Proteins Flashcards
What elements are in proteins?
Carbon
Hydrogen
Oxygen
Nitrogen
Sometimes - Sulfur and Phosphorus
What are the functions of proteins?
Catalysts Transporting substances around the body Movement of the body Cell recognition Transport across cell surface membrane Formation of connective tissue and structural components of the body Protection against foreign bodies Hormonal control
Example of catalyst protein?
Enzymes
Example of the proteins that transport substances around the body?
Haemoglobin
Example of the proteins that help movement of the body?
Actin and myosin in muscles
Example of the proteins for cell recognition?
Antigens
Example of the proteins that help transport across cell membrane?
Intrinsic protein channels
Example of the proteins that form connective tissue and structural components?
Keratin or collagen
Example of the proteins for protection against foreign bodies?
Antibodies
Example of the proteins for hormone control?
Insulin
What is the monomer for proteins?
Amino acids
What bonds are proteins held together by?
Peptide bonds
How many different occurring amino acid monomer units are there? How many essential ones?
20
Only 8 are essential to build the others
What are two amino acids joined together called?
Dipeptides
What are many amino acids joined together called?
Polypeptides
What is the structure of an amino acid?
An asymmetrical carbon atom bonded to 4 different groups
Carboxylic acid group - COOH
Amino Acid group - NH2
One hydrogen
R - variable group
What are optical isomers?
They are mirror image isomers
Eg Alpha amino acids and Beta amino acids
What amino acids are all living things made from?
Alpha amino acid
What word are amino acids described as? What does this mean?
Amphoteric
The amino acids can act as both acids and bases
How can the amino acids act as both acids and bases?
The amino group (NH2) can accept a hydrogen becoming NH3+ (alkaline)
The carboxylic acid group can lose a hydrogen ion and become COO- (acid)
What reaction is used to form a dipeptide?
Condensation reaction
What is removed in a condensation reaction?
Water
What are the two products in a condensation reaction of two amino acids?
Dipeptide and water
What are the types of structures of proteins?
Primary
Secondary
Tertiary
Quaternary
What is primary structure? Bonds involved?
The sequence of amino acids in the polypeptide chain which determines the shape and function - an unbranched polypeptide chain
Peptide bonds
What is secondary structure? Bonds involved?
Polypeptide chains can twist into a 3D shape
Weak hydrogen bonds
What are the two types of secondary structures?
Alpha helix
Beta pleated sheet
How does an alpha helix structure work?
Weak hydrogen bonds between NH group of one amino acid and the CO group of the neighbouring amino acid to cause the coil
Making fibres
What is alpha helix found in?
Keratin - hair and nails
Collagen - tendons
How does the beta pleated sheet work?
Hydrogen bonds form parallel chains to produce a flat structure that then folds
Creates great strength
What is beta pleated sheet found in?
Silk
What are the two types of proteins?
Fibrous
Globular
What is the structure and use of fibrous proteins?
Made of long parallel fibres Linked by cross-bridges (very stable) Lots of molecules involved Regular and repetitive structure Insoluble
Used as structural molecules
What is the structure and use of globular proteins?
Rounded molecules Fewer molecules used Unstable Irregular structure Soluble
Often used for metabolic functions
What is tertiary structure? Bonds involved?
A precise 3D structure of protein formed by coiling of secondary proteins
Hydrogen bonds (weak, easily broken) Di-sulphide bridges (covalent bonds of sulphur atoms in the R group) Ionic bonds (between amino or carboxyl groups that aren’t involved in peptide bonds) - weak and broken by changes in pH
What is quaternary structure? Bonds involved?
Large proteins consisting of a number of polypeptide chains together
Also,
Non-protein groups can be joined to the polypeptide called a prosthetic group
Hydrogen
Ionic
Di-Sulphide bridges
What do di-sulfide bridges do?
Joins or binds the polypeptide chains together
How do you test for proteins?
Add equal volume of sodium hydroxide to the sample
Add Biuret reagent (copper sulphate solution)
If protein is present a purple/lilac colour will be indicted
