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Flashcards in Membrane Transport Deck (70):
0

Fluid mosaic model

Reflects the allowable movement of proteins within the phospholipid bilayer

1

Polar

Any molecule carrying charge or having an unequal distribution of electrons

Hydrophilic and lipophobic

Ex. Water, ions, carbs

Can't diffuse across the membrane

2

Amphipathic

Half polar, half non polar,

3

Non polar

They are hydrophobic and lipophillic
Can diffuse across the membrane

4

Brownian motion

Says molecules are moving in random patterns, as they move they bump into each other and then move apart (they bounce off of each other )
Over time they will spread as far apart as possible

5

Dynamic equilibrium

Diffusion will continue until this is reached
At this point there is no NET shift in movement, but the molecules are still constantly moving ( in both directions)

6

Diffusion

Is passive (requires no energy)
Molecules move down the concentration gradient
Continues until dynamic equilibrium is reached
Occurs faster when:
-larger conc. gradient
-smaller distance
-higher temp.
-smaller molecules

7

Molecules the membrane is permeable to

O2, CO2, lipids, small non polar molecules

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Molecules the membrane is selectively permeable to

Ions, polar molecules, water, glucose, large molecules (most proteins)

These need help (sometimes energy) to get across the membrane

9

Passive transport

Movement must be with the concentration gradient
Can be simple (diffuse freely across membrane) or mediated (uses channels or carrier proteins)

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Simple diffusion

Type of passive transport
Non polar molecules (lipids and steroids) can cross the membrane
Rate depends on solubility of the molecule in lipids
Rate is proportional to the surface area and conc. gradient
Rate is inversely proportional to the thickness of the membrane

Cell can not control this movement

Permeability follows ficks law

11

Ficks law

Determines rate of effusion
-more surface area = faster rate if diffusion
-bigger conc. gradient = faster rate of diffusion
-increased permeability = faster rate of diffusion
-increased membrane thickness= slower rate of diffusion

12

Protein channels

Assist in mediated diffusion- still has to go in direction of conc. gradient
Are made of several subunits, are polar on the inside to allow polar molecules to diffuse
Channels are close able- so they are selectively permeable
Are usually gated, so have a trigger causing it to open

13

Carriers or pumps

Assist with mediated transport and active transport
Can open to outside of the cell, then change conformation to allow the molecule to enter the inside of the cell
Can be controlled by closing, or fully pinching the membrane and removing the protein front the membrane
Specific to a molecule

Can move with conc. gradient or against them ( if energy is provided)

14

Chemically gated channels

Specific molecules bind and cause the channel to open/close
Neurons, muscle cells, smell and taste receptors

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Voltage gated channels

Electrical state of the membrane opens or closes the channel
Neurons, muscle cells

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Mechanically gated channels

Physical force opens or closes the channel

Touch receptors

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Time gated channel

A specific unit if time passes before they change configuration

Heart muscle cells

18

Light gated channel

Change configuration based on exposure to photons of light

In retina, photoreceptors cells

19

3 properties of mediated transport

Specificity, saturation, competition

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Active transport

Moves against conc. gradient
Requires cellular energy
Creates disequilibrium

Exhibit competition, saturation, specificity and are limited by amount of energy

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Primary active transport

Uses ATP as energy source
Transporter protein = ATPase, this breaks down ATP to ADP and P, the protein is phosphorylation and undergoes a conformational change which allows the molecule to be transported

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Secondary active transport

Uses an electrochemical gradient as energy source

The movement of an ion down its concentration gradient is used to move another molecule with it

23

Na/k pump

3 na out, 2 k in
Uses ATP
Creates both chemical and electrical disequilibrium -- creates potential energy that can be used later via secondary transport

24

Osmosis

Diffusion of water, it moves across a semi permeable membrane in response to a conc. gradient

Moves from a higher [water] to a lower [water], aka water moves from a lower [solute] to a higher [solute]

25

Osmolarity

The number of particles in a solution-- how much osmotic pressure it creates

Different from molarity because it takes dissociation into account. Ex 1M nacl is 2in osmolarirty

26

Tonicity

Is the relative osmolarity of a solution surrounding a cell.
It describes the changes in cell volume if a cell is placed in a solution.

Is determined by the permeability of the solutes
- if solute can penetrate the membrane, it will move so no net water movement and no volume change
- if solute can't penetrate, the water will move by osmosis

27

Can urea penetrate the membrane? Can glucose?

Urea can- is lipophillic
Glucose can slowly with the help of carriers

28

Crenate

To shrink/shrivel ( if outside has a higher [solute]

29

Hemolysis

When red blood cells swell and burst due to tonicity

30

What happens if you put a cell in a concentrated saline solution?

Is it permeating? No

The cell shrinks

31

What happens if you put a cell in distiller water?

Water rushes in, the cell swells

32

What happens if you put a cell in a high urea solution?

Is it permeating? Yes

The urea will move, no change in cell size

33

Phagocytosis

Rids the extra cellular space of unwanted material. Involves digestion

34

Ligand

Something that binds to a receptor

35

Cytokines

A chemical used for communication. More for local communication, rarely travels in bloodstream

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Hormone

A chemical secreted into the blood stream, used for communication. Is systemic. In the blood stream

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Systemic

All over the body

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Endogenous

Coming from within

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Exogenous

Coming from outside

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Electrical signals

Changes in ion concentrations

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Chemical signals

Chemicals are secreted into the extra cellular fluid

42

Gap junctions

Method of cell to cell communication.
Two neighboring cells join plasma membranes and share interstitial fluid

43

Contact dependent signals

Molecules on the surface of one cell interact with molecules on the surface of another. The cells must be physically close
Involves a receptor and ligand
Binding of ligand triggers intercellular changes

44

Local communication

One cell secretes a chemical into the ECF and it is detected by receptors on neighboring cells
Example. Scrape on arm, histamine is released, but only locally

45

Autocrine

One cell secretes a substance and activates itself

46

Paracrine

One cell secretes a substance to activate the cells around it

47

Long distance communication

Electrical, chemical or both.
Can only be carried out by certain cell types
- endocrine cells: secrete chemicals into blood stream. Can have effects all over the body, on cells that have receptors
-nervous system: achieves communication by changing ion conc. in and out of a cell, para cringe signaling between one cell and another

48

Long distance communication endocrine example

Breast tissue has receptors for estrogen.
Estrogen triggers breast cell reproduction, tissue growth and Oreo for lactation
If patients are given estrogen after menopause it still triggers these responses and can cause breast cancer

49

Long distance communication nervous system example

Electronic signal travels down an axon, reaches the end and triggers the release if a chemical into a synapse with another cell. The chemical binds to receptor on the next cell and triggers a response

50

Cytokines

Usually work in short distances, are less specific
Work on many cell types
Made on demand

51

Differences between cytokines and hormones

They work on many cell types and are made on demand, are not stored,

52

Cytokine storm

In rare cases systemic cytokines secretion can lead to severe disease or death
Some cytokines work on a positive feedback loop, once you get above threshold the positive feedback loop rages out of control and leads to severe inflammations

Happens in sepsis, SARS,

53

Lipophillic ligands

Bind to intracellular receptors
Are slow acting ( over an hour)
Usually turn on gene transcription or proteins synthesis (actions that happen within ht nucleus)

54

Lipophobic ligands

Bind to membrane receptors
Very fast-- within seconds
Usually change ion flow or intracellular responses

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Lipophillic ligand
Receptor location/cellular action?

Cytosol, protein synthesis

Or nucleus, gene transcription

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Lipophobic ligand
Receptor location/cellular action?

Membrane, ion permeability or other cellular changes

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Receptors can be...

Transcription factors, kinases that trigger signaling cascades, ion channels, water channels, enzymes

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Kinase

Catalyzes transfer of phosphate from ATP to a protein. Changes protein shape, can alter signaling and function. Molecular change means molecular function change.

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Down regulation

A decrease in the number or sensitivity of receptors in response to a high concentration of ligand over time

Ex type II diabetes

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Up regulation

An increase in the number or sensitivity orpf receptors in response to a low concentration of ligand. This increases the sensitivity of the cell.
Ex low levels of a hormone, also a treatment for diabetes.

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How to stop a signaling pathway

Remove the signal, remove the receptor

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Ways to remove the signal

Extra cellular: have enzymes that degrade the signal in the ECF
Intracellular: have pumps that sequester the intracellular signal

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Agonists

Excites, mimic signal molecules and cause action.
Ex. Artificial estrogen in birth control

64

Antagonists

Inhibitors, block receptor and signal blockers.
Ex beta blockers to control high blood pressure.

65

Functional Unit

The smallest portion of a whole that is capable of carrying out the entire function.

66

4 types of tissues

epithelial, nervous, muscle, connective

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What % of body is water?

55-60

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How much is intracellular? extracellular?

2/3 intra, 1/3 extra

69

What % of ECF is plasma?

20-25%