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MolBio and Genetics
| Term | Definition |
|---|---|
| DNA | stores information defining life which encodes the primary amino acid sequence of proteins |
| DNA | serves as a template for its own replication during cell division and as template for RNA synthesis |
| RNA | serves as template for synthesis of proteins whose amino acid sequence determines their 3D shape which defines their function |
| mRNA | the message is translated into a specific protein which serves some function in the organism |
| Sum of protein functions | is life |
| Flow of information from DNA to mRNA | is one way, no transfer of information from proteins back to DNA sequence |
| Mendel pea plants | demonstrated that physical traits, like stem length, seed shape, and flower color could be passed from generation to generation; theory of inheritance predicted that each unit of heredity would pass through a hybrid unchanged |
| Fruit flies | used because of shorter time between conception and birth of offspring; studies showed specific traits are always transmitted along with a specific chromosome, suggesting genes are on chromosomes; many genes per chromosome |
| Chromosomes | composed of DNA and protein |
| Genetic material is DNA | bacteria inherited characteristic could be transferred from one bacterium to another by transfer of DNA (transformation), phages and viruses use cellular machinery to produce new phage which are comprised of DNA core with protein shell |
| Hershey-Chase experiment | established DNA as genetic material; phage DNA labelled with P32 and protein with S35, bacteria had P32 establishing only phage DNA enters infected bacteria, protein stays on surface |
| DNA structure | predicted by Watson and Crick to consist of 2 polynucleotide strands coiled around each other |
| Rosalind Franklin | worked with Wilkens, showed Watson and Crick X-ray diffraction pattern of DNA |
| DNA strand | is a linear polymer of nucleotides; backbone contains sugar (deoxyribose) linked by phosphate groups |
| Deoxyribose | 5 carbon sugar with a hydrogen instead of OH at 2 prime carbon. Attached to each is one of 4 different nitrogenous bases |
| Primary structure of DNA | covalent bonds linking nucleotides by sugar-phosphate links is generated by DNA-polymerase |
| Nucleotide | consists of a sugar, nitrogenous base, at least one phosphate group |
| Secondary structure of DNA | two strands of DNA held together by weak non-covalent hydrogen bonds between complementary bases projecting into space between the two strands |
| Complementary base pairing | Hydrogen bonds of A fit the hydrogen bonds of T and bonds in G match bonds in C |
| DNA strand polarity | a 5'phosphate end and a 3'OH end. The paired strands in DNA are anti-parallel (oriented in opposite directions) |
| Tertiary structure | consists of two strands of DNA twisted together to form a double helix |
| Parental strand sequence | dictates the sequence of the daughter strand during replication assuring fidelity of DNA sequence |
| DNA repair enzymes | recognize the incorporation of a wrong base into the strand |
| Heat denaturation | denatures the hydrogen bonds responsible for base pairing, important for PCR. Because GC pairs with 3 bonds and AT pairs with 2, the GC rich DNA requires higher temperatures for denaturation |
| Eukaryotic nucleus | contains about 2 meters of DNA |
| Histones | to avoid tangling and to maintain function, DNA is packaged by being wound around histones which are basic proteins that bind to the negative charges of phosphate groups |
| Chromatin | Histones pack closely to form larger coils organized with this scaffolding protein |
| Chromosome | highly compacted form of DNA and proteins that is visible during cell division. Humans have 46 chromosomes in 23 pairs |
| Gene | segment of DNA needed to direct the synthesis of a protein with a specific function |
| Mutations | lead to disease, change the organism (evolution) |
| Semi-conservative model | incorporation of radioactive nucleotides into DNA during consecutive cycles of synthesis |
| Accuracy is achieved through | DNA serving as the template or pattern for its own replication |
| Proofreading functions of DNA polymerase | and existence of nucleotide excision repair and mismatch repair systems also help to ensure fidelity |
| Unwinding | hydrogen bonds between two DNA strands are broken by enery-requiring ATP topoisomerases which control supercoiling of DNA |
| Complementary base pairing | unpaired bases generated by unwinding pair with free nucleotides in solution in the nucleus |
| Joining | DNA polymerase makes covalent bonds between deoxyribose and phosphate |
| DNA polymerases | catalyzes the addition of an incoming NTP to the 3'OH of the deoxribose at the end of the growing DNA chain. The released 2phosphate drives the endergonic reaction, making it irreversible |
| DNA synthesis | in the 5'to 3' direction |
| Number of DNA polymerases and location | 4 in the nucleus and 1 in mitochondria that differ in the activities they possess |
| Replication | is semi-discontinuous |
| Replication fork | Y shaped junction or bubble where the 2 DNA strands are unwinding |
| DNA synthesis proceeds in this direction | bi-directional |
| Origin of replication | site where replication is initiated |
| Leading strand | new DNA strand that extends continuously in the 5' to 3' direction as the replication fork advances |
| Lagging strand | extended in 5' to 3' direction is synthesized discontinuously as additional single-stranded parental DNA becomes exposed at the replication fork |
| Okazaki fragments | newly synthesized 1000 to 2000 discontinuous fragments are covalently linked by an ATP-dependent DNA ligase to complete synthesis of the lagging strand |
| DNA polymerase synthesizes both DNA strands simultaneously | but can only move in the 5' to 3' direction |
| Eukaryotic vs prokaryotic nucleus replication fork | in the eukaryotic nucleus, a replication fork moves slowly in comparison to prokaryotes, even though there is about 1000x more DNA to replication in a human cell |
| Eukaryote origin of replication | eukaryotes utilize multiple origins of replication on each chromosome |
| New phenotype production in nature | produced by chromosomal recombination |
| Frequency of spontaneous mutation | very low, about 1/10 billion base pairs during replication |
| Mutation | stable heritable alteration in the base sequence of an organism's DNA; must be perpetuated by replication to have a major effect, and must be present in the germ cell lines to be passed on to the next generation of the organism |
| Most mutations | do not affect cell function; sometimes the cell with the mutation is lost by cell death |
| If cell survives after mutation, the mutation may not have any effect because | mutation can occur in non-coding regions of DNA (introns), in a gene with a functional homologue (another protein duplicates the mutated proteins's lost function, silent (same amino acid coded), alters amino acid seq, but no change in protein function |
| Point mutation | one base-pair replaces another in DNA; naturally occuring (DNA poly error) or induced by environmental factors (chemical mutagen) |
| Radiation damage | environmental, UV light, ionizing radiation (X-rays or cosmic gamma rays) |
| Insertion or deletion of bases | produce frame shifts; intercalation of chemical mutagens into the DNA helix (chemical mutagen), viruses |
| Point mutations caused by | incorporation of base analogues (chemicals resembling authentic bases in DNA, can change the base pairing); chemical mutagens that modify bases already in DNA (nitrous oxide) |
| Nitrous oxide | removes an amino group from C or A by oxidative deamination. Nitrite, the conjugate base, is a preservative used in prepared meats because it prevents growth of C.botulinum |
| Point mutations caused by radiation damage | can bread the phosphodiester bonds that link nucleotides together in DNA causing single or double strand breaks in DNA; UV light induces covalent linkages between 2 adjacent pyrimidines (T-T dimers) |
| T-T dimers | cause skin cancers and xeroderma pigmentosum, a disease resulting from abnormal DNA repair; can't dix TT dimers |
| Intercalation of chemical mutagens into DNA helix | planar aromatic compounds, EtBr, benzopyrene, and actinomycin D, bind to DNA by intercalation (slipping between stacked bases in the DNA helix). Increasing distance between 2 consecutive base pairs and resulting in insertion/deletion of nucleotides |
| EtBr | exhibits strong fluorescence under UV light when bound to DNA |
| Benzopyrene | component of cigarette smoke |
| Actinomycin D | antibiotic that binds to DNA helix and prevents it from being an effective template for RNA synthesis in both pro- and -eukaryotic cells; inhibits growth of rapidly dividing cells and can be an effective therapeutic agent, treating some cancers |
| Mismatch repair | damaged base that doesn't pair correctly with its corresponding base in the other strand is recognized and excised. Several nucleotides are removed and new DNA is synthesized to fill the gap. |
| Nucleotide Excision Repair | recognizes large distortions in the DNA helix, like T-T dimer or large chemical adducts. Many enzymes and proteins involved. A number of nucleotides are removed and new DNA synthesized to fill in the gap. Repair enzymes recognize a distorted helix. |
| Photo-reactivation | DNA photolyase uses visible light energy to cleave covalent links between T-T dimers and directly restores damaged DNA to its original state |
| Xeroderma pigmentosum | rare, autosomal recessive, one of the enzymes involved in nucleotide excision repair is missing, so cells can't repair damaged DNA; extensive mutations accumulate especially in skin cells |
| RNA | transfers and translates the information encoded in DNA into functional components (proteins) in the cell |
| RNA vs DNA | ribose is the sugar in RNA, uracil replaces thymine, much shorter (usually contains information for only 1 gene), single stranded, RNA can loop around and base pair with itself |
| Transcription | synthesis of RNA from DNA; catalyzed by DNA-dependent RNA polymerases. Eukaryotes have 3 RNA polymerases, one for each type of RNA: mRNA, tRNA, and rRNA |
| RNA poly binding to DNA | searches for promoter sites (special DNA sequences that initiate transcription) When promoter found, RNA poly unwinds a short stretch of DNA to produce a single stranded DNA template |
| RNA polymerase | initiates synthesis of RNA molecule that is complementary to the DNA template. Building blocks are ATP, GTP, CTP, and UTP. |
| Elongation | about 12 to 15 bases of the RNA are base-paired with the DNA template. DNA is read in 3' to 5; direction and RNA is made in the 5' to 3' direction |
| Transcription termination | termination sites; special protein binds to the 3' end of the new RNA molecule, facilitating termination |
| Base sequence of RNA | exactly complementary to template strand from which it is transcribed and identical to the non-template strand (coding strand) except that U in RNA replaces T in DNA |
| Transcription versus replication | both strands of DNA are copied during replication, but only 1 strand is transcribed into RNA; all of DNA is copied in replication, only 1 gene is copied at 1 time in transcription; both strands copied simultaneously in replication, 1 gene is transcribed; |
| Transcription versus replication (2) | replication 1 copy is made, transcription many copies made; after replication DNA strands join, in transcription RNA is processed and moves from nucleus to cytoplasm |
| mRNA | carries the genetic message in DNA to the cytoplasm where the order of bases will specify the order of amino acids of a protein that will be synthesized |
| tRNA | transports specific amino acids into the correct position for incorporation into the growing protein. Helps decode genetic information in mRNA into a protein |
| rRNA | forms a scaffold or framework along with a number of proteins, on which the actual process of protein synthesis occurs |
| mRNA in detail | contains genetic info that specifies order of amino acids in protein, relatively short lived, amount of protein made can be controlled by variations in the rates of which mRNA is made and destroyed; more heterogeneous in size than rRNA or tRNA |
| mRNA details (2) | multiple copies of mRNA species produced, providing gene amplification (controlling # of mRNA copies made for a given gene controls amount of coded protein that will be produced); primary RNA transcript must be processed to form the mature mRNA molecule |
| mRNA 5' cap | contains a 5' cap which is an altered nucleotide (7-methylguanine) that is added post-transcriptionally, protects mRNA transcript from exonucleases (hydrolytic enzymes that remove bases from ends of nucleic acids) and facilitates export and translation |
| mRNA poly-A tail | string of A added to the 3'OH end of mRNA post-transcriptionally, variable length (100 to 200), stabilizes mRNA, may aid in export from nucleus; variable length may control mRNA stability |
| mRNA splicing | protein-coding portions of DNA are discontinuous |
| Introns | stretches of DNA, ranging from a few base pairs to over 10,000, that intervene in the coding region of the gene; not present in the final mature mRNA, nor do they encode proteins |
| Exons | portion of the gene that do appear in the mature mRNA and are expressed as protein |
| Splicing | mediated by small nuclear ribonucleoprotein particles (snRNPs) or small nuclear RNAs in association with proteins |
| Systemic lupus erythromatosus (Lupus) | painful and often fatal inflammatory disease resulting from an autoimmune response against snRNPs |
| Thalassemias | group or hereditary anemias characterized by abnormal Hg molecules, often result of aberrant mRNA splicing |
| Eukaryotic cells have interrupted genes | each exon may represent a protein domain, exons may be assembled in different combinations, need for splicing allows for additional transcriptional regulation, introns may have been maintained through evolution as a reservoir of DNA sequences, introns |
| Interrupted genes (2) | introns may be left over genes no longer required for life, or may be junk DNA |
| Example of regulation of protein expression by alternative RNA splicing | different exon splicing of some primary mRNA transcript results in 2 forms of IgM immunoglobulin, one membrane-associated and one soluble (secreted) |
| tRNA | transfers amino acids from cytoplasm to the growing peptide chain of a protein; less than 100 nucleotides long, form characteristic clover-leaf structures comprised of hair-pin loops formed by intrachain complementary base pairing. |
| tRNA (2) | made from larger precursor molecules that must be trimmed and processed (adding of CCA seq to 3' end and modification of bases at specific positions to produce unusual bases) |
| specific binding in tRNA | Each tRNA is bonded to its specific amino acid by an ester link between the carboxyl of the amino acid and the free 3'OH on ribose at the 3' end of the tRNA chain; at least 1 specific tRNA molecule for each amino acid |
| Anticodon | each tRNA has a specific sequence of 3 bases which recognizes its complementary codon in the mRNA; bind to codons in mRNA by complementary base pairing |
| rRNA | ribosomes are large cytoplasmic RNA-protein complexes where protein synthesis occurs; in eukaryotes 4 RNA molecules and 75 proteins; large and small unit separated by groove through which the mRNA moves; the subunits associate only in prot syntheis |
| Ribosome binding sites | 2 binding sites for tRNA molecules; acceptor and peptide site. Peptide site holds pre-existing protein while A accepts the tRNA bringing in the next amino acid to be incorporated. Together P and A cover 2 adjacent triplet codons on mRNA |
| Prokaryotic vs eukaryotic ribosomes | prokaryotic ribosomes are somewhat smaller; in mitochondria and choloroplasts resemble prokaryotic ribosomes consisting with theory that these organelles evolved from engulfed bacteria |
| Translation | conversion of information in the mRNA into the specific amino acid sequence of a protein |
| Amino acids | encoded by a 3-base triplet which comprises a codon; codons make up the genetic code; sequence of nucleotides in a codon, in mRNA, or any nucleic acid polymer is always written in the 5' to 3' direction |
| Degenerate | different codons can specify the same amino acid, but a given codon specifies only 1 amino acid |
| Exact base tells where translation begins | determines meaning of the message; division into codons in 3 ways: reading frame, codon that is a start (AUG) |
| The stop codons | UAA, UAG, UGA |
| Genetic code is | specific (1 amino acid/codon), universal (same in almost all organisms), degenerate (more than 1 codon for each amino acid), comma-less (nothing between codons) |
| Components required for translation | amino acids, tRNAs, mRNA, ribosomes, phosphate energy (ATP and GTP), mutiple proteins/enzymes |
| Reading frame | sequence of a protein depends on where division into base triplets initiates |
| Steps in translation | initiation (assembly of components before peptide bond forms), elongation (addition of amino acids to carboxyl end), translocation (ribosome moves along mRNA), termination (end of protein synthesis) |
| Peptidyl transferase | component of the ribosome; catalyzes formation of a peptide bond between the two amino acids at the P and A sites |
| New protein is formed from | NH2 terminus to the carboxyl end. |
| Multiple copies of same protein | a single mRNA molecule (polysome) can be translated into multiple copies of the same protein by many ribosomes at the same time |
| Membrane proteins | targeted for secretion are synthesized on ribosomes associated with the endoplasmic reticulum membrane system |
| Antibiotics | many exert their effects by disrupting synthesis of proteins in some way |
| Side effects of antibiotics | due to their deleterious effects on mitochondrial protein synthesis |
| Life is dynamic | organisms must be able to respond to changes in their environment which involves changes in gene expression |
| Transcription factors | specific proteins that interact with these regulatory elements to modulate the binding and activity of RNA polymerase, thereby controlling the amount of transcription of specific genes |
| Constitutive expression | all the time in relatively constant amounts; not much subject to regulation and are usually present in abundant amounts |
| Regulated expression | produced at only certain times in the life of a cell or are subject to fluctuating amounts depending on the needs of the cell |
| Functional activity regulation | allosteric activation, inhibition, phosphorylation, dephosphorylation |
| Repressor | in prokaryotes; negative regulators that bind to a specific site (base sequence) on the DNA in block transcription |
| Inducer | positive regulators that bind to activator sites on theDNA to activate transcription |
| Operon | cluster of genes with related function; in prokaryotes groups of related genes are often under the control of a common regulatory system |
| Bacteria and glucose | glucose preferred energy source, but can use lactose when glucose not present |
| Repressed state | repressor for the lac operator which codes for proteins that metabolize lactose, is expressed constitutively. Repressor binds to lac operator (lacO) and prevents transcription of operon messages |
| Induced state | when lactose present, it acts as an inducer of the lac operon by binding to the repressor thereby preventing it from binding to the operator locus |
| Reason for gene regulation in prokaryotes | adapt to environmental changes rapidly and efficiently |
| Eukaryotic gene expression | gene regulation enables cell specialization as well as response to changing conditions or environments |
| Transcriptional units for RNA polymerase | regulated by at least 2 important control elements, promoters and enhancers |
| Promoter | DNA sequence that promotes the binding of RNA polymerase, the initiating step in transcribing a gene; located a short distance upstream (5' to actual coding region |
| Enhancer | enhance the transcription of groups of genes, but these can be located thousands of bases from the promoter site be either up or down stream to the genes they help regulate. |
| Transcription factors | facilitates binding of RNA polymerase and transcription of the target gene |
| Steroid and thyroid hormones | Hydrophobic hormones include steroid hormones derived from cholesterol (cortisol, androgens, estrogens) and thyroid hormones (thyroxines, iodinated derivatives of the amino acid tyrosine) help control the overall activities of important metabolic pathways |
| Metabolic pathways controlled by hormones | energy metabolism by regulating the expression of large numbers of related genes by entering cells then binding to their receptors in the cytosol and moving into the nucleus where the complex serves as transcriptional enhancer |
| Enhancer (hormone) | induces the transcription of a particular set of 50 to 100 genes |
| Gene regulation | by a wide variety of signals: hormones, growth factors, cell contact, cell division |
| Mutations and recombination in nature | occur randomly but very infrequently |
| Recombinant DNA technology | comprises a group of techniques and tools that enable different DNA molecules to be cut up and then joined to produce new or recombinant DNA |
| Plasmid | circular, double-stranded extrachromosomal DNA molecules which encode proteins useful but not essential to the bacteris in which they reside; capable of autonomous replication but can only replicate inside the cell using host machinery |
| Antibiotic resistance | benefit the host since they encode enzymes that break down antibiotics allowing bacteria containing them to survive exposure to the antibiotic |
| Plasmids in lab | used as vectors for the amplification of specific DNA segments, DNA fragments as large as 20kb can be inserted into plasmids |
| Transformation | bacteria can take up plasmids using this method |
| Growth in presence of antibiotic | used to select bacteria that have acquired the plasmid carrying both the desired gene and the gene encoding a protein which degrades the added antibiotic |
| To be useful for cloning plasmids need | origin of replication, selectable marker, cloning site (where restriction endonucleases cut the DNA) |
| Restriction endonucleases | (restriction enzymes) cut foreign double stranded DNA at specific base sequences; recognize symmetrical polindromic sequences of 4 to 12 bases in DNA;make it possible to break up DNA into pieces of manageable size in the lab |
| Multiple cloning site | region of DNA sequences engineered into a plasmid that has the recognition sites for many different restriction nucleases |
| DNA fragment charge | negative charge due to all phosphate groups in the sugar-phosphate backbone |
| DNA ligase | enzymes that join pieces of DNA; use phosphate energy from ATP to covalently link DNA pieces together by forming the phosphodiester links that join adjacent nucleotides in the DNA strands |
| Sticky ends easier to join | they have already formed hydrogen bonds between complementary bases in the overlapping portions of the two pieces to be joined, stabilizing DNA and holding the strands in place as DNA ligase can form the covalent phosphodiester bonds that link the two |
| DNA cutting with enzymes | any piece of DNA cut with a given enzyme that makes sticky ends can be ligated to any other piece of DNA that has also been digested with the same enzyme |
| Subcloning DNA | process of introducing foreign DNA into a plasmid |
| Transformation | process by which bacteria takes up a plasmid from its surroundings |
| DNA library | collection of DNA molecules; population of vectors each carrying a different complete gene or cDNA with all the DNA sequences represented proportionally |
| Genomic DNA library | prepared by initially cleaving the entire genome (all the DNA) of a cell, including exons, introns, regulatory and non-functional regions |
| cDNA library | prepared using only those DNA sequences that are transcribed into RNA |
| Nucleic acid hybridization | utilizes complementary base pairing to identify specific DNA sequences |
| DNA probe | small single stranded DNA molecule that has a base sequence exactly complementary to a part of the DNA sequence to its desired gene |
| Use of hybridization | isolate cDNA clone containing the desired DNA |
| Sanger method | based on controlled termination of DNA synthesis; incorporated bases are labelled with fluorescent dyes for each base |
| Polymorphisms | variation in the DNA sequences of individuals of a given species; conserved sequences occasionally differ in a single base pair |
| Protein coding genes in human genome | 30k to 40k |
| most DNA is | noncoding |
| Southern blotting | very sensitive hybridization technique used to identify a specific sequence of DNA in a mixture of DNA fragments; ds DNA digested with restriction enzyme, fragments separated using agarose gel, ds DNA on gel exposed to alkaline denaturing, nitrocellulose |
| Northern blotting | mRNA species are separated on the gel instead of DNA fragments, probe is still a cDNA complementary to the same sequence in the desired mRNA molecule, measures gene expression |
| Western blotting | proteins from mixture are separated on gel according to size, transferred to filter, exposed to antibody specific for a given protein |
| PCR | exponentially amplifies a selected segment of DNA; useful for detecting small amounts of DNA |
| Primer | short pieces of DNA complementary to the DNA to be amplified;provide starting point for DNA polymerase to begin reading the template strands and making new DNA |
| Restriction Fragment Length Polymorphism | useful to identify characterization and in tracking diseases and genetic mutations through families and populations |
| Single nucleotide polymorphisms | most prevalent form of genetic variation; generate or destroy a restriction enzyme cut site so the sizes of DNA pieces following nuclease digestion changes |
| Transgenic organisms | carry genes which have been introduced into their genome; added genes usually do not replace the endogenous gene but rather additional or altered copies are presen |
| Allele | alternative form of a gene at the same genetic locus (same position on each of a pair of chromosomes); if two alleles are identical the organism is homozygous for that gene |
| Phenotype | visible or measurable make up or appearance of an organism |
| Genotype | actual genetic make up of the organism |
| Somatic cells | diploid, contain 23 pairs of chromosomes (22 somatic, 2 sex chromosomes) |
| Germ cells | gametes, haploid, (22 somatic chromosomes and 1 sex chromosome) |
| Mendel's principle of segregation | 2 alleles for each gene, at homologous positions on a pair of chromosomes, the 2 alleles separate to form haploid genes |
| Mendel's principle of independent assortment | genes on different chromosomes segregate independently of each other when gametes form, but genes on the same chromosome go together. Random selection on which two somatic chromosomes are selected when gametes form |
| Punnett square | useful for predicting the probability of genetic events |
| Mutations | stable heritable mutations in the base sequence of an organism's DNA. |
| Missense | change in 1 amino acid which may or may not affect protein function |
| Nonsense | often produce premature stop codon producing shortened or no protein products or misfolded proteins with drastically altered amino acid sequences |
| Proteasomes | degrade proteins to amino acids inside cells |
| Monogenic disorders | caused by a single mutant gene; inherited in simple Mendelian pattern; many diseases are also influenced to some degree by environmental factors; include autosomal recessive, autosomal dominant, and X linked recessive |
| Chromosomal disorders | caused by chromosomal rearrangement, affect many genes; chromosomal nondisjunction, chromosome breakage, and translocation |
| Multifactorial disorders | determined by many genes and often significantly influenced by environmental factors; don't show a strictly Mendelian mode of inheritance, strongly influenced by genetic constitution of the individual. diabetes mellitus, hypertension, manic-depressive, |
| Cause of most genetic diseases | autosomal recessive alleles |
| Autosomal recessive disorders | expressed equally in both sexes and transmitted equally to both sexes; one good copy is enough; onset early in life; rare, catabolic pathways or lysosomal storage; Tay Sachs, PKU, Sickle Cell, Cystic fibrosis |
| Advantages of heterozygosity | Sickle cell anemia: increased resistance to malaria |
| Balanced polymorphism | allele that is highly deleterious in a homozygote persists in population because the heterozygote state is advantageous; sicke cell anemia heterozygotes |
| PKU | autosomal recessive; defect in phenylalanine hydroxylase (can't convert phenylalanine to tyrosine) |
| Autosomal dominant | single mutant allele causes disease; observed in heterozygotes, mutant protein is bad; do not skip generations; equal numbers of sexes affected; delayed age of onset; brain or nervous system affected; key structural or metabolic pathway proteins |
| Autosomal dominant diseases | familial hypercholesterolemia (defect in LDL receptor), Huntington's disease (extra copies of CAG codon coding for glutamine, nonfunctional copy is toxic and kills neurons) |
| Fragile X syndrome | chromosome breakage, caused by expansion of CGG or CCG codons in noncoding region of gene |
| X linked disorders | mutant allele is on the X chromosome; females are carriers, unaffected; males have disease; hemophilia, color blindness, Duchenne muscular dystrophy |
| How mutant proteins actually cause disease? | protein may not be synthesized (STOP codon premature); mutant protein inactive or inefficient (LOF), rogue protein (does something bad, GOF), misfolds and is mistargeted or rapidly degraded |
| Mutations in all kinds of proteins cause disease? | enzymes; carrier proteins (Hg), membrane transport/channel proteins (CFTR) |
| Recombination | genes can be altered by the natural movement of large blocks of DNA which contribute to genetic diversity |
| Meiosis | independent assortment of the chromosomes in each pair, one chromosome from each of the 23 pairs is randomly selected to form the gamete |
| Homologous recombination | crossing over; sometimes occurs during meiosis; align and exchange segments of DNA usually with similar base sequences; doesn't happen for sex chromosomes and autosomal chromosomes |
| Chromosomal disorders | affect many genes because result in gross alterations of chromosomes instead of point mutations in the base sequence |
| Chromosomal nondisjunction | failure of homologous chromosomes to separate during meiosis results in a gamete that have an extra chromosome; Down (Trisomy 21) |
| Chromosome 21 | smallest autosomal chromosome; only changes in the number of sex chromosomes (which are small) or the smallest autosomal chromosome produce relatively healthy infants |
| Probability of Down syndrome | increases markedly with the mother's age |
| Karyotyping | detects abnormal chromosome number and gross chromosome additions and deletions; map of chromosomes obtained from single WBC and examine using calchinine |
| Calchicine | mitotic spindle inhibitor that stops cell division at metaphase when chromosomes are condensed and ready to separate is added for karyotyping |
| Turner syndrome | too few sex chromosomes; XO genotype; sterile female; all or part of 1 X chromosome missing; fold of skin along neck, low hairline at nape of neck, shield shaped chest, failure to develop adult sex characteristics at puberty |
| Klinefelter syndrome | too many sex chromosomes; XXY; sterile males; small testes, long legs and arms, somewhat diminished verbal skills |
| Tall Mentally Slow Males | too many sex chromosomes; XYY; generally over 6 ft tall, below average intelligence; comprise 1/1000 of all males |
| Gross alterations in chromosome structures | duplications of a chromosome segment; indel of chromosome segment; inversion of a gene on a chromosome; translocation of a portion of 1 chromosome to another |
| Genetic defects result from | chromosome translocations and breakage |
| Chromosome translocation | part of one chromosome moves spontaneously to new location on different chromosome; Burkitt's lymphoma and chronic myelogeneous leukemia; over 30 types of cancers |
| Burkitt's lymphoma | part of chr. 8 is translocated to chr. 14 to activate an oncogene (controls cell division). Relocates MYC, a gene that regulates cell growth. MYC now heavily influenced by immunoglobulin gene in WBC and is rapidly transcribed causing WBC to grow rapidly |
| Burkitt where is MYC inserted | downstream from the strong immunoglobulin gene promoter; mutation occurs in a somatic WBC so not inherited; viral infections can also cause this |
| Chromosome breakage | part of a chromosome breaks off; Fragile X; |
| Fragile X syndrome | triplet repeat disease; CGG or CCG in the 5' upstream noncoding region of a gene is expanded; up 600 copies of repeat; tip of the X chromosome long arm breaks off; most common type of mental retardation |
| Radiation disease | radiation breaks chromosomes |
| Detection of genetic disorders | family pedigree, karyotyping, RFLP analyses (of specific segments of DNA) |
| Prenatal diagnosis | involves collection of fetal cells for analysis |
| Amniocentesis | needle is inserted through mother's abdominal and uterine walls using ultrasound to determine correct location, a few ml of amniotic fluid is withdrawn which contains fetal skin cells; cultured or using PCR; can't be performed before 14 to 20 weeks |
| Chorionic villus sampling | fetal cells harvested from portion of placenta that derived from fetal tissue can be done at 10 to 12 weeks and results obtained 1 to 2 weeks later |
| Preimplantation genetic testing | done at the 8 cell embryo stage prior to implantation of an in vitro fertilized egg |
| Sex determination | karyotyotyping reveal the sex of the fetus |
| Number of disorders that can be detected using prenatal techniques | more than 200 different disorders |
| Amanitin | mushroom toxin; block mRNA synthesis in eukaryotic cells by binding to an inhibiting DNA poly II (no transcription); doesn't affect bacteria |
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