Biological molecules Flashcards
Define a monomer
Smaller units that join together to form larger molecules
Monosaccharides (glucose, fructose and galactose)
Amino acids
Nucleotides
Define a polymer
Molecules formed when many monomers join together
Polysaccharides
Proteins
DNA/RNA
What happens in a condensation reaction?
A chemical bond forms between 2 molecules and a molecule of water is produced
What happens in a hydrolysis reaction?
A water molecule is used to break a chemical bond between 2 molecules
Name the 3 hexose monosaccharides
Glucose
Fructose
Galactose
Name the type of bond formed when monosaccharides react
1,4 or 1,6 glycosidic bonds
2 monomers = 1 chemical bond = disaccharide
Multiple monomers = many chemical bonds = polysaccharide
Name 3 disaccharides and describe how they form
Condensation reaction forms glycosidic bond between 2 monosaccharides
Maltose = glucose + glucose Sucrose= glucose + fructose Lactose= glucose + galactose
Describe the structure and functions of starch
Storage polymer of a-glucose in plant cells
insoluble = no osmotic effect on cells large = does not diffuse out of cells
Describe the structure and functions of glycogen
Main storage polymer of a-glucose in animal 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 b-glucose, gives rigidity to plant cell walls
1,4 glycosidic bonds
Straight chain, unbranched
Alternate glucose molecules rotated at 180 degrees
H-bond crosslinks between parallel strands form microfibrils = high tensile strength
Describe the Benedict’s test for reducing sugars
- Add an equal volume of Benedict’s reagent to a sample
- Heat the mixture in a water bath at 100 degrees for 5 minutes
- Positive result = colour change from blue to orange/ brick red
Describe the Benedict’s test for non reducing sugars
- Negative result = Benedicts reagent remains blue
- Hydrolyse non reducing sugars e.g sucrose into their monomers by adding 1cm3 of HCL. Heat in a water bath for 5 minutes
- Neutralise the mixture using sodium carbonate solution
- Proceed with the Benedicts test as usual
Describe the test for starch
- Add iodine solution
2. Positive result = colour change from orange to blue-black
Describe how to test for lipids
- Dissolve solid samples in ethanol
- Add an equal volume of water and shake
- Positive result = milky white emulsion forms
How do triglycerides form?
Condensation reaction between 1 molecule of glycerol and 3 fatty acids forms ester bonds
What is a saturated fatty acid?
Contain only single bonds
Straight chain molecules have many contact points
Higher melting point = solid at room temperature
Found in animal fats
What is an unsaturated fatty acid?
Contain c=c doubl bonds
Kinked molecules have fewer contact points
Lower melting point = liquid at room temperature
Found in plant oils
Relate the structure of triglycerides to their functions
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
Describe the structure and function of phospholipids
Glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophobic polar phosphate head
Forms phospholipid bilayer in water = component of membranes
Tails can splay outwards = waterproofing
Compare phospholipids and triglycerides
Both have a glycerol backbone
Both may be attached to a mixture of saturated, monounsaturated and polyunsaturated fatty acids
Both contain the elements C, H, O
Both formed by condensation reactions
What are the differences between phospholipids and triglycerides?
Phospholipids:
2 fatty acids and 1 phosphate group
Hydrophilic head and hydrophobic tail
Used in membrane function
Triglycerides:
3 fatty acids attached
Entire molecule is hydrophobic
Used as a storage molecule
Are phospholipids and triglycerides polymers?
No; they are not made from a small repeating unit. They are macromolecules
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
- NH2 amino group
Describe how to test for proteins in a sample
Biuret test- presence of peptide bond
- Add equal volume of sodium hydroxide to sample at room temperature
- Add 2 drops of dilute copper sulfate solution
- Positive result: color changes from blue to purple
Negative result: solution remains blue
How many amino acids are there and how do they differ from one another?
20
How do dipeptides and polypeptides form?
Condensation reaction forms peptide bond and eliminates a molecule of water
Dipeptide: 2 amino acids
Polypeptide: 3 or more amino acids
How many levels of protein structure are there
4
Define a primary structure of a protein
The sequence of amino acids
Determined by sequence of codons on mRNA
Define a secondary structure of a protein
Alpha helix or Beta pleated sheet
Define the tertiary structure of a protein
3D structure formed by further folding of the polypeptide
Disulfide bridges
Ionic bonds
Hydrogen bonds
Define the quaternary structure of a protein
Functional proteins may consist of more than one polypeptide
Precise 3D structure held together by the same bonds as the 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
Involved in metabolic processes e.g enzymes and haemoglobin
Describe the structure and function of fibrous proteins
Can form long chains or fibres
Insoluble in water
Useful for structure and support
What are enzymes?
Biological catalysts for reactions
Specific tertiary structure determines shape of active site, complementary to a specific substrate
Formation of enzyme substrate complexes lowers activation energy of metabolic reactions
Explain the induced fit model of enzyme action
Shape of active site is not directly complementary to substrate and is flexible
Conformational change enables ES complexes to form
This puts strain on substrate bonds, lowering activation energy
How have models of enzyme action changed?
Initially lock and key model: rigid shape of active site complementary to only 1 substrate
Currently induced fit model: also explains why binding at allosteric sites can change shape of active site
What are 5 factors that affect the rate of enzyme controlled reactions
Enzyme concentration Substrate concentration Concentration of inhibitors pH Temperature
How does substrate concentration affect rate of reaction?
Enzymes concentration is fixed so rate increases proportionally to the substrate level
Rate levels off when maximum number of ES complexes form at any given time
How does enzyme concentration affect rate of reaction?
Substrates are in excess so the rate increases proportionally to enzyme concentration
Rate levels off when maximum number of ES complexes form at any given time
How does temperature affect rate of reaction?
Rate increases as kinetic energy increases and peaks at optimum temperature
Above optimum, ionic and H bonds break so the active site is no longer complementary to the substrate
How does pH affect rate of reaction?
Enzymes have a narrow optimum pH range
Outside the range they denature
What are the differences between competitive and non competitve inhibitors?
Competitive inhibitors:
Similar shape to substrate = bond to active site
Do not stop reaction; ES complex forms when inhibitor is released
Increasing substrate concentration decreases their effect
Non-competitive inhibitors:
Bind to anywhere other than the active site
May permanently stop reaction; triggers active site to change shape
Increasing substrate concentration has no impact on their effect
