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Chapter 10 Genetics


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Nitrogenous bases of Nucleotides
2 kinds: purines (nine-member double ring) and pyrimidines (six-member single ring).
2 types: adenine, guanine
Genetic Material of Viruses
some viruses contain an RNA core rather than DNA
Tetranucleotide hypothesis
because a single covalently bonded tetranucleotide structure was relatively simple, geneticists believed nucleic acids could not provide the large amount of chemical variation expected for the genetic material. Proteins, on the other hand, contain 20 diff. a.a. affording the basis for substantial variation'.
more compact DNA. Bases are slightly tilted due to dehydration.
*Watson and Crick
In 1953, they proposed that DNA is a right-handed double helix; its strands are antiparallel running from 5' to 3'. They are connected by A=T and G=C complementary base pairing. There are 10 base pairs per helix turn. Model is based on B-DNA.
*X-ray Diffraction Analysis of DNA
showed a 3.4 angstrom periodicity, characteristic of a helical structure. Discovered by who?
Nucleotides found in RNA
A, C, G, U
Four Characteristics of Genetic Material
replication, storage of information, expression of info., variation by mutation
*What did Erwin Chargaff do?
used base composition studies and found the amount of A=T, and C=G; the amount of purines=pyrimidines. The % of C&G may not equal that of A&T. The more G&C that is present, the more stable the molecule is because there are
Template for RNA synthesis
*Avery, McLeod, and McCarty Experiment
demonstrated that the transforming principle was DNA, not protein
*What does the C-3' have attached to it in DNA and RNA?
component of ribosomes for protein synthesis in the process of translation
Central dogma of molecular genetics
DNA makes RNA, which makes proteins.
Why would DNA have several forms?
DNA might have to assume a different structure as it functions as genetic material. The strands of the helix must separate and become accessible to large enzymes and proteins.
Transfection of viral DNA into bacterial protoplasts showed that only viral DNA is needed for production of more viruses.
*Phosphodiester bonds
links nucleotides between phosphate at the C-5' and C-3' position at the hydroxyl groups
Direct Evidence Supporting DNA as Genetic Material in Eukaryotes
recombinant DNA technology: segments of eukaryotic DNA corresponding to specific genes are isolated and literally spliced into bacterial DNA.
What distinguishes DNA between RNA in structure?
Attached to the pentose sugar- DNA has a hydrogen atom at the C-2' position rather than a hydroxyl group as in RNA.
Transformation: Frederick Griffith
Performed experiments with virulent/avirulent strains of Diplococcus pneumoniae. Showed the avirulent could be transformed into virulent. Questioned transforming principle- thought to be a physiological modification event, not genetic?
RNA replicase
used in the replication of viral RNA; RNA was synthesized in vitro using this enzyme
InDirect Evidence Supporting DNA as Genetic Material in Eukaryotes
DNA is found only where primary genetic function occurs, whereas protein is found thoughout the cell. Correlation between DNA quantity in haploid vs. diploid cells. Mutagenesis w/ UV light.
a nucleotide w/o a phosphate (contains a purine or pyrimidine base and a sugar)
Is RNA always single stranded?
Some form double-stranded regions as they fold into secondary structures. Example is tRNA. Also some animal viruses have ds RNA.
phosphate, contributes an H by changing the OH- DNA can be prevented from growing?
*Hershey and Chase Experiment
demonstrated DNA, not protein, enters the bacterial cell during phage infection and directs viral reproduction (lytic cycle).
Phage (TQ: point of discovery)
*Bacteriophage T2, E. coli's infecting virus used in the Hershey/Chase Exp.
Ultraviolet light is most mutagenic at the wavelenght of 260nm.
Nucleotide, nucleoside diphosphate, nucleoside triphosphate
sugar base w/ one phosphate, two phosphates, three phosphates
*Nucleotides found in DNA
A, C, G, T
Abundant in cells with 20 different amino acids. Account for more than 50% of the dry weight of cells.
(Spheroplasts) enzymatically treated cells that contain only the cell membrane as their outer boundary. These cells from E. coli were treated with lysozyme to remove the cell wall.
enzyme that degrades enzymes of a ribosome
another form of DNA that is tilted slightly compact and turning to the left
carries amino acids to the ribosome during translation for protein synthesis
How does RNA originate
All RNA's (tRNA, mRNA, rRNA) originate as complementary copies of one of the two strands of DNA segments during transcription.
the biologically significant form of DNA
Pentose sugars found in nucleid acids give them their name.
RNA- contains ribose; DNA contains deoxyribose
the sugar ribose replaces dexoyribose and the nitrogenous base uracil replaces thymine. Most RNA is single-stranded.
carry genetic information from the DNA of the gene to the ribosome, where translation occurs. Template for protein synthesis.
3 types: cytosine, thymine, and uracil
Retroviruses: Reverse Transcription
reverse transcriptase to produce single stranded DNA, the ssDNA is made into dsDNA using DNA polymerases, this is incorporated into the genome of a host cell,
Backbone of DNA and RNA
the linkage between the phosphates and sugars with phosphodiester bonds
the building blocks of all nucleic acid molecules (DNA); aka mononucleotides. Consist of three essential components: nitrogenous base, pentose sugar, and a phosphate group.

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