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bio a-level > 2.5 cell membranes > Flashcards

2.5 cell membranes Flashcards

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Biology 101 flashcards
1
Q

name all the structures in a cell membrane

A
  • phospholipids - phosphate head, fatty acid tails
  • glycolopids
  • glycoproteins
  • intrinsic proteins
  • extrinsic proteins - channel proteins, gated proteins, carrier proteins
  • cholesterol
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2
Q

explain the role of glycolipids

A
  • lipids attached with carbohydrate chains
  • act as antigens so that cells can be recognised by the cells of immune system
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3
Q

explain the role of glycoproteins

A
  • proteins with carbohydate chains attached
  • plays a role in cell adhesion and as receptors for cell signaling
  • when chemical binds to receptor it elecits a response from the cell - cell signaling eg. receptors for neurtransmitters at nerve cells synapses, neurtoransmiiters bind to receptors or receptors used for peptide hormones
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4
Q

explain role of channel proteins

A
  • provide a hydrophyllic channel that allow passive movement of polar molecules and ions down a concentration gradient
  • held in position by intercation between the hydrophylic core of the membrane and the hydrophylic R-groups on the outside of the protiens
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5
Q

explain the role of gated proteins

A
  • channel can open or close in a reponse to a particular signal
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6
Q

explain the role of carrier proteins

A
  • important in role of passive and active transport
  • requires energy ATP to release energy to change shape for sepecific molecules
  • specific types of carrier protiens for different types of molecules
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7
Q

explain the role of cholesterol

A
  • attach to the fatty acid tails to give stabilty and structure to the membrane
  • at low temperatures : cholesterol increases fluidity of the membrane stopping the phospoholipid tails packing too close
  • at high temperatures : cholesterol decreases fluidity of the membrane by making the phospholipid tails packing closer together
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8
Q

what factors affect membrane stucture

A
  • temperature
  • solvents
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9
Q

how does temperature affect the membrane structure

A
  • when temp high: phospholipids have gain more kinetic energy so move more therefore make the membrane more fluid and loose structure, permeability increases making it easier for particles to cross it
  • when temp really high - proteins denature making the membrane even more permeable and destroying the cell structure
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10
Q

how do solvents affect membrane structure

A
  • organic solvents dissolve membranes disrupting the membrane structure
  • if solvent is alcohol - causes damage to the cell membrane sllowing non-polar molecules to enter the cell membrane which disrupts the membrane, when the membrane is disrupted it becomes more fluid and more permeable
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11
Q

give the definition of active transport

A

movement of molecules or ions through a cell membrsne from a region of lower concentration to a regio of higher concentration using energy from respiration

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12
Q

what is active transport used in

A
  • reabsorption of useful molecules and ions into blood after filtration in the kidney tubules
  • absorption of some products of digestion eg. glucose into the blood
  • loading of sugar from photosynthesis cells of leaves into phloem tissue for transport around plants
  • loading of organic ions from soil to root hair
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13
Q

explain the process of active transport through the use of carrier proteins in cells

A
  1. the molecule or ion that needs to be transported binds to receptors in the carrier protein
  2. on the otehr side of the cell ATP binds to the carrier prteisn and is hydrolysed into ADP and P(phsophate)
  3. Binding of P to carrier protein causes the protien to change shape - openign up tot he other side of the membrane
  4. molecule or ion is released to the inside or outside of the cell
  5. phsophate released from carrier protein and recombine with ADP to form ATP
  6. carrier protien returns to original shape
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14
Q

what is bulk transport

A
  • trasnportz larg quantities of maferials in or out of cells
  • carry large rnolecules such as protein or pollysacharides
  • carry parts of cell
  • carry whole cells eg. bacteria (lysomes)
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15
Q

what are the differen types of bulk transport

A
  • endocytosis - phagoctosis for solids or pinocytosis for liquids (includes micropinocytosis and macropinocytosis)
  • exocytosis
  • ATP needed for movement of these vesicles along the cytoskeleton
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16
Q

describe the process of endocytosis

A
  1. cell membrane invaginates when it comes into contact with the material that needs to the teansported
  2. the membrane enfolds the material until the membrane fuses forming a vesicle
  3. vescile moves into the cytoplasm to transfer material further for prcoessing
17
Q

what si phagocytosis

A
  • bulk transport of solid materials
  • cells that specialise in the process are called phagocytes
  • vacuoles formed are called phagocytic vacuoles
  • occurs when engulfing bacteria by phagocytic white blood cells
18
Q

what is pinocytosis

A
  • bulk intake of liquids
  • if the vesicle that is formed is extermely small the process is called micropinocytosis, opposite for macropinocytosis
19
Q

desfibe the process of exocytosis

A
  • substances to be transported are pachaged in secretory vesucles formed by the golgi appratis
  • secretory vesicles move tot he cell surface membrane
  • the contents gets released outside of the cell
20
Q

definition of diffusion

A

net or overall movement of particles from a region of higher concentration to an area of lower concentration
will ocntinue until there is an equilibrium

21
Q

*

what are the factors affecting diffusion

A
  • temperature
  • concentration difference
  • surface area
  • properties of molecules/ions
22
Q

how does temp affect the rate of diffussion

A

the higher temp the higher the difference in conc between 2 regions the faster the rate of diffusion because overall movement from higher to lower conc will be longer

23
Q

how does concentration difference affect the rate of diffussion

A

the greater the difference in conc between 2 regions the faster the rate of diffusion bc of overall movment from higher to lower conc will be longer

24
Q

****

how does surface area affect the rate of diffussion

A
  • the grater the surface area accross which diffsuion takes place the higher the no. of molecules/ions can cross at any one moement therefore facster rate of diffusion
25
Q

how do properties of molecules/ions affect the rate of diffussion

A
  • large molecules diffuse slower as they require more energy to move eg. H2O
  • uncharged and non-polar molecules diffuse directly through and as they are soluble in the non-polar phospholopid bilayer
26
Q

what is simple diffusion

A
  • down a concentration gradient
  • non-polar molecules
  • steroid hormones eg. oestrogen, testosterone
  • lipid soluble vitamins eg. vitamin A and D
  • small polar molecules eg. H20 but very slowly
27
Q

**

what is facilitated diffusion

A
  • diffusion accros membrane through protein channels
  • used for large polar molecules eg. glucose and amino acids, or ions eg. Na+ and Cl-
28
Q

how are channel proteins used in facilitated diffusion

A
  • water filled poer
  • all charged substanced to diffuse through membrane by making them soluble
  • diffsuon of these ions doesn;t occur freely - most proteins are gated so it allows the cells to havr more control over exchange of molecules
29
Q

how are carrier proteins used in facilitated diffusion

A
  • they can switch between shaped causing the binding site to be open to which ever side of the membrne has a higher conc then hnages shape to allow it to oepn to otehr side to allow molecule to go to side of lower conc
30
Q

**

osmosis definition

A

moevemnt of water through a partially permeable membrane from an are of high water potential to an area of lower water potential

31
Q

defintion of water potential

A

measur eof the quanity of water compared ot solute mesured as pressure vreated by water molecules in kilopascales (KPa)

32
Q

Describe osmosis in plant cells

A
  • when high water potential outside cell and lower inside the cell becomes turgid as water enters the cell
  • when same water potential inside and outside the same rate of osmosis occurs
  • when higher water potential inside than outside the cell becomes flaccid water exits the cell as protoplast shrinks from cell wall
  • when even higher water potenial inside than outside the cell becomes plasmolysed water exits the cell and proteoplats shrinks completely
32
Q

describe osmosis in animal cells

A
  • when cell in a hypertonic solution (low water potential) cell becomes crenated as water exits the cell
  • when cell in an isotonic solution water diffuses in and out at same rate as water potential same on inside and outside
  • when cell in a hypotonic solution (high water potenial) cell become shaemolysed as water moves into the cell

bio a-level (3 decks)

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