2.1.2 Biological molecules Flashcards
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 (O𝛿- H𝛿+)
- There are intermolecular forces of attraction between a lone pair of O𝛿- of one molecule and H𝛿+ on an adjacent molecule
2
Q
State 7 biologically important properties of water
A
- Water more dense than ice
- High surface tension
- Solvent for chemical reactions
- High specific heat capacity
- High latent heat of vaporisation
- Cohesion
- Incompressible
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 (earthworms)
4
Q
Explain why ice floats on water. Why is this important for organisms?
A
- Ice is less dense than water because hydrogen bonds hold molecules in fixed positions further away from each other
- Insulates water in arctic climates so aquatic organisms can survive
5
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
6
Q
Why is water an important solvent for organisms
A
Polar universal solvent dissolves and transports charged particles involved in intra and extracellular reactions
7
Q
Why are the high specific heat capacity and latent of heat vaporisation of water important for organisms
A
- Acts as a temperature buffer which enables endotherms to resist fluctuations in core temperature to maintain optimum enzyme activity
- Cooling effect when water evaporates from skin surface as swear or from mouth when panting
8
Q
Define monomer and polymer with 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
9
Q
What happens in condensation and hydrolysis reactions
A
- Condensation: chemical bond forms between 2 molecules and a molecule of water is produced
- Hydrolysis: a water molecule is used to break a chemical bond between 2 molecules
10
Q
Name the elements found in carbohydrates, lipids, proteins and nucleic acids
A
- Carbohydrates and lipids: C, H, O
- Proteins: C, H, O, N, S
- Nucleic acids: C, H, O, N, P
11
Q
Describe the properties of 𝛼 glucose
A
- Small and water soluble = easily transported in bloodstream
- Complementary shape to anti port for co-transport for absorption in gut
- Complementary shape to enzymes for glycolysis = respiratory substrate
12
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 = may chemical bonds = polysaccharide
13
Q
Name 3 disaccharides and how they form
A
- Condensation reaction forms glycosidic bond between 2 monosaccharides
- Maltose: 𝛼 glucose + 𝛼 glucose
- Sucrose: glucose + fructose
- Lactose: glucose + galactose
14
Q
Describe the structure and functions of starch
A
- Storage polymer of 𝛼 glucose in plant cells:
- insoluble = no osmotic effect on pressure
- large = doesn’t diffuse out of cells
- Made from amylose
- 1,4 glycosidic bonds
- helix with intermolecular hydrogen bonds =
compact - Made from amylopectin
- 1,4 and 1,6 glycosidic bonds
- branched = many terminal ends for hydrolysis
into glucose
15
Q
Describe the structure and function of glycogen
A
- Main storage polymer of 𝛼 glucose in animal cells
- 1,4 and 1,6 glycosidic bonds
- Branched = many terminal ends for hydrolysis
- Insoluble = no osmotic effect and doesn’t diffuse out of cells
- Compact
16
Q
Describe the structure and function of cellulose
A
- Polymer of β glucose giver 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°
- Hydrogen bond crosslinks between parallel strands form microfibrils = high tensile strength
17
Q
How do triglycerides form
A
- Condensation reaction between 1 molecule of glycerol and 3 fatty acids
- Forms ester bonds
18
Q
Contrast saturated and unsaturated fatty acids
A
Saturated:
- only contains single bonds
- straight chain molecules have many contact points
- high 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
19
Q
Relate the function of triglycerides to their functions
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
20
Q
Describe the structure and function of phospholipids
A
- 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
21
Q
Are phospholipids and triglycerides polymers
A
- No
- They are not made from a small repeating unit
- They are macromolecules
22
Q
Describe the structure and function of cholesterol
A
- Steroid structure of 4 hydrocarbon rings
- Hydrocarbon tail on one side, hydroxyl group on the other side
- Adds stability to cell surface phospholipid bilayer by connecting molecules and reducing fluidity
23
Q
How do peptides form
A
- Condensation reactions between amino acids form peptide bonds
24
Q
Define the 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 O𝛿- attached to -C=O and H𝛿+ attached to -NH
25
Describe the 2 types of secondary protein structure
𝛼-helix:
- All N-H bonds on same protein chain
- Spiral shape
- Hydrogen bonds parallel to helical axis
β-pleated sheet:
- N-H and C=O groups alternate from one side to the other
26
Describe the tertiary structure of a protein. Describe the bonds present
- 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 binds to break)
- Hydrogen bonds: numerous and easily broken
27
Define the quaternary structure of a protein
- Functional proteins may consist of more than 1 polypeptide
- Precise 3D structure held together by the same types of bond as tertiary structure
- May involve addition of prosthetic groups
28
Describe the structure and function of globular proteins
- Spherical and compact
- Hydrophilic R groups face outwards and hydrophobic R groups face inwards
- Involved in metabolic processes
29
Describe the structure of haemoglobin
- Globular conjugated protein with prosthetic group
- 2 𝛼 chains, 2 β chains, 4 prosthetic hem groups
- Water soluble so dissolves in plasma
- Fe2+ harm group forms coordinate bond with O2
- Tertiary structure changes so its easier for subsequent O2 molecules to bind (cooperative binding)
30
Describe the structure and function of fibrous proteins
- Can form long chains or fibres
- Insoluble in water
- Useful for structure and support e.g. collagen in skin
31
List the functions of collage, elastin and keratin
- Collagen: component of bonds, 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
32
Describe how to test for proteins in a sample
- Biuret test confirms presence of peptide bones
1. Add equal volume of sodium hydroxide to sample at room temperature
2. Add drops of dilute copper (II) sulphate solution. Swirl to mix
3. Positive result = colour changes from blue to purple
33
Describe how to test for lipids in a sample
1. Dissolve solid sample in ethanol
2. Add an equal volume of water and shake
3. Positive result - milky white emulsion forms
34
Describe how to test for reducing sugars
1. Add an equal volume of benedicts 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 ad brick red precipitate forms
35
Describe the Benedict's test for non reducing sugars
1. Negative result: benedicts reagent remains blue
2. Hydrolyse non reducing sugars e.g. sucrose into their monomers by adding 1cm^3 of HCl. Heat in a boiling water bath for 5 mins
3. Neutralise the mixture using sodium carbonate solution
4. Proceed with benedicts test as usual
36
Describe the test for starch
- Add iodine solution
2. Positive result = colour changes from orange to blue black
37
State the role and chemical symbol of nitrates and ammonium
- NO3- is used to make DNA, amino acids, NADP for photosynthesis and NAD for respiration
- NH4+ can be converted to NO3- during nitrogen cycle
38
State the role and chemical symbol of hydroxide and phosphate ions
- OH- ions affect pH and can interact with bonds in 3° protein structure to cause denaturation
- PO4 3- is a component of ATP/ADP for energy release
39
State the role and chemical symbol of sodium, potassium and chloride ions
- Na+ and K+ are involved in maintenance of resting potential of neurone/ generation of acton potentials. Na+ is also involved in co-transport mechanisms
- Cl- is involved in inhibitory synapses to cause hyper polarisation
40
State the role and chemical symbol of calcium ions
- Ca2+ is used to make calcium pectate to add stability to middle lamella of plant cell walls
- Regulates exocytosis of neurotransmitter
- Binds to troponin to stimulate muscle contraction
41
How can concentration of a solution be measured quantitatively
- Use colorimetry to measure absorbance/ % transmission
- Create a calibration curve from solutions of known concentrations
42
Outline the principles and processes of paper/ thin layer chromatography
1. Use capillary tube to spot solution onto pencil start line 1cm 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
43
What are Rf values? How can they be calculated
- Ratios that allow comparison of how far molecules have moved in chromatograms
- Rf value = distance between origin and centre of pigment spot / distance between origin and solvent front
