S1-L4: Lipids

Question 1

What are lipids?

Answer 1

• Large molecules formed from C/ H/ O & sometimes P

- are not polymers- just large

Question 2

Describe the “non-polarity” feature of lipids

Answer 2

• largely non-polar–> mostly C-H/ C-C bonds
• ->largely insoluble in water
• soluble in non-polar solvents like hexane
• hydrophobic interactions caused by lipids grouping together in H2O

Question 3

Outline examples of lipids

Answer 3

• Fats (solids)-a.r.t
• oils (liquid)- a.r.t
• waxes (solid v. hydrophobic)- a.r.t
• phospholipids (form membrane bilayers)
• steroids (derived from lanosterol)

Question 4

What are triglycerides? (refer to figure 1)

Answer 4

-type of dietary fat

Question 5

Outline the structure of triglycerides

Answer 5

-formed from 2 components:
1x Glycerol–> backbone AND 3x fatty acid chains
-fatty acid chains linked to glycerol backbone via ester bond

Question 6

From which process are triglycerides formed?

Answer 6

-formed via dehydration synthesis–> condensation reaction

Question 7

How are triglycerides broken down and what conditions are required for this process?

Answer 7

• broken down via hydrolysis

- requires intestinal enzyme–> triglyceride lipase + H2O

Question 8

Why is the digestion for triglycerides beneficial?

Answer 8

-free fatty acids absorbed in to gut easier AND transported

Question 9

Outline the two classes of fatty acids and give an example of each

1-saturated
2-unsaturated

Answer 9

1- contain single C-C bonds such as Palmitate

2- contain 1+ C=C double bond like Oleate

Question 10

What are Omega-3 fatty acids? (figure 2)

Answer 10

-polyunsaturated fatty acids characterised by C=C presence 3 atoms away from terminal methyl group

Question 11

How are Omega-3 fatty acids named?

Answer 11

• named by location of first C=C which counted from methyl end
• when not part of triglyceride–> Free Fatty Acids (FFA’s)

Question 12

Are FFA’s important?

Answer 12

-some FFA’s essential–> can’t synthesis in body

Question 13

Describe saturated (SFA’s) and unsaturated (UFA’s) fatty acids at room temperature

Answer 13

• SFA’s: from compact and closely packed triglycerides solid at room temp
• ->E.G: Palmitic acid (16 C) present in plant + animal fats
• UFA’s: form loosely packed triglycerides due to cis double bond which liquid at room temp
• ->like olive oil>80% oleic acid (18 C)

Question 14

What are steroids?

Answer 14

-4 fused C ring with various side groups attached

Question 15

What is lanosterol and how is it formed? (refer to figure 3)

Answer 15

• building blocks for all steroids

- formed by cyclization of squalene

Question 16

Outline the following examples of steroids:

1-Cholesterol (figure 4)
2-Sex hormones (figure 5-oestrogen)
3-Corticosteroids 
4-Aldosterone (figure 6)
5-Cortisol 
6-Vitamin D-cholecalciferol  (figure 7)

Answer 16

1-diagram 
2-oestrogen/ progesterone/ testosterone 
3-many functions (inflammation/fluid balance)
-->produced in adrenal cortex 
4-mineralocorticoid 
5-glucocorticoid 
6- a secosteroid 
--> at least one of ring structure broken up

Question 17

Outline and describe phospholipids (figure 8)

Answer 17

• lipid with phosphate group (PO4 2-) covalently bonded to glycerol backbone instead of fatty acid
• phosphate group: polar/water soluble (hydrophilic)/is head
• fatty acid groups: non-polar/water insoluble (hydrophobic)/ is tail

Question 18

Phospholipid examples

Answer 18

• H–> phosphatic acids
• Ethanolamine–> phosphatidylethanolamine
• Serine–> phosphatidylserine
• choline–> phosphatidylcholine
• Inositol–> phosphatidylinositol

Question 19

What are the following? :

1-Micelle
2-Bilayer

Answer 19

1-spherical arrangement of lipid molecule

2-composed of 2 layers of lipids organised in to sheets

Question 20

How do phospholipids organise themselves in water?

Answer 20

-the phospholipids organise themselves to keep hydrophilic heads “wet” AND hydrophobic tails “dry”

Question 21

Describe cell memebranes

Answer 21

• complex structure-physically separates cell interior from outside environment to confer protection from surrounding
• ->also provide role in anchoring extracellular structured AND other cells needed for tissue formation

Question 22

Outline glycolipids and their use

Answer 22

• lipid covalently attached to oligosaccharide
• forms part of cell membrane AND glycocalyx
• determines ABO blood group

Question 23

What are lipoproteins? (figure 9)

Answer 23

-soluble complexes which transport lipids AND synthesised in liver

Question 24

Describe the structure of lipoproteins

Answer 24

• spherical compounds with central hydrophobic core:
• -> triglyceride
• ->esterified cholesterol (cholesteryl ester)
• -> small amounts of other lipids + fat soluble vitamins
• external hydrophobic layer:
• -> phospholipids
• ->cholesterol (OH functional group outermost)
• ->apoproteins- stabilise structure + regulate enzyme activity at lipoprotein interface

Question 25

Analyse figure 10 showing lipoprotein classification

Answer 25

-figure 10- table

Question 26

Outline each of the following lipoprotein classifications:

1-Chylomicron
2-VLDL
3-IDL/LDL
4-HDL

Answer 26

1- carry dietary fat from small intestine to liver
2- Very Low Density Lipoprotein
–> produced in liver from synthesised TG’s + CE & carry fat to target tissues
3-TG’s gradually removed from circulating VLDL whcih become IDL (Intermediate Density Lipoprotein) THEN LDL (Low Density Lipoprotein)
4-High Density Lipoprotein
–>carries cholesterol to liver (“good cholesterol” reducing atherosclerosis)
–>Atherosclerosis: arteries clogged with fatty material- sites of fatty deposition called plaques

Question 27

What is the optimal lipoprotein profile in terms of HDL/LDL/TG’s/Total Cholesterol?

Answer 27

• HDL: >60 mg/dL
• LDL: 60-130 mg/dL
• TG’s: <150 mg/dL
• Total Cholesterol: <200 MG/dL

Question 28

Describe the key feature of TG’s and how it alongside FFA’s are useful

Answer 28

• TG’s largely non-polar AND relatively compact

- TG’s + FFA’s have energy-rich C-H bonds available for chemical reactions within cells

Question 29

Outline the storage of TG’s

Answer 29

-stored as lipid droplets in cytoplasm of adipocyte cells in adipose tissue

Question 30

What is White adipose tissue and what is it used for?

Answer 30

• cushions internal organs like shock-absorber

- give insulation-protecting internal organs from temp change AND reducing heat loss

Question 31

Similarly, outline what Brown adipose tissue is

Answer 31

• used to generate body heat

- ->brown adipocytes contain numerous fat vacuoles AND mitochondria

Question 32

Where is white adipose tissue located?

Answer 32

-analyse figure 11

Question 33

How can having excess adipose in the body increase the risk of disease? (figure 12)

Answer 33

• exerts undue pressure on organs
• is major endocrine organ–> produces pro-inflammatory hormones like Leptin/ cytokine TNFa
• diseases which could get are atherosclerosis/stenosis. AND aneurysms

Question 34

What are the three diseases which can form as stated previously from excess adipose?

Answer 34

• Thrombosis: clotting of circulating blood
• Stenosis: abnormal narrowing of body passage such as blood vessel
• Aneurysms: blood-filled bulge in blood vessel

Question 35

Explain how phospholipids are involved in electrical insulation inside the body

Answer 35

• phospholipids from myelin insulation around nerve fibers
• myelin–> increases speed of nervous impulses
• Schwann cell produce myelin peripherally
• ->oligodendrocytes produce myelin centrally

Question 36

What is the link between Vitamins A/D/E/K and fats, lipids and steroids?

Answer 36

• fat soluble

- some are also lipid/steroid derived

Question 37

Briefly explain what each of the following Vitamins

1-A
2-D
3-E
4-K

Answer 37

1- retinol/ retinoic acid/ carotenoids + healthy teeth/skin/sight
2-cholecalciferol + derivatives AND helps body absorb Ca2+ for healthy bones
3-tocopherol (antioxidant) found in oils AND anit-oxidant protects cell from damage
4-phylloquine + menaquinone AND important for coagulation of blood

Question 38

What are hormones? (refer to figure 13)

Answer 38

• chemical messengers

- ->steroidal hormones derived from cholesterol

Question 39

What is Eicosanoids?

Answer 39

-derived from w-3 AND w-6 fatty acids

Question 40

Outline what 1-postaglandins/2-leukotrienes and 3-thromboxane’s are used for

Answer 40

1-inflammation/vascular tone
2-asthma/allergy
3-vascualr tone/platelet aggregation (platelets clumping together)

Question 41

With reference to figure 14 and 15 how do lipids prevent moisture loss?

Answer 41

• lipid layer able to inhibit water evaporation
• skin moisture loss reduced by lipid layers
• lipid layer on tear film reduces moisture loss from cornea
• so lipids control what goes in and out of body
• lipids prevent tears drying out so eyes not dry out

Question 42

Summary of lecture

Answer 42

1-lipids–>non-polar macromolecules (mostly C-H + C-C bonds)
–> C/ H/ O & P atoms
2-triglycerides main dietary fat source
–>3 fatty acid chains esterified to glycerol backbone
3-saturated VS mono-/poly-unsaturated fatty acids impact on fluidity
4-steroids have key functional roles
–>cholesterol/hormones/Vitamin D
5-phospholipids able to form membrane bilayers
–>glycocalyx/glycosphingolipids
6-Lipoprotein profile influence susceptibility to cardiovascular disease
–>HDL Vs LDS
7-white VS brown adipose tissue
–>different location + functions
8-phospholipids form myelin sheath around nerve fibres
9-lipids prevent water loss skin AND eye