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A Level Biology Paper 1 > Transport Across Membranes > Flashcards

Transport Across Membranes Flashcards

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1
Q

Explain the orientation of phospholipids in the membrane

A

The phosphate group has a negative charge, so hydrophilic
So orientate outwards towards other polar molecules such as aqueous cytoplasm or extracellular fluid

Hydrophobic fatty acid tail orientated toward the middle away from water

Forming a self sealing double membrane (bilayer)

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2
Q

Why is it called the fluid mosaic model

A 
Model = representation of a structure
Fluid = phospholipid bilayer is constantly moving
Mosaic = proteins unevenly distributed throughout so look like a mosaic
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3
Q

What does selectively permeable mean

A

Only allows the passage of certain substances

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4
Q

What determines selective permeability

A

The type, number and distribution of specific proteins in the membrane

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5
Q

What is the function of the phospholipids in membrane

A

Allows lipid soluble substances to enter/leave cell
Prevents water soluble substances entering/leaving cell
Makes the membrane flexible and self sealing

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6
Q

What is the function of the phospholipid bilayer

A

Keeps organelles in cell
Protects organelles
Controls what enters/leaves cell
Transports toxic substances out of cell

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7
Q

What is found in the cell membrane

A 
Proteins (carrier/channel)
Phospholipids
Glycoproteins
Glycolipids
Cholesterol
Receptor molecules
Aquaporins
Enzymes
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8
Q

Cholesterol function in membrane

A

Decreases permeability and increases stability
More = less fluid
~25% (20-30 in most cells)
Different cells have different amounts because different functions

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9
Q

Channel proteins in cell membrane

A

Pore like structures
Only allow specific charged ions or small molecules to move across membrane by facilitated diffusion
Open or closed
Intrinsic
Proteins so have specific tertiary structure so complementary to one type of molecule so only transport one type of molecule

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10
Q

Channel proteins transport…

A

Small molecules
Charged ions
By facilitated diffusion

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11
Q

Carrier protein function in cell membrane

A

Aid transport of ions/polar molecules and large molecules like glucose and amino acids
By active transport of facilitated diffusion
Proteins so have specific tertiary structure so complementary to one type of molecule so only transport one type of molecule

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12
Q

Carrier proteins transport…

A

Ions/polar molecules
Large molecules
By active transport or facilitated diffusion

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13
Q

Receptor protein function in cell membrane

A

Proteins so have specific tertiary structure so complementary to one type of molecule so only one type of molecule can bind
Specific cells have specific receptors based on function
Hormones can bind to receptors
Allows the cell to respond (eg by increasing permeability)

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14
Q

Enzyme function in cell membrane

A

Active site complementary to substrate so can only form an ESC with one that type of molecule
Embedded within membrane

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15
Q

Glycoprotein function in cell membrane

A

Carbohydrates and proteins on the surface of the cell membrane important for cell recognition
Often act as antigens
Immune cells detect specific shapes of glycoproteins to identify whether self/non-self
Produced in the golgi body by the cell displaying them
All cells have them

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16
Q

Glycolipid function in cell membrane

A

Carbohydrates and lipids on the surface of the cell membrane important for cell recognition
Often act as antigens
Immune cells detect specific shapes of glycolipids to identify whether self/non-self
Produced in the golgi body by the cell displaying them
All cells have them

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17
Q

Types of transport across membranes

A 
Diffusion
Facilitated diffusion
Active transport
Osmosis
Bulk transport (exocytosis/endocytosis)
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18
Q

How can proteins be integrated into phospholipids

A

Proteins are charged in parts and so attracted to hydrophilic phosphate head and aqueous solutions in/out of cell
Non-polar parts associate with hydrophobic fatty acid tails

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19
Q

What is diffusion

A

A passive process
Not requiring ATP
The net movement of a substance from a higher concentration to a lower concentration across a partially permeable membrane

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20
Q

Diffusion transports…

A

Small, lipid soluble molecules

Oxygen, Carbon Dioxide, Oestrogen

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21
Q

When will net diffusion stop

A

When number of molecules either side of a partially permeable membrane reaches equilibrium
Equal number on either side
Net stays 0 but diffusion can still occur

22
Q

Ficks Law

A

Rate of diffusion = (concentration gradient x surface area)/diffusion distance

23
Q

Factors that affect the rate of diffusion

A

Temperature
Surface area
Concentration gradient
Diffusion distance

24
Q

How does temperature affect rate of diffusion

A

Increased temperature means increased kinetic energy of molecules
Faster rate of diffusion

25
Q

How does surface area affect the rate of diffusion

A

Larger surface area means more space for molecules to pass through
So more can pass through at once
More space for proteins for active transport or facilitated diffusion
Microvilli

26
Q

How does concentration gradient affect the rate of diffusion

A

As difference increases so does the rate of diffusion

27
Q

How does diffusion distance affect the rate of diffusion

A

Shorter means faster because shorter distance to diffuse through
Time to cross membrane decreases
Determined by length of fatty acid tails

28
Q

What is facilitated diffusion

A

Passive process
Does not require ATP
Uses channel or carrier proteins to transport water soluble, charged or large molecules that are unable to pass between the hydrophobic fatty acid tails across the membrane
Transports molecules from an area of higher concentration to an area of lower concentration across a partially permeable membrane

29
Q

Facilitated diffusion transports…

A

Water soluble molecules
Charged molecules
Large molecules

30
Q

Why can’t hydrophilic substances pass through membrane

A

They can’t pass through the hydrophobic tails of phospholipid bilayer
Because the fatty acid tails repel them due to being non-polar

31
Q

When does facilitated diffusion stop

A

When all carrier proteins are saturated (binding sites all occupied)
Substance concentration has reached equilibrium (isotonic)

32
Q

What is osmosis

A

The net movement of water from an area of higher water potential to an area of lower water potential
Across a selectively permeable membrane
Via aquaporins

33
Q

What is water potential

A

Free water molecules are able to move around and collide with membrane
Exerting a pressure on it
This is known as water potential in kPa
More free molecules means more collisions and so greater potential and higher water potential

34
Q

Explain a lower water potential

A

More solute dissolved in water, more negative the water potential
Because water is a dipole molecule its attracted to the solutes molecules charges and so the number of free moving water molecules decreases

35
Q

Explain higher water potential

A

Less solute dissolved in water, less negative water potential
More free moving water molecules so more collisions and more pressure means higher water potential

36
Q

Explain pure water

A

0kPa
Nothing dissolved in it and so every water molecule is free moving
Highest water potential

37
Q

What happens when water potential is higher than in a cell

A

Water moves in to cell via osmosis down a water potential gradient
Causing swelling and osmotic lysis
Destroying cells contents
Cellulose cell wall prevents lysis in plants

38
Q

What happens when water potential is lower than in a cell

A

Water moves out of cell via osmosis down a water potential gradient
Animals = crenation = shrivelling
Plant = plasmolysed = cell membrane pulls away from cell wall

39
Q

Describe isotonic

A

No net movement of water in or out of cell

No water potential gradient so no gain or loss in mass

40
Q

What is active transport

A

Transport of molecules across a membrane against a concentration gradient from an area of lower concentration to an area of higher concentration
By carrier proteins with specific complementary shapes
Active process so requires ATP

41
Q

How is ATP used in active transport

A

Carrier proteins require energy source, supplied by ATP which is produced during aerobic respiration via condensation reaction
The hydrolysis of ATP into ADP and Pi provides a small amount of energy/phosphorylates the carrier protein
Causing a conformational change in shape so it can transport the molecule into an area of higher concentration against a gradient

42
Q

Explain exocytosis

A

Method of bulk transport that uses golgi vesicle to move very large quantities of molecule from inside to outside of cell
Used to move enzymes and glycoproteins from the golgi apparatus to the cell surface membrane to secrete proteins
ATP is required to move the vesicles to the cell surface
Vesicle fuses with cell membrane

43
Q

Why is ATP required in exocytosis

A

Requires the energy provided by breakdown of ATP into ADP and Pi to move the vesicles to the cell surface membrane so it can fuse with the membrane

44
Q

Explain endocytosis

A

Method of bulk transport in which the cell surface membrane is pulled inwards to create a vesicle
Any molecules next to that part of cell membrane are enclosed in the vesicle
Requires breakdown of ATP into ADP and Pi
Part of reason why membrane must be flexible

45
Q

Why do cells using active transport have lots of mitochondria

A

Mitochondria are the site of aerobic respiration and therefore ATP production
Active transport needs the small amount of energy and inorganic phosphate group (Pi) produced from the breakdown of ATP during aerobic respiration
So there is enough energy and Pi for the carrier protein

46
Q

What happens if the tertiary structure of a channel/carrier protein changes

A 
The binding site will change shape
No longer complementary to its molecule
Won't bind
No ESC
Can't be transported and so facilitated diffusion or active transport can't occur
47
Q

How does a respiratory inhibitor affect active transport

A

A respiratory inhibitor prevents mitochondria from making ATP
When the inhibitor is added, the rate of uptake will decrease rapidly, indicating energy is needed
Graph will also plateau when all carrier proteins saturated

48
Q

How does a respiratory inhibitor affect diffusion

A

As concentration gradient across membrane increases so does the rate of uptake
Uptake not affected by respiratory inhibitor because does not require energy provided by ATP since it is a passive process
Curve won’t plateau because no proteins to be saturated and concentration keeps increasing

49
Q

How does a respiratory inhibitor affect facilitated diffusion

A

Prevents mitochondria making ATP
When inhibitor added no change on rate of uptake since its passive
Curve plateaus because all carrier proteins saturated

50
Q

Define intrinsic and extrinsic

A 
Intrinsic = spans both sides of membrane
Extrinsic = spans only one side of the membrane

A Level Biology Paper 1 (16 decks)

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