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Bio 152 > Cell Membranes And How They Work > Flashcards

Cell Membranes And How They Work Flashcards

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0
Q

Why is water vital for life?

A

It is an excellent solvent.

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1
Q

What percentage of the volume of a typical cell is made up of water?

A

~75%

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2
Q

What is a solvent?

A

An agent, like water, for dissolving substances and getting them into a solution

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3
Q

What is a solute?

A

Substances that are dissolved by solvents

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4
Q

Why is it important for vital substances to dissolve

A
  • Your body depends on direct physical interactions between molecules.
  • Substances are more likely to come into contact with one another and react as solutes.
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5
Q

Why is water such an efficient solvent?

A

1) O-H bonds are polar thanks to the electronegativities of hydrogen and oxygen (slightly positive and slightly negative).
2) The molecule is bent, giving the water molecule and overall polarity.
3) Due to the polarities substances (usually ionic) can dissolve in water

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6
Q

When two water molecules approach each other, what type of bond is formed?

A

Hydrogen bond (the strongest type of dipole-dipole bond)

Note: not as strong as ionic or covalent bonds

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7
Q

Define hydrophilic

A

“water-loving”

  • substances that interact with water by forming hydrogen bonds.
  • usually ions and polar molecules
  • dissolve in water
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8
Q

Define hydrophobic

A

“water-fearing”

  • substances that do not interact (or interact very little) with water.
  • water does not form hydrogen bonds with hydrophobic molecules
  • water molecules are forced to form hydrogen bonds with other water molecules - makes hydrophobic interactions more stable.
  • do not dissolve
  • usually covalent or non-polar molecules
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9
Q

What other properties of water are important for life?

A
  1. Cohesion
  2. Adhesion

Both necessary for water movement through roots of plants

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10
Q

Define cohesion

A

Attraction between like molecules.

water molecules stick together

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11
Q

Define adhesion

A

Attraction between unlike molecules

Eg. Water stick to glass

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12
Q

Surface tension

A
  • When water molecules are at the surface, there are no molecules above them for hydrogen bonding.
  • As a result form stronger attractive forces between their nearest neighboring molecule
  • Tensions form that minimize surface area causing any force that depresses water surfaces to meet with resistance
  • light object will not break the surface
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13
Q

Function of the plasma membrane (cell membrane)

A
  1. Plasma membrane serves as a selective barrier: it keeps damaging compounds out and vital compounds in.
  2. Sequesters the appropriate chemicals in an enclosed area, reactants collide more frequently and more efficiently
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14
Q

What is a lipid?

A

Lipids (fats/oils) are carbon-containing compounds that are largely non-polar and hydrophobic. They are mainly hydrocarbons.

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15
Q

What are hydrocarbons?

A

Molecules that contain only carbon and hydrogen (many times in long chains).

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16
Q

Are hydrocarbons hydrophobic? Why or why not?

A

Yes - are hydrophobic because electrons are shared equally in C-H bonds due to approximately equal electronegativity.

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17
Q

Are lipids hydrophobic?

A

Yes because they have a significant hydrocarbon component.

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18
Q

What are fatty acids?

A

A simple lips consisting of a hydrocarbon chain bonded to a carboxyl group (-COOH).

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19
Q

Hydrocarbons that contain only single bonds between carbon are called __________. Give example

A

Saturated

Beeswax and butter

Note: usually solid and room temp

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20
Q

Hydrocarbons that contain double bonds between carbon are called __________. Give example

A

Unsaturated

Safflower oil

Note: usually liquid at room temp

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21
Q

What do double bonds do to the structure of a hydrocarbon?

A

Forms kinks (bends structure)

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22
Q

What are three types of lipids found in cells?

A
  1. Fats
  2. Steroids
  3. Phospholipids
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23
Q

Structure of fats

A

Are non-polar molecules composed of three fatty acids that are linked to a three carbon molecule called glycerol.

They are called triglycerides for this reason

24
Q

Primary function of fats in organisms

A

Energy storage

25
Q

Structure of phospholipid

A

Consists of a glycerol that is linked to a phosphate group and two hydrocarbon chains

In Archea: hydrocarbon chains are isoprenoids
In Bacteria and Eukarya: hydrocarbon chains are fatty acids.

26
Q

Main roles of lipids

A
  • act as pigments that capture and respond to light
  • serve as signals between cells
  • form waterproof coatings on leaves and skin
  • act as vitamins used in many process

IMPORTANT: form cell membranes

27
Q

Structure of membrane lipids

A

Not all lipids can form membranes

Must have a polar, hydrophilic region, in addition to the non-polar, hydrophobic region

28
Q

Compounds that contain both hydrophilic and hydrophobic elements are called __________.

A

Amphipathic

29
Q

What are Micelles?

A

Tiny droplets created when hydrophobic heads of a set of lipids face the water and their hydrophobic tails interact with each other away from water.

30
Q

What is a lipid bilayer?

A

Are when two sheets of lipid molecules align. The hydrophilic heads of each layer face outwards, towards the water. The hydrophobic tails face one another inside the bilayer, away from water.

31
Q

Are phospholipid bilayers formed spontaneously?

A

Yes - no required energy needed to form

32
Q

What is selective permeability

A

That some substances cross a membrane more easily than other substances do.

Lipid bilayers are highly selective

33
Q

Permeability scale of phospholipid bilayer

A

High permeability
10^0 - small, non-polar molecules (oxygen, nitrogen, CO2)
10^-2
10^-4 - small, uncharged polar molecules (water, glycerol)
10^-6
10^-8 - large, uncharged polar molecules (glucose, sucrose)
10^-10 - ions (Cl-)
10^-12 - ions (K+, Na+)
Low Permeability

34
Q

How does bond unsaturation affect membrane fluidity and permeability?

A

When unsaturated hydrocarbon tails are packed into a lipid bilayer:

  • kinks created by double bonds produce spaces among the tail
  • spaces reduce strength of van der Walls forces
  • weakening barrier to solutes
35
Q

How does bond unsaturation affect membrane fluidity and permeability?

A

Packed saturated hydrocarbon tails have fewer spaces

  • created stronger van der Waal interactions
  • tail length increase
  • forces that hold the tails together also grow
  • making membrane denser
  • strengthening barrier
36
Q

How does cholesterol reduce membrane permeability?

A

When adding cholesterol molecules to liposomes the permeability of the lipid bilayer is decreased dramatically.

  • cholesterol has steroid rings that at bulky
  • adding cholesterol fills gaps that would otherwise be present in the hydrophobic section
  • blocks substances from passing through
37
Q

Diffusion

A

Movement of molecules and ions that results from their kinetic energy

Particles are always moving and in random directions

38
Q

Concentration gradient

A

A diffenece in solute concentration

39
Q

Osmosis

A

The movement of water between two solutions separated by a membrane that allows water to cross, but holds back some or all the solutes.

40
Q

Water movement direction

A

Only unbound water molecules can move a across a membrane

Flow from the solution with the lowest solute concentration to the highest solute concentration

41
Q

Result of movements with a hypotonic solution outside

A

Hypotonic - low tone - very dilute concentration of solute outside

  • Water inside the vesicle moves outside
  • Vesicles shrink
42
Q

Result of movements with a hypertonic solution outside

A

Hypertonic - excess tone - very concentrated solute outside

  • Net flow of water into cells
  • Vesicles swell and may burst
43
Q

Result of movements with a isotonic solution outside

A

Isotonic - equal tone - equal concentration outside and inside

  • Net flow of water inside and out are equal
  • No change
44
Q

Name of proteins found on the surface of the membrane

A

Peripheral membrane protein

45
Q

Name of proteins that pass through the membrane

A

Transmembrane protein, integral membrane proteins

46
Q

Facilitated Diffusion

A

Diffusion through the membrane via channel proteins.

  • no energy is required
  • net movement a result of concentration gradient
  • and, for charged substances, the electrochemical gradient
  • most common form of ion movement through membrane (ion channels)
47
Q

What is the electrochemical gradient?

A

The difference between charges of two different regions separated by a membrane caused by different concentration of of charged particles

Controls ion movement through membrane

48
Q

How are ion channels involved in cystic fibrosis?

A
  • Cystic Fibrosis (CF) is a genetic disease that affects cells the produce mucus, sweat and digestive juice.
  • Usually these secretions are thin and slippery but with CF become abnormally concentrated and sticky
  • CF causes a defect in the membrane protein (CFTR) that allow Cl- ions to move across the membrane
  • a reduction in chloride ion movement also decrease water movement attracted across by Cl-.
  • since water is not pulled from the cells properly, the proper mucus consistency is not kept
49
Q

How are channel proteins selective?

A

Each channel protein has a specific structure that allows only a particular type of ion or small molecule to pass through

50
Q

What are gated channels?

A

Channel proteins that close or open depending on a response to a signal,

  • such as the binding of a particular molecule
  • a change in electrical voltage across the membrane
  • most channels are controlled
51
Q

Passive transport

A
  • powered by diffusion along an electrochemical gradient

- channel proteins simply enable ions or polar molecules to move across lipid bilayers efficiently

52
Q

Facilitated diffusion definition 2

A

The passive transport of substances that otherwise would not cross a membrane readily

53
Q

Carrier proteins

A

Specialized membrane proteins that change shale during the transport process

54
Q

How does GLUT-1 work?

A
  1. Unbound protein: GLUT-1 is a transmembrane transport protein, shown with its binding site facing the outside of the cell.
  2. Glucose binding: glucose binds to GLUT-1 from outside the cell
  3. Conformational change: glucose binding causes a change in structure, transporting glucose into the interior of the cell
  4. Release: glucose moves inside the cell. Steps may repeat or reverse, depending on the concentration gradient
55
Q

Active transport

A

Transport against an electrochemical gradient that requires energy

56
Q

What molecule provides the energy for active transport?

A

Usually ATP - provides energy by transferring a phosphate group and an active transport protein, called a pump

57
Q

Sodium-Potassium transport pump steps

A
  1. Unbound protein: three binding sites within the protein have a high affinity for sodium ions
  2. Sodium binding: three sodium ions from the inside of the cell bind to these three sites
  3. Shape change: a phosphate group from ATP binds to the protein and in response the protein changes shape.
  4. Release: the sodium ions leave the protein and move to the exterior of the cell
  5. Unbound protein: in this conformation, the protein has binding sites with a high affinity for potassium ions.
  6. Potassium binding: two potassium ions bind to the pump
  7. Shape change: the phosphate group is cleaved from the protein, allowing the pump to return to its original shape.
  8. Release: the potassium ions leave the protein and diffuse to the interior of the cell.

Steps repeat

Bio 152 (7 decks)

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