Structure of Proteins Flashcards
What are the functions of proteins and provide examples?
- protein structure - collagen (main component of connective tissue) - transport molecules - heamoglobin (oxygen) , LDL and LDL receptor (cholesterol) - defense - antibodies - regulation of genes - Lac repressor (controls expression of proteins metabolising lactose in bacteria - repressor binds to DNA and prevents expression of gene in absence of lactose)
What causes the function of proteins?
due to the property of specific binding - binding depends on conformation
What is the result of change of conformation?
change in activity
What is the general structure of an AA?
What defines the structure and function of a protein?
the chemical properties of the R group
What are the hydrophylic AA?
- basic
acidic - polar
What AA are basic?
argenine, lysine, histidine
What makes an AA basic?
heir side chains contain nitrogen and resemble ammonia, which is a base. Their pKa’s are high enough that they tend to bind protons, gaining a positive charge in the process.
- form salt bridges (stabilize protein structure)
What AA are acidic?
aspartic acid/aspartate and glutamic acid/glutamate,
What makes an AA acidic?
acidic side chains at neutral pH, carboxylic acid groups, pKas are low enough to loose protons becoming negatively charged in the process
- forms salt bridges (stabilize protein structure)
What AA are polar? (8)
- glutamine
- asparagine
- histidine
- serine
- threonine
- tyrosine
- cysteine
- tryptophan
What makes an AA polar?
with uncharged R groups
- Polar amino acids are those with side-chains that prefer to reside in an aqueous environments - exposed on the surface of a protein
- usually participate in hydrogen bonds as proton donors or acceptors
What AA are hydrophobic? (8)
- Alanine
- Isoleucine
- Leucine
- Methionine
- Phenylalanine
- Valine
- Proline
- Glycine
What makes an AA hydrophobic?
- composed mostly of carbon and hydrogen
- have small dipole movements
- repelled from water - found in protein core
Structure of glycine?
Structure of proline?
Structure of cysteine?
Structure of histidine?
Structure of aspartate?
Define polypeptide?
a polymer of AA joined by peptide bonds
Define AA residue?
when two or more AA join to form a peptide, the elements of water are removed, and what remains of the AA is the AA residue
Define prosthetic?
a non protein group forming part of the protein or combined with the protein
What does pKa mean?
pKa of an acid is equal to the pH at which half the molecules are dissociated
How is pKa important in the function of proteins?
local environmnet can influence pKA - Dissociation largely occurs over 2 pH units centered on the pKa - The overall charge of an AA varies with pH - Close to the pKa, small changes in pH can cause significant change in the charge carried
How is a peptide bond formed?
