lecture 3-protien classification Flashcards
List the paramaters used to classify protiens?
- composition→ simple or conjugated
- native or derived
- Solubility
- Ultracentrifugation properties→mass and density
- Electrophoretic properties→charge, MW, IEP
what does ultracentrifugation of protiens seperate them by?
seperates them on the basis of MW and shape
Describe what a simple protien is vs a conjugated protien
simple protien→ are protiens which contain only amino acids in their molecules and these are divided into 2 groups: globular and fibrous protiens
conjugated protien→ are protiens that contain amino acids and are conjugated with another molecule like carbohydrates, lipids or a mineral
List which simple protiens are globular and which are fiborous
Globular= albumins,globulins,glutelins,prolamins, histones, protamines
Fiborous=collagen,elastin
what are the general differences between fiborous and globular protiens?
shape: fiborous are long and narrow while globular are round/spherical
purpose: fiborous have a purpose in structure and globular have functional purposes
AA sequence: fiborous have a repatative amino acid sequence and globular have an irregular acid sequence
Durability: fibourous is less sensative to changes in pH and temperature compared to globular who is really sensative
solubulity: generally fiborous class of protiens is insoluble in water and globulins are soluble
What are albumins soluble in?
soluble in neutral, salt free water and dilute salt soluations and dilute acids and bases
what perticipates albumins?
percipitated with a saturated solution of salt such as ammonium sulphate
what coagulates albumins\
heat
give three examples of albumins
- serumbumin (blood)
- lactalbumin (milk)
- egg white (ovolbumin)
What are globulins soluble/ insoluble in?
they are soluble in neutral salt solutions and then almost insoluble in water
what are globulins percipated in?
percipated with half saturated solution of ammonium sulphate
describe some characteristcs of globulins
they are coagluated by heat. They are a diverse group of protiens with many functions (actually almost every protien)
give examples of globulins
Myosin (muscle)
actin (muscle
beta-lactoglobulin (milk)
what are glutelins soluble/insoluble in?
soluble in dilute acid or base and insoluble in neutral solvents (distilled water, dilute salt solution, alcohol)
describe some important characteristcs of glutelins
They are rich in hydrophobic amino acids → making them not soluble in certain solutions. They can form disulfide bonds between molecules especially during baking
give an example of a glutelin
glutenin which is in wheat and is one of the protiens of gluten
what are prolamins soluble and insoluble in?
they are insoluble in water and absolute alcohol and are soluble in 70 to 80% alcohol
what are the 2 protiens of gluten
glutenin and gliadin
give some characteristics of prolamins
they are coagulated by heat, they are rich in proline and glutamine and are found in plants
give an example of a prolamin
gliadin in wheat which is actually the protien responsible for sensitivity, allergy and celiac diease
What are histones soluble in?
water
what are histones percipitated by?
ammonia
describe characertics of histones and what they are
They are weakly basic protiens that are NOT coagulated by heat and have a high content of arginine and lysine
DNA is compated into chromatin which is wrapped around histones complexes, it is bound by hydrogen bonds with phosphoric acid
what is the signficane of lysine in histones
Lysine residues are often sites for methylation/acetylation. In histones this is significant because it is important in the regulation of chromatin and gene expression. Lysine acetylation and methalyation leads to the relaxtion of chromatin which means greater transcription
how does lysine hydroxylation impact gene expression and chromatin sructure
because it can prevent or modify acetylation/methylation of lysine which normally would lead to the relaxation of chromatin allowing for greater trasncription
What are protamines soluble in?
water and ammonium hydroxide solution
what are some characteristcs of protamines?
they are strongly basic protiens that are not coagulated by heat but rich in arginine and lysine.
what perciptiates protamines
aqueous solution of alcohol
describe protamines and DNAs relationship
Protamines binds with DNA in the embryonic stage and is later replaced by histones
describe the general structure of fiborous protiens
made up of polypeptide chains that are elongated. they have a sheet like structure. They are mechincally quite strong.
describe the structure of collagen
It is a triple helix structure. The amino acid sequence is repeating Gly-X-Y. X is often proline which is hydrophobic and Y is either hydroxyproline or hydroxlysine
describe how the structure of collagen is related to its function
the triple helix provides external protection, shape, support and form
Describe what hydroxyproline do for collagen or how it affects it
Have OH which increase polarity and hydrophilicity. Hydroxyproline maintains collagen rigidty and elasticity as hydrogen bonds with water molecules and other amino acids stabilize collagen structure.
Explain what happens to lysine in collagen
it undergos hydroxylation to form hydroxylysine which will increase polarity and hydrophilicty which allows for hydroxyl groups to form hydrogen bonds and interact with other polar groups increasing stability. Not only that but hydroxylysine serves as an attachment site for carbohydrate groups further increasing the structural integrity of collagen
describe elastin and its structure
Stretchy protien rich in glycine, valine, alanine and proline which are all hydrophobic.
what are prosthetic groups?
the non protien part of conjugated protiens
List the types of conjugated protiens and briefly describe them
- metalloprotiens (aa+ metal ions)
- chromoprotiens (aa + colored pigments)
- nucleoprotiens ( aa+ nucleic acids→DNA/RNA)
- phosphoprotiens ( protiens+ phosphoric acid)
- glycoprotiens( carbs and protien)
- lipoprotien( lipid + protien)
briefly describe lipoprotiens
lipid + protien. They have excellent emulsifying capacity they are found in milk, egg yolk, plasma membrane and as LDL and HDL
what are the linking type of glycoprotiens
N or O linked
Give an example of phosphorotiens and explain the process of their phosphorlyation
example= milk caesin
Phosphorylation typically happens on specific amino acids like serine, threonine and tyrosine which have hydroxide groups.
protamines or histone are nucleoprotiens?
yes they are the phosphate group on nucleic acid binds with amide group on protien
give some examples of chromoprotiens
haemoglobin, myoglobin, chlorophyll, flavoprotiens
give example of metalloprotiens and describe them a little
They have metal ions connected to them like iron, copper, zinc, maganese, and cobalt. An example would be hemoglobin. But they function in a wide variety of biological processes.
describe derived protiens
They are protiens that have been modified by physical or chemical means. This normally results in a physical change like in solubility or hydrophobicity. They are classified by the extent of change into primary and secondary derivived protiens
describe primary derived protiens
These protien derivatives are fromed by processes causing only slight changes in the protien molecule and its properties so there is no or very little hydrolytic cleaving
give examples of primary derived protiens
metaprotien: it is produced by the action of an acid or base @ 30-60 degrees. It is water insoluble but soluble in dil acid/alkali. An example of this is curd
coagulated protien: this is produced by the action of heat or alcohol on protien. It is insoluble in wateer. an example is a coagulated egg
Define secondary derivatives
more extensivly changed protiens, they are formed by progressive hydrolytic cleavage of peptide bonds or by the action of strong acid or digestive enzymes
how are secondary derivatives grouped and what happens as you get smaller?
They are grouped based on average molecular weight. As they are hydrolyzed they will become smaller decreasing in molecular weight. The more you break down a protien the more soluble the protien because lower molecular weight meaning they will not be coagulated by heat. The ranking is as follows proteoses (10-100 kDa), peptones (1 kDa to 10) and peptides (less then 1 kDa)
What can dervived secondary protiens be used for
Yeast extract and vegtable protien is often hydrolyzed to enhance flavor because upon hydrolysis free glutamic acid is released which gives that unami taste. Hydrolysis of protiens can also be used to modify allergenic properties of protiens, like in baby infant fromula
Classify protiens based on biological function and provide a brief description
- Catalytic protien: catalyze biochemical reactions (enzymes, coenzymes)
- structural protien: structural componenets ( collagen, elastin)
- nutrient protien: have nutrional value (milk)
- regulatory protien: regulates metabolic and cellular activities (hormones)
- defense protien: provides defensive mechanisms against pathogens in immune systme ( antibodies, complement protiens)
- transport protiens: transport nurtrients/molecules from one ogran to another ( haemoglobin)
- storage protien: store molecules and ions in cells (ferrtin store iron)
- contractile or mobile protien: help in movement of various body parts (actin, myosin)
- toxic protien: toxic and can damage (snake venom, bacterial exotoxins)
