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SP MCAT Biochem > Biological Membranes > Flashcards

Biological Membranes Flashcards

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MCAT flashcards
1
Q

Fluid Mosaic Model

A

accounts for presence of lipids, proteins, and carbohydrates in a dynamic semisolid plasma membrane surrounding cells

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2
Q

Phospholipids

A

move rapidly in the plane of the membrane through simple diffusion

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3
Q

Lipid Rafts

A
  • collections of similar lipids with or without associated proteins that serve as attachment points for other biomolecules
  • travel slowly within the plane of the membrane
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4
Q

Flipases

A

enzymes that assist in the flipping/movement of lipids between the membrane layers

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5
Q

What are the different components of a membrane?

A
  • lipids (fatty acids, triacylglycerols, glycerophospholipids, sphingolipids, cholesterol, steroids)
  • Proteins
  • Carbohydrates
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6
Q

Lipids

A
  • most plentiful in the cells membrane

- most are phospholipids and few are free fatty acids

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7
Q

Triacylglycerols

A
  • storage lipids involved in metabolic processes

- contain 3 fatty acid chains esterified to a glycerol backbone

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8
Q

Unsaturated Fatty Acids

A
  • “healthier”
  • one or more double bonds
  • exist in liquid form at room temperature
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9
Q

Saturated Fatty Acids

A
  • main component of animal fat
  • exist as solids at room temperature
  • “less healthy”
  • decrease membrane fluidity
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10
Q

Glycerophospholipids

A
  • replace one fatty acid with a phosphate group which is often linked to other hydrophobic groups
  • used for membrane synthesis
  • can produce a hydrophilic surface layer of lipoproteins like VLDL
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11
Q

Sphingolipids

A
  • contain a hydrophilic region and two fatty acid derived hydrophobic tails
  • classes: ceramide, spingomyelins, cerebrosides, gangliosides
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12
Q

Cholesterol

A
  • regulates membrane fluidity
  • necessary for synthesis of steroids
  • contains hydrophilic and hydrophobic region
  • increases fluidity at low temperatures and decreases fluidity at high temperatures
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13
Q

What are the functions of proteins in a cell membrane?

A
  • transporters
  • cell adhesion molecules
  • enzymes
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14
Q

Transmembrane Proteins

A
  • have one or more hydrophobic domains

- function as receptors or channels

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15
Q

Embedded Proteins

A
  • either part of a catalytic complex or involved in cellular communication
  • usually linked to nearby enzymes
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16
Q

Peripheral Proteins

A

involved in signaling or are recognition molecules on the extracellular surface

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17
Q

Carbohydrates

A
  • usually attached to proteins on extracellular surface
  • generally hydrophilic and can form protective glycoprotein coat
  • function in signaling and recognition
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18
Q

Cell Adhesion Molecules

A
  • typically compose cell-cell junctions

- proteins that allow cells to recognize each other and contribute to cell differentiation and development

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19
Q

Gap Junctions

A
  • allow direct cell-cell communication
  • found in small bunches
  • made up of connexons which are formed by alignment and interaction of pores composed of 6 molecules of connexin
  • permit movement of water and some solutes (ions) directly between cells
  • essentially like a tunnel that connects two cells
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20
Q

Tight Junctions

A
  • not used in intercellular transport
  • form a water tight seal and prevent paracellular transport of water and solutes
  • found in epithelial cells
  • function as physical link between cells
  • limit permeability enough to create a transepithelial voltage difference
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21
Q

Desmosomes

A
  • anchor cytoskeletons of adjacent cells together via interactions between transmembrane proteins associated with intermediate filaments
  • ions and water can flow between cell gaps
22
Q

Where do tight junctions occur in the human body?

A
  • bladder
  • intestines
  • kidney
23
Q

Where do desmosomes occur in the human body?

A
  • skin

- intestines

24
Q

Where do gap junctions occur in the human body?

A

cells/tissue that spread action potential or cells that use electrical coupling

  • cardiac muscle
  • neurons
25
Q

Passive Transport

A
  • spontaneous processes that don’t require energy (- delta G)
  • includes: diffusion, facilitated diffusion, osmosis
  • primary thermodynamic motivator is an increase in entropy (delta S)
26
Q

Simple Diffusion

A

involves movement of small, nonpolar, lipid-soluble molecules down their concentration gradient

27
Q

Osmosis

A
  • movement of water through aquaporins from an area of low solute concentration to a high solute concentration
  • referred to when a specific solute is impermeable
28
Q

What is the osmolarity of red blood cells?

A

300 mOsm / L

29
Q

Hypotonic

A
  • internal solute concentration > external solute concentration
  • leads to swelling of cell
30
Q

Hypertonic

A
  • internal solute concentration < external solute concentration
  • leads to cell shriveling
31
Q

Isotonic

A

solutions inside and outside of cell are equimolar

32
Q

Osmotic Pressure

A
  • colligative property [physical property of solutions that depends on the concentration of dissolved particles and not their chemical identity]
  • the pressure applied to a pure solvent to prevent osmosis and is used to express the concentration of the solution
33
Q

Facilitated Diffusion

A
  • uses transport proteins to move impermeable solutes across the cell membrane
  • transports large, polar, charged molecules across the membrane
34
Q

Active Transport

A
  • non-spontaneous processes that require energy (+ delta G)
  • results in net movement of solute against its concentration gradient
  • includes: primary active, secondary active
35
Q

Primary Active Transport

A
  • uses ATP directly or use of transmembrane ATPase

- Ex. Sodium/Potassium pump

36
Q

Secondary Active Transport

A
  • no direct coupling to ATP hydrolysis
  • uses an electrochemical gradient – generated by active transport – as an energy source to move molecules against their gradient, and thus does not directly require a chemical source of energy such as ATP
  • can transfer molecules in a symport or antiport direction
37
Q

Endocytosis

A
  • cell membrane invaginates and engulfs material to bring into cell
  • initiated by substance binding to specific receptors then carried out by vesicle-coating proteins (ex. clathrin)
  • includes: pinocytosis, phagocytosis
38
Q

Pinocytosis

A

endocytosis of fluids and dissolved particles

39
Q

Phagocytosis

A

endocytosis of large solids like bacteria

40
Q

Exocytosis

A
  • secretory vesicles fuse with membrane and release material into extracellular fluid
  • important in neurotransmitter release and intercellular signaling
41
Q

Membrane Potential

A

different in electrical potential across cell membranes

42
Q

Leak Channels

A

allow ions to passively diffuse down their concentration gradient through the cell

43
Q

What type of leak channel occurs most in neurons?

A

K+ leak channels

44
Q

Sodium/Potassium Pump

A
  • primary active transport
  • pumps 3 Na+ out of the cell and 2 K+ into the cell
  • maintains low concentration of sodium ions and high concentration of potassium ions intracellularly
45
Q

Nernst Equation

A

used to determine the membrane potential from the intra- and extracellular concentrations of various ions

46
Q

Goldman-Hodgkin-Katz Voltage Equation

A

flows from the Nernst Equation but takes into account the relative contribution of each major ion to the membrane potential

47
Q

How do Mitochondria produce ATP?

A

oxidative phosphorylation

48
Q

Outer Mitochondrial Membrane

A
  • highly permeable to ions and small proteins because has many large pores
  • small intermembrane space between outer and inner membranes
49
Q

Inner Mitochondrial Membrane

A
  • more restricted permeability
  • membrane lacks cholesterol
  • contains cristae (infoldings of the membrane) which increases surface area for integral proteins associated with the ETC and ATP synthesis
  • encloses the mitochondrial matrix
  • contains a high level of cardiolipin
50
Q

What important process occurs in the mitochondrial matrix?

A

Citric Acid Cycle

51
Q

Does a pH gradient exist between the cytoplasm and intermembrane space in the mitochondria?

A

No – this is because the outer membrane has such a high permeability to biomolecules

SP MCAT Biochem (16 decks)

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