Molecular Genetics

• polymer composed of repeating units called nucleotides
• two polynucleotide chains that are linked together by hydrogen bonds between the nitrogenous bases
• double helix (2 strands run antiparallelI)
• sugar-phosphate backbones
• Van der Waals attractions between adjacent stacked bases

• phosphate
• 5-carbon sugar (deoxyribose)
• 1 or 4 different nitrogenous bases

• double-ringed purines : adenine and guanine
• smaller, single-ringed pyridimines : cytosine and thymine
• A=T
• G=C
• ratio of (A/T):(C/G) varies from species to species

• phosphate bound to 5'C on the deoxyribose molecule
• nitrogenous base bound to 1'C of the deoxyribose molecule
• enzyme DNA polymerase attaches the phosphate of one nucleotide (5' end) to the 3'C of th next nucleotide via condensation

• antiparallel
• 5'-->3' strand runs counter to the 3'-->5' strand
• 2 ends:
• * a 3' end with a free hydroxyl group attached
• * a 5' end with a phosphate group attached

• occurs prior to mitosis (S phase)
• an enzyme separates the 2 strands
• DNA polymerase takes free nucleotides from the cytoplasm and pairs up the nucleotides needed to match the exposed nucleotides of the strand
• semiconservative DNA replication
• result is 2 identical copies of DNA

• results in 2 identical copies of DNA
• each new DNA molecule contains one of the original strands and a newly synthesized complementary strand

• RNA is smaller (typically one-stranded)
• Uracil replaces Thymine
• sugar component is ribose
• several forms of RNA (one major form of DNA)

carries the complementary strand from DNA in the nucleus to ribosomes in the cytoplasm

• process of making an mRNA copy of DNA
• occurs in the nucleus

• enzyme that transcribes DNA into RNA
• produces a complementary RNA strand from one of the DNA strands

• a group of 3 mRNA nucleotides
• codes for one specific amino acid

• an organelle consisting of rRNA and various proteins
• "reads" the mRNA message and converts it into a protein

process of combining a specific number of amino acids together in a specific sequence, as determined by the mRNA sequence

• attached to a specific amino acid that matches with the codon
• enzyme aminoacyl-tRNA synthetase attaches amino acid to tRNA by condensation

a group of 3 nucleotides that are complementary to codons on the mRNA

the ribosome hydrolyzes the amino acid from the tRNA and attaches it (by condensation) to the polypeptide chain by forming a peptide bond

• any change in the DNA
• base substitutions (silent mutation, missense mutation, nonsense mutation)
• base deletion/insertion

one nucleotide is replaced by another

a base substitution does not cause a change in the final amino acid sequence of a protein

the altered codon still codes for an amino acid, but for a different one

• the altered codon becomes a stop codon; the translation is stopped prematurely
• creates a nonfunctional protein

• one or more nucleotides are removed/added, respectively, from the DNA
• all nucleotides downstream will be improperly grouped into codons, leading to extensive missense
• nonfunctional protein

• replacing a nonpolar amino acid with another nonpolar amino acid may not affect the function/structure of the enzyme/protein produced (likewise for polar amino acid replacement)
• replacing a nonpolar amino acid witha polar amino acid may cause a dramatic change in how the protein functions

• used as powerful tools in molecular biology
• bacterial enzymes that recognize a specific sequence in DNA and cleaves it near that spot (recognition site)
• creates a blunt or sticky end
• very specific
• used to help recognize and destroy foreign DNA (ex phages)
• act as a primitive immune system

• adds methyl groups to nucleotides that could be reconized by restriction enzymes
• protects bacteria's own DNA from hydrolysis

• DNA ligase can be used to rejoin sticky fragments and seal the strands
• foreign piece of DNA may thus be incorporated into the DNA
• if inserted into a bacterium, it can then create the foreign gene products

... electrophoresis gel.

• DNA digested by restriction enzymes
• dye is applied to DNA
• DNA placed into wells in the aragose gel
• electrical current applied to gel
• DNA fragments move through the gel

... inversely proportional to their size.

negative; positive