Proteins Flashcards
DNA
- software
- nucleotides chemically similar
proteins
- hardware
- amino acids chemically distinct
building blocks of proteins
amino acids
general structure of amino acids
- amino group
- R side chain
- carboxyl group
zwitterionic form of the general structure of amino acids
- NH+
- COO-
no. of common amino acids
20
variation in R groups
- size
- shape
- charge
- polarity
- solubility
groups of different amino acids
- polar, uncharged
- nonpolar, hydrophobic
- electrically charged
R group of polar, uncharged amino acids
- OH
- amide
- sulfhydryl/thiol groups
- can H-bond with water
where are polar, uncharged amino acids found
surface of globular proteins
where are polar, uncharged amino acids soluble
aqueous solutions
what are the polar, uncharged amino acids
- serine
- threonine
- cysteine
- asparagine
- glutamine
R group of non-polar, hydrophobic amino acids
- aliphatic
- aromatic
where are non-polar, hydrophobic amino acids found
interior of globular proteins
core of non-polar, hydrophobic amino acids
insoluble core
what are the non-polar, hydrophobic amino acids:
aliphatic
- glycine
- alanine
- proline
- valine
- leucine
- isoleucine
- methionine
what are the non-polar, hydrophobic amino acids:
aromatic
- phenylalanine
- tyrosine
- tryptophan
what are the negatively charged R groups
- aspartate
- glutamate
what are the postively charged amino acids
- lysine
- arginine
- histidine
- formed by dehydration synthesis
- allows free rotation of attached atoms
- various shapes of the polypeptide
peptide bond
how are peptide bonds formed
by dehydration synthesis
unbranched chain of amino acids
polypeptide chain
how many amino acid chains are there to be considered as a polypeptide chain
> 10 amino acids
may consist of one or more polypeptide chains
protein
directionality of polypeptide chains
N-terminus to C-terminus
levels of protein structure
- amino acid residues
- α Helix
- polypeptide chain
- assembled subunits
sequence of amino acids linked together by peptide bonds, forming a polypeptide
primary structure
local regions of the resulting polypeptide can then be coiled into an α helix
secondary structure
- regions of secondary structure associate with each other in a specific manner
- describes the final folding of the polypeptide
tertiary structure
association of two or more polypeptides as they interact to form the final, functional protein
quaternary structure
aa sequence ->
3D structure (non-covalent bonds) -> cellular function
where did the mutation happen in sickle cell anemia
codon 6 of beta-globin
organization in secondary structure
localized organization
stabilizes the secondary structure
hydrogen bonds
where does the hydrogen bond stabilize in secondary structure
- between 2 peptide bonds
- between peptide bond and side chain
- between 2 side chains
- spiral
- each turn has 3.6 amino aicds
- symbolized by barrel/rod/coiled ribbons
- most common secondary structure
α-helix
amount of amino acids in each turn of α-helix
3.6 aa
symbolizes α-helix
barrel/rod/coiled ribbons
stabilizes α-helix
almost linear hydrogen bonds
where is the hydrogen bond in α-helix
between NH and CO groups
linkages in α-helix
disulfide linkages (S-S) (cysteine aa)
eg. of α-helix
α-keratin in hair
most common type of secondary structure
α-helix
- peptide planes are arranged like a regularly sheet/pleated
- h-bonds can only form between neighboring chains within a sheet
- symbolized by arrow
- strength and stability in structural proteins
β pleated sheet
how are β pleated sheet arranged
regularly sheet/pleated
where do hydrogen bonds form in β pleated sheet
between neighboring chains within a sheet
symbolizes β pleated sheet
arrow
purpose of β pleated sheet
strength and stability of structural proteins
eg. of β pleated sheet
silk fibroin
- U-shaped
- reverses direction of peptide chain
- for building compact globular protein
- usually glysine (small R side chain) or proline (with built-in bend)
β-turn or β-bend
shape of β-turn or β-bend
U-shaped
what do β-turns do
reverses direction of peptide chain
no. of amino acids in β-turn
~4 aa
purpose of β-turn or β-bend
building compact gobular protein
amino acids that are usually associated with β-turns
- glysine (small side chain)
- proline (with built-in bend)
small side chain
glysine
with built-in bend
proline
- important constituents of the connective tissue matrix
- stabilized by the associateion of 3 α helices to form a right-handed collagen triple helix
collagen helix
imporance of collagen helix
constituents in connective tissue matrix
stabilizes collagen helix
3 α helices
what is formed by the 3 α helices
right-handed collagen triple helix
- the 3d/overall conformation of a polypeptide chain
- stabilized by hydrophobic interactions
- highest level of organization of large proteins
teritary structure
stabilizes tertiary structures
hydrophobic interactions
Two general shapes of tertiary structures
- fibrous proteins
- globular proteins
- polypeptide chains are arranged or coiled around a single dimension often in parallel bundles
- for exteral protection and support, form, shape
fibrous proteins
how are fibrous proteins arranged
around a single dimension often in parallel bundles
eg. of fibrous proteins
- keratin
- collagen
functions of fibrous proteins
- external support
- support, form, shape
external support
- hair
- feather
- skin
- nail
- horn
support, form, shape
- tendons
- cartilage
- bone
- deeper layers of skin
fiber used to make silk cloth
protein fibroin
consists of layers of antiparallel beta sheets rich in ala and gly residues
fibroin
- polypeptide chains are tightly folded into compact 3D structure
- more complex than fibrous proteins
globular proteins
how are globular proteins folded
compact 3D structure
eg. of globular proteins
- enzymes
- globin proteins
location of amino acids in globular proteins
- exterior
- interior
- both interior and exterior
exterior aa
hydrophilic/polar aa
interior aa
hydrophobic/nonpolar aa
amino acids that are both interior and exterior
- pro
- ser
- ala
- tyr
- thr
- cys
- gly
forces that stabilize the tertiary structure of globular proteins
- hydrogen bonds
- ionic interactions
- hydrophobic interactions
- covalent cross linkages
hydrogen bond in tertiary structure of globular proteins
between R groups of aa residues in adjacent loop of chain
ionic interactions in tertiary structure of globular proteins
- oppositely charged R groups
- R group and water
- R group and ions
eg. of covalent cross linkages in tertiary structure of globular proteins
disulfide bonds
general principle of secondary structure
determined by short range sequences of R groups
general principle of tertiary structure
conferred by longer range aspects of aa sequence
determines the formation of bends in polypeptide chain
precise location of aa
quaternary structure:
the number of relationships of sub-units in a __ protein
multimeric
biological functions of proteins
- enzyme
- transport
- storage
- contractile or motile
- structural
- defense
- regulatory proteins
- allosteric proteins
eg. enzyme
- ribonuclease
- spliceosome
- replisome
eg. transport protein
- hemoglobin
- myoglobin
- lipoprotein
eg. storage protein
- gliadin (wheat)
- ovalbumin (egg)
- casein (milk)
eg. contractile or motile protein
- actin
- myosin
- tubulin
eg. structural protein
- keratin
- fibroin
- collagen
- elastin
- proteoglycans
eg. defense proteins
- antibodies
- fibrinogen
- snake venom
eg. regulatory proteins
- insulin
- growth hormone
- repressors
- transcription factors
eg. allosteric proteins
have 2 or more slightly diff. conformations which can havve alternative functions
apoenzyme+cofactor
holoenzyme
protein portion
apoenzyme
non-protein portion
cofactor
- where substrate binds to
- formed by aa whose side chains have two principal roles
active site of enzyme
two principal roles of aa side chains that form the active site
- contact residue
- catalytic residue
- attract and orient the substrate in a specific way
- determines substrate specificity
contact residue
what does the contact residue determine
substrate specificity
- participate in the formation of temporary bonds with substrate
- triggers catalytic change/events
catalytic residue
what does the catalytic residue trigger
catalytic change/events
enzymes that exist in alternative conformations
allosteric enzymes
two binding sites of allosteric enzymes
- active site
- allosteric/effector site
site for substrate
active site
site for regulatory molecule
allosteric/effector site
where are allosteric enzymes involved in
- cell signaling
- regulation of metabolism
multiple forms of an enzyme
isozymes or isoenzymes
isozymes have same __, different __
same reaction, different aa sequence
example of isozyme
lactate dehydrogenase
protein structure determines its interaction with other molecules
- protein-protein interaction
- protein-RNA
- protein-DNA
- protein-drug or chemical
- regular combination of secondary structure that has a particular topology
- organized into a characteristic 3D structure
motif
Motifs of DNA-binding proteins that regulate transcription
- zinc finger
- helix-turn-helix
- leucine zipper
- helix-loop-helix
- copper fist
fingerlike projection consisting of ~30aa
zinc finger
two types of zinc finger
- 2 cys + 2 his (C2H2 finger)
- 4 cys (C4 finger)
coordinate a single zinc ion
2 cys + 2 his (C2H2 finger)
regulatory protein transcription
4 cys (C4 finger)
interacts with major groove of DNA
alpha helix
structure of zinc finger
- 2 beta strands
- 1 alpha helix
function of zinc finger
binding in the major groove of the DNA
- 2 alpha helixes + 1 beta turn
- recognition helix binds specific sequence in the major groove of the DNA while the second helix stabilizes the configuration
helix-turn-helix
structure of helix-turn-helix
- 2 alpha helixes
- 1 beta turn
two parts of helix-turn-helix motif
- recognition helix
- second helix
helix-turn-helix:
binds specific sequence in the major groove of the DNA
recognition helix
helix-turn-helix:
stabilizes the configuration
second helix
- contains a leucine every 7th aa
- amphiphatic helix
- form dimers (homo- or hetero-)
leucine zipper
there is leucine in every __ aa in leucine zipper
7th
each monomer in leucine zipper contain:
- dimerization domain
- DNA-binding domain
dimerization domain
C-terminal (leu-rich)
DNA-binding domain
N-terminal (rich in basic aa)
each monomer with dimerization domain and DNA-binding domain
helix-loop-helix
almost all in the DNA-binding domain are __ aa
basic
- first structure formed around 8 Cu ions which interact with cys residues on the protein
- knuckles contain basic aa that interact with DNA
copper fist
where does the copper fist motif interact
cys residues on protein
contain basic aa that interact with DNA in copper fist
knuckles
function of copper fist
- electron transfer
- redux reduction
- stabilization of protein
- small proteinaceous infectious particles
- no nucleic acid
- neurodegenerative disease in mammals
prions
post mortem brain with large vacuoles in the cortex and cerebellum
Spongiform Encephalopathy or Prion Disease
where prions were first discovered
scrapie in sheep
who first discovered prions
Stanley Prusiner (1892)
prion disease:
mink
transmissible mink encephalopathy
prion disease:
muledeer, elk
chronic wasting disease
prion disease:
cows
bovine spongiform encephalopathy
prion disease:
humans
Creutzfeldt-Jakob disease
early stages of prion disease
- loss of muscle control
- personality changes
- impaired memory, judgement, thinking
- impaired vision
- insomnia
- depression
- dementia/insanity
later stages of prion disease
- involuntary muscle jerk
- blindness
- paralysis, wasting
- coma
- death, typically following pneumonia
visible end results at post mortem of prion disease
- non-inflammatory lesions
- vacuoles
- amyloid protein deposits
- astrogliosis
- first known prion disease
- geographically isolated tribes in the highlands of New Guinea
- by ingesting brain tissue of dead relatives for religious reasons
Kuru
a prion is a modified form of __
PrPc (prion protein cellular)
where are prions encoded
single exon of single copy located at chromosome 28
where are prions found
predominant on surface of neurons
function of prions
synaptic function
characteristic of prions
- non-immunogenic, protease-sensitive
- subviral agent
modified form of PrPc
PrPsc (prion protein scrapie)
where does PrPsc accumulate
cytoplasmic vesicles of diseased indiv.
where PrPc is found
predominantly at alpha helix
where PrPsc is found
predominantly at beta-sheet (mostly globular)