Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BIOSCI 107 > Section 5: Cell Processes > Flashcards

Section 5: Cell Processes Flashcards

1
Q

Plasma membrane structure

A

A thin, 8nm flexible and sturdy barrier that surrounds cytoplasm of a cell
2 back-to-back layers of 3 types of lipid molecules; glycolipid and cholesterol, which are scattered among a double row of phospholipid molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Fluid mosaic model

A

Describes membrane structure

‘sea of lipids in which proteins float’

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What makes up the membrane? (%)

A

50% lipid and 50% protein, held together by H bonds
Lipid is barrier to entry/exit of polar substances
Proteins are ‘gatekeepers’ - regulate traffic across lipid bilayer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Why is the plasma membrane critical for cellular function and evolution?

A

DNA, mitochondria and cytoplasm can’t be freely floating around in primordial suit and must be contained in a membrane so there’s a difference between the inside and outside of the cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the ‘outside’ for a single cell

A

The outside world, so must have a barrier which enables it to partition itself from the outside world

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Phospholipids - lipids

A

Comprises 75% of lipids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Phospholipid bilayer

A

2 parallel layers of molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Phospholipid - amphipathic

A

Phospholipids will orient themselves to provide the lowest energy structure
Each molecule has both a polar and non-polar region
Non-polar hydrophobic tails face each other and exclude water so water is outside of lipid bilayer
Water interacts with polar head groups - excluded from hydrophobic core

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Membrane fluidity

A

Membranes are fluid structures and lipids can move around within the plane of the membrane leaflet and allow lateral diffusion of proteins within the lipid bilayer
Lipids rarely flip flop between membrane leaflets –> lipid composition of leaflets can be asymmetric

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Fluidity of membrane is determined by…

A

Lipid tail length: longer tail = less fluid
No. of double bonds: more double bonds = increased fluidity
Amount of cholesterol: more cholesterol embedded = decreased fluidity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What does fluidity determine

A

Properties of lipid bilayer - how many molecules can get through it
Can maintain differences in lipid composition - diff on one side of membrane facing inside and membrane facing outside
e.g. water diffusion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Membrane fluidity - double bonds

A

Introduces kinks in the tail, which allows them to pack less tightly to give more fluidity –> membrane is less stable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Types of membrane proteins

A

Integral proteins

Peripheral proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Integral proteins

A

AKA transmembrane protein
Amphipathic
Extend into / completely across cell membrane - able to sense molecules on outside and inside of cell for movement across membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Peripheral proteins

A

Attached to either inner or outer surface of cell membrane and are easily removed from it (by changes in ionic strength)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Peripheral membrane proteins - cytoskeleton proteins

A

Linked to membrane proteins embedded in lipid bilayer, which can bend and change shape of membrane or hold membrane proteins in a particular place
Can easily break these interactions by exposing membrane to an ionic solution to break chemical bonds and strip peripheral proteins from membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Integral proteins - hydrophobic regions

A

Have hydrophobic regions that span hydrophobic core of lipid bilayer
Usually consist of non-polar amino acids coiled into helices to form a protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Integral proteins - hydrophilic ends

A

Interact with aqueous solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Removal of an integral protein

A

Must break interactions between hydrophobic lipids and hydrophobic amino acids
To break the lipid, use detergent to dissolve lipid and stabalise membrane –> isolate integral membrane proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Membrane proteins can act as…

A

Receptor proteins - sense signals, e.g. from blood, and bind those receptors and transfer signals inside the cell
Cell identity markers - can be a sense of ‘self’
Linkers - provide links to other cells, sheets of tissue, or parts of CT e.g. tendons and BM
Enzymes - on surface of membrane, can catalyse enzymatic activity, e.g. break down glucose
Ion channels and transporter proteins - move molecules across cell membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Ion channels vs transporters

A

Transport diff things and use diff forces to do the transferring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Membrane - selective permeability

A

Membrane allows some substances to cross but excludes others because of the way specific molecules interact with lipid bilayer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the lipid bilayer (im)permeable to

A

Permeable to:

  • nonpolar, uncharged molecules (O2, N2, benzene)
  • lipid soluble molecules (steroids, fatty acids, some vitamins)
  • small uncharged polar molecules (water, urea, glycero, CO2)

Impermeable to:

  • large uncharged polar molecules (glucose, amino acids)
  • ions (Na+, K+, Cl-)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Why are ions impermeable

A

Although they are small, they have an electric charge and so will be repelled by non-polar hydrophobic core of lipid bilayer - can only be moved through integral proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Diffusion

A

The random mixing of particles in a solution as a result of the particle’s kinetic energy
More molecules move away from an area of high conc to an area of low conc until conc across the membrane is equal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Factors affecting rate of diffusion

A

Greater diff in conc between 2 sides of membrane = faster rate
Higher temp = faster rate
Larger size of diffusing substance = slower rate
Increased SA available for diffusion = faster rate
Increased diffusion distance = slower rate
Thicker membrane = slower rate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Diffusion - size limit

A

Rate of diffusion sets limit on size of cells of about 20μm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What diffuses down concentration gradient

A

Non-charged molecules diffuse down conc gradients

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Electrical gradient

A

Membrane potential

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Electrochemical gradient

A

Movement of ions will be influenced by the electrochemical gradient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Passive transport

A

If there is a conc gradient and membrane is permeable, molecules will rapidly move until they reach an equal conc on both sides of membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Membrane charge

A

Across the cell membrane, there is a membrane charge which determines how molecules move across the cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Movement of ions influenced by…

A

Sum of electrical and chemical (electrochemical) gradient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Selective permeability - conc gradient

A

Selective permeability of membrane enables a difference in conc (gradient) across the membrane to be established
Cells can maintain a difference in charged ions between the inside and outside of membrane, establishing gradient / membrane potential

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Membranes - capacitors

A

Membranes mimic capacitors and can separate and store charge
Cytoplasm: -vely charged
ECM: +vely charged

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Why is it important that the lipid bilayer is not permeable to ions

A

If membrane had holes in it that allows ions to diffuse down, you could never have a conc gradient
Crucial for establishing conc differences across the membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What do ion gradients represent

A

Stored charge and energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Extracellular ion concentrations

A

High Na+: 150 millimoles
Low K+: 5 millimoles
High Cl-: 150 millimoles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Cytoplasmic ion concentrations

A

Low Na+
High K+
Low Cl-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

How much resting energy do cells use to maintain conc and electrical gradients

A

~30% of resting energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

Accumulation of ions on one side of a membrane creates a…

A

Concentration difference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Electrochemical gradient - Na+

A

Product of conc gradient
Directed into the cell where there is a -ve membrane potential so electrical and conc gradient of Na+ will always be directed inside the cell
Na+ always want to move into cell down its electrochemical gradient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

Osmosis

A

Diffusion of water across membranes
Net movement of water through a selectively permeable membrane from an area of high water conc to an area of lower water conc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

When does osmosis occur

A

Only occurs if membrane is permeable to water but not to certain solutes, e.g. biological membranes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

If an osmotic gradient exists…

A

Water will want to move to eliminate it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

Electrochemical gradient - K+

A

K+ moves out of cell and down conc gradient until electrical gradient puts a brake on and slows it down –> reaches electrochemical equilibrium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

Electrochemical gradient - Cl-

A

One vector with high Cl- conc wanting to pull it into the cell, but inside the cell is a -ve membrane potential - not attracted –> 2 opposing vectors; conc wanting to push in and electrical gradient wanting to push out
If membrane potential becomes less -ve than norm (-80mV), it depolarises and Cl- comes into cell. if it hyperpolarises, Cl- will leave the cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

What is used to establish gradients

A

Energy of metabolism, Na/K ATPase used to establish gradients and put in chemical work to create gradients that can then create other forms of energy to do numerous cellular processes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

Membrane permeability to water (Pw)

A 
Pw = Pd + Pf
Where Pd = through lipid bilayer
Pf = through water channel
Pf > Pd
Pf mediated by aquaporins (9 isoforms)
Cells have diff Pw because they express diff aquaporin isoforms
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

Membrane permeability to water - properties

A

Pd:
Small
Mercury insensitive
Temp dependent (lipid fluidity)

Pf:
Large
Mercury sensitive
Temp independent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

Osmotic pressure

A

The pressure applied by a solution to prevent inward flow of water across a semi-permeable membrane
Hypersmotic solution –> hyperosmotic solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

Types of transport across plasma membrane

A

Non-mediated transport

Mediated transport:
Passive transport
Active transport
Vesicular transport

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

Why are there a variety of processes for transport across plasma membrane

A

Lipid bilayer has certain permeability to diff molecules so there will be diff ways to get molecules across lipid bilayer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

What type of transport do ions undergo

A

Non-mediated transport, as they don’t involve a transport protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

Why don’t non-mediated transport need integral membrane proteins

A

They’re permeable across hydrophobic core / bilayer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

Non-mediated transport

A

Does not directly use a transport protein
Always passive diffusion
Important for absorption of nutrients and excretion of waste
Soluble, non-polar, hydrophobic molecules, e.g. O2, CO2, fatty acids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

Diffusion through ion channels - speed

A

Ions don’t bind to channel pore, therefore transport is very fast (passive diffusion)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

Diffusion through ion channels - process

A

Within the ion channel there are many charged (hydrophilic) amino acids, creating a pathway for ions to get through hydrophobic core
Channel forms a water-filled pore that shields ions from hydrophobic core of lipid bilayer
Water in ions flow through channel across bilayer down electrochemical gradient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

Ionic selectivity

A

Large diversity of ion channels specific for a particular ion
Specific amino acids lining pore determine selectivity of channel to ions
By being selective to a particular ion, the channel can harness energy stored in diff ion gradients

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
60
Q

Ionic selectivity - factors

A 
Individual amino acids in protein backbone with a -ve charge effectively repel -ve ions going through the channel
Shape of selectivity filter can discriminate between diff ions based on size of ions and amount of water they have around them --> specific filter that allows only one class of ions to go through it
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
61
Q

If there was no lipid bilayer with a hydrophobic core…

A

Ions would be allowed to go through it and there wouldn’t be an ion gradient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
62
Q

Channels - gating

A

Channels contain gates that control opening and closing of the pore
Diff stimuli can control gate channel opening and closing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
63
Q

Channels - gating - stimuli

A

Voltage - a change in membrane potential can open an ion channel and cause generation of an action
Ligand binding - a molecule from blood binds to channel, causing it to open
Cell volume - can be sensed by cytoskeleton, causing it to stretch and open channel
pH - can change through differences in metabolism; if O2 deficit, can go into anaerobic metabolism –> can open ion channel
Phosphorylation - phosphorylate ion channels and open them to change properties of cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
64
Q

Channels - open gate

A

Allows ions to flow down electrochemical gradient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
65
Q

Patch clamp technique

A

Used to measure ion channel function

Isolates a small patch of membrane that contains one of the channels - can see current flowing through channel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
66
Q

Patch clamp technique - current

A

Diffusion of > 1 million ions / sec through a channel generates a measurable current
Flow of ions is a pA (10^-12 amp) current
Current fluctuations represent conformational changes in channel structure associated with channel gating

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
67
Q

Patch clamp technique - binding pocket

A 
When molecule (e.g. acetyl choline) binds to closed channel, it causes it to open --> current starts to flow
When molecule is removed, channel closes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
68
Q

Carrier mediated transport

A

Substrate to be transported directly interacts with transporter protein
For a molecule to be transported from one side to the other, must first bind to binding pocket, which induces a change in structure of that protein (e.g. binding of ion to protein)
Carrier changes its conformation and allows molecule to go across the membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
69
Q

Carrier mediated transport - rate

A

Since transporter undergoes a conformational change, transport rates are slower than those obtained for channels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
70
Q

Carrier mediated transport - properties

A

Similar to those of enzymes
Specificity - fits into binding pocket - specific for shape of a specific molecule
Inhibition - if inhibit/change the binding pocket of transporter, can block transport across - can be competitive or non-competitive
Competition - if 2 diff molecules can fit in binding pocket, it slows down rate of transport as they will compete for binding pocket
Saturation (transport max) - limited no of binding pockets; after a while if you keep increasing conc gradient, no effect

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
71
Q

Do transport proteins catalyse chemical reactions

A

No, they mediate transport across cell membrane at a faster than normal rate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
72
Q

Mediated transport can be…

A

Passive (facilitated) or active

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
73
Q

Glucose transport - saturation

A

Occurs until all binding sites are saturated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
74
Q

Facilitated diffusion of glucose - steps

A
  1. Glucose binds to transport protein (GLUT) - NOT a glucose channel or electrochemical gradient
  2. Transport protein changes shape. Glucose moves across cell membrane (down conc gradient)
  3. Kinase enzyme reduces glucose conc inside cell by transforming glucose into glucose-6-phosphate - conversion maintains conc gradient for glucose entry
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
75
Q

Active transport

A

Uses energy to move molecules and ions against their concentration or electrochemical gradients

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
76
Q

Forms of active transport

A

Primary:
- energy directly derived from hydrolysis of ATP
- typical cell uses 30% of energy (ATP) on primary active transport
- establishes ion gradients
Secondary:
- energy stored in an ionic conc gradient is used to drive active transport of a molecule against its gradient

Work together to do active transport

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
77
Q

Primary active transporters: Na/K ATPase - overall mechanism

A

3 Na+ ions removed from cell as 2 K+ brought into cell

Pump generates a net current and is electrogenic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
78
Q

Primary active transporters: Na/K ATPase - steps

A
  1. Na+ binds to binding pocket (carrier). Binding converts ATP –> ADP, leaving a phosphate on the ion channel, so ATPase part of carrier protein attaches a phosphate group to it
  2. Phosphate has a -ve charge, so changes conformation of protein so sodium binding sites are opened up to outside of cell –> Na+ pushed out
  3. K+ binds, causing phosphate molecule to fall off –> changes conformation back to resting state where binding sites are now inside membrane –> K+ pushed in
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
79
Q

Primary active transporters: H/K

A

Pumps H out to create acidic environment, e.g. low pH in stomach

80
Q

Primary active transporters: Na pump function

A

Maintains low conc of Na+ and high conc of K+ in cytosol

81
Q

Why is diff in conc of Na+ and K+ important

A

Maintains RMP
Electrical excitability
Contraction of muscle
Maintenance of steady state cell volume
Uptake of nutrients via secondary active transporters
Maintenance of intracellular pH by secondary active transporters

82
Q

Pump-leak hypothesis

A

Since Na and K are continually leaking back into cell down their respective gradients, the pump works continuously to compensate

83
Q

Secondary active transport

A

Uses energy stored in ion gradients created by primary active transporters to move other substances against their own conc gradient
Transporters indirectly use energy obtained by hydrolysis of ATP

84
Q

Cells - secondary active transport

A

Cells have many secondary active transporters powered by Na+ gradient initially established by Na pump

85
Q

Types of secondary active transporters

A

Na+ antiporter or exchangers:

  • Na+ ions rush inward
  • Ca2+ or H+ pushed out
  • movement of Na+ is passive and occurs when Ca2+ binds and goes against its electrochemical gradient
  • uses energy of Na+ gradient to actively remove H+ from cells

Na+ symporters or co-transporters:
Glucose or amino acids rush inward together with Na+ ions

86
Q

Epithelial tissues consist of…

A

Cells arranged in continuous sheets in either single or multiple layers

87
Q

Epithelial tissue - physical breakdown

A

Subject to physical breakdown and injury, so undergo constant and rapid renewal process

88
Q

How are epithelial cells separated

A

Separated from their neighbours by lateral intercellular/paracellular space

89
Q

How are epithelial cells held together

A

Held together at their luminal edges (apical membrane) by tight junctions

90
Q

Tight junction structure

A

Composed of thin bands that encircle the cell and make contact with thin bands from adjacent cells
More ridges = more tightly packed cells tgt
In ECM it appears the membranes are fused together
In freeze fracture, it appears as an interlocking network of ridges in the plasma membrane

91
Q

Tight junction function

A

Barrier - restrict movement of substances through intercellular space between cells
Fence - prevent membrane proteins from diffusing in lane of lipid bilayer

Hence, they separate epithelial cells into 2 distinct membrane domains; apical and basolateral

92
Q

Epithelial cells - apical and basolateral membrane

A

Apical/luminal/mucosal membrane - faces lumen of organ or body cavity
Basolateral: adheres to adjacent BM (made up of collagen) and interfaces with blood

93
Q

Epithelial transport properties

A

Distinct membrane domains - diff transport proteins can be inserted into either the apical or basolateral layer
Transport can occur via paracellular, transcellular pathway or both

94
Q

Paracellular transport is governed by…

A

Laws of diffusion and tightness of junctions

95
Q

Paracellular transport - electrical resistance

A

Electrical resistance to ion flow (current) through tight junctions can be measured
Higher electrical resistance to ion flow = greater no of tight junction strands holding cell tgt

96
Q

Paracellular transport

A

Allows some molecules to cross them but not others

Gradients set up by transcellular transport for paracellular transport

97
Q

Tight junction proteins

A

Many diff tight junction proteins have distinct permeabilities to diff ions and diff proteins

98
Q

Functional classification of epithelial tissues

A

Leaky epithelium - paracellular transport dominants

Tight epithelium - transcellular transport dominates

99
Q

Leaky epithelium

A

Provides a low resistance pathway for ion movement via the paracellular pathway

100
Q

Tight epithelium

A

No transport via paracellular pathway because junctions are very tight and electrical resistance is very high

101
Q

Changes in tight junction resistance

A

Tight junction resistance changes in a proximal to distal direction in the GI tract and kidney

102
Q

Changes in tight junction resistance - proximal

A 
Leaky epithelium
Low electrical resistance
Low no of strands
Bulk transport (paracellular)
e.g. duodenum, proximal tubule
103
Q

Changes in tight junction resistance - distal

A 
Tight epithelium
High electrical resistance
High no of strands
Hormonally controlled (transcellular)
e.g. colon, collect duct
104
Q

Transcellular transport

A

Epithelial cells use primary and secondary active transport often in combination with passive diffusion through ion channels to produce transport across epithelial tissues
Diff ion channels and carrier mediated proteins in basolateral and apical membrane produce transport across tissue

105
Q

Types of transcellular transport

A

Absorption: transport from lumen to blood
Secretion: transport from blood to lumen

106
Q

Transepithelial transport - rules

A

Entry and exit steps: entry for absorption is apical but for secretion is basolateral membrane - diff transport proteins in diff membranes depending on which direction it is going in
Electrochemical gradient: is the entry or exit step passive or active
Electroneutrality: movement of a positive or negative ion will attract a counter ion
Osmosis: net movement of ions will establish a difference in osmolarity that will cause water to flow by osmosis

107
Q

Membrane permeability to water

A

Membrane very permeable to water = lots of aquaporins

Membrane not very permeable to water = no aquaporins

108
Q

Aquaporin

A

If there is an osmotic gradient across the membrane, water will flow through aquaporin, but if there’s no aquaporins, there’ll be no water flow
Can dissociate water flow from ion flow by presence of aquaporin

109
Q

Transepithelial transport - cells can select from…

A

Repertoire of primary active transporter, entry step and exit step

110
Q

Which surface are tight junctions found

A

Only on lumen surface not blood surface

111
Q

Transepithelial transport - secretion

A

Must have energy to carry out secretion - requires primary active transporter (Na/K ATPase sets up Na+ electrochemical gradient which can be used to drive secretion)
Entry step in basolateral membrane
Exit step in apical membrane

112
Q

Transepithelial transport - absorption

A

Primary active transporter set up ion gradients, which are utilised to drive absorption
Entry step in apical membrane
Exit step in basolateral membrane

113
Q

If we move a positive ion across the cell…

A

A negative ion will want to come via the paracellular pathway

114
Q

If create a conc / osmotic difference…

A

Water will want to flow, but only if the tight junctions allow those molecules to flow through them, i.e. must have both the gradient and junctions that allow it to happen

115
Q

Leaky and tight epithelium - movement

A

Leaky junctions give rapid movement via paracellular pathway in response to absorption driven by transcellular pathway
Tight epithelium where resistance is low, will be little movement via this pathway because junctions are very tight

116
Q

Glucose absorption in small intestine / kidneys - net effect

A

Absorbed glucose, NaCl, and water
Absorbed water so there’s no change in volume
Isotonic fluid absorption

117
Q

Oral rehydration therapy

A

The ability of glucose to enhance absorption of Na+ and hence Cl-, and water is exploited in oral rehydration therapy
A simple sugar solution when given to dehydrated babies suffering from diarrhea saves millions of lives per year

118
Q

Glucose-galactose malabsorption syndrome

A

A mutation to the glucose symporter (SGLT) in the small intestine means glucose is retained in the intestine lumen
Increased conc of glucose –> increased osmolarity of lumen of intestine –> creates osmotic gradient that requires water to move to make conc on either side of small intestine equal
The associated increase in lumen osmolarity induces a water efflux - not absorbing glucose –> lose water –> water moves from blood into small intestine to make conc on either side of epithelial wall the same –> diarrhoea

119
Q

What is galactose

A

The sugar in milk

120
Q

Treatment for glucose-galactose malabsorption

A

Remove glucose and galactose from diet
Use fructose as as source of carbohydrate, which can be moved across basolateral membrane
Utilises a factilitative transporter (GLUT5) that is specific for fructose

121
Q

Glucose reabsorption in kidneys

A

In kidneys, glucose in plasma is filtered and needs to be reabsorbed or it will appear in urine
Not a primary absorption - only re-absorption

122
Q

Glucose re-absorption in kidney - amount absorbed

A

100% uptake of all glucose that is filtered

60-80% water re-absorbed in proximal tube (small part of kidney)

123
Q

Glucosuria

A

Most common cause is diabetes mellitis because insulin activity is deficient and blood sugar is too high (> 200mg/mL)
In diabetes, the glucose symporter can’t absorb glucose fast enough and glucose appears in urine

124
Q

Glucose in urine - transporter kinetics

A

If glucose absorption is impaired or transporter is saturated, glucose will appear in urine
All filtered glucose is reabsorbed until renal threshold is reached
Once renal threshold is reached and glucose has saturated all binding pockets, there’s no further increase of transport and glucose appears in urine

125
Q

Glucose in urine - transporter kinetics - renal threshold

A

Reflects transport maximum of SGLT

Once this maximum is exceeded, there is no more uptake of glucose and instead starts to appear in urine

126
Q

Chloride secretion - net result

A

Accumulates Na+, Cl- and water

127
Q

Isotonic solutions and blood

A

Have same osmolarity, so by moving Na+ and Cl- in same conc as blood across lumen and moving water with it, it moves the same type of solution as the blood to the other side of the tissue

128
Q

Chloride secretion - rate limiting step

A

Cl- can’t leave the cell unless the Cl- channel is open; if channel is shut, no Cl- moves across apical membrane –> no isotonic fluid secretion
Opening of Cl- channel is strictly regulated (gated), so is the rate limiting step of Cl- secretion

129
Q

Cystic Fibrosis Transmembrane conductance Regulator (CFTR)

A

Cl- channel identified at molecular level as CFTR
Regulated by protein kinase A dependent phosphorylation of R domain and binding of ATP to NBD (nucleotide binding domain)
Contains 2 NBDs
CFTR over-stimulation has been implicated in secretory diarrhoea and its dysfunction causes cystic fibrosis; everyone has CFTR - only a defect/mutation in Cl- channel causes cystic fibrosis

130
Q

What is secretory diarrhoea caused by

A

Excessive stimulation of secretory cells in crypts of small intestine and colon, which could be due to abnormally high conc of endogenous secretagogues produced by tumours or inflammation
More commonly due to secretion of enterotoxins from bacteria, e.g. vibrio cholerae (contaminated water –> die of dehydration)

131
Q

Secretory diarrhoea - what do enterotoxins do

A

Irreversibly activate adenylate cyclase, causing maximal stimulation of CFTR –> secretion that overwhelms absorptive capacity of colon

132
Q

Secretory diarrhoea - over-stimulation

A

Overly stimulated secretory cells –> pump out lots of Cl-, Na+ and H2O which exceeds capacity to absorb fluid –> ends up with lots of fluid in gut –> secretory diarrhoea

133
Q

Molecular mechanism of cholera - normal

A

Bind to GPCR which releases a G-protein which binds to adenylate cyclase
ATP converted into cAMP –> acts on protein kinase A –> phosphorylates CFTR –> allows it to open –> chloride secretion
Stop by removing GPCR –> turns off adenylate cyclase –> remove phosphorylation, channel shuts –> Cl- secretion stops

134
Q

Molecular mechanism of cholera - affected by cholera toxin

A

Cholera toxin irreversibly binds to adenylate cyclase and causes activation of CFTR, i.e. bypasses GPCR
Produces lots of cAMP –> phosphorylates CFTR –> channel permanently open
Effectively gotten rid of rate limiting step and all ion gradients are accumulating Cl- into cell and Cl- immediately leaves via CFTR

135
Q

Secretory diarrhoea: Secretion vs absorption - normal and over-stimulation

A

In normal circumstances, secretion and absorption are matched
If overstimulation of secretion, overwhelms ability for absorption –> secretory diarrhoea

136
Q

Crypt cells vs villus cells

A

Crypt cells - epithelial cells involved in Cl- secretion
Villus cells - cells involved in Na+ absorption

Crypt cells migrate and change properties and become absorption cells - ~5 day life cycle of crypt –> villus cell

137
Q

Treatment after survival of initial insult of cholera toxin (secretory diarrhoea)

A

Maintain hydration - use oral rehydration therapy

Stimulates water influx and tries to offset some effects of overstimulation

138
Q

What is cystic fibrosis

A

A complex inherited disorder than affects children and young adults
Mortality usually due to respiratory failure
Exhibit defects in Na+ absorption and Cl- secretion in the lung

139
Q

Cystic fibrosis (CF) - genes

A

Inherited in an autosomal recessive fashion
Heterozygotes have no symptoms but are carriers
Children of 2 carriers have a 1/4 chance of getting CF

140
Q

Cystic fibrosis - disease frequency

A

Less common in other ethnic groups

141
Q

Sickle cell anaemea provides protection against…

A

Malaria, so its been maintained in the population

142
Q

CF - symptoms

A

Diverse range

Common theme is involvement of epithelial tissues

143
Q

CF - most cases of mortality are due to…

A

Respiratory failure

144
Q

Organs affected by cystic fibrosis - airways

A

Clogging and infection of bronchial passages impede breathing
Infections progressively destroy lungs
Lung disease accounts for most deaths from cystic fibrosis

145
Q

Organs affected by cystic fibrosis - liver

A

Plugging of small bile ducts impedes digestion and disrupts liver function

146
Q

Organs affected by cystic fibrosis - pancreas

A

Occlusion of ducts prevents pancreas from delivering critical digestive enzymes to bowel
Diabetes can result

147
Q

Organs affected by cystic fibrosis - small intestine

A

Obstruction of gut by thick stool necessitates surgery; particularly newborns

148
Q

Organs affected by cystic fibrosis - reproductive tract

A

Absence of fine ducts renders most males infertile

Occasionally women are made infertile by a dense plug of mucous that blocks sperm from entering uterus

149
Q

Organs affected by cystic fibrosis - skin/sweat gland

A

Malfunctioning of sweat glands causes perspiration to contain excessive salt (NaCl)

150
Q

Clinical management of cystic fibrosis

A

Chest percussion to improve clearance of infected secretions; clear mucous –> less infections
Antibiotics to treat infections of bacteria in lungs
Pancreatic enzyme replacement; eating meals with pills that contain enzymes required to break down food that are no longer being produced by pancreas
Attention to nutritional status

151
Q

CF - median survival

A

38 years of age

152
Q

Cystic fibrosis: Defect in Cl- secretion - normal lung epithelial cells

A

Balance between secretion and absorption keeps lung surface moist but prevents excessive fluid build up
Enough water so there’s a fluid surface for gas exchange, but not full of secretions

153
Q

Cystic fibrosis: Defect in Cl- secretion - lung epithelial cells in CF

A

Defective/absent Cl- channel prevents isotonic fluid secretion and enhances Na+ absorption through open Na+ ion channel –> not secreting, reabsorbs more –> dry lung surface

154
Q

Blocking Cl- secretion: Lung pathology - pathway

A 
CFTR gene defect -->
Defective ion transport -->
Airway surface liquid depletion -->
Defective mucocillary clearance -->
Cycle of:
Mucous obstruction --> infection --> inflammation
155
Q

Lung pathology: normal lung

A

Moist surface through Cl- secretion and Na+ reabsorption
Layer of mucous that floats above cells, which have cilia which beat to move mucous
Protects from particles of bacteria that are inhaled into lung surface as it sticks to mucous and is moved out towards back of throat and coughed out

156
Q

Lung pathology: CFTR lung

A

Dry dehydrated lung surface
Mucous sticks to cells and becomes a rich environment allowing bacteria to proliferate
Infection and immune system starts to attack bacteria
Overtime, results in damaged tissue which are no longer available for gas exchange - decreased SA eventually becomes fatal

157
Q

Lung pathology: CFTR lung - therapies

A

Remove mucous and target infection by having specific antibodies to try break the cycle
Eventually, you can’t overcome that so intervene with gene therapy, where rather than treating symptoms, treat the cause by trying to replace gene with a functional copy to have good ion transport
Or, increase ion transport by bypassing CFTR gene to stop symptoms occurring

158
Q

CF - sweat formation

A

People with CF have a very salty sweat

159
Q

Formation of sweat - processes

A

2 stage process:

  • a primary isotonic secretion of fluid by acinar cells
  • a secondary reabsorption of NaCl but NOT water –> hypotonic solution
160
Q

What causes salty sweat in CF patients

A

Failure of epithelial cells in ducts of sweat glands to reabsorb NaCl

161
Q

Purpose of sweat production

A

Remove heat to surface where it can evaporate

Wet surfaces remove heat better

162
Q

Sweat production - Hypotonic solutions

A

Don’t want to put ions (Na+ and Cl-) that a lot of time is spent absorbing in diet out with sweat, so want to have more hypotonic solutions which don’t have same osmolarity as body fluids
At surface where Na+ and Cl- was re-absorbed has less salt and more water –> hypotonic

163
Q

Sweat formation - acinar channels

A

2 diff channels that can mediate Cl- release:
CFDR - stimulation causing cyclic AMP, which stimulates protein kinase A to phosphorylate channel to open it
CLCA - activated by elevated intracellular Ca2+ to open and cause Cl- to be secreted
In both, the final pathway in Cl- secretion occurs because Cl- is elevated above electrochemical equilibrium by secondary active transporter

164
Q

Sweat formation - duct cells

A

Only have CFTR and Na+ channel
Cl- comes into cell through CFTR down electrochemical gradient where it can be removed from lumen of duct
Water doesn’t move even though there’s an osmotic diff because cells aren’t permeable to water (no aquaporin)

165
Q

Sweat production - no cystic fibrosis genes

A

No Cl- secretion at CFTR or Cl- reabsorption occurring, but instead will have another mechanism producing isotonic fluid secretion

166
Q

CF and sweat formation - normal sweat duct

A

-ve membrane potential is depolarised and Cl- wants to enter cell down its electrochemical gradient and Na+ moves with it –> removes Na and Cl, and water doesn’t flow –> water retained in lumen –> hypotonic sweat

167
Q

CF and sweat formation - CF patients

A

In CF patients, CFTR channel is defective and Cl- accumulates –> affects movement of Na –> Na and Cl retained in duct lumen –> salty sweat

168
Q

What is osmolarity measured in

A

Osmoles

169
Q

Osmolarity - when comparing a solution to the reference solution…

A

If solution has same osmolarity –> isosmotic
If solution has lower osmolarity –> hyposmotic
If solution has higher osmolarity –> hyperosmotic

170
Q

Osmolarity - body fluids

A

~300 mOsmol
Osmolarity of intracellular and extracellular fluids must be equal (isosmotic) so no net water flow (osmosis) occurs
If osmosis occurs, change in cell volume occurs

171
Q

Tonicity

A

The effect a solution has on cell volume

Depends on membrane permeability of solute, so osmolarity doesn’t always indicate effect if will have on cell volume

172
Q

Osmolarity vs tonicity

A

Not always the same thing - can have same osmolarity but diff tonicity

173
Q

Effects of tonicity on RBCs

A

Isotonic solution: no change in cell volume - no net water movement
Hypotonic solution: cause cell swelling and eventually cell lysis (hemolysis) - net gain of water
Hypertonic solution: cause cell shrinkage (crenation) - net water loss

174
Q

Effects of membrane permeable osmolytes - NaCl

A

Na pump maintains steady-state cell volume by effectively making Na+ completely impermeable because it always removes it when it comes into the cell
Not balancing Na conc, instead balancing osmolarities inside and outside the cell - no net water flow, and at steady-state, there’s no change in volume

175
Q

Effects of membrane permeable osmolytes - urea

A

Lipid permeable, so can cross hydrophobic core of lipid bilayer –> can diffuse down conc gradient into the cell, which can change the osmolarity inside the cell –> osmolarity increases –> water flows into cell –> swell and potentially burst
In some cases, urea will keep moving into the cell until it reaches an equilibrium –> won’t be any change in net volume

176
Q

Cl- changes its direction of movement based on…

A

Changes in membrane potential which changes electrical gradient and chemical equilibrium –> drives Cl- movement either into or out of the cell, or maintaining it at electrochemical equilibrium

177
Q

Glucose in kidney vs gut

A

In kidney, always have glucose being filtered
In the gut, only have glucose to be re-absorbed when you’re eating
If fasting, no reabsorption occurs because no glucose to absorb across the membrane - conc gradient for glucose favours uptake of glucose from the blood by facilitated diffusion

178
Q

Is the lipid bilayer formed by cholesterol

A

No

179
Q

How does Ca2+ move across a membrane

A

Against its chemical gradient by its electrochemical gradient

180
Q

Cl- when MP = -80mV

A

Electrochemical gradient for Cl- drives no net diffusion of Cl-
Passive diffusion of Cl- increases if MP is depolarised

181
Q

Flow of an ion through an ion channel is often determined by…

A

Ion selectivity filter

182
Q

Isotonic fluid secretion is stimulated by…

A

Oral rehydration therapy

183
Q

In Cl- secretion, changing gating of CFTR from closed to open drives…

A

Isotonic fluid secertion

184
Q

In sweat glands, acinar cells produce a primary ______ secretion and secondary ____ secretion

A

Primary isotonic secretion

Secondary hypotonic secretion

185
Q

Epithelial transport in tight epithelium is often under…

A

Hormonal control

186
Q

Cl- secretion - secretagogues

A

Binds to receptors in basolateral membrane to activate signalling pathways that activate CFTR in apical membrane

187
Q

Hyperosmotic solution of 0.15 NaCl and 0.05M urea will cause…

A

An initial cell swelling before returning to the original volume
Urea goes through membrane and water follows, so cell swells. Since hyperosmotic, goes back down since water moves out of cell

188
Q

Placing RBCs into an isosmotic solution of a membrane permeable solute causes…

A

Swelling and rupture

189
Q

Sodium dependent amino acid transporters expressed in apical membrane in small intestine

A

Used to accumulate amino acids above their conc gradient

190
Q

Glucose uptake in small intestine drives…

A

Isotonic fluid reabsorption

191
Q

Tight junctions - transmission electron microscopy

A

Appear as membrane fusions

192
Q

Diffusion of water - water channels

A

Diffusion of water through a cell membrane is increased by presence of water channels

193
Q

When does swelling of cells occur when placed in an isosmotic solution

A

When solution contains a membrane permeable solute

194
Q

CFTR - ATP binding

A

Only occurs if R domain is phosphorylated

195
Q

Uptake of amino acids from gut lumen is mediated by….

A

Secondary active transport

196
Q

Apical membrane of duct cells - permeability to water

A

Low permeability to water

BIOSCI 107 (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions