lipids Flashcards
Functions of lipids?
Store energy
Water repellent
Buoyancy control and acoustics in marine animals
Cofactors for enzymes
Protect organs
Insulation from environment
Pigments
Digestion
Membrane structure
Signalling molecules
Antioxidants
What is a FFA?
Free fatty acid
Not a component of another lipid
Describe fatty acid structure
Fatty -hydrocarbon chain
Acid - carboxyl group
How long can the fatty acid hydrocarbon chain be?
2-24 carbons
Why is the hydrocarbon chain hydrophobic?
can’t form hydrogen bonds with H2O
What are SFAs?
Saturated fatty acids
no double bonds in hydrocarbon chain
What are MUFAs?
Mono unsaturated fatty acids
Have 1 C=C in hydrocarbon chain
Usually has a kink
What are PUFAs?
Polyunsaturated fatty acids
Multiple C=C in hydrocarbon chain
How does the number of C=C in the hydrocarbon chain affect fatty acid boiling point?
More C=C lowers the boiling point
e.g
olive oil - oleic acid - PUFA - liquid at room temp
butter - mostly SFAs - solid at room temp
Naming fatty acids, which is carbon 1?
carbon of carboxyl group
What is the second carbon in fatty acids called?
α carbon or carbon 2
If the name of a fatty acid has 14:3 included, what does this mean?
14 - number of carbons
3 - number of C=C
What is the Δ used for when naming fatty acids?
Shows position of double bond
E.g Δ 5,9 shows there are double bonds on carbons 5 and 9
What does it mean if a double bond is:
Cis
Trans
Cis - H atoms on same side of double bond
Trans - H atoms on opposite sides of double bond
All natural fatty acids are cis or trans?
cis
What is the last carbon in the hydrocarbon chain called?
Omega ( ω ) carbon
What does it mean if a FA is an:
omega 3 FA
omega 6 FA
omega 3 - first C=C is on the 3rd carbon counting from the ω carbon
omega 6 - first C=C is on the 6th carbon counting from the ω carbon
Omega-3 fatty acids are considered…
Anti-inflammatory
Omega-6 fatty acids are considered…
Pro-inflammatory
Example of an omega-6 fatty acid?
Arachidonic acid
example of an omega-3 fatty acid?
Eicosapentaenoic acid (EPA)
3 derivatives of arachidonic acid and their functions
Prostaglandins
fever, renal blood flow, mucosal protection, inflammation
Thromboxanes
formation of blood clots
Leukotrienes
inflammation, smooth muscle contraction in lungs
What is arachidonic acid made from?
what enzyme does it use?
Cell membrane phospholipids
uses phospholipase enzyme
what are the 3 arachidonic acid derivates?
- leukotrienes
- prostoglandins
- thromboxane and prostaglandins
what pathway is leukotrienes produced by?
lipoxygenase pathway
what pathway are prostaglandins and thromboxane produced by?
cyclooxygenase pathway
what is needed to produce (prostaglandins and thromboxane)
cox-1
what is needed to produce just prostaglandin
cox-2
is cox 1 physiological or inducible?
physiological
is cox 2 physiological or inducible?
inducible
What will inhibit the production of arachidonic acid?
Corticosteroids
What will inhibit the production of both thromboxane and prostaglandins?
NSAIDS - non-steroidal anti-inflammatory drugs
Examples of NSAIDS?
Ibuprofen
Phenylbutazone
Diclofenac
Describe COX-2 preferential NSAIDs and examples of them
Affect COX-2 more than COX-1
Meloxicam
Carprofen
Example of COX-2 specific NSAID
coxibs
Why shouldn’t you use steroids and NSAIDs together?
Steroids reduces arachidonic acid formation
no need for NSAIDs too
more side effects
What are TAGs?
Triacylglycerols/ triglycerides
Describe the structure of TAGs
- 3 fatty acids
- can be different
- 1 glycerol
- Fatty acids joined to glycerol by ester bonds ( C=O-O-C) : each of the 3 OH groups in glycerol forms an ester bond with the carboxyl group of a fatty acid
How are the ester bonds in TAGs broken?
hydrolysed by lipases or esterases
Can TAGs cross the cell membrane?
no
What are the main lipid components of dietary fats?
TAGs
how are TAGs digested
- TAGs are digested into FA and monoacylglycerol components in the small intestine.
- Re-constituted into TAGs within enterocytes.
- Packaged in the ER of enterocytes into
chylomicrons. - Enter the lymphatic system via the lacteal where they join lymph fluid to become chyle fluid.
Chyle returns to vascular system through venous return and then supplies tissues with TAGs.
what are chylomicrons?
- lipoproteins: composed of phospholipids and
apolipoproteins - transport fat from small intestine (where absorbed) to liver and adipose tissues
Where are lacteals found?
In small intestine villi
What is chyle fluid?
Lymph fluid containing many chylomicrons
When are fatty acids used for energy?
Fasting/starvation
Where are TAGs stored?
adipocytes
What is excess glucose converted to?
Fatty acids
Glycerol
stored in apodicytes
Is storage of TAGs in apodicytes short or long term?
long term
When would there be an excess glucose?
Energy requirements met
Glycogen store full
When does lipogenesis occur?
Glucose surplus + glycogen store full
Transported to liver in blood
Converted to fatty acids and glycerol in the liver
Describe the pathway of lipogenesis
Glucose synthesises glycerol
Glycolysis of glucose produces pyruvate
Pyruvate forms acetyl coA
Provides 2C at a time
NADPH needed to form fatty acids from acetyl coA
What are lipoproteins transported from hepatocytes as?
VLDL - very low density lipoprotien
Describe lipoproteins
Same structure as chylomicrons
Transport TAGs and cholesterol
Higher cholesterol than chylomicrons
Named according to density
less cholesterol = higher density
VLDL, IDL, LDL, HDL
Transport fats around the body
How are fatty acids freed from lipoproteins?
Lipoprotein lipases
What is lipolysis?
Breakdown of stored TAGs in apodicytes to fatty acids and glycerol
What induces lipolysis?
Several hormones:
glucagon
cortisol
adrenaline
When does lipolysis occur?
After 24 hour fasting
Endurance exercise - ‘going through the wall’ switch from glucose metabolism to lipid metabolism
Why can FFAs exist in the blood freely?
How do they usually travel in the blood?
Have carboxyl group - hydrophilic
Bound to albumin
What can use FFAs freely?
What can’t and why?
Muscle + the liver
Brain:
FA too large to cross blood brain barrier
How are fatty acids metabolised?
Β-oxidation
In mitochondria
Can fatty acids cross the mitochondrial double membrane?
No
Transported in by carnitine shuttle
Where can large FA be oxidised?
Peroxisomes
Steps of the carnitine shuttle
- Fatty acid binds to coA ⇒ fatty acyl coA via fatty acyl CoA synthase (FACS) in cytoplasm
- CoA exchanged for carnitine ⇒ acyl carnitine using CPT 1 (carnitine palmitoyltransferase I)
- Acyl carnitine translocated by facilitated diffusion using an unbound carnitine via CAT (Acylcarnitine translocate)
- Carnitine of the acyl carnitine exhanged for coA via CTP 2 ( carnitine palmotoyltransferase II)⇒ fatty acyl coA reformed - B-oxidation can now occur
Steps of the carnitine shuttle
- Fatty acid binds to coA ⇒ fatty acyl coA
- CoA exchanged for carnitine ⇒ acyl carnitine
- Acyl carnitine translocated by facilitated diffusion using an unbound carnitine
- Carnitine of the acyl carnitine exhanged for coA ⇒ fatty acyl coA reformed - B-oxidation can now occur
Describe B-oxidation
2 carbons removed from fatty acid chain at a time
produces acetyl coA
produces NADH and FADH2
Acetyl coA then used for krebs/TCA cycle
NADH and FADH2 used in oxidative phosphorylation (ETC)
What happens when there is excess acetyl coA?
Goes into ketogenesis cycle
What happens in ketogenesis?
Excess acetyl coA converted into ketones
What can be smelled on the breath of an animal suffering from ketoacidosis?
Acetone - sweet smelling/ pear drops
e.g milk fever, uncontrolled diabetes
what can be produced from ketogenesis?
- acetoacetate
- b- hydroxbutyrate
- acetone
What is pregnancy toxaemia in sheep also known as?
twin lamb disease
Describe twin lamb disease
- affects ewes in late gestation
- often those with more than one lamb
- inadequate nutrition during late gestation/ anorexia
- foetal glucose demands can’t be met by the ewe/gluconeogenesis
- adipose stores are mobilised and fatty acids are b-oxidised
- excess fatty acid metabolism results in ketone formation and ketoacidosis- pregnancy toxaemia
Describe milk fever
Bovine toxosis
Usually affects dairy cow in early lactation
Caused by inadequate nutrition in last gestation + early lactation
Glucose requirements for milk production not met by gluconeogenesis
Adipose stores mobilised
B-oxidation of fatty acids
Excess metabolism causes ketone formation
excess acetone= ketoacidosis
What are phospholipids also called?
Glycerophospholipids
Components of phospholipds
- 2 fatty acids
*usually one saturated, one unsaturated - Phosphate group
*bound to 3’ C of glycerol - Glycerol
*Polar head group can vary
Why are phospholipid heads hydrophilic?
Phosphate group is negatively charged
Describe the most common phospholipid in the plasma membrane
Phosphoatidylcholine
has choline polar head group
Which glycerophospholipid is involved in cell-signalling processes?
Phosphoatidylinositol 4,5 -biphosphate
Describe cardiolipin
Phospholipid
Found in cardiac tissue and mitochondria
Biomarker for apoptosis
Head group is another phospholipid
4 fatty acids in the molecule overall
What are sphingolipids? How do they relate and differ to phospholipids (structure)
Lipids found in plasma membrane
Both have hydrophilic/phobic parts
Sphingolipids only have one fatty acid
Sphingolipid structure
Fatty acid linked to sphingosine
no glycerol
Head group attached to sphingosine
head group + sphingosine = sphingoid base
Structure of sphingomyelin?
Fatty acid
Sphingosine
Phosphocholine head group
3 functions of sphingomyelin
Myelin sheath surrounding + insulating nerve cell axons
Role in action potential transduction
Involved in apoptosis
What are glycosphingolipids?
Example?
Sphingolipids with carbohydrate head group
Blood group
diff carb head group = diff blood group
What is cholesterol the starting point for?
Many sterols
Why are sterols very hydrophobic?
High carbon content
How can you tell a sterol apart from other lipids?
Conserved ring structure
4 carbon rings
3 hexagonal
1 pentagonal
What is cholesterol needed for?
Proper membrane function
Steroid hormone synthesis
How do animals obtain cholesterol?
Dietary source
Synthesise from acetyl coA
2 examples of sex hormones
Testosterone
Oestrogen
What is cortisol?
Importance?
Excessive amounts can cause?
Stress response steroid hormone
Induce gluconeogenesis when starvation
Cushing’s disease
Importance of aldosterone?
Causes Na retention and K excretion in kidneys
This causes water retention
Which disease results in reduced/no production of aldosterone?
What does this cause?
Addison’s disease - destroys aldosterone producing cells
Electrolyte imbalance, dehydration, death
2 steroid drugs used in practice
Prednisone
Prednisolone
Steroid hormone found in cabbages?
Brassinolide
Cholesterol is the starting point for the synthesis of…
Bile acids
Why are bile acids important?
Detergents
Emulsify lipids
allow lipase to break lipid down
Cholesterol homeostasis
too much cholesterol = make more bile acids
Describe the path from primary bile acids to secondary to conjugated
Primary bile acid dehydoxylated
hydroxyl group removed
Secondary bile acid made
then conjugated by glycine or taurine
Makes conjugated bile acid
now hydrophilic
How do bile acids aid in fat digestion?
Break fats into smaller droplets/micelles
Allows pancreatic lipases to break lipid down
Hydrophobic/philic parts of the bile acid?
Phobic- sterol
Philic - conjugated amino acid
what are the fat soluble and water soluble vitamins?
fat soluble- K A D E
water soluble- B C
How is vitamin D3 manufactured?
Cholesterol in skin
Presence of sunlight
uv-b radiation
processes in skin, liver, kidney
What is vit D3 needed for?
What happens if deficient?
Calcium absorption in small intestine
Rickets - bones not developed properly
What is retinol?
vitamin A
Is vitamin A derived from cholesterol?
No - doesn’t have 4 ring structure
Is retinol hydrophilic or hydrophobic?
Hydrophobic
What is retinol produced from?
B-carotene
found in carrots
Split into 2 identical molecules - retinol
How is retinal converted to retinoic acid? What is this important for?
11-cis- retinal oxidised
forms retinoic acid
Why is vitamin E hydrophobic?
Large carbon chain
Role of vitamin E
antioxidant properties
- the important antioxidant in hydrophobic environments such as within cell membranes
- protects fatty acids within cell membranes from oxidation
Differences and similarities of vitamins C and E
Similarities - both antioxidant
Diff - vit C is hydrophilic
Vit C works in aqueous environments - not hydrophobic
Importance of vitamin K
Cofactor in blood coagulation pathway
Is vitamin K hydrophobic or hydrophilic?
hydrophobic
Describe the blood coagulation pathway
Vit K is a cofactor for Vit-K dependent carboxylase enzyme
Enzyme adds carboxyl group to glutamate residues in certain clotting factors
makes carboxyglutamate residues
CG residues chelate Ca ions
enables clotting factors to bind to cell membranes and form a clot
What happens to vitamin K in the blood coagulation process?
What must be done to maintain balance?
oxidised in process so needs to be reduced
How does warfarin work?
Inhibits enzyme that oxidises reduced Vitamin K
Vitamin K is not active whilst it is reduced
Means that blood cannot clot
How can you treat a dog that has eaten rat poison?
Make them sick
If late , oversupply with vitamin K
Which vitamin is the liver very rich in?
Vitamin A
3 things vitamin A is needed for
Vision
Gene regulation
Appropriate bone turnover
Excess of vitamin A causes.. (bones)
Excessive breakdown of bone
by osteoclasts
Causes loss of bone from general skeleton
High Ca released from lost bone in skeleton
Circulates and deposits in inappropriate locations
New bone formed in inappropriate locations
Why is vitamin A toxic at high doses but vitamin C isn’t?
Vit C water soluble - can be excreted
Vit A hydrophobic
needs to be converted to hydrophilic in order to be secreted
Vit A stored in adipose tissue
not accessible to drug metabolism enzymes
Structure of waxes
Long chain fatty acid
Long chain alcohol
Joined by ester bond
Functions of waxes
Plankton use as energy store
Waterproofing feathers
Protection + pliability of hair and skin
Beeswax
Who makes polyketides?
What do we used them for?
Plants and fungi
Drugs
Many pigments are ___ - based
fat
