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biology a level > Biological Molecules > Flashcards

Biological Molecules Flashcards

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AP® Biology flashcards
1
Q

Define monomer and polymer. Give some examples.

A 
monomer: smaller units that join together to form larger molecules
●monosaccharides(glucose,fructose,
galactose,ribose)
● amino acids 
● nucleotides

polymer: molecules formed when many monomers join together
● polysaccharides
● proteins
● DNA/ RNA

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2
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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3
Q

Describe the properties of 𝛼 glucose.

A

● Small and water soluble = easily transported in bloodstream.
● Complementary shape to antiport for co-transport for absorption in gut.
● Complementary shape to enzymes for glycolysis = respiratory substrate.

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4
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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5
Q

Name 3 disaccharides. Describe how they form.

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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6
Q

Describe the structure and functions of starch.

A

Storage polymer of 𝛼-glucose in plant cells:
● insoluble = no osmotic effect on cells
● large = does not diffuse out of cells

made from amylose:
● 1,4 glycosidic bonds
● helix with intermolecular
H-bonds = compact

and amylopectin:
● 1,4 & 1,6 glycosidic bonds
● branched = many terminal ends
for hydrolysis into glucose

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7
Q

Describe the structure and functions of glycogen.

A

Main storage polymer of 𝛼-glucose in animal cells (but also found in plant cells):
● 1,4 and 1,6 glycosidic bonds.
● Branched = many terminal ends for hydrolysis.
● Insoluble = no osmotic effect and does not diffuse
out of cells.
● Compact.

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8
Q

Describe the structure and functions of cellulose.

A

Polymer of 𝛽-glucose gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up).
● 1,4 glycosidic bonds.
● Straight-chain, unbranched molecule.
● Alternate glucose molecules are rotated 180°.
● H-bond crosslinks between parallel strands form
microfibrils = high tensile strength.

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9
Q

How do triglycerides form?

A

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

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10
Q

Contrast saturated and unsaturated fatty acids.

A 
Saturated:
● contain only single bonds
● straight-chain molecules
have many contact points
● higher melting point = solid
at room temperature
● found in animal fats
Unsaturated:
● contain C=C double bonds
● ‘kinked’ molecules have
fewer contact points
● lower melting point = liquid
at room temperature
● found in plant oils
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11
Q

Describe the structure and function of phospholipids.

A

Amphipathic: glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head.
● Forms phospholipid bilayer in water = component of membranes.
● Tails can splay outwards = waterproofing e.g. for skin.

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12
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 and reducing fluidity.

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13
Q

What is the general structure of an amino acid?

A
  • COOH carboxyl / carboxylic acid group.
  • R variable side group consists of carbon chain and may include other functional groups e.g. benzene ring or -OH (alcohol).
  • NH2 amino group.
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14
Q

How do polypeptides form?

A

Condensation reactions between amino acids form peptide bonds (-CONH-).
There are 4 levels of protein structure.

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15
Q

Relate the structure of triglycerides to their functions.

A

● High energy:mass ratio = high calorific value from oxidation (energy storage).
● Insoluble hydrocarbon chain = no effect on water potential of cells and used for waterproofing.
● Slow conductor of heat = thermal insulation e.g. adipose tissue.
● Less dense than water = buoyancy of aquatic animals.

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16
Q

Define primary and secondary structure of a protein.

A

Primary: sequence, number and type of amino acids in the polypeptide, determined by sequence of codons on mRNA.
Secondary: hydrogen bonds form between O 𝛿- attached to ‒C=O and H 𝛿+ attached to ‒NH.

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17
Q

Describe the 2 types of secondary protein structure.

A

α-helix:
● All N-H bonds on same side of protein chain.
● Spiral shape.
● H-bonds parallel to helical axis.
β-pleated sheet:
● N-H and C=O groups alternate from one side to the other.

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18
Q

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

A

3D structure formed by further folding
● Disulfide bridges: strong covalent S-S bonds between molecules of the amino acid cysteine.
● Ionic bonds: relatively strong bonds between charged R groups (pH changes cause these bonds to break).
● Hydrogen bonds: numerous and easily broken.

19
Q

Define ‘quaternary structure’ of a protein.

A

● Functional proteins 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 e.g metal ions or phosphate groups.

20
Q

Describe the structure and function of globular proteins.

A

● Spherical and compact.
● Hydrophilic R groups face outwards and hydrophobic
R groups face inwards = usually water-soluble.
● Involved in metabolic processes e.g. enzymes
such as amylase, insulin (2 polypeptide chains linked by 2 disulfide bonds), haemoglobin.

21
Q

Describe the structure of haemoglobin.

A

● Globular conjugated protein with prosthetic group.
● 2 𝛼-chains, 2 𝛽-chains, 4 prosthetic haem groups.
● Water-soluble so dissolves in plasma.
● Fe2+ haem group forms coordinate bond with O2.
● Tertiary structure changes so it is easier for subsequent
O2 molecules to bind (cooperative binding).

22
Q

Describe the structure and function of fibrous proteins.

A

● Can form long chains or fibres.
● Insoluble in water.
● Useful for structure and support e.g.
collagen in skin.

23
Q

List the functions of collagen, elastin and keratin.

A

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

24
Q

Describe how to test for proteins in a sample.

A

Biuret test confirms presence of peptide bond
1. Add equal volume of sodium hydroxide to sample at room temperature.
2. Add drops of dilute copper (II) sulfate solution. Swirl to mix. (steps 1 and 2 make Biuret reagent).
3. Positive result: colour changes from blue to purple
Negative result: solution remains blue.

25
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
26
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°C for 5
    mins.
  3. Positive result: colour changes from blue to orange and
    brick-red precipitate forms.
    Or use test strip coated in a reagent that changes colour if reducing sugar is present.
27
Q

Describe the Benedict’s test for non-reducing sugars.

A
  1. Negative result: Benedict’s reagent remains blue.
  2. Hydrolyse non-reducing sugars e.g. sucrose into their
    monomers by adding 1cm3 of HCl. Heat in a boiling
    water bath for 5 mins.
  3. Neutralise the mixture using sodium carbonate solution.
  4. Proceed with the Benedict’s test as usual.
28
Q

Describe the test for starch.

A
  1. Add iodine solution.
  2. Positive result: colour changes from
    orange to blue-black.
29
Q

State the role and chemical symbol of nitrates and ammonium.

A

NO3- is used to make DNA, amino acids, NADP 3
for photosynthesis and NAD for respiration.
NH4+ can be converted to NO3- by saprobionts
during nitrogen cycle. Produced by deamination
of amino acids during ornithine cycle in liver.

30
Q

State the role and chemical symbol of hydroxide and phosphate ions.

A

OH- ions affect pH and can interact with bonds in 3° protein structure to cause denaturation.
PO43- is a component of ATP/ ADP for energy
release and NADP.

31
Q

How can the concentration of a solution be measured quantitatively?

A

● Use colorimetry to measure absorbance/ %transmission. Interpolate a calibration curve from solutions of known concentration.
● Use biosensors. A bioreceptor detects the
presence of a chemical. A transducer converts the
response into a detectable electrical signal.

32
Q

Outline the principles and process of paper/ thin-layer chromatography.

A
  1. Use capillary tube to spot solution onto pencil ‘start line’ (origin) 1 cm above bottom of paper.
  2. Place chromatography paper in solvent. (origin should be above solvent level).
  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.
33
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 moved by the solute / distance moved by the solvent

34
Q

structure of a water molecule

A

Water molecules consist of 2 hydrogen molecules covalently to an oxygen molecule.
The molecules are slightly polar because the oxygen nucleus pulls the shared electrons away from the hydrogen nuclei. Giving the oxygen nuclei a δ- charge, and the hydrogen nuclei a δ+ charge.
The polarity of water causes attraction between water
molecules. This force of attraction is called a hydrogen bond

35
Q

properties of water

A
  • liquid medium
  • metabolite
  • high specific heat capacity
  • high latent heat of vapourisation
  • cohesion of molecules
  • surface tension
  • good solvent and transport medium
  • good reactant
  • incompressible
36
Q

why is liquid medium property useful for water

A

Provides habitats for aquatic organisms, medium for chemical reactions & used for transport

37
Q

why is metabolite property useful for water

A

Used in hydrolysis and condensation reactions

38
Q

why is having a high specific heat capacity useful for water

A

Keeps aquatic and cellular environments stable

39
Q

why is having a high latent heat of vapourisation useful for water

A

Evaporation has a cooling effect on organisms

40
Q

why is cohesion of molecules useful for water

A

Water is drawn up the xylem

41
Q

why is surface tension useful for water

A

Allows pond-skaters to walk on the surface

42
Q

why is water being a good solvent useful for

A

Dissolves ionic and polar molecules, allowing them to

easily be transported

43
Q

why is water being a good reactant useful for

A

The cytoplasm in cells is an aqueous solution where many chemical reactions happen

44
Q

why is water being incompressible useful for

A

Can prevent plants from wilting and act as a hydrostatic

skeleton for invertebrates

biology a level (8 decks)

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