Proteins Flashcards
Chain of amino acids
Polypeptide
Tertiary structure
Twisted around
Different groups in amino acid structure
NH2 = amine group
R = R group (side chain)
CO2H = carboxyl group
Charges of groups and how they are held together in the secondary structure
-NH and -C=O on the ends of the chain
H = overall positive charge
O = negative charge
Opposite charges attract
2 groups form weak hydrogen bonds
Amino acid structure
N - C - C in middle
N attached to 2 hydrogen
C attached to R and H
C attached to H on top and O=H on bottom
How do the weak hydrogen bonds affect the secondary structure of the protein
Cause long polypeptide chain to be twisted into an alpha helix coil
Process called in which many amino acid monomers can be joined together
Polymerisation
Primary structure
—————-
What does the primary structure determine in the protein
Ultimate shape and function
Quaternary structure
Large number of proteins linked together, lots of twisted chains
How is a peptide bond formed
Combining the carboxyl group with an -H from another amino acid is lost
2 amino acids become linked when water is removed
Forming a peptide bond between amino acids
3 bonds in tertiary structure
Disulfide bond = strong
Ionic bonds = between carboxyl and amino groups, weak
Hydrogen bonds = weak
Secondary structure
VVVVV——-
What is the reaction called with the removal of water
Condensation reaction
Test for proteins
1) Place sample in test tube and add equal volume of sodium hydroxide solution
2) Add few drops of dilute copper solfate and mix
3) Purple = presence of peptide bonds, so presence of protein
Blue = no presence
What is changed among different amino acids
Their side group differs (R group)
Reaction that forms dipeptides and polypeptides
Condensation
Difference between dipeptide and polypeptide
Dipeptide = 2 amino acids
Polypeptides = many amino acids
What are fibrous proteins for
Structural function
What do globular proteins do
Metabolic functions
Describe fibrous proteins structure
Long chains which run parallele to one another
Linked by cross-bridges forming stable molecules
Describe each of the stages when forming a quaternary protein
1) Primary = sequence of amino acids determining protein’s shape and function
2) Secondary = polypeptide chain twisted into alpha helix due to hydrogen bonding because of different charges in amino acid
3) Tertiary = polypeptide helix twisted into compact structure with bonds disulfide, hydrogen, ionic
4) Quaternary = Many different polypeptide chains forming protein molecule
What type of chains can be contained in the quaternary structure of the protein formed
both protein and non-protein groups
What is chromatography
Technique to separate a mixture into its individual components
Relies on differences in solubility with different attractions to the mobiel and stationary phase
Method of paper chromatography with amino acids
1) Use paper chromatography to separate amino acids
2) Spot placed on line at bottom of paper
3) Spots of known standard solutions placed on line beside unkown sample spot
4) Chromatography paper suspended in solvent
5) Amino acids separate depending on their charge and size
6) Compare unkown to known and math with chromatograms
What are the two shapes that can form due to the secondary structure of a protein
Alpha helix
Beta pleated sheet
Differencebetween alpha helix and beta pleated sheet
Alpha = H2 form every fourth peptide
Beta = protein folds so two parts of the polypeptide are parallel so H2 form between parallel peptide bonds
How can hydrogen bonds break
High temps and ph changes
What structure do the two types of proteins have
Fibrous protein = secondary
Globular protein = tertiary
What bonds do secondary have
Peptide and hydrogen
What bonds do primary have
Peptide
What bonds do tertiary hav
Peptide hydrogen disulphide ionic and hydrophobic interactions
Describe disfulfide bonds
Strong covalent
Form R groups
Disulfide bridges strongest but occur less frequently
Stabilise proteins
Broken by reduction
Describe ionic bonds
Form between NH3+ and COO- when water removed
Ionic bonds are stronger than hydrogen bonds but not common
Broken by pH changes
Describe h ydrogen bonds
Form between strong polar R group
Most common but weakest
Hydrophobic interactions
Non-polar R groups within interior of proteins
Name of protein test
Biuret test
Describe globular proteins
Compact, spherical, soluble in H2O
Why are globular proteins spherical
Non polar hydrophobic R group orientate towards centre of protein and polar hydrophilic R group orientates to outside
How are globular proteins fit for their role
Orientation = water molecules can surround polar hydrophilic R group
Solubility = can be easily transported around organisms for metabolic reactions
Folding = enzymes and immunoglobins
Conjugated = contain prosthetic group
Describe fibrous proteins
Long strands of polypeptide chains that have cross linkages due to H2 bonding
Little or no tertiary structure
Why are fibrous proteins fit for their role
Insoluble = larhe number of hydrophobic R groups
Organised = highly repetitive
Good for structure e.g. collagen
Compare globular and fibrous proteins
SHape: G is circular, F is long strands
AMino acid sequence: G is irregular and wide range of R groups, F is repetitive with limited range of R groups
Function: G is metabolic/ functional, F is structural
G is haemoglobin, enzymes, immunoglobulin, insulin. F is collagen, keratin, myosin, actin, fibrin
Solubility: G is soluble, F is insoluble
What is collagen
Most structural protein found in vertebrates
What does collegen form
Tendons cartilage ligaments bones teeth skin walls of blood vessels cornea on eeye
Describe collagens structure
-Triple helix = 3 polypeptide chains held together close by H2 bonds
-Glycine = every third amino acid is glycine, contains H atom found inside polypeptide chains to form tight triple helix
-Fibrils = covalent bonds cross link R groups interacting triple helices when they are arranged parallele ot eachother
-Fibres = fibrils arranged together form fibres
Collagens function
-Flexible structural protein form connective tissue
-H2 bonds in triple helix = very strong, withstand large pulling forces without stretching or breaking
-Staggered ends in fibrils = strength
-Stable = lots of proline and hydroxyproline amino acids so more stable as R groups repel eachother
-Length of collagen = too long to dissolve in water
Uses of amino acids
Protein synthesis/ Building polypeptides
Respiration
How does the secondary structure determines the proteins overall structure
H2 bonding between C=O and NH every 4 amino acids along the chain
Protein forms a righ thanded alpha helix
A beta pleated sheet forms by folding the chain back on itself in a zig zag plane
Both extend its 3D shape
What is a prosthetic group
Non amino acid section of a protein
Covalently bonded to the polypeptide sections
Describe haemoglobins structure
4 separate polypeptide chains bonded together
Each polypeptide bonded to a haem group which binds to O2
Beneits of haemoglobins structure in mammals
Function = bind to O2 in lungs and release O2 at respiring tissues
Binding of O2 to one haem increases affinity of haemoglovin for O2
Changing shape of whole protein makes it easier to bind another O2 and harder to unbind
Haemoglobin can deliver O2 readily to tissues that require it most
Define “r” group
Functional group
If an amino acid is non-polar where will it be in a globular protein
Centre
Non-polar amino acids are hydrophobic and polar ones at the surface (in contact with water)
Why is a sickle cell less soluble
Non plar amino acid at surface
Non polar do not interact with water
How are dipeptides formed
Two amino acids joined by peptide bond
Condensation reaction occurs forming peptide bond
Between amine and carboxylic group of adjacent amino acids
How are functional proteins different from a polypeptide
Polypeptide chains are primary structures
Functional proteins are formed from more than one polypeptide chains
Functional protein has tertiary or quaternary structure with hydrogen, ionic and disulfide
How is a polypeptide formd
Condensation between many amino acids
Why are cellular enzymes made from proteins
Shape relates to function
Structure determines by primary structure
Primary structure folds into tertiary which has a 3D shape
Shape of primary determines by bonds occur between amino acids within primary sequence
Bonds inclue hydrogen, ionic, disulfide
Order of amino acids changed affects bonds between amino acids altering the shape
