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Membranes & Proteins Can lead to the formation of excess CHOLESTEROL Steroid that helps stabilize membranes of animal cells So why are saturated fats bad for me? Is there such a thing as a “good” fat? Polyunsaturated fats (>1 double bond) contain essential fatty acids (omega-3)

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is there such a thing as a good fat
Is there such a thing as a “good” fat?
  • Polyunsaturated fats (>1 double bond) contain essential fatty acids (omega-3)
  • First double bond located 3 carbons from the methyl end of the fatty acid (-CH3)
  • Methyl end = omega end
  • May protect against heart disease
  • Oily fish like salmon and tuna (not canned), flax & walnuts
my favourite fat
My Favourite Fat
  • Has two saturated stearic acids and one unsaturated oleic acid
  • Solid at room temperature but melts quickly in your fingers
cocoa butter

H O

| ||

H – C – O – C – stearic acid

O

||

H – C – O – C – oleic acid

O

||

H – C – O – C – stearic acid

|

H

Cocoa butter!!!!
membranes aren t just made of phospholipids
Membranes aren’t just made of phospholipids
  • Lots of protein (more than 50% of a membrane)!!
what is a protein

Carboxyl (acid) group

Amino group

What is a protein?
  • Basic unit is the amino acid (e.g. glycine)

H

|

H – N – C – C – OH

| | ||

H H O

  • Amino acids differ by the type of side chain located on the central carbon
primary structure
Primary Structure
  • A series of amino acids linked together
  • Condensation synthesis removes a water molecule between each amino acid
  • Results in a peptide bond between the amino acids
condensation synthesis

H

|

H – N – C – C

| | ||

H H O

H

|

N – C – C – OH

| | ||

H H O

H2O

Peptide bond

Condensation Synthesis

H

|

H – N – C – C – OH

| | ||

H H O

H

|

H – N – C – C – OH

| | ||

H H O

secondary structure
Secondary Structure
  • The amino acid chain (polypeptide) folds back on itself to create 2 different structures:

1. Alpha helices (alpha helix)

2. Beta pleated sheets

tertiary structure
Tertiary Structure
  • More folding
  • Bond interactions between the amino acid side chains
  • A variety of bonds involved:

Polar covalent bonds (hydrophilic interactions)

Non-polar covalent bonds (hydrophobic interactions)

Ionic bonds (ionized side chains)

covalent vs ionic bonds
Atoms ionize = electron is donated from one atom to another (no sharing)

Results in a full charge on the atom

Strong bonds in air

Weak in water (e.g. table salt)

Electrons are shared

Polar covalent bonds result in partial charges (unequal sharing)

Nonpolar bonds result in no charge (equal sharing)

Strong bonds

Covalent VS. Ionic Bonds
polar covalent bonds
Polar Covalent Bonds
  • Tug-of-war but no one wins
  • Oxygen can’t pull the electrons completely away from hydrogen
ionic bonds
Ionic Bonds
  • One molecule wins the tug-of-war
  • Electrons are completely shifted from one atom to another
quaternary structure
Quaternary Structure
  • Is not exhibited by all proteins
  • Separate protein subunits interact via hydrogen bonds
  • A globular protein like hemoglobin has 4 protein subunits
  • A fibrous protein like collagen has 3 subunits
who cares21
WHO CARES?!?
  • Prion diseases (e.g. mad cow disease, Creuzfeldt-Jakob)
  • Spongiform encephelopathy
  • Prions are infectious proteins
  • Caused by normal proteins that are folded improperly
  • Still don’t know much!