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BIOLOGY OCR A > 2.2 Biological Molecules > Flashcards

2.2 Biological Molecules Flashcards

1
Q

How do hydrogen bonds form between water molecules?

A

Water is polar Forms O𝛿- (slightly negative) & H𝛿+ (slightly positive).
There are intermolecular forces of attraction between a on O𝛿- of one molecule & H𝛿+ on an adjacent molecule.

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2
Q

State 7 biologically important properties of water.

A

reaches maximum density at 4 degrees celcius
high surface tension
incompressible
solvent for chemical reactions
high specific heat capacity
high latent heat of vaporisation
cohesion between molecules

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3
Q

Why is the incompressible nature of water important for organisms?

A

Provides turgidity to plant cells.
Provides hydrostatic skeleton for some small animals

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4
Q

Explain why ice floats on water. Why is this important for organisms?

A

Ice is less dense than water because H-bonds hold molecules in fixed positions further away from each other.
Insulates water in arctic climates so aquatic organisms can survive

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5
Q

Why is the high surface tension of water important for organisms?

A

Slows water loss due to transpiration in plants.
Water rises in narrow tubes, lowering demand on root pressure.
Some insects can skim across the surface of water.

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6
Q

Why is water an important solvent for organisms?

A

Polar universal solvent dissolves

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7
Q

Why are the high specific heat capacity and latent of vapourisation of water important for organisms?

A

Cooling effect when water evaporates from skin surface as sweat/ from mouth when panting.

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8
Q

Define monomer and polymer. Give some examples.

A

monomer: smaller units that join together to form larger molecule
monosaccharides (glucose, fructose, galactose, ribose)
amino acids
nucleotides
polymer: molecules formed when many monomers join together
polysaccharides
proteins
DNA/ RNA

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9
Q

What happens in condensation and hydrolysis reactions?

A

Condensation: chemical bond forms between 2 molecules & a molecule of water is produced.

Hydrolysis: a water molecule is used to break a chemical bond between 2 molecules

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10
Q

Name the elements found in carbohydrates, lipids, proteins and nucleic acids.

A

carbohydrates & lipids: C, H, O
proteins: C, H, O, N, S
nucleic acids: C, H, O, N, P

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11
Q

Draw the structure of alpha-glucose and beta-glucose.

A

:)

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12
Q

Describe the properties of alpha glucose.

A

Small & water soluble

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13
Q

Draw the structure of ribose.

A

:)

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14
Q

What type of bond forms when monosaccharides react?

A

(1,4 or 1,6) glycosidic bond
2 monomers = 1 chemical bond = disaccharide.
Multiple monomers = many chemical bonds = polysaccharide.

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15
Q

Describe how disaccharides form.
Name 3 disaccharides.
Molecular formula

A

Condensation reaction forms glycosidic bond between 2 monosaccharides.
maltose: glucose + glucose
sucrose: glucose + fructose
lactose: glucose + galactose
all have molecular formula C12H22O11

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16
Q

Describe the structure and functions of starch.

A

Storage polymer of alpha glucose in plant cells:
insoluble
large
made from amylose:
1,4 alpha glycosidic bonds
helix
and amylopectin:
1,4 & 1,6 alpha glycosidic bonds
branched = many ends for hydrolysis into glucose

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17
Q

Describe the structure and functions of glycogen.

A

Store of alpha glucose
1,4 & 1,6 glycosidic bonds.
Branched = many ends for hydrolysis.
Insoluble
Compact.

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18
Q

Describe the structure and functions of cellulose.

A

Polymer of beta-glucose gives rigidity to plant cell walls
1,4 glycosidic bonds.
Straight-chain, unbranched molecule.
Alternate glucose molecules are rotated 180°.
H-bond crosslinks between parallel strands

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19
Q

How do triglyglcerides form?

A

Condensation reaction between 1 molecule of glycerol &
3 fatty acids
forms ester bonds.

20
Q

Contrast saturated and unsaturated fatty acids.

A

Saturated:
contain only single bonds
straight-chain molecules
higher melting point = solid at room temp
found in animal fats
Unsaturated:
contain C=C double bonds
kinked molecules
lower melting point = liquid at room temp
found in plant oils

21
Q

Relate the structure of triglycerides to their functions.

A

High energy:mass ratio = energy storage
Insoluble hydrocarbon chain = waterproof plants
Slow conductor of heat = thermal insulation
Less dense (floats) water = buoyancy of aquatic animals.

22
Q

Describe the structure and function of phospholipids.

A

glycerol attached to 2 hydrophobic fatty acid tails & 1 hydrophilic polar
phosphate head.
Forms phospholipid bilayer in water = component of membranes.
Tails can splay outwards = waterproofing

23
Q

Are phospholipids and triglycerides polymers?

A

No. They are macromolecules.

24
Q

Describe the structure and function of cholesterol.

A

Steroid structure of 4 hydrocarbon rings. Hydrocarbon tail on one side, hydroxyl group (-OH) on the other side.
Adds stability to cell surface phospholipid bilayer by connecting molecules & reducing fluidity.

25
Q

What is the general structure of an amino acid? Draw it

A

-COOH carboxyl group
-R variable side group
-NH2 amine group

26
Q

How do polypeptides form?

A

Condensation reactions between amino acids form peptide bonds
(-CONH-)

27
Q

Define primary structure of a protein.

A

Primary: straight chain of amino acids, determined by sequence of codons on mRNA.

28
Q

Describe the 2 types of secondary protein structure.

A

alpha-helix:
All N-H bonds on same side of protein chain.
Spiral shape.
H-bonds parallel to helical axis.
beta-pleated sheet:
N-H & C=O groups alternate from one side to the other.
Pleated sheet

29
Q

Define tertiary structure of a protein. Describe the bonds present.

A

3D structure formed by further folding
Disulfide bonds: strong covalent S-S bonds (cysteine only)
Ionic bonds: strong bonds between charged R groups
Hydrogen bonds: numerous & easily broken.

30
Q

Define quaternary structure of a protein.

A

May consist of more than one polypeptide.
Precise 3D structure held together by the same types of bond as tertiary structure.
May involve addition of prosthetic groups

31
Q

Describe the structure and function of globular proteins.

A

Spherical & compact.
Hydrophilic R groups face outwards & hydrophobic R groups face inwards = water-soluble.
Involved in metabolic processes (enzymes)

32
Q

Describe the structure of haemoglobin.

A

Globular conjugated protein with prosthetic group.
2 alpha-chains, 2 beta chains, 4 prosthetic haem groups.
Water-soluble
Fe2+ haem group bonds with O2.
Tertiary structure changes so it is easier for O2 to bond

33
Q

Describe the structure and function of fibrous proteins.

A

Can form long chains or fibres.
Insoluble in water.
Useful for structure and suppor

34
Q

List the functions of collagen, elastin and keratin.

A

Collagen: component of bones, cartilage, tendons.
Elastin: provides elasticity to connective tissue, arteries, skin, lungs,
Keratin: structural component of hair, nails, hooves/ claws,

35
Q

Describe how to test for proteins in a sample.

A

Biuret test #
1. Add biurets regenat
3. Positive result: colour changes from blue to purple
Negative result: solution remains blue.

36
Q

Describe how to test for lipids in a sample.

A
  1. Dissolve solid samples in ethanol.
  2. Add an equal volume of water and shake.
  3. Positive result: milky white emulsion forms
37
Q

Describe how to test for reducing sugars.

A
  1. Add an equal volume of Benedict s reagent to a sample.
  2. Heat the mixture in an electric water bath at 100℃ for 5 mins.
  3. Positive result: colour changes from blue to orange & brick-red precipitate forms.
38
Q

Describe the Benedict s test for non-reducing sugars.

A
  1. Negative result: Benedict s reagent remains blue.
  2. Add Hydrochloric acid
  3. Heat in a boiling water bath for 5 mins.
  4. Neutralise the mixture using sodium carbonate solution.
  5. Proceed with the Benedict s test as usual - positive test means non-reducting sugar
39
Q

Describe the test for starch.

A
  1. Add iodine solution.
  2. Positive result: colour changes from orange to blue-black.
    Negative - orange
40
Q

How can the concentration of a solution be measured quantitatively?

A

Use colorimetry to measure absorbance/%transmission. use a calibration curve from solutions of known concentration.

41
Q

Outline the process of paper chromatography.

A
  1. spot solution onto pencil start line (origin) 1 cm above bottom of paper.
  2. Place chromatography paper in solvent.
  3. Allow solvent to run until it almost touches other end of the paper.
    Molecules in mixture move different distances based on relative solubility in solvent/attraction to paper.
42
Q

What are Rf values? How can they be calculated?

A

Ratios that allow comparison of how far molecules have moved in chromatograms.
Rf value = distance between origin / distance between origin and solvent front.

43
Q

What is ATP, what does it do

A

Adenosine triphosphate, nitrogenous base, pentose sugar, and 3 phosphate groups

Releases immediate energy, by breaking the bond between phosphate groups forming ADP, during a hydrolysis reaction

44
Q

What is the ATP reaction to release energy

A

ADP + water -> ADP + P + energy

45
Q

What is phosphorylation

A

ADP attaching to a phosphate group, during a condensation reaction

46
Q

What is some properties of ATP

A

Small - moves in and out of cells
Water soluble - happens in aqueous environments
Intermediate energy - used in cellular reactions
Releases is small quantities - not wasted as heat
Easily recharged

BIOLOGY OCR A (6 decks)

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