Biological Molecules Flashcards
(44 cards)
Define monomer and polymer. Give some examples.
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
Name the elements found in carbohydrates, lipids, proteins and nucleic acids.
carbohydrates & lipids: C, H, O
proteins: C, H, O, N, S
nucleic acids: C, H, O, N, P
Describe the properties of 𝛼 glucose.
● 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.
What type of bond forms when monosaccharides react?
(1,4 or 1,6) glycosidic bond
● 2 monomers = 1 chemical bond =disaccharide.
● Multiple monomers = many chemical bonds = polysaccharide.
Name 3 disaccharides. Describe how they form.
Condensation reaction forms glycosidic bond between 2 monosaccharides. ● maltose: glucose + glucose ● sucrose: glucose + fructose ● lactose: glucose + galactose all have molecular formula C12H22O11
Describe the structure and functions of starch.
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
Describe the structure and functions of glycogen.
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.
Describe the structure and functions of cellulose.
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.
How do triglycerides form?
Condensation reaction between 1 molecule of glycerol and 3 fatty acids which forms ester bonds.
Contrast saturated and unsaturated fatty acids.
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
Describe the structure and function of phospholipids.
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.
Describe the structure and function of cholesterol.
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.
What is the general structure of an amino acid?
- 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.
How do polypeptides form?
Condensation reactions between amino acids form peptide bonds (-CONH-).
There are 4 levels of protein structure.
Relate the structure of triglycerides to their functions.
● 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.
Define primary and secondary structure of a protein.
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.
Describe the 2 types of secondary protein structure.
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.
Define ‘tertiary structure’ of a protein. Describe the bonds present.
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.
Define ‘quaternary structure’ of a protein.
● 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.
Describe the structure and function of globular proteins.
● 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.
Describe the structure of haemoglobin.
● 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).
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.
List the functions of collagen, elastin and keratin.
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.
Describe how to test for proteins in a sample.
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.
