F212 Biological Molecules Flashcards
Water
Polar Molecule
There is a slight positive charge (from the hydrogen nuclei) on the hydrogen atoms in a water molecule
There is a slight negative charge (from the electrons around the oxygen) on the oxygen atom in a water molecule
Water
Molecule
H2O
Each hydrogen atom shares its electron with the outer shell of the oxygen atom which stabilises the oxygen
Water
Intermolecular Hydrogen Bonds
Hydrogen bonds occur between the negatively charged oxygen atom of one molecule and the positively charged hydrogen atom of another molecule
Water
Liquid at Room Temperature
The intermolecular bonds between water molecules at room temperature hold the molecules together making water a liquid at room temperature rather than a gas
This allows water to act as a liquid transport medium in living things
E.g. blood in animals, the vascular system in plants
Water
Solvent
As water is a polar molecule it is a good solvent for other polar molecules and ionic compounds
When the attraction of the water is stronger than the intramolecular forces of the solute then the solute will be pulled apart e.g. ionic compound
In a polar molecule the charged parts of the water surround the charged parts of the solute separating the molecules and keeping them dissolved
Metabolic processes in all living organisms rely on chemicals being able to react in solution
Water
Thermal Stability
The hydrogen bonds between water mean that a relatively large amount of energy is required to increase the temperature
Large bodies of water provide fairly stable environments
Makes evaporation of sweat a very effective cooling mechanism
Water
Cohesion
Water molecules stick together because of the intramolecular hydrogen bonds, it also causes surface tension
Transport of water in the xylem relies on water molecules sticking to each other as they are transported up the xylem in the transpiration system
Water
Chemical Reactions
Waters thermal stability and solvent properties make it an ideal environment for chemical reactions
Water is also a reactant e.g. hydrolysis reactions and photosynthesis
Hydrophobic
Water repelling
Hydrophilic
Associates easily with water molecules
Proteins
Function
Structure Transport Enzymes Antibodies Most hormones
Proteins
Monomer
Amino Acids
Proteins
Polymer
Polypeptides
Amino Acid
Structure
Amine group H-N-H
|
Residual R-C-H
|
Carboxylic Acid group O=C-OH
Breaking A Peptide Bond
With a hydrolysis reaction - adding water
Residual
Differentiates between different amino acids
Forming A Peptide Bond
A condensation reaction removes OH from the carboxylic acid group of one amino acid and the H from the amine group of another amino acid
-a water molecule (h2O) is released and the bond forms
Dipeptide
Two amino acids joined together by a peptide bond
Polypeptide
A chain of amino acids joined together by peptide bonds
Primary Structure
The sequence of amino acids in a polypeptide chain
Protease Enzyme
An enzyme that breaks down proteins
Secondary Structure
Assumed in the rough endoplasmic reticulum The coiling of an amino acid chain into an alpha helix held together by hydrogen bonds
Polypeptide chains can link together with hydrogen bonds holding the parallel chains in beta pleated sheets
Both alpha helices and beta pleated sheets can occur in the same protein
Tertiary Structure
The secondary structure of the polypeptide chain bends and folds to produce a precise 3D structure
This is held together by:
Hydrogen Bonds
Ionic Bonds
Disulphide Bonds
Quaternary Structure
Several polypeptide chains linked together
Denaturation
An irreversible change in the tertiary structure of a protein molecule
Leading to a loss of function in most proteins
Haemoglobin
A transport protein
Haemoglobin
Structure
Water soluble
Globular protein
Made up of four separate polypeptide chains, a quaternary structure
Two called alpha chains and two called beta chains
Haemoglobin
Function
High affinity for oxygen
Bonds oxygen in the lungs and carries it to the tissues where it releases it
An oxygen atom can bind to the iron in a haem group
haemoglobin + oxygen = oxyhemoglobin
One complete haemoglobin molecule can bind up to four oxygen molecules
Tertiary Structure
Disulphide Bond
Forms between two sulphur containing R groups
A covalent bond
Collagen
Structure
A collagen molecule is made up of three polypeptide chains wound around each other like a twisted rope
Each chain is made up of around 1000 amino acids
Hydrogen bonds between the chains giving the structure strength
Each collagen molecule forms covalent bonds, cross links, with the molecules next to it
This structure is a fibril many fibrils together form a collagen fibre
Collagen
Function
To provide mechanical strength
Walls of the arteries have a layer of collagen to prevent blood being pumped at high pressure from bursting the walls
Tendons are mostly collagen
Bones are formed from collagen and reinforced with calcium phosphate
Cartilage and connective tissue are made of collagen
Collagen
A structural protein
Proteins
Test
Biuret Test
- Add Biuret reagent which contains sodium hydroxide and copper sulphate to the sample
- These chemicals react with the peptide bonds found in proteins
- If protein is present the colour changes from blue to purple/lilac
Tertiary Structure
Ionic Bonds
From between polar R groups
R groups are polar if the electrons are unevenly distributed
Non polar R groups will be at the centre of the protein because they are hydrophobic and the protein is formed inside a cell so is surrounded by water
Carbohydrates
Function
Immediate energy source e.g. glucose
Energy store e.g. starch
Structural molecule e.g. cellulose
Monosaccharides
Properties
Soluble in water - means that they affect water potential for osmosis - can be transported easily in solution Sweet tasting Form crystals
Monosaccharides
How Are They Grouped
Grouped according to the number of carbon atoms in the molecule
Triose Sugars
Monosaccharides with three carbon atoms per molecule
Pentose Sugars
Monosaccharides with five carbon atoms per molecule
Hexose Sugars
Monosaccharides with six carbon atoms per molecule
Glycosidic Bond
Covalent bond formed between two monosaccharide molecules
Formed by a condensation reaction
Notation x-y glycosidic bond
- bond between the carbon x atom of one molecule and the carbon y atom of another molecule
- e.g. 1-4 glycosidic bond
Breaking a Glycosidic Bond
Hydrolysis reaction
Disaccharide
Two monosaccharide molecules joined together by a glycosidic bond
Disaccharides
Examples
Sucrose
Maltose
Lactose
Maltose
Structure
Glucose + Glucose
Monosaccharides
Examples
Alpha Glucose
Beta Glucose
Fructose
Galactose
Lactose
Structure
Glucose + Galactose
Sucrose
Structure
Glucose + Fructose
Carbohydrates
Monomer
Monosaccharides - simple sugars
Carbohydrates
Polymer
Polysaccharides
Polysaccharides
Polymers of monosaccharides consisting of hundreds to thousands of monosaccharide molecules joined together by glycosidic bonds
Polysaccharides
Examples
Starch - Amylose - Amylopectin Glycogen Cellulose
Polysaccharides
Properties
Insoluble in water
Amylose
Structure
Polymer of many alpha glucose monomers
Joined together by 1-4 glycosidic bonds
One un branched chain
Long chains of amylose coil into spirals go because of the shape of the glucose molecules and the formation of glycosidic bonds
There are 6 alpha glucose molecules in each turn of the spiral
Amylose
Test
Add iodine
If present colour change from yellow/brown to deep blue
Amylopectin
Structure
Polymer of alpha glucose molecules
Branched chain
1-4 glycosidic bonds hold the molecules in each branch together
1-6 glycosidic bonds hold the branches together
Amylopectin
Test
Add iodine
If present colour change from yellow/brown to red/purple
Starch
Structure
Long amylose chains
Plus branched chains of amylopectin
Starch
Properties
Insoluble
Compact
Easier to break down
Energy storage molecule
Starch
Function
Energy storage molecule in plants
Starch
Test
Add iodine
If present colour change from yellow/brown to blue/black
Cellulose
Structure
Polymer of beta glucose molecules
Adjacent molecules are opposite ways up
1-4 glycosidic bonds hold long chains of beta glucose together
Hydrogen bonds between chains
Cellulose
Properties
Insoluble
Structural molecule
Humans do not have an enzyme which can break down cellulose
Very strong
Cellulose
Function
Forms cell walls in plants
Forms fibre/roughage in a human diet to keep digestive system functioning
Glycogen
Structure
Polymer of alpha glucose molecules Large branched molecule 1-4 glycosidic bonds in branches 1-6 glycosidic bonds between branches Shorter 1-4 linked branches than starch and more branches
Glycogen
Properties
Insoluble
More compact than starch
Energy storage molecule
Glycogen
Function
Energy storage molecule in animals
Reducing Sugars Test
- Add Benedict’s Solution
- Heat in a water bath at 80°C
- If present colour change from blue to the formation of orange/red precipitate
- The darker the red of the precipitate the more reducing sugar there is
Other Names for Lipids
Fats
Oils
Non-Reducing Sugars Test
- If a reduce sugars test is negative
- Add hydrochloric acid and boil
- Cool
- Neutralise with sodium hydrogen carbonate or sodium carbonate
- Repeat the reducing sugars test
- if the second test is positive the a non reducing sugar was present in the original sample
Three elements found in lipids
Carbon
Oxygen
Hydrogen
Determining Glucose Concentration Using Colorimetry
- Pour 5ml of glucose solutions of known concentration into test tube
- Add Benedict’s solution
- Heat in a water bath at 80°C
- Pass each through filter paper to remove the orange/red precipitate
- Use a sample of water to get a 100% transmission reading from the colorimeter
- Put each concentration in the colorimeter and plot the results on a graph to draw a calibration curve
- Repeat the process with the unknown sample
- Read of the graph the concentration that would produce the colorimeter reading of the sample
Structure of Lipids
Three fatty acid chains joined by an ester bond from a condensation reaction to one molecule of glycerol
Glycerol
Structure
H
|
H-C-OH
|
H-C-OH
|
H-C-OH
|
HCarbohydrates
Contain Which Atoms
Oxygen
Hydrogen
Carbon
Fatty Acid
Structure
A carboxylic acid group on the end of a hydrocarbon chain
Carbon Atom Bonds
Each carbon atoms can only have four bonds
Unsaturated
Has double bonds
Saturated
Only single bonds
Carboxylic Acid Group
OH-C=O
Phospholipid
Structure
A glycerol molecules bonded to two fatty acid chains and a phosphate
Triglyceride
Structure
One glycerol molecule
Three fatty acid chains joined to the glycerol molecule by an ester bond
Cholesterol
Structure
Four carbon-based ring structures joined together
Phospholipid
Function
Forms a molecule that is part hydrophobic and part hydrophilic, ideal for cell membranes
Phosphate group may have carbohydrates attached, these glycolipids are used for cell signalling
Cholesterol
Function
Forms a small thin molecule that fits into the lipid bilayer to give strength and stability
Used to form the steroid hormones
Triglyceride
Function
Compacts energy store
Insoluble in water so it doesn’t affect cell water potential
Stored as fat which also has thermal insulation and protective properties
Emulsion Test for Lipids
Mix the sample with ethanol in a test tube so that some of it dissolves
Pour the liquid (ethanol) into another texture containing water
Cloudy emulsion on the surface indicates the presence of lipids
