The Plasma Membrane (2.3)

Question 1

State what controls plasma membrane impermeability to polar molecules

Answer 1

The phospholipid bilayer

Question 2

Describe the impact of temperature on the fluidity of the cell membrane (absence of cholesterol)

Answer 2

low temp - rigid, low flexibility (membrane may break)

high temp - fluid, high flexibility (membrane won’t hold shape)

Question 3

Describe amphipathic

Answer 3

Both hydrophobic and hydrophilic regions

Question 4

Provide one example of an amphipathic structure

Answer 4

Phospholipids

Question 5

Describe lateral movement of phospholipids

Answer 5

Rotate to switch places horizontally

Question 6

Describe transverse movement (flip-flopping) of phospholipids

Answer 6

Rotate to switch places vertically

Question 7

Define phospholipid bilayer

Answer 7

Two layers of phospholipids with hydrophobic fatty acid tails projecting inwards and hydrophilic glycerol and phosphate head groups projecting outwards

Question 8

Describe polar and non-polar organisation of plasma membranes

Answer 8

Glycerol and phosphate head group - polar

Fatty acid tails - non-polar

Question 9

Describe temperature as a factor affecting the fluidity of the plasma membrane

Answer 9

High temp = High fluidity

Low temp = High viscosity (saturated hydrocarbon tails)

Question 10

State whether a phospholipid head is hydrophilic or hydrophobic

Answer 10

Hydrophilic

Question 11

State whether a phospholipid tail is hydrophilic or hydrophobic

Answer 11

Hydrophobic

Question 12

State 4 functions of peripheral proteins

Answer 12

• Enzymes
• Receptors
• Structural attachment points
• Recognition sites

Question 13

Describe 2 major functions of the plasma membrane

Answer 13

1. Controls entry and exit of substances into and out of the cell (differentially permeable)
2. Separates internal and external environment

Question 14

Describe the structure of the plasma membrane

Answer 14

Double layer of phospholipids with proteins scattered throughout which creates a differentially permeable barrier between the intracellular and extracellular fluid

Question 15

Compare and contrast membrane fluidity and viscosity (Describe phospholipid composition and structure)

Answer 15

Fluidity: Unsaturated hydrocarbon tails prevent packing
Viscosity: Saturated hydrocarbon tails pack together

Question 16

Describe transmembrane proteins

Answer 16

Integral proteins that span both phospholipid layers

Question 17

Describe integral proteins

Answer 17

Proteins that are a permanent part of the plasma membrane

Question 18

Describe peripheral proteins

Answer 18

Proteins that are a temporary part of the plasma membrane

Question 19

Describe why peripheral proteins are a temporary part of the plasma membrane

Answer 19

Not embedded in the phospholipid bilayer

Question 20

State 2 structures which peripheral proteins attach to on the plasma membrane

Answer 20

1. Phospholipid molecules

2. Integral proteins (either layer of the plasma membrane)

Question 21

State classification of a phospholipid with a cis double bond

Answer 21

Unsaturated

Question 22

State classification of a phospholipid without a cis double bond

Answer 22

Saturated

Question 23

State the 6 major functions of integral proteins

Answer 23

1. Act as transport channels
2. Function as enzymes
3. Involved in signal transduction
4. Cell-to-cell recognition
5. Attach to cytoskeleton/extracellular matrix
6. Intercellular joining

Question 24

Describe impact of cis double bonds on fluidity of the plasma membrane

Answer 24

Creates kinks in the unsaturated fatty acid chains of the plasma membrane - less easy to pack together
(increasing membrane fluidity)

Question 25

Describe lipophilic

Answer 25

(Hydrophobic) | Not water soluble - substances easily cross membrane

Question 26

Describe hydrophobic

Answer 26

Not water soluble - 'water hating'

Question 27

Describe hydrophilic

Answer 27

Water soluble - 'water loving'

Question 28

Describe why proteins group in clusters

Answer 28

- similar functions | - same biochemical pathways

Question 29

Outline what the fluid mosaic model proposes

Answer 29

Phospholipids and unanchored proteins are free moving, with anchored proteins scattered throughout.

Question 30

State 3 materials which are scattered throughout the plasma membrane

Answer 30

1. Proteins 2. Carbohydrates 3. Cholesterol

Question 31

Define phospholipid

Answer 31

Essential component of the plasma membrane, comprised of a hydrophilic glycerol and phosphate head group and two hydrophobic fatty acid tails

Question 32

Define plasma membrane

Answer 32

Semi-permeable boundary that regulates the movement of substances between the extracellular to intracellular fluid, composed of a phospholipid bilayer

Question 33

State the 2 forms of phospholipid tails

Answer 33

1. Saturated | 2. Unsaturated

Question 34

Describe the hydrophobic and hydrophilic regions of the phospholipid bilayer

Answer 34

Hydrophobic interior and hydrophilic exterior

Question 35

State what 2 types of regions integral proteins have

Answer 35

- Hydrophobic | - Hydrophilic

Question 36

State 2 major carbohydrate forms found within the plasma membrane

Answer 36

- Glycoproteins (attached to proteins) | - Glycolipids (attached to lipids)

Question 37

Describe the extracellular matrix

Answer 37

Collection of extracellular molecules secreted by cells that provides biochemical support to surrounding cells

Question 38

State the 2 common locations of proteins within the plasma membrane

Answer 38

- Clustered in groups | - Distributed randomly throughout the membrane

Question 39

State 3 major functions of carbohydrates within the plasma membrane

Answer 39

- Cell-to-cell recognition - Cell adhesion - Recognition of antibodies, hormones and viruses

Question 40

Describe how compartmentalisation within eukaryotes optimises cellular efficiency

Answer 40

Groups particular enzymes and reactants for particular functions in high concentrations at optimal levels

Question 41

Describe the structure of phospholipids

Answer 41

Composed of a hydrophilic glycerol and phosphate head group and two fatty acid tails

Question 42

Phospholipids will react with the presence of water. True/False

Answer 42

True

Question 43

State 4 major functions of the plasma membrane

Answer 43

1. Active boundary 2. Cell identity 3. Receiving external signals 4. Transport

Question 44

Classify non-polar molecules as hydrophilic or hydrophobic

Answer 44

Hydrophobic

Question 45

Classify polar molecules as hydrophilic or hydrophobic

Answer 45

Hydrophilic

Question 46

Relate the characteristics of phospholipids to the arrangement of the plasma membrane

Answer 46

Phospholipids are amphipathic - Fatty acid tails have a low interaction with water - Phosphate head groups have a high interaction with water Phospholipids aggregate by orientating hydrophobic tails towards one another

Question 47

Describe the structure of glycolipids as an amphipathic protein

Answer 47

Sugar group (hydrophilic) and covalently bonded lipid tail (hydrophobic)

Question 48

Describe the structure of cholesterol as an amphipathic protein

Answer 48

Hydroxyl group (-OH) (hydrophilic) and hydrocarbon chain and steroid (hydrophobic)

Question 49

State in which plasma membranes cholesterol is present

Answer 49

Animal cells

Question 50

Describe the effect of cholesterol on the plasma membrane in high temperature

Answer 50

Prevents increase in fluidity

Question 51

Describe the effect of cholesterol on the plasma membrane at low temperatures

Answer 51

Prevents increase in viscosity

Question 52

Describe the effect of cholesterol on the movement of phospholipids at various temperatures

Answer 52

Restricts phospholipid movement and acts as a buffer for changing temperatures

Question 53

State 2 characteristics of membrane proteins in relation to plasma membrane structure

Answer 53

- Move within the bilayer | - Attach to cytoskeleton

Question 54

State the 3 factors that influence the fluidity of the plasma membrane

Answer 54

- Phospholipid composition and structure - Temperature - Cholesterol

Question 55

Describe what cholesterol is composed of

Answer 55

4 fused carbon rings

Question 56

Describe phospholipid composition and structure as a factor affecting plasma membrane fluidity

Answer 56

Increase saturated fatty acid tails = low fluidity | Decrease saturated fatty acid tails and increase unsaturated fatty acid tails = high fluidity

Question 57

Describe how compartmentalisation within eukaryotes decreases cell vulnerability to environmental changes

Answer 57

Separates processes inside the cell (an environmental change would affect the cell cytosol more than individual membrane bound organelles)

Question 58

Describe 2 factors supporting the importance of plasma membrane fluidity

Answer 58

- Substance permeability | - Capacity for proteins to move across the membrane to particular cell areas

Question 59

Describe vesicle

Answer 59

Structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer.

Question 60

State whether or not carrier and channel proteins are considered permanent or temporary parts of the plasma membrane and identify the overall protein classification

Answer 60

Permanent | Transmembrane proteins

Question 61

Provide an example of a peripheral protein in function

Answer 61

Proteins involved in controlling the synthesis/destruction of the cell membrane