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Biology Module 2 > Cell Membranes > Flashcards

Cell Membranes Flashcards

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1
Q

What are the two types of membranes?

A
  • plasma membranes; at the surface of cells
  • membranes within cells
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2
Q

What is compartmentalisation and why is it important?

A
  • the formation of separate membrane bound areas inside a cell
  • vital as metabolism includes many different and often incompatible reactions so this separation allows specific conditions required for cellular reactions such as chemical gradients being maintained
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3
Q

Outline 3 functions of plasma membranes

A
  • they allow recognition by other cells
  • they allow cell communication/cell signalling
  • they act as barriers between the cell and environment controlling what leaves and enters
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4
Q

Describe the permeability of plasma membranes

A
  • they are partially permeable
  • substances can move across via diffusion, osmosis or active transport
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5
Q

Outline the Cell Membrane Theory

A
  • the fluid-mosaic model
  • describes the arrangement of molecules within the membrane
  • phospholipids form a continuous bilateral and are constantly moving (fluid)
  • protein molecules vary in shapes and sizes and are scattered through the bilayer (mosaic)
  • cholesterol, glycoproteins and glycolipids are present
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6
Q

What are intrinsic proteins

A
  • transmembrane proteins embedded through both layers of a membrane
  • have amino acids with hydrophobic R-groups which interact with the hydrophobic core of the membrane, keeping them in place
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7
Q

What are examples of intrinsic proteins

A
  • channel proteins
  • carrier proteins
  • glycoproteins
  • glycolilpids
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8
Q

What are channel proteins

A
  • intrinsic proteins
  • they provide a hydrophilic channel that allows the diffusion of polar molecules and ions
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9
Q

What are carrier proteins

A
  • intrinsic proteins
  • play an important role in the passive/active transport into cells; often involves the protein changing shape
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10
Q

What are glycoproteins? Descrive their structure and function

A
  • intrinsic proteins which are embedded in the plasma membrane with attached carbohydrate chains of varying lengths and shapes
  • play a role in cell adhesion and as receptors for chemical signals (cell communication/signalling)
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11
Q

Give 3 examples where glycoproteins act as receptors for cell signalling

A
  • receptors for neurotransmitters (eg acetylcholine) at synapses where the binding triggers/prevents an impulse
  • receptors for peptide hormones (eg insulin and glucagon) in the storage and uptake of glucose
  • drugs such as b-blockers to reduce the response of the heart to stress
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12
Q

What are glycolipids? Describe their structure and function

A
  • intrinsic proteins; lipids with attached carbohydrate chains
  • known as cell markers or antigens and can be recognised by cells of the immune system as self or non-self
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13
Q

What are extrinsic proteins?

A
  • are present in one side of the bilayer
  • have hydrophilic R groups on their surface which interact with the polar heads of the phospholipids or intrinsic proteins
  • can be in either layer and can move between layers
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14
Q

What is an example of an extrinsic protein

A
  • cholesterol
  • regulates membrane fluidity
  • has a hydrophobic end which interact/binds with the hydrophilic tail of the phospholipid
  • has a hydrophilic end which interact/binds with the hydrophobic head of the phospholipid
  • make the membrane less fluid by binding and packing closely together
  • makes the membrane more fluid by preventing the phospholipids from packing too close together
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15
Q

How does temperature affect membrane permeability

A
  • increased temp means phospholipids will have more kinetic energy and therefore move more, making the membrane more fluid as it will begin to lose structure, if it gets too high the membrane will break down
  • the loss in structure increases the permeability so particles can easily cross it
  • high temperatures can denature the proteins, affecting permeability as transport of substances may be impacted
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16
Q

How do solvents affect membrane permeability

A
  • organic solvents such as alcohol can dissolve membranes
  • pure/strong alcohol is toxic and will destroy cells but less concentrated alcohol will just cause damage
17
Q

How can less concentrated alcohol damage membranes

A
  • the non polar alcohol molecules can enter the membrane and the presence of them between the phospholipids disrupts the membrane making it more fluid and permeable
  • this prevents the membrane from being able to carry out functions (e.g the transmission of nerve impulses)
18
Q

Define diffusion

A
  • the net movement of particles from a region of high concentration to a region of low concentration until it reaches equilibrium
    (down a concentration gradient)
19
Q

What factors affect rate of diffusion

A
  • temperature; higher temp means higher rate of diffusion as particles have more kinetic energy and move at higher speeds
  • concentration difference; the greater conc difference means faster rate of diffusion as overall movement will be larger
20
Q

Why are membranes described as partially permeable

A
  • non polar molecules (oxygen) can diffuse freely
  • ions cannot easily pass through
  • polar molecules (water) can diffuse through membranes but at a slow rate
21
Q

How does SA and thickness affect rate of diffusion

A
  • the larger the SA, the higher rate of diffusion
  • the thinner the exchange surface, the higher rate is diffusion
22
Q

What is facilitated diffusion

A
  • the diffusion across a membrane through protein channels
  • can also involve carrier proteins which change shape when a specific molecule binds
23
Q

Why are membranes with protein channels selectively permeable

A
  • most protein channels are specific to one molecule or ion
24
Q

What other factors affect the rate of facilitated diffusion

A
  • the number of protein channels present
  • the more present the higher rate of diffusion overall
25
Q

Define active transport

A
  • movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration
  • particles are moving up a concentration gradient so therefore the process requires energy which is supplied by ATP
26
Q

Describe the general process of active transport

A
  • the carrier protien spans the membrane
  • the molecule will bind to receptors in the channel of the carrier protien
  • on the inside of the cell ATP will bind to the carrier protein and is hydrolysed into APD and phosphate
  • the phosphate binds to the carrier protein causing it to change shape and opens up the inside of the cell
  • the molecule is then released into the cell
  • the phosphate molecule is released from the carrier protein and recombines with ADP to form ATP
  • the carrier protein returns to its original shape
27
Q

Why is active transport selective

A

specific substances are transported by specific carrier proteins

28
Q

What is bulk transport

A
  • form of active transport
  • large molecules such as enzymes are too large to fit through channel or carrier proteins so are transported by bulk transport
29
Q

What is endocytosis? What are the two types?

A
  • the bulk transport of material into cells
  • phagocytosis (solids) and pinocytosis (liquids)
30
Q

Describe the process of endocytosis

A
  • the material will come into contact with the membrane which then invaginates (bends inwards)
  • the membrane enfolds the material until it eventually fuses, forming a vesicle
  • the vesicle pinched off and moves into the cytoplasm to transfer the material for further processing
31
Q

Define exocytosis

A
  • vesicles (normally formed by the golgi) move towards and fuse with the membrane
  • contents of the vesicle are then released outside of the cell

Biology Module 2 (2 decks)

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