BIO 1140 Lecture Notes - Lecture 4: Motor Protein, Centrosome, Mitosis

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Proteins
Primary structures
Appear very linear
As radical groups get closer, a secondary structure is imposed
Secondary structure
Two main secondary structures: alpha helix or beta pleated sheet
Beta sheet appears more rigid, fibre structures -
Charged polar proteins – alpha helix (more twisty, less rigid)
Tertiary Structure
Disulphide bonds contribute to the folding and also solidify the folding (it is not
temporary)
Hydrogen bonds are still present
Can assembly more than one tertiary structures into a quaternary structure; you need 4-
5 subunits to make a functional protein
Assembling different subunits together = quaternary structure
Proteins can come as a single strand or can be built by combining different portions of tertiary
structures.
Within a polypeptide, there are areas that form alpha helixes (polar) and other areas
that form beta pleated sheets (nonpolar) – these areas are called domains
Hemoglobin – an example of a protein that needs two alphas and two betas (more than one
subunit)
Must be correctly folded and assembled to function properly
Binds oxygen and transports it
Its most efficient structure is quaternary
When things go wrong….
It is degraded in the lysosomes to use the amino acids for another purpose
Sickle cell anemia = the hemoglobin is not successfully degraded and remains in the
body in its bad form
Single nucleotide changes on the gene that translates into a single amino acid
Four very large subunit and only ONE subunit is different
That single change results in hemoglobin not being folded in the same structure; instead
of its globular structure, it has a long, inflexible chain-like, linear shape
So inflexible that they completely distort the shape of red blood cells; clump together
Hemoglobin: a red protein responsible for transporting oxygen in the blood of vertebrates. Its
molecule comprises four subunits, each containing an iron atom bound to a heme group.
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One small change in a protein’s amino acid creates an entirely different structure and entirely
new set of reactions – the function is very strongly affected
FORM AND FUNCTION GO HAND-IN-HAND
Midterm question
Functions of Proteins
Hormones, receptors, contractile, motor, structural
Hormonal = globular
Structural = fibres/beta pleated
Enzymes, storage, defense mechanisms, transport
Transport proteins have two personalities
Need to span the membrane – comfortable in a hydrophobic environment
Depending on what they let through (often polar) the interior has to be hydrophilic
Tertiary structure needs to reflect these domains
Domains that are both hydrophobic and hydrophilic within that structure
Carbon chains
4-5 carbon atoms… non-polar
longer it is, the more non-polar it is
REVIEW
polarity determining orientation, direction of motor proteins
intermediate filaments don’t have any polarity – doesn’t participate in any transport
activities
Ifs still important for the cells – contributes to structure (springs), helps with
microfilaments, used in ANCHORING JUNCTIONS (desmosomes) – structure made of
keratin
Ifs are made of keratins – accumulates as plaques to form a type of anchoring junction
called desmosomes
Microtubules don’t go all the way to the membrane…
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