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Biocheem > Lecture 24 > Flashcards

Lecture 24 Flashcards

1
Q

What type of side chains make up most of the helix surfaces that face lipid tails in integral membrane proteins?

A

Non-polar side chains

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2
Q

Where are polar side chains in integral membrane proteins more common?

A

Interacting with the lipid head groups in a solvent

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3
Q

What type of side chains interact with the solvent in integral membrane proteins?

A

Polar side chains like Asp, Glu, Lys, Arg

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4
Q

What is the biggest difference between soluble globular proteins and integral membrane proteins?

A

In integral membrane proteins, a portion of the membranes surface is going to be hydrophobic, in the region where the protein is interacting with the core of the phospholipid membrane

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5
Q

What is the core of soluble globular proteins generally rich in?

A

Regular secondary structure

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6
Q

What does regular secondary structure of proteins allow for?

A

They allow for satisfaction of hydrogen bonding potential of the polypeptide backbone because there is nothing to H-bond to in the H-bond core environment

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7
Q

What kinds of structures in integral membrane proteins traverse the membrane of the phospholipid bilayer?

A

Regular secondary structure and beta sheets (beta barrel)

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8
Q

Why does secondary structure transverse the membrane in integral membrane proteins?

A

Regular secondary structure because it satisfies its own secondary structure by H-bonding of the back bone

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9
Q

What is a Beta-Barrel?

A

A variation of a beta-sheet structure that satisfies the H-bonding potential of protein secondary structure so it transverses the membrane

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10
Q

What is the phobicity of amino acids the form a transmembrane alpha helix?

A

They are generally hydrophobic

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11
Q

What is the fluid mosaic model of membrane strucutre?

A

A dynamic, non-covalent, complex assembly of lipids and proteins (and carbohydrates)

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12
Q

What is the movement of lipids and proteins in the fluid mosaic model?

A

Both lipids and proteins move laterally but cannot (easily) undergo transverse movement

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13
Q

What can the movement of proteins be limited by?

A

The cytoskeleton

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14
Q

What are carbohydrate chains attached to in the fluid mosaic model?

A

they are attached to the extracellular surface of some proteins and lipids

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15
Q

Through what kind of interactions do integral membrane proteins associate with the bilayer?

A

Through non-covalent interactions ex. The hydrophobic effect, Van der Waals interactions

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16
Q

Through what interactions do lipids in the bilayer interact with each other?

A

Through non-covalent interactions ex. The hydrophobic effect, Van der Waals interactions

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17
Q

What is the speed of the different types of movement that membrane lipids can undergo?

A

Transverse (from one leaflet to another) is very slow while lateral diffusion is quick

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18
Q

Where on the phospholipid bilayer are the carbohydrates usually found?

A

On the extracellular face

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19
Q

What is the difference in mobility between embedded proteins and peripheral membrane proteins?

A

Peripheral membrane proteins are more mobile than proteins embedded in the membrane

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20
Q

What is the lipid bilayer membrane stabilized by?

A

Hydrophobic interactions between the lipid molecules and integral membrane proteins

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21
Q

What kinds of molecules can cross the lipid bilayer by simple diffusion?

A
  • Gases
  • Hydrophobic molecules
  • Small polar molecules (H2O, Ethanol)
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22
Q

What molecules cannot cross the lipid bilayer by simple diffusion?

A

Large Polar molecules and charged molecules

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23
Q

What does the rate of simple unmediated diffusion depend on?

A
  • Size of molecule
  • Concentration gradient
  • Lipid solubility
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24
Q

Why can’t large polar molecules diffuse across the lipid bilayer?

A

Because polar molecules have extensive interactions with water and if you try and place them in the core you have to break all the interactions and this is energetically costly

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25
Q

How does a size of the molecule affect the rate of diffusions?

A

Smaller molecules move faster than larger ones

26
Q

How does the concentration gradient affect the rate of unmediated diffusions?

A

Larger gradient increases rate of diffusions

27
Q

How does lipid solubility affect the rate of simile unmediated diffusion?

A

Greater solubility increases diffusion rate

28
Q

How does the polarity affect the rate at which a molecules passes through membrane?

A

The more polar a molecules the more slowly it transverses

29
Q

What is energy like going from an area of high concentration to an area of low concentration?

A

It is energetically favorable and energy is released

30
Q

What is energy like going from an area of low concentration to an area of high concentration?

A

It is energetically unfavorable and energy is required

31
Q

What are the two major types of transport across biological membranes?

A

Passive and active

32
Q

What is the equation for 𝛥G?

A

𝛥G = RTln ([X] destination/[X] source)

33
Q

What characteristics gives pass (spontaneous) transport?

A

𝛥G is negative. The concentration of the molecules is greater at the source than the destination giving the a ratio <1

34
Q

What characteristics give active pass transport?

A

The ration of the molecule destination to source is >1 and 𝛥G is positive

35
Q

What does it mean if 𝛥G is positive?

A

Energy must be provided to make transport occur

36
Q

What overall must 𝛥G be for transport to occur?

A

𝛥G < 0

37
Q

How do transport proteins affect the activation energy barrier for transport?

A

The reduce the activation energy barrier for transport

38
Q

What are the two types of passive transporters?

A

Porins and Ion channels

39
Q

What are the characteristics of transporters?

A
  • Most are trimers (3 subunits)
  • Each subunit contains a pore
  • Non-selective
40
Q

What do Porins contain?

A

A relatively non-specific, water-filled pore in the center of a β-barrel

41
Q

What is the channel formed between in ion channels?

A

It is found between subunits

42
Q

What is the selectivity of ion channels

A

They are highly selective

43
Q

What kind of structure is a Porin?

A

It’s a beta-barrel, usually a homotrimer so it contains three of the same subunits and has quaternary structure

44
Q

Up to what size can porins allow things in?

A

Up to 1.5kDa or 1500g/mol

45
Q

What does selectivity of an ion channel depend on?

A

Size of the pore and the properties of side chains/functional groups found there

46
Q

What is the core of the K+ ion channel made of?

A

A series of carbonyls from the polypeptide backbone to interact with the potassium ion to replace it original interactions with water

47
Q

What is the main distinction of Transporter Proteins?

A

Conformational change alternates opening from one side from the membrane to the other

48
Q

What is the main difference between Transporter (carrier) protein and ion channels and porins?

A

The conformation of carrier proteins change as part as part of the transport process

49
Q

What kind of Transport do carrier proteins have?

A

They can either be passive or active

50
Q

What is the limit of speed of Porins and Ion Channels?

A

There is no limit to how fast the diffusion process can go

51
Q

What does a graph of the kinetics of carrier proteins look like?

A

They have a hyperbolic relationship of the concentration of the solute and the rate the solute is moved across the membrane

52
Q

What is the speed of passive transport by carrier proteins?

A

They have a maximum speed

53
Q

Why don’t porins and ion channels have a maximum speed?

A

Because they aren’t changing conformation

54
Q

What do uniports transport?

A

A single solute

55
Q

What do symports and antiports transport?

A
  • Symport - two solutes in same direction

* Antiport - two solutes in different directions

56
Q

What does Primary active transport use for energy?

A

ATP

57
Q

What does secondary active transport use for energy?

A

An ion gradient

58
Q

What is the free energy change associated with active transport?

A

𝛥G > 0

59
Q

What does net energy change need to be in order for transport to occur?

A

𝛥G < 0

60
Q

What does the some of free energy for active transport have to add up to?

A

𝛥G < 0

Biocheem (38 decks)

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