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Membranes & Lipids Phosphate head group Fatty acid tails Membranes ALL cells are surrounded by at least one membrane Membranes are composed of phospholipids Phospholipid Bilayer Membrane Structure Hydrophobic tails interact with each other Hydrophilic head groups interact with water

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membranes

Phosphate head group

Fatty acid tails

Membranes
  • ALL cells are surrounded by at least one membrane
  • Membranes are composed of phospholipids
membrane structure

Phospholipid Bilayer

Membrane Structure
  • Hydrophobic tails interact with each other
  • Hydrophilic head groups interact with water
interactions with water
Molecules with charges (hydrophilic) will be able to interact with water

sugar in your coffee

Molecules that are uncharged (hydrophobic) will NOT be able to interact with water

oil and vinegar in your salad dressing

Interactions with Water
why do only charged hydrophilic molecules interact with water
Why do only charged HYDROPHILIC molecules interact with water?

The 2 hydrogen atoms share their electrons with oxygen (covalent bond)

BUT the electrons from the hydrogens spend more time around the oxygen atom (polar covalent bond)

summary
Summary
  • Oxygen tries to suck electrons away from other atoms (highly electronegative)
  • This creates polar covalent bonds between the oxygen and hydrogen atoms in the same water molecule
  • Polar molecule = parts of the same molecule have opposite charges
  • Hydrogen bonds form between water molecules because of the attraction between these charges
covalent vs hydrogen bonds
Polar covalent bonds result from unequal sharing of electrons (O-H)

Nonpolar covalent bonds result from equal sharing (C-H)

Strong bonds that are difficult to break

H - O - H

Interactions between polar molecules

Partial+ charge on one molecule

Attracted to partial- charge on another molecule

Opposites attract

Weak bonds like Velcro

H2O ------ H2O

Covalent VS. Hydrogen bonds
phospholipid structure

O H H H H H H H H

| | | | | | | |

C – C – C – C – C – C – C – C – C – H

| | | | | | | |

OH H H H H H H H H

H2O

Phospholipid Structure

Glycerol backbone

Fatty Acid

H

|

H – C – OH

|

H – C – OH

|

H – C – OH

|

H

Hydroxyl Group - because of the oxygen, there is polarity

Condensation synthesis = the molecules join together with the removal of water.

Carboxyl group- makes the hydrocarbon polar so it can interact with other polar molecules

saturated vs unsaturated fatty acids
Saturated fatty acids are saturated with hydrogens

Results in a “stiff” phospholipid

Unsaturated fatty acids have double bonds between the carbons

Results in a more fluid phospholipid

O H H H H

| | | |

C – C – C – C – C H

| | | |

OH H H H C – C – H

| |

H H

O H H H H H H H H

| | | | | | | |

C – C – C – C – C – C – C – C – C – H

| | | | | | | |

OH H H H H H H H H

Saturated vs. Unsaturated Fatty Acids
slide12
Proportions can change seasonally
  • Usually have the consistency of salad oil
saturation affects membrane fluidity
Saturation Affects Membrane Fluidity
  • Hot springs bacteria - have more saturated fatty acids in their membranes (membranes are more stable at high temperatures)
  • Arctic fish - have more unsaturated fatty acids (membranes are more fluid at low temps.)
fats oils
Fats & Oils
  • Saturated fats are produced by animals and are solid at room temp.
  • Unsaturated fats (oils) are produced by plants and are liquid at room temp.
  • Structurally similar to phospholipids
  • Instead of a phosphate head group, have a third fatty acid
so how do you make a solid margarine from canola oil
So how do you make a solid margarine from canola oil?
  • Plant oils are unsaturated (lots of double bonds & very kinky)
  • Hydrogenation gets rid of the double bonds and makes the oil act like a fat
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!!!!