FLC: intro to the living cell Flashcards
What are proteins?
Polymers of amino acids
What is the structure of amino acids?
-Amine group(NH3+)
-Carboxyl group(COO-)
-R group(side chain)
-Central Carbon atom
-Hydrogen
Structure of amino acid at low pH
-Amine group(NH3+)
-Carboxyl group(COOH)
-R group(side chain)
-Central Carbon atom
-Hydrogen
Structure of amino acid at intermediate pH
Zwitterion at intermediate pH
-Amine group(NH3+)
-Carboxyl group(COO-)
-R group(side chain)
-Central Carbon atom
-Hydrogen
Structure of amino acid at high pH
-Amine group(NH2)
-Carboxyl group(COO-)
-R group(side chain)
-Central Carbon atom
-Hydrogen atom
What are proteins polymers of?
Polymers of 20 different amino acids
How is a peptide bond formed between amino acids?
Formation of a peptide bond by condensation
What is the sequence of amino acids called and what are the terminal ends called?
The sequence of amino acids is called
the primary structure of a protein
-Amino-terminal end
-Carboxyl-terminal end
What are the 4 levels of protein structure and what is included in them?
Primary structure
-Amino acid residues
Secondary structure
-Alpha helix
Tertiary structure
-Polypeptide chain
Quaternary structure
-Assembled subunits
What are amino acids joined by in the primary structure?
Amino acids are joined by
strong covalent bonds in
the primary structure.
What are higher orders of protein structures dependant on?
Higher orders of structure
are mostly dependent on
weak bonds (ionic,
hydrogen and hydrophobic)
but may be stabilized by
covalent bonds.
What is the secondary structure of proteins made by?
-Alpha helices
-Beta pleated sheets
What are beta pleated sheets?
Beta-pleated sheet is a series of anti-parallel chains of covalently linked amino acids with adjacent chains linked by hydrogen bonds
What is alpha helix and what is it stabilised by?
Alpha helix is a motif and right handed helix stabilized by H-bonds between the amide H of one amino acid and the carbonyl group 4 residues along the chain.
What do side chains in alpha helix do and what can these residues be?
Side chains protrude
from sides of the helix.
In some cases residues
are hydrophilic on one
side of the helix and are
hydrophobic on the
other.
What happens to helices and sheets in the tertiary structure?
Helices and sheets are folded up into more densely packed globular structures.
What does formation of tertiary structures depend on?
Formation of these structures depends on weak chemical bonds between side chains.
What may structures be stabilised with in tertiary structure?
The structures may be stabilized by covalent disulfide bonds between cysteine residues.
What happens to form a quaternary structure?
In some cases, ≥2 folded polypeptides may be combined to form the mature protein.
What is the quaternary structure of haemoglibin?
hemoglobin containing 4 polypeptides + 4 heme groups
What are examples of non-covalent interactions in proteins
-Ionic bonds
-Hydrogen bonds
-Van der Waals attractions
What is the stabilisation of 3 degree and 4 degree structure?
-Disulfide bonds
-Sulfhydryl side chain of cysteine:
May Crosslink a single polypeptide
chain (3° structure) or two separate
molecules (4° Structure).
How are protein structures determined?
Protein structure may be determined in various ways, principally
X-ray crystallography and nuclear magnetic resonance (NMR)
spectroscopy.
What shape do water soluble proteins tend to be?
Water soluble proteins are often globular in shape:
* Hydrophilic residues mostly on the external surface.
* Hydrophobic residues usually buried inside the protein.
How are membrane proteins organised?
- Membrane spanning regions have externally located
hydrophobic residues that interact with the membrane lipids. - They may have hydrophilic central channels.
What helix does collagen have?
Collagen has a triple helix (NOT an alpha helix).
How may collagen fibres assemble?
Collagen molecules may assemble into long fibres or sheets.
What does the primary sequence of the protein determine?
The primary sequence determines the folding of the polypeptide into the
functional protein structure.
What is sickle cell anaemia caused by?
Caused by a mutation that changes a single amino acid in the beta chain of haemoglobin:
Glu (negative) is replaced by Val (hydrophobic ) at position 6.
What does mutant haemoglobin(HbS) form in the deoxygenated state?
In the deoxygenated state, the mutant haemoglobin (HbS) forms insoluble fibres (the
HbS molecules stick together).
