The Molecular Basis of Inheritance Flashcards
DNA
the molecule of heredity; make up chromosomes and genes are located on chromosomes
Proteins as the Molecule of Heredity
In the 1940s, many scientists believed that proteins made up genes because proteins are a major component of all cells and are complex macromolecules that exist in limitless variety and have specificity of function. Also, very little was known about DNA.
Bacterial Transformation
Bacteria have the ability to transform harmless cells into virulent ones by transferring some genetic factor from one bacteria cell to another. Can be artificial or natural and small pieces of extracellular DNA are taken up by a living bacterium leading to a stable genetic change.
Bacterial Transformation
Bacteria have the ability to transform harmless cells into virulent ones by transferring some genetic factor from one bacteria cell to another.
Avery, MacLeod and McCarty (1944)
Found that Griffith’s Transformation Factor was DNA. Their research proved DNA carried genetic characteristics from virulent dead bacteria to living non-virulent bacteria. Provided evidence that DNA was the genetic material.
Hershey and Chase (1952)
They tagged bacteriophages with the radioactive isotopes of phosphorous and sulfur. Proteins contain sulfur but not phosphorous and the opposite is true for DNA, the radioactive P labeled the DNA and the radioactive S labeled the protein coat. They found that when bacteria were infected the radioactive phosphorous entered the cell while the sulfur stayed outside the cells. Proved that DNA was infecting bacteria.
Rosalind Franklin (1950-53)
Carried out an X-ray crystallography analysis of DNA which showed DNA to be a helix. Essential to the DNA model now.
Watson and Crick (1953)
Using evidence from others, they proposed the double helix model of DNA. The biochemical analysis of DNA (Erwin Chargaff) and the x-ray diffraction analysis (Franklin) were very important.
Meselsohn and Stahl (1958)
Bacteria in a heavy nitrogen medium were allowed to divide and replicate. Then, these bacteria were transferred to a light nitrogen medium and allowed to replicate once. The resulting bacteria were spun in a centrifuge and they demonstrated that the new DNA consisted of one light and one heavy strand.
X-Ray Crystallography
Purified samples of DNA are crystallized and bombarded with X-rays. The rays are scattered by the DNA molecule and the diffraction pattern is captures on photographic film. This allows us to determine the 3D structure of a molecule.
Deoxyribonucleic Acid
It’s a double helix with strand running in opposite directions (antiparallel). One runs 5’ to 3’ and the other 3’ to 5’. It is a polymer of repeating nucleotides. The genetic material that makes up chromosomes and contains genes.
Nucleotides of DNA
5-carbon sugar, nitrogenous base, and a phosphate group
Nitrogenous Bases of DNA
adenine (A), thymine (T), guanine (G), cytosine (C); paired to one another (purine:pyrimidine) by hydrogen bonds
Purines
adenine and guanine
Pyrimidines
uracil/thymine and cytosine
Adenine and Thymine
paired together by double hydrogen bonds
Ribonucleic Acid
Single strand helix consisting of: A + Uracil; C + G. The 5-carbon sugar is ribose.
Ribonucleic Acid
Single strand helix consisting of: A + Uracil; C + G. The 5-carbon sugar is ribose.
DNA Replication
DNA double helix unzips and serves as a template or the formation of a new strand composed on complementary nucleotides. The two new molecules consists of one new and one old strand.
DNA Replication: Replication Bubble
Replication begins at the origins of replication where strands separate to form replication bubbles. Thousands are located along the DNA molecule. They speed along the process of replication and expand as replication proceeds on opposite directions. At the end of each is a replication fork. Eventually all replication bubbles fuse.
DNA Replication: DNA Polymerase
The DNA polymerase enzyme catalyzes the elongation of the new DNA strands. It builds strands from 5’ to 3’ moving along the template strand and pushing the replication fork above it. It cannot initiate synthesis, it can only add nucleotides to the 3’ end of a preexisting chain. It also carries out mismatch repair (proofreading).
DNA Replication: Preexisting Chain
DNA polymerase adds nucleotides to the 3’ end. This chain consists of RNA and is called and RNA primer. an enzyme called primase joins RNA nucleotides to make the primer.
DNA Replication: Leading Strand
5’ to 3’ direction; this is formed toward the replication fork in an unbroken, linear fashion
DNA Replication: Lagging Strand
3’ to 5’ direction; formed away from the replication fork in a series of segments called Okazaki fragments with are 100-200 nucleotides long
DNA Replication: DNA Ligase
joins Okazaki fragments into a lone continuous strand
DNA Replication: Helicase
untwists the double helix at the replication fork
DNA Replication: Single-Strand Binding Proteins
hold the two DNA strands apart
DNA Replication: Topoisomerases
make cuts in the DNA that lessen the tension on the wounded helix
Telomeres
nonsense nucleotide sequences placed at the end of chromosomes and repeat thousands of times; protect against the loss of genes because each time DNA replicates this occurs
DNA → RNA → Protein
The TRIPLET CODE in DNA is TRANSCRIBED to a new CODON SEQUENCE in messenger-RNA inside the nucleus. Next, the new RNA strand is processed in the nucleus (Pre-RNA). The, the codon sequence is translated to an amino acid sequence in the cytoplasm at the ribosome.
DNA → RNA → Protein
The TRIPLET CODE in DNA is TRANSCRIBED to a new CODON SEQUENCE in messenger-RNA inside the nucleus. Next, the new RNA strand is processed in the nucleus (Pre-RNA). The, the codon sequence is translated to an amino acid sequence in the cytoplasm at the ribosome.
Transcription: RNA Types
The process by which DNA makes RNA. Messenger RNA carries messages directly from DNA to the cytoplasm and varies in length. Transfer RNA carries amino acids to the mRNA at the ribosome. Ribosomal RNA is structural and makes up the ribosome formed in the nucleolus.
Transcription: Initiation
RNA polymerase recognizes and binds to DNA at the promoter region. Transcription factors recognize the TATA box and mediate binding of RNA polymerase to the DNA. Once RNA polymerase is attached to the promoter, DNA transcription of the DNA template begins.
Transcription Initiation Complex
the completed assembly of transcription factors and RNA polymerase bound to the promoter
Transcription: Elongation
RNA polymerase adds nucleotides to the 3’ end of a growing chain. RNA polymerase pries two strands of DNA apart and attaches RNA nucleotides. The transcription unit is the new mRNA strand. Each unit consists of triplets of bases called codons that code for specific amino acids. A single gene can be transcribed into mRNA by several molecules of RNA polymerase following each other.
Transcription: Termination
Final stage; Elongation continues for a short distance after the RNA polymerase transcribes the termination sequence. At this point, mRNA is cut free from the DNA template.
RNA Processing: 5’cap and Poly A tail
Before pre-RNA is shipped to the cytoplasm it is processed by a series of enzymes. A 5’ cap is added to the 5’ end to help the RNA strand bing to the ribosome in the cytoplasm. A poly A (adenine) tail is added to the 3’ end to protect the RNA strand from degradation by hydrolytic enzymes, to help ribosomes attach to RNA, and to facilitate release of the RNA into cytoplasm.
Translation: Transfer RNA
The process by which the codons of an mRNA sequence are changed into an amino acid sequence. Amino acids present in the cytoplasm are carried by tRNA molecules to the codons of the mRNA strand at ribosome. One end of the tRNA has a specific amino acid and the other has an anticodon. MRNA is broken down but tRNA is used repeatedly.
Translation: Transfer RNA
The process by which the codons of an mRNA sequence are changed into an amino acid sequence. Amino acids present in the cytoplasm are carried by tRNA molecules to the codons of the mRNA strand at ribosome. One end of the tRNA has a specific amino acid and the other has an anticodon. MRNA is broken down but tRNA is used repeatedly.
Translation: What provides the energy?
GTP - guanosine triphosphate
Translation: aminoacyl-tRNA synthetase
the enzyme that joins each amino acid to the correct tRNA; there are 20 for each amino acid
AUG Codon
codes for both methionine and the start codon
UAA/UGA/UAG
stop codons that terminate sequences
Translation: Wobble
Some tRNA molecules have anticodons that can recognize one or mote codons. This occurs because the pairing rules for the third base are not as strict as for the first two (Ex. UCU/UCC/UCA/UCG all code for serine)
Translation: Initiation
Begins as mRNA becomes attached to a subunit of the ribosome. The first codon is always AUG and it must be positioned correctly in order for translation to begin.
Translation: Termination
Completed when a ribosome reaches one of three termination/stop codons. A release factor breaks the bond between the tRNA and the last amino acid of the polypeptide chain. The polypeptide chain is freed from the ribosome and mRNA is broken down.
Translation: Termination
Completed when a ribosome reaches one of three termination/stop codons. A release factor breaks the bond between the tRNA and the last amino acid of the polypeptide chain. The polypeptide chain is freed from the ribosome and mRNA is broken down.
Gene Mutation
Mutations are changes in genetic material. They occur spontaneously and at random. They can be caused by mutagenic agents such as radiation. If the mutation is in the somatic cells it is called a genetic or hereditary disease. Mutations that occur in gametes can transmit to offspring and change the gene pool. They are important because they’re material for natural selection.
Point Mutation
A base-pair substitution, a chemical change in just one base pair in a single gene. Sickle cell anemia is caused by a point mutation. Wobble and point mutations could results in a positive change.
Insertion Mutation
Results in a frameshift; the addition of a letter into the DNA sequence
Missense Mutation
When a point mutation changes a codon within a gene into a stop codon.
Missense Mutation
When a point mutation changes a codon within a gene into a stop codon.
Virus
A parasite that can live only inside another cell, It commandeers the host cell machinery to transcribe and translate all the proteins it needs to fashion new viruses. The host cell is often destroyed and the virus consists of RNA or DNA.
Capsid
A protein coat that envelopes the DNA or RNA.
Viral Envelope
Some viruses have this and it is derived from membranes of host cells, cloaks the capsid, and aids the virus in infecting the host.
Virus Specificity
Each type of virus can infect only one specific cell type because it gains entrance into a cell by binding to specific receptors on the cell surface.The virus that causes colds on humans only infect the membranes of the respiratory system and the virus that causes AIDs only infects one type of white blood cell.
Host Range
One virus can usually infect one species. The range of organisms that a virus can attack. Mutations can expand host ranges.
Bacteriophages
The most complex and best understood virus that infects bacteria. Can reproduce through lytic cycle or lysogenic cycle.
Bacteriophages: Lytic Cycle
Phage enters a host cell, takes control of the cell machinery, replicates itself and causes the cell to burst and release a new generation of infectious phage viruses. The new viruses infect thousands more cells.
Bacteriophages: Lysogenic Cycle
Viruses replicate without destroying the host cell. The phage virus become incorporated into a specific site in the host’s DNA. It remains dormant within the host genome and is called a prophage. As the host cell divides the phage is replicated with it. At some point a trigger causes a switch to the lyctic phase.
Temperate Viruses
Viruses capable of both modes of reproducing, lytic and lysogenic, within a bacterium.
Retroviruses
Viruses that contain RNA not DNA. Following infection, the RNA serves as a template for the synthesis of complementary DNA (cDNA) because it is complementary to the RNA from which it was copied. The retroviruses reverse the usual flow of information from DNA to RNA. It will become a permanent resident in the host genome and is capable of making multiple copies for years. Polio and HIV are retroviruses.
Reverse Transcriptase
Enzyme that directs reverse transcription.
Transduction
The process that leads to genetic recombination because phage viruses acquire bits of bacterial DNA as they infect one cell after another.
Restricted Transduction
Involves the transfer of specific pieces of DNA and when the phage ruptures out of the host DNA later, it sometimes carries a piece of adjacent host DNA with it and inserts this host DNA into the next host it infects.
Restricted Transduction
Involves the transfer of specific pieces of DNA and when the phage ruptures out of the host DNA later, it sometimes carries a piece of adjacent host DNA with it and inserts this host DNA into the next host it infects.
Bacterial Chromosome
A circular, double-stranded DNA molecule tightly condensed into a structure called a nucleoid, which has no nuclear membrane.
Theta Replication
Bacteria replicate their DNA in both direction from a single point of origin by this process.
Conjugation
Bacteria can reproduce by this primitive sexual method.
Binary Fission
Main mode of bacterial, asexual reproduction. It results in a population with all identical genes but mutations occur occasionally. Bacteria reproduce by the millions.
Plasmid
A foreign, small, circular, self-replicating DNA molecule that inhabits a bacterium.
F Plasmid
The first plasmid discovered and F stands for fertility. F+ bacteria contains the plasmid and F- bacteria does not. It contains genes for the production of pili.
R Plasmid
Makes the cell in which it is carried resistant to specific antibiotics such as ampicillin or tetracycline. It can be transferred to other bacteria by conjugation. Bacteria that contains this plasmid have an evolutionary advantage.
R Plasmid
Makes the cell in which it is carried resistant to specific antibiotics such as ampicillin or tetracycline. It can be transferred to other bacteria by conjugation. Bacteria that contains this plasmid have an evolutionary advantage.
Operon
It was discovered in E. coli and is an important model of gene regulation. It is a set of genes and the switches that control the expression of those genes. The Lac operon is switched off until it is needed and the tryptophan operon is always on until it is not needed and becomes repressed.
Lac Operon
In order for lactose to be used three structural genes must be transcribed to produce enzymes necessary for the breakdown of lactose into glucose and galactose.
Lac Operon’s 3 Enzymes
b-galactosidase, permease, and transacetylase
Lac Operon: Noncompetitive Inhibition
Both RNA polymerase and the repressor are competing for two active sites, one of which coincidentally blocks the other.
Lac Operon: Noncompetitive Inhibition
Both RNA polymerase and the repressor are competing for two active sites, one of which coincidentally blocks the other.
Tryptophan Operon Process
The repressor molecule encoded by the regulator gene is initially inactive. Therefore, RNA polymerase is free to bind to the promoter and transcribe structural genes. When the inactive repressor combines with a corepressor molecule (tryptophan) it changes conformation and binds to the operator preventing transcription of the structural genes. If tryptophan is an allosteric effector and if levels are high then no more is synthesized.
Prions
Cells and not viruses. They are misfolded versions on a protein found in the brain. If they get in the brain, the cause normal versions of the protein misfold in the same way. They can cause scrapie in sheep, mad cow disease in cow, and Creutzfeldt-Jakob disease in humans.
Prions
Cells and not viruses. They are misfolded versions on a protein found in the brain. If they get in the brain, the cause normal versions of the protein misfold in the same way. They can cause scrapie in sheep, mad cow disease in cow, and Creutzfeldt-Jakob disease in humans.
Transposons
Transposable genetic elements sometimes called jumping genes. Discovered by Barbara McClintock. Some cut-and-paste from one part of the genome to another. Others make copies of themselves that move to other regions onto another region of the genome and leave the original behind.
Transposons: Complex Transposons
Longer insertion sequences and include extra genes, such as a gene for antibiotic resistance or seed color. McClintock hypothesized that genes could move because patterns in corn color only work is they could.
Transposons: Complex Transposons
Longer insertion sequences and include extra genes, such as a gene for antibiotic resistance or seed color. McClintock hypothesized that genes could move because patterns in corn color only work is they could.
Human Genome
3 billion base pairs and 30,000 genes. 97% of human DNA is junk. Of noncoding DNA, some are regulatory sequences that control gene expression some are introns and most are repetitive sequences that never get transcribed. Some coding regions of DNA are polymorphic regions and are highly variable from one region to the next.
Tandem Repeats
Back-to-back repetitive sequences. Huntington’s disease is caused by abnormally long stretches of tandem repeats within affected genes. Many tandem repeats make up telomeres.
Recombinant DNA
Taking DNA from two sources and combining them into one molecule. This occurs after viral transduction, bacterial transformation, conjugation, and when transposons jump around. Recombinant DNA techniques used in science for practical purposes such as biotechnology and genetic engineering.
Cloning Genes Purpose
To produce a protein product such as human insulin. To replace a nonfunctioning gene in a person’s cells with a functioning gene by gene therapy, this can result in human subjects because a virus is used as a vector or the gene will insert successfully and produce proteins for a short time. To prepare multiple copies of a gene itself for analysis. To engineer bacteria to clean up bacteria such as toxic waste.
Techniques of Gene Cloning
Isolate a gene of interest. Insert the gene into a plasmid. Insert the plasmid into a vector such as bacterium. The bacterium must be made competent for this. The gene is clone as it reproduces by fission. The gene that contains the selected gene is harvested for culture.
Vector
the cell that will carry the plasmid
Restriction Enzymes
They cut DNA at specific recognition sequences and these cuts are staggered leaving sticky ends to form a temporary union with other sticky ends. The fragments that result are called restriction fragments.
Restriction Enzymes Examples and Discovery
Discovered in the late 1960s and are extracted from bacteria which use them to fend of attacks by invading bacteriophages. Common examples are EcoRI, BamHI, and HindIII.
Gel Electrophoresis
Separates large molecules of DNA (can also separate proteins and amino acids) on the basis of their rate of movement through an agarose gel in an electric field. The smaller the molecule the faster it runs. DNA is negative so it runs from the cathode (-) to the anode (+). It must be cut by restriction enzymes first. Once separated by the gel, it can be sequenced or compared with other samples.
DNA Probe
Radioactively labeled single strand of nucleic acid molecule used to tag a specific sequence in a DNA sample. It bonds to the complementary sequence where it occurs and the radioactivity allows us to find its location. This can identify a person who carried an inherited genetic defect (sickle cell; Tay-Sachs; Huntingtons).
Polymerase Chain Reaction
Cell-free automated technique in which a piece of DNA can be rapidly amplified. The DNA sequence is placed in a test tube with Taq polymerase, along with a supply of nucleotides and primers necessary for DNA synthesis.
Taq Polymerase
heat-stable form of DNA polymerase extracted from extremophile bacteria
PCR: Limitations
Some information about the nucleotide sequence must be known in advance to make primers. The size of the amplified piece must be short. Contamination if a major problem and could make accurate results difficult.
Restriction Fragment Length Polymorphisms
A restriction fragment results when DNA is treated with restriction enzymes. When junk DNA is compared across a population they discovered that the restriction fragment pattern is different. It gives a DNA fingerprint that looks like a bar code.
RFLP: Uses
They are unique and inherited in Mendelian fashion so, they can be used in paternity suits to determine if a man is the father of the child. In addition, they can be use in rape/murder cases.
Complementary DNA
Introns present a problem when scientists try to clone. So, scientists extract processed mRNA from cells and use reverse transcriptase to make DNA sequences of interest without introns.
Safety
Milk production is increased in cows with the bovine growth hormone and many wonder if it will cause a problem for people who drink it.
Privacy
DNA probes coupled with technology of the semiconductor industry can produce DNA chips with information about someone’s genetic makeup. The chips scan for mutations or predispositions. Many don’t like this because if the health insurance finds out about defects based on disabilities in the future they can refuse to carry a person.
