Key Concepts for Week 5: Lectures 13-15
Monday, Oct. 26, Lecture 13: (Transcription and) Translation
 DNA  mRNA (occurs in the nucleus)
 Initial DNA strand used to create primary transcript (mRNA)
 Codon: three nucleotide sequence that codes for an amino acid (20 AAs) – triplet of nucleotides is the smallest
unit to code for all AAs
o 64 codons total with 3 being STOP codons to end translation
 Template strand: one DNA strand that is designated for transcription
 Steps of transcription:
o Initiation
 Promoter region important for initiating transcription
 Transcription factors bring in machinery needed for starting transcription (e.g. allowing binding
of RNA polymerase)
 Transcription initiation complex
o Elongation
 DNA double helix untwists as RNA polymerase moves and transcribes strand
o Termination
 5’ end gets a nucleotide cap (G-cap)
 3’ end gets a poly A tail
 Modifications at ends of strand help protect strand from degradation and allows transport of
mRNA out into nucleus for translation
 mRNA  protein (occurs in the cytoplasm)
 tRNA – transfer RNA used to translate mRNA message into a protein
o Each tRNA has an anticodon that pairs with the complementary codon on mRNA
 Aminoacyl-tRNA synthetase matches a specific amino acid with its particular tRNA
 Ribosomes specifically couple tRNA anticodons with mRNA codons – ribosomes have 3 sites
o P site: holds tRNA that has the polypeptide chain
o A site: holds tRNA that holds the next amino acid that needs to be added
o E site: exit site where tRNAs leave
 Steps of translation
o Initiation: start codon (AUG) begins translation
o Elongation
 Amino acids are running one by one to the preceding amino acid
 tRNA shifts from P – E ribosomal site until it hits a stop codon
o Termination
 When stop codon reaches A site of ribosome, A site accepts a protein called a release factor
 Release factor adds H20 onto peptide instead of amino acid
 Polyribosomes
o Multiple ribosomes that can perform translation simultaneously, forming a polyribosome (efficient
translation machinery)
 Creating a functional protein requires modification following translation
o Specific proteins need to go to specific areas in the cell
o Proteins in the cytosol mostly made by free ribosomes
o Proteins secreted or used in endomembrane system made by bound ribosomes (review of earlier lecture
series)
o Signal recognition particle (SRP): signal telling where a peptide belongs
 Gene mutations
o Point mutations
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Nucleotide pair substitutions
Silent mutations
Missense mutations
Nonsense mutations
Nucleotide pair insertions/deletions
Wednesday, Oct. 28, Lecture 14: ATP, Enzymes
 What is ATP?
o Used for mechanical and chemical work
o Structure of ATP
 Endergonic and exergonic reactions
o Exergonic:
 Reaction that releases energy, occurs spontaneously
 Hydrolysis of ATP  ADP + P (releases energy and requires an enzyme, ATPase)
o Endergonic:
 Reaction that takes in energy, occurs nonspontaneously
 Energy used towards converting ADP + P  ATP
 Enzymes
o Catalysts – speed up chemical reactions by lowering energy barrier
o Have high substrate specificity – each enzyme has an active site that substrate binds onto, causing a
change in enzyme shape
Friday, Oct. 30, Lecture 15: Cellular Respiration
 Redox reactions
o Mechanism behind cellular respiration
 Oxidation: loss of electrons
 Reduction increase of electrons
 “OIL RIG”: oxidation is losing electrons, reduction is gaining electrons
 Mitochondria is where cellular respiration takes place
o O2 + C6H12O6 (glucose)  CO2 + H2O and energy
 O2 gains a H+ (and electron), to make H2O  is reduced
 Glucose loses H+ (and electron), to make CO2  is oxidized
 Cellular respiration (3 steps) – outlined in Fig 9.6
o Glycolysis
 Glucose  pyruvate (occurs in cytosol)
 Basic way to generate ATP (2 ATP)
o Pyruvate oxidation and the citric acid cycle
 Pyruvate goes into mitochondrial matrix and gets converted into acetyl CoA
 Acetyl CoA conversion generates NADH and FADH2 that goes to electron transport chain
 2 ATP for every turn of cycle
o Oxidative phosphorylation: electron transport and chemiosmosis
 Majority of ATP generated here (32 ATP)
 Electron transport chain
 NADH and FADH2 donate electrons  energy exchange yields H20
 Controlled release of energy
 Pumps H+ across membrane
 Chemiosmosis
 H+ gradient provides basis for cell to make ATP