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Biology > Lipids 🟡 > Flashcards

Lipids 🟡 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are lipids?

A

Macromolecules which contain carbon, hydrogen and oxygen atoms.

However, unlike carbohydrates lipids contain a lower proportion of oxygen

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2
Q

What are three types of lipids?

A

− Triglycerides (fat for energy store, insulation, protection of organs)
− Phospholipids (to make membranes)
− Cholesterol (for membrane stability and make hormones)

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3
Q

What is the structure of a fatty acid molecule?

A

Fatty acids all have the same basic structure, but have a variable R group which is a long hydrocarbon chain.

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4
Q

Why do we need lipids?

A

-insulation
-layer of fat around most internal organs for protection
-some organisms use it for water proofing- waxy cuticle, leaves and stick insects

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5
Q

When are fatty acids saturated?

A

If there are no double covalent bonds between carbon molecules in the chain, they are saturated.

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6
Q

When are fatty acids unsaturated?

A

If there is one or more double bonds, they are unsaturated.

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7
Q

What does a double bond in the chain cause in a fatty acid?

A

A double bond causes a kink in the chain, as you can see in the below diagram.

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8
Q

What is the shorthand chemical formula for a fatty acid?

A

RCOOH

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9
Q

What do fatty acids contain?

A

Fatty acids contain a methyl group at one end of a hydrocarbon chain known as the R group (chains of hydrogens bonded to carbon atoms, typically 4 to 24 carbons long) and at the other is a carboxyl group

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10
Q

What are Triglycerides?

A

Non-polar hydrophobic tails

Formed by the condensation of one molecule of glycerol and three molecules of fatty acid.

An ester bond is formed and a water molecule is released.

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11
Q

Draw the structure of triglycerides…

A
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12
Q

How are ester bonds broken?

A

By hydrolysis reaction

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13
Q

What is glycerol?

A

An alcohol (an organic molecule that contains a hydroxyl group bonded to a carbon atom)

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14
Q

How are the properties of a triglyceride molecule important for its function as an energy store?

A

-The fatty acid tails are hydrophobic (repel water). This means that they gather together to form droplets in cells; the glycerol end faces outwards and the fatty acid tails face inwards away from any water.

-The hydrocarbon tails release a lot of energy when they are broken down.

-They are insoluble (do not dissolve in water), which means they don’t affect the water potential of a cell and don’t draw in water by osmosis. This is good, otherwise cells storing lots of triglycerides would soon swell up

The low density of fat tissue increases the ability of animals to float more easily

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15
Q

How do fatty acid chains determine the properties of triglyceride?

A

Length of the hydrocarbon chain (R group)

The fatty acid chain (R group) may be saturated (mainly in animal fat) or unsaturated (mainly vegetable oils, although there are exceptions e.g. coconut and palm oil)

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16
Q

What is the structure of saturated fatty acids?

A

All C-C single bonds in the chain

17
Q

What is the structure of monounsaturated fatty acids?

A
18
Q

What is the structure of polyunsaturated fatty acids?

A
19
Q

What is the emulsion test used for and how is it efficient?

A

It’s used to determine whether or not a lipid is present

It can be carried out quickly and easily in a lab

20
Q

What type of test is the emulsion test?

A

The test is qualitative-it does not give a quantitive value as to how much lipid may be present in a sample.

21
Q

What are the results of the emulsion test?

A

If lipids are present, a milky emulsion will form ; the more lipid present, the more obvious the milky colour of the solution.

22
Q

What is the method for the emulsion test for a solid lipid?

A
  1. Grind the food sample (2cm^3) with a small amount of ethanol using a pestle and mortar
  2. Put resulting ‘paste” in a test tube with 5cm^3 of ethanol and shake well
  3. Filter to remove solids
  4. Add 5cm^3 of water to filtrate and shake
  5. A cloudy-white colour indicates the presence of a lipid.
  6. As a control repeat the procedures using water instead of the sample, the final result should remain clear.
23
Q

What is the method for the emulsion test for a liquid lipid?

A
  1. Add 5cm^3 of ethanol to a 2cm^3 sample + shake well to dissolve any lipid.
  2. Decant into Test Tube B (filled with 2/3 water) and shake gently.
  3. A cloudy-white colour indicates the presence of a lipid.
  4. As a control repeat the procedures using water instead of the sample, the final result should remain clear.
24
Q

When are fatty acids cis and when are they trans?

A

If H atoms are on the same side of the double bond they are cis-fatty acids and are metabolised by enzymes

If H atoms are on opposite sides of the double bond they are trans-fatty acids and cannot form enzyme-substrate complexes, therefore, are not metabolised. They are linked with coronary heart disease

25
Q

How are triglycerides important for energy storage?

A

The long hydrocarbon chains contain many carbon-hydrogen bonds with little oxygen (triglycerides are highly reduced)
So when triglycerides are oxidised during cellular respiration this causes these bonds to break releasing energy used to produce ATP

Triglycerides therefore store more energy per gram than carbohydrates and proteins (37kJ compared to 17kJ)

The oxidation of the carbon-hydrogen bonds releases large numbers of water molecules (metabolic water) during cellular respiration
Desert animals retain this water if there is no liquid water to drink
Bird and reptile embryos in their shells also use this water

26
Q

Why are triglycerides usually liquids at room temperature?

A

due to the presence of double bonds which add kinks to the fatty acid chains altering their properties

Their fat molecules do not stack easily, so they cannot form a solid at this temperature.

27
Q

Why is a colorimeter better when carrying out the Benedict’s Test.

A

A more accurate and quantitative way to measure glucose concentration after the Benedict’s test (judging colour is subjective and more affected by human error.)

28
Q

What is the method for The Benedict’s Test using a colorimeter?

A

When the precipitate is filtered out of the solution, the solution left is the Benedict’s reagent → more glucose = more precipitate = the less blue the remaining solution will be

• A colourimeter measures absorbance of light → lower absorbance = more blue colour lost = more glucose

• Zero the colorimeter to distilled water to make sure values are comparable

• Can use a serial dilution of a known concentration of glucose to produce a calibration curve

29
Q

How are triglycerides important for insulation?

A

Triglycerides are part of the composition of the myelin sheath that surrounds nerve fibres

This provides insulation which increases the speed of transmission of nerve impulses
Triglycerides compose part of the adipose tissue layer below the skin which acts as insulation against heat loss (eg. blubber of whales)

30
Q

How are triglycerides important for protection?

A

The adipose tissue in mammals contains stored triglycerides and this tissue helps protect organs from the risk of damage

31
Q

What are phospohlipids?

A

It’s a type of lipid however unlike triglycerides, there are only two fatty acids bonded to a glycerol molecule in a phospholipid as one has been replaced by a phosphate ion (PO4^3-)

32
Q

What are the properties of phospholipids?

A

They are polar, it is soluble in water (hydrophilic)

The fatty acid ‘tails’ are non-polar and therefore insoluble in water (hydrophobic).

They are amphilpathic (they have both hydrophobic and hydrophilic parts).

As a result of having hydrophobic ad hydrophilic parts phospholipid molecules form mono layers and belayers in water.

33
Q

What is the structure of phospholipids?

A
34
Q

Diagram of the phospholipid monolayer and bilayer…

A
35
Q

Why are cell membranes partially / selectively permeable?

A

Each phospholipid has a hydrophilic head that is attracted to water.

Each phospholipid also has two hydrophobic fatty acid tails that are repelled by water

When many phospholipids are put in a watery solution, they therefore spontaneously form spheres called liposomes that point all the water-loving heads toward the water and shield all of the water-fearing tails from it.

The result of the hydrophobic center of the membrane is that molecules that dissolve in water are not capable of passing through the membrane.

Charged atoms (ions) and polar molecules such as glucose are repelled by the hydrophobic center of the membrane (these molecules can, however, pass through with the help of membrane protein channels).

On the other hand, hydrophobic molecules such as lipids can pass through the membrane, as can small non-polar molecules (such as oxygen gas or carbon dioxide).

36
Q

How is the structure of phospholipids related to their properties?

A

They are polar meaning in an aqueous environment, phospholipid molecules form a bilayer within cell-surface membranes. As a result, a hydrophobic barrier is formed between the inside and outside of the cell

The hydrophilic phosphate ‘heads’ of phospholipid molecules help to hold at the surface of the cell-surface membrane.

The phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell-membrane.
These glycolipids are important in cell recognition.

37
Q

What are the roles of phospholipids?

A

The main component (building block) of cell membranes
Due to the presence of hydrophobic fatty acid tails, a hydrophobic core is created when a phospholipid bilayer forms
-This acts as a barrier to water-soluble molecules

The hydrophilic phosphate heads form H-bonds with water allowing the cell membrane to be used to compartmentalise
-This enables the cells to organise specific roles into organelles helping with efficiency

Composition of phospholipids contributes to the fluidity of the cell membrane
If there are mainly saturated fatty acid tails then the membrane will be less fluid
-If there are mainly unsaturated fatty acid tails then the membrane will be more fluid

Phospholipids control membrane protein orientation
-Weak hydrophobic interactions between the phospholipids and membrane proteins hold the proteins within the membrane but still allow movement within the layer

38
Q

Triglycerides vs phospholipids…

A

Biology (56 decks)

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