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Lipids/ Transport Across Membrane Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are lipids

A

Non-polar, hydrophobic
Made up of carbon, hydrogen, oxygen (same as carbs)
No general formula, lower proportion of O:H (diff from carbs)
Insoluble in water, soluble in organic solvents (ethanol, ether and trichloromethane, chloroform) -> extracted using OS

Classification of lipids
1. Simple (joining of fatty acids to an alcohol by ester linkages) -> TRIGLYCERIDES
2. Complex (lipid and non-lipid component) -> PHOSPHOLIPIDS and GLYCOLIPIDS
3. Steroids (carbon skeleton consisting of 4 fused rings) and sterols (steroid nucleus+OH hydroxyl group; eg cholesterol, sex hormones)

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2
Q

What are simple and complex lipids made out of

A

Glycerol
- alcohol with 3 hydroxyl groups
- soluble in water (OH groups interact with water)

Fatty acids
- long chained carboxylic acids containing an even number of C atoms (14-22)
- consists of long hydrocarbon chain (hydrophobic) and a carboxylic acid [-COOH] (hydrophilic)
- differ in degree of saturation, length of hydrocarbon chain = affect melting point

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3
Q

Saturated fatty acids vs unsaturated fatty acids + effect on melting point

A

Saturated
- No C=C carbon double bond
- each carbon has maximum number of H atoms attached
- eg stearic acid

Unsaturated
- Have C=C carbon double bond
- C=C double bond creates a “kink” in hydrocarbon tail

The greater the number of C=C, the greater the number of kinks in the hydrocarbon tails of the molecule = weaker IMFA between fatty acid molecules = lesser energy needed to weaken hydrophobic interactions = lower mp

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4
Q

How does hydrocarbon chain length affect melting point

A

The longer the hydrocarbon tail (greater number of C atoms), the higher the surface area available for hydrophobic interactions between hydrocarbon chains = higher amount of energy needed to weaken hydrophobic interactions between the hydrocarbon chains of the fatty acids

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5
Q

How is a triglyceride formed

A

1 glycerol (-OH) + 3 fatty acids (-COOH) via ester bonds (-COO-)

Formation of ester bonds between glycerol and fatty acids via removal of 1H2O = condensation reaction

Due to condensation reaction, no polar groups present in triglyceride = hydrophobic although fatty acids and glycerol are hydrophilic

3 fatty acids can differ = different properties (eg mp)

RECALL : DRAWING

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6
Q

How are phospholipids formed

A

1 glycerol +2 fatty acids + 1 phosphate group (-ve charged) = 3 condensation reactions

Glycerol + 2 fatty acids joined via condensation reactions (2 ESTER bonds formed, 2H2O produced)

Glycerol + phosphate group joined via condensation reaction (PHOSPHOESTER bond formed, 1H2O produced)

Major component of cell membrane

Ampithatic (hydrocarbon tails are hydrophobic; phosphate heads are hydrophilic)

Additional small molecules (charged/polar) can be linked to phosphate group = variety of phospholipids

Hydrophobic hydrocarbon tails = saturated/unsaturated/mixture = affect membrane fluidity

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7
Q

Triglyceride function

A
  1. Storage form of energy
    - long term
    - large & uncharged = insoluble in water -> can be stored in large amounts w/o affecting wp of cells + prevented from diffusing out of cells
    - yields twice the amt of energy as carbs = reduced weight but more energy
    - lipids are much more reduced (more C-H bonds, lesser C-OH/C=O) = to fully oxidise lipids to co2 and h2o, more oxidation steps required = more reduced NAD and FAD formed = more ATP formed
  2. Source of metabolic water
    - formation of ester bond releases water
    - hydrogen part of triglyceride and carb molecules yields water upon oxidation -> triglyceride has 2x more H atoms than carbs
  3. Good thermal insulator
  4. Provides buoyancy for aquatic mammals
  5. Protective layer for delicate internal organs (eg kidney)
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8
Q

Phospholipid function

A
  1. Constitutes basic bilayer structure of membrane due to amphipathic nature
    - polar hydrophilic heads point outwards, interact w aq environment and cytoplasm; hydrophobic hydrocarbon tails point inwards = hydrophobic core
    - ensures stability of membrane as polar heads interact w aq env via H bonds
  2. Separates cell content from surroundings = separate entity
  3. Compartmentalisation within cell = formation of specialised organelles as enzymes and reactants are enclosed within specific compartments
  4. Allows fat soluble molecules & small molecules (co2, o2) to move across easily; acts as barrier to most water-soluble molecules & ions (hydrophobic core)
  5. Provides fluidity to membrane
  • variations in phospholipids (degree of saturation/length of fatty acids) affect fluidity and hence permeability of membrane
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9
Q

Biochemical test for lipids

A

Solid sample
1. Crush food sample and place in dry test tube
2. Add ethanol to 2cm3 above level of sample, shake throughly
3. Allow solid to settle (about 3mins) to allow lipid to be extracted
4. Decant ethanol into another test tube
5. Add 2cm3 deionised water to second test tube
6. Make observations

Liquid sample
1. Add few drops of liquid food sample to test tube
2. Add 2cm3 ethanol and shake throughly
3. Add 2cm3 deionised water
4. Make observations

Observations
1. Colourless, no emulsion = lipids not present
2. Layer of cloudy white suspension formed at top of solution = lipids present

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10
Q

Explain the Fluid Mosaic Model of the cell membrane

A

Fluid: ability of phospholipids and proteins in cell membrane to move laterally within a monolayer (LATERAL MOVEMENT)

Mosaic: patchwork distribution of proteins within phospholipid bilayer

Membrane is held together mainly by hydrophobic interactions between hydrocarbon tails of phospholipids

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11
Q

Size of cell membrane

A

Thickness of 5-10nm, average 7.5nm

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12
Q

Components of cell membrane

A
  1. Phospholipids
  2. Proteins
  3. Cholesterol
  4. Carbohydrates (attached to some lipid and protein molecules= glycolipids & glycoproteins; extend from EXTERIOR surface of csm only)
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13
Q

Overall structure of cell membrane

A
  • Phospholipids form a bilayer structure (amphipathic nature; polar heads with hydrophobic tails)
  • Proteins scattered in patchwork arrangement within bilayer; either loosely attached to phosphate heads or embedded in bilayer
  • Phospholipids and proteins exhibit lateral movement within bilayer
  • Asymmetric cell membrane : 2 sides differ in lipid & protein composition (ext=more proteins -> receptors for attachment of signal molecule)
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14
Q

Interactions that stabilise cell membrane

A

Hydrophilic interactions exist between
- hydrophilic portions of proteins and phosphate groups of phospholipids with aqueous medium of cytoplasm and ext env
- carbohydrate antennae (hydrophilic) and aq medium outside of cell

Hydrophobic interactions exist between
- hydrophobic portions of proteins and hydrocarbon tails of phospholipids

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15
Q

Roles and functions of cell membrane

A
  1. Act as barrier between contents of cell and ext env = separate entity, constant env within cell
  2. Regulate passage of substances into and out of cells (selectively permeable)
    - diffusion of o2 and glucose into cells for respiration (ATP)
    - excretion of waste (co2)
    - secretion of extracellular enzymes
    - maintains suitable pH and ionic concentration within cell for enzyme activity
  3. Cellular communication with external environment
    - membrane contains receptors (glycoproteins) and enzymes that allow cells to respond to chemical messengers (hormones)
    - glycoproteins and glycolipids act as receptor sites for cell to cell recognition (self vs other) for immune response
  4. Maintains structural relationships with neighbouring cells (cell to cell adhesion for tissue formation)
  5. Within cell: compartmentalisation = formation of organelles
    - set up of different conditions in organelles to provide optimum conditions for enzymes
    - membrane bound organelles = structural adaptations eg infolding of membrane to increase SA for attachment of more proteins/enzymes
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16
Q

Explain how the structure of the membrane allows for compartmentalisation

A
  • Made up of phospholipid bilayer
  • Phosphate heads are hydrophilic and interact with aq env both inside and outside of organelle
  • Hydrocarbon tails form hydrophobic core which prevents water-soluble particles to pass through
  • Membrane has specific protein channels that transport specific water-soluble particles
  • Controlled transport of substances across membrane via protein transporters
17
Q

Components of cell membrane and its function : cholesterol

A

How it fits
- Has a hydrophilic region (-OH) and hydrophobic region
- Fits between phospholipid molecules: -OH + phospholipid heads ; hydrophobic portion fits between fatty acid hydrocarbon chains

Function
1. Mechanical stability of membrane
2. Maintains membrane fluidity when temperature changes
3. Reduces uncontrolled leakage by diffusion of certain molecules and ions through membrane -> diverted into proper channels where movement is regulated instead (eg myelin sheath in nerve cells, prevention of leakage of ions, else nervous transmission slows down)

18
Q

Components of membrane : proteins

A
  1. Peripheral proteins (extrinsic)
    - loosely attached at polar surfaces of phospholipids/proteins; found on interior/exterior of cells
  2. Integral proteins (intrinsic)
    - either partially penetrate or span the entire membrane (transmembrane proteins)
    - strongly attached
    - have hydrophilic and hydrophobic regions
19
Q

Functions of proteins in cell membrane

A

Functions
1. Transport proteins (water-soluble ions, glucose, AAs, proteins)
- cannot enter via diffusion = move through carrier/channel proteins or protein pumps

  1. Energy transducer
    - electron carriers and ATP synthase allow transport of electrons and protons respectively during respiration and photosynthesis for ATP synthesis
  2. Cell surface receptor
    - binds with chemicals (hormones), allows cell to respond to external stimuli eg G protein linked receptor
  3. Enzymes
  4. Structural support
    - integral proteins attached to extracellular matrix gives cell membrane stronger framework
20
Q

Components of cell membrane + function : carbohydrates

A

Short carb chain (oligosaccharides) + proteins/lipids = glycoproteins/glycolipids

Attached to exterior surface of membrane, form antennae layer (5-10nm) = GLYCOCALYX (visible on external surfaces of membranes)

Functions
1. Orientation of membrane structures
- carbs are hydrophilic, help orientate glycoproteins/lipids to face exterior
- forms H bonds with water = stabilised structure

  1. Cell communication (cell-to-cell recognition : recognition of same cell type for immune responses)
  2. Structural relationships (glue for cell-to-cell adhesion for tissue formation)
21
Q

Significance of fluidity of membrane

A

Allows membrane to fuse
- important for self-repair/sealing and fusion of transport vesicles to organelles or cell surface membrane;
- ease of binding of hormones to surface receptors;
- activity of membrane-bound enzyme and transport of enzyme

Decreased fluidity = decreased ability to fuse, inactivation of membrane-bound enzymes and transport proteins = reduction in membrane permeability

22
Q

Factors affecting fluidity of membrane

A
  1. Temperature
  2. Length of hydrocarbon tails/chains of phospholipids
  3. Degree of saturation of hydrocarbon chains of phospholipids
  4. Presence of cholesterol
23
Q

Factors affecting fluidity of membrane : temperature

A

Increase temp = increase KE of phospholipids = breaks of intermolecular interactions and bonds between components = increase fluidity

24
Q

Factors affecting fluidity of membrane : length of hydrocarbon tails/chains of phospholipids

A

Increase length = greater/more intermolecular interactions between hydrocarbon tails = decrease fluidity

25
Q

Factors affecting fluidity of membrane : degree of saturation of hydrocarbon chains of phospholipids

A

More unsaturated = more kinks = no close packing of phospholipids = weaker intermolecular interactions between chains = more fluid

26
Q

Factors affecting fluidity of membrane : presence of cholesterol

A

Acts as a buffer to resist changes caused by temperature, helps membrane achieve optimal fluidity

Low temp : cholesterol disrupts close packing of phospholipids = lowers temp at which membrane solidifies = increase fluidity

High temp: hinders movement of phospholipids by interacting with hydrocarbon chains = decrease fluidity

27
Q

Methods of transport across membranes

A
  1. Simple diffusion
  2. Facilitated diffusion
  3. Osmosis
  4. Active transport
  5. Bulk transport
28
Q

Transport across membrane : simple diffusion

A

Net movement down concentration gradient till equilibrium is achieved

Passive transport, no energy expenditure by cell needed -> energy is provided by KE of particles

Small, non-polar, lipid soluble, hydrophobic substances (o2, co2, lipid) enter cell via simple diffusion

29
Q

Facilitated diffusion

A

Net movement of particles down concentration gradient; energy from ATP hydrolysis not required

Transport polar, water soluble molecules

Protein molecules embedded in plasma membrane needed : charged particles (ions) and polar molecules (glucose) are insoluble in lipids = cannot pass through hydrophobic core of phospholipid bilayer; protein channels and carriers shield them

Occurs via
1. Channel proteins
2. Carrier proteins

30
Q

Facilitated diffusion - channel proteins

A

Form water-filled pore in membrane, lining is hydrophilic so water-soluble substances (ions) can pass through

Some channels open and close like gates
Open: appropriate signal received (binding of hormone or ligand to site on channel protein etc)

31
Q

Facilitated diffusion - carrier proteins

A

Each type of carrier protein has 1/more binding sites for a specific solute (molecules, ions)
Solute is transported via conformation change of protein

Two conformational forms
1. Binding site of solute is exposed to outside of cell
2. Exposed to inside of cell

Reversible conformation change
- Binding of solute to carrier protein on one side of membrane triggers conformational change in carrier protein = exposure of binding site to other side of membrane, subsequent release of solute = reverts back to original conformation

32
Q

Facilitated diffusion : characteristics of transport proteins

A
  1. Specific (can only transport one substance/ group of structurally similar ones across membrane)
  2. Can be saturated (only a certain number of each type of transport protein in plasma membrane = all transport protein shld b utilised)
  3. Can be inhibited (by molecules which are structurally similar to normal diffusing substances = competition)
33
Q

Transport across membrane : osmosis

A

Net movement of water molecules (polar, uncharged) from region of higher wp to lower wp through a selectively permeable membrane

Water crosses cell membranes by
1. Movement through lipid bilayer (via osmosis due to small size, but polar nature = rate is slow)
2. Movement through water channels called aquaporins (integral membrane proteins)

34
Q

Transport across membrane : active transport

A

Movement of polar, water-soluble ions/molecules across a membrane from a region of lower concentration to a region of higher concentration (against concentration gradient) by means of specific transport proteins and with expenditure of energy (ATP hydrolysis) by cell

Allows cell to take up nutrients/get rid of waste

Differs from facilitated diffusion by:
1. Carrier proteins for AT can bind w molecule/ion at ONE SIDE of the membrane (vs both for fd)
2. Conformation change of protein requires energy input

Carrier proteins pump molecules/ions from one side of membrane to the other = PROTEIN PUMPS (eg proton H+ and Na+-K+ pumps)

35
Q

Transport across membrane : bulk transport

A

For substances that are too large to cross membrane via transport proteins (proteins, polysaccharides)

Is the transport of material into/out of cell by enclosing material within a fluid-filled membrane-bound sac called a vesicle, requires ATP

Two types
1. Exocytosis (materials released to outside of cells)
2. Endocytosis (materials taken into cells)

36
Q

Explain how the structure of the glucose channel protein allows it to be embedded within a membrane and perform its function. [3]

A

The amino acids of the channel protein are arranged such that the hydrophilic R groups project into the channel/ hydrophilic(polar) amino acids forms the region of the polypeptide chain surrounding the pore;

While the hydrophobic R groups face/interact with the hydrocarbon tails of the phospholipids bilayer;

The hydrophilic amino acids also face/interact with the polar heads of the phospholipids;

And polar water molecules of the extracellular and intracellular environment;

37
Q

Transport across membrane : bulk transport - exocytosis

A

Exocytosis (materials released to outside of cells)
- secretion of extracellular enzymes, hormones, antibodies, removal of waste products of digestion, insulin
- vesicles (containing particles) pinched off from Golgi apparatus move towards cell surface -> fuses with plasma membrane -> vesicle opens to exterior -> contents leave cell

38
Q

Transport across membrane : bulk transport - endocytosis

A

Endocytosis (materials taken into cells)
- (I) Pinocytosis [cell drinking] (not selective)
cell takes up droplets of extracellular fluids in tiny vesicles, any solutes dissolved in fluid is taken in

  • (II) Phagocytosis [cell eating] (selective)
    engulfs large particle by sending out pseudopodia (extensions of cytoplasm) to surround particle -> ends of pseudopodia join, food vacuole (phagosome) formed within cell -> lysosome fuses with phagosome = phagolysosome -> hydrolytic enzymes digest large particles
  • (III) Receptor mediated endocytosis (selective)
    enables cell to take up large quantities of specific substances even though substance may not be concentrated in extracellular env
    extracellular macromolecules bind to cell surface receptor proteins embedded in membrane
    proteins (clathrin) form a coated pit at cytoplasmic side -> helps in formation of coated vesicle within cytoplasm
    once vesicle is formed within cytoplasm, clathrin disassembles (uncoating), is recycled

biology (13 decks)

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