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CIE AS Biology 2023 > UNIT 2 - Biological Molecules > Flashcards

UNIT 2 - Biological Molecules Flashcards

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1
Q

What is the test for reducing sugars?

A

Benedicts test.

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2
Q

How might you carry out the Benedicts test?

A

Create solution. Add equal amount of reagent to solution. Shake + heat in water bath. Partially quantitative.

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3
Q

What is the test for non-reducing sugars?

A

Modified Benedicts test.

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4
Q

How might you carry out the modified Benedicts test?

A

Hydrolyse by boiling in dilute HCL. Once cooled, neutralise with sodium hydrogen carbonate. Check with pH paper and repeat Benedicts test.

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5
Q

What are the results of the Benedicts test?

A

Blue - green - yellow - orange - brick red precipitate.
from lowest concentrate to highest.

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6
Q

What is the test for proteins?

A

Biuret test. Detects presence of peptide links.

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7
Q

How might you carry out the test for proteins?

A

Create solution. Add potassium hydroxide to substance, then add copper sulphate + shake.

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8
Q

What are the results of the test for proteins?

A

Blue (not present)
Lilac (present)

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9
Q

What is the test for lipids?

A

Emulsion test

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10
Q

How might you carry out the test for lipids?

A

Add sample to ethanol + shake, allow to settle, empty liquid into test tube w/water.

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11
Q

What are the results of the test for lipids?

A

Clear/colourless (not present)
Milky white emulsion ( if present)

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12
Q

Name the three types of carbohydrates

A

monosaccharides, disaccharides and polysaccharides

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13
Q

What is the function of monosaccharides?

A

Used as a source of energy in
respiration.
Building blocks for larger molecules.

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14
Q

Give examples of monosaccharides.

A

Glucose, fructose + galactose.

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15
Q

What does glucose do?

A

Plants make it through photosynthesis, transport it in blood for respiration, building block for larger molecules (cellulose, starch + glycogen), major energy source.

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16
Q

What is the formula of glucose?
What type of sugar is it?

A

C6H12O6.
Hexose sugar.

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17
Q

Give examples of disaccharides. What monosaccharides are each of them made of?

A

Maltose (a-glucose + a-glucose)
Sucrose (a-glucose + fructose) Lactose (a-glucose + galactose)

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18
Q

Glucose exists in two structurally different forms

A

alpha (α) glucose and beta (β) glucose and is therefore known as an isomer

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19
Q

How might a disaccharide be broken down?

A

A hydrolysis reaction.

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20
Q

Give 4 main properties of disaccharides.

A

Same general formula (C12H22O11)
Taste sweet
Soluble
Sugars

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21
Q

Give examples of reducing sugars.

What disaccharide is not a reducing sugar?

A

Glucose, fructose, galactose, maltose + lactose.

Sucrose.

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22
Q

What are the 3 most important polysaccharides and their uses?

A

Starch (energy store)
Glycogen (energy store)
Cellulose (structure)

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23
Q

How is starch stored in seeds + chloroplasts?

A

Starch grains. It is stored as granules in plastids

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24
Q

Why is starch such a good storage molecule?

A

Compact (so large quantities can be stored)
Insoluble (so will have no osmotic effect, unlike glucose which would cause too much water to move into cells - burst if they were animal cells)

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25
Q

Starch takes longer than glucose to digest, why?

A

Due to the many monomers in a starch molecule, it takes longer to digest than glucose

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26
Q

What type of molecule is starch due to it being made of amylose and amylopectin?

A

A composite molecule.

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27
Q

Starch is constructed from two different polysaccharides

A

Amylose (10 - 30% of starch)
-Unbranched helix-shaped chain with 1,4 glycosidic bonds between α-glucose molecules
-The helix shape enables it to be more compact and thus it is more resistant to digestion

Amylopectin (70 - 90% of starch)
-1,4 glycosidic bonds between α-glucose molecules but also 1,6 glycosidic bonds form between glucose molecules creating a branched molecule
-The branches result in many terminal glucose molecules that can be easily hydrolysed for use during cellular respiration or added to for storage

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28
Q

How is glycogen stored?
Where?
What are its properties?

A

Granules.
Liver and muscle cells in mammals - visible as granules
Compact (which helps animals store more) insoluble, no unbranched chains, shorter chains than amylopectin + more terminal glucoses enabling faster hydrolysis

29
Q

Cellulose is a polysaccharide. True or false?

A

True

30
Q

Explain the structure of cellulose

A

Cellulose is a polymer consisting of long chains of β-glucose joined together by 1,4 glycosidic bonds
As β-glucose is an isomer of α-glucose to form the 1,4 glycosidic bonds consecutive β-glucose molecules must be rotated 180° to each other
*Due to the inversion of the β-glucose molecules many hydrogen bonds form between the long chains giving cellulose it’s strength

31
Q

What is the function of cellulose?

A

Cellulose is the main structural component of cell walls due to its strength which is a result of the many hydrogen bonds found between the parallel chains of microfibrils,
The high tensile strength of cellulose allows it to be stretched without breaking which makes it possible for cell walls to withstand turgor pressure
The cellulose fibres and other molecules (eg. lignin) found in the cell wall form a matrix which increases the strength of the cell walls
The strengthened cell walls provides support to the plant
Cellulose fibres are freely permeable which allows water and solutes to leave or reach the cell surface membrane
As few organisms have the enzyme (cellulase) to hydrolyse cellulose it is a source of fibre

32
Q

What elements do lipids contain? Which element is in highest proportion?
What type of molecule is a lipid?

A

Carbon, hydrogen + oxygen. More hydrogen. Less oxygen than carbohydrates.
Large macromolecules, not polymers.

33
Q

Are lipids soluble or insoluble? Are they hydrophobic or hydrophilic? Are they polar or non- polar?

A

Insoluble in water.
Hydrophobic.
Non - polar.

34
Q

What can lipids dissolve in?

A

Organic solvents (ethanol, propanone + ether)

35
Q

What are the 4 main types of lipids?

A

Triglycerides (fats + oils), phospholipids (cell membranes), waxes + steroids

36
Q

What are triglycerides made of? How are they formed? What do they clump into?

A

3 fatty acid molecules combined to glycerol (alcohol) molecule, condensation reaction between fatty acid + glycerol, hydrophobic properties (aggregate) into globules so they seem like macromolecules.

37
Q

What can they be broken into? What do fatty acids in fats/oils have? Why are they hydrophobic?

A

Fatty acids + glycerol.
Long hydrocarbon chains that contain 16-18 carbon atoms.
Long hydrocarbon tails.

38
Q

When the functional group of 3 fatty acids (-COOH) react with 3 functional groups of glycerol (-COH), what do they form? What type of bonds are they?

A

Triglyceride with ester bonds.

39
Q

What’s the difference between an unsaturated and a saturated fatty acid in terms of melting temperature?

A

Unsaturated melts at a lower temp because their hydrocarbon tails don’t pack so closely together.

40
Q

In triglycerides, for each ester bond formed a water molecule is released. How many water molecules are released for one triglyceride to form?

A

three water molecules are released

41
Q

Explain the structure of phospholipids

A

Phospholipids are a type of lipid, therefore they are formed from the monomer glycerol and fatty acids.
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 (PO43-).
As the phosphate is polar it is soluble in water (hydrophilic).
The fatty acid ‘tails’ are non-polar and therefore insoluble in water (hydrophobic).

42
Q

In what way is the structure of a triglyceride and a phospholipid different?

A

In a phospholipid, one of the fatty acids is replaced by an ionised phosphate group (PO4^3-)

43
Q

Why are phospholipids important?

A

They determine the structure and function of the cell surface membrane.

44
Q

What happens when phospholipids are mixed with water?

A

Phospholipids are amphipathic (they have both hydrophobic and hydrophilic parts), therefore they form monolayers or bilayers in water.

45
Q

Why are proteins extremely important?

A

they form all of the following:
Enzymes
Cell membrane proteins (eg. carrier)
Hormones
Immunoproteins (eg. immunoglobulins)
Transport proteins (eg. haemoglobin)
Structural proteins (eg. keratin, collagen)
Contractile proteins (eg. myosin)

46
Q

What elements do proteins contain?

A

Carbon, hydrogen, oxygen, nitrogen + (usually) sulfur.

47
Q

What are proteins composed of? What is their basic structure?

A

Proteins are polymers made of monomers called amino acids.
central carbon atom bonded to:
An amine group -NH2
A carboxylic acid group -COOH
A hydrogen atom
An R group (which is how each amino acid differs and why amino acid properties differ e.g. whether they are acidic or basic or whether they are polar or non-polar)

48
Q

How many amino acids are there found in proteins common to all living organisms?

A

20

49
Q

What determines that primary structure of a protein?

A

DNA of a cell determines the primary structure of a protein by instructing the cell to add certain amino acids in specific quantities in a certain sequence. This affects the shape and therefore the function of the protein

50
Q

What are the 2 most common secondary structures of proteins?

How are they held together?

A

a-helix (coiled) or B-pleated sheets (parallel/antiparallel)

Hydrogen bonds.

51
Q

When does the α-helix shape occur?

A

When the hydrogen bonds form between every fourth peptide bond (between the oxygen of the carboxyl group and the hydrogen of the amine group)

52
Q

When does the β-pleated sheet shape form?

A

When the protein folds so that two parts of the polypeptide chain are parallel to each other enabling hydrogen bonds to form between parallel peptide bonds

53
Q

Most fibrous proteins have secondary structures. Give examples

A

Collagen and keratin

54
Q

Can the hydrogen bonds can be broken by high temperatures and pH changes?

A

Yes

55
Q

How is tertiary structure made permanent?

A

4 types of bond: hydrogen (R groups), ionic (R groups w/charges), disulfide bonds (R groups w/sulphur) + hydrophobic interactions (non-polar/polar)

56
Q

What happens when globular proteins are in solution?

A

Hydrophobic groups point in whilst hydrophilic groups point outwards.

57
Q

Quaternary occurs in proteins that…

A

have more than one polypeptide chain working together as a functional macromolecule, for example, haemoglobin.

58
Q

Explain the structure of fibrous proteins

A

Fibrous proteins are long strands of polypeptide chains that have cross-linkages due to hydrogen bonds.
They have little or no tertiary structure.

59
Q

Give examples of fibrous proteins and their uses.

A

Fibrin (blood clotting), collagen (tendons linking muscle to bone) + keratin (hair/horn/nails)

60
Q

What role do globular proteins have? Give 3 examples?

A

Metabolic role. Enzymes, antibodies + hormones. e.g. haemoglobin.

61
Q

Give properties of globular proteins?

A

Globular proteins are compact, roughly spherical (circular) in shape and soluble in water, hydrophobic interactions, less stable than fibrous (metabolic role).

62
Q

Explain the structure of haemoglobin.

A

Haemoglobin is a globular protein which is an oxygen-carrying pigment found in vast quantities in red blood cells.
It has a quaternary structure as there are four polypeptide chains. These chains or subunits are globin proteins (two α–globins and two β–globins) and each subunit has a prosthetic haem group.

63
Q

What is the function of haemoglobin?

A

Haemoglobin is responsible for binding oxygen in the lung and transporting the oxygen to tissue to be used in aerobic metabolic pathways.
As oxygen is not very soluble in water and haemoglobin is, oxygen can be carried more efficiently around the body when bound to the haemoglobin.

64
Q

What does haemoglobin consist of?

A

4 separate polypeptide chains held together by disulphide bridges. (2 a-polypeptide chains + 2 B-polypeptide chains) with a haem group containing iron in centre.

65
Q

What strange properties does water have?

A

Polar, hydrogen bonds, adhesion, cohesion, high specific heat, high freezing point, chemical buffer + density anomality (ice)

66
Q

What functions might water have?

A

Transport (cohesion/adhesion), chemical reactions (photosynthesis), temp control (buffer), support (Turgidity), movement (nastic) + reproduction (fertilisation).

67
Q

What are the properties of water?

A

Water has many essential roles in living organisms due to:
The polarity of water molecules.
The presence and number of hydrogen bonds between water molecules.

68
Q

How might you carry out the Benedicts test?

A

Create solution. Add equal amount of reagent to solution. Shake + heat in water bath. Partially quantitative.

CIE AS Biology 2023 (5 decks)

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