Unit 1 Topic 1 Biological Molecules Flashcards
Explain how the properties of water make it an ideal transport medium
- Water is a solvent / dissolves substances
- Because water molecules surround polar molecules by forming hydrogen bonds between water molecules and solute molecules
- Water is a liquid so there is cohesion between water molecules
How are primary proteins formed
- Primary: sequence of amino acids joined by peptide bonds in a polypeptide chain
- Peptide bonds between the carboxyl group of one amino acid and the amino group of another amino acid
How are secondary proteins formed
- Secondary: coiling of polypeptide chain into an α-helix / folding of polypeptide chain into a β-pleated sheet
- Hydrogen bonds between oxygen in the carboxyl groups and hydrogen in the amino acids at different locations in polypeptide chain
How are tertiary proteins formed
- Tertiary: 3D conformation of polypeptide resulted from folding of α-helix or β-pleated sheet due to hydrogen bonds, disulfide bonds, ionic bonds and hydrophobic interactions between side chains of amino acids
How are quaternary proteins formed
- Quaternary: 3D conformation of protein consists of 2 or more polypeptide chains binding together
What are the properties of starch?
- Many α-glucose joined by formation of glycosidic bonds by condensation
Compare the properties of amylose and amylopectin
- Amylose: α-glucose joined by 1,4-glycosidic bond, unbranched and coils into spiral shape, less readily hydrolysed: stable energy storage molecule
- Amylopectin: α-glucose joined by 1,4-glycosidic bonds and some 1,6-glycosidic bonds, branched (1,6 connects amylose), more readily hydrolyzed (more enzymes catalyze hydrolysis) - more rapid supply of glucose as fuel for cellular respiration
Properties of glycogen
- Energy storage molecule in animals
- Many α-glucose joined by 1,4-glycosidic bonds and many 1,6-glycosidic bonds
- readily hydrolyzed: allow more rapid supply of glucose as fuel for cellular respiration
Properties of cellulose
- Constituent of plant cell walls -> strong building materials
- Unbranched, straight polymer of β-glucose joined by 1,4-glycosidic bonds by condensation
- Hydrogen bonds hold parallel cellulose molecules
Compare and contrast the molecular structures of globular and fibrous proteins.
- Both are chains of amino acids joined by peptide bonds
- Both contain named bonds (i.e. hydrogen bonds, disulfide bonds, ionic bonds)
- Globular proteins have hydrophilic groups on the outside whereas fibrous proteins have hydrophobic groups on the outside
- Globular have tertiary or quaternary structures whereas fibrous have little or no tertiary structure
- Globular are folded into compact shapes whereas fibrous have long chains
Explain the relationship between the composition of starch and the rate of hydrolysis by enzymes (hint: amylose content increases, percentage of starch hydrolyzed decreases)
- As amylose content increases, the percentage of starch hydrolyzed decreases
- The less amylose present, the greater the proportion of amylopectin
- Amylose is unbranched / amylopectin is branched
- Amylopectin contains (1,4- and) 1,6-glycosidic bond
- {Branches} increases the rate of hydrolysis
Define ionic bond
strong attraction between oppositely charged ions
Define covalent bond
- Strong attraction between atoms that share a pair of electrons in their outermost electron shell
- More electronegative atom pulls shared electrons in covalent bond more strongly towards itself
Define polar bond
- Covalent bond with unequal share of electrons
- Polar molecules:
a) shared electrons in covalent bonds are not equally shared by atoms
b) Leads to separation of charges in the molecules
c) Dipole (molecule with partially positive and partially negative charges)
Define hydrogen bonds
- the weak electrostatic force of attraction between a partially positive hydrogen atom in a polar molecule and an electronegative atom of another molecule
- Oxygen atom of one water molecule is joined to the hydrogen atom of another water molecule by a hydrogen bond
- Formed between intermolecular molecules, not within intramolecular
Properties of water
- High specific heat capacity (absorb large amounts of energy to raise temperature)
- High latent heat of vapourization (energy needed for water to evaporate)
- High surface tension of water
- Lower density of ice than liquid water -> floating ice forms insulating layer to prevent remaining water from freezing
***5. Powerful solvent -> polar -> dissolve substances in water
- Incompressible (e.g. turgor pressure, hydrostatic pressure)
- Cohesion: water molecules attach with each other
- Adhesion: water molecules attach to other molecules (e.g. xylem)
Name organic compounds and inorganic compounds
Organic:
- Nucleic acids
- Proteins
- Lipids
- Carbohydrates
Inorganic:
- Water
- Mineral ions / salts
Organic compounds: examples of functional groups of organic compounds
HYDROXYL - polar -> more electronegative -> soluble
CARBOXYL -> polar -> more electronegative -> soluble
CARBONYL -> releases H+ -> acidic (pH drop)
AMINO -> accepts H+ -> basic (pH rise)
Functions of monosaccharides
- Energy source for metabolism
- Major fuel for cellular respiration -> oxidized respiration: release energy stored in ATP (provide energy for metabolic need)
- Carbon skeletons for synthesis of other organic molecules
alpha-glucose vs beta-glucose
2 Ring forms of glucose
- Alpha: hydroxyl group on carbon 1 is below the plane of the ring
- Beta: hydroxyl group on carbon 1 is above the plane of the ring
Disaccharides
2 monosaccharides joined by formation of a glycosidic bond by condensation
Why are polysaccharides good energy storage molecules?
1.Compact molecules -> large amount of energy can be stored in a small space
2.Insoluble
- No osmotic effect, doesn’t affect water potential
- When water potential of the cell is less than the water potential of the surrounding, there is a net movement of water molecules into cells by osmosis, causing the cell to burst
- As they are insoluble, they will not diffuse down the concentration gradient
3.Physically and chemically inactive -> will not affect other metabolic activities
Principle of Benedict’s test
- To test for the presence of reducing sugars
- Cu2 + e- -> Cu+
- Reducing sugars can reduce blue copper 2+ ions in Benedict’s solution into C+ ions, which forms brick-red precipitate (Copper I oxide) -> insoluble
- Benedict’s solution should be in excess, and should be heated in boiling water bath
Quantitative vs semi-quantitative vs qualitative
Quantitative: results in numerical values
- use calibrated instruments
- objective data
Semi-quantitative: provides approximate measurements (e.g. high, low)
- results are scaled or ranked
Qualitative: non-numerical observations
- descriptive results
Benedict’s test result analysis
a) Comparison of blue colour intensity of filtrate
- Blue colour comes from Cu2+ ions in the Benedict’s solution which are not reduced
b) Lower reducing sugar content in sample
c) Less Cu2+ ions in the Benedict’s solution reduced by reducing sugars
d) More Cu2+ ions in Benedict’s solution not reduced
e) Intensity of blue colour of the filtrate is higher
f) Absorbance of orange light (complementary to the blue colour)
g) Deeper colour, absorbs more light
- Higher absorbance, less reducing sugar content
Polyunsaturated properties
- 2/2+ C-C double bonds
a) Can cause the hydrocarbon chain in unsaturated fatty acids to bend / create kinks
b) Prevents the molecules from packing closely together
c) Smaller intermolecular force among the molecules
d) Less energy is needed to separate them
- The greater the number of C-C double bond, the lower the melting point of the fatty acid
- Fat has more saturated fatty acids, higher melting point than unsaturated
Solubility of globular protein
a) Hydrophilic, polar side chains of amino acids are usually on the surface of protein while
b) The hydrophobic, non-polar side chains of amino acids in globular proteins are usually at the centre of the protein
Collagen
- A fibrous protein consisting of 3 polypeptide A-chains held by hydrogen bonds
- Three polypeptides supercoil to form a triple helical structure of great tensile strength, which has resistance to breaking under tension when being stretched
- Each polypeptide A-chain in collagen already consists of hundreds of amino acids in repeating sequences of amino acids
DNA properties
- Double stranded: consists of 2 polynucleotide chains formed with deoxyribonucleotides, where two chains twist to form a double helix
- Anti parallel: 2 polynucleotide chains run in opposite directions, held by hydrogen bonds between nitrogenous base pairs
Describe how an unsaturated triglyceride is synthesized
- 1 glycerol and 3 fatty acids
- Joined by ester bonds by condensation
- More than 1 fatty acid is {unsaturated / has a c-c double bond}
Which polypeptide does the liver store
glycogen
Which carbohydrates can be digested to release glucose
Lactose and sucrose
Explain the role of primary structure in determining the properties of protein of cell membrane
- because the sequence of amino acids determine the {tertiary / quaternary} structure of the protein (1)
- by determining the {position / type} of bonds that form between the R groups (1)
- {hydrophobic / non-polar} {(R) groups / amino acids on (the outside of) the part of the protein that is embedded in the fatty acid tails (1)
- {hydrophilic / polar} {(R) groups / amino acids} (on the outside of) the part of the protein that is {amongst the phosphate heads / facing the cytoplasm / facing the aqueous environment} (1)
Explain how the structure of glycogen relates to its role as an energy storage molecule.
- {polymer of glucose / polysaccharide} therefore has a high energy content (1)
- {large molecule / polymer / polysaccharide} therefore {insoluble / has no osmotic effect} (1)
- branched structure therefore {broken down / energy released / hydrolysis is} faster (1)
- compact therefore has a high energy density (1)
Explain the properties of amino acids located on the outer surface of proteins.
- must have R groups that are {polar / hydrophilic} (1)
- so that the {haemoglobin / protein} {can dissolve in (red blood cell) cytoplasm / is soluble in water} (1)
Explain how dietary antioxidants reduce the risk of CVD. (3)
- because antioxidants reduce free radicals (1)
- free radicals cause {cell damage /tissue damage / oxidative stress / damage to endothelial lining} (1)
- (antioxidants) reduce {plaque / atheroma} formation (1)
(past paper: spec) Carbohydrates used as energy storage molecules include glycogen and starch. Compare and contrast the structures of glycogen and starch. (4)
Similarities
- glycosidic bonds
- both polysaccharides / alpha glucose monomers
Differences
- starch: 2 polysaccharides, glycogen: 1
- amylose is straight / helical shape, while amylopectin and glycogen are branched
