3.1.4.1 General properties of proteins Flashcards
what are the monomers from which proteins are made?
amino acids
what is the general structure of an amino acid (draw it out)?
NH2 represents an amine group, COOH represents a carboxyl group and R represents a side chain
what element does the R group in an amino acid generally contain?
carbon
which amino acid’s R group only contains hydrogen?
glycine
which amino acid’s R group contains sulfur?
cysteine
how many amino acids are common in all organisms?
20
what is the only way that the amino acids differ from each other?
the R (side) groups can differ
what reaction joins two amino acids?
a condensation reaction
what bond is formed when two amino acids combine?
a peptide bond
where is the peptide bond formed between two amino acids?
one amine group joins to a carboxyl group from another amino acid
how are dipeptides formed?
by the condensation reaction between the amine and carboxyl group of two amino acids
how are polypeptides formed?
by the condensation reaction between 2 or more amino acids
draw the formation of a dipeptide and circle the peptide bond?
what does a functional protein contain?
may contain one or more polypeptides
what is the structure of a protein determined by?
the position of amino acids / R groups / interactions
how many structural levels are there to proteins?
4 (primary, secondary, tertiary and quaternary)
what is the primary structure of a protein?
the sequence and number of amino acids
what is the secondary structure of a protein?
- hydrogen bonds
- forming an α-helix or a β-pleated sheet
where do hydrogen bonds form in the secondary structure of a protein?
between NH group of one amino acid and C=O group
what is the tertiary structure of a protein?
- formed by interactions between R groups
- the 3D shape of a polypeptide chain
- this determines the function of the protein
which bonds are involved in the tertiary structure of a protein?
- hydrogen bonds
- ionic bonds
- disulfide bridges
- covalent bonds
- hydrophobic interactions
–> these are all known as ‘interactions’
which bonds maintain the tertiary structure of a protein?
- hydrogen bonds
- ionic bonds
- disulfide bridges
what is the property of hydrogen bonds in proteins?
they are numerous but easily broken
what is the property of ionic bonds in proteins?
they are weaker than disulfide bonds and are easily broken by changes in pH
where do ionic bonds form?
between R groups of different amino acids
what is the property of disulfide bridges in proteins?
they are resistant to chemical and physical attack and therefore cannot be easily broken
where do disulfide bridges form?
between R groups of different amino acids
what is the quaternary structure of a protein?
- more than one polypeptide chain
- other non-protein groups can also be associated
- formed by interactions between polypeptides
what is the function of fibrous proteins?
structural (collagen)
what is the function of globular proteins?
metabolic (haemoglobin / enzymes)
what does it mean if a protein is denatured?
- bonds which hold the secondary and tertiary structure break
- unique 3D shape is lost
what are the conditions that denature a protein?
- too high a temperature (too much kinetic energy can break intermolecular bonding)
- too high / low a pH (too many H+ or OH- ions can disrupt ionic charges in R groups)
what happens if one amino acid changes in the primary structure of a protein?
- different sequence of amino acids
- causes hydrogen / ionic / disulfide bonds to form in a different place
- this results in a different 3D shape
what is the food test for proteins?
- add biuret’s solution to sample
- if protein is present, colour change from blue to purple
