3. Lipids, membranes and transport Flashcards
What elements are in Lipids
C H O
What are lipids
Group of non-polar molecules
Insoluble in water
dissolve easily in organic solvents
What are the important groups of lipids
Triglycerides and phospholipids
What is a triglyceride
Made of 3 fatty acids and 1 molecule of glycerol
How is a triglyceride formed
Glycerol has 3 OH- groups.
Each bind to a fatty acid
Condensation reaction
Produce 3 molecules of H2O
Ester bonds between OH and COOH
What is a fatty acid made from
A COOH- group and a long hydrocarbon chain (Unsaturated or Saturated)
Why are triglycerides not classified as polymers
They are not made of monomers.
They are made of 2 different types of molecules
What are the biological roles of triglycerides
Storage of energy
Insulation - electrical and heat
Protection
How do the structure and properties of a triglyceride relate to its function
High ratio of energy storing C-H bonds to C atoms = good source of energy
Low mass to energy ratio = Good storage molecules as lots of energy stored in small volume
Large, non-polar, insoluble in water molecules = no osmotic effect and dont effect water potentiels
What is a phospholipid
Lipids where one fatty acid is substituted for phosphate group
- Polar/hydrophilic head (Glycerol and phosphate)
-2 Non-Polar/hydrophobic tails (Fatty acids)
What is the test for lipids
Ethanol emulsion test
- Add ethanol to the sample to be tested
- Shake thoroughly to dissolve any lipid in sample
- Then add water to sample and shake gently
-A milky white emulsion indicates the presence of lipid
What are the 3 functions of plasma membranes
- Control the transport of substances into and out of cell or organelle - Partially permeable
- Act as a receptor site - Recognise chemicals that need to enter the cell
- Separate off the cell from the environment and the different reactions - Different concs can be maintained
What molecules do plasma membranes not let through
Water-soluble
Charged
Polar
What molecules are in a membrane structure
- Phosphlipids
- Membrane proteins
-Glycoproteins - Glycolipids
-Cholesterol
What do phospholipids do in the membrane structure
Form a bilayer
Hydrophobic tails point towards eachother
Hydrophilic head point out into the water
What do membrane proteins do in the membrane structure
Float about in bilayer - fluid mosaic structure
May be in one layer (Extrinsic) or across the whole membrane (Intrinsic) .
May be fixed in one place or float about
Often have hydrophilic channels in the middle
What is the function of an Intrinsic protein
Transport - channels and carriers
What is the function of extrinsic proteins
Enzymes
Receptors
Antigens
What is a glycoprotein and its function in the membrane structure
Short, branching carbohydrate chains attached to proteins in the membrane.
Act as receptors for hormones and neurotransmitters or antigens
What is a glycolipid
Made of a carbohydrate covalently bonded to a lipid.
Act as recognition sites
Help maintain stability of the membrane and help cells attach to one another forming tissues
What is cholesterol
Restrict the movment of other molecules in the membrane
Increase the strength and stability of membranes by making them less flexible
Prevents loss of water and dissolved ions
What is the fluid mosaic structure
Fluid = All different molecules can move
Mosaic = Different types of molecules. Some can float within the bilayer
What can molecules in the plasma membrane do
-Move sideways
-Leave the membrane to form vesicles
-Join memranes from vesicles
Why does should a membrane be fluid
Cells can change their shapes e.g phagocytes
What are 4 ways substances can be exchanged
Diffusion
Osmosis
Active transport
Endo/Exocytosis
What is diffusion
The movement of substances from a region of higher concentration to a region of lower concentration down a concentration gradient
How does surface area affect rate of diffusion
The greater the surface area of the membrane over which diffusion occurs the greater the rate of diffusion
How does the thinckness of exchange surface affect the rate of diffusion
the thinner the surface the faster the rate of diffusion (shorter diffusion pathway)
How does the conc gradient affect the rate of dissusion
the steeper the gradient the faster the rate of diffusion
How does the size of the diffusing molecule affect rate of diffusion
the smaller the molecule the faster the rate of diffusion (can diffuse through the phospholipid bilayer easier)
How does temperature affect the rate of diffusuion
the higher the temperature the faster the rate of diffusion (more kinetic energy)
How does water solubility/ polarity affect the rate of diffusion
Molecules that are water-soluble/polar/ charged generally diffuse slower than lipid-soluble/non-polar/uncharged ones (non-polar can pass through hydrophobic region of the phospholipid bilayer easier)
What is Ficks law
Rate of diffusion (is proportional to) (SA x difference in conc) / thickness of exchange surface
How do you increase the rate of diffusion
- Maximise the SA
- Maximise concentration difference
- Minimise the thickness of exchange surface
What is simple diffusion
Diffusion of substances directly across the phospholipid bilayer
Molecules that are non-polar and smaller can diffuse through
What is facilitated diffusion
Molecules diffuse through bilayer through intrinsic proteins.
The substances are specific to the proteins
Passive
Moves charges, polar or hydrophilic substances.
Channel proteins for ions, carrier proteins for others
What is osmosis
the movement of water across a partially permeable membrane down a water potential gradient from higher (less negative) to lower (more negative) water potential.
What is water potentiel
The tendency for water to move from one place to another
Measure in KPa
Pure water has WP of zero, all others are negative
What happens to an animal cell in a hypertonic solution
lower water potential than the cell
Water leaves cell
cell shrinks (crenate)
What happens to an animal cell in a hypotonic solution
Higher WP than cell
water enters cell
Cell swells and bursts - osmotic lysis
What happens to an animal cell in isotonic solution
Same WP as cell
no net osmotic movment
What happens to a plant cell in hypertonic solution
Lower WP than cell
Water leaves cytoplasm and vacuole
Cytoplasm shrinks away from cell wall and leaves a gap
Gap filled with concentrated salt solution
Plasmolysis
What happens to a plant cell in a hypotonic solution
Higher WP than cell
water enters the cell
Cytoplasm and vacuole gain water
Due to high tensile strength of cell wall - cell will not burst
Turgid
What happens to a plant cell in an isotonic solution
Same WP
No net osmotic movment
What is active transport
Needs ATP
Movment against a concentration gradient
Needs specific proteins carriers/ pumps
Factors affecting respiration affect AT
When does endo/exocytosis occur
When a cell needs to transport large amounts of materials across their plasma membrane
What is endo/exocytosis
Cells make containers out of the plasma membrane
Makes vesicles
Endocytosis is importing materoials into the cell
Excocytosis is exporting materials out of the cell
Both require ATP
