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In 1928 this person studied the pathogenicity of Streptococcus pneumonia
Fredrick Griffith
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Fredrick Griffith used Koch's postulates to demonstrate that mixing these two benign strains of Streptococcus pneumonia formed a pathogenic strain
- non-encapsulated
- heat killed encapsulated
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in 1944 Avery, McLeod, & McCarty extracted this chemical which explained the process behind Griffith's modified Streptococcus pneumonia
DNA
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This occurs when DNA is taken up by a cell and new traits appear
Transformation
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In 1953 James Watson & Francis Crick defined the structure of this
DNA
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Describe the structure of DNA
Double sided helix composed of deoxyribose nucleotides which are connected lengthwise through a phosphate group and width wise to one other nucleotide (to one other sidegroup)
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What is the name for a sugar bound to a purine or pyrimidine?
nucleotide
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List the nucleobases (nitrogenous, heterocyclic, aromatic organic molecules) of DNA
- Purine: adenine, guanine
- Pyrimidine: cytosine, thymine
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Define nucleotide
A sugar bound to a purine or pyrimidine
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How are nucleotides bound to each other?
- Hydrogen Bonds
- A-T has 2
- G-C has 3
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What results from the extra hydrogen bond between G-C (as compared to A-T)
The 3rd hydrogen bond requires additional heat to break apart--therefore DNA having a high G-C concentration will be harder to dissociate
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In the presence of certain enzymes DNA will unwind. What benefit does this provide?
It allows replication: the hydrogen bonds can be broken and free nucleotides in the cytoplasm will pair up w/nucleotides along each backbone
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What is the name of the point at which DNA separates into two strands for replication?
Replication Fork
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What is the catalyst for the stringing together of individual nucleotides?
DNA polymerase
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Which structure provides the blueprint for the proteins within a cell?
DNA
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What type of molecules are transcribed from DNA
mRNA, tRNA, rRNA
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Describe the structure of RNA
single sided helix composed of "oxy" ribose nucleotides
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What is the name of the process in which RNA is synthesized from DNA
transcription
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What is the process in which proteins are made from mRNA?
Translation
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What structure codes for proteins?
mRNA
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What is the central dogma of molecular biology?
Information flows from DNA to RNA to protein
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Architecture analogy for DNA, RNA, proteins:
- DNA: master blueprint kept at the home office
- mRNA: copies of the master blueprint which are used at each building site
- Proteins: the homes being built in a subdivision
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What nucleotide substitution is made in RNA (vs. DNA)?
RNA uses uracil instead of thymine
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What is the function of mRNA?
mRNA is synthesized from a specific gene (section of DNA) as a template for protein synthesis. mRNA is composed of nucleotides which are complementary to those on the source DNA
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Which structure facilitates protein translation?
Ribosome
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What is the function of tRNA?
tRNA binds specific amino acids and brings them to the ribosome for translation from mRNA
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What is a codon?
A sequence of 3 nucleotides
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What is an anticodon?
A 3 nucleotide sequence on tRNA which juts out to connect to mRNA and determines the protein which tRNA carries
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When two tRNA molecules have been lined up along an mRNA strand, what occurs before the first tRNA is released?
A peptide bond is formed between the two amino acids, releasing the first amino acid from the first tRNA
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How many different tRNAs can be bound to an particular/specific amino acid?
Between 3 and 4
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How does the amino acid sequence relate to the DNA and mRNA sequence?
It matches the DNA sequence and is complementary to the mRNA sequence
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This mutation occurs when the wrong amino acid is encoded due to one nucleotide getting changed
Missense mutation
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Stop codon
A codon which signals the ribosome to stop protein elongation/synthesis
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What are the 2 stop codons?
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This mutation occurs when a nucleotide is altered such that if forms a stop codon and results in the protein being too short
Nonsense mutation
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This mutation occurs when a nucleotide is lost and causes each subsequent amino acid to be incorrect
Frameshift mutation
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How does DNA introduce variations in a population
Via mutations which may be passed from one generation to another
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Why is the genetic variation created by DNA mutations important for bacteria?
Because bacteria reproduce asexually, they cannot benefit from the variation which occurs from crossover and recombination. Therefore, they must rely on DNA mutation to produce variation from one generation to the next
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What is the benefit of genetic variation?
It allows for the survival of the species (e.g. some mutated bacteria may have an antibiotic resistance and thus can continue to propagate)
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Why is horizontal gene transfer and uncommon occurrence?
- Enzymes w/in the cell break up little pieces of DNA
- DNA is a large molecule and thus has a difficult time crossing the plasma membrane
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Which organism has received the greatest amount of research of conjugation?
E. coli
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This is an extra piece of DNA carried by some bacteria in addition to their chromosome. It is replicated and passed on in much the same way, and may carry genes for specific traits. Additionally, it may be transferred from one cell to another during conjugation via a sex pilus
Plasmid
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What structure is formed during conjugation in order to join two bacteria?
Sex pilus
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This is a process in which bacteria will join to each other via the formation of a sex pilus which allows the sharing of DNA and thus introduces variation into the population
Conjugation
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Component which allows the transfer of plasmid/DNA across a conjugation bridge
- F factor
- Bacteria which contain fplasmid are F+
- Bacteria w/o fplasmid are F- (even if they contain a plasmid)
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What prevents an fplasmid from transferring and entire chromosome via horizontal gene transfer?
The conjugation pilus cannot be sustained long enough
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In this form of genetic diversity DNA is introduced by a virus/bacteriophage
Transduction
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Virus which injects DNA into bacteria
Bacteriophage
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What is the process of Transduction?
- Bacteriophage (virus) injects DNA into a bacterium
- Foreign DNA directs bacterium to make new bacteriophages
- Pieces of host chromosome may be incorporated into bacteriophage
- Bacterium lyses dispersing bacteriophage
- Bacteriophage injects DNA from previous host into new bacterium
- New bacterium incorporates chromosome from original host
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This is the process whereby certain molecules (mRNA, proteins, etc.) are made only when they are needed
Regulation (of genetic expression)
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This is the term used to describe the overall result of transcription of DNA into mRNA followed by translation of mRNA into protein
Expression
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What benefit may be provided by researching genetic "regulation"?
- Understand embryonic development
- Understand cancer
- Develop transplantable tissues
- Understand how pathogens respond to their environments and may/may not cause disease accordingly
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How do histones aid in regulation of genetic expression
They allow a strand of DNA to be tightly packaged thus requiring "unpacking" in order to be utilized
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Why are prokaryotes unable to use DNA unpacking as a means of genetic regulation?
Why is DNA unpacking unnecessary for prokaryotes?
Prokaryotes lack the level of supercoiling of eukaryotes and thus do not need to "unpack" DNA from histones in order to utilize it
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How do histones aid in gene regulation?
They create an armature around which DNA is wrapped/packed and must be unpacked in order to be utilized
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How might transcription be related to gene regulation?
Repression or Induction of transcription (to mRNA) may be used to effect gene regulation: If a protein is not needed, the mRNA required to produce the protein will not be transcribed.
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This occurs when a protein binds to a certain operon and prevents the transcription of structural genes
Repression
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This occurs when a certain protein binds to the operator of an inducible operon, thereby allowing the transcription of the corresponding structural gene
Induction
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This inducible operon is attached to structural genes required for catabolism of lactose. It is generally blocked by a repressor, but in the presence of lactose the repressor is inactivated and cannot inhibit the operon.
lac operon
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What is the inducer for the lac operon?
Allolactose (produced from lactose) will bind the lac operon repressor, thereby acting as an inducer
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How is transcription-level gene regulation effected in eukaryotes?
- The regulatory protein may affect genes on multiple chromosomes
- (**It involves complex assemblies of proteins**)
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How is transcription-level gene regulation effected in prokaryotes?
Related genes are clustered together and thus controlled by action on a single operon (e.g. genes involved in uptake and utilization of a particular sugar will be grouped together and thus regulated together)
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This strand of prokaryotic DNA consists of a promoter (which binds RNA polymerase), an operator (which provides a site for repressor/inducer proteins to bind), and a series of genes called structural genes (which code for enzymes, cellular structures, etc)
Operon
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This series of DNA will produce a repressor protein when an operon requires repression
Regulatory gene
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How is the addition of a cap & tail used in gene regulation (eukaryotes only)?
'G' cap is added to 5' end and poly adenosine tail is added to 3' end to protect the mRNA from cellular enzymes
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How is splicing used in genetic regulation (eukaryotes only)?
Introns are removed from a segment of DNA while exons remain and therefore are expressed
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How is breakdown of mRNA used in genetic regulation?
- mRNA is broken down by cytoplasmic enzymes
- Prokaryotes break it down w/in minutes
- Eukaryotes break it down w/in hours or weeks
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How is translation used in gene regulation for eukaryotes?
microRNA or ssRNA (short strand RNA) will bind complementary mRNA effectively blocking protein production
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How is translation used in gene regulation for prokaryotes?
mRNA folds back on it self as a riboswitch and attach to complementary nucleotides effectively inhibiting translation
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How is translation used in gene regulation?
Via cleavage for example
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How is feedback used in gene regulation?
- The production of a certain protein may act as an upstream repressor or inducer
- The production of a certain protein may repress or induce another repressor or inducer
- An end product of metabolism may act as a repressor to eliminate the production of a specific protein critical to the given metabolic pathway, as a result, the metabolic pathway is interrupted/cannot be completed
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How does trp (tryptophan) act as a repressor?
Once the cell has produced enough trp, the excess trp will bind to the operator (which is located within the tryptophan operon). This will block the RNA polymerase from proceeding to the structural genes which code for trp
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How is protein breakdown used for gene regulation?
Breakdown of proteins makes them unavailable for use as repressors, inducers, etc.
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On a strand of DNA this site occurs in front of structural genes (genes which encode specific proteins) and acts as a binding site for RNA polymerase
Promotor
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This substance binds to DNA at the promotor and initiates the production of RNA. Additionally, it facilitates the transcription process by helping to string nucleotides together
RNA polymerase
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This is a specific DNA sequence at the end of a structural gene which signals the release of mRNA from RNA polymerase
Terminator
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Where on the string of DNA would a repressor bind?
Onto the operator
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