by two scientists named James Watson & Francis Crick. - Watson & Crick proposed that DNA is shaped like a “twisted ladder.” - This twisted ladder is also called a “Double Helix.” - They used the findings of the other scientists for their model.
II.DNA A.What is DNA ? Stands for Deoxyribonucleic acid Functions: 1. Transmit genetic info. to next generation 2. Controls all cell activities, including protein synthesis
B.Structure of DNA - DNA is made of nucleotides. 1. Nucleotides consist of the following: a. Deoxyribose – a sugar b. A Phosphate Group c. A Nitrogen Base 1. Four possibilities a.Adenine(A) b.Guanine(G) c.Cytosine(C) d.Thymine(T)
- These nucleotide bases join together to form a long single strand. - Each long single strand of nucleotides connects to “another” single strand of nucleotides. - The two strands are held together by hydrogen bonds.
C.Base Pairing Rules 1. Adenine always pairs with Thymine. 2. Cytosine always pairs with Guanine. - The different order of these bases is what makes organisms different. Example: Strand 1:A – G – T – T – C – T – A – G Strand 2:T – C – A – A – G – A – T – C Sample Exercise: Strand 1:C – G – A – T – G – T – A – C Strand 2: – – – – – – –
Sample Exercise: Strand 1: T – C– A – A – C – G – C – C Strand 2: – – – – – – – - The more closely related two organisms are the more alike the order of their nucleotides in their DNA will be. Example: Humans Chimps Gorillas Orangutans
Purines vs. Pyrimadines Adenine and Guanine are PURINES Thymine and Cytosine are PYRIMIDINES Remember:
Purines and Pyrimidines Purines can only pair with pyrimidines due to their size and shape.
III.DNA Terminology A. Chromosomes - Tightly compacted strands of DNA found when a cell is dividing! (Needs to be compact to fit in a small space!) - Hold all genetic information. - Chromosomes are passed on to an offspring by its parents. Examples:Fruit Fly = 8 Humans = 46 Shrimp = 254 Chimps = 48 Chicken = 78 Gorilla = 48 Wolf = 78
B.Chromatin - When a cell is not dividing, DNA is in the form of chromatin. - Loosely packed DNA that is wrapped around proteins (called histones)
C.Genes - A section of DNA on a chromosome that codes for a specific protein.
IV.DNA ReplicationSECTION 2 A. DNA is copied before a cell divides so that each new cell has it’s own genetic copy. B. There are 4 main steps: STEP 1: - DNA is unzipped by the enzyme HELICASE and now two single strands begin to unwind. - Hydrogen bonds are broken. - This is called a replication fork
STEP 2: - Each unwound strand of DNA acts as a template to produce two new strands of DNA. STEP 3: - An enzyme named DNA Polymerase will read each unwound strand and join new complimentary nucleotides to each.
STEP 4: - This occurs until the whole strand is replicated. - Now there are two identical DNA molecules. - Each strand contains one original and one complimentary strand. Click image for animation!