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A-Level EDUQUAS Biology > Core Concepts: Cell Membranes > Flashcards

Core Concepts: Cell Membranes Flashcards

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1
Q

What is the structure of phospholipids?

A
  • one phosphate group and 2 fatty acid chains
  • Hydrophilic head (the negatively charged phosphate group)
  • Hydrophobic tails (non polar fatty acids)
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2
Q

What is the width of a membrane?

A

7nm

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3
Q

What are membranes?

A
  • partially permeable barriers

- made up of proteins and a phospholipid bilayer

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4
Q

What are the roles of a plasma cell membrane?

A
  • separate cell contents from outside environment
  • regulate transport of nutrients in and out of cells
  • receptor sites (hormones and neurotransmitters fit into specific receptor proteins)
  • recognition as cell membranes have antigens (glycoproteins), enabling cells to recognise other cells and to behave in an organised way
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5
Q

What are the roles of internal membranes?

A
  • holds components of some metabolic pathways in place
  • separate cell components from cytoplasm
  • chemical reactions take place on membranes
  • enzymes are attached to membranes
  • ribosomes are attached to membranes of the endoplasmic reticulum
  • nuclear pore permit mRNA and ribosomes to leave the nucleus
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6
Q

Who proposed the Fluid Mosaic Model?

A

Singer and Nicholson in 1972

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7
Q

What are the main features of the Fluid Mosaic Model?

A
  • phospholipid bilayer
  • intrinsic proteins (span the bilayer)
  • extrinsic proteins (only on one side of the bilayer)
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8
Q

Why is the model called the Fluid Mosaic Model?

A

Fluid: the phospholipids and proteins move around each each other

Mosaic: proteins are arranged between the phospholipids

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9
Q

Describe the phospholipids bilayer

A
  • bilayer acts as a barrier to the larger polar molecules (e.g. glucose and amino acids) and ions (e.g. Na+ and Cl-)
  • freely permeable to non-polar molecules (e.g. lipids and oxygen) and very small polar molecules (e.g. H2O and CO2)
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10
Q

Describe the cholesterol in context of cell membranes

A
  • Cholesterol provides the membrane with stability and rigidity by fitting between the fatty acid tails.
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11
Q

Describe channel proteins

A
  • act as hydrophilic pores
  • water filled channels which allow water soluble molecules to pass through
  • usually small and highly selective, only allowing specific molecules through
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12
Q

What are other functions for proteins in the membrane?

A
  • act as carriers in active transport (carrier proteins)
  • form receptor sites for hormones
  • cell recognition
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13
Q

Describe polysaccharides in context of the cell membranes

A
  • found in the membrane
  • if it’s attached to a protein it’s called a glycoprotein
  • if it’s attached to a phospholipid it’s called a glycolipid
  • their function is for cell communication
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14
Q

What structure are all the proteins found in a plasma membrane?

A

tertiary -> 3D globular protein

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15
Q

What is an intrinsic protein?

A

Proteins that span the whole membrane

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16
Q

What is an extrinsic protein?

A

Proteins that only span part of the bilayer

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17
Q

What is the structure of cholesterol?

A
  • Made up of a Hydrocarbon tail

- a ring structure region with 4 hydrocarbon rings and a hydroxyl group

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18
Q

What is the effect of heat on membranes?

A
  • temperature increasing cause the molecules making up the membrane to gain more KE and move faster
  • causes the membrane to become more fluid (molecules are free to move), more permeable
  • any pigments in the innermost compartments to spill out
  • proteins may denature and leave gaps from molecules and ions to move completely freely in or out
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19
Q

Describe the permeability of the membrane

A
  • lipid-soluble substances, very small or non-polar molecules dissolve in the phospholipids and diffuse across the membrane
  • water-soluble substances, polar molecules or larger molecules must pass through intrinsic protein molecules (channel or carrier), which form water-filled channels across the membrane, as they are insoluble in the bilayer
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20
Q

What is the definition for diffusion?

A

The passive movement of a molecule or ion down a concentration gradient, form a region of high concentration to a region of low concentration

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21
Q

When does diffusion occur?

A
  • there is a concentration gradient
  • molecules have kinetic energy
  • doesn’t require ATP (passive process)
  • no specific proteins are required
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22
Q

What are the 7 things that affect the rate of diffusion?

A
  1. the concentration gradient
  2. diffusion distance
  3. thickness of membrane
  4. surface of the membrane
  5. size of the molecule
  6. lipid solubility
  7. temperature
23
Q

What is the definition for facilitated diffusion?

A

The passive transfer of molecules or ions down a concentration gradient, across a membrane, by protein carrier molecules in the membrane

24
Q

How do hydrophilic channel proteins work in terms of facilitated diffusion?

A
  • act as pores in the membrane
  • specific to the type of ion
  • channels are hydrophilic and ions being water soluble, pass through
  • can also be gated so they open/close in specific circumstances
25
Q

How do carrier proteins work in terms of facilitated diffusion?

A
  • allows the diffusion of large polar molecules across the membrane (e.g. glucose and amino acids)
  • a molecules attaches to the binding site on the protein, causes the protein to change shape, releasing the molecules through the membrane
26
Q

What is the definition of active transport?

A

The movement of molecules or ions across a membrane, via carrier proteins. From a low to high concentration, against the concentration gradient, using energy from the hydrolysis of ATP

27
Q

What are the features of active transport?

A
  • requires ATP, anything that affects respiration will affect active transport (e.g. cyanide respiratory inhibitor)
  • occurs through intrinsic carrier proteins
  • rate can be limited by the number and availability of carrier proteins
28
Q

What are the processes that include active transport?

A
  • protein synthesis
  • muscle contraction
  • nerve impulse transmission
  • absorption of mineral salts by plant roots
  • cells performing active transport are packed with mitochondria
29
Q

What is the process of active transport?

A
  • molecule/ion combines with a specific protein on the outside of the membrane
  • ATP transfers a phosphate group to protein on the side inside the cell
  • protein changes shape, carries the molecule/ion across membrane, releasing it into the cytoplasm
  • phosphate ion released and recombines with ADP to form ATP in cytoplasm
  • carrier protein returns to original shape
30
Q

What is the definition of osmosis?

A

Movement of water from an area of high water potential to an area of low water potential, down a water potential gradient, across a partially permeable membrane.

31
Q

What is water potential?

A

The tendency for water molecules to enter or leave a solution by osmosis. Water can move more freely in a dilute solution compared to a more concentrated one

32
Q

What is the water potential of pure water?

A

0KPa -> the highest water potential

33
Q

What are some facts about water potential?

A
  • adding solutes to water makes water potential lower (negative)
  • water potential represented by psi (Ψ)
  • measured in kilopascals (KPa)
34
Q

How does water move within cells?

A

Water moves from the cell with higher water potential to the cell with the lower water potential

35
Q

What is a hypertonic solution?

A

Have lower water potential that the cell cytoplasm. It contains more solutes

36
Q

What is an isotonic solution?

A

Have the same water potential than the cell cytoplasm. It contains the same concentration of solutes

37
Q

What is a hypotonic solution?

A

Has a higher water potential than the cell cytoplasm. It contains less solutes.

38
Q

Is water a solvent or a solute?

A

Water is a solvent, it can have substances (solutes) dissolved into it

solute + solvent = solution
e.g. sugar + water = sugary water

39
Q

What is the equation that’s used to show the relationship between different forces in plant cells?

A

Ψ = Ψs (solute potential) + Ψp (pressure potential)

40
Q

Explain the parts of the equation

A
  • The concentration of dissolved solute in the cell vacuole = solute potential.
  • (when) Water enters the cytoplasm and the vacuole by osmosis, a hydrostatic pressure is made and contents push out on cell
  • Pressure builds, cell wall develops opposing force = pressure potential
41
Q

What is the definition of turgid?

A

A plant cell that holds as much water as possible. Further entry of water is prevented as the cell wall cannot expand further

42
Q

Describe and draw a plant cell placed in a hypotonic solution

A
  • plant cell expands to full turgor

- at turgor, plant cell Ψ = 0 as Ψp = Ψs

43
Q

Describe and draw a plant cell placed in an isotonic solution

A
  • plant cell shows incipient plasmolysis

- Plant cell Ψ = Ψs as Ψp = 0

44
Q

Describe and draw a plant cell placed in a hypertonic solution

A
  • plant cell is plasmolysed
  • when complete the cell is said to be flaccid
  • plant cell Ψ = Ψs, Ψp = 0
45
Q

What are the 3 definitions of incipient plasmolysis?

A
  1. For 1 cell - cell membrane just begins to move away from cell wall
  2. For a tissue - 50% cells are turgid, 50% plasmolysed
  3. Water movement - there is no net movement of water
46
Q

Describe what bulk transport is

A

Bulk transport of substances into the cell that are too large for other processes. Uses ATP to move membrane to form vesicles to contain substances as it enters the cell

47
Q

What is endocytosis?

A

the active process of the cell membrane engulfing material, bringing it into the cell in a vesicle

48
Q

What are the two types of endocytosis?

A
  1. Phagocytosis -> solid materials

2. Pinocytosis -> liquids

49
Q

What are the steps for endocytosis & draw a diagram? (for a bacterium)

A
  1. cell surface receptor binds to antigen on bacterium
  2. the cell membrane invaginates and the bacterium is taken into a phagosomes by endocytosis
  3. Lysosomes fuse with phagosome and secrete digestive enzymes into it
  4. The bacterium is digested
  5. Products of digestion are adsorbed into the cytoplasm, any substances that aren’t useful removed by exocytosis
50
Q

What is exocytosis?

A

The process by which substances may leave the cell, having been transported through the cytoplasm in a vesicle, which fuses with the cell membrane
- digestive enzymes are often secreted in this way

51
Q

What do exocytosis and endocytosis have in common?

A

Both active processes, both require ATP

52
Q

What is the word for when animal cells shrivel up?

A

crenates

53
Q

What is the word for when a animal cell bursts?

A

lysis

haemolysis in red blood cells

A-Level EDUQUAS Biology (24 decks)

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