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lipids Flashcards

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Biology 101 flashcards
1
Q

what is a fat

A

Any molecule which is solid at room temperature and soluble in an organic solvent

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2
Q

what is an oil

A

Any molecule which is liquid at room temperature and soluble in an organic solvent

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3
Q

what are lipids

A

Lipids are biological molecules which are soluble in organic solvents (e.g. acetone, ethanol, hexane).
Generally proteins and carbohydrates are insoluble in organic solvents.

At room temperature some lipids may be fats, others may be oils

The term ‘lipid’ encompasses a large and diverse range of compounds.

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4
Q

what are the 4 major functions of lipids in the body

A

Structural elements of biological membranes

Some (e.g. triacylglycerols) serve as highly efficient energy reserves and also provide insulation.

Many vitamins and hormones are lipids or derivatives of lipids.

Some (e.g. bile acids) help to solubilise other lipids during digestion.

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5
Q

explain the generalised lipid structure

A

NON-POLAR TAIL, Hydrophobic (water hating)

POLAR HEAD GROUP, Hydrophilic (water loving)

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6
Q

what is amphipathic

A

when Compounds which exhibit both hydrophilic (water loving) and hydrophobic (water hating) properties

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7
Q

what can amphipathic substances form in water

A

peculiar substances

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8
Q

what forms when we put lipids in water

A

a monolayer

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9
Q

how does a monolayer form

A

from the hydrophobic tails sticking away from the water

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10
Q

how are micelles formed

A

when the lipid / water mixture is vigorously stirred:

they are circular and look like the structure of a ‘smartie’ ( w outer chocolate layer being the heads and then the middle chocolate being the tails)

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11
Q

explain the biological membranes bilayer

A

this is structure of cell membrane

Hydrocarbon tails tend to lie in roughly parallel arrays.

Interaction is via Van der Waals forces

Polar head group is heavily hydrated

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12
Q

what are the 5 lipid categories

A
  • Fatty acids
  • Triacylglycerols
  • Phospholipids
    Phosphoglycerides
    Sphingolipids
  • Glycosphingolipids
  • Cholesterol
    Steroid hormones
    Bile acids
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13
Q

explain fatty acid structure

A

A fatty acid consists of a hydrocarbon chain with a terminal carboxylic acid group: CH3(CH2)nCOOH
Have carboxylic acid group with long polar tail

Because of the carboxylic acid group, fatty acids are weakly acidic and have a pKa of around 4.5

Because physiological pH is around 7.4, fatty acids therefore are ionised and amphipathic in behaviour

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14
Q

what are fatty acids in relation to lipids

A

they’re the building block of lipids

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15
Q

in biological systems are the fatty acid carbon numbers odd or even

A

even

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16
Q

how are fatty acids categorised

A

by chain length

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17
Q

explain fatty acids chain lengths

A

Short chain fatty acids C2 – C8 (volatile and smelly) ex; parmesan cheese

Medium chain fatty acids C10 - C14
ex; goats cheese

Long chain fatty acids C16 - C18 (most common) ex; palmitic acid found in palm oil (liquid), lard

Very long chain fatty acids C20 – C26
ex; cod liver oil

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18
Q

what do fatty acids vary in their degree of, and how

A

unsaturation

as;
- They may be saturated with no double bonds,
- Unsaturated with one double bond (monunsaturated),
- Or unsaturated with more than one double bond (polyunsaturated),

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19
Q

in most naturally occurring fatty acids the orientation around the double bond is in what conformation

A

cis rather than trans

20
Q

why is the cis conformation important for structure

A

because each cis double bond inserts a bend into the hydrocarbon tail

With no double bonds theyre straight
With 1 double bond they have a slight bend
With 2 theyre more kinked
With 3 theyre even more kinked
And with 4 they basically fold

21
Q

explain the physiological functions of fatty acids

A

Low levels of free fatty acids exist in all tissues

Poor solubility in water means they have to be transported in the blood by albumin (this likes hydrophobic molecules) – a plasma protein

Fatty acids are the precursors of many other lipids, see later

They provide about 9kcal/g compared to 4kcal/g for carbohydrates and proteins

In the form of triacylglycerols, they serve as the major energy reserves in the body and serve an insulatory function.

Essential fatty acids: linoleic & linolenic acid must be obtained from the diet, important in infant development and later life.

22
Q

what are triacylglycerol’s sometimes called

A

triglycerides or fats

23
Q

whats the structure of Triacylglycerols

A

Three fatty acids are covalently linked via an ester bond to a molecule of glycerol

The three fatty acids can all be different, all the same, or only two the same.

24
Q

what can the Chain lengths of the fatty acids in triacylglycerols can be from
and whats the most common length of chain

A

4 - 22 carbon atoms

16 and 18 are the most common

Shorter chain lengths are found in butter and cheeses (characteristic smells)

25
Q

Most natural fats contains a complex mixture of triacylglycerols what happens to the melting point due to this

A

they can melt over a broad range of temps

eg. Cocoa butter is unusual in that it is mostly a single triacylglycerol (composed of palmitic, oleic and stearic acids) and has a fairly sharp melting point (so chocolate melts in the mouth without feeling greasy and melts quick).

26
Q

where is the majour storage site of triacylglycerols in mammals

A

the cytoplasm of adipose cells (fat cells)

adipose cells are huge compared to normal cells

27
Q

phat are phocpholipids structure

A

Are polar, ionic compounds composed of an alcohol, attached by a phosphodiester bridge to either diacylglycerol or sphingosine.

28
Q

what does it mean that phospholipids are amphipathic

A

Polar head = phosphate group plus whatever is attached to it
Hydrophobic = hydrocarbon tail

29
Q

The hydrophobic portion of phospholipids associates with what other non-polar components of membranes,

A

Glycolipids
Sphingosine
Protein
Cholesterol

30
Q

what 2 categories can phospholipids be sub divided into

A

Phosphoglycerides
Sphingolipids

31
Q

what are Phosphoglyceride and its structure

A

Are the major class of phospholipids which make up a large proportion of the membrane in mammals, bacteria and plants

Phosphoglycerides contain a glycerol backbone with 2 fatty acids bound, 1 at top and one at middle of the glycerol
and they have a phosphate group bound to end of glycerol with an alcohol group attached to it

32
Q

what are the names of Phosphoglycerides based off of

A

the alcohol group attached

33
Q

what are sphingolipids and their structure

A

Are not derived from glycerol

Backbone of sphingolipids is sphingosine, an amino alcohol that contains a long, unsaturated hydrocarbon tail

34
Q

how is ceramide obtained from sphingolipids

A

If a fatty acid is linked via an amide bond to the amino group of sphingosine

35
Q

what does further additions of the hydroxyl group lead to on sphingolipids
and give and ex and explain its structure

A

a variety of other membrane lipids

One important example is sphingomyelin, which is highly concentrated in the brain and nervous tissue.
In sphingomyelin one hydroxyl group is phosphorylated and a choline group attached

36
Q

explain Glycosphingolipids structure

A

In glycosphingolipids, the alcohol group of sphingosine is attached to one or more sugar molecules, usually glucose or galactose.

Note that they do no contain phosphate and therefore are not classed as phospholipids.

37
Q

what are the simplest glycosphingolipids and explain their structure and where theyre found

A

cerebrosides – in which there is usually only one sugar molecule attached

These are usually found in brain and neural tissue.

38
Q

name a complex glycosphingolipid and its structure and where its found

A

gangliosides, contain a branched chain of up to 7 sugar residues.

These are normally found in nerve tissue

39
Q

what group is cholesterol a member of

A

steroids

40
Q

what does a steroidal compound (cholesterol) contain

A

a fused ring system, labelled A, B, C and D.

41
Q

why is cholesterol incorporated into cell membranes

A

as it gives them rigidity

42
Q

what other biological important molecules are derived from cholesterol

A
  • steroid hormones: sex hormones - testosterone , progesterone
  • corticosteroids, such as cortisol
  • mineralocorticoids - such as aldosterone
  • bile salts
43
Q

what are bile salts structure

A

Polar derivatives of cholesterol

44
Q

what do bile salts act as in the small intestine and why

A

Act as detergents in the small intestine to aid digestion of fats

45
Q

what is the major mammalian bile salt called

A

glycoholate

biomolecular science (6 decks)

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