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A Level Biology > Biological Molecules > Flashcards

Biological Molecules Flashcards

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1
Q

How do hydrogen bonds form between water molecules

A

Water is polar: O more electronegative than H, so attracts electron density in covalent bond more strongly
Forms O δ- and a H δ+
There are intermolecular forces of attraction between a lone pair on O δ- and H δ+ on an adjacent molecule

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2
Q

State 7 biologically important properties of water

A

Reaches maximum density at 4C
High surface tension
Incompressible
Metabolite / solvent for chemical reactions in the body
High specific heat capacity
High latent heat of vapourisation
Cohesion between molecules

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3
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
Insulated water in arctic climates so aquatic organisms can survive
Water acts as a habitat

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4
Q

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

A

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

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5
Q

Why is water an important solvent for organisms

A

Polar universal solvent dissolves and transports charged particles involved in intra and extra cellular reactions e.g.[PO4]3+ for DNA synthesis

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6
Q

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

A

Cooling effect when water evaporates from skin surface as sweat / from mouth when panting
Acts as a temperature buffer which enables endotherms to resist fluctuations in core temperature to maintain optimum enzyme activity

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7
Q

Define monomer and give some examples

A

Monomer: smaller units that join together to form larger molecules
- Monosaccharides
- Amino acids
- Nucleotides

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8
Q

Define polymer and give some examples

A

Polymer: Molecules formed when many monomers join together
- Polysaccharides
- Proteins
- DNA / RNA

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9
Q

What happens in condensation reactions?

A

Chemical bond forms between 2 molecules and a molecule of water is produced

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10
Q

What happens in a hydrolysis reaction?

A

A water molecule is used to break a chemical bond between two molecules

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11
Q

Name the elements found in carbohydrates and lipids

A

C, H, O

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12
Q

Name the elements found in Proteins

A

C, H, O, N, S

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13
Q

Name the elements found in nucleic acids

A

C, H, O, N, P

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14
Q

Describe the properties of alpha glucose

A

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

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15
Q

What type of bond forms when monosaccharides react

A

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

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16
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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17
Q

Describe the function of starch

A

Storage polymer of alpha glucose in plant cells
Insoluble so no osmotic effect on cells
Large so does not diffuse out of cells

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18
Q

Describe the structure of amylase

A
  • 1,4 glycosidic bonds
  • Helix with intermolecular H-bonds = compact
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19
Q

Describe the structure of amylopectin

A

1,4 and 1,6 glycosidic bonds
branched so many terminal end for hydrolysis into glucose

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20
Q

Describe the function of glycogen

A

Main storage polymer of a alpha glucose in animal cells (but also found in plant cells)

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21
Q

Describe the structure of glycogen

A

1,4 and 1,6 glycosidic bonds
Branched so many terminal ends for hydrolysis
insoluble so no osmotic effect and does not diffuse out of cells
Compact

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22
Q

Describe the function of cellulose

A

Polymer of Beta glucose gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up)

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23
Q

Describe the structure of cellulose

A

1,4 glycosidic bonds
Straight chain, unbranched molecules
Alternate glucose molecules are rotated 180 degrees
H-bond crosslinks between parallel strands form microfibrils = high tensile strength

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24
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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25
Q

Describe the features of a saturated fatty acid

A

Contain only single bonds
Straight chain molecules have many contact points
Higher melting point = solid at room temperature
Found in animal fats

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26
Q

Describe the features of an unsaturated fatty acid

A

Contain C=C double bonds
Kinked molecules have fewer contact points
Lower melting points = liquid at room temperature
Found in plant oils

27
Q

Relate the structure of triglycerides to their function

A

High energy : Mass ratio = high calorific value from oxidation
Insoluble hydrocarbon chain = no effect on water potential of cells and used for waterproofing
Slow conductor of heat = thermal insulation
Less dense than water = buoyancy of aquatic animals

28
Q

Describe the function of phospholipids

A

Forms phospholipid bilayer in water = component of membranes
Tails can splay outwards = waterproofing e.g. for skin

29
Q

Describe the structure of phospholipids

A

Amphipathic: glycerol backbone attached to 2 hydrophobic fatty acid tails and one hydrophilic polar phosphate head

30
Q

Are phospholipids and triglycerides polymers

A

No; they are not made from a small repeating unit. They are macromolecules

31
Q

Describe the structure of cholesterol

A

Steroid structure of 4 hydrocarbons rings
Hydrocarbon tail on one side, hydroxyl (-OH) group on the other side

32
Q

Describe the function of cholesterol

A

Adds stability to cell surface phospholipid bilayer by connecting molecules and reducing fluidity

33
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 function groups e.g. benzene ring or -OH group
-NH2 amine / amino group

34
Q

How do polypeptides form

A

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

35
Q

Define primary structure of proteins

A

Sequence, number and type of amino acids in the polypeptide, determined by the sequence of codons on mRNA

36
Q

Describe secondary structure of proteins

A

Hydrogen bonds form between O δ- attached in -C=O and H δ+ attached to -NH

37
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 sheets
- N-H and C=O groups alternate from one side to the other

38
Q

Describe the tertiary structure of a protein
Describe the bonds present

A

3D structure formed by further folding
- Disulphide 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)
- H-bonds: numerous and easily broken

39
Q

Describe the 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

40
Q

Describe the structure of globular proteins

A

Spherical and compact
Hydrophilic R groups face outwards and hydrophobic R groups face inwards - usually water soluble

41
Q

Describe the function of globular proteins

A

Involved in metabolic processes e.g. enzymes such as amylase, insulin (2 polypeptide chains linked by 2 disulphide bonds), Haemoglobin

42
Q

Describe the structure of haemoglobin

A

Globular conjugated protein with prosthetic group
2 alpha chains and 2 beta 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)

43
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

44
Q

What is the function of collagen

A

Component of bones, cartilage, connective tissues and tendons

45
Q

What is the function of elastin

A

Provides elasticity to connective tissue, arteries, skin, lungs, cartilage and ligaments

46
Q

What is the function of keratin

A

Structural component of hair. nails, hooves, claws and epithelial cells of outer layer of skin

47
Q

Describe how to test for proteins in a sample

A

Biuret test confirms presence of peptide bond
1. Add equal volume 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

48
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
49
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

50
Q

Describe the Benedicts test for non-reducing sugars

A
  1. Negative result: Benedicts 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
51
Q

Describe the test for starch

A
  1. Add iodine solution
  2. Positive result: colour changes from orange to blue-black
52
Q

State the role and chemical symbol of Nitrates

A

(NO3)- is used to make DNA, amino acids, NADP for photosynthesis and NAD for respiration

53
Q

State the role and chemical symbol of ammonium

A

(NH4)+ can be converted to (NO3)- by saprobionts during nitrogen cycle. Produced by deaminated of amino acids during ornithine cycle in liver

54
Q

State the role and chemical symbol of hydroxide ions

A

OH- ions affect pH and can interact with bonds in tertiary protein structure to cause denaturation

55
Q

State the role and chemical symbol of phosphate ions

A

(PO4)3- is a component of ATP/ADP for energy release and NADP

56
Q

State the role and chemical symbols of Potassium and Sodium ions

A

Na+ and K+ are involved in maintenance of resting potential of neurones and generation of action potentials
Na+ is also involved in the co-transport mechanisms

57
Q

State the role and chemical symbol of chlorine ions

A

Cl- is involved in inhibitory synapses to cause hyperpolarisation

58
Q

State the role and chemical symbol of Hydrogen ions

A

Forms in organisms when CO2 dissolves in water
H+ regulates pH and can interact with bonds in tertiary protein structure to cause denaturation. H+ pump is involved in chemiosmosis and active loading in translocation

59
Q

State the role and chemical symbol of hydrogen carbonate ions

A

(HCO3)- forms in organisms when CO2 dissolves in water

60
Q

State the role and chemical symbol of calcium ions

A

Ca2+ is used to make calcium pectate to add stability to middle lamella of plant walls
Regulates exocytosis of neurotransmitter
Binds to troponin to stimulate muscle contraction

61
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 concentrations
• Use biosensors. A bioreceptor detects the presence of a chemical. A transducer converts the response into a detectable electrical signal

62
Q

Outline the principles and process of thin layer spectroscopy

A
  1. Use capillary tube to spot solution onto pencil start line (origin) 1cm from the bottom of the paper
  2. Place chromatography paper into solvent (origin should be above solvent level)
  3. Allow solvent to run until it almost touches the other end of the paper. Molecules in mixture move different distances based on relative solubility in solvent / attraction to paper
63
Q

What are Rf values

A

Ratios that allow comparison of how far molecules have moved in chromatograms

64
Q

How do you calculate Rf values

A

Rf value = distance between origin and centre of pigment spot / distance between origin and solvent front

A Level Biology (25 decks)

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