Genetic Chapter 10, 13, 14, 20 (sec 1)

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45 Terms

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Genetic Material
information contained in genes that gets passed onto new generation

→ source of variability among organism
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Criteria for Genetic Material, molecule must be able to …

(4 things)

1. replicate
2. store information
3. express information
4. allow variation by mutation
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Central Dogma of molecular genetics
Central Dogma of molecular genetics
DNA → RNA → PROTEIN

DNA makes RNA (transcription), which makes PROTEINS (translation)

DNA → Transcription → Translation
DNA → RNA → PROTEIN 

DNA makes $$RNA (transcription)$$, which makes $$PROTEINS (translation)$$ 

DNA → Transcription → Translation
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In 1940s, geneticists favored ____ as genetic material
proteins
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Proteins and _____ acids were major candidates for genetic material
nucleic
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Proteins were diverse and abundant in ____.
cells
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Tetranucleotide hypothesis 

* Phoebus Levene
Tetranucleotide hypothesis

* Phoebus Levene
→ DNA contains = amounts of 4 nucleotides

→ Postulated identical groups and repeats of 4 components was basis for DNA structure

→ Lack of chemical diversity inn DNA = could not store extensive g.i.

→ Proteins favored as g.i.
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DNA
DNA
→ Composed of 2 strand (coiled) helical

→ Each strand is composed of subunits (nucleotides)

→ Each nucleotide consists of :

* 1 PENTOSE SUGAR (deoxyribose molecule)
* 1 PHOSPHATE GROUP
* 1 NITROGENOUS BASE
* adenine
* cytosine
* guanine
* thymine
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2 Kinds of Nitrogenous Bases
2 Kinds of Nitrogenous Bases

1. Purines (9 member ring)
2. Pyrimidines (6 member ring)
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Purines - 9 member ring
Purines - 9 member ring
→ Adenine ; A

→ Guanine ; G
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Pyrimidines - 6 member ring
Pyrimidines - 6 member ring
→ Cytosine ; C

→ Thymine ; T

→ Uracil ; U
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DNA contains ____
DNA contains ____
deoxyribose

* deoxy - without an oxygen
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RNA contains _____ sugar
RNA contains _____ sugar
ribose
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Bases of DNA and RNA
DNA bases ;

* A, C, T, G

RNA bases ;

* A, C, U, G

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Only DNA contains T

Only RNA contains U
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Nucleoside
Nucleoside
→ Contains nitrogenous base & pentose sugar

→ molecule is composed of purine or pyrimidine base and ribose or deoxyribose sugar
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Nucleotide
Nucleotide
→ Nucleoside with phosphate group added
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Phosphodiester Bonds
→ Nucleotides are linked by phosphodiester bonds between phosphate group at C - 5’ position and O H group on C - 3’ position
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Nucleoside Monophosphates ; NMP
a nucleotide
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Nucleoside Diphosphate ; NDP
Nucleotide with addition of 2 phosphate groups
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Nucleoside Triphosphate ; NTP
Nucleotide with addition of 3 phosphate groups
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Triphosphate
→ Serve as precursor molecule during nucleic acid synthesis
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ATP and GTP
→ Adenosine triphosphate and guanosine triphosphate

→ large amount of energy involved in adding/removing terminal phosphate group
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Watson and Crick 1953
Proposed the structure of DNA as a double helix
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Chargaff 1949-1953
→ Proposed base composition

→ Amount of A is proportional to T

→ Amount of C is proportional to G

→ Percentage of C + G does not equal percentage of A + T
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Base composition analysis (Chargaff) and X-ray diffraction provided crucial data to _____ and Crick
Watson
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X-ray Diffraction
→ studies by Rosalind Franklin 50-53 showed DNA had a 3.4 angstrom periodicity, characteristic of helical structure
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Watson and Crick Model of DNA :
→ Double helix

→ 2 anti-parallel strands connected by base pairing

→ Stacked nitrogenous bases
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Base Pairing --- Hydrogen Bonds
→ Chemical affinity produces hydrogen bonds in pair of bases

* A-T and G-C base provides complementarity of 2 strands and chemical stability to the helix
* A-T ; Double bond
* G-C ; Triple bond
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Watson and Crick : Semiconservative Model
→ Storage of genetic information in sequence of bases

→ Mutations or genetic changes that could result in alteration of bases
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Nucleotide Bonding
→ @@Each nucleotide is bound to a nucleotide on the other chain by weak hydrogen bonds between specific pairs of bases@@

→ A pairs w/ T

→ G pairs w/ C

→ 2 chains are complementary w/ opposite polarities
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Genetic Code : Translation
→ involves the synthesis of proteins consisting of a chain of amino acids whose sequence id specified by the coding information in mRNA

* mRNA carries the “genetic code” = chemical info. originating in DNA which specifics the primary structure of proteins
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Translation of mRNA
→ Biological polymerization of amino acids into polypeptide chains
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Translation requires : (4)

1. Amino acids
2. mRNA
3. tRNA
4. Ribosomes
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tRNAs
→ adapt genetic information present as specific triplet codons in mRNA to corresponding amino acid

→ tRNA anticodons complement mRNAs

→ tRNAs carry corresponding amino acids
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Ribosomes
→ Essential role in expression of genetic information

→ Consist of ribosomal proteins and ribosomal RNAs

→ Consists of large and small subunits

\
* Prokaryote ribosomes are 70s
* Eukaryote ribosome are 80s
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tRNAs characteristics
→ small in size and very stable

→ 75-90n nucleotides

→ transcribed from DNA

→ Contain posttranscriptional modified bases

* important for hydrogen bonding
* confer structural stability

→ tRNAs have a cloverleaf structure
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Anticodon
→ tRNA has anticodon that complementarily base-pairs w/ codon in mRNA

→ Corresponding amino acid is covalently linked to CCA sequence at 3’ end of all tRNAs
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Translation
→ tRNAs are covalently attached to specific amino acids and contain anti-codon complementary to the mRNA codon

→ Base pairing between the tRNA anti-codon and the mRNA codon on the ribosome places amino acids in the correct linear sequence in translation
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Translation of mRNA divides into 3 steps :

1. Initiation
2. Elongation
3. Termination
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Initiation of Translation requires :

1. Small and large ribosomal subunits
2. mRNA molecule
3. GTP
4. Charged initiator tRNA
5. Mg^2+
6. Initiation factors
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Elongation
→ Both ribosomal subunits assembled w/ mRNA

→ Forms P site and A site
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Termination
→ signaled by stop codons (UAG, UAA, UGA) in A site

→ Codons do not specify any amino acid
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GTP-dependent release factors
→ Stimulates hydrolysis of polypeptide from peptidyl tRNA - released from translation complex
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Charging tRNA
→ Aminoacylation : tRNA charging

* before translation can proceed, tRNA molecules must be chemically linked to respective amino acids
* Aminoacyl tRNA synthetase
* enzyme that catalyzes aminoacylation

→ 20 different synthetases, 1 for each amino acid

→ Highly specific; recognize only 1 amino acid
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Gene Expression Principles
→ Gene expression involves processes of transcription and translation which result in the production of proteins whose structure is determined by genes