Unit 6: Gene Expression

• DNA monomer: nucleotides
• Nucleotide structure

  5 carbon sugar, phosphate group, nitrogenous base
• Nitrogenous bases in DNA

  Adenine, Thymine, Cytosine, Guanine
• DNA structure: DNA consists of two long chains of nucleotides twisted into a double helix and joined by hydrogen bonds between the complementary bases adenine and thymine or cytosine and guanine
• Founders of the Structure of DNA: Watson, Crick, and Franklin
• Base pairing in DNA:

  • A - T
  • G - C
• 3' end of DNA: refers to the end that has a hydroxyl group attached to the number 3 carbon of deoxyribose AND attaches to the 5' phosphate group of the incoming nucleotide.
• Antiparallel: referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in opposite 5' -3' directions).
• Gene: sequence of DNA that codes for a protein and thus determines a trait
• Genome: the complete instructions for making an organism, consisting of all the genetic material in that organism's chromosomes
• DNA in prokaryotes: DNA is contained in the cytoplasm and consists of a ring of DNA
• Chromosome: a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
• Histones: protein molecules around which DNA is tightly coiled in chromatin
• Nucleosome: repeating subunit of chromatin fibers, consisting of DNA coiled around histones
• Euchromatin: The less condensed form of eukaryotic chromatin that is available for transcription.
• Heterochromatin: DNA that is densely packed around histones. The genes in heterochromatin are generally inaccessible to enzymes and inactive.
• DNA replication: the process of making a copy of DNA
• Helicase: The beginning of DNA replication. An enzyme that untwists the double helix at the replication forks, separating the two parental strands and making them available as template strands.
• DNA topoisomerase: An enzyme that unwinds and winds coils of DNA that form during replication and transcription.
• DNA polymerase: Enzyme involved in DNA replication that joins individual nucleotides to produce a DNA molecule. Can only add nucleotides to the 3' end of a strand. (5' to 3' direction)
• RNA primase: An enzyme that creates an RNA primer for initiation of DNA replication.
• leading strand: the new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5' to 3' direction
• lagging strand: A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5' to 3' direction away from the replication fork.
• Okazaki fragments: Small fragments of DNA produced on the lagging strand during DNA replication, joined later by DNA ligase to form a complete strand.
• semiconservative: method of replication that implies that each new strand of DNA is half original and half new
• Telomeres: DNA at the tips of chromosomes
• RNA vs DNA: RNA has:

  1) A ribose sugar instead of deoxyribose

  2) Substitution of uracil for thymine (as a nitrogenous base)

  3) Single-stranded instead of double-stranded
• List the types of RNA: messenger RNA, transfer RNA, ribosomal RNA
• Protein Synthesis: the formation of proteins by using information contained in DNA and carried by mRNA
• Transcription: the organic process whereby the DNA sequence in a gene is copied into mRNA. Occurs in the nucleus.
• polycistronic transcript: An mRNA transcript that encodes multiple genes and is translated into multiple proteins in bacterial cells
• monocistronic transcript: In Eukaryotes, means one gene gets translated to one mRNA which gets translated into one protein
• Sense strand/Coding Strand: The DNA strand which is always represented on paper. The strand is always the one running from the 5' to the 3'. mRNA is identical to the strand except Thymine is replaced with Uracil.
• RNA polymerase: Enzyme similar to DNA polymerase that binds to DNA and separates the DNA strands during transcription. Builds RNA molecule from 5' to 3', so it binds to the 3' end of the template strand. Does not need RNA primers.
• Exons: Coding segments of eukaryotic DNA.
• Introns: sequence of DNA that is not involved in coding for a protein
• Splicing: the process of removing introns and reconnecting exons in a pre-mRNA
• spliceosome: A large complex made up of proteins and RNA molecules that splices RNA by interacting with the ends of an RNA intron, releasing the intron and joining the two adjacent exons.
• polyA tail: After an mRNA is transcribed from a gene, the cell adds a stretch of A residues (typically 50-200) to its 3' end.
• 5 GTP cap: substance that is added to newly synthesized mRNA in RNA processing to the 5' end