Bio 101

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Bio 101
2012-05-07 14:32:40

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  1. For a recessive sex-linked trait to be expressed
    • A female needs two copies of the allele
    • A male needs only one copy of the allele
  2. Sex-linked recessive disorders are much more common in males than in females
    For instance, recessive alleles causing color blindness are carried on the X chromosome. Fathers transmit this and other sex-linked alleles to all daughtersbut to no sons. Any male who inherits such an allele from his mother will express the trait
  3. chromosomes have __ # of genes
    Each chromosome has hundreds or thousands of genes
  4. Liked genes
    Genes located on the same chromosome that tend to be inherited together
  5. Linked genes tend to be inherited together
    because they are located near eachother on the same chromosome.
  6. Genetic recombination and linkage
    The farther apart two genes are, the higher the probability that a crossover will occurbetween them and therefore the higher the recombination frequency.
  7. Exceptional inheritance patterns
    Genomic Imprinting and Organelle geneInheritance
  8. Genomic Imprinting
    for a few mammalian traits, the phenotype depends on which parent passed along thealleles for those traitsSuch variation in phenotype is called genomic imprinting
  9. DNA
    is the genetic matterial
  10. DNA structure
    Nucleic acids are polymers called polynucleotides. Each polynucleotide is made ofmonomers called nucleotides. Each nucleotide consists of a nitrogenous base, a pentose sugar, and a phosphate group.
  11. polynucleotides.
    Nucleic acids are polymers called Each polynucleotide is made of monomers called nucleotides.
  12. nucleotides
    is made of monomers Each nucleotide consists of a nitrogenous base, a pentose sugar, and a phosphate group.
  13. DNA nucleotide
    • Sugar= deoxyribose
    • Base= A, T, C, G
    • Usually double-stranded
  14. RNA nucleotide
    • Sugar= ribose
    • Base= A, U, C, G
    • Usually single-stranded
  15. Nucleotide polymers are linked together by
    covalent bonds to build a polynucleotide.These bonds create a backbone of sugar-phosphate units with nitrogenous bases asappendages.
  16. The two polynucleotides, or strands, as they are called, are held together by
    hydrogen bonds, forming a double helix
  17. The nitrogenous bases pair up and form hydrogen bonds:
    • adenine (A) pairs withthymine (T) in DNA,
    • (adenine pairs with uracil in RNA) and
    • guanine (G) pairs withcytosine (C).
  18. DNA synthesis
    The Basic Principle: Base Pairing to a Template StrandReplication begins at special sites called origins of replication, where the two DNAstrands are separated, opening up a replication “bubble”
  19. Enzymes work in DNA replication
    • 1. DNA polymerase catalyzes the elongation of new DNA at a replication fork
    • 2. DNA ligase joins Okazaki fragments in lagging strand
    • 3. Primase synthesizes a short primer
    • 4. helicase: enzymes that untwist the double helix at the replication forks
    • 5. topoisomerase corrects “overwinding” ahead of replication forks by breaking,swiveling, and rejoining DNA strands
    • 6. single-strand binding proteins bind to and stabilizes single-stranded DNA untilit can be used as a template
  20. DNA polymerase catalyzes the elongation of new DNA at a replication fork
    DNA polymerases cannot initiate synthesis of a polynucleotide; they can only addnucleotides to the 3′ end. The initial nucleotide strand is a short RNA primer.
  21. helicase
    enzymes that untwist the double helix at the replication forks
  22. topoisomerase
    corrects overwinding ahead of replication forks by breaking wiveling and rejoining DNA strands
  23. single strand binding proteins
    bind to and stabilizes single strand DNA until it can be aas a template
  24. Antiparallel Elongation􀁺
    • 􀁺 The antiparallel structure of the double helix (two strands oriented in oppositedirections) affects replication
    • 􀁺 DNA polymerases add nucleotides only to the free 3′ end of a growing strand;therefore, a new DNA strand can elongate only in the 5′ to 3′ direction
    • 􀁺 Along one template strand of DNA, the DNA polymerase synthesizes a leadingstrand continuously, moving toward the replication fork
    • 􀁺 To elongate the other new strand, called the lagging strand, DNA polymerasemust work in the direction away from the replication fork
    • 􀁺 The lagging strand is synthesized as a series of segments called Okazakifragments, which are joined together by DNA ligase
  25. The antiparallel structure of the double helix
    (two strands oriented in oppositedirections)
  26. Leading strand
    • 􀁺 Elongates continuously
    • 􀁺 One primer is required
  27. Lagging strand
    • 􀁺 Is synthesized discontinuously
    • 􀁺 Each fragment must be primed separately
    • 􀁺 DNA polymerase I and DNA ligase are required
  28. :􀁺 Incorrect base pairing during DNA replication
    • 􀁺 DNA can be damaged by chemicals, radioactive emissions, X-rays, UV light, andcertain molecules (cigarette smoke, etc.) after DNA replication
    • 􀁺 DNA polymerases proofread newly made DNA, replacing any incorrectnucleotides
    • 􀁺 In mismatch repair of DNA, repair enzymes correct errors in base pairing
    • 􀁺 In nucleotide excision repair, a nuclease cuts out and replaces damagedstretches of DNA
  29. In nucleotide excision repair,
    a nuclease cuts out and replaces damagedstretches of DNA
  30. Central dogma & genetic codens
    The central dogma is the concept that cells are governed by a cellular chain ofcommand: DNA → RNA → protein
  31. RNA is the intermediate
    between genes and the proteins for which they code
  32. Transcription
    is the synthesis of RNA under the direction of DNATranscription produces messenger RNA (mRNA)
  33. Translation
    is the synthesis of a polypeptide, which occurs under the direction ofmRNA
  34. Ribosomes
    are the sites of translation
  35. Codons: Triplets of Bases
    Genetic information is encoded as a sequence of nonoverlapping base tripletsThe genetic code is redundant but not ambiguous; no codon specifies more thanone amino acid.Codons must be read in the correct reading frame
  36. The genetic code is
    nearly universal, shared by the simplest bacteria to the most complexanimals.
  37. Transcription
    : Transcription is the DNA-directed synthesis of RNA RNA synthesis is catalyzed by RNA polymerase, which pries the DNA strands apartand hooks together the RNA nucleotides
  38. RNA synthesis follows the same base-pairing rules as DNA, except
    uracil substitutesfor thymine
  39. The three stages of transcription & translation
    • Initiation
    • Elongation
    • Termination
  40. Initiation (transcription)
    • Promoters signal the initiation of RNA synthesis
    • Transcription factors mediate the binding of RNA polymerase and theinitiation of transcription
    • The completed assembly of transcription factors and RNA polymerase bound to a promoter is called a transcription initiation complex
    • A promoter called a TATA box is crucial in forming the initiationcomplex in eukaryotes
  41. Elongation (transcription)
    • The RNA polymerase adds nucleotides to the 3’ end of the growing RNA molecule
    • A gene can be transcribed simultaneously by several RNApolymerases
  42. Termination (transcription)
    • In bacteria, the polymerase stops transcription at the end of theterminator
    • In eukaryotes, the pre-mRNA is released after the polyadenylationsignal (AAUAAA) sequence is transcriped
  43. Eukaryotic cells modify
    RNA after transcription
  44. Each end of a pre-mRNA molecule is modified in a particular way
    • The 5′ end receives a modified nucleotide 5′ cap
    • The 3′ end gets a poly-A tail
  45. These modifications share several functions:
    • They seem to facilitate the export of mRNA
    • They protect mRNA from hydrolytic enzymes
    • They help ribosomes attach to the 5′ end
  46. intervening sequences, or introns
    The noncoding regions are called
  47. exons
    because they are eventually expressed, usuallytranslated into amino acid sequences
  48. RNA splicing
    removes introns and joins exons, creating an mRNA molecule with acontinuous coding sequence
  49. Translation
    • tRNA
    • A cell translates an mRNA message into protein with the help of transfer RNA (tRNA)
    • Molecules of tRNA are not identical:
    • 1)Each carries a specific amino acid on one end
    • 2) Each has an anticodon on the other end; the anticodon base-pairs with acomplementary codon on mRNA
  50. Ribosome
    • Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons inprotein synthesis
    • The ribosomes are made of proteins and ribosomal RNA (rRNA)
  51. Initiation (translation)
    • The initiation stage of translation brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits. This complex iscalled the translation initiation complex.
    • Start codon signals the start of translation.
    • Translation initiation requires energy in the form of GTP.
  52. Elongation (translation)
    Elongation occurs in a three-step cycle: codon recognition, peptide bondformation and translocation
  53. Termination
    • Termination occurs when a stop codon in the mRNA reaches the A site ofthe ribosome
    • The A site accepts a protein called a release factor
  54. mutations
    Mutations are changes in the genetic material of a cell or virus
  55. point mutations
    are chemical changes in just one base pair of a geneThe change of a single nucleotide in a DNA template strand can lead to theproduction of an abnormal protein
  56. silent mutations
    have no effect on the amino acid produced by a codon because ofredundancy in the genetic code
  57. missense mutations
    still code for an amieno acid, but not necessarily the right aminoacid
  58. nonsence mutations
    change an amino acid codon into a stop codon, nearly alwaysleading to a nonfunctional protein
  59. Insertion or deletion
    • are additions or losses of nucleotide pairs in a gene.
    • These mutations have a disastrous effect on the resulting protein more oftenthan substitutions do. Insertion or deletion of nucleotides may alter thereading frame, producing a frameshift mutation