Principles of molecular genetics (replication of DNA, transcription of RNA, Protein synthesis, Mundelein laws of genetics)
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DNA is the genetic material
DNA is the substance of inheritance
Hereditary information is encoded in the chemical language of DNA and reproduced in all the cells of your body
The DNA program directs the development of many different types of traits
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DNA is a double-stranded helix
In 1953, James Watson and Francis Crick proposed a double-helical model for the structure of DNA
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DNA is a double-stranded helix
Hydrogen bonds between bases hold the strands together
Each base pairs with a complementary partner: A with T, G with C
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DNA and RNA are polymers of nucleotides
RNA uses the sugar ribose and has a nitrogenous base uracil (U) instead of thymine
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Nucleotide structure:
Nitrogenous base (can be A, G, C, or T)
Phosphate group
Sugar (deoxyribose for DNA, ribose for RNA)
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The nitrogenous bases of DNA are Thymine (T), Cytosine (C), Adenine (A), and Guanine (G)
Thymine and Cytosine are pyrimidines, while Adenine and Guanine are purines
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The nitrogenous bases of DNA hydrogen-bond in specific pairs
Two sugar-phosphate chains on the outside run in opposite directions (anti-parallel)
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Genetic information is stored in DNA
Each strand of DNA acts as a template for building a new strand in replication
DNA replication is semi-conservative
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DNA replication depends on specific base pairing
The structure of DNA suggested the basic mechanism of its replication
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In DNA replication, the parent molecule unwinds and two new daughter strands are built based on base-pairing rules
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DNA replication is initiated by the separation of DNA strands at origins of replication by helicase enzymes
This separation causes the formation of a replication bubble
The two separated DNA strands act as templates for new DNA
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RNA primase synthesizes short DNA strands called Okazaki fragments
The replication causes the appearance of two Y-shaped forks at the two sides of the bubble
The replication is continuous until new DNA is formed
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Summary of DNA replication:
Replication begins at specific sites where the two parental strands separate and form replication bubbles
The bubbles expand laterally as DNA replication proceeds in both directions
Eventually, the replication bubbles fuse, and synthesis of the daughter strands is complete
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Table 16.1 Bacterial DNA Replication Proteins and Their Functions
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The flow of genetic information from DNA to RNA to protein
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Basic Principles of Transcription and Translation
Transcription is the synthesis of RNA under the direction of DNA
Translation is the actual synthesis of a polypeptide under the direction of mRNA
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Genetic information written in codons is translated into amino acid sequences
A gene is a region of DNA that can be expressed to produce a functional product
The genetic code consists of triplets of nucleotides called codons
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The genetic code dictates how codons are translated into amino acids
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Transcription consists of three regions: promoter, coding region, and terminator
RNA transcription is catalyzed by RNA polymerase
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Transcription from DNA to RNA involves initiation, elongation, and termination
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Transcription process:
Initiation:
RNA polymerase binds to the promoter
DNA strands unwind
RNA synthesis starts at the start point on the template strand
Elongation:
Polymerase moves downstream
DNA unwinds
RNA transcript elongates
DNA strands re-form a double helix
Termination:
RNA trans cript is released
Polymerase detaches from the DNA
Transcription from DNA to RNA
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Bacterial cell vs Eukaryotic cell:
Bacterial cell:
Lacks a nucleus
mRNA produced by transcription is immediately translated without additional processing
Eukaryotic cell:
Nuclear envelope separates transcription from translation in space and time
Original RNA transcript (pre-mRNA) is processed in various ways before leaving the nucleus as mRNA
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Molecular components of translation:
mRNA
Transfer RNA (tRNA)
Ribosomes
Ribosomes facilitate the specific coupling of tRNA anticodons with mRNA codons during protein synthesis
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tRNA molecules:
Each carries a specific amino acid on one end
Each has an anticodon on the other end
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Ribosome has three binding sites for tRNA:
P site
A site
E site
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Steps in protein synthesis:
mRNA is transcribed inside the nucleus
mRNA goes out to the cytoplasm through nuclear holes
Each three nucleotides on the mRNA strand represent a codon
Codons are translated into amino acids
5' end of mRNA in AUG Codon unites with small subunit of ribosome
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More steps in protein synthesis:
Large subunit is connected with small subunit
tRNA is linked to the mRNA
Each amino acid is brought into the ribosome by tRNA
tRNA consists of two parts: upper part carries the amino acid, lower part contains the anticodon region
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More steps in protein synthesis:
Large subunit consists of three regions: A, P, and E
In Area A, the amino acid is brought by tRNA to the mRNA by connecting the codon and anticodon regions
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More steps in protein synthesis:
In the P region, amino acids are bonded to each other by peptide bonds
In Area E, the tRNA separates from mRNA
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More steps in protein synthesis:
Process continues until the release agent is bound to the stop code on mRNA
Polypeptide chain is released from the P region
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Transcription and translation:
RNA polymerase transcribes DNA into mRNA in the nucleus
mRNA undergoes processing (intron removal, addition of cap and tail)
mRNA is elongated with the help of amino acids and tRNA
Ribosomal subunits facilitate the coupling of codons and anticodons
ATP and enzymes are involved in the initiation and attachment of amino acids
Translation occurs