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OCR Biology A Level > 2.1.5 Biological Membranes > Flashcards

2.1.5 Biological Membranes Flashcards

1
Q

What model and why is the plasma membrane described as?

A

Fluid mosaic model
- ‘Fluid’ = phospholipids are constantly moving around
- ‘Mosaic’ = proteins are scattered throughout
- ‘Model’ = best representaion based on evidence available - may be updated if new information is discovered

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2
Q

What components make up the plasma membrane?

A
  • phospholipids
  • glycoproteins
  • glycolipids
  • cholestrol
  • intrinsic proteins
  • extrinsic proteins
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3
Q

Describe the structure and function of phospholipids

A
  • form a bilayer - hydrophobic fatty acid tails face inwards, hydrophilic phopshate heads face outwards
  • allows lipid-soluble and non polar substances to enter + leave the cell
  • prevents large molecules, water-soluble molecules, and polar substances from entering + leaving the cell
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4
Q

Describe the structure and function of glycoproteins

A
  • proteins with sugar molecules attached
  • cell adhesion + receptors for cell signalling (neurotransmitters and hormones)
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5
Q

Describe the structure and function of glycolipids

A
  • phospholipids with sugar molecules attached
  • act as recognition sites and antigens - allows the body to detect which cells are self or non-self
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6
Q

Describe the structure and function of cholesterol

A
  • lipid which slots in between the phospholipid tails
  • increases packing of the membrane - regulating stability + fluidity
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7
Q

Describe the structure and function of intrinsic proteins

A
  • proteins which span both bilayers of the membrane
  • act as channels or carrier proteins & transport water-soluble molecules
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8
Q

Describe the structure and function of extrinsic proteins

A
  • proteins found on the surface of the membrane
  • examples are enzymes
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9
Q

Describe the structure and function of channel and carrier proteins

A

Channel Proteins
- transport of ions by facilitated diffusion
- act as “pores” in the membrane + allow specific ions through
- Tcan be gated so they only open/close in specific circumstances

Carrier Proteins
- facilitated diffusion of large molecules
- only allow specific large molecule to pass through
- changes shape and transfers the molecule to the other side of the membrane
- active transport of water soluble molecules and charged ions using ATP

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10
Q

What is the thickness of the plasma membrane?

A

7nm

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11
Q

Jobs of membranes outside + inside cells

A

Inside
- produce different compartmenmts in cells
- sites of chemical reactions
- provide attachment sites for enzymes
- provide attachment sites for pigments
- form vesicles for the transport of proteins
- allow cellular compartments to have different conditions
Outside
- seperates cell contents from the external environment
- cell signalling
- cell rocignition

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12
Q

Define cell signalling

A

Processes that lead to communication and coordination between cells, so that they can work together to trigger a response

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13
Q

Explain cell signalling

A
  • Receptor in plasma membrane picks up signals - in form of a hormone or chemical mediator binding to the receptor
  • signals secreted from cell and travel in blood
  • binding brings about actions within cell
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14
Q

Explain key aspects of hormone receptors

A
  • protein and glycoprotein receptors stick out target cells
  • specific shape
  • shape is complementory to shape of specific signalling molecule
  • hormone binds to receptor - cell responds in particular way
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15
Q

What does cell signalling allow?

A
  • communication between cells
  • cells to coordinate actions
  • trigger reponses inside cells
  • cell recognition+ identification
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16
Q

Explain cell signalling in the context of controlling high blood glucose levels

A
  • insulin hormoner releasedwhen blood sugar increases
  • insulin receptors on liver + muscle cells bind insulin - cells take in more glucose to reduce blood glucose concentration
  • insulin receptors have specific shape - complementory to shape of insulin molecule
17
Q

Define and explain key aspects of diffusion

A

The net passive movement of molecules down a concentration gradient from a higher to lower concentration
- passive - doesn’t require ATP
- will continue until equilibrium between two areas
-faster over short distances - slower over long
- happens in gases + liquids - particles have kinetic energy

18
Q

What molecules diffuse accross the phospholipid bilayer?

A
  • lipid soluble e.g. steroid hormones
  • small + non polar e.g. CO2, O2
  • small + polar e.g. H20
19
Q

What factors affect the rate of diffusion and why?

A
  • temperature = more kinetic energy
  • concentration gradient = steeper - faster rate of diffusion
  • stirring motion = more kinetic energy
  • surface area = more space for molecules to move accross
  • diffusion distance - smaller distance to move
  • size of molecule - larger molecules diffuse smaller than smaller ones
20
Q

Why can’t large or polar membranes, as well as charged ions cross a membrane?

A

Can’t pass througfh phospholipid bilayer - require carrier + channel proteins for facilitated diffusion

21
Q

Key aspects of facilitated diffusion

A
  • there is a concentration gradient
  • no ATP required
  • protein + carrier proteins present
  • polar molecules + ions have kinetic energy
22
Q

Explain facilitated diffusion in channel + carrier proteins

A

Channel Proteins
- act as pores
- some only allow specific ions through e.g. Na+ Ca2+
- can be gated

*Carrier Proteins**
- only allow specific large molecules through e.g. glucose
- when molecule binds, it changes shape and transfers it to the other side

23
Q

Define and explain key aspects of active transport

A

The movement of molecules or ions against a concentration gradient, from a lower to high concentration. using ATP and a transport/carrier protein
- ATP required
- only carrier proteins required
- moves substances against concentration gradient
- selective process

24
Q

How is one way flow ensured in active transport?

A
  • ATP changes shape of carrier proteins
  • energy changes shape and releases molecule
25
Q

Define and explain key aspects of bulk transport using endocytosis

A

The bulk movement of substances into the cell with ATP. Substances have part of the membrane surrounding them, which pinces off to form a vesicle inside the cell
- into the cell
- cell surface membrane bends inwards
- membrane engulfs material
- membranes fuse together + vesicle formed
- ATP required

26
Q

Define and explain key aspects of bulk transport using exocytosis

A

The bulk movement of substances out of the cell with ATP. Inside the cell, esicles containing substances fuse with the plasma membrane releasing material outside the cell.
- out of the cell
- vesicle fuses with the membrane
- contents of vesicle released outside the cell
- vesicle usually formed by golgi apparatus
- ATP required

27
Q

Names for when solids vs lipids transported

A

solids = phagocytosis
- liquids = pinocytosis

28
Q

Define and explain key aspects of bulk water potential

A

A measire of the tendency of water molecules to diffuse from one place to another
- uses the units kilo Pascals kPa - ψ
- pure water has a water potential of 0kPa
- the more solute dissolved the lower the water potential - less free water molecules to move
- solutions always have negative water potential

29
Q

Define and explain key aspects of osmosis

A

The net movement of water molecules accross a partially-permeable membrane from a less negative water potential to a more negative water potential down a water potential gradient

30
Q

Explain hypotonic, hypertonic and isotonic solutions

A
  • isotonic = the solution surrounding the cell has the same water potential as the cell
  • hypertonic = the solution surrounding the cell has a lower water potential than the cell (e.g. concentrated sugar solution)
  • hypotonic= the solution surrounding the cell has a higher water potential than the cell (e.g. pure water)
31
Q

List factors that affect the fluidity of the plasma membrane

A
  • temperature
  • presence of alcohol
  • number of cholesterol molecules = more cholesterol between fatty acid chains means membrane becomes less fluid, vise versa
  • short chains in fatty acids = shorter chains = more fluid membrane
  • number od double bonmds between carbon atroms in fatty acid chains - more kinky faty acid - can’t pack as closely together
32
Q
A

OCR Biology A Level (11 decks)

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