BIOL 1202 Lecture : BIOL 1202 Notes Since Jan 31
Chapter 17/18: Gene Expression
and Regulation 1/31/2012 6:00:00 PM
How are Genes and Proteins related?
• Hypothesis for one gene to one protein
• Multiple proteins for one gene
• Gene splicing and introns and exons can create differences
• How do we go from genes to physical structure
• Genes determine protein structure
• Protein structure determines the way the processes of life are carried out
o Enzymes that speed up chemical reactions
o Substrate are like catalyzed reactions
o Structure
▪ Primary: Amino acid strand
▪ Secondary: Coil
▪ Tertiary: Fold in again, beta sheaths
Loving water and hating water, grab onto substrates to ball up more
Disulfide bridges
So specific that it can bind to one and do one thing then bind to a
different one and do something different
Change active site and can change quality of functioning
▪ 50 trillion cells that determine what it can do
How are genes and proteins related?
• Gene→RNA to make protein
• Gene: segment of DNA located at a particular place on a chromosome
o Chromosome contains DNA
o RNA contains code to create proteins
o Transcribed
o Glycolysis
• DNA sequence to compare
• DNA codes for specific amino acid sequence in a protein or for the RNA that helps make
proteins (rRNA)
DNA vs. RNA
• Viruses use different genomes from eukaryote and prokaryotes
• DNA
o Double stranded
o Deoxyribose nucleic acid
o A, T, G, C
• RNA
o Single stranded
o Ribose nucleic acid
o A, U, G, C
o Can fold in on itself like proteins (because of amino acids on polypeptide strand)
▪ RNA folds over because I can base pair with itself
Three Types of RNA
• mRNA: messenger
• rRNA: ribosomal RNA contains a small subunit and large subunit that contains a catalytic site
o has secondary specific structure with specific function to form ribosomes
• tRNA: transfer RNA that contains anticodons with three exposed end tails; tRNA docking sites
in the large subunit of the rRNA on the ribosome
Eukaryotic cell
• Transcription in nucleus: mRNA
• Translation in cytoplasm: protein
• DNA→RNA→protein
Transcription: First Two Steps
• Chromosome is not in condensed form (meiosis and mitosis)
• Unwind part of it that is to be used
• Enzymes enter the strand to turn on or turn off the genes
• RNA Polymerase (enzyme) comes and transcribes the strand of the DNA as a template
• According to base pairing 5’ to 3’
• DNA polymerase comes and creates the DNA
• Elongation
o Creates the strand of RNA and makes it longer and longer
• Termination
o Cuts the RNA
• Winds DNA strand back up
Translation
• RNA produces a protein
Language Barrier
• Nucleotides
o DNA: 4 nucleotides
o RNA: 4 nucleotides
• Protein: 20 amino acids on a polypeptide strand
Genetic Code
• Consists of codons
o Triplets of nucleotides
o AUG: methionine
o 64 possible combinations
o Codes for one specific amino acid
o Three stop codons: UAA, UAG, UGA
• Table 10-3 in power point will be on exam 1
Translation: Protein Synthesis
• Requirements
o mRNA
o tRNA
o rRna
o ATP: energy
• Steps
o Initiation
o Elongation: adding on amino acids to make a longer polypeptide chain
o Termination
Translation: initiation
• Has secondary structure
• Can base pair with itself
• Contains a small ribosomal subunit (rRNA) and associates it with tRNA
• mRNA brings the strand of RNA or DNA into the subunit
• tRNA searches for AUG because that is the starting codon
• Use tRNA to bind to initiation complex
• Frame: set of three codons
• The large ribosomal subunit binds and it is the one that contains a catalytic binding site
• Three nucleotides are exposed as they move through the ribosomal subunit
• Since the first amino acid coded for was AUG or methionine, it gets pushed to the first tRNA
site in the large ribosomal subunit
• As the codons are translated, they are base paired
• Three codons are pushed into the subunit and are then coded into the corresponding protein
• The mRNA pushes the formed protein out and adds an amino acid onto the ever growing
peptide chain
• The used anticodon gets pushed out of the first site and the next one moves to the first site
and the second site will be empty
• Finds stop codon UAG and that terminates the translation
