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Biology > Chapter 5 - Plasma membranes > Flashcards

Chapter 5 - Plasma membranes Flashcards

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1
Q

Carrier Proteins

A

transport molecules and ions across membrane via faciliated diffusion and active transport
- carrier proteins can switch between two shapes
-> causes the binding site of the carrier protein to be open to one side of the membrane first + then open to the other side of the membrane when the carrier protein switches shape
- net diffusion of molecules or ions into or out of a cell will occur down a concentration gradient

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2
Q

Channel Proteins

A
  • water-filled pores
  • allow charged substances (eg. ions) to diffuse through the cell membrane
  • fixed shape
  • diffusion of these ions does not occur freely, most channel proteins are ‘gated’ meaning that part of the channel protein on the inside surface of the membrane can move in order to close/open the pore
  • allows the channel protein to control the exchange of ions
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3
Q

other possible proteins

A

➜ act as a receptor for molecules in cell signalling

➜ when a molecule binds to protein - triggers a chemical reaction in cell

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4
Q

Glycolipids and Glcyoproteins

A

➜ stabilise the membrane by forming H bonds with surrounding water molecules (attaching to water molecules)
➜ act as receptors for cell signalling
➜ acting as antigens ;
➜ identification / recognition of cells as
non-self
➜ cell signalling
➜ receptor / binding site, for, hormone/ signal/drugs
➜ cell adhesion

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5
Q

Cell signalling

A

➜ communication between cells
➜ one cell releases a messenger molecule
➜ this molecule travels to another cell
➜ messenger molecule attaches to /
causes change in another cell

➜ release of signal molecule by exocytosis / secretion
➜ proteins / glycoproteins / glycolipids act as receptors
➜ receptor is specific
➜ shape of receptor and signal are complementary
➜ attachment of signal molecule causes change in cell
➜ cell surface membrane allows entry of some signal
molecules

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6
Q

cell surface membrane

A
  • separates the internal cell environment from the external environment
  • compartmentalisation
  • controls what substances enters and leaves the cell
  • form vesicles
  • site of chemical reactions
  • site for attachment of, enzymes
  • has antigens, so the organism’s immune system can recognise the cell as itself and not attack it
  • may release chemicals that signal to other cells
  • contains receptors for such chemical signals, -> a site for cell communication or signalling; hormones + drugs may bind to membrane-bound receptors
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7
Q

The fluid mosaic model describes cell membranes as ‘fluid’

A
  • The phospholipids and proteins can move around via diffusion
  • The phospholipids mainly move sideways, within their own layers
  • The many different types of proteins interspersed throughout the bilayer move about within it (a bit like icebergs in the sea) although some may be fixed in position
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8
Q

The fluid mosaic model describes cell membranes as ‘mosaics’

A

-The scattered pattern produced by the proteins within the phospholipid bilayer looks somewhat like a mosaic when viewed from above

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9
Q

The fluid mosaic model of membranes

A

Phospholipids
Cholesterol
Glycoproteins and glycolipids
Transport proteins

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10
Q

Phospholipids

A

form the basic structure of the membrane (the phospholipid bilayer)
- form a hydrophobic core
- Phospholipids bilayers act as a barrier to most water-soluble substances (the non-polar fatty acid tails prevent polar molecules or ions from passing across the membrane)
- ensures water-soluble molecules such as amino acids cannot leak out of the cell + unwanted water-soluble molecules cannot get in

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11
Q

Cholesterol

A
  • increases the fluidity of the membrane, stopping it from becoming too rigid at low temperatures, allowing cells to survive at lower temperatures
  • cholesterol stops the phospholipid tails packing too closely together
  • Interaction between cholesterol and phospholipid tails also stabilises the cell membrane at higher temperatures by stopping the membrane from becoming too fluid
    = cholesterol molecules bind to the hydrophobic tails of phospholipids, stabilising them and causing phospholipids to pack more closely together
    = impermeability of the membrane to ions is also affected by cholesterol
  • increases the mechanical strength and stability of membranes or membranes would break down and cells burst
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12
Q

Glycolipids and glycoproteins

A

Glycolipids and glycoproteins contain carbohydrate chains that exist on the surface, which enables them to act as receptor molecules
- glycolipids and glycoproteins bind with certain substances at the cell’s surface

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13
Q

3 main receptor types for glycolipids + proteins

A
  • signalling receptors for hormones and neurotransmitters
  • receptors involved in endocytosis
  • receptors involved in cell adhesion + stabilisation
  • act as cell markers or antigens, for cell-to-cell recognition
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14
Q

Transport proteins

A

create hydrophilic channels to allow ions + polar molecules to travel through the membrane.

2 types:
Channel proteins
Carrier proteins (change shape to transport a substance across the membrane)

Each transport protein is specific to a particular ion or molecule
Transport proteins allow the cell to control which substances enter or leave

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15
Q

Factors Affecting Membrane Structure & Permeability

A

Temperature
Solvent concentration

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16
Q

Temperature

A
  • proteins + lipids are both affected by temperature
  • as temp increases, lipid becomes more fluid
  • increased fluidity reduces the effectiveness of the cell membrane as a barrier to polar molecules = polar molecules can pass through
  • at higher temp, any diffusion taking place through the cell membrane will also occur at a higher speed (due to increased kinetic energy)
  • reversible changes in membrane fluidity
  • temps around 40, many proteins begin to denature -> disrupts the membrane structure (not an effective barrier)
  • substances can pass freely through the disrupted membrane
  • irreversible process
17
Q

Solvent concentration

A

Organic solvents can increase cell membrane permeability as they dissolve the lipids in the membrane, causing the membrane to lose its structure

18
Q

Diffusion

A

The net movement of a substance from a region of its higher concentration to a region of its lower concentration.
- molecules or ions move down a concentration gradient
The random movement is caused by the natural kinetic energy of the molecules or ions

19
Q

The rate at which a substance diffuses

A

Steepness of conc gradient
Temperature
Surface area
Properties of molecules

20
Q

Steepness of conc gradient

A
  • greater diff in conc = greater diff in the number of molecules passing in the 2 directions + so a faster rate of diffusion
21
Q

Temperature

A
  • molecules + ions have more KE at higher temps
  • move faster = higher rate of diffusion
22
Q

SA

A
  • greater SA, greater number of molecules/ions that can cross it at any 1 moment -> faster diffusion
  • SA of cell membrane increased by folding
  • cell increases in size, SA:V ratio decreases which slows the rate substances can diffuse through a cell as distance required becomes too great
23
Q

Properties of molecules

A
  • large molecules diffuse more slowly than smaller ones as they require more energy to move
  • uncharged + non-polar molecules diffuse directly across phospholipid bilayer
  • non-polar molecules diffuse more quickly than polar ones as they are soluble in the non-polar phospholipid bilayer
24
Q

Facilitated diffusion

A
  • certain substances cannot diffuse through the phospholipid bilayer of cell membranes including large polar molecules such as glucose and amino acids + ions such Na+ and Cl-
25
Q

Active transport

A
  • movement of molecules and ions through a cell membrane from a region of lower concentration to a region of higher concentration using ATP
  • requires carrier proteins
  • energy is required to make the carrier protein change shape, allowing it to transfer the molecules or ions across the cell membrane
  • energy required is provided by ATP produced during respiration. The ATP is hydrolysed to release energy
26
Q

Importance of active transport

A
  • the reabsorption of useful molecules + ions into the blood after filtration into the kidney tubules
  • the absorption of some products of digestion from the digestive tract
  • the loading of sugar from the photosynthesising cells of leaves into the phloem tissue for transport around the plant
  • the loading of inorganic ions from the soil into root hairs
27
Q

Endocytosis

A
  • the process by which the cell surface membrane engulfs material, forming a small sac around it
  • phagocytosis and pinocytosis
28
Q

Phagocytosis

A
  • bulk intake of solid material by a cell
    -cells that specialise in this process are called phagocytes
  • vacuoles formed are phagocytic vacuoles
    eg. engulfing of bacteria by phagocytic white blood cells
29
Q

Pinocytosis

A
  • the bulk intake of liquids
    I- f the vacuole (or vesicle) that is formed is extremely small then the process is called micropinocytosis
30
Q

Exocytosis

A

process by which materials are removed from, or transported out of, cells
- substances to be released like enzymes, hormones are packaged into secretory vesicles formed from the Golgi body
- these vesicles then travel to the cell surface membrane
- fuse with the cell membrane and release their contents outside of the cell
eg. secretion of digestive enzymes from pancreatic cells

31
Q

Osmosis

A

net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane

32
Q

Animal cells losing water in hyper

A

If an animal cell is placed in a solution with a lower water potential than the cell, water will leave the cell through its partially permeable cell surface membrane by osmosis and the cell will shrink and shrivel up (crenation) - for hypertonic environment eg. the solution outside of the cell has a lower water concentration than the inside of the cell

33
Q

Animal cells gaining water

A
  • water will enter the cell through its partially permeable cell surface membrane by osmosis
  • cell will continue to gain water by osmosis until the cell membrane is stretched too far and the cell bursts (cytolysis), as it has no cell wall to withstand the increased pressure created
    -lysis occurs when the cell is in a hypotonic environment (the solution outside of the cell has a higher water concentration than the inside of the cell)
    This is why a constant water potential must be maintained inside the bodies of animals
34
Q

Plant cells losing water

A
  • a plant cell is placed in a solution with a lower water potential than the plant cell, water will leave the plant cell through its partially permeable cell surface membrane by osmosis
  • As water leaves the vacuole of the plant cell, the volume of the plant cell decreases
  • protoplast gradually shrinks + no longer exerts pressure on the cell wall
  • the protoplast continues to shrink + it begins to pull away from the cell wall
    This process is known as plasmolysis
35
Q

Effect of high temp on structure

A

phospholipids vibrate more + have more kinetic energy
increases size of gaps in membrane
bilayer becomes more fluid
proteins denatured

36
Q

structure and function of plasma membrane

A
  • phospholipids form bilayer
    provide barrier to large / polar ions
  • proteins form carriers
    for cotransport / facilitated diffusion

cholesterol molecules fit within bilayer / between
phospholipid
stabilise membrane (structure) / regulates fluidity

  • glycoproteins / glycolipids sticking out
    from surface (of cell surface membrane)
    FOR cell signalling / receptor sites / adhesion / antigens / recognition

Biology (25 decks)

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