BIOL 2061: GENETICS
35 Cards in this Set
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DNA structure
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- Double stranded helix
- sugar/phosphate backbone
- Hydrogen-bonded nitrogen bases
- Nucleotides added to 3' hydroxyl group
- H attached to 2' carbon
- The phosphate group gives DNA its negative charge
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Purines
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Pur As Gold
Purines: Adenine (A), Guanine (G)
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Pyrimidines
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-CUT the Py
- Pyrimidines: Cytosine (C), Uracil (U) for RNA only, Thymine (T) for DNA only
C-G (3 H bonds)
T-A (2 H bonds), U-A (2 H bonds) for RNA
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DNA Replication
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- Leading strand is synthesized continuously
- Lagging strand is synthesized in pieces ( Okazaki fragments)
- The strands are synthesized in the 5’ to 3’ direction
- DNA polymerase I removes RNA primers
- Lygase joins the fragments
- Lagging strand has higher probability of…
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RNA vs DNA: RNA
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= single stranded, has Uracil instead of Thymine, & 2' extra OH on ribose
= codes for proteins
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RNA vs. DNA: DNA
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deoxyribose sugar, Thymine
has H on 2'
information storage, stability, east of packaging, long double strand, flexibility allows for easier storage - histones
- function for genetic
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mRNA
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- Messenger RNA
- codes for amino acids
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tRNA
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- Transfer RNA
- brings amino acids to ribosome
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rRNA
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- Ribosome RNA
- component of ribosome
- is made at rRNA
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DNA transcription
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DNA -> mRNA
occurs in nucleus
initiation -> elongation -> termination
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Transcription: Initiation
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- occurs at the promoter (region where RNA polymerase binds)
- RNA polymerase begins to unwind DNA (this requires energy)
- Promoter region contains sequence T-A-T-A (called TATA box)
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Transcription: Elongation
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- Assembles RNA nucleotides using one strand of DNA as a template
- Assembles in 5' to 3' direction
- Only 1 DNA strand is transcribed
- Primers are not required
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Transcription: termination
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Occurs when RNA polymerase reaches a special sequence of nucleotides that serve as a termination point
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mRNA Processing
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- Cleave introns and splice exons
- Exons are expressed
- Introns are in between
- Add 5' cap and 3' poly-A-tail
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Translation
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mRNA to proteins
mRNA attaches to ribosome (in cytoplasm)
initiation -> elongation -> termination
energy provided from several GTP
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Translation: ribosome
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- A site (amino acid): 1st position, accepts incoming tRNA carrying an amino acid
- P site (polypeptide): 2nd position, holds tRNA with a growing chain of amino acids (polypeptide)
- E site (exit): 3rd position, holds tRNA after it gives up its amino acid
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Translation: initiation
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- small ribosomal subunit attaches near the of mRNA
- tRNA (w/ anticodon UAC) carrying methionine attaches to mRNA at the start codon AUG
- Large ribosomal subunit attaches to mRNA with tRNA (bearing a methionine)
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Translation: elongation
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- Additional tRNA attaches to A site, tRNA is always base-paired with mRNA codon
- Amino acid on tRNA in P site is transferred to newly arrived amino acid in A site to create a peptide bond
- Translocation: ribosome moves over one binding site (tRNA in P site moves into E site, tRNA in …
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Translation: termination
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- Stop codon (UGA, UAA, UAG) is recognized by release factor, and protein is released from ribosome.
- Interactions among amino acids give it its 2o and 3o structures
- ER or Golgi may make final modifications before the protein functions as a structural element or an enzyme
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Stop Codons
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UGA: U Go Away
UAG: U Are Gone
UAA: U Are Alienated
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Mutation
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- Sequence of nucleotides in a DNA does not match with one in copied DNA
- Can occur as a result of replication errors, radiation, reactive chemicals
- Mutagens are mutation caused by radiation and chemicals
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Point Mutation
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A single nucleotide error and includes: substitution, deletion, insertion, frameshift mutation
- May or may not have a significant phenotypic effect
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Silent mutation
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- mRNA is produced from a DNA segment that contains a point mutation
- when new codon still codes for the same amino acid
gga (Gly) -> ggg (Gly)
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Missense mutation
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- mRNA is produced from a DNA segment that contains a point mutation
- when the new codon codes for a new amino acid
gga (Gly) -> age (Arg)
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Nonsense mutation
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- mRNA is produced from a DNA segment that contains a point mutation
- when the new codon codes for a stop codon
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Chromosomal aberrations
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Substantial changes in chromosome structure
Typically affect more than one gene
are quite common
Caused by nondisjunction (failure of chromatids to separate)
Turner Syndrome, Klinefelter Syndrome, Down Syndrome, Super male
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Degeneracy
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Amino acids have more than 1 codon
(64 codons code for 20 amino aids)
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Wobble Pairing
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Allows 1 tRNA anticodon to pair with more than 1 codon
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Monohybrid Cross
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Cross, or mating, between organisms that involves only one pair of contrasting traits.
(Aa x Aa)
Genotype: 1:2:1 --> 1 AA: 2Aa: 1aa
Phenotype: 3 dominant, 1 recessive
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Dihybrid cross
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a cross in which the inheritance of two characteristics are tracked at the same time
AaBb x AaBb
Genotype: 1:1:2:2:4:2:2:1:1
Phenotype: 9 dom/dom: 3 dom/rec: 3 rec/dom: 1 rec/rec
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Autosomal Recessive Pedigree
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Affects any chromosome other than a sex chromosome
Trait skips a generation
Males and females are affected and transmit trait in approx. equal proportions
When both parents are unaffected, ALL offspring will be affected
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Autosomal Dominant Pedigree
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Affected individuals have at least one affected parent
Phenotype appears in every generation
Males and females are affected and transmit trait in approx. equal proportions
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Sex chromosomes
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- One pair in mammal that does not have exactly the same gene
- Are 2 of 46 chromosomes in human genome
- XX = female
- XY = male
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X-linked Recessive Pedigree
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- males are hemizygous for traits in the x chromosome
- carrier females can pass the trait to sons
, males will only pass the allele to daughters
- daughters will only be affected if a copy of the allele is inherited from both parents
- E.g. baldness, blindness, hemophilia
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eukaryote
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BIOL 2061: ENDOCRINE SYSTEM