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Bio 107 > Membrane Structure and Function (Ch. 7) > Flashcards

Membrane Structure and Function (Ch. 7) Flashcards

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1
Q

About how thick is the plasma membrane?

A

About 8 nm

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2
Q

What is selective permeability?

A

A property of biological membranes whereby it allows some substances to cross it more easily than others

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3
Q

What are the most important ingredients of membranes?

A

Lipids and proteins mostly; some carbohydrates

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4
Q

What are the most abundant lipids in the membrane?

A

Phospholipids

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5
Q

Are phosopholipids hydrophilic, hydrophobic, or both?

A

Both – this is called being amphipathic. They have a hydrophilic region and a hydrophobic region

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6
Q

How are phospholipids and proteins arranged in the membranes of cells?

A
  • They are arranged in the fluid mosaic model.
  • The membrane is a fluid structure with a mosaic of various proteins embedded in or attached to a phospholipid bilayer.
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7
Q

Envision:

  • Fibers of extra-cellular matrix
  • Glycoproteins
  • Carbohydrates
  • Glycolipids
  • Integral proteins
  • Membrane proteins
  • Cholesterol
  • Microfilaments of cytoskeleton
A
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8
Q

What primarily holds together membranes?

A

Mostly hydrophobic interactions. Much weaker than covalent bonds.

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9
Q

How and how often do the proteins and lipids in the bilayer shift around?

A

Laterally – very often, 10^7 times per second

Vertical flip-flop - rarely, once per month

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10
Q

What causes kinks in the tails of bilayer lipids, and what effect do those kinks have? Why?

A

Kinks are caused by double bonds that create unsaturated hydrocarbons. The kinks lower the solidification temperature of the membrane because the layers cannot pack together as closely as saturated tails.

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11
Q

What does cholesterol do to the membrane?

A

Cholesterol is a “fluidity buffer” that makes it resist changes in membrane fluidity caused by temprature.

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12
Q

Describe evolution and its impact on cell membrane lipid composition.

A

Adaptations to environments: Fish living in cold environments evolved bilayers with lots of unsaturated lipid tails; bacteria in super hot geysers developed bilayers with lipids that prevented excessive fluidity.

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13
Q

What are the two major populations of membrane proteins?

A
  1. Integral proteins
  2. Peripheral proteins
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14
Q

Describe integral proteins.

A

Integral proteins penetrate the hydrophobic interier.

Most are transmembrane proteins, spanning the whole membrane.

Others go only part way into the hydrophobic interior.

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15
Q

Describe peripheral proteins.

A

Peripheral proteins are not embedded in the bilayer; they are appendages loosely bound to the surface of the membrane, often to exposed parts of integral proteins.

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16
Q

What are the six major functions performed by proteins of the plasma membrane?

A
  1. Transport
  2. Enzymatic activity
  3. Signal Transduction
  4. Cell-cell recognition
  5. Intercellular joining
  6. Attachment to the cytoskeleton and extracellular matrix
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17
Q

What membrane macromolecule is most crucial to cell-cell recognition?

A

Membrane carbohydrates are the most important.

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18
Q

Describe the structure of membrane carbohydrates. How long are they?

A

They are usually short, branched chains of fewer than 15 sugar units. They might be bonded covalently to lipids (–> glycolipids) or proteins (–> glycoproteins)

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19
Q

Are membranes sided? If so, how does that sidedness arise?

A

The asymmetrical arrangement of proteins/lipids/carbs in the membrane is determined as the membrane is being built by the ER and Golgi apparatus

20
Q

Describe the steps of membrane synthesis

A
  1. Membrane proteins and lipids are synthesized in the ER.
  2. In Golgi, glycoproteins’ carbs are modified, and lipids get carbs, becoming glycolipids
  3. Glycoproteins, glycolipids, and secretory proteins are transported in vesicles to the membrane
  4. Vesicles fuse with the membrane and release the secretory proteins (exocytosis)
21
Q

What moves easily across the plasma membrane in both directions?

A

small molecules, ions, nonpolar molecules (because they are hydrophobic)

Polar molecules have trouble because they are hydrophilic, Charged molecules/atoms also have trouble because they’ll have a surrounding shell of water.

22
Q

How can some specific ions and a varity of polar molecules pass through the cell membrane? How does it work?

A

transport proteins (aka channel proteins) that span the membrane.

They act as a sort of tunnel through the membrane

23
Q

What transports water (polar…) across the membrane?

A

transport proteins called aquaporins

24
Q

What are carrier proteins?

A

Carrier proteins are a type of transport protein that hold onto their passengers and change shape enough to send them across.

25
Q

What is diffusion?

A

Diffusion is the movement of molecules to spread out evenly into an available space, caused by thermal energy of the molecules

26
Q

Define osmosis

A

the diffusion of free water across a selectively permeable membrane. aims to establish water balance.

27
Q

Define tonicity, hypertonic, hypotonic, isotonic

A

concentration and membrane permability

more concentrated

less concentrated

equally concentrated

28
Q

Compare the effects of different tonicities in animal/plant cells without/with a cell wall

A
29
Q

Define facilitated diffusion

A

When a molecule (particularly a polar molecule or an ion) diffuses passively through the membrane with the help of transport transmembrane protein.

30
Q

What is the difference between channel proteins and carrier proteins?

A

Channel proteins are corridors; carrier proteins actually change shape to bring the molecule across the membrane.

31
Q

What are ion channels?

A

Ion channels are channel proteins that channel ions

32
Q

What are gated channels?

A

Gated channels are a type of ion channel (a type of channel protein) that open or close in response to a stimulus.

Stimulus could be electrical or when a specific third-party substance binds to the channel

33
Q

Define active transport

A

using energy to pump a solute across a membrane against its gradient.

34
Q

Describe the nature of the K+ and Na+ concentrations in an animal cell

A

An animal cell needs way more K+ compared to Na+, so it needs sodium-potassium pumps to maintain this

35
Q

Describe the steps of a sodium-potassium pump

A
  1. Cytoplasmic Na+ binds to the pump, because it is in its high-Na+-affinity shape
  2. Na+ binding stimulates phosphorylation by ATP (now ATP is a P – on the protein – and ADP)
  3. Phosphorylation makes the protein change shape, releasing Na+ outside
  4. The new shape likes K+, which binds on the outside and triggers the release of the phophate inside
  5. The loss of the phosphate group restores original shape
  6. K+ is released; cycle repeats
36
Q

What is membrane potential?

A

The voltage across a membrane caused because the cytoplasmic side is negative in charge compared to the extracellular side.

37
Q

Which way does the membrane potential favor movement (re: voltage across the cell)

A

Because the inside of the cell is negative compared with the outside, the potential favors the passive transport of cations (+) into the cell and anions (-) out of the cell.

38
Q

What drives diffusion of an ion across a membrane? What is this called?

A
  1. Chemical Force (ion’s concentration gradient)
  2. electrical force (effect of the membrane potential on the ion’s movement)

Together, called the elctrochemical gradient

39
Q

What is an electrogenic pump?

A

A transport protein that generates voltage across a membrane. Think: Na-K pump. Pumps out three Na+ for 2 K+ in; that’s a net +1 getting pumped out.

40
Q

What is the main electrogenic pump in plants, fungi, and bacteria?

A

Proton pump.

Actively transports protons out of the cell. Transfers positive charge from cytoplasm to extracellular solution.

41
Q

What is cotransport?

A

Cotransport is when a pump uses active transport and then the molecule that was pumped out diffuses down into the cell again, but this time via a cotransporter that brings another molecule along with it.

42
Q

What is exocytosis? What are some examples of its use?

A

How the cell secretes certain biomolecules by fusing vesicles with the plasma membrane

Ex.:

  1. Pancreas cells that make insulin secrete insulin
  2. neurons release neurotransmitters
  3. plant cells delivering proteins and carbs from Golgi vesicles outside the cell when they are making walls
43
Q

Define endocytosis

A

Takes in biomolecules by forming new vesicles from the plasma membrane.

44
Q

What are the three types of endocytosis?

A
  1. phagocytosis (“cellular eating”)
  2. pinocytosis (“cellular drinking”)
  3. receptor-mediated endocytosis
45
Q

What is an example of receptor-mediated endocytosis?

A

Taking in cholesterol for membrane synthesis and the synthesis of other steroids

Bio 107 (4 decks)

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