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22 Cards in this Set
- Front
- Back
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Describe chromatin structure. What does "beads on a string" refer to? |
-DNA exists in the condensed, chromatin form in order to fit into the nucleus. Negatively charged DNA loops twice around positively charged histone octamer to form nucleosome "beads on a string." Histones are rich in the amino acids lysine and arginine. H1 binds to the nucleosome and to "linker DNA," thereby stabilizing the chromatin fiber. In mitosis, DNA condenses to form chromosomes. DNA and histone synthesis occur during S phase. |
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What is heterochromatin? |
Condensed DNA, appears darker on EM. Transcriptionally inactive, sterically inaccessible. HeteroChromatin= Highly Condensed Barr bodies (inactive X chromosomes) are heterochromatin. |
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What is euchromatin? |
Less condensed DNA, appears lighter on EM. Transcriptionally active, sterically accessible. |
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How does DNA methylation work, and what is its effect on transcription? |
Template strand cytosine and adenine are methylated in DNA replication, which allows mismatch repair enzymes to distinguish between old and new strands in prokaryotes. DNA methylation at CpG islands represses transcription. (Methlyation makes DNA Mute) |
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What is the effect of histone methylation on DNA transcription? |
Usually reversibly represses DNA transcription, but can activate it in some cases depending on methylation location. Histone methylation mostly makes DNA mute. |
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What is the effect of histone acetylation on DNA transcription? |
It relaxes DNA coiling, allowing for transcription. Histone acetylation makes DNA active. |
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Nucleotides: Which are purines and which are pyrimidines? |
Purines: Adenosine and Guanine (PUR As Gold) Pyrimidines: Cytosine, Thymine, Uracil (CUT the PY) |
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What do you have to remember about thymine? |
Thymine has a methyl group. Thymine= methyl |
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How do you get from cytosine to uracil? |
Deamination of cytosine makes uracil. |
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Difference between DNA and RNA nucleotides? |
Uracil is found in RNA, and thymine is found in DNA. |
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Which bond is stronger, the one between C-G nucleotides or the one between A-T nucleotides? |
C-G bond is stronger (3 H bonds) than the A-T bond (2 H bonds). Higher C-G content means a higher melting temperature of the DNA. |
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Which 3 amino acids are necessary for purine synthesis? |
GAG Glycine, Aspartate, and Glutamine. |
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What is the difference between a nucleoside and a nucleotide? |
Nucleoside= base +deoxyribose sugar Nucleotide= base + deoxyribose sugar + phosphate, linked by 3'-5' phosphodiester bonds. |
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See de novo pyrimidine and purine synthesis pathway on page 63. |
bleh |
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See purine salvage deficiencies on p 64 |
more bleh |
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What is adenosine deaminase deficiency? What disease is it associated with? |
Excess ATP and dATP imbalances nucleotide pool via feedback inhibition of ribonucleotide reductase; this prevents DNA synthesis and thus decreases the lymphocyte count. One of the major causes of autosomal recessive SCID. |
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What causes Lesch-Nyhan syndrome? What are some of the characteristic symptoms? What is the treatment (2 drugs)? |
LN syndrome is caused by defective purine salvage due to absent HGPRT, which converts hypoxanthine to IMP and guanine to GMP. Results in excess uric acid production and de novo purine synthesis. X-linked recessive. H- hyperuricemia, G- gout, P-pissed off (aggression, self-mutilation), R-retardation (intellectual problems), T- dysTonia Treatment is allopurinol or febuxostat |
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Genetic code features: What is unambiguous? |
Each codon specifies only 1 amino acid. |
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Genetic code features: What is degenerate/redundant? |
Most amino acids are coded by multiple codons. Exceptions: methionine and tryptophan encoded by only 1 codon (AUG and UGG, respectively). |
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Genetic code features: What is commaless/non-overlapping? |
Read from a fixed starting point as a continuous sequence of bases Exceptions: Some viruses |
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Genetic code features: What is universal? |
Genetic code is conserved throughout evolution. Exception in humans : mitochondria |
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What are the four features of the genetic code? |
Unambiguous, degenerate, nonoverlapping, and universal. |
