Basic Concepts, Amino Acids, Proteins Flashcards
Milli-
10__
Micro-
10__
Nano-
10__
M
mol/L
%
weight/volume (usually g/dL)
Equivalent
available charges of the particular ion
Units of activity
Defined in terms of some effect
Osmolarity
moles of solute particles in a solution
Henderson-Hasselbach
pH= pKa + log ([A_]/[HA])
α-amino acids
- Carboxylic acid with amine group on the α-carbon
- R-groups change (most are L-amino acids)
Non Polar Aliphatic Amino Acids
Glycine, Alanine, Proline, Valine, Leucine, Isoleucine
(GAP, LIV)
Glycine
Gly
Non Polar aliphatic
Alanine
Ala
Non polar Aliphatic
Proline
Pro
Non Polar Aliphatic
Valine
Val
Non Polar Aliphatic
Branched Chain
Leucine
Leu
Non polar Aliphatic
Branched Chain
Isoleucine
Ile
Non polar Aliphatic
Branched chain
most hydrophobic (charges are very balanced)
Aromatic Amino Acids
Phenylalanine, Tyrosine, Tryptophan
Phenylalanine
Phe
Aromatic
Tyrosine
Tyr
Aromatic
Tryptophan
Trp
Aromatic
Polar, Uncharged Amino Acids
Asparagine, Glutamine, Serine, Threonine
Typically found on the surface
Asparagine
Asn
Polar/Uncharged
Glutamine
Gln
Polar, uncharged
Serine
Ser
Polar, uncharged
Threonine
Thr
Polar, uncharged
Sulfur-containing Amino Acids
Methionine, Cysteine
Methionine
Met
Sulfur-containing
Cysteine
Cys
Sulfur-containing, so can form disulfide bonds
Cystine = 2 cysteines bound by disulfide bond
Negatively charged Amino Acids
Aspartate, Glutamate
Acidic Amino Acids
Positively Charged Amino Acids
Arginine, lysine, histidine
Basic amino acid
Aspartate
Asp
Negatively charged (acidic)
Glutamate
Glu
Negatively charged (acidic)
Arginine
Arg
Positively charged (basic)
Most hydrophilic (very polar)
Lysine
Lys
Positive charge (basic)
Histidine
His
Positively charged (basic)
Hydropathy
How hydrophilic/phobic an anima acid is
pI
The pH at which the net charge on an amino acid is 0
Selenocysteine
- Modification fo a serine bound to a unique tRNA to selenocycteine
- Found in a few enzymes, where it is essential for activity
Types of amino acid modifications
- Carbohydrate addition
- Lipid addition (can anchor to protein membrane or be involved in regulation)
- Regulation
O-glycosylation
Occurs on the OH of ser, thr, tyr
Carbohydrate addition
N-glycosylation
Occurs on the NH2 of asn
Carbohydrate addition
Palmitoylation
Occurs on the internal SH of cys
Lipid addition
Myristolation
Occurs on the NH of the N-terminal of gly
Lipid addition
Prenylation
Occurs on the Sh of cys
Lipid addition
Phosphorylation
Occurs on the OH of ser, thr, tyr
is reversible
Acetylation
Occurs on the NH2 of lys (N-terminus)
Reversible
ADP-ribosylation
Occurs on the N of arg, gln, cys
Reversible
Carboxylation
Turns gutamyl residues into Ɣ-carboxylglutamyl residues
Oxidation
Pro/lys into hydroxylpro/hydroxylys
Peptide bond
- Bond b/t the α-carboxyl grp of 1 AA and the α-amino group of another AA
- Is planar
- Adjacent R-groups are almost always trans
Proteins
linear polymers of α-amino acids bound together by peptide bonds
Primary structure of proteins
- Amino acyl sequence of proteins
- N-terminal = amino
- C-terminal = carboxyl
Polymorphism
- genetic variation with a species
- Can produce a variation in phenotype which could be deleterious
Developmental variaion
- Different protein isoforms/isozymes may be expressed at different developmental stages of an organism
- Ex: HbF, HbA, and other hemoglobins
Tissue-specific Isoforms
- Different protein isoforms/isozymes are expressed simulteneously in one organism, but are restricted to different tissues
- Ex: creatine kinase isozymes and lactate dehydrogenase isozymes
Secondary Structures
Recurring, localized structures found within regions of a poly peptide chain
Alpha – Helix
- Helical structure stabilized by hydrogen bonds (b/t amino and carboxyl O atom of 2nd AA 4 residues down the chain)
- AA R-group projects outward from the axis of the helix
- Proline cannot be a part of a α-helix
Beta-Pleated Sheet
- somewhat planar surface stabilized by H-bonds b/t amide hydrograns and carboxyl Os
- AA R-groups are perpendicular to the plane of the sheet
- surfaces formed by β-sheets are often twisted
Parallel β-pleated sheets
2 polypeptide chains are oriented in the same direction relative to the N/C termini
Anti-Parallel β-pleated Sheets
2 polypeptide cains are oriented in opposite directions relative to their N/C termini
Domain
Part of a secondary structure that can exist on its own
Motif
- Type of supersecondary structure that is found in an array of different proteins (can make up a domain)
- Ex: helix-turn-helix motifs are found in many DNA-binding proteins
Teriary Structures
The folding pattern of the secondary structural elements into a 3D conformation
Forces involved in 3º structures
H-bonds, Salt bridges, Hydrophobic interactions, Van der Wall forces, Disulfide bridges
Globular protein properties
- Core is usually hydrophobic AA
- Surface is usually charged/polar AA (so hydrophilic) that interacts w/ a polar/aqueous environment and forms salt bridges to stabilize the structure
Transmembrane proteins typically have what types of 2º and 3º structures?
- 2º: usually α-helices that have hydrophobic residues that are embedded in the lipid/hydrophobic layer of the membrane
- 3º: hydrophilic residues interact extra/intracellularly
Quaternary structure
The individual subunits form a functional protein
What determines the protein type?
The number of subunits determines what about the protein?
Forces in 4º structure in globular proteins
H-bonding, Hydrophobic interactions, salt bridges/ionic bonds, rarely disulfide bonds (no covalent bonds)
Forces in 4º structure in fiborus/structural proteins
Extensive covalent bonds
What are the functional aspects of 4º structure
- Increased stability (bc increased # of interactions b/t AA)
- Cooperativity b/t subunits (Ex: hemoglobin-O2 binding)
- Different subunits may have different activities
Protein folding
- 1º structure of protein determines folding
- Some fold spontaneously while others require specific cellular processes to promote proper folding
Heat Shock Proteins
- Some prevent improper folding
- Others requires ATP energy to promote folding
Cis-trans isomerases and disulfide isomerases promote what?
What non HSP function to promote proper protein folding?
Size Exclusion Chromatography
- Uses porous beads
- Larger proteins elude 1st bc smaller proteins get caught in the pores of the beads
Ion Exchange Chromatography (Cation)
- bound chemicals have a negative charge
- Cations adhere to the negatively charged column
- charges on proteins are pH dependent
Ion Exchange Chromatography (Anion)
- bound chemicals have positive charge
- Anions adhere to the positively charged column
- Charges on proteins are pH dependent
Hydrophobic Interaction Chromatography
- Medium contains hydrophobic groups
- Proteins w/ hydrophobic groups adhere to the column
Affinity Chromatography
- Medium has a bound, protein specific ligand
- Proteins that bind to the ligand adhere to the column
High-Pressure Liquid Chromatography (HPLC)
- Eluent pumped thru column under high pressure
- Typically looking for hydrophobic interaction chromatography (aka reversed phase)
- Separation is faster and at higher resolution
Electrophoresis
Separation based on mirgration of charged molecules applied in an electrical field
Native electrophoresis
- Separates by differences in charges due to the 1º structure
- Ex: hemoglobin isoforms, some isozymes (LDH, CK)
SDS-PAGE
- Protein molecules interact with the detergent (SDS) to produce proteins of about = charge-to-mass ratios
- SDS disrupts 4º structures (proteins become monomers
- migration thru the gel is based on size: smaller proteins go faster
Iso-Electric Focusing (IEF)
- Buffers generate a pH gradients within a PA gel
- Proteins migrate to pI=pH of gel
2D Electrophoresis
Uses both IEF and SDS-PAGE
Western blot
- Proteins are separated via electrophoresis and transferred to synthetic membrane (incubated w/ antibodies for specific protein
- 2nd antibody conjugated w/ reporter molecule to help visualize the specific protein
Mass Spect
- Separates molecules based on their mass
- Can identify proteins thru determination of masses of peptides produced thru tryptic digestion of proteins
- detects covalent modifications of a protein