Tutorial - Week 5 - Lipids & biomembranes Flashcards
Key concept: Understand the classification of lipids
Key concept: Become familiar with the structure and nomenclature of lipids
- Fatty acids (acyl chain + carboxylic group)
- Saturated vs unsaturated chains (no double bonds
vs double bonds) - Triacylglycerols (glycerol + 3 fatty acids)
- Waxes (long alcohol + long fatty acid)
- Phospholipids (glycerol + phosphate + polar group
+ 2 fatty acids) - Sphingolipids (sphingosine + 1 fatty acid (+ polar
group)) - Sterols (e.g. cholesterol)
Key concept: Gain knowledge on the major biological functions of lipids
- Energy storage
- Structural components of membranes
- Signaling
Key concept: Understand the structure and function of biomembranes
- Composition: Lipids + proteins
- Structure: fluid mosaic (i.e. lipid bilayers with proteins embedded
associated via non-covalent bonds) - Organisation: lipid asymmetry (across layers) and within layer
- Proteins associated with membranes: embedded, peripheral, or lipid-linked
What are lipids?
Lipids are molecules that are soluble in organic solvents:
- Insoluble in water (hydrophobic: ‘water phobia’)
- Do not form polymers (in contrast with other biomolecules)
- Possess different forms, properties and functions
What are the important biological functions that lipids have? (3 points)
- Energy storage (highly efficient form to store energy)
- Structural components of biological membranes (i.e. form barriers)
- Signaling (intra and extracellular, e.g. hormones, vitamins)
Name the three lipid functions and give examples within each:
- Energy Storage
* Fatty acids
* Triacylglycerols
* Waxes - Structure
* Phospholipids
* Sphingolipids
* Sterols
*Biomembranes
* Lipid bilayer organisation and properties
* Structure & function - Signaling
* Steroid hormones
* Eicosanoids
* Vitamins
What are fatty acids?
Fatty acids are carboxylic acids with hydrocarbon chains
Do fatty acids have an even or uneven number of carbons?
Normally have an even number of carbons (4 – 36 carbons)
What is the difference between saturated and unsaturated fatty acids?
Saturated (all carbons are saturated, full hydrogenated, only single bonds, C-C)
Unsaturated (some carbons have double bonds, C=C)
* Monounsaturated (one double bond)
* Polyunsaturated (more than one double bond)
Name the type of fatty acid
Name the type of fatty acid
How are fatty acids named?
Named by the Number of C atoms : number of double bonds (position of double bonds)
- Carbons are numbered from the carboxyl (COOH) end
- ∆ is used to denote double bond
Name this fatty acid correctly
What is the storage lipid?
Triacylglycerol
Fatty acids normally exist as __________, known as _____________
derivatives
triacylglycerol
Esterified definition?
changed into an ester (= a chemical compound produced by a reaction between an acid and an alcohol, in which the hydrogen of the acid has been replaced by an alkyl group of atoms): Esterified oils produce less greasy donuts than liquid oils, but they are expensive and can have flavour issues.
Other names for triacylglycerol and what they are, structurally speaking?
Triacylglycerol (triglyceride, or just fat): glycerol esterified with 3 fatty acids
Label
What are Saturated Fats?
Triacylglycerols with saturated fatty acids (no double bonds)
What are Unsaturated Fats?
Triacylglycerols with unsaturated fatty acids (with double bonds)
If saturated, fatty acid tails are…? (Structure and interactions)
Example?
Straight and packed tightly (stronger
van der Waals interactions)
‘Hard fats’, like butter and other
mammalian fats are solid at room
temperature (not so healthy)
If unsaturated, fatty acid tails have…? (Structure and interactions/bonds)
Example?
Kinks and cannot pack tightly (weaker van der Waals interactions)
Oils obtained from plants and fish (e.g.
olive oil) are liquid at room temperature
(healthier than saturated
Label both
Double bonds in naturally occurring unsaturated fatty acids are in which configuration and what is the structural result?
cis configuration and get a kink
Name the type of fatty acid, it’s state at room temperature, and why it has that state
Name the type of fatty acid, it’s state at room temperature, and why it has that state
Name the type of fatty acid, it’s state at room temperature, and why it has that state
Why did the food industry start to process vegetable oils? Why was it a necessity?
How do they process them/what process do they use?
Vegetable oils are normally liquid at room temp (not great to bake), and turn rancid when exposed to oxygen in the air (become rancid via cleavage of double bonds.
Hydrogenation is used to add H to the double bonds to convert some of the double bonds in single bonds)
Results in:
- Improve shelf life of vegetable oils
- More solid and more spreadable (e.g. cooking margarine)
- More resistant to high temperatures (e.g. blended oils used for deep-
frying)
What process turns unsaturated fats into saturated fats?
Hydrogenation
What are the storage lipids?
Waxes
Structure of waxes?
- long chain of saturated or
unsaturated fatty acids (C14 to C36) - long chain alcohol (C14 to C30)
- Linked by an ester bond
Function of waxes?
- Energy Storage (e.g. plankton)
- Water repellent (e.g. beeswax)
Name the molecule and the bond
What is the consistency of wax, melting point, and is it higher than those of TAGs (triacylglycerides)?
Firm consistency (Melting points (60-100 o C) higher than those of TAGs)
Beeswax is an ester of…?
Palmitic acid with alcohol triacontanol
What are the 3 structural lipids with roles in the biomembrane?
- Phospholipids (e.g. phosphatidylcholine)
- Sphingolipids (e.g. sphingomyelin)
- Sterols (e.g. cholesterol)
What are phospholipids also known as?
Are they the most abundant in cell membranes?
Are they hydrophobic or hydrophilic?
What does their structure contain?
Glycerophospholipids
Most abundant lipid in cell membranes
Amphipathic (polar and non-polar regions)(hydrophilic and hydrophobic)
Structure contains:
* Glycerol
* Phosphate often linked to a polar group (R)
* 2 fatty acids (linked via ester bond
I’m what ways does the head group in the phospholipid vary?
In size and charge
What does the head group of a phospholipid define?
The class of phospholipid
Define zwitterion
a molecule or ion having separate positively and negatively charged groups
Main characteristics of each?
- Phosphatidic acid (PA):
- Phosphatidylethanolamine (PE):
- Phosphatidylcholine (PC):
- Phosphatidylserine (PS):
- Phosphatidylglycerol (PG):
- Phosphatidylinositol (PI):
- very small, negative
- small, zwitterion
- zwitterion
- negative, multiple charged groups
- negative
- negative, carbohydrate
The fatty acids in the phospholipids also vary. How?
- Length (C12-24)
- Saturated vs unsaturated (1, 2 and 3 double bonds)
- Modulate fluidity of the phospholipid
What are the structural lipids called?
Sphingolipids
Characteristics of sphingolipids:
- Derivatives of sphingosine (long-chain amino alcohol)
- No glycerol
- Amphipathic (polar & non-polar regions)
(Hydrophilic & hydrophobic
What does the structure of sphingolipids contain?
- sphingosine
- long chain fatty acid
- Polar head group (via glycosidic or phophodiester bond
The head group of a sphingolipid defines the…?
Head group defines the class of sphingolipid:
Sphingolipids:
- Ceremide = ?
- Sphingomyelin is the most…?
- Glycolipids have…?
- sphingosine + fatty acid
- the most common sphingolipid in membranes
- carbohydrate instead of a phosphate group
What is the most common phospholipid class in mammalian membranes?
Phosphatidylcholine
What is the most common sphingolipid class in mammalian membranes?
Sphingomyelin
What are the two types of glycolipids?
Glycosylated Phospholipids or Sphingolipids
What are the three main points of glycolipids?
- What groups do they have attached?
- Where are they found?
- What is their function?
- Have attached sugar groups
- Found on the non-cytosolic side of a cell membrane bilayer
- Function in cell recognition
Sterols are ________ lipids present in __________ of most ___________ cells
structural
membranes
eukaryotic
- What is the most common sterol?
- Similar sterols exist in…?
- Can bacteria synthesise sterols
- The most common sterol is mammalian cells is cholesterol
- Similar sterols exist in plants and fungi
- Bacteria cannot synthesise sterols
What does the cholesterol structure contain?
Cholesterol structure contains:
- 4 fused rings: 3 with 6C, 1 with 5C
- Hydrocarbon side chain (non-polar)
- Polar head group
What is the function of cholesterol? (4 points)
- Integral part of biological membranes
- Increases the rigidity of membranes
- Increases the impermeability of membranes
- Very important to maintain the integrity of cells
T/F: Phospholipids, sphingolipids and cholesterol are virtually insoluble in water
T/F: They are also amphipathic
True
True
What happens when lipids of the lipid bilayer are mixed with water?
When mixed with water they cluster together and from aggregates
Fatty acid chains are hidden in the interior of the lipid membrane via ______________ (reduction of contact
with water), and once in close proximity can establish van der Waals interactions
Hydrophobic effect
The polar group of the lipid bilayer are exposed to water and can establish _______ with water molecules
H-bonds
Phospholipids/sphingolipids with unsaturated fatty acids are less packed, the membrane is more ______
Fluid
Phospholipids/sphingolipids with ________________ can pack better and establish stronger van de
Waals interactions (more rigid, thicker)
saturated fatty acids
Label each
Label
Cholesterol - describe (4 main points)
- Polar group located close to the polar head of phospholipids
- Ring structure is planar and rigid:
- It Inserts in the hydrophobic region of the bilayer
- Immobilises fatty acid chains of phospholipids - Increases rigidity and thickness of bilayers
- Decreases permeability
Describe the Fluid mosaic model
What are the interactions between?
How can the components move?
- mosaic with a pattern (lipid and protein organization), but fluid, dynamic
- Interactions between its components are noncovalent
- Components can move laterally in the plan of the membrane
Label the blue and red lines
What are the lipid components of membranes?
- Phospholipids (e.g. phosphatidylcholines, phosphatidylserines)
- Sphingolipids (e.g. sphingomyelin & glycolipids)
- Cholesterol
List the Protein components of membranes…
- How are they attached?
2/3. Which portions are where
- Proteins are embedded in the bilayer
- Hydrophobic portions are in the interior of the bilayer
- Hydrophilic portions exposed to the outside & inside the cell are different
T/F: Lipid bilayers are symmetrical
False - they are asymmetric
Label
Lipid organisation within membranes:
- Are there different lipids in each layer?
- What effects membrane charge?
- Lipid distribution also affects what?
- What is on the outer leaflet, how are they exposed, and what role do they play?
- What about the lipid bilayer modulate the distribution of which important macromolecule?
- Certain macromolecules interact together - which ones?
- Different lipids in each bilayer
- Lipid distribution affects membrane charge (negative lipids are located in the intracellular side)
- Lipid distribution affects membrane fluidity
- Glycolipids on the outer leaflet: carbohydrates are surface exposed and have a role in cell recognition
- Lipid bilayer composition and organisation modulate protein distribution
- Certain lipids interact with membrane proteins
Describe lipid rafts (3 points)
- What are they?
- Physical characteristics (2 points)
- Associations?
Lipid rafts:
1. Clusters in membranes enriched in cholesterol (Chol) and sphingomyelin (SM)
2. Thicker & more rigid
3. Some proteins associate with lipid rafts
Label
Which one is fluid and which is more rigid?
Label
List the three types of Membrane proteins:
- Integral (AKA as transmembrane or embedded)
- Peripheral (associated loosely via ionic bonds
and H-bonds with polar headgroups or other
proteins) - Lipid-anchored
What are these all examples of?
_________________ are mainly located in the hydrophobic region of the lipid bilayer. They avoid contact
with water
Hydrophobic amino acids
_____ & ______ are amphipathic amino acids, and they normally locate at the interface of polar headgroup and the
apolar hydrocarbon region
Trp and Tyr
___________ (___________) are found in the aqueous phase (intracellular or extracellular portions)
Charged residues (Lys, Arg, Glu, Asp)
What are the two intracellular lipids involved in signalling?
- Phospholipids (e.g. phosphatidylinositols)
- Sphingolipids (e.g. ceramide)
What are the extracellular lipids that are involved in signalling?
Extracellular: Hormones (endocrine/paracrine)
1. Eicosanoids (paracrine: act locally)
2. Steroids (endocrine: travel via blood stream)
3. Vitamin D
List the three steps to this process of membrane lipids involved in intracellular signaling
List the two steps of membrane lipids involved in intracellular signaling
What carry messages to nearby cells
Eicosanoid hormones
Describe eicosanoids (4 points)
- Essential fatty acids are required for their synthesis
- Derivatives of fatty acids with 20 Carbons (i.e. arachidonic acid 20:4 (D5,8,11,14 )
- Some have 5-, or 6-membered ring
- Paracrine hormones (i.e. act close to the site of synthesis))
Label
- NSAIDs meaning?
- What do they do?
- NSAIDs: nonsteroidal
anti-inflammatory drugs
(e.g. aspirin, ibuprofen) - Block the formation of prostagladins and thromboxanes by inhibiting the
enzyme prostaglandin H2 synthase (also known as cyclooxygenase)
Pain killer & anti-coagulant properties
Where do steroid hormones carry messages between?
Tissues
Steroid hormones:
- What do they function as?
- What are they (in terms of sterol?)
- Their structure?
- More or less polar than cholesterol?
- How do they move through the bloodstream?
- What do they bind to and where?
- Trigger what?
- They function as endocrine hormones (i.e. secreted in
the blood steam to act in distinct tissues) - Oxidised derivatives of sterols (e.g. cholesterol)
- Have the sterol rings but lack the alkyl chain
- More polar then cholesterol
- Move through the blood stream (on protein carriers) to target tissues
- Bind to highly specific receptor proteins in the nucleus
- Trigger changes in gene expression (activation/inhibition)
Label
Give three examples of steroid hormones and describe
Also label these
- Sex hormones
Androgens (e.g. testosterone expressed in the testes)
Estrogens (e.g. estradiol expressed in the ovaries) - Hormones produced by adrenal cortex
Cortisol, regulates glucose metabolism
Aldosterone, regulates salt excretion
3.Steroid drugs
Strong anti-inflammatory activity
Treatment of asthma and rheumatoid arthritis
What are the three types of steroid drugs and what do each do?
- Anabolic steroid drugs:
- Mimic androgens, such as testosterone
- Drugs that help the growth and repair of muscle tissues
- Pharmaceutical use to treat hormonal problems or muscle loss
- Used as performance and image enhancing drugs (PIEDs) - Corticosteroids (e.g. prednisone & cortisone)
- Mimic hormones from adrenal cortex
- Suppress immune system (e.g. used during organ transplants)
- Reduce inflammatory conditions (e.g. arthritis, asthma or skin rashes) - Contraceptive steroids
- Mimic estrogens and progestins
- Used for birth control
T/F: Some vitamins are lipids & hormone precursors
True
Four main points of Vitamin D:
Vitamin D (or calcitriol)
- 7-dehydrocholesterol is activated by UV light in the skin (Vit D3) and converted into calcitrol in the liver and kidney
- Vit D3 & Vit D2 (similar structure) are present in some foods, or added as supplements
- Calcitriol is a hormone that regulates calcium levels in the intestine, kidney & bone
- Deficiency in calcitriol leads to defective bone formation and the disease of rickets
Vitamin A (or all-trans retinol) - 2 main points:
- b-________ is obtained from?
- its __________ regulate what?
- b-carotene is obtained from diet
- its metabolites regulate processes of cell growth and
differentiation, and vision
Key concept: Lipids involved in signalling
- Cell membrane lipids (intracellular, second messengers)
- Steroid hormones (sex hormones, adrenocortex hormones)
- Eicosanoids, derivatives of 20C fatty acids
- Vitamins (e.g. A & D are hormone precursors)
