Unit 1 Flashcards
H-H Equation
pH = pKa + log (A- / HA)
Kw Equation
10^-14 = (H+) x (OH-)
pKa > pH
Protonated
Main Cell Parts (4)
Cytoplasm
Plasma membrane
DNA
Ribosomes
Free Energy Equation
ΔG = ΔH - TΔS
Rate Law
Rate (Product) = k [Reactants]
What is Keq
Keq = (kforward / kreverse)
How far a reaction proceeds in a net direction until equilibrium is reached
RNA World Hypothesis
Life may have started with a self-replicating RNA
Why is RNA possibly the start of life
RNA is a carrier of genetic info
RNA is a catalyst
Phosphate Buffer
Ionization is important
Buffer important for maintaining pH in cells
Decent butter (5.86 to 7.86)
Bicarbonate
Buffer important for maintaining pH in blood
Equilibrium with CO2 (g)
Isoelectric Point
pH where net charge = 0
How does a peptide bond form
Condensation Rxn
Middle amino acids lose their amino and carboxyl ends
Post Translational modification
After a protein is made in the cell, it can be chemically modified by enzymes
Enzymes that modify proteins recognize specific target peptide sequences
What proteins are detected by UV
Tryptophan
Tyrosine (inefficient)
Ion Exchange Chromatography
Column is the stationary phase (opposite charge than proteins)
Positive proteins stick to negative beads
Proteins move through column at a speed dependent on net charge
Most attracted = last and least attracted = first
Remove protein from ion exchange chromatography
Change the salt conditions
Size Exclusion Chromatography
Porous column = molecular sieve
Smaller molecules get stuck in pores
Largest molecules come off first, smallest molecules are last
Affinity Chromatography
Protein interacts with ligand and is captured
Unwanted proteins come off first
Remove protein from affinity chromatography
Use excess free ligand
Specific activity
Specific activity = purity of protein
Specific activity = (activity / total protein)
Electrophoresis
Separation on the basis of charge via eclectic field
Separation based on size when the protein is denatured by a detergent (SDS Page)
Negative proteins move to positve end
Method to separate proteins based on their charge and size
SDS Page
Codes all proteins with a negative charge
Unfolds proteins for constant shape
Detergent
Isoelectric Focusing
Protein sample applied to an end of a gel strip with pH gradient
pH goes from high to low (basic to acidic)
Method to separate proteins based on their isoelectric point
Mass Spectrometry
Get molecules to fly in gas phase (electrospray ionization)
Separate ions by mass in a vacuum
Method to determine the mass and sequence of proteins
Lighter ones go further
Protein gains + charge
Primary Structure
Sequence of amino acids
Peptide bond is planar due to partial double bond (C - N)
Secondary Structure
Local 3D configuration
Tertiary Structure
Multiple secondary structures together
Quaternary Structure
Assembled subunits (tertiary structures)
Alpha Helix
3 amino acids per turn
Right handed
Side chains protrude out
of H-bonds in a helix
Number of amino acids - 4
of Turns in a Helix
(# of amino acids) / 4
Length of a Helix
(# of turns) x (A length)
Beta Sheet
Hydrogen bonds formed between strands
Sheets have a twist (not flat)
Side chains on alternate sides of the sheet (pleated)
Parallel Beta Sheet
Strands run in the same direction
Less stable due to H-bonds at an angle
Antiparallel Beta sheet
Strands run in opposite directions
Tertiary structure motif
Tertiary structures made from arrangements of secondary structures
Smaller tertiary units make bigger tertiary structures
Source of protein stability
Hydrophobic effect
Why do proteins have a size limit
More efficient to build large structures from lots of small ones
Error rate of protein synthesis is 1 mistake per 10,000 amino acids
Fibrous Proteins
Highly extended
Exhibit repeating structure
Fibrous Proteins Ex
Keratin, collagen
Globular Proteins
Compact
Globe shaped
Heme Binding Iron
Porphyrin ring provides 4 N ligands to iron (helps stabilize Fe2+)
Protein fold stabilizes Fe2+ (binds O2)
R to T Change
Oxygen binding moves the histidine → pulls on the helix → changes to R state
Oxygen + R State
Oxygen binds more strongly to R state
Stabilizes R state
Kd
concentration when 50% of the ligand is bound
Myoglobin
Not suitable as an oxygen transporter
Binds oxygen too tightly
Monomer (no 4° structure)
Hemoglobin
Tetramer
Blood transporter
4 binding sites for oxygen