lipids and membranes Flashcards
(81 cards)
1
Q
What are lipids?
A
Lipids are biological molecules that contain the elements carbon, hydrogen and oxygen
2
Q
What elements are lipids made out of?
A
C,H,O
3
Q
What are the properties of lipids?
A
• macromolecules
• insoluble
• dissolve in ethanol
• compact
• they have many carbon bonds
4
Q
What are the roles of lipids?
A
• energy supply
• structural component
• waterproofing
• insulation
• protection
5
Q
How do lipids act as an energy supply?
A
Lipids can be oxidised to provide energy
6
Q
How are lipids structural components?
A
Phospholipids are used in cell membranes
7
Q
How are lipids used in water proofing?
A
Insoluble lipids are used to form water resistant barriers
8
Q
How do lipids act as insulation?
A
Lipids can help retain heat or active electrical insulators
9
Q
How do lipids carry out protection?
A
Delicate organs are surrounded by a layer of fat
10
Q
What do fatty acids consist of?
A
They consist of a carboxyl group (-COOH) group attached to a hydrocarbon chain (R-group)
11
Q
What are lipids made of?
A
Most lipids are made up of a fatty acid combined with an alcohol (usually glycerol)
12
Q
What is a saturated fatty acid?
A
• All carbon atoms are bonded to the maximum number of hydrogen atoms
• no carbon double bonds
• they have higher melting points and our solids at room temperature (fats)
13
Q
What is the structure of a saturated fatty acid?
A
• regular straight chains
• packed parallel
14
Q
What are unsaturated fatty acids?
A
• do not contain the maximum number of hydrogen atoms bonded to the carbon atoms
• has at least one carbon double bond
Lower melting points and usually liquid at room temperature (oils)
15
Q
What is the structure of unsaturated fatty acids?
A
• double bond,
• kinks
• more fluid structure
16
Q
What does monounsaturated mean?
A
One double bond
17
Q
What does polyunsaturated mean?
A
Two or more double bonds
18
Q
What do you use to test for lipids?
A
Ethanol
19
Q
How do you carry out a test for lipids?
A
- Food sample may need to be crushed
- Add 2 cm² of ethanol
- Shake
- Add 2 cm³ of distilled water
- If lipids are present, a Milky white emulsion will be present
20
Q
What type of molecule is a triglyceride?
A
A nonpolar molecule
21
Q
How do triglycerides form?
A
A condensation reaction (esterfication)
22
Q
What is a triglyceride made up of?
A
Glycerol and three fatty acids
23
Q
What bond forms between glycerol and three fatty acids and triglyceride?
A
An ester bond
24
Q
How do you break an ester bond?
A
Hydrolysis reaction
• adding H2O breaks the ester bonds
25
What type of molecule is a phospholipid?
A polar molecule
26
What are phospholipids used for?
A structural component
27
What are phospholipids composed of?
A phosphate, glycerol and two fatty acids
28
How are phospholipids polar?
A hydrophilic head (glycerol and phosphate) and a hydrophobic tail (contains fatty acids)
29
How does the hydrophilic head do its job?
It attracts water
30
How does a hydrophobic tail do its job?
It repels water
31
What does the phospholipid bilayer do?
It stops polar molecules from entering cells
32
How does a phospholipid bilayer work?
Hydrophilic heads face outwards and the hydrophobic tails face inwards
When phospholipids are in water, they arrange themselves into a bilayer (double)
33
What does cholesterol do?
It increases the stability of the cell membrane
Used to make vitamin D and steroid hormones and bile
34
What type of molecule is cholesterol?
A polar molecule
35
What is cholesterol made up of?
The hydroxyl group (OH) is hydrophilic whereas the rest of the molecule is hydrophobic
36
How does cholesterol work?
Cholesterol binds to phospholipids the fatty acid tail causing them to pack closer. This reduces the fluidity of the cell membrane.
At low temperatures, cholesterol keeps phospholipids apart and at high temperatures they keep them together
Low temp - increased fluidity
High temp - decreased fluidity
37
Why is the phospholipid bilayer described as a fluid mosaic model?
Fluid - phospholipid formed bilayer in which the phospholipid molecules are constantly moving
Mosaic- there are proteins of different sizes and shapes and bedded in the phospholipid bilayer
38
What are the components of the fluid mosaic model?
• glycoprotein (sugar chain and attached to a carbohydrate)
• cholesterol
• channel protein (intrinsic protein)
• Carrier protein
• phospholipids (attached to a carbohydrate)
39
How thick is the phospholipid bilayer?
1nm
40
How does the fluid mosaic model transport substances
Hydrophilic heads are outwards and hydrophobic heads are inwards. This creates a hydrophobic centre so that water soluble substances can’t pass through. Fat soluble substances can dissolve in the bilayer and pass directly through the cell membrane.
41
What are intrinsic proteins?
Intrinsic proteins are embedded through both sides of the bilayer
Channel and carrier proteins which transport large molecules and ions across the membrane
42
What are extrinsic proteins?
Extrinsic proteins are present on only one side of the bilayer
These proteins provide support to the membrane or maybe involved in cell signalling
43
What are glycoproteins?
Intrinsic proteins attached to carbohydrates
44
What are glycolipids?
Lipids attached to carbohydrates
45
What are the functions of the plasma membrane?
• Cell adhesion
- Attachment of cells to one another
• partially permeable barrier between cell and its environment
• membrane around organelles
- Barrier between the organelle and cytoplasm
- Divide the cell into different compartments
• transport
- Selectively permeable membrane which controls what gets in and out of the cell
• cell recognition
- Cells of the immune system to recognise self and non-self cells
• cell signalling
- Communication between cells
46
What are the functions of membranes within cells?
• divide cells
• barrier within organelles
• site of chemical reactions
- folded, increasing surface area making chemical reactions efficient
• partially permeable
- Controls what goes in and out
• forms vesicles to transport substances
47
What happens if the permeability of membranes is affected?
Changes to the structure of cell membranes can increase their permeability, allowing more substances to pass through
48
What factors affect the permeability of membranes?
• temperature
• solvents
49
How does temperature affect the permeability of membranes?
Temperature affects the movement of phospholipids in the structure of proteins in the cell membrane
50
Temperature at low temperatures
At low temperatures (below 0 degrees)
• Phospholipids do not have much kinetic energy. They are packed closely together to form a rigid cell membrane, decreasing the permeability of the membrane
51
Temperature at medium temperatures
At median temperature (0-40 degrees)
As temperature increases, the phospholipids have more kinetic energy so they move faster and aren’t pact as closely together. This increases the permeability of the membrane.
52
Temperature at high temperatures
At high temperatures (above 40 degrees)
The phospholipid bilayer breaks down. Channel and carrier proteins denature, meaning they cannot control what enters or leaves the cell. These affects increase the permeability of the membrane.
53
How do solvents affect the permeability of membranes?
Solvents are liquids that have the ability to dissolve substances
When cells are placed in a solvent such as ethanol, the phospholipids dissolve causing the membranes to become fluid. This disrupts the structure of the cell membrane to make it more permeable increase in the concentration of the solvent more further increase the permeability of the cell membrane.
54
What is diffusion?
Diffusion is the net movement of particles from a area of lower concentration to an area of higher concentration through a partially permeable membrane
55
How do particles diffuse with a gradient?
Particles diffuse down a concentration gradient and eventually reach equilibrium in which all particles are evenly distributed (but still moving)
56
What type of process is diffusion?
A passive process
• does not require energy
57
What are the two type types of diffusion?
Simple diffusion and facilitated diffusion
58
What is simple diffusion?
Some molecules can diffuse directly across cell membranes in a process known as simple diffusion
Oxygen and carbon dioxide can diffuse into cells via simple diffusion
59
Why can oxygen and carbon dioxide diffusing into the cells via simple diffusion?
This is because they are
• small- means that they can pass through the spaces between phospholipids
• non-polar- means that they can dissolve in the hydrophobic core of the cell membrane
60
What proteins are used in facilitated diffusion?
Carrier proteins and channel proteins
Each carrier or channel protein is highly specific allowing one or two types of molecule to pass through
61
How do carrier proteins carry out facilitated diffusion?
Transports large molecules against the cell membrane
• a large molecule attaches to a carrier protein
• this causes the carrier protein to change shape
• the carrier protein releases the molecule on the opposite side of the membrane
- Doesn’t require energy
- Amino acids and glucose
62
How to channel proteins carry out facilitated diffusion?
Transport ions across the cell membrane
These proteins form pores in the cell membrane which ions can travel free
63
What factors affect the rate of diffusion?
• temperature
- At higher temperatures particles have more kinetic energy and diffuse faster
• concentration gradient
- The steep of the concentration gradient the faster the rate of diffusion
• thickness of membrane
-The particles travelled shorter distances through thin exchange surfaces so diffuse faster
• surface area
- Larger surface areas mean more particles can cross the membrane at once making diffusion faster
• number of carrier or channel proteins
- The mole of these proteins the fast the rate of facilitated diffusion
64
What is active transport?
Active transport is the movement of particles from an area of lower concentration to an area of higher concentration. This process requires energy from respiration in the form of ATP.
65
What type of process is active transport?
An active process
• energy is needed as particles move up or against a concentration gradient
66
How does active transport work?
• the molecule or ion binds to the carrier protein
• ATP binds for the carrier protein
• hydrolysis of ATP and ADP and phosphate (pi) causes the carrier protein to change shape. This releases the molecule or ion on the opposite side of the membrane.
• the phosphate (pi) is released from the carrier protein causing the carrier protein to return to its original shape ready to be used again
67
What factors affect the rate of active transport?
• Temperature
-Respiration increases very high temperatures in nature carrier proteins decrease in the rate of active transport
• thickness of membrane
-Particles travelled shorter distance distances through thin exchange surfaces so they travel faster
• number of carrier proteins
• rate of respiration
-The more respiration the more ATP available for active transport
68
What is bulk transport?
Large molecules such as enzymes or hormones can’t be transported through channel or carrier proteins. Instead they are moved into and out of cells using another form of active transport known as bulk transport.
69
What are the two types of bulk transport?
Endocytosis and exocytosis
70
What is endocytosis?
Process in which large molecules are transported into cells at once
71
How does endocytosis work?
The cell surface membrane engulfs the material to form a vesicle which is them moved into the cytoplasm then the materials can be processed
Uses ATP
E.g proteins, lipids, some carbs
E.g phagocytosis - uptake of solid materials
72
What is exocytosis?
A process in which large molecules, many molecules,out of cells
73
How does exocytosis work?
Vesicles (mostly formed by the Golgi apparatus) move towards and fuse with the cell surface membrane where materials are released outside the cell
E.g hormones, enzymes, neurotransmitters
74
What are solutions?
Solutions are mixtures made up of a solute (e.g glucose) dissolved in a solvent (e.g water)
75
What is water potential?
The tendency of water to move from one area to another due to osmosis
Water potential is the pressure exerted by water molecules on the membrane surrounding a solution. It is measured in kilopascals.
76
Water potential
High water potential- this means the solution has a higher water concentration
Lower water potential - this means the solution has a low water concentration
Pure water has a water potential of 0 kPa and the value decreases as more sloute is added
77
What is osmosis?
Osmosis is the diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential
Water molecules are small and can diffuse directly through the cell membrane whereas large solute molecules can’t
78
How do water molecules diffuse?
Molecules diffuse down a water potential gradient until the water potential is equal on both sides of the membrane (equilibrium)
79
Osmosis in animal cells
Hypotonic solutions
• a hypotonic solution has a higher water potential than the cell
• water molecules move into the cell
• the cell swells and bursts
Isotonic solutions
• an isotonic solution has the same water potential as the cell
• there is no net movement
• the cell stays the same
Hypertonic solutions
• a hypertonic solution has a lower water potential than the cell
• water molecules move out of the cell
• the cell shrinks
80
Osmosis in plant cells
Hypotonic solutions
• a hypotonic solution has a higher water potential than the cell
• water molecules move into the cell
• the cell swells and becomes turgid
Isotonic solutions
• an isotonic solution has the same water potential as the cell
• there is no movement of water
• the cell stays the same
Hypertonic solutions
• a hypertonic solution has a lower water potential than the cell
• water molecules move out of the cell
• the cell shrinks and becomes plasmolysed
81
What factors affect the rate of osmosis?
• Temperature- more kinetic energy so diffusers faster
• Water potential gradient- the steeper the gradient, the faster the diffusion
• thickness of membrane- short distance so diffuses faster
• surface area- larger surface area means faster osmosis
