Unit 6: Gene Expression and Regulation

• Transcription factors are proteins that regulate gene expression by binding to specific DNA sequences near genes, either enhancing or inhibiting their activity.
• Protiens', a macromolecule, monomer is amino acids and its polymer is polypeptides
• Lipids' monomer is Glycerol and Fatty acids, and it doesn't have any true polymers
• Carbohydrates' monomer is monoscharides and polymer is polyscharides
• Nucleic Acids' monomer is nucleotides and the polymer is DNA and RNA
• The process of Transcription converts DNA to RNA. The process of Translation turns RNA into proteins
• In eukaryotic (animal) cells transcription occurs within the nucleus and translation happens in the cytoplasm
• The genetic code is read in groups of three that are called codons or triplet code
• The template strand, otherwise known as the antisense strand or the noncoding strand, is the strand of DNA transcribed during transcription
• DNA is comprised of two strands that are parallel but run opposite to each other, 3’ hydroxyl end of one strand is the opposite to the 5’ phosphate group of the same strand. 
• The complementary base pairing rule is A to T (double bond) and C to G (triple bond) in DNA.
• Purine bases are A and G and Pyrimidine bases are T and C.
• mRNA nucleotide triplets are called codons. These code for amino acids.
• Redundancy in the genetic code helps to minimize harmful effects that incorrectly placed nucleotides can have on translation/protein synthesis.
• 3 steps of transcription are Initation, Elongation, and Termination
• Initation (transcription):

  • RNA Polymerase must bind to transcribe DNA but in order for this to happen transcription factors must first bind to the DNA. Transcription factors (proteins) bind to the promoter region (the TATA box which is upstream of the gene of interest), then the DNA unwinds/unzips and RNA Polymerase can now bind and begin transcription.
• Elongation (transcription)

  • RNA Polymerase adds the corresponding nucleotides (A to U, T to A, and C to G) in the direction along the 3’ - 5’ end, continuously adding new nucleotides to the 5’ end to form a new and growing strand of mRNA
• Termination (transcription):

  RNA Polymerase reaches the termination sequence (the stop codon) and mRNA detaches itself from DNA → then RNA Polymerase is released from DNA. The mRNA that was just released is known as pre-mRNA and needs to go through modifications in order to be ready to be translated
• A promoter region is the site of transcription. It is upstream of the gene.
• If the promoter region was mutated, RNA polymerase may not be able to bind there, and if that happened, transcription would not occur. If transcription does not occur, then translation is not occurring.
• The pre-mRNA would not be able to leave the nucleus and without a poly-A tail + 5’ cap the mRNA would not be protected from dehydration nor would the ribosomes be able to attach to the 5’ of the mRNA.
• Introns play an important role in the process of alternative splicing. This is when an mRNA is spliced to form different protein variants.
• The modifications given to pre-mRNA in eukaryotic cells is RNA spilicing, given a poly-A tail, and then given a 5' cap
• tRNA has an anticodon region which is complementary and antiparallel to mRNA.
• translation occurs in the ribosome
• the very first tRNA anticodon will be placed at the P site on the ribosome
• the first codon tRNA will carry to start the translation process is AUG and this codes for the amino acid methoionine
• The three steps of translation are Initiation, Elongation, and Termination
• Initiation (transaltion) is where the mRNA will bind to the small ribosomal subunit and call for the start codon AUG, tRNA will then bring the anti codon UAC in order to start the sequence
• Elongation (translation)

  • tRNA comes to the correct position as called by mRNA when read in the 5’ - 3’ direction
  • The appropriate anti-codon of the next tRNA goes into the correct position (E P A)
  • Peptide bonds are formed that transfer the polypeptide to the A-site tRNA
  • The tRNA in A-site will move into P-site, the tRNA that was in P-site will now move to the E-site, and now the A-site is open for the next tRNA piece (a continuous cycle until the ribosomal unit reads the stop codon)
• Termination (translation)

  • Will occur when the stop codon is reaches the A-site
  • Stop codons don’t code for any amino acids, they simple tell the ribosome to stop calling anti-codons when reading mRNA
  • The bond that holds the polypeptide chain to the P-site will then be hydrolyzed, allowing the polypeptide to release and all translational units disassemble
• DNA comparisons can show how similar some species are, which reflects shared ancestry of life proving the idea of common ancestry
• protein synthesis occurs in two stages, transcription and translation.
• Translation is the synthesis of polypeptides (proteins) using information from mRNA, it occurs in the ribosome (the cytoplasm).
• Translation will stop when a stop codon reaches the A site
• The proteins will move from the rough endoplasmic reticulum to the cis face of Golgi via vesicles. It will then be processed, modified, and tagged, exit the Golgi trans face via vesicles and then leave the cell through exocytosis or be transported and used at a location inside the cell.
• In eukaryotes, transcription and translation take place in different cellular compartments: transcription takes place in the membrane-bounded nucleus, whereas translation takes place outside the nucleus in the cytoplasm. This process is called asynchronous. In prokaryotes, the two processes are tightly coupled, meaning the process is synchronus.
• Transcription factors bind to DNA sequences that regulate gene expression