Biochemistry: Proteins Flashcards
What are proteins?
biopolymers
- composed of amino acids
- connected by peptide bonds
What are the functions of proteins?
- structural tissue
- transport molecules
- catalysts
How are proteins classified?
- primary
- secondary
- tertiary
- quartenary
What is the primary structure of proteins?
- particular sequence of amino acids
- backbone of a peptide chain or protein
What are amino acids connected by?
peptide bonds
What is the secondary structure of proteins?
- hydrogen bonding
the structures have well defined shapes. hydrogen bonding is responsibel for the define shapes.
Where is hydrogen bonding located in peptides?
amino group and carbonyl group of antiparallel polypeptide chains
What are the two possible secondary structures of amino acids?
- alpha helix (spiral shape)
- beta pleated sheet (parallel lines)
What proteins is the beta pleated sheet typical for?
beta pleated sheet is typical for fibrous proteins.
What proteins is the alpha helix typical for?
alpha helix is typical for globular proteins
What is an additional secondary structure?
the triple helix
Where is the triple helix usually found?
collagen, connective tissue, skin, tendons, and cartilage.
What is the tertiary structure of proteins?
formed due to interactions between R-groups (side groups), giving a protein its specific three dimentional structure.
What is the tertiary structure of polypeptides stabilised by?
- hydrophobic and hydrophyllic interactions
- salt bridges
- hydrogen bonds
- disulfide bonds
What is the quartanary structure of polypeptides stabilised by?
the same interactions found in tertiary structures
What is the quaternary structure of proteins?
- combination of two or more tertiary structure proteins
How is a peptide name formed?
the end -yl,
which is joint to the name of amino acid starting from the amino-end in sequence and the full amino acid name of the amino acids in the carboxyl-end.
Where is the amino and carboxy group located in proteins?
amino group- beggining of chain
carboxy- end of chain
Describe the insulin protein.
- primary structure of two polypeptide chains linked by disulfide bonds.
What are the bonds in the different interactions of proteins? summary
primary- peptide
secondary- hydrogen
tertiary- interactions of amino acid side groups
quartenary- two or more tertiary structures
What is the function of proteins related to?
its structure
Explain the structure- function relationships of proteins.
ENZYMES:
- active site of enzymes
TRANSPORT PROTEINS:
- bind of oxygen to heam
STRUCTURAL:
- fibrous (eg. collagen), super-helical cable (very strong)
What are the physical properties of proteins?
- colloidal properties
- scatter light
- excert osmotic pressure
- molecular weights are important
- shape varies
- isoelectric pH of amino acids
- pI of amino acids
What is the pI of a protein? What does “pI” stand for?
- isoelectric point (pI)
- the pH of a solution at which the net charge of a protein becomes zero.
How are proteins classified?
- catalytic
- structural
- contractile
- transport
- regulatory proteins or hormones
- genetic proteins (histones)
- protective proteins (immunoglobins)
What are conjugated proteins?
proteins which contain permanently associated chemical components in addition to amino acids.
What is the name of the non-amino acid part of a conjugated protein called?
prosthetic group
What is a prosthetic group?
the non-amino acid part of a conjugated protein
How are proteins classified based on shape?
- globular
- fibrous
Explain the structure of globular proteins.
- compact, spherical structure.
- carry out synthesis, transport, and metabolism in the cells.
- eg. myoglobin
Explain the structure of fibrous proteins.
- long, fiber-like structure
- eg. alpha keratins making up hair, skin, wool, nails
- contain large amounts of beta pleated sheets
How are amino acids classified based on nutritional value?
- nutritionally rich proteins (complete proteins)
- incomplete proteins
- poor proteins
What are nutritionally rich proteins?
- contain all essential amino acids in the required proportion
What are incomplete proteins?
- lack 1 amino acid
- cannot promote body growth in children
- sustain body weight in adults
What are poor proteins?
- lack many essential amino acids
- diet based on these proteins does not sustain the body weight
What is denaturation? What do proteins loose when they are denatured?
- quartenary, tertiary, secondary structure of a protein is disrupted and may be destroyed
- proteins loose their biological activity
How can proteins be denatured?
BREAKING OF H-BONDS:
- heating
- organic compounds
BREAKING H-BONDS BETWEEN POLAR R-GROUPS:
- acids
- bases
REACT S-S BONDS TO FORM SOLIDS:
- heavy metal ions
STRETCHES PEPTIDE CHAINS UNTIL BONDS ARE BROKEN:
- agitation (eg. whipping)
What is coagulation?
coagulable proteins are heated at their pI pH, a series of changes occurs:
- dissociation of the protein (disruption of the quartenary structure)
- uncoiling of the polypeptide chains (disruption of the tertiary and secondary structure)
- matting together of the uncoiled polypeptide chains (coagulation)
How is the primary structure of proteins destroyed?
hydrolysis (water is joined, bonds are destroyed)
Explain protein hydrolysis.
- peptide bond is split (giving smaller peptides and amino acids)
- occurs in the digestions of proteins
- occurs when amino acids are needed to synthesise new proteins or repair tissues (in cells)
What does the hydrolysis of a peptide require?
- acid/base
- water
- heat
in the body: enzymes catalyze the hydrolysis of proteins.
What is the progressive hydrolysis of preteins?
protein –> peptone –> peptide –> amino acids
What is another property of proteins?
precipitation
What causes precipitation of proteins?
Any factor which neutralizes the charge or removes water of hydration.
What does the stability of proteins depend on?
the charge and hydration
What do polar groups of proteins tend to do?
attract water molecules around them to produce a shell of hydration
What procedures are used for proteins precipitation?
- salting out
- isoelectric precipitation
- precipitation by organic solvents
- precipitation by heavy metal ions
- precipitation by alkoloidal reagents
What are derived proteins?
degredation products of native proteins
What is the difference between protein denaturation and coagulation?
Denaturation is the permanent alteration of protein structures by heat, acid or agitation.
- It breaks the chemical bonds (hydrogen and disulphide bonds) that hold amino acids together and unravels the helical structure.
Coagulation is the “setting” of protein when heat or acid is added. It traps liquids inside a solid.
denaturation- permanently
coagulation- reconfiguration can occur
State an example of denaturation and coagulation of proteins.
denaturation: fried egg
coagulation: warmed milk
How are proteins classified based on composition and solubility?
simple proteins and complex (conjugated) proteins
State examples of simple proteins
- albumins
- globulins
- protamines
- prolamins
- lectins
- scleroproteins
State examples of conjugates (complex) proteins.
- glycoproteins (protein+carbohydrate)
- lipoproteins (protein+lipid)
- nucleoproteins (protein+nucleic acid)
- chromoproteins (protein+coloured prosthetic groups) eg. heamoglobin (red), flavoproteins (yellow), visual purple (vitamin A, purple).
- phosphoproteins (protein+phosphorus)
- metalloproteins (protein+metal ions) eg. heamoglobin (iron), cytochrome (iron), tyrosine (copper), carbonic anhydrase (zinc).
What is an ogliopeptide?
a peptide made from 10 or less amino acids
State examples of biologically active ogliopeptides.
- thyrotropin releasing hormone
- glutathione
- oxytocin
- vasopressin
- angiotensin
- polypeptide hormones
