30.2- PEPTIDES, POLYPEPTIDES, AND PROTEINS Flashcards
What do amino acids link together to form?
peptides
What are molecules containing up to about 50 amino acids referred to as?
polypeptides
What is it called when there are more than 50 amino acids?
proteins
Examples of naturally occurring proteins? (4)
enzymes
wool
hair
muscles
What is the functional group of an amide?
-CONH2
What can the amine group of one amino acids react with a carboxylic acid group of another to form?
amide linkage -CONH-
What are compounds formed by the linkage of amino acids called?
peptides
What is a peptide with two amino acids called?
dipeptide
What groups does a dipeptide retain?
retains -NH2 and -CO2H groups and so can react further to give tri- and tetra-peptides, and so on
What is the primary structure of a protein?
fixed sequence of amino acids
What type of polymers are polypeptides and proteins?
condensation polymers
Why are polypeptides and proteins condensation polymers?
as a small molecule eliminated as each link of chain forms
What happens when a protein or peptide is boiled with HCl of conc. 6moldm-3 for about 24hrs?
breaks down to mixture of all amino acids that made up original protein or peptide
What happens to the peptide linkages when a protein or peptide is boiled in HCl of conc. 6moldm-3 for about 24 hrs?
all peptide linkages hydrolysed by acid
How is the complex shape of proteins held in position?
by hydrogen bonds + other intermolecular forces + sulfur-sulfur bonds
Example of how the shape of proteins are vital to their functions?
enzymes + structural materials in living things
What structure do many proteins have?
helical
What is the helix of proteins held by?
hydrogen bonding
What is another structure of proteins other than the helix?
pleated sheet
What is wool?
protein fibre with helix held together by hydrogen bonds
What happens to the hydrogen bonding and fibre when wool is gently stretched?
hydrogen bonds stretch + fibre extends
When releasing wool after it has been stretched, what does this allow?
allows hydrogen bonds to return to their normal length + fibre returns to its original shape
What can washing wool at high temps do?
permanently break hydrogen bonds + garment may permanently lose its shape
How can the amino acids in a protein chain bond together (3)
hydrogen bonding
ionic attractions
sulfur-sulfur bonds
What three levels of structure do all proteins have?
primary, secondary and tertiary
What is the primary structure of a protein held by?
covalent bonding
As the primary structure of a protein is held by covalent bonding, what is its stability like?
relatively stable
What is the secondary structure of a protein?
protein may form helix or folded sheet
What is the secondary structure held in place by?
hydrogen bonding
What is the strength of hydrogen bonding like on comparison to covalent bonds?
hydrogen bonds much weaker than covalent bonds
How can the secondary structure of proteins be disrupted?
by gentle heating or changes in pH
What is the tertiary structure?
α-helix or β-pleated sheet being folded into a three dimensional shape
What is the tertiary structure held in place by?
mixture of hydrogen bonding, ionic interactions and sulfur-sulfur bonds
What shapes do most proteins fold into?
globular shapes
Example of techniques used to determine the secondary and tertiary structures of proteins and what it can do?
X-ray diffraction- can locate actual positions of atoms in space
What is the first step in determining the primary structure?
find out number of each type of amino acid present in protein
How is the process if determining the primary structure of protein done?
protein refluxed with 6moldm-3 HCl
process called hydrolysis
breaks amide bonds between amino acids and results in mixture containing all individual amino acids in original protein
