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3.2 Cells > 3.2.3 Transport across cell membranes > Flashcards

3.2.3 Transport across cell membranes Flashcards

1
Q

All membranes around and within all cell have the same basic structure and are known as what?

A

Plasma membranes

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2
Q

The basic structure of all cell membranes, including cell-surface membranes and the membranes around the cell organelles of eukaryotes is…

A

The same

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3
Q

The basic structure of all cell membranes, including cell-surface membranes and the membranes around the cell organelles of eukaryotes is…

A

The same

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4
Q

Cell surface membrane

Definition

A
  • the plasma membrane that surrounds the cell

- forms the boundary between the cell cytoplasm and the environment

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5
Q

Cell surface membrane

Function

A

-allows for different conditions to be established inside and outside the cell

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6
Q

The roles of membranes at the surface of cells

A

-separate the cell from environment
-control the entry and exit of molecules
-use of phospholipid layer preventing passage of polar substances  
-facilitated diffusion
└using channel proteins
-phagocytosis/ endocytosis/exocytosis
-cell recognition using cell surface antigens
-cell adhesion
-receptor for hormones and neurotransmitters

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7
Q

The roles of membranes within cells

A

-compartmentalise/surrounds organelles
-prevents disruption of reactions and process
└so they are more efficient
-reactions take place on membranes
-enzymes are attached to membrane
-separates DNA in the nucleus
└however nuclear pore permits RNA to leave nucleus
-forms organelles
└such as endoplasmic reticulum, vesicles, lysosomes
-attachment of ribosomes
-intracellular transport
-protects cells from contents of lysosomes;
-tonoplast surrounds vacuole

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8
Q

Permeability of cell surface membrane

Substances that CAN pass through

A
  • lipid soluble
  • non-polar
  • very small
  • not charged
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9
Q

Permeability of cell surface membrane

Substances that can NOT pass through

A
  • water soluble
  • polar
  • large
  • charged
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10
Q

Why WATER SOLUBLE substances can NOT pass through the cell surface membrane

A
  • not lipid soluble

- can’t pass through phospholipid bilayer

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11
Q

Why POLAR substances can NOT pass through the cell surface membrane

A

-can’t pass through non-polar hydrophobic tails

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12
Q

Why LARGE substances can NOT pass through the cell surface membrane

A

-too large to pass through channel proteins in membrane

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13
Q

Why CHARGED substances can NOT pass through the cell surface membrane

A
  • even if small enough

- repelled by charged channel proteins

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14
Q

EQ: Why antigens are not able to pass through the cell-surface membranes of other epithelial cells

A
  • not lipid soluble
  • too large to diffuse through the membrane
  • antigens do not have the complementary shape so cannot bind to receptor/channel/carrier proteins in membranes of other epithelial cells
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15
Q

How can cell membranes be affected by temperature

A

-affects how much phospholipids and bilayer can move

└affects membrane structure and permeability

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16
Q

Cell membranes and temperature

Below 0◦C

A

-phospholipids don’t have much kinetic energy
└can’t move very much
└=compact rigid membrane
-carrier and channel proteins in membrane are denatured
└=↑ permeability of membrane

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17
Q

Cell membranes and temperature

Between 0◦C-45◦C

A 
-phospholipids have more kinetic energy
└can move more 
└= less compact and rigid
└=partially permeable membrane
-↑temperature = ↑ permeability of membrane
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18
Q

Cell membranes and temperature

Above 45◦C

A

-phospholipid bilayer starts to melt
└↑permeability
-carrier and channel proteins in membrane are denatured
└=↑ permeability of membrane

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19
Q

Fluid mosaic model of membrane structure

A

-individual phospholipids can move relative to each other
└gives membrane flexible structure
-molecules including proteins that are embedded on the phospholipid bilayer vary in shape, size and pattern, like a mosaic

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20
Q

Cell membrane structure

components

A
  • Phospholipids
  • Proteins (extrinsic and intrinsic)
  • Cholesterol
  • Glycolipids
  • Glycoproteins
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21
Q

Phospholipid bilayer

Structure

A
  • hydrophilic phosphate head pointing outwards
  • hydrophobic fatty acid tail pointing inwards
  • automatically arranges into a bilayer
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22
Q

Phospholipid bilayer

Function in cell surface membrane

A

-acts as a barrier to polar / charged /water soluble substances
-allows passage of lipid soluble substances
└e.g. water, oxygen, carbon dioxide
-makes the membrane flexible and self-sealing

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23
Q

What are the two main ways proteins can be embedded in the membrane?

A
  • on the surface

- across the entire span of the membrane

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24
Q

2 types of proteins that span the whole membrane

A

Protein channels

Protein carriers

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25
Carrier protein | Function in cell surface membrane
-span the plasma membrane -move large molecules across membranes -Carrier proteins have specific binding sites └a large molecule binds to the receptor site └=the protein changes shape: releases molecule on the other side of the membrane
26
Channel protein | Function in cell surface membrane
-water-filled hydrophilic channels across the membrane -allow specific water-soluble ions to pass through └channels are SELECTIVE (open to a specific molecule)
27
Cholesterol | Function in cell surface membrane
- stabilise the membrane - restricts movement - reduces permeability to polar/charged substances - storage - makes the membrane less fluid at high temperatures
28
Cholesterol | Structure
- inserts into phospholipid bilayer | - between fatty acid tails
29
Glycolipid | Structure
- carbohydrate | - covalently bonded with a lipid
30
Glycolipid | Function
- act as recognition sites (cell recognition) - help maintain the stability of the membrane - help cells to attach to one another and so form tissues (cell adhesion)
31
Glycoprotein | Structure
-protein embedded in the membrane | └with branched carbohydrate chain projecting out from the surface of the cell
32
Glycoprotein | Function in cell surface membrane
-act as an ANTIGEN └for CELL RECOGNITION(as self or non-self) -receptors for cell signalling -cell communication └responds to chemical signal from another cell -receptor/binding site for hormones/ chemicals / drugs -RECEPTOR/binding site on transport proteins -CELL ADHESION └to hold cells together in a tissue -BIND TO WATER MOLECULES via hydrogen bonds └TO STABILISE MEMBRANE
33
EQ: How a glycoprotein can act as a receptor
-the receptor is a specific and complimentary shape to the trigger └so it binds to the receptor
34
Cell signalling | Definition
-communication between cells -cell recognition └cells work together to trigger a response inside the cell
35
Movement across membranes occur by:
- simple diffusion - facilitated diffusion - osmosis - active transport - co-transport
36
Simple diffusion
-net movement of substances from a higher to a lower concentration └down a concentration gradient -passive process └does not require energy/ATP
37
Simple diffusion | Substances
-Small / non-polar / lipid-soluble molecules | └pass via phospholipid bilayer
38
Particles in diffusion and other passive forms of transport
-all particles are constantly in motion └due to the kinetic energy that they possess -motion is random -particles are constantly bouncing off one another as well as off other objects
39
EQ: How they enter a cell through the cell surface membrane | small, non-polar substances
-diffuse through phospholipid bilayer
40
Facilitated diffusion
``` -movement of substances from a higher to a lower concentration └down a concentration gradient -using carrier/channel proteins -passive process └does not require energy/ATP ```
41
Facilitated diffusion | Substances
-large / polar / water-soluble molecules | └go through proteins
42
Facilitated diffusion | Role of carrier proteins
-span the plasma membrane -move large molecules across membranes -Carrier proteins have specific binding sites └a large molecule binds to the receptor site └=the protein changes shape: releases molecule on the other side of the membrane
43
Facilitated diffusion | Role of channel proteins
- channel protein forms passage through centre of the protein - it is water lined so there are hydrophilic conditions - allow, small / charged/ polar/ water soluble molecules through membrane/phospholipid bilayer
44
EQ: Explain why the diffusion of chloride ions involves a membrane protein and the diffusion of oxygen does not
-chloride ions are water soluble/charged/polar └so cannot cross lipid bilayer of membrane └chloride ions transported by facilitated diffusion └involving channel/carrier protein -oxygen not charged/non-polar -so can diffuse across lipid bilayer
45
EQ: How they enter a cell through the cell surface membrane | Large/polar substances
-through channel/carrier proteins
46
Osmosis
-movement of water from a higher to a lower water potential └down a water potential gradient -through a selectively permeable membrane └through aquaporins/water channels -passive process └does not require energy/ATP
47
Water potential | Definition
-the pressure created by water molecules
48
Water potential | Units
- represented by Ѱ | - measured in kiloPascals
49
Water potential of water under standard conditions
0
50
The more negative the water potential value…
the lower the water potential
51
Solution | Definition
-a solute dissolved in a solvent
52
Solute | Definition
-any substance that is dissolved in a solvent
53
Isotonic | Definition
2 solutions with the same water potential
54
Hypotonic | Definition
A solution that has less solute and more water than another solution
55
Hypertonic | Definition
A type of solution that has a greater concentration of solutes on the outside of the cell compared with the inside of the cell
56
EQ: Kwashiorkor is a disease caused by a lack of protein in the blood. This leads to a swollen abdomen due to a build-up of tissue fluid. Explain why a lack of protein in the blood causes a build-up of tissue fluid.
Water potential in capillary is higher/less negative so the water potential gradient is reduced - so less water removed - by osmosis
57
EQ: Why do people that can’t digest lactose get diarrhoea when they drink milk?
- there is a lower water potential in the gut | - so water leaves cells and enters gut by osmosis
58
Active transport
-movement of substances from a lower to a higher concentration └against a concentration gradient -using carrier proteins -requires energy in the form of ATP (from respiration) └as is an active process
59
Active transport | Role of carrier proteins
- carrier protein - attaches on one side of the membrane - and the protein changes shape - and releases on other side of the membrane
60
Active transport | Importance of the hydrolysis of ATP
-ATP is hydrolysed into ADP and Pi └releases energy required for active transport └as is against concentration gradient
61
EQ: Differences between active transport and facilitated diffusion
Active transport: - uses energy/ATP - is against concentration gradient / low to high concentration - does not use channel proteins / only uses carrier proteins
62
Name the mechanism by which glucose and amino acids are absorbed from the ileum into the blood
Co-transport using sodium and potassium pump
63
Co-transport
-when more than one molecule/ion may be moved in the same direction at the same time by active transport -concentration gradient of one of the molecules is used to move the other molecule against its concentration gradient -energy is not required for protein carrier to function └is required to provide concentration gradient
64
Co-transport | e.g. in the absorption of sodium ions and glucose by cells lining the mammalian ileum
-Na+ ions LEAVE epithelial cell and ENTER blood └by active transport └via a carrier protein (sodium/potassium punp) └using ATP -So, NA+ CONCENTRATION IN CELL IS LOWER than in lumen of gut └Sodium/Na+ ions ENTER epithelial cells by facilitated diffusion └down the concentration gradient └through a different carrier protein └Glucose absorbed with Na+ ions against their concentration gradient down an electrochemical gradient
65
The ileum | Structure
-one of three regions in the small intestine -it has many tiny folds in the wall (villi) └villi all have their own microvilli which └=large surface area available for absorption. -the villus also have a network of blood capillaries for absorption and transport of food. -beneath the villi are glands called the crypts of Lieberkuhn └contain goblet cells to secrete mucus.
66
The ileum | Function
-to absorb vitamin B12 and bile salts
67
EQ: How the epithelial cells that line the small intestine are adapted for the absorption of glucose
-they have microvilli └which increase surface area -many mitochondria └produce ATP in respiration for active transport -many carrier proteins └for active transport and facilitated diffusion └for co-transport of sodium (ions) and glucose -membrane-bound enzymes └digest disaccharides / produce glucose
68
Cell adaptations for rapid transport across their internal or external membranes
- increase in surface area of membranes | - increase in the number of protein channels and carrier molecules in their membranes
69
Rate of diffusion is proportional to
(area of diffusion surface x concentration difference) / thickness of surface
70
Factors effecting the | Rate of simple diffusion
- concentration gradient - thickness of exchange surface - surface area
71
Rate of simple diffusion | Concentration gradient
``` -higher concentration gradient └=faster diffusion -as diffusion takes place └concentration decreases until an equilibrium is reached └so diffusion slows with time ```
72
Rate of simple diffusion | Thickness of exchange surface
└shorter distance for particles to travel | └=faster diffusion
73
Rate of simple diffusion | Bigger surface area
└more particles can diffuse across the surface at one time | └=faster rate of diffusion
74
Rate of simple diffusion | Example
-microvilli increase surface area └more particles can diffuse across the surface at one time └=faster rate of diffusion
75
Factors effecting the | Rate of facilitated diffusion
- concentration gradient | - number of carrier/channel proteins
76
Rate of facilitated diffusion | Concentration gradient
-higher concentration gradient | └=faster diffusion
77
Rate of facilitated diffusion rate | Number of carrier/channel proteins
-increase number of transport proteins └=increase rate of facilitated diffusion -once all channel proteins are in use └facilitated diffusion cannot occur faster even if the concentration is increased
78
Factors effecting the | Rate of osmosis
- water potential gradient - thickness of exchange surface - surface area of exchange surface
79
Rate of osmosis | Water potential gradient
-higher water potential gradient | └=faster rate of osmosis
80
Rate of osmosis | Thickness of exchange surface
└shorter distance for particles to travel | └=faster rate of osmosis
81
Rate of osmosis | Surface area of exchange surface
└shorter distance for particles to travel | └=faster rate of osmosis
82
Factors affecting rate of active transport
- speed of individual carrier proteins - number of carrier proteins present - rate of respiration/availability of ATP
83
How factors affect the rate of movement across cell membranes -surface area
-increase surface area └=more particles can diffuse across the surface at one time └=faster rate of diffusion
84
How factors affect the rate of movement across cell membranes -number of channel or carrier proteins
-increase number of transport proteins └=increase rate of facilitated diffusion -once all channel proteins are in use └facilitated diffusion cannot occur faster even if the concentration is increased
85
How factors affect the rate of movement across cell membranes differences in gradients of concentration or water potential
-higher water potential/concentration gradient | └=faster rate of osmosis

3.2 Cells (8 decks)

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