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50 Cards in this Set
- Front
- Back
Genetics
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The study of what genes are, how they carry information, how information is expressed, and how genes are replicated
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Gene
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A segment of DNA that encodes a functional product, usually a protein
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Chromosome
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Structure containing DNA that physically carries hereditary information; the chromosomes contain the genes
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Genome
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All the genetic information in a cell
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Genomics
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The molecular study of genomes
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Genotype
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The genes of an organism (DNA)
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Phenotype
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Expression of the genes
(ex: hair color, eye color) |
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DNA
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-Polymer of nucleotides: Adenine, Thymine, Cytosine, Guanine
-Double helix associated with proteins -"Backbone" is deoxyribose-phosphate -Strands are held together by hydrogen bonds between AT and CG -Strands are antiparallel (5' to 3' and 3' to 5') |
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DNA Replication
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-Semiconservative
---1 parent strand (original) and 1 newly made strand (daughter strands have) |
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DNA Synthesis
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-DNA is copied by DNA polymerase
---in the 5'-->3' direction ---initiated by an RNA primer ---leading strand is synthesized continuously ---lagging strand is synthesized discontinuously ---Okazaki fragments ---RNA primers are removed and Okazaki fragments joined by a DNA polymerase and DNA ligase |
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DNA Synthesis
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-single strand binding protein
*keeps strands seperate -primase *builds primers -ligase *seals over the gaps |
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Steps of DNA Replication
(ON TEST!!) |
1. Topoisomerase relaxes supercoiled DNA
2. Helicase unwinds the double helix by breaking hydrogen bonds between the base pairs 3. Destabilizing Enzymes (SSB) bind to the single strands to keep the strands seperated 4. Primase adds RNA primers to initiate DNA synthesis 5. DNA polymerase 3 binds at the RNA primers, DNA polymerase 1 removes primers and DNA polymerase 3 synthesizes new DNA in the 5' to 3' direction on both the leading and lagging strands 6. Fragments of DNA (Okazaki fragments on the lagging strand) are joined by the enzyme DNA ligase |
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Information Transfer
(ON TEST!!!) |
Transcription- RNA is made from DNA code. The RNA has complementary bases to the DNA
**DNA--->RNA Translation-RNA is used as a template to make protein Amino acids, protein building blocks are coded by the base pairs on the RNA **RNA--->Protein |
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Transcription
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-DNA is transcribed to make RNA (mRNA, tRNA, and rRNA)
-Transcription begins with RNA polymerase binds to the promoter sequence -Transcription proceeds in the 5'--->3' direction -Transcription stops when it reaches the terminator sequence |
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RNA Processing in Eukaryotes
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-Occurs between transcription and translation
-INTRON: intervening sequence, removed by RNA splicing -EXON: coding sequence, "stay" |
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Translation
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-Protein is synthesized based on code in mRNA
-The mRNA nucleotides are arranged in 3 nucleotide units called codons. Codons do not overlap. -CODON: Group of three nucleotides on mRNA that codes for an amino acid -DEGENERATE CODE: Most amino acids specified by more than one codon |
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The Genetic Code
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-64 sense codons on mRNA encode the 20 amino acids (redundancy)
**redundant: more than 1 codon codes for the same amino acid -Translation of mRNA begins at the start codon: AUG -Translation ends at nonsense codons:UAA, UAG, UGA -tRNA carries the complementary anticodon |
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3 Types of RNA
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1. messenger RNA (mRNA)
2. transfer RNA (tRNA) 3. ribosomal RNA (rRNA) |
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messenger RNA
(mRNA) |
Carries DNA message through complementary copy: message is in triplets called codons
**product of transcription** |
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transfer RNA
(tRNA) |
Secondary structure creates loops; bottom loop exposes a triplet of nucleotides called anticodon which designates specificity and complements mRNA; carries specific amino acids to ribosomes
**translation** |
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ribosomal RNA
(rRNA) |
component of ribosomes where protein synthesis occurs
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Steps to Translation
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1. Translation of mRNA begins at the start codon: AUG
2. Translation ends at a STOP codon 3. The large and small ribosomal subunits and tRNA with UAC anticodon and corresponding methonine amino acid assemble at the AUG start codon 4. The first tRNA moves to the P site of the ribosome and the second tRNA with the next amino acid enters A site of the ribosome 5. The ribosome joins the two amino acids with a peptide bond 6. The first tRNA molecule leaves the ribosome and the second tRNA moves into P site while the third tRNA and its amino acid enters A site 7. The process proceeds down the mRNA and amino acid chain is formed 8. Translation ends when one of three nonsense (stop codons) UAA, UAG, UGA is reached and the ribosome subunits separate from the mRNA and release the polypeptide chain, tRNA |
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Process of Translation
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Three phases:
1. initiation 2. elongation 3. termination |
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Three Locations for tRNA
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1. P site
2. A site (arrival) 3. E site |
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The Regulation of Bacterial Gene Expression
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-Constitutive genes are expressed at a fixed rate
-Other genes are expressed only as needed **Repressible genes (normally on, can be turned off) **Inducible genes (normally off, can be turned on) **Catabolite repression |
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Inducible Operon: Lac Operon
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-Normally off, can be turned on
-Genes required for lactose metabolism in E. coli are inducible -B-galactosidase breaks down lactose into glucose and galactose -When no lactose is present in the media, E. coli do not make B-galactosidase -When lactose is present in the media it is converted by the cell to allolactose -Allolactose induces the transcription of B-galactosidase. -SUMMARY: when lactose is present, allolactose is present which turns on B-galactosidase to process the lactose |
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Lac Operon genes
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I- Gene for repressor protein
P- Promoter O- Operator lac Z- Gene for B-galactosidase lac Y- Gene for B-galactosidase permease lac A- Gene for B-galactosidase transacetylase |
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Repressible Operon: Tryptophan Operon
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-Normally on, can be turned off
-Genes required for tryptophan synthesis are normally transcribed -When excess tryptophan is present, it can act as a corepressor **catabolic activating protein (positive regulation): ---glucose is high, CAMP is low, and CAP is not active, will not bind promoter, no transcription of operon ---glucose is low, CAMP is high, CAMP binds CAP, CAP is active, binds promoter, transcription of lac operon |
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Mutation
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-A change in the genetic material
-Mutations may be neutral, beneficial, or harmful -MUTAGEN: Agent that causes mutations -SPONTANEOUS MUTATIONS: Occur in the absence of a mutagen |
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Four Types of Mutations
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1. Base substitution (point mutation): Change in one base
2. Missense mutation: Result in change in amino acid 3. Nonsense mutation: Results in a change nonsense codon 4. Frameshift mutation: Insertion or deletion of one or more nucleotide pairs |
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The Frequency of Mutation
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-Spontaneous mutation rate=1 in 10^9 replicated base pairs or 1 in 10^6 replicated genes
-Mutagens increase to 10^-5 or 10^-3 per replicated gene |
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Radiation
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-Ionizing radiation: (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone
-UV radiation causes thymine dimers |
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Repair
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-Photolyases separate thymine dimers
-Nucleotide excision repair |
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Ames Test for Chemical Carcinogens
(POSSIBLE ESSAY QUESTION!!) |
-Salmonella (will not grow on media, lacking histidine)
**HIS- (requires histidine in media to grow) **Back mutates to HIS+ (is able to make its own histidine and can grow on media lacking histidine) |
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Genetic Transfer and Recombination
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Vertical gene transfer
-Occurs during reproduction between generations of cells -parent cell-->daughter cell Horizontal gene transfer -The transfer of genes between cells of the same generation -expression |
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Genetic Recombination
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-Exchange of genes between two DNA molecules
**crossing over occurs when two chromosomes break and rejoin |
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Genetic Recombination in Bacteria
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1. Conjugation
2. Transformation 3. Transduction |
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Genetic Transformation
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Transformation: chromosomes fragments from a lysed cell are accepted by a recipient cell
*S. pneumonial with capsule -->smooth colonies (killed the mice) *S. pneumonial without capsule -->rough colonies |
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Bacterial Conjugation
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-Conjugation: transfer of a plasmid or chromosomal fragment from a donor cell to a recipient cell via direct connection
---gram negative cell donor has a fertility plasmid (F plasmid, F' factor) that allows the synthesis of a conjugation (sex) pilus ---High frequency recombination: the donor's fertility plasmid has been integrated into the bacterial chromosome |
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Transduction by a Bacteriophage
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Transduction: bacteriophage serves as a carrier of DNA from a donor cell to a recipient cell
*Generalized *Specialized |
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Plasmids
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-Plasmids: small, self-replicating, circular DNA
**Conjugative plasmid: carries genes for sex pili and transfer of the plasmid **Dissimulation plasmids: encode enzymes for catabolism of unusual compounds **R factors: encode antibiotic resistance |
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Transposons
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-Segments of DNA that can move from one region of DNA to another
-Contain insertion sequences for cutting and resealing DNA (transposase) -Complex transposons carry other genes |
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Genes and Evolution
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-Mutations and recombination provide diversity
-Fittest organisms for an environment are selected by natural selection |
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DNA Gyrase
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Relaxes supercoiling ahead of the replication fork
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DNA Ligase
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Makes covalent bonds to join DNA strands; joins Okazaki fragments and new segments in excision repair
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DNA Polymerase
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Synthesizes DNA; proofreads and repairs DNA
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Helicase
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Unwinds double-stranded DNA
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RNA Primase
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An RNA polymerase that makes RNA primers from a DNA template
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Topoisomerase
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Relaxes supercoiling ahead of replication fork; separates DNA circles at the end of DNA replication
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Catabolic Activating Protein: positive regulation
(ON TEST!!!) |
-Glucose is high, CAMP is low, and CAP is not active, will not bind promoter, no transcription of operon
| | V -Glucose is low, CAMP is high, CAMP binds CAP, CAP is active, binds promoter, transcription of lac operon |