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Biology > Biological Membranes > Flashcards

Biological Membranes Flashcards

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1
Q

What molecules are allowed through the lipid bilayer? What does this make it?

A
  • small, polar molecules
  • dissolve in lipid layer and pass through
  • special protein channels or carrier proteins

Partially permeable

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2
Q

What are the roles of plasma membranes?

A
  1. separates cell’s (organelle) components from external
  2. regulates transport of materials into and out
  3. contain enzymes
  4. antigens for cell recognition
  5. cell signalling
  6. receptors as site of cell signalling and communication
  7. chemical reactions
  8. can form vesicles for transport
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3
Q

Describe the fluid mosaic model

A

Phospholipid bilayer. Bilayer is fluid because phospholipids are constantly moving with proteins floating in it making a mosaic pattern

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4
Q

Describe how cholesterol achieves role of stability in the cell membrane

A

Cholesterol

  • small steroid, hydrophobic, fit in between tails
    1. binds to tails causing them to pack closer together, less fluid and more rigid
    2. makes barrier complete so substances can’t easily pass through
    3. maintain mechanical stability
    4. resist effects of temperature changes
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5
Q

Describe the role of transport in the cell membrane

A

Channel proteins
- integral proteins
- surrounded by water
1. allows movement of some substances (small, hydrophilic, ions)
Carrier proteins
- change their shape
1. moves large ions and molecules by active transport

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6
Q

Describe the role of recognition and communication in the cell membrane

A

Glycoproteins
- carbohydrate chain attached to protein
- made of glycocalyx, very hydrophilic
1. cell signalling as receptors
2.bind cell cells together, helps cell interact with watery environment
Glycolipids
- phospholipid attached to a carbohydrate
1. cell signalling as receptors
2. some binding

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7
Q

Describe the role of metabolic in the cell membrane

A

Enzymes

  • globular proteins control rate of reaction
    1. speeds up some reactions
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8
Q

Discuss other cell membranes

A
  • neurones: myelin sheath (more lipid)
  • white blood cells: protein receptors so that they can recognise antigens
  • root hair cells: carrier proteins AT nitrate ions
  • mitochondria: electron carriers and hydrogen channels ATP synthase (more protein)
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9
Q

Describe simple diffusion

A
  • the net movement of molecules from a region of high concentration to a region of lower concentration down a concentration gradient
  • small molecules and lipids (dissolve in bilayer) can pass through
  • water diffuses across but when a high rate of water movement is required aquaporins allow water to cross
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10
Q

Explain how the concentration gradient is maintained

A

Example

  • oxygen diffusing into the cytoplasm of respiring cells then diffuses into mitochondria and used for an aerobic respiration
  • CO2 diffuse into the palisade mesophyll cells of a plant leaf will then diffuse into chloroplasts used for photosynthesis
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11
Q

Describe the factors that affect the rate of simple diffusion

A
  1. temperature - molecules have more kinetic energy so rate increases
  2. diffusion distance - slower the rate
  3. surface area - more diffusion across larger SA
  4. size of diffusing molecule - smaller molecules diffuse more rapidly
  5. concentration gradient - steeper grad, faster the diffusion
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12
Q

Describe facilitated diffusion

A
  • the net movement of molecules from a region of high concentration to a region of low concentration assisted by channel or carrier proteins down a concentration gradient
  • small polar molecules can’t interact with phobic part, they must diffuse through channels
  • trans membrane carrier proteins allow glucose through (it is too big)
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13
Q

Define osmosis

A

the net diffusion of water molecules by diffusion from a region of high water potential to a region of low water potential across a partially permeable membrane down a water potential gradient

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14
Q

Define water potential

A

The measure of how free the water molecules are to move from one area to another. A type of pressure measured in kPa

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15
Q

Describe what happens to animal and plant cells in a hypotonic solution (pure water)

A

Enters the cell (more negative)
Animal Cell – becomes haemolysed (cytolysis)
Plant Cell – cell wall prevents bursting. The membrane pushes against the cell wall and the cell becomes turgid

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16
Q

Describe what happens to animal and plant cells in a hypertonic solution (low water potential)

A

Leaves the cell (less negative)
Animal Cell – shrinks and appears wrinkled and the cell becomes crenated
Plant Cell – the membrane pulls away from the cell wall and the cell becomes plasmolysed and flaccid (suffer dehydration and metabolism can’t proceed as enzyme catalysed reactions need to be in solution)

17
Q

Outline what happens to animal and plant cells in an isotonic solution

A

Equal moving in and out
Animal cell - normal
Plant cell - flaccid

18
Q

Define active transport

A

The movement of substances against their concentration gradient from low to high concentration of that substance across a cell membrane using ATP and protein carriers

19
Q

Explain how carrier proteins work

A

Carrier proteins - sites that combine reversibly with a certain ion or solute molecule, there is a region that binds to and allows the hydrolysis of ATP (enzymes) The energy changes the proteins conformation shape and carriers one side of the cell membrane to the other

20
Q

Explain how anti ports work

A

3x Na and 2x K

  1. the sodium potassium pump binds 3 Na and a molecule of ATP
  2. splitting ATP (hydrolysis into ADP and Pi) provides energy to change the shape of the channel, Na move out of channel
  3. Na ions released to outside the membrane and the new shape of the channel allows 2 K ions to bind
  4. release of the phosphate allows the channel to revert to its original form, releasing K ions to the other side
21
Q

Explain neuron cell membranes

A

Protein channels and carriers covering the long axon allow the transport of ions to bring the conduction of electrical impulses along their length
They have a myelin sheath of flattened cells around them several times to give more membrane layers and to insulate the electrical impulses

22
Q

What is endocytosis?

A
  • a segment of the plasma membrane surrounds and encloses the particle and brings it into the cell, enclosed in a vesicle
  • phagocytosis = solid pino(endo)cytosis = liquids
  • ATP is needed to provide energy to form the vesicles and move them using motor proteins along cytoskeleton threads into the cell interior
23
Q

What is exoxytosis?

A
  • a vesicle containing the large molecule is moved towards and then fuses with the plasma membrane
    1. a membrane bound vesicle containing the substance to be secreted is moved towards the cell surface membrane (by motor proteins along the cytoskeleton = ATP)
    2. the cell surface membrane and the membrane of the vesicle fuse together
    3. the fused site opens, releasing the contents of the secretory vesicle
  • synapses, vesicle is brought to presynaptic membrane, fuse, neurotransmitter chemicals released into synaptic cleft
24
Q

Explain the affect of decreased temperature on membrane structure

A
  • saturated fatty acid acids become compressed
  • unsaturated fatty acids maintain fluidity as the kinks in their tails push the other phospholipids away
  • cholesterol also buffers this as it prevents phospholipid molecules packing too tightly
  • molecules have lowered kinetic energy so move slower
25
Q

Explain the affect of increased temperature on membrane structure

A
  • molecules have more kinetic energy so move faster
  • membrane fluidity increases as phospholipids have more kinetic energy
  • permeability increases
  • affects way that proteins in membrane are positioned (drift sideways which could alter rate of reactions)
  • fluidity may affect the infolding of the membrane during phagocytosis
  • affect ability of cell to signal to other cells during exocytosis
  • cholesterol acts as a temperature buffer as it provides more stability reduces increase in fluidity
26
Q

What is the effect of solvents on phospholipids?

A

Organic solvents such as acetone and ethanol will damage cell membranes as they dissolve lipids

27
Q

Explain the affect of temperature on proteins

A
  • cause atoms to vibrate and this breaks the hydrogen bonds and ionic bonds
  • tertiary structure changes and can’t change back = denatured
  • cytoskeleton threads becomes denatured then the plasma membrane will begin to fall apart, fully permeable
  • enzymes will denature, active site changes , rate of reaction slows
28
Q

What is the effect on temperature on beetroot cell membranes

A
  • beetroot large vacuole surrounded by tonoplast
  • inside are water soluble pigments called betacyanins, betalain
  • if heated, pigment will leak out
  • amount of leakage of red pigment is proportional to the degree of damage to the beetroot plasma and tonoplast (colorimeter)

Biology (12 decks)

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