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Biology Alevel > Biological Membranes > Flashcards

Biological Membranes Flashcards

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1
Q

Role of cell surface membrane/membranes within cells ?

A
  • creates enclosed space separating internal environ from external environ/ organelles and cytoplasm (COMPARTMENTALISATION)
  • form partially permeable barrier between cell and environment , between cytoplasm and organelles etc
  • site of chemical reactions (membrane within cells)
  • sites of cell signalling
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2
Q

What is the fluid mosaic model?

A

Explains how biological membranes are arranged to from cell membranes

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3
Q

Role and structure of phospholipids ?

A

HYDROPHOBIC TAIL - forms hydrophobic core (inner part of membrane)
HYDROPHILIC HEAD - forms outer part of membrane

Role : acts as a barrier to water soluble substances - non polar hydrophobic tail prevent polar molecules from passing across
- ensures water-soluble molecules such as sugars, amino acids and proteins cannot leak out of the cell

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4
Q

How can phospholipids act as signalling molecules ?

A
  • moving within bilayer to activate other molecules
  • being hydrolysed, releasing water soluble molecules that bind to specific receptors in cytoplasm
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5
Q

Role of Cholesterol?

A

STABILITY OF MEMBRANE
→ controls fluidity of membrane :
- stops phospholipid tails packing too close tgt - stops it from being too rigid at low temps, so cells survive at low temps
- At high temps, they fit in between phospholipid tails - causing phospholipids to pack closer tgt —> less fluid

Makes membrane more impermeable - cholesterol fill in all gaps
Increases mechanical strength/stability of membrane

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6
Q

Role of glycoplipids and glycoproteins ?

A

Stabilise membrane by forming hydrogen bonds with surrounding water molecules
- Contain carbohydrate chains that exist on surface , so can act as RECEPTOR molecules for cell signalling
- some act as ANTIGENS for cell to cell recognition
- site where drugs/hormones and antibodies bind

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7
Q

Role of transport proteins ?

A

Create hydrophilic channels to allow ions/polar molecules to travel through membrane
- allow cell to control what substances enter/leave
2 types :
CHANNEL proteins
CARRIER proteins - change shape to transport substance

Each transport protein is specific to a particular ion or molecule

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8
Q

How does temperature effect permeability of cell membranes ?

A

At low temps : phosphilids don’t have a lot of energy so can’t move around - packed very closelytgt/rigid
- channel proteins and carrier proteins deform= more permeable
Ice crystals may pierce membrane making it more permeable when it thaws

  • phospholipids can move around more as have more energy/not packed tightly tgt- partially permeable
  • temp increases, lipids are more FLUID - INCREASING PERMEABILITY - any diffusion happens at higher rate
  • changes in fluidity are reversible

At high temps , protein denature- disrupts structure of membranes - more permeable
- denaturation is irreversible
- phospholipid bilayer starts to melt =permeable
Water in cell expands and puts pressure on membrane

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9
Q

How does solvent concentration effect permeability of membranes ?

A

Increase permeability , as they dissolve lipids in membranes , so loses structure

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10
Q

What is diffusion?

A

The movement of a substance from high conc to low conc , due to random motion of molecules/ions
- down thee conc gradient

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11
Q

What factors effect rate of diffusion?

A

Steep conc grad : difference in conc of the substance on two sides
Temperature : molecule/ions have more kinetic energy , so move faster = increased rate of diffusion
Surface area : faster rate of diffusion , bc more particles can pass at one time
Thickness of surface - thinner diffusion distance, faster rate of diffusion
Properties of molecules/ions : larger molecules diffuse more slowly as require more energy to move
- non polar molecules diffuse quicker than polar molecules - SOLUBLE in non polar bilayer

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12
Q

What is facilitated diffusion?

A

Using carrier/channel proteins to diffuse through the phospholipid bilayer
- as larger polar molecules/ions cannot pass through phospholipids bilayer by normal diffusion - not soluble in non polar phospholipid bilayer

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13
Q

Function of carrier proteins in facilitated diffusion?

A
  • move large molecules into/out cell down the conc grad
  1. Large molecule attaches to carrier protein
  2. Protein changes shape
  3. Releases molecule on opposite side of membrane
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14
Q

Function of channel proteins in facilitated diffusion?

A

They form pores in the membrane for charged particles to diffuse through
- different channel proteins facilitate diffusion of different charged particles
- channel proteins are ‘GATED’ - part of channel protein can move to open/close the pore

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15
Q

What is active transport ?

A

Movement of molecules/ions through cell membrane from lower conc to region of higher conc using ENERGY from respiration
- against conc grad
-requires carrier proteins - energy is used to change protein shape

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16
Q

Process of active transport ?

A

Molecule attaches to carrier protein , and protein changes shape
- molecule released on other side membrane

Energy used from ATP to move solute against conc grad

17
Q

What is endocytosis ?

A

process by which the cell surface membrane engulfs material, forming a small sac (or ‘endocytic vacuole’) around it
- bulk transport into cells

18
Q

2 forms of endocytosis ?

A

PHAGOCYTOSIS : bulk intake of solid material by a cell
PINOCYTOSIS : bulk intake of liquids

19
Q

What is exocytosis and the process?

A

process by which materials are removed from, or transported out of, cells (the reverse of endocytosis)

  1. Substances to be released (enzymes, hormones or cell wall building materials) packaged into secretory vesicles formed from Golgi body
  2. vesicles travel to cell surface membrane and fuse with cell surface membrane/release contents outside cell or into plasma membrane
    USES ATP
20
Q

What is osmosis?

A

the diffusion of water molecules from a dilute (higher water potential) solution to a more concentrated (lower water potential) solution across a partially permeable membrane
- down water potential gradient

21
Q

Meaning of hypotonic , isotonic and hypertonic in animal cells?

A

HYPOTONIC : solution has higher water potential (dilute) than cell (water moves into cells -> cell bursts)
ISOTONIC : solution with same water potential as cell
HYPERTONIC : solution with lower water potential (concentrated ) than cell (water moves OUT cells , so shrinks )

22
Q

What happens if cell is hypotonic /hypertonic in plant cells ?

A

HYPOTONIC : water moves into cell , so vacuole swells
- vacuole/cytoplasm push against cell wall —> cell is TURGID
- TURGID - provide support/strength to plant

HYPERTONIC : water moves out cell —> becomes FLACCID
Cytoplasm/membrane pull away from cell wall - plasmolysis

23
Q

PRACTICAL : permeability of cell membrane

A
  1. Cut 5 equal pieces of beatroot/rinse to remove pigment caused by cell damage when cutting
  2. Place pieces in 5 test tubes , each with 5cm cubed of water
  3. Place each test tube in water bath at different temps for same length of time
  4. Remove pieces from liquid
  5. Use colorimeter to measure absorbance —> higher the permeability , more pigment released , higher absorbance
24
Q

PRACTICAL : investigate water potential

A
  1. Prepare sucrose solutions by serial dilutions (0M, 0.2M , 0.4M , 0.6M, 0.8M, 1.0M)
  2. Use cork borer to cut potatoes into same sized pieces
  3. Measure mass of the potatoes (when in groups of 3)
  4. Place each group in one solution /leave for 20 mins
  5. Remove/pat dry with paper towel
  6. Weigh each group again/calculate % mass change /plot graph
25
Q

PRACTICAL : investigate diffusion in model cells

A
  1. Make agar jelly with phenolpthalein/sodium hydroxide
  2. Fill beaker with HCl /use scalpel to cut out cubes of jelly /add to acid
  3. Cubes will turn colourless , as acid diffuses into jelly/neutralises NaOH

Can use this to investigate factors like :
SUFRACE AREA : cut the jelly into different sized cubes /Time how long it takes to go colourless
CONC GRAD : use different concs of HCL /Tim how long it takes to go colourless
TEMPERATURE : put HCL into test tubes , in different water baths /put jelly /time how long to takes to go colourless

26
Q

Role of cell membrane receptors?

A
  • receptor proteins have specific shapes,which only messenger molecules with a complementary shape can bind to
  • cells that respond to particular messenger molecules are called TARGET CELLS
27
Q

Why can’t polar/large molecules and ions move through membrane by normal diffusion?

A

Cannot diffuse through fatty acid tails

28
Q

Why does the ‘fluid mosaic model’ describe cell membranes as ‘fluid’ and ‘mosaic’ ?

A

Fluid becuase :
- phospholipids/proteins can move around via diffusion
- phospholipids move sideways,within their own layers
- many different types of proteins interspersed throughout the bilayer move about within it

‘mosaics’ because:
The scattered pattern produced by the proteins looks like a mosaic when viewed from above

29
Q

Why is active transport important?

A
  • reabsorbtion of useful molecules/ions into blood
  • loading of inorganic ions from soil into root hairs
30
Q

Edocytlsis process?

A

Some substance too large to be taken into cells by carrier proteins
(Proteins,lipids, carbs)
- cell surrounds substance with section of its plasma membrane
- membrane pinches off to form vesicle inside cell
USES ATP

31
Q

Examples of the role of cell membrane receptors in cell signalling?

A

GLUCAGON :
Hormone released when not enough glucose in blood
- bind to receptors on liver cells - cause liver cells to break down glycogen to glucose

ANTIHISTAMINES (drug):
Antihistamines block histamine receptors on cell surface - prevent histamine from binding to the cell/ stop inflammation

Biology Alevel (25 decks)

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