BIOL 1080 Study Guide - Final Guide: Spindle Apparatus, Nuclear Pore, Histone H1

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20 Apr 2012
Deoxyribonucleic Acid (DND
Each subunit is a nucleotide comprised of : a phosphate group; a five carbon sugar; one of four
cyclic nitrogenous bases;
Four Nucleotides of DNA
Pyrimidine nucleotides 1) Deoxythymidine monophosphate, dMTP 2) Deoxycyidine
monophosphate, dCMP
Purine Nucleotides 3) Deoxyadenosine monophosphate, dAMP 4) Deoxyguanosine
monophosphate, dGMP
-both types connected by phosphodiester bonds
Double-stranded and the strands are antiparallel
Strands are held together by hydrogen bonds between bases on opposing strands and by
hydrophobic interactions between adjacent stacked bases
Strands are polar; 5’ end has a free phosphate group; 3’ end has a free hydroxyl group;
Two grooves of different width: major (bigger) minor (smaller)
Supercoiled > relaxed covalently closed DNA; relaxed, nicked circular DNA; negatively
supercoiled, covalently closed DNA (chromosome)
Prokaryotic chromosome highly compact supercoiled ‘flower’
Bacterial, eukaryotic similar DNA found in mitochondria & chloroplasts exist in circular
chromosomes (resemble prokaryotic)
Eukaryotic chromosome comprised of proteins, DNA, RNA
Levels of Condensation
1. Packaging DNA as a negative supercoil into nucleosomes (linker DNA wrapped around
nucleosome core linker region is susceptible to digestion by enzyme endonuclease)
DNA is wrapped around a nucleosome core of 8 histone proteins and anchored by a 9th
2. An additional folding or supercoiling of the 11nm fibre to produce a 30nm fibre; driven by
nucleosomal interactions; histone H1 involved; models: solenoid & zigzag; 30nm fibre is the
basic structure unit of the metaphase chromosome (DNA in its most condensed form);
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3. Attachment of the 30nm fibre at many positions to a (non-histone) protein scaffold
(2-nm DNA molecule > 11nm nucleosomes > 30nm chromatin fiber > metaphase chromosome
Protect chromosome ends
Resists degradation by DNases
Prevent fusion of chromosomal ends
Facilitate replication of the ends of the linear DNA
Provide the point of attachment of chromosomes to microtubules in the mitotic spindle
(spindle-fiber microtubule = glue)
Yeast centromeres three essential regions
In multicellular eukaryotes are larger & more complex
RNA polymerase moves the transcription bubble, a stretch of unpaired nucleotides, by breaking
the hydrogen bonds between complementary nucleotides. (Splits DNA)
RNA polymerase adds matching RNA nucleotides that are paired with complementary DNA
bases. (Copies)
RNA sugar-phosphate backbone forms with assistance from RNA polymerase. (Prints)
Hydrogen bonds of the untwisted RNA+DNA helix break, freeing the newly synthesized RNA
strand. (Releases)
If the cell has a nucleus, the RNA is further processed (addition of a 3' poly-A tail and a 5' cap)
and exits through to the cytoplasm through the nuclear pore complex. (Into cytoplasm)
Read 3’ > 5’, created 5’ > 3’
RNA uses the pyrimidine URACIL instead of THYMINE
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Messenger RNA (mRNA) produced by Transcription is decoded by the ribosome to produce a
specific amino acid chain (or polypeptide) that will later fold into an active protein
In bacteria: occurs in cytoplasm, where large and small subunits of the ribosome are located,
and bind to the mRNA
In Eukaryotes: occurs across membrane of ER in a process called vectorial synthesis; ribosome
facilitates decoding by inducing the binding of tRNAs with complementary anticodon sequences
to that of the mRNA; tRNAs carry specific amino acids that are chained together into a
polypeptide as the mRNA passes through and is read by the ribosome
No spaces between codons; codons are adjacent
Genetic code is non-overlapping; each nucleotide is part of one codon
Genetic code degenerate; most amino acids with similar properties are specified by related
Genetic code is (nearly) universal with minor exceptions, each triplet/codon has the same
meaning in all organisms
Interphase G1 (growth, cellular metabolism); S (DNA replication, chromosome
duplication); G2 phase (preparation for mitosis); M (chromosomal “pas de deux” and
Prophase initiation of spindle formation; condensation of duplicated chromosomes;
fragmentation of ER and Golgi; nucleolus disappears; nuclear membrane breaks down;
spindle microtubules invade the nuclear space;
Prometaphase chromosome move toward he equator of the spindle
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