1
Q
What are lipids?
A
Lipids are large biological molecules that encompass fats, phospholipids, and steroids. They have poor or no mixing ability with water.
2
Q
What is a fatty acid?
A
- A fatty acid is a carboxylic acid characterized by a long carbon chain.
- These chains can vary in length and possess different numbers and locations of double bonds.
3
Q
saturated Fats?
A
Saturated fats have fully hydrogen-saturated fatty acid chains:
= making them solid at room temperature
= contributing to the rigidity of cellular membranes.
4
Q
Unsaturated Fats?
A
- Unsaturated fats are liquid at room temperature :
- due to have fewer hydrogen atoms, + double bonds between carbons,
- creating bends in fatty acid chains.
= This enhances membrane fluidity, allowing more movement. - In cellular membranes, unsaturated phospholipids result in increased membrane fluidity:
= allowing for more movement.
5
Q
How is melting point related to the level of saturation in fatty acids?
A
- saturated fats have a higher melting point and are more viscous.
- Higher unsaturation (double bonds) leads to lower melting temperatures and less viscosity.
6
Q
Variations in lipid composition of cell membranes of many species appear to be due to:
A
- to specific environmental conditions.
- These adaptations help maintain membrane fluidity and functionality in different habitats and temperature ranges.
7
Q
What are some examples of variations in the cell membrane lipid compositions of species?
A
- fish in cold environments have membranes rich in unsaturated hydrocarbon tails for fluidity.
- Thermophilic bacteria and archaea in hot springs use unique lipids to maintain membrane stability at extreme temperatures.
8
Q
What is the plasma membrane?
A
- the boundary membrane of every cell, functioning as a selective barrier that regulates the cell’s chemical composition.
- composed of bilayers of phospholipids.
9
Q
What are the roles of the plasma membrane?
A
Compartmentalization: Creating separate compartments within the cell.
Site for Biochemical Activities: Hosting various cellular processes.
Selective Permeable Barrier: Regulating what enters and exits the cell.
Transporting Solutes: Facilitating the movement of substances.
Responding to External Stimuli: Participating in signal transduction.
Intercellular Interaction: Enabling communication with other cells.
Energy Transduction: Playing a role in energy-related processes.
10
Q
What is a phospholipid? Which regions are hydrophobic?hydrophilic?
A
- A phospholipid is a lipid composed of glycerol linked to two fatty acids and a phosphate group.
- The hydrocarbon chains of the fatty acids are nonpolar and hydrophobic, meaning they repel water.
- The phosphate group, along with the glycerol, forms a polar, hydrophilic head, which interacts with water and is attracted to it.
- This dual nature of phospholipids, with hydrophobic tails and hydrophilic heads, is essential for their role in forming cell membranes.
11
Q
Why are phospholipids said to be amphipathic?
A
because it has both a hydrophilic region and a hydrophobic region
12
Q
How are phospholipids assembled?
A
- Phospholipids assemble into bilayers, with their hydrophilic (polar) heads facing the surrounding polar water molecules and their hydrophobic tails oriented away from water.
- The bilayer structure restricts the passage of polar molecules across the membrane.
13
Q
The diversity in the membrane composition of phospholipids can vary based on what?
A
can vary significantly between species, as well as within organs, tissues, and individual cells.
14
Q
A
Phospholipids can differ based on:
- Fatty acid chains
= (length, number, and position of double bonds). - Fatty acid linkage
= (ester versus ether). - Head group
= (e.g., phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, etc.).
15
Q
Membrane fluidity
A
ability of lipid molecules to move laterally within the membrane plane, creating a “fluid mosaic” of phospholipids and proteins.
16
Q
Factors Affecting Membrane Fluidity:
A
Lipid Composition: Short unsaturated chains increase fluidity, while saturated chains decrease it.
Temperature: Fluidity decreases in colder conditions.
Cholesterol: Reduces fluidity at moderate temperatures by limiting phospholipid movement but prevents solidification at low temperatures by disrupting regular packing.
17
Q
What does increased fluidity cause?
A
enhances membrane permeability and the functioning of membrane proteins.
18
Q
Describe the permeability of cell membrane.
A
- selectively permeable, allowing only specific substances to pass through.
- diffusion rates of different substances through the membrane can vary widely
19
Q
Permeability Is higher for..
A
- smaller molecules
- less polar (charged) molecules
- more hydrophobic molecules
- highly lipid-soluble substances
- gas (ex: O2, CO2…)
- water, urea, CO2, O2
20
Q
What are transport proteins?
A
- transmembrane proteins that temporarily modify membrane permeability
= assisting the selective passage of specific molecules into or out of the cell. - They provide a means for cells to regulate permeability as needed.
21
Q
What is Fick’s Law of Diffusion?
A
Fick’s Law states that the flux of molecules moves from areas of high concentration to areas of low concentration.
This movement is a result of the random motion of individual molecules in all directions.
22
Q
What is the chemical gradient?
A
- difference in solute concentration across a membrane.
- It drives the movement of ions from areas of high concentration to areas of low concentration
= helping restore equilibrium.
23
Q
Movement of Charged Molecules depedent on what 2 gradients:
A
If a molecule is charged, its net movement depends on both the
1. chemical gradient (concentration difference)
- electric gradient (charge difference)
across the plasma membrane.
24
Q
What is passive diffusion?
A
- a type of simple diffusion across the phospholipid bilayer that doesn’t require energy (no ATP).
- involves the random movement of molecules, equalizing their concentration.
- Molecules move along their concentration gradient.
- At equilibrium, an equal number of molecules move in both directions.
- Examples include
1. water
2. fat,
3. fat-soluble molecules
4. oxygen
5. nitrogen
6. carbon dioxide
7. alcohol.
25
Can diffusion be facilitated?
Yes.
- Facilitated diffusion occurs with the assistance of highly selective membrane transport proteins (channels) that enable specific molecules to pass through,
= aquaporins in kidney duct
26
Rate of passive diffusion depends on
Gradients of concentration
* Electrical gradients
* Mass of the molecules
* Temperature
* Solvent density
* Lipid solubility
* Membrane surface area
* Distance travelled by molecules
* Hydrostatic pressure or partial pressure
* Transport proteins
* Membrane fluidity
27
How is the cell able to modify (regulate) the entry/exit of molecules?
Cells regulate molecule entry/exit through:
- Gene expression changes for membrane transport proteins.
- Temporary opening and closing of transport proteins.
28
What are the two key factors that a cell can maintain within its membrane?
1. specific solute concentrations
2. electric potential across the membrane.
29
Why is the inside of the cell negative?
1. because of the presence of negatively charged phosphate groups and proteins in the cytoplasm
2. the movement of ions in and out of the cell.
30
where does the net movement of a population of molecules go towards
lower concentrations (chemical gradient)
31
T/F
when at concentration equilibrium, there is no movement of molecules
FALSE
although low, there can still be movement across the plasma membrane, in equal numbers to keep equilibrium
32
T/F
diffusion can be facilitated by membrane transport protein (channels)
true, channels are highly selective, only let specific molecules through
33
T/F
can never have molecule go against concentration gradient
FALSE
can have few molecule go against their concentration gradient, but net movement will be towards concentration gradient
34
T/F, the inside of the cell in positively charged relative to the outside of the cell, why?
FALSE, inside is more negative
presence of phosphate groups and proteins (both negatively charged)
35
membrane potential (aka electrical potential)
charge difference (voltage) across the plasma membrane
the attraction of opposites charges across the plasma membrane is a source of potential energy
36
resting membrane potential
aka baseline membrane potential
-70mV
37
38
depolarization
increase of membrane potential (becoming less negative)
39
T/F
FALSE, approaches the equilibrium potential of the ion
40
which way do Na+ and Ca2+ diffuse towards and why
inside the cell, low potential/slow current
41
which way do K+ and Cl- diffuse towards and why
outside the cell, high potential/high current
42
what ions are used in neuron signal transmission and why
K+
Na+
Cl-
to create action potential
43
what is Ca2+ used in
signaling pathways
neurotransmitter exocytosis
muscle contraction
44
osmosis
diffusion of free water across a selectively permeable membrane.
It depends on the concentration of non-penetrating molecules inside and outside the cell.
45
osmolarity
Osmolarity is the concentration of all solutes in a solution, including both penetrating and non-penetrating solutes,
it's typically measured in osmoles per liter (osmole/L).
46
hyperosmotic solution
solution with a higher concentration of solutes than the cell
47
hypoosmotic solution
solution with a lower concentration of solutes than the cell
48
isosmotic solution
solution with the same concentration of solutes as the cell
49
tonicity
refers to a solution's ability to cause a net movement of water into or out of a cell.
specifically considers the concentration of non-penetrating solutes only.
related to effective osmolarity, which determines osmotic pressure, and is typically measured in effective osmoles per liter (effective osmole/L).
50
hypertonic solution
solution with a higher concentration of non-penetrating solutes than the cell
51
hypotonic solution
A hypotonic solution has a lower concentration of non-penetrating solutes (solutes that cannot easily cross the cell membrane) compared to the cell.
52
isotonic solution
has the same concentration of non-penetrating solutes (solutes that cannot easily cross the cell membrane) as the cel
53
T/F,
water moves through a semipermeable membrane from a region of lower concentration of non-penetrating molecules to a region of higher concentration of non-penetrating molecule
TRUE
, therefore, water moves from a compartment that is HYPOTONIC to a compartment that is HYPERTONIC
54
T/F
ionic compounds (NaCl, KCl, HCl) dissociate in water
True, therefore the osmolarity and tonicity of these molecules is doubled when in solution or inside the cell
55
what are the effects of movement of water inside and outside the cell through osmosis
- creates osmotic pressure
- change the volume of the cell
56
osmotic pressure of a cell
Osmotic pressure of a cell is the minimum pressure required to prevent the movement of water across a semi-permeable membrane.
It depends on the difference in the concentration of non-penetrating molecules.
57
T/F,
lower tonicity inside the cell increases the osmotic pressure inside the cell
FALSE, higher tonicity increases the osmotic pressure
58
T/F, cell wall in plants helps resist increased osmotic pressure
true
59
osmoregulation
Osmoregulation is the control of solute concentrations and water balance in an organism.
It is a necessary adaptation for life in various environments.
60
why is the maintenance of osmotic pressure important in plants?
Maintaining osmotic pressure is crucial for the transport of water across the vegetative and photosynthetic parts of plants.
61
T/F freshwater protist are hypotonic compared to their environment
FALSE
they are hypertonic compared to their environment -> movement of water inside cell by osmosis
a contractile vacuole pumps water out of the cell so it doesnt burst
62
membrane proteins what do they do
facilitate diffusion following concentration gradient
63
uniporter
a type of transport protein that moves a single molecule across a biological membrane.
64
what activates a uniporter
binding of a specific ligand (molecule)
stress (physical deformation)
changes in membrane voltage
may be always on.
65
Ion Channel:
is a protein that allows ions to pass through it in either direction, as it is open on both sides simultaneously.
66
Ion Channel Example
is the sodium (Na+) voltage-dependent or voltage-gated channel
which plays a crucial role in generating action potentials in neurons.
67
Aquaporin (AQP1):
is a water channel protein found in the cells of the nephron collecting duct, which are the filtering units in the kidney.
It assists water reabsorption in the kidney.
expressed in cells as a response to ADH aka vasopressin (produced in hypothalamus)
68
T/F, alcohol can inhibit secretion of ADH by blocking voltage-gated calcium channels in the neurohypophyseal nerve
TRUE
- AQP1 expression is then turned off in the nephron cells and kidneys no longer retain water
69
carrier proteins
membrane proteins that change their shape to facilitate the passage of molecules
in either one direction or the other but not both simultaneously.
70
Carrier Protein Example:
the glucose transporter GLUT1,
= which facilitates the uptake of glucose in various tissues.
71
T/F
membrane proteins can transport molecules AGAINST their concentration gradient
true
72
what does the transportation of molecules by membrane proteins require energy from
The transportation of molecules by membrane proteins can require energy from two sources:
Hydrolysis of ATP by ATPase enzymes --> leading to primary active transport.
2. The potential energy stored in ionic gradients maintained by the cell --> leading to secondary active transport.
73
T/F, some active proteins are carriers
FALSE
- all are carriers, aka pumps
- help maintain specific intracellular concentration gradient
= by carrying molecules in only 1 direction (against concentration gradient)
74
how many molecules can secondary active transporters carry at a time
2, or more (cotransporter)
one provides energy (down its conc gradient), other is carried against its concentration gradient
75
symporter
moves two molecules in the same direction
76
antiporter
moves two molecules in opposite directions
77
primary active transport
uses ATP as an energy source
78
example of primary active transport
sodium-potassium pump.
which actively transports three sodium ions (Na+) out of the cell and two potassium ions (K+) into the cell, against their concentration gradients (from low to high concentrations).
This pump helps maintain concentration gradients and the resting membrane potential in cells.
79
Importance of Sodium-Potassium Pump in Fish:
- plays a crucial role in osmoregulation in fish.
- Marine fish consume large quantities of saltwater, and this pump helps them pump out excess sodium chloride (NaCl) that is absorbed by their tissues back into the marine environment.
- by maintaining the appropriate ion balance, the pump helps marine fish adapt to their saline habitats and prevents them from accumulating excessive salts.
80
primary active transport example #2
Ca2+ ATPase, a uniporter that actively transports calcium ions (Ca2+)
back into the sarcoplasmic reticulum during muscle fiber relaxation,
which occurs after muscular contraction.
This transport process helps regulate calcium ion levels in muscle cells, allowing for proper muscle function and relaxation.
81
explaining the role of angiotensin-converting enzyme 2 (ACE2) and its connection to SARS-CoV-2:
ACE2 is a membrane protein found in various tissues, including the intestine, kidneys, testes, gallbladder, and heart.
It serves as the port of entry for the SARS-CoV-2 virus into human cells, facilitating viral infection.
The virus's spike protein exhibits complementarity to the ACE2 receptor allowing viral entry.
- ACE2 also plays a role in the renin-angiotensin-aldosterone system (RASS)
= catalyzing the hydrolysis of angiotensin II, a hormone that raises blood pressure.
- This enzymatic action by ACE2 helps lower blood pressure.
82
describing lipid-anchored proteins:
covalently bonded to a lipid group that resides within the cell membrane.
The lipid group can be :
- phosphatidylinositol,
- a fatty acid
- glycosylphosphatidylinositol (GPI).
These proteins are diverse and serve various functions, including acting as:
- hydrolytic enzymes
- adhesion molecules
- receptors within the cell membrane.
83
Peripheral Proteins:
- Located on the membrane surface.
- Noncovalently bonded to the lipid bilayer's polar head groups or integral membrane proteins.
- Functions include involvement in membrane sugar, lipid, and protein metabolism (e.g., oxidases, oxygenases, lipases).
84
integral proteins
- Penetrate the lipid bilayer
= embedded in the membrane.
- Contain transmembrane helices.
- Examples include:
= ion channels
= transporters
= receptors.
- Pass multiple times through the hydrophobic part of the plasma membrane.
85
be able to draw protein structures
do it on paper (check photos after done)
86
Quaternary Structure:
- Involves 2 or more polypeptides.
- Represents the overall protein structure formed by aggregating polypeptide subunits, each coded by a single gene.
87
Tertiary Structure Determined/Stabilized by:
- Hydrophobic interactions:
= Nonpolar amino acids cluster in the protein core away from water.
- Covalent bonds
= (disulfide bridges).
- Van der Waals interactions
= (between hydrophobic amino acid chains).
- Hydrogen bonds.
- ionic bonds.
88
tertiary structure
The 3D shape of a protein, stabilized by interactions between its amino acid side chains (R groups).
89
what does the secondary structure result from
results from :
- hydrogen bonds between the amino group (-NH)
- carboxyl group (-CO) in the protein backbone
not the side chains.
90
Two types of secondary structure
α helix and β pleated sheet
91
T/F, the sequence of amino acids is always the same in every protein
FALSE, sequence is specific to the
- function of the protein
- its localization
- interactions with other molecules
92
what does primary structure determine
- secondary structure (α helices and β pleated sheets)
- tertiary structure
= due to the chemical nature of the backbone and the side chains (R groups) of the amino acids along the polypeptide
93
primary structure of protein
linear sequence of amino acids of a protein
order of amino acids is determined by the DNA sequence of the gene that codes for the protein
94
what is on the 2 ends of the polypeptide chain
The polypeptide chain has:
- a free amino group (N-terminus) at one end
- a free carboxyl group (C-terminus) at the other end.
95
what are amino acids bound together by:
1- Amino acids are joined together by peptide bonds
- which form between :
1. the carboxyl group (COOH) of one amino acid
2. the amino group (NH2) of another amino acid.
96
What are proteins made of?
long chains of amino acids.
97
NKCC1 (Na-K-Cl) cotransporter:
- A symporter
- transports 1 Na+, 1 K+, and 2 Cl- ions into the cell
- crucial in fluid secretion
- located on the basolateral membrane
- drives water movement out of the cell into the lumen.
98
where does the glucose go after it goes inside the cell
After glucose enters the cell through the glucose transporter GLUT2, it is transported outside the cell and into the bloodstream through the basal membrane.
99
what creates a gradient of Na+ concentration
The Na+/K+ pump on the basal membrane actively transports sodium (Na+) out of the cell, creating a concentration gradient with higher sodium levels outside the cell. This gradient is essential for the SGLT1 transporter to carry glucose into the cell against its concentration gradient.
100
example of secondary active transport
SGLT1, located on the apical membrane of small intestinal cells, transports two sodium ions (Na+) and one glucose molecule into the cell during digestion.
101
Secondary Active Transport (Cotransporters)
Uses ionic concentration gradients to move molecules against their concentration gradient.
102
another example of primary active transport
Calcium ATPase (Ca2+ ATPase):
This uniporter moves calcium ions (Ca2+) back into the sarcoplasmic reticulum after muscle fiber contraction
= aiding in muscle relaxation.
103
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