Biology Honors Pre-IB (Protein Synthesis/DNA)

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Fedrick Griffith 1928

1. Studied pathogenic bacteria
2. Streptococcus pneumoniae - cause pneumonia
3. Two kinds of SP: Smooth (pathogenic), rough (harmless)
4. S strain injected to mouse: died
5. R strain injected to mouse: lived
6. Heat killed S strain injected to mouse: lived
7. Heat killed S strain mixed w/ R strain: died
8. Examined blood & R strain changed to S strain
9. Concluded that "something" in dead S strain passed info. to R strain to become pathogenic - transforming principle
10. Now called transformation

Avery, MacLeod, & McCarty repeating Griffith's experiment 1944

1. attempted to determine what in the S strain was changing the R strain to be pathogenic
2. broke the S strain bacteria into component parts (nucleic acid, protein, carbohydrate, lipid)
3. Ejected each component mixed w/ live R strain into mouse (nucleic acid caused to mouse to die only)
4. Further substantiated their conclusions by treating nucleic acid with DNA, mixing with live R strain: lived
5. First experiment to assert that DNA carried the genetic info.

Hershey & Chase 1952

1. Used the T2 virus that attacks bacterial cells
2. Bacteriophage to prove DNA not protein is genetic material
3. Viruses are made of DNA surrounded by a protective coat
4. T2 contains phosphorus only in its DNA
5. T2 contains sulfur only in its proteins
6. "Labeled" one group of viruses with radioactive sulfur & another group w/ radioactive phosphorus
7. Viruses weren't allowed to attack bacterial cells
8. New viruses retrieved from bacteria contained radioactive phosphorus and no radioactive sulfur
9. Indicated that only the DNA entered the bacterial cell, the protein coats were left behind outside of the bacterial cell and therefore could not play a role in directing the activities of the bacterial cell in making offspring viruses

Chargaff's Rules 1949

1. Studied the propertied of DNA
2. Discovered that individuals of t he same species have the same % of each of the 4 bases that never varies
3. DNAs fom similar species have similar base compositions
4. The # of adenines is always = to thymine
5. the # of cytosines are always = to guanines
6. The # of purines (A,T) are always = to pyrimidines (C,G)

Structure of DNA

1. Made of a long chain of nucleotides
2. Each nucleotide has 3 parts (Phospate group, deoxyribose sugar, and nitrogen containing base)

Nitrogen Containing Bases

Are the only difference in the four nucleotides (adenine, thymine, cytosine, guanine)

Watson & Crick

1. Determined the 3-D structure of DNA by models
2. Realized that DNA is a double helix that is made up of a sugar-phosphate backbone on the outside w/ bases on the inside
3. Discovery was built on the work of Rosalind Franklin & Erwin Chargaff

Rosalind Franklin

1. X-ray images suggested that DNA was a double helix of even width

Nucleotides

1. Always pair the same way (A=T, C=G)
2. B/c a pyrimidine (single ring) pairs w/ a purine (double ring), the helix has a uniform width
3. Backbone is connected by covalent bonds
4. The bases are connected by hydrogen bonds b/c of the positive & negative charge
5. A T has 2 hydrogen bonds
6. C G has 3 hydrogen bonds

DNA Replication

1. Proteins carry out the process
2. DNA serves as the template
3. Enzymes do the actual work
4. Enzymes unzip the double helix
5. Free floating nucleotides form hydrogen bonds w/ the template strand
6. DNA polymerase enzymes bond the nucleotides together to form the new daughter strand
7. The new molecules of DNA are formed, each w/ an original strand and a newly formed strand
8. This process is semi-conservative

RNA

1. Carries DNA's instructions
2. Info flows in one direction from DNA to RNA to proteins
3. Is a link between DNA and proteins

Protein Synthesis

1. Involves 2 processes: (transcription, translation)
2. Each gene codes for diff. trait
3. "A" pairs up w/ "U" (uracil)

RNA differs from DNA

1. RNA has ribose sugar
2. RNA has uracil instead of thymine
3. RNA is a single stranded structure

Transcription

1. One DNA strand (template strand), provides a template for making an RNA molecule

Translation

1. Blocks of 3 nucleotides (condons) are decoded into a sequences of amino acids
2. Converts an mRNA message into a polypeptide, or protein
3. A cell interprets a series of codons along a mRNA molecule
4. Converts mRNA messages into polypeptides
5. Continues until ribosome reaches a termination codon or stop codon

Types of RNA

1. Messenger RNA (mRNA)
2. Transfer RNA (tRNA)
3. Ribosomal RNA (rRNA)

Messenger RNA (mRNA)

1. The "copy" of the DNA that is used to specify the sequence of amino acids in the proteins
2. Nucleotides are read in groups of 3 (codons)
3. Each codon codes for a specific amino acid
4. Complementary copy of DNA - travels out of nucleus to cytosplasm
5. Detaches from the DNA once the gene is transcribed

Transfer RNA (tRNA)

1. Bring amino acids to the ribosome during protein synthesis
2. Each tRNA carries a specific type of amino acid
3. Each tRNA can recognize a specific mRNA codon b/c it has a complementary anticodon
4. Anticodon matches the codon
5. Transfers amino acids from the cytoplasm's pool to a ribosome
6. The ribosome adds each amino acid carried by tRNA to the growing end of the polypeptide chain

Anticodon

Sequence of three bases that associates w/ the codon by base pairing

Ribosomal RNA (rRNA)

1. Forms part of the ribosome
2.

Steps of RNA

1. Transcription copies DNA to make a strand of mRNA
2. Transcription is catalyzed by RNA polymerase
3. Nucleotides pair with one strand of DNA
4. RNA polymerase bonds the nucleotides together
5. The DNA helix winds again as the gene is transcribed

Amino Acid

1. Are coded by mRNA base sequences
2. Are put in a specific order to form a protein - the order of them is determined by the order of the codons
3. Regardless of the organism, codons code for the same amino acid

Ribosomes

1. Consist of 2 subunits: Large subunit, Small subunit
2. Link amino acids together by peptide bonds

Large Subunit

Has three binding sites for tRNA

Small Subunit

Binds to mRNA

Step 1 of RNA

1. A special initiator tRNA attaches to the start codon
2. The large subunit of the ribosome closes over the tRNA
3. In all organisms, protein synthesis begins with the start codon AUG (codes for methionine)

Step 2 of RNA

1. The polypeptide chain grows as new tRNA molecules move into position by complementary base pairing of their anticodon w/ the next codon on the mRNA
2. The genetic code matches each codon to its amino acid

Stop Codon

1. Codons that do not code for an amino acid
2. Indicates that ribosome has reached the end of the message

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