DNA-notes - DNA RNA replication translation and...

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© M. S. Shell 2009 1/12 last modified 10/27/2010 DNA, RNA, replication, translation, and transcription Overview Recall the central dogma of biology: DNA (genetic information in genes) barb2right RNA (copies of genes) barb2right proteins (functional molecules) DNA structure One monomer unit = deoxyribonucleic acid composed of a base, a sugar ( deoxy ribose), and a phosphate directionality along the backbone barb2right 5’ (phosphate) to 3’ (OH) Double-strand pairing: complementary base-matching : A-T, C-G base-matching achieved by H-bonding and geometry (long vs short nucleotides) antiparallel (one strand 5’ barb2right 3’, the other 3’ barb2right 5’) Helical shape 10.4 nucleotides per turn diameter = 2 nm both major and minor grooves called B-DNA . The helix twist and diameter can also change under dehydrating conditions and methylation to A-DNA and Z-DNA Base-pairing and strand interactions A, G are long (double ring purines) C,T are short (single ring pyrimidines) need one long and one short nucleotide per pair C-G have three hydrogen bonds (slightly stronger matching) A-T have two hydrogen bonds (slightly weaker matching)
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© M. S. Shell 2009 2/12 last modified 10/27/2010 base stacking of aromatic rings allows sharing of pi electrons and adds stability to interior structure of DNA barb2right some hydrophobic driving force as well pair structure allows template for semi-conservative copying Information in DNA sequence is the genome genes are stretches of information in the sequence that encode for particular function (usually a particular protein, but sometimes also an RNA sequence) about 20,000 genes in humans typically 1000s of nucleotides long genes can be expressed (use to make proteins) or repressed (not used) regions of DNA are divided into coding and non-coding segments over 50% of human DNA is non-coding genes can be spliced together genes are organized in the large-scale structure of the DNA in the nucleus In bacteria, genome usually circular The genome in eukaryotes is organized into chromosomes each chromosome a separate DNA molecule human cells contain 46 chromosomes (22 each from mother and father) chromosomes are extended and replicated during interphase portion of the cell cycle barb2right extended allows for gene expression chromosomes are condensed, visible with light during cell division ( M phase ) Special DNA sequences exist in each chromosome replication origins – multiple locations where the replication machinery first binds to start replication centromere – center “pinch point” of a chromosome that allows one copy of each to be pulled apart into two daughter cells during division
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© M. S. Shell 2009 3/12 last modified 10/27/2010 telomere – specialized sequences at the chromosomes end that facilitate replication there Higher-order DNA structure How do cells efficiently store very long chains of DNA?
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