ap bio unit 6

Cards (43)

  • DNA is located in the nucleoid region in prokaryotes and are smaller and often circular
  • mRNA- messenger between DNA and the ribosomes
    rRNA- structural components of ribosomes
    tRNA- bring amino acids to ribosomes
    miRNA and siRNA- regulators of genes
  • DNA replication is semiconservative, meaning that each strand in DNA acts as a template for the synthesis of a new, complementary strand
  • helicase- unwinds the DNA at replication forks (breaking the hydrogen bonds between the nitrogenous base pairs)
    single-strand binding proteins- keep the separated strands from coming back together
  • in E. coli, DNA polymerase III can only add nucleotides to the 3' end of an existing DNA strand (synthesizing the new strand in the 5 to 3 direction)
    • needs the enzyme called primase to make an RNA primer that is complementary to the template
  • leading vs. lagging strand:
    • leading is synthesized TOWARDS the replication fork, while lagging is synthesized AWAY from the replication fork
  • okazaki fragments- new DNA is made in these fragments on the lagging strand
  • topoisomerase- prevents the DNA double helix ahead of the replication fork from getting too tightly wound as the DNA is opened up by helicase
  • DNA polymerase I- RNA primers are removed and replaced by DNA
    • the spaces that remain after the primers are replaced get sealed by DNA ligase
  • chargaff's rules- A = T and C = G
  • eukaryotic RNA modifications after transcription:
    • protection- 5' cap and poly-A tail to protect the mRNA transcript from attack by enzymes in the cytoplasm called exonucleases
    • splicing- remove the introns (sequences of RNA that don't contain any information) from the mRNA transcript using spliceosomes
  • transcription steps:
    1. initiation- RNA polymerase binds to the promoter of DNA (beginning of gene) and separates the DNA strands
    2. elongation- RNA polymerase reads DNA template strand and builds RNA strand of complementary nucleotides
    3. termination- terminator sequence signaling
  • transcription- nucleus
    translation- ribosome
  • alternative splicing- more than one mRNA can be made from the same gene
  • translation:
    • initiation- ribosome assembles around mRNA, tRNA carrying MET matches AUG codon and is necessary to begin translation
    • elongation- amino acid chain gets longer
    • termination- stop codon enters ribosomes, triggering events that separate chain from tRNA
  • coding strand = mRNA
  • eukaryotes: transcription in nucleus, translation in ribosomes in cytosol
    prokaryotes: transcription AND translation in cytosol
  • RNA in retroviruses
  • lac operon (inducible)-
    • can be turned on by allolactose (inducer)
    • lac repressor originally blocks RNA polymerase from transcribing the lac operon when lactose is NOT AVAILABLE
    • when lactose IS AVAILABLE, allolactose (rearranged lactose) binds to the lac repressor, allowing it to change shape and not bind to the DNA
    • RNA polymerase can now transcribe the operon in order to BREAK DOWN LACTOSE
  • the lac operon turns ON when glucose is UNAVAILABLE and lactose is AVAILABLE
    • the promoter region is the binding site for RNA polymerase
    • the operator region is the binding site for a repressor protein
  • trp operon (repressible)-
    • can be turned off by tryptophan (corepressor) binding to the trp repressor
    • when tryptophan IS AVAILABLE, it is bound to the trp repressor and transcription is turned OFF
    • when tryptophan is NOT AVAILABLE, the trp repressor is NOT BOUND and RNA polymerase can make tryptophan
  • tryptophan is present = trp repressor bound, trp operon NOT TRANSCRIBED
    tryptophan is NOT present = trp repressor unbound, trp operon is TRANSCRIBED to CREATE TRYPTOPHAN
  • lac and trp operons are examples of gene regulation in BACTERIA
  • eukaryotic gene regulation: growth factors
    • growth factor binds to receptor protein
    • triggers chemical events that activate transcription factors
    • transcription factors bind to DNA and cause transcription
  • in prokaryotes, RNA polymerase attaches right to the DNA of the promoter, initiating transcription
    in eukaryotes, transcription factors help RNA polymerase attach to the promoter
  • bacteria reproduce by splitting in two via binary fission
    • binary fission makes clones
  • genetic variation in prokaryotes:
    • transformation- a bacterium takes up a piece of DNA floating in its environment
  • genetic variation in prokaryotes:
    • transduction- DNA is accidentally moved from one bacterium to another by a virus
    • these viruses that infect bacteria are called bacteriophages
  • genetic variation in prokaryotes:
    • conjugation- DNA is transferred from one bacterium to another through a pilus
  • DNA cloning- process of making multiple identical copies of DNA
    • restriction enzyme: DNA-cutting enzyme that recognizes a specific target sequence and cuts DNA into two pieces at that site
    • joined together by DNA ligase
  • bacterial transformation and selection in DNA cloning step 2-
    • plasmids and other DNA can be introduced into bacteria through transformation
    • during transformation, high temperature encourages the bacteria to take up foreign DNA
    • a plasmid typically contains an antibiotic resistance gene, which allows bacteria to survive in the presence of a specific antibiotic
    • bacteria without a plasmid will die, while bacteria carrying a plasmid can live and reproduce
  • polymerase chain reaction (PCR): used to make many copies (millions) of a particular region of DNA
    1. denaturation: separate the DNA strands using heat
    2. annealing: primers can bind to their complementary sequences by cooling the reaction
    3. extension: raising the reaction temperatures for synthesis of new strands of DNA
  • gel electrophoresis: used to separate DNA fragments based on their size and charge
    • DNA has a negative charge due to phosphate groups on backbone, so they start moving towards the positive pole
    • shorter DNA travel LONGER DISTANCES
  • frederick griffith:
    • when the mice were exposed to an R strain (non-virulent) and a heat-killed S strain, they actually developed pneumonia and died
    • concluded that the R strain bacteria transformed and became a virulent strain
  • mRNA modifications:
    • 5’ Guanine cap: signals the start of mRNA transcript for the ribosome to bind to; facilitates export from nucleus
    • Poly-A-tail: inhibits degradation of hydrolytic enzymes in cytosol
  • Regulation of gene expression:
    • methylation- stop
    • acetylation- activate
  • signal transduction pathways are highly specific and regulated
    • one molecule can cause a cascade effect of thousands of molecules
    • these pathways evolved from a COMMON ANCESTOR
  • lac operon is INDUCIBLE, trp operon is REPRESSIBLE
  • the same transcription factor often regulates different genes