B1.1 Carbohydrates and lipids

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What bonds does carbon form ?

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1

What bonds does carbon form ?

covalent bonds ( electrons are shared )

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2

Consequence of covalent bonds

stable molecules based on carbon can be produced

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3

How many bonds can carbon form?

4

  • 4 single covalent bonds

  • 2 single and 1 double

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4

What are the 4 major classes of carbon compounds used by living organisms ?

Hydrogen, Oxygen, Nitrogen, Phosphorus

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5

Define monomer

Small building blocks to make polymers ( subunit )

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6

Define polymer

Long molecules made up of many similar building blocks (monomers)

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7

What happens in a condensation reaction?

Two molecules are linked together at the same time a smaller molecule is released ( water )

A hydroxyl group (-OH) and a hydrogen (H) is removed from the 2 molecules which allows a bond to be made to bridge the 2 molecules.

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8

How are macromolecules constructed?

Energy is needed to construct polysaccharides, polypeptides and nucleic acids by condensation.

  • Energy is supplied by ATP

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9

What do hydrolysis reactions do?

Deconstruct macromolecules

  • occur during digestion

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10

How does digestion occur outside the cell ?

Occurs outside the cell in the gut of animals. Decomposers will release digestive enzymes into the environment around them in order to break down polymers.

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11

What's a monosaccharide?

single sugar molecule that has between 3-7 carbons

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12

Properties of glucose

Soluble, energy yield when oxidised, chemically stable,

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13

Explain the chemical stability of glucose

  • Very chemically stable which is useful for food storage but if stored in large quantities it causes osmosis problems. Usually converted to starch or glycogen

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14

What are the two types of starch molecule?

amylose and amylopectin

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15

What is amylopectin?

branched chain of alpha glucose linked by 1 - 4 glycosidic bonds but there are some 1-6 glycosidic bonds ( causes the branch )

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16

What is amylose ?

unbranched chain of alpha glucose linked by 1-4 glycosidic bonds

  • due to bond angles structure is helical rather than straight

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17

What are the energy stores for plants and animals ?

Plants: starch Animals: glycogen

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18

How can glucose be removed from starch + glycogen when needed ?

A hydrolysis reaction breaks the 1-4 glycosidic bond to separate one glucose molecule from the end of the chain. This allows it to be transported or used in the cell.

  • happens quicker in amylopectin as branched structure provides more ends of chains

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19

What is the structure of glycogen ?

Same as amylopectin

  • Alpha glucose molecules linked by 1-4 glycosidic bonds and branched by the 1-6 glycosidic bond

  • more branched than amylopectin

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20

Why can starch or glucose be used as storage ?

they have a large size which gives them a low solubility meaning they contribute little to the osmosis concentration

  • branched structure makes them compact

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21

Consequence of limitless addition/removal of glucose ?

Starch and glucose do not have a fixed molecular mass so molar solutions cannot be made

  • concentrations have to be expressed in percentage terms

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22

Define polysaccharide

Complex sugars that can be broken down ( carbohydrates )

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23

What are the consequences of the strength of cellulose in the plant cell wall ?

The strength prevents plant cells from bursting even when high pressure have developed inside the cell due to osmosis.

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24

Describe the structure of cellulose myofibrils

Cellulose is constructed in a straight chain which causes the molecules to lie parallel to each other. Hydroxyl groups are regularly spaced along each molecule allowing hydrogen bonds to form between them.

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25

Compare structure of alpha and beta glucose

The -OH on carbon 1 points 'up' in beta glucose and 'down' in alpha glucose

Beta glucose leads to an unbranched chain

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26

What's the function of glycoproteins ?

Glycoproteins attach to the plasma membrane of cells with carbohydrates facing outwards. These carbohydrates serve as a distinct marker for each cell allowing other cells to recognize them. The glycoprotein will be recognized by a receptor on another cell.

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27

What does cell to cell recognition help with ?

Helps with the organization of tissues and can allow foreign bodies or infected cells to be recognized and destroyed.

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28

What are glycoproteins composed of ?

polypeptides with carbohydrates attached

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29

What are the 3 possible oligosaccharides that can be present on glycoproteins ?

O, A, B

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30

What are the consequences of receiving blood containing a different glycoprotein ?

Glycoprotein A and B must only be transfused if the person produces it themselves otherwise it will be rejected

Glycoprotein O does not cause rejection as it has the same structure as A and B with one less monosaccharide so it is not recognised as foreign.

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31

Why are lipids said to be hydrophobic ?

Lipids are only slightly soluble in aqueous solvents. However they are not repelled by water they are just more attracted to non-polar substances.

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32

What are the classes of commonly occurring lipids ?

Fats, Oils, Waxes, Steroids

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33

Characteristics/ Structure of Oil:

  • Melting point below 20 degrees therefore solidifies at low temperatures

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34

Characteristics/ Structure of Fats:

  • melting point between 20 and 37 degrees

  • solid at room temperatures

  • liquid at body temperatures

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35

Characteristics/ Structure of Steroids:

  • Molecules with a 4 ring structure

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36

Characteristics/ Structure of Waxes:

  • Melting point above 37 degrees

  • liquify at high temperatures

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37

What bonds form during the condensation reaction that results in a triglyceride ?

Three individual fatty acid molecules are linked to a singular glycerol through condensation so 3 water molecules are made.

  • The links between each fatty acid and glycerol is an ester bond

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38

When are ester bonds formed?

When an acid reacts with the hydroxyl group ( -OH ) in alcohol

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39

Where does the reaction occur during the formation of triglycerides ?

Reaction is between the carboxyl group ( -COOH ) on the fatty acid and a hydroxyl on the glycerol.

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40

Why are triglycerides entirely hydrophobic ?

The carboxyl and the hydroxyl groups are the hydrophilic parts of the molecules and they are entirely used up in the condensation reactions.

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41

What do phospholipids contain?

glycerol, 2 fatty acids, and a phosphate group

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42

Why are phospholipids both hydrophilic and hydrophobic ?

The phosphate is hydrophilic but the glycerol and fatty acids are hydrophobic

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43

Describe the structure of a generalised fatty acid

  • Unbranched chain of carbon atoms with hydrogen atoms covalently bonded ( hydrocarbon chain )

  • carboxyl group ( -COOH ) at one end -> acid part

  • methyl group ( -CH3) at the other end

They can have single or double bonds between carbon atoms

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44

What's the difference between saturated and unsaturated fatty acids ?

Saturated: A fatty acid with all single bonds between carbon atoms Unsaturated: Fatty acids that contain one or more double bonds as they contain less hydrogen than they could

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45

Monounsaturated

fatty acid with 1 double bond

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46

Polyunsaturated:

fatty acids with more than 1 double bond

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47

Cis-fatty acids

Naturally occurring unsaturated fatty acids in which carbon moieties lie on the same side of the double bond.

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48

Trans-fatty acids

Hydrogens are on the opposite side to the double bond

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49

Characteristics of Cis fatty acids

Bend in hydrocarbon chain due to double bond

  • low melting point as not closely packed together

  • liquid at room temp ( oils )

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50

Characteristics of Trans fatty acids

  • straight chains

  • Higher melting point

  • Solid at room temperatures

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51

How are trans fatty acids produced ?

Artificially produced by partial hydrogenation of vegetable or fish oils

  • used in margarine and processed foods

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52

What properties make triglycerides suitable for long term energy storage ?

  • Chemically stable

  • immiscible with water

  • Release twice as much energy per gram in respiration compared to carbohydrates

  • Poor heat conductors

  • Liquid at room temperature

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53

Where are triglycerides stored?

adipose tissue

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54

Why does chemical stability mean Triglycerides are suitable for long term storage ?

Energy is not lost over time

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55

Why does water immiscibility mean Triglycerides are suitable for long term storage ?

They naturally form droplets in the cytoplasm which do not have osmotic or other effects on the cell

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56

Why does energy release mean Triglycerides are suitable for long term storage ?

Enough energy can be stored in half the body mass.

  • Important for animals that move/fly

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57

Why does poor heat conduction mean Triglycerides are suitable for long term storage ?

They can be used as thermal insulators in animals that need to conserve body heat

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58

Why does liquidity at body temperatures mean Triglycerides are suitable for long term storage ?

They can act as shock absorbers

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59

What adaptation of adipose tissue allows it to be a good insulator ?

Animals that require more thermal insulation have thick layers of subcutaneous adipose tissue

( Blubber in marine animals )

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60

Amphipathic

A molecule that has both a hydrophilic region and a hydrophobic region.

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61

Hydrophilic

Attracted to water

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62

Hydrophobic

Repelled by water

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63

Outline the amphipathic properties of phospholipids

Hydrophilic: phosphate group Hydrophobic: 2 hydrocarbon chains

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64

Why do phospholipids form a bi-layer in water ?

The phosphate heads are attracted to water but the tails are attracted to each other more than the water.

  • This causes a double layer arrangement

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65

Properties of steroids

  • 4 fused rings of carbon atoms

  • 3 cyclohexane rings

  • 1 cyclopentane ring

  • 17 carbon atoms in total in the rings

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66

Why can steroids pass through the phospholipid bilayer ?

They are mostly hydrocarbon and therefore hydrophobic

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