Intro to Molecular Genetics (Base Pairing Rules (Rule 1 (chargaff…
Intro to Molecular Genetics
Is it always DNA to RNA to proteins?
hypothesis: central dogma
central dogma: hypothesis of DNA to RNA to proteins
coined by Francis Crick
DNA Structure and Replication
DNA replication- the process in which a cell's entire DNA is copied or replicated.
DNA replication process occurs during the Synthesis (S) phase of the eukaryotic cell cycle.
as each DNA strand has the same genetic information, both strands of the double helix can serve as templates for the reproduction of a complementary new strand. The two resulting double helices, which each contain one "old" strand and one "new" strand of DNA, are identical to the initial double helix.
DNA replication is said to be semi-conservative because of this process of replication, where the resulting double helix is composed of both an old strand and a new strand.
the semi-conservative mechanism of replication was one of three models originally proposed for DNA replication:
conservative replication would leave the two original template DNA strands together in a double helix, with the new DNA composed entirely of two new strands.
dispersive replication would produce two copies of the DNA, both containing a mixture of old and new material.
semiconservative replication would produce two copies that each contained one of the original strands and one new strand.
Central Dogma of Molecular Biology
DNA or deocyribonucleic acid- contains the genes that determine who you are
DNA contains insructions for all the proteins your body makes
Proteins- determine the structure and function of all your cells.
What determines a proteins structure?
it begins with the sequence of amino acids that make up the protein. instructions for making proteins with the correct sequence of amino acids are encoded in DNA.
DNA is found in the chromosomes.
in eukaryotic cells: chromosomes always remain in the nucleus but proteins are made at ribosomes in the cytoplasm.
How do the instructions in the DNA get to ythe site of protein synthesis outside the nucleus?
Using the nucleic acid is RNA (ribonucleic acid)- RNA is a small molecule that can squeeze through pores in the nuclear membrane- it carrries the information from DNA in the nucleus to a ribosome in the cytopasm and then helps assemble the protein
THE SHORT VERSION
DNA→ RNA → proteins
discovering this sequence of events was a
in molecular biology, it is called the central dogma of molecular biology- the two process in the central dogma are transcription and translation
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RNA transfers the informati0on from the nucleus to the cytoplasm for the formation of protein
Genetic information in in DNA is first transcribed into RNA in the nucleus then translated into protein in the golgibody
smallest to largest: gene, chromosome, nucleus
Base Pairing Rules
chargaff determines that in DNA a purine always approximately equals the amount of a pyrimidine
specifically that in any double stranded DNA the number of G equals approximately the number of C units and the number of A equals approximately the number of T
Human DNA is 30.9% A; 29.4% T; 19.9% G; 19.8% C
The rule consists of base pairs in the DNA double helix: A always pairs with T ; G always pairs with C.
Chargaff also domonstrated that the purines (A+G) always approximates the number of pyrimidines (T+C) an obvious consequence of the base- pairing nature of th e DNA double helix
purine : two rings
pyrimidine : one rings
Chargaff showed that the compisition of DNA in terms of the relative amounts of the A,C,G,T bases varies in one species to another, this molecular diversity added evidence that DNA could be the genetic material
DNA is composed of nucleotides- contains a nitrogen containing base, a five-carbonsugar (deoxyribose), and a phsphate group.
in these nucleotides- 1/4 possible bases: adenine (A) guanine (G) cytosince (C) or thymine (T)
A and G- purine bases
C and T are prymidine bases
how do these four structures form DNA
the model of DNA predicts how the DNA sequence can code for proteins and how the meolecule can be replicated but one initial significant step was to understand the base pairing rules
what is RNA?
another type of nucleic acid
DNA is somehow transferred into RNA, and that the information in RNA is then used to make the protein.
the ribosomes are the sites of protein synthesis
RNA is relatively small and is easily able to carry information out of the nucleus
gene expression occurs only when the gene product is required by the cell this process begins with the information in a gene being transcribed into an RNA molecule, a process called transcription.
DNA nucleotide monomers include a phosphate group, a nitrogenous base, and dexoytibose sugar
DNA helicase is the ezyme that breaks hydrogen bonds holding the two DNA strands together during DNA replication
the closer the evolutionary relationship is between two species, the more similar their DNA sequences will be
the four letter code is the four different types of nitrogenous bases
Primase is an emzyme that builds a short RNA primer on the lagging strand during DNA replication
during replication, the lagging strand is synthesized in short segnants known as Okazaki fragments
DNA polymerase is the enzyme that builds a new DNA strand during replication.