Chapter 16
Radioactive isotope phosphorus to tag DNA and radioactive sulfur to tag protein
- Showed onl DNA entered bacteria infected by virus, so DNA must be the genetic
material
Sugar phosphate backbone, rungs of nitrogenous bases (sugar attached to phosphate and
nitrogen base)
- Adenine - thymine
- Guanine - cytosine
Antiparallel: 5-3 v 3-5
1.
2.
3.
4.
5.
6.
Helicase unwinds helix
DNA polymerase III adds nucleotides in 5-3 direction (leading strand)
Lagging strand is done in okazaki fragments bc it has to be done in 5-3 direction
Primase makes RNA primer for okazaki fragment
DNA pol I removes primer and replaces it with DNA
sealed with ligase
Mismatch repair: repair enzymes to fix incorrectly pair nucleotides
Nucleotide excision repair: incorrectly placed nucleotides are removed with nucleases and filled
in correctly
DNA pol can only on the 3 end bc there was no way to complete the 5 end
- Small portion of tip is removed
- To avoid losing terminal genes, linear ends are capped w telomeres
Eukaryotes: need RNA processing to get to final mRNA after transcription from DNA, need
transcription factors to get RNA pol II to bind to promoter, add 5 cap and poly-A tail for export
from nucleus so they won’t get broken down and will attach to ribosome
- RNA splicing: splice out parts of RNA strand: introns (everything else is exon) catalyzed
by snRNA (ribozyme)
- Splicing depends on which polypeptide is being made
RNA pol: attaches at promoter (DNA sequence), separates DNA strands, connects RNA
nucleotides, ends when gets to terminator
tRNA: amino acids to ribosome, each type is specific for amino acid. Binds amino acid on one
side and anticodon on other side will pair with complementary codon on mRNA
Wobble: third base isn’t strict
rRNA: 2 subunits to make ribosomes, 3 binding sites for tRNA
1. P: where the polypeptide chain is
2. A: carries amino acid that’s going to be added next
3. E: exit
Translation:
1. Ribosomal subunit binds to mRNA so first codon (AUG) is placed right
2. tRNA with anticodon UAC H bonds ot first codon w help of initiation factors
3. Large subunit of ribosome attaches so tRNA attaches to P site
4. A site is now available for the next tRNA to bring the second amino acid
5. Hydrolysis of GTP increases accuracy of codon to amino acid pairing
6. Large subunit helps create peptide bond between amino group and carboxyl end of
growing polypeptide (removes polypep from tRNA in P side and attaches it to amino acid
in A site)
7. Translocation
8. Release factor binds to stop codon
Polypeptide folds, may receive signal peptide
Point mutations: just one base pair of a gene
Nucleotide pair substitution: replace pair of nucleotides w another
Missense: codon still codes for amino acid
Nonsense: makes stop codon
insertions/deletions: interfere w codon groupings (frameshift mutation: when read incorrectly)
Bacteria: genes clustered into operons
- Operator: controls access of RNA pol to genes
- Promoter: where RNA pol attaches
- Genes: DNA required for enzymes produced by operon
Regulatory genes: repressor proteins that bind to operator and block RNA pol (operon off)
Repressible operon: (anabolic) normally on but can be inhibited, repressor protein is inactive,
corepressor can activate it and shut down operon
Inducible operon: (catabolic) normally off but can be activated, repressor active, inducer can
inactivate it so RNA pol can come in
Differential gene expression: leads to different cell types
More tightly bound DNA is to histones is, the less accessible it is to transcription
DNA methylation: add methyl groups to DNA, makes it more tightly packed, less gene
expression
Histone acetylation: acetyl groups added to amino acids, less tightly packed, more transcription
Epigenetic inheritance: inheritance of traits by mech not involved in nucleotide sequence
Transcription initiation complex: enhances gene expression
Enhancer regions: bound to promoter region by activators
Eukaryotes do not have operons
RNA complex w proteins to influence gene expression (miRNA and siRNA) bind to mRNA and
degrade it or block translation
Cytoplasmic determinants: maternal substances in egg affect early development
Cell cell signals: growth factors, induction (leads to differentiation)
Pattern formation: body plan, cytoplasmic determinants + inductive signals
- Morphogens: causes diffs in where head, tail, arms, etc are placed by uneven
distribution
Homeotic genes: master control that control pattern formation
Virus surrounded by protein coat
- Capsid: protein shell
- Viral envelope: surround capsid
- Limited host range
Lytic cycle:
1. Phage injects DNA in host cell
2. Uses host cell to make new copies of viral DNA
3. Self assemble
4. Lyse
5. Release copies of virus
6. Kills cell
Lysogenic cycle:
1. Phage DNA incorporated into host cell DNA
2. Replicated w it
3. May enter lytic cycle
Retrovirus: RNA viruses use reverse transcriptase to transcribe DNA from RNA, DNA integrates
into chromosome in nucleus of animal cell, viral DNA makes into RNA to make viral proteins, to
be released and infect more
Restriction enzymes: cut strands of DNA @ restriction sites = restriction fragments with sticky
end which form hydrogen bonds with complementary DNA, sealed w ligase
DNA microarray assays: DNA fragments of different genes on glass slide (DNA chip), mRNA
isolated and converted to cDNA by reverse transcriptase, tagged w fluor dye, cDNA bonds to
ssDNA to show which genes are on (actively producing mRNA)
RFLPs: small diffs in DNA shown by electrophoresis
Gel electrophoresis: separate DNA by size, distance DNA travels is inversely proportional to
length, each band has DNA of same length, negatively charged DNA move toward positive
electrode, shorter molecules moving faster than longer ones