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49 Cards in this Set
- Front
- Back
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FREDERICK GRIFFITH
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he discovered what he called a transforming principle, which is today known to be DNA. He did this through an experiment with mice and injecting them with 3 different types of bacteria.
Type IIR, mice lived Type IIIS: living, mice died Type IIIS: heat killed, mice lived Type IIR and Type IIIS: heat killed, mice died |
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Oswald T Avery
Colin M. MacLeod Maclyn McCarty |
Discovered that DNA is the substance that causes bacterial transformation. There experiment tried to purify and characterize the "transforming principle" responsible for the transformation phenomenon first described in Griffith's experiment of 1928: type III-S: heat killed, when injected along with living but non-virulent type II-R , resulted in a deadly infection of type III-S. Avery and his colleagues suggest that DNA, rather than protein as widely believed at the time, may be the hereditary material of bacteria, and could be analogous to genes and/or viruses in higher organisms.
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Hershey- Chase
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confirming that DNA was the genetic material, conducted their experiments on the T2 phage, a virus whose structure had recently been shown by electron microscopy. The phage consists only of a protein shell containing its genetic material. In a first experiment, they labeled the DNA of phages with radioactive Phosphorus-32. They allowed the phages to infect E. coli, then removed the protein shells from the infected cells with a blender and a centrifuge. They found that the radioactive tracer was visible only in the bacterial cells and not in the protein shells.
In a second experiment, they labeled the phages with radioactive Sulfur-35. After separation, the radioactive tracer then was found in the protein shells, but not in the infected bacteria, confirming that the genetic material which infects the bacteria is DNA. |
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Structure of DNA
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base pairs are .34 nm apart
1 complete turn of the helix takes 3.4nm deoxyribose (phosphate) phosphodiester bonds |
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RNA
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RNA and DNA are both nucleic acids, but differ in three main ways.
is a single-stranded molecule in most of its biological roles and has a much shorter chain of nucleotides while DNA contains deoxyribose, RNA contains ribose the complementary base to adenine is uracil contain self-complementary sequences that allow parts of the RNA to fold and pair with itself to form double helices. |
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complementary base pair
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The specific A-T and G-C base pairs in double stranded DNA. The bases are held together by hydrogen bonds between the purine and pyrimidine bases in each pair.
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pyrimidines
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A type of nitrogenous base. Cytosine is a pyrimidine in DNA, and uracil is a pyrimidine in RNA.
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PURINES
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A type of nitrogenous base. In DNA and RNA purines are adenine and guanine.
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PHOSPHODIESTER BOND
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A covalent bond in RNA and DNA between a sugar and a phosphate.
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HYDROGEN BOND
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A hydrogen bond is the attractive force between one electronegative atom and a hydrogen covalently bonded to another electronegative atom. The energy of a hydrogen bond is comparable to that of weak covalent bonds.
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antiparallel strands
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showing opposite polarity; in the case of double stranded DNA, this means that the chemical polarity of one chain is the opposite to the chemical polarity of the other chain.
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PRIMER
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is a strand of nucleic acid that serves as a starting point for DNA replication. They are required because the enzymes that catalyze replication, DNA polymerases, can only add new nucleotides to an existing strand of DNA. The polymerase starts replication at the 3'-end of the primer, and copies the opposite strand.
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DNA/RNA HYBRID
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Double-stranded polynucleic acids in which one strand is DNA and the other strand is the complementary RNA; formed during transcription and during multiplication of oncogenic RNA viruses.
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WATSON & CRICK MODEL
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A three-dimensional model of the DNA molecule, consisting of two complementary polynucleotide strands wound in the form of a double helix and joined in a ladderlike fashion by hydrogen bonds between the purine and pyrimidine bases.
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Rosalind Franklin
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studied isolated fibers of DNA by using the X-ray diffraction technique. The beam is diffracted by the atoms in a pattern that is characteristic of the atomic weight and spatial arrangement.
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Bonding properties of G-C & A-T
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hydrogen bonds connect the 2 bases
A-T is a double bond and the stronger one G-C is a triple bond, easier to break due to electron cloud |
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(A+T)/(G+C) base ratio always equals 1
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(A+T)/(G+C) base ratio always equals 1
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Meselson & Stahl
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demonstrated that DNA replication was semiconservative. Semiconservative replication means that when the double stranded DNA helix was replicated, each of the two double stranded DNA helices consisted of one strand coming from the original helix and one newly synthesized.
They proved this using an isotope of 15N and 14N and atomic weight |
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DNA Synthesis
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4 components must be present
1. All 4 dNTPs 2. A fragment of DNA 3. DNA polymerase I 4. Magnesium ions (Mg2+) |
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Replicon
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is a DNA molecule or RNA molecule, or a region of DNA or RNA, that replicates from a single origin of replication.
For most prokaryotic chromosomes, the replicon is the entire chromosome. For eukaryotic chromosomes, there are multiple replicons per chromosome. |
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Replisome
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The replisome is a complex molecular machine that carries out replication of DNA. It is made up of a number of subcomponents that each provide a specific function during the process of replication.
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Okasaki fragments
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Short DNA fragments of about 1000-2000 nucleotides long formed during DNA replication of the lagging strand by discontinuous replication of DNA. Okasaki fragments are later joined together by ligation.
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Origin of Replication
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is a particular sequence in a genome at which replication is initiated. This can either be DNA replication in living organisms such as prokaryotes and eukaryotes, or RNA replication in RNA viruses, such as double-stranded RNA viruses. DNA replication may proceed from this point bidirectionally or unidirectionally.
The specific structure of the origin of replication varies somewhat from species to species, but all share some common characteristics such as high AT content. The origin of replication binds the pre-replication complex, a protein complex that recognizes, unwinds, and begins to copy DNA. |
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Replication Fork
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The replication fork is a structure that forms within the nucleus during DNA replication. It is created by helicases, which break the hydrogen bonds holding the two DNA strands together. The resulting structure has two branching "prongs", each one made up of a single strand of DNA, that are called the leading and lagging strands. DNA polymerase creates new partners for the two strands by adding nucleotides.
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Leading Strand
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The leading strand is the DNA strand at the opposite side of the replication fork from the lagging strand. It goes from a 5' to 3' direction, because DNA Polymerase can only synthesize a new DNA strand in a 5' to 3' manner. On the leading strand, DNA polymerase III (DNA Pol III) "reads" the DNA and adds nucleotides to it continuously.
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Lagging Strand
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The lagging strand is the DNA strand opposite the replication fork from the leading strand. It goes from a 3' to 5'.
When replicating, the original DNA splits in two, forming two "prongs" which resemble a fork (i.e. the "replication fork"). DNA has a ladder-like structure; imagine a ladder broken in half vertically, along the steps. Each half of the ladder now requires a new half to match it. Pol III, the main DNA replication enzyme, cannot work in the 3' to 5' direction of the template strand, and so replication of the lagging strand is more complicated than of the leading strand. |
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Telomerase
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is an enzyme that adds specific DNA sequence repeats ("TTAGGG" in all vertebrates) to the 3' end of DNA strands in the telomere regions, which are found at the ends of eukaryotic chromosomes. The telomeres contain condensed DNA material, giving stability to the chromosomes. The enzyme is a reverse transcriptase that carries its own RNA molecule, which is used as a template when it elongates telomeres, which are shortened after each replication cycle. Telomerase was discovered by Carol W. Greider and Elizabeth Blackburn in 1985 in the ciliate Tetrahymena.
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Helicase
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a class of enzymes vital to all living organisms. They are motor proteins that move directionally along a nucleic acid phosphodiester backbone, separating two annealed nucleic acid strands (i.e. DNA, RNA, or RNA-DNA hybrid) using energy derived from ATP hydrolysis.
Helicases are often utilized to separate strands of a DNA double helix or a self-annealed RNA molecule using the energy from ATP hydrolysis, a process characterized by the breaking of hydrogen bonds between annealed nucleotide bases. They move incrementally along one nucleic acid strand of the duplex with a directionality and processivity specific to each particular enzyme. |
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DNA Polymerase I
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is an enzyme that participates in the process of DNA replication in prokaryotes. It is composed of 928 amino acids, and is an example of a processive enzyme - it can sequentially catalyze multiple polymerisations.
Pol I possesses three enzymatic activities: A 5' -> 3' (forward) DNA polymerase activity, requiring a 3' primer site and a template strand A 3' -> 5' (reverse) exonuclease activity that mediates proofreading A 5' -> 3' (forward) exonuclease activity mediating nick translation during DNA repair. |
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DNA Polymerase III
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is the primary enzyme complex involved in prokaryotic DNA replication.
the DNA Pol III holoenzyme also has proofreading capabilities that correct replication mistakes by means of exonuclease activity working 3'->5'. DNA Pol III is a component of the replisome, which is located at the replication fork. |
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DNA Primase
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is an RNAP enzyme involved in the replication of DNA.
Primase synthesizes a short RNA segment (called a primer) complementary to a ssDNA template. Primase is of key importance in DNA replication because no known DNA polymerases can initiate the synthesis of a DNA strand without an initial RNA or DNA primer (for temporary DNA elongation). |
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DNA Ligase
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is a special type of ligase that can link together two DNA strands that have double-strand break (a break in both complementary strands of DNA). The alternative, a single-strand break, is fixed by a different type of DNA ligase using the complementary strand as a template but still requires DNA ligase to create the final phosphodiester bond to fully repair the DNA.
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SSB Proteins
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binds single stranded regions of DNA to prevent premature reannealing. The strands have a natural tendency to revert to the duplex form, but SSB binds to the single strands, keeping them separate and allowing the DNA replication machinery to perform its function.
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RNA Polymerase
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is an enzyme that produces RNA. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses.
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Promoter
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is a region of DNA that facilitates the transcription of a particular gene. Promoters are typically located near the genes they regulate, on the same strand and upstream (towards the 5' region of the sense strand).
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5' Cap
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is a specially altered nucleotide on the 5' end of precursor messenger RNA and some other primary RNA transcripts as found in eukaryotes. The process of 5' capping is vital to creating mature messenger RNA which is then able to undergo translation. Capping ensures the messenger RNA's stability while it undergoes translation in the process of protein synthesis, and is a highly regulated process which occurs in the cell nucleus.
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poly A tail
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The 3' poly(A) tail is a long sequence of adenine nucleotides (often several hundred) at the 3' end of the pre-mRNA. This tail promotes export from the nucleus and translation, and protects the mRNA from degradation.
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Exons
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is a nucleic acid sequence that is represented in the mature form of an RNA molecule after a) portions of a precursor RNA, introns, have been removed by cis-splicing or b) two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA or a functional form of a non-coding RNA such as rRNA or tRNA. Depending on the context, exon can refer to the sequence in the DNA or its RNA transcript.
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Introns
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is a DNA region within a gene that is not translated into protein. These non-coding sections are transcribed to precursor mRNA (pre-mRNA) and some other RNAs (such as long noncoding RNAs), and subsequently removed by a process called splicing during the processing to mature RNA. After intron splicing (ie. removal), the mRNA consists only of exon derived sequences, which are translated into a protein.
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Splice Variants
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Alternative splicing is the RNA splicing variation mechanism in which the exons of the primary gene transcript, the pre-mRNA, are separated and reconnected so as to produce alternative ribonucleotide arrangements. These linear combinations then undergo the process of translation where specific and unique sequences of amino acids are specified, resulting in isoform proteins. In this way, alternative splicing uses genetic expression to facilitate the synthesis of a greater variety of proteins.
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snRNPs
small nuclear ribonucleoproteins |
are particles that combine with pre-mRNA and various proteins to form spliceosomes (a type of large molecular complex). SnRNPs "recognize" the places along a strand of pre-mRNA and are essential in the removal of introns. These molecules are found within the nuclei of eukaryotic cells. The two essential components of snRNPs are protein molecules and RNA. The RNA found within each snRNP particle is known as small nuclear RNA, or snRNA.
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Spliceosome
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is a complex of specialized RNA and protein subunits that removes introns from a transcribed pre-mRNA (hnRNA) segment. This process is generally referred to as splicing.
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Transcription Factors
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is a protein that binds to specific DNA sequences and thereby controls the transfer (or transcription) of genetic information from DNA to RNA.
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Messenger ribonucleic acid (mRNA)
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is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein.
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Ribosomal RNA (rRNA)
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is the central component of the ribosome, the protein manufacturing machinery of all living cells. The function of the rRNA is to provide a mechanism for decoding mRNA into amino acids and to interact with the tRNAs during translation by providing peptidyl transferase activity.The tRNA then brings the necessary amino acids corresponding to the appropriate mRNA codon.
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Transfer RNA (tRNA)
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is a small RNA molecule (usually about 74-95 nucleotides) that transfers a specific active amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. It has a 3' terminal site for amino acid attachment. This covalent linkage is catalyzed by an aminoacyl tRNA synthetase. It also contains a three base region called the anticodon that can base pair to the corresponding three base codon region on mRNA. Each type of tRNA molecule can be attached to only one type of amino acid, but because the genetic code contains multiple codons that specify the same amino acid, tRNA molecules bearing different anticodons may also carry the same amino acid.
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Small nuclear RNA (snRNA)
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is a class of small RNA molecules that are found within the nucleus of eukaryotic cells. They are transcribed by RNA polymerase II or RNA polymerase III and are involved in a variety of important processes such as RNA splicing (removal of introns from hnRNA), regulation of transcription factors (7SK RNA) or RNA polymerase II (B2 RNA), and maintaining the telomeres. They are always associated with specific proteins, and the complexes are referred to as small nuclear ribonucleoproteins (snRNP) or sometimes as snurps. These elements are rich in uridine content.
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Peptide Bond
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is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amine group of the other molecule, thereby releasing a molecule of water (H2O). This is a dehydration synthesis reaction (also known as a condensation reaction), and usually occurs between amino acids.
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Amino Acids
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Twenty standard amino acids are used by cells in protein biosynthesis, and these are specified by the general genetic code.[2] These 20 amino acids are biosynthesized from other molecules, but organisms differ in which ones they can synthesize and which ones must be provided in their diet. The ones that cannot be synthesized by an organism are called essential amino acids.
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