3: Lipids, Membranes, & Transport Flashcards
What elements are in lipids?
C, H, O
Lipid Definition:
large and varied groups of non-polar molecules that are insoluble in water, but easily dissolve in organic solvents like alcohols
Name two examples of lipids in everyday life:
What state are they at room temp?
- Fats + Oils
- Fats: solid + Oils: liquid
What are the two main groups of Lipids?
- triglycerides
- phospholipids
What are Triglycerides?
type of lipid, made of 3 fatty acids combined with 1 glycerol molecule
______ has 3 (OH) groups, each of which combine with a ____ ____ forming triglyceride
- glycerol
- fatty acid
What are Fatty Acids made up of?
- carboxyl group and a long hydrocarbon group of varying length
Saturated Definition:
Unsaturated Defintion:
- no double bond between C atoms
- one or more double bonds between C atoms
What type of reaction is the formation of a triglyceride?
What type of reaction is the breaking down of a triglyceride?
- condensation
- hydrolysis
How many molecules of water is produced from the formation of a triglyceride?
3
What type of bond forms when triglycerides form?
Where does this bond form?
- ester bond
- between the -OH (hydroxyl group) and the -COOH (carboxyl group) of the fatty acid. It forms between a C and an O when water is lost
What type of bond is an ester bond?
strong covalent
Name 3 roles of Triglycerides:
- storage of energy
- insulation of heat + electricity
- protection
How are Triglycerides suited to their function?
- they have a high ratio of ENERGY STORING Carbon-Hydrogen bonds to Carbon atoms, which makes them a good storage of energy
- they have a low mass to energy ratio, which means they can store a large amount of energy in a small volume, making them a good storage molecule
- they are large, non-polar molecules, which are insoluble therefore causing no osmotic effect, and do not affect the water potential in cells
What are Phospholipids?
- lipids of which are composed of a phosphate and glycerol molecule making up the head, and 2 fatty acid molecules making up the tails
The head of a phospholipid is ______ and _____, however the tails are ______ and _____
- hydrophilic
- polar
- hydrophobic
- non-polar
Why can the hydrophilic head attract with water?
since the phosphate is _______, it _____ other fats
- it is charged
2. charged (-), repels
The hydrophobic tail _____ water
repels
Test for Lipids:
Ethanol Emulsion Test:
1. Add ethanol to sample in dry, clean test tube
2. Shake thoroughly to dissolve the sample
3. Add water and shake gently
4. A milky, white emulsion indicates the presence of a Lipid
Plasma Membranes are present in all cell _______ and ___________ ________
- surface membranes
- organelle membrane
What are the 3 functions of the Plasma Membranes?
- To control the transport of substances into and out of the cell, since they only allow certain molecules to pass through as they are PARTIALY PERMEABLE
- To act as a Receptor Site, to recognise chemicals which need to enter the cell/organelle
- To separate the cell from its environment, allowing different reactions to occur at different conditions by the forming of organelles (compartmentalisation), with different concentrations allowed to be maintained on either side of membranes
What is the Bilayer made out of?
Phospholipids
Explain the structure of the Bilayer?
- two layered structure, with the hydrophilic heads pointing out towards the water on both sides since it is charged, with the hydrophobic tails pointing out towards each other in the middle
What is allowed to pass in between the Phospholipid Bilayer?
- non-polar/lipid soluble/non-charged/smaller molecules
e.g water, O2, CO2, ethanol, lipids
What are ions repelled by?
Not the hydrophilic heads since they are negatively charged, but they are repelled by the non-charged hydrophobic tails
What is the exception that can pass in between the Phospholipid Bilayer?
Water even though it is polar
What does the Phospholipid Bilayer act as a barrier to?
-polar/charged/water soluble molecules e.g amino acids, glucose, Na+ ions
How wide is the Membrane?
7nm
What is an Intrinsic Protein and its function?
- protein floating in the bilayer, that is across the WHOLE membrane (fluid)
- Transport:
1. Hydrophilic Channels (Charges)
2. Carriers (Rest)
What is an Extrinsic Protein and its functions?
- protein floating in the bilayer, that may only be in one layer and not across the whole membrane
- enzymes e.g maltose
- Receptors - binds to hormones
- Antigens - for cell recognition
What are Glycoproteins and its functions?
- short, branching carbohydrate chains attached to proteins in the membrane
- they act as receptors for neurotransmitters and hormones, or antigens
What are Glycolipids and its functions?
- lipid covalently bonded to a carbohydrate
1. act as recognition sites
2. maintain stability of membrane
3. help attach cells to each other, forming tissues
What is Cholesterol and its functions?
- restricts the movement of other molecules making up the membrane
- provides strength and stability to membrane by making them less flexible
- helps prevent the loss of water + dissolved ions from the cell/organelle
What is Fluid Mosaic?
The structure of the plasma membrane, referring to the different molecules (mosaic), can move around (fluid)
The molecules in the Membrane can:
- move around sideways in the membrane
- leave the membrane to form vesicles in the cell’s cytoplasm
- join the membrane from vesicles in the cell’s cytoplasm
Which transports are passive & which are active?
- passive: Diffusion + Osmosis
- active: Active Transport
What does passive mean?
- does not require energy in the form of ATP
Diffusion Definition: (simple)
- the movement of substances from a region of higher concentration to lower concentration, so DOWN a concentration gradient until equilibrium is reached
Why is a ‘dynamic equilibrium’ met after simple diffusion?
since molecules are constantly moving down the concentration gradient, eventually the gradient would be equal
The rate of diffusion across a phospholipid bilayer is _______ _______ to the concentration of substance
- directly proportional
What are the 6 factors of Rate of Diffusion?
- Surface Area of which diffusion occurs: the greater the surface area of the membrane of which the diffusion occurs the greater the rate
- Thickness of exchange surface (NOT MEMBRANE): thinner the surface, faster rate as shorter diffusion pathway
- Conc. Gradient: Larger gradient, higher rate
- Size of diffusing molecule: smaller the size, higher rate
- Temperature: higher temp, higher rate due to KE
- Polarity: non-polar molecules diffuse faster than polar ones
What is Ficks law?
Rate of Diffusion ∝
surface area x concentration gradient / thickness of exchange surface
Why can non-polar substances easily undergo simple diffusion?
- since they are lipid soluble
Why does oxygen rapidly diffuse through the phospholipid bilayer?
- small
- non-polar
Why can water diffuse by simple diffusion, even though it is polar?
- even though it is polar, they are so small they can still diffuse
- this is the case with more molecules
What are the proteins in Facilitated Diffusion?
- intrinsic proteins: Channels (charges), Carriers (rest)
Explain Facilitated Diffusion:
- movement of molecules down the concentration gradient, without requiring energy in the form of ATP
- it moves the polar/large/water-soluble with Channels (charges), Carriers for the rest
- Each intrinsic protein has complementary shapes to its specific molecule, hence only transporting certain molecules
How do you tell whether the structure is a glycolipid or glycoprotein?
- glycolipid can go into the membrane as the have lipids
How does the Protein Channels work?
- channel proteins are tubes filled with water, allowing water-soluble ions to pass through selectively (only open when needed)
How do Carrier Proteins work?
- bind with a molecule, e.g glucose, causing a change in shape of protein allowing the substances to move through
Explain a graph of Rate of Facilitated Diffusion:
- movement down concentration gradient, which is dependent on concentration of substance, to a point
- however, above a certain concentration the rate of diffusion will level off, due to the fact that the number of carrier/channel proteins are limiting
How could cells be adapted for Facilitated Diffusion?
- an increase in number of transportation, intrinsic proteins
What is Osmosis Defintion?
Osmosis is the movement of water across a partially permeable membrane down a water potential gradient (High water potential -> Low water potential)
A concentrated glucose solution would have a ____ Water potential
A dilute glucose solution would have a ____ Water potential
Pure water would have the ____ Water potential
- low
- high
- maximum
What is water potential measured in?
kPa
Why can’t osmosis come into ‘dynamic equilibrium’ from pure water?
- only water is allowed to move down the concentration gradient
What is the maximum water potential?
- pure water
- 0 kPa
All water potential values are ______ until the maximum
negative
Animal Cell in Hypertonic Solution Osmosis:
- a concentrated salt solution has a lower water potential than the animal cell, so water leaves the cell by osmosis, causing the cell to shrink (crenate)
Animal Cell in Hypotonic Solution Osmosis:
- a dilute/pure water will have a higher potential than the animal cell, so water enters the cell by osmosis, causing the swelling and bursting of the cell (osmotic lysis)`
Animal Cell in Isotonic Solution Osmosis:
- same water potential, so no water potential gradient
Why won’t plant cells undergo osmotic lysis?
- cell wall present, which provides high tensile strength preventing osmotic lysis
Plant cell walls are ______ _______
freely permeable
Plant cell in Hypertonic Solution:
- concentrated salt solution would have a lower water potential than the cell, so water leaves the cell through the cytoplasm and vacuole
- this causes the cytoplasm to shrink away from the cell wall, leaving gaps between the cell membrane and cell wall
- these gaps are filled with the salt solution (plasmolysis)
Plant Cell in Hypotonic Solution:
- diluted solution has higher water potential than cell, so water enters the cell by osmosis
- cytoplasm and vacuole will gain some water but cell will not burst due to the high tensile strength of the cellulose cell wall
- this cell is turgid
Plant Cell in Isotonic Solution:
no water potential gradient, no movement of water
Active Transport defintion:
- an active process, movement of molecules against the concentration gradient
Explain Active Transport:
- movement of molecules against the concentration gradient
- active process, so requires ATP
- selective process as it requires specific carrier proteins which will only bind to molecules with complementary shapes
- carrier proteins act as pumps to transport the molecules
- carrier proteins contain an enzyme to hydrolyse the ATP
What factor could reduce the rate of Active Transport?
- any factor that reduces the rate of respiration, due to less ATP
What process do roots uptake ions?
active transport
Why does endocytosis and exocytosis occur?
- some material are in too large amounts to be moved by other processes
How does Endocytosis work?
How does Exocytosis work?
- process of transporting materials into the cell through vesicles
- process of transporting materials out of the cell through vesicles
Does Endocytosis and Exocytosis require ATP?
Yes
