2.1.2 - Biological Molecules Flashcards
How does hydrogen bonding occur between water molecules?
Water is a polar molecule due to the unevenly distributed charge so hydrogen bonds form between the oxygen and a hydrogen atom as the positive and negative regions interact with each other. Individual hydrogen bonds are weak but collectively provide strength
What are the 4 key properties of water?
- A solvent as polar molecules dissolve readily in water due to the slight positive charge on hydrogen atoms which attract negative solutes and the slight negative charge on the oxygen atoms of water which attract any positive ions in solutes. The cytoplasm in eukaryotic and prokaryotic cells is mainly water so this ensures many solutes can dissolve within the cell and then be easily transported
- A transport medium as there is cohesion between the water molecules so they stick together forming a continuous column which can move through the xylem for transpiration
- A coolant as it has high specific heat capacity meaning a lot of energy is required to break the hydrogen bonds between the water molecules so the internal temperature of plants and animals should remain relatively constant and enzymes should not denature. It also has a large latent heat of vaporisation meaning a lot of energy is required to break the hydrogen bonds between water molecules to turn it into a gas which has a cooling effect when water is evaporated
- A habitat as water buffers temperature meaning it provides a stable environment for aquatic organisms and cohesion provides surface tension so small invertebrates can live on the surface of water. Ice is also less dense than liquid water due to the hydrogen bonds meaning ice floats providing a surface habitat for animals
What are monomers?
Smaller units which can create larger molecules
What are polymers?
Large molecules made from lots of monomers bonded together
What is a condensation reaction?
When monomers are joined together to form a polymer with the elimination of a water molecule
What is a hydrolysis reaction?
When bonds between polymers are broken down into monomers using a water molecule
Which chemical elements make up carbohydrates?
C, H and O
Which chemical elements make up lipids?
C, H and O
Which chemical elements make up proteins?
C, H, O, N and S
Which chemical elements make up nucleic acids?
C, H, O, N and P
What is the structure of glucose?
It has a ring structure and is a hexose monosaccharide
What are the two isomers of glucose?
Alpha and beta glucose
What is the difference between the two isomers of glucose?
The hydrogen and hydroxide on the right side of the molecule are flipped
What is the structure of a ribose sugar?
It is a pentose monosaccharide
What is the difference between a hexose and a pentose monosaccharide?
A hexose monosaccharide has 6 carbons whereas a pentose monosaccharide has 5 carbons
How are disaccharides formed?
By joining two monosaccharides with a glycosidic bond
How are polysaccharides formed?
By connecting many monosaccharides with a glycosidic bond
How is the disaccharide maltose made?
Glucose + glucose = maltose
How is the disaccharide sucrose made?
Glucose + fructose = sucrose
How is the disaccharide lactose made?
Glucose + galactose = lactose
What is the structure of starch?
- Made from alpha glucose
- Has 1-4 glycosidic bonds in amylose and 1-4 and 1-6 in amylopectin
- Made of 2 polymers - amylose which is an unbranded helix and amylopectin which is a branched molecule
What is the function of starch and how does its structure lead to its function?
- Store of glucose
- Helix can compact to fit a lot of glucose in a small space
- Branched structure increases surface area for rapid hydrolysis back to glucose
- Insoluble so it won’t affect the water potential
What is the structure of cellulose?
- Made from beta glucose
- Has 1-4 glycosidic bonds
- Polymer forms long straight chains
- Chains are held in parallel by many hydrogen bonds to form fibrils. Macrofibrils combine to form a cellulose fibre
What is the function of cellulose and how does its structure lead to its function?
- Structural strength for cell wall
- Many hydrogen bonds provide collective strength
- Insoluble so it won’t affect water potential
What is the structure of glycogen?
- Made from alpha glucose
- Has 1-4 and 1-6 glycosidic bonds
- A highly branched molecule
What is the function of glycogen and how does its structure lead to its function?
- Store of glucose
- Branched structure increases surface area for rapid hydrolysis back to glucose
- Insoluble so it won’t affect water potential
What is the structure of a triglyceride?
They are synthesised by the formation of 3 ester bonds between one glycerol molecule and 3 fatty acids which is esterification
How do the properties of triglycerides relate to their functions in living organisms?
- As lipids are large hydrophobic molecules they are insoluble in water which means they will not affect the water potential and osmosis
- Lipids are relatively low in mass which means a lot can be stored in an animal without it increasing the mass and preventing movement
- Due to the high ratio of hydrogen to oxygen atoms they can act as a metabolic water source. This is because triglycerides can release water if they are oxidised which is essential for animals in the desert such as camels
- Due to the large ratio of energy storing carbon hydrogen bonds compared to the number of carbon atoms a lot of energy can be transferred when it is broken down
What is the structure of a phospholipid?
Made of a glycerol molecule bonded to 2 fatty acid chains by 2 ester bonds and a phosphate group attached to the glycerol
How do the properties of phospholipids relate to their functions in living organisms?
- Hydrophilic head of a phospholipid can attract with water as it is charged and due to the phosphate being charged it repels other fats
- The fatty acid chain is not charged but it is hydrophobic so it repels water but will mix with fats
- Phospholipids have two charged regions so they are polar
- They form a phospholipid bilayer which makes up the plasma membrane around cells
How do the properties of cholesterol relate to their functions in living organisms?
- Is a sterol which has 4 carbon rings and a hydroxyl group at one end and they both have hydrophobic and hydrophilic regions
- Is embedded within cell membranes to impact fluidity by reducing the fluidity of membranes at high temperatures and increase fluidity at low temperatures
What is the difference between saturated and unsaturated fatty acids?
Unsaturated fatty acids have once or more double bonds (C=C)
What is the general structure of an amino acid?
R - side chain
COOH - carboxyl group
NH2 - amine group
How are dipeptide and polypeptide molecules formed?
A dipeptide molecule is formed by the condensation of two amino acids forming a peptide bond and a polypeptide is formed by the condensation of many amino acids
What is the primary structure?
The number and sequence of amino acids in the polypeptide chain
What is the secondary structure?
Hydrogen bonds form between some amino acids to pleat or twist a polypeptide. A single hydrogen bond is weak but many hydrogen bonds give these structures stability
What is the tertiary structure?
The final 3D specific shape of the polypeptide is held in place by ionic bonds, disulphide bonds and hydrogen bonds between R groups. It is also determined by the hydrophobic and hydrophilic interactions
What is the quaternary structure?
Separate twisted or folded polypeptides linked together. Prosthetic groups may be associated with proteins having a quaternary structure
What is the structure of globular proteins?
- Polypeptide chains ‘roll up’ into a spherical shape
- Unstable structure
- Soluble
What is the function of globular proteins?
Involved in metabolic processes
What is the structure of fibrous proteins?
- Polypeptide chains form long twisted strands linked together
- Stable structure
- Insoluble in water
What is the function of fibrous proteins?
Strength gives structural function
What is an example of a conjugated protein?
- Haemoglobin
- Globular protein
- Made of four polypeptide chains and four haem prosthetic groups that contain an iron ion
What are two other examples of globular proteins?
- Insulin which is a protein involved in controlling blood glucose levels. It is made of two polypeptide chains which are joined by disulphide bonds. It is specific to the shape of membrane receptors.
- Pepsin which is an enzyme that functions in the acidic environment of the stomach. It has a few basic R groups, hydrogen bonds and a disulphide bond.
What are three examples of fibrous proteins?
- Collagen is found in bones and tendons allowing them to withstand large pulling forces. It is also found in artery walls to allow them to cope with high pressures.
- Keratin is a strong molecule that has a large number of cysteine amino acids and so many disulphide bonds. It is found in hooves, horns and fingernails.
- Elastin is found in the walls of blood vessels, the lungs and the bladder
What are cations?
Positive ions
What are anions?
Negative ions
What is the biological function of calcium ions (Ca2+)?
Involved in the transmission of nervous impulses, regulation of protein channels, muscle contractions and hardening of teeth and bones
What is the biological function of sodium ions (Na+)?
Involved in transmission of nervous impulses, active transport as an Na+ pump and co transport of glucose and amino acids across membranes
What is the biological function of potassium ions (K+)?
Involved in transmission of nervous impulses, active transport and plant cell turgidity
What is the biological function of hydrogen ions (H+)?
The higher the concentration the lower the pH of bodily fluids
What is the biological function of ammonium ions (NH4+)?
Source of nitrogen used to make organic molecules
What is the biological function of nitrate ions (NO3-)?
Source of nitrogen for organic molecules
What is the biological function of hydrogen carbonate ions (HCO3-)?
Involved in the regulation of blood pH and transport of carbon dioxide in the blood
What is the biological function of chloride ions (Cl-)?
Involved in transport of carbon dioxide in blood through the chloride shift
What is the biological function of phosphate ions (PO43-)?
Components of biological molecules such as nucleotides, ATP and the formation of the phospholipid bilayer
What is the biological function of hydroxide ions (OH-)?
The higher the concentration the higher the pH of bodily fluids
What is the chemical test and results for proteins?
- Biuret test is added to the sample in solution
- Leave for 5 mins and observe for colour change
- Positive result is purple
What is the chemical test and results for starch?
- Iodine is dripped on to a sample
- Positive test turns solution from yellow to blue/black
What is the chemical test and results for lipids?
- The sample is dissolved first in ethanol, then water is added and then the sample is shaken
- If lipids are present the solution goes milky white
What is the chemical test and results for reducing sugars?
- Benedict’s reagent is heated to 80C with a solution of the sample
- Reagent test strips can be used for semi quantitative results
- On heating if a reducing sugar is present there will be a red or orange precipitate
- Use colorimetry and a calibration curve to quantify reducing sugars in sample
What is the chemical test and results for non reducing sugars?
- If a reducing sugar is not present heat with hydrochloric acid to reduce the non reducing sugar
- Sodium hydrogen carbonate solution is added to neutralise the acid
- The Benedict’s reagent is added before heating to 80C
- On heating if a non reducing sugar is present there will be a red or orange precipitate
How are colorimeters used?
- Set the filter in the colorimeter
- Calibrate using distilled water
- Insert samples from your biochemical test
- Measure the percentage transmission of light
- A calibration curve can be created using the results from know concentrations of glucose
How are biosensors used?
- A single strand of DNA or protein which are complementary to the test sample is immobilised. When the sample is added it will bind to the immobilised DNA/protein
- This binding causes a change in a transducer and as a result an electronic current is released
- This current is processed to determine the concentration of the sample present
What is the formula for the Rf value?
Rf = distance moved by the solute/distance moved by the solvent
