Topic A: BIOMOLECULES Flashcards
What is the structure of monosaccharides?
General formula: (CH2O)N
Has a carbonyl group (C=O) and multiple hydroxyl groups. (C=O is part of the aldehyde or ketone group)
It makes it either and aldose or ketose.
What is the structure of glucose?
Chemical formula of C6H12O6
In solution, glucose alternates between straight chains and ring structures freely. It exists mainly in ring structure, and only a small proportion exists in straight chain.
There are two possible ring structure of glucose. A-glucose and B-glucose. A-glucose has OH on the bottom part of the C1. B-glucose has OH on the top part of C1 glucose.
What is a hydrolysis reaction?
The glycosidic bond is broken between 2 monosaccharides in a hydrolysis reaction with the addition of one molecule of water, to form the hydroxyl group on 2 different monosaccharides.
How are polysaccharides designed for storage?
They are large and insoluble, exerting no osmotic effect on cells when stored in large amounts and do not interfere with chemical reactions of the cells.
They are large and unable to diffuse out of the cells.
They fold into compact shapes and thus large amounts can be stored within fixed volume.
They are easily hydrolysed into monosaccharides when required by the cells.
How are polysaccharides designed for STRUCTURE?
Structural polysaccharides are unbranched polymers.
They form long straight chains which are ideal for formation of strong fibres.
What is the structure of starch?
Starch is a polymer consisting of A-glucose moleqs.
Consists of a mixture of 2 types of polymers, amylose and amylopectin.
What is the structure of amylose?
Amylose:
Consists of several thousand A-glucose.
Linked by A-1,4-glycosidic bonds
Unbranched chain polymer, coiling into a helical compact structure stabilised by H bonds.
Hydroxyl groups on C2 of each glucose residue projects into the middle of the helix, H bonds are formed between the -OH group of adjacent glucose residues.
What is the structure of amylopectin?
Twice as many glucose residues as amylose.
Linked by A-1,4-glycosidic bonds and A-1,6-glycosidic bonds.
Branched chain polymer. Coils into a helical, compact structure stabilised by hydrogen bonds.
Hydroxyl groups on C2 of each glucose residue projects into the middle of the helix and hydrogen bonds are formed between -OH group of adjacent glucose residues.
What is the structure of starch in relation to its function?
Main energy storage in plants.
Accumulates to form starch grains in the chloroplast of plant cells
Compact structure allows many glucose molecules to be stored in a small volume within the cell.
Can be easily converted back into glucose for use in respiration to produce ATP. When necessary, free sugars are released by hydrolysis of starch.
What is the structure of glycogen?
Glycogen has a structure similar to amylopectin.
It consists of A-glucose residues
Linked by A-1,4-glycosidic bonds and A-1,6-glycosidic bonds.
More extensive branching as compared to amylopectin, resulting in a more compact structure.
Coils into a helical, compact structure stabilised by H bonds.
What is the function of glycogen?
Main energy storage molecule in animals.
Accumulates to form gylcogen granules in liver and muscle cells.
Compact structure allows many glucose molecules to be stored in a small volume within the cell.
Easily hydrolysed into glucose when required by the cells.
What is the structure of cellulose?
Consist of B-glucose residues.
Linked by B-1,4-glycosidic bonds
Adjacent glucose molecules are rotated 180. with respect to each other.
Unbranched chain polymer
Straight chain of B-glucose run parallel to each other with numerous H bonds.
The cellulose chains associate in group to form bundles called microfibril, later forms macrofibrils
Macrofibrils of successive layers are interwoven and are embedded in a gel-like matrix, has high tensile strength
What is the function of cellulose?
Main component of cellulose cell wall of plants for structural support.
Large intermolecular spaces between macrofibrils cause the cell wall to be permeable, allowing free movement of molecules in and out.
How are triglycerides formed?
Triglycerides are formed from 3 fatty acid moleqs with 1 glycerol molecules by condensation.
3 ester bonds are formed with the removal of 3 water molecules.
The resulting triglyceride is non-polar
Each hydroxyl group in glycerol reacts with a carboxyl group in a fatty acid molecule to form an ester bond/linkage
Ester bonds can be broken by hydrolysis
What are the properties of triglycerides?
Triglycerides can be classified as fats or oils. Fats are solid at 20°C. Consists of long saturated fatty acid chains Presence of single bonds thus packed tightly and more compact. More hydrophobic interactions between the fatty acid chains, resulting in higher melting points.
Oils are liquid at 20°C. Consists of relatively short unsaturated fatty acid chains Presence of double bonds results in kinks in the fatty acid chain, thus packed less tightly and less compact. Less hydrophobic interactions between fatty acid chains, resulting in lower melting points.
Solubility: They are insoluble in water but soluble in organic solvents
Density: Triglycerides have lower density than water and thus floats on water.
Why are lipids adapted for energy storage?
There are more, but the ones here are the most relavant
Triglycerides are a respiratory substrate, having long hydrocarbon chains that can be hydrolysed and oxidised during respiration to produce energy in the form of ATP. Lipids have a higher calorific value than other respiratory substrates, releasing a higher amount of metabolic energy per unit mass as are there are more C-H bonds to release more ATP upon hydrolysis.
Lipids (38.9KJ/g) yield double the amount of metabolic energy on Oxidation than carbohydrates (17.2kJ/g). Triglycerides release twice as much metabolic water (1.07g/g lipid) as compared to carbohydrates (0.56g/g lipid) when oxidised in respiration.
Lipids can be stored in large amounts without exerting any osmotic effect on cells. They are large molecules and non-polar due to the presence of hydrocarbon tails thus insoluble in water. Therefore, they are unable to diffuse out of cells. They are less dense than carbohydrates as they are more compact and are unhydrated. Main energy source for highly active animals due to the demands of locomotion. Main energy storage for seeds dispersed by wind, resulting in a light seed which can be caried over longer distances.
What is the structure of phospholipids?
Phospholipids are lipids containing a phosphate group
Made up of 1 glycerol molecule, 2 fatty acid molecules and 1phosphate group formed when one of the three hydroxyl groups in glycerol reacts with phosphoric acid and the other two -OH groups react with fatty acids as in the formation of triglycerides
Formed by a condensation reaction resulting in the formation of two ester bonds and one phosphoester bond with the removal of 3 water molecules
Amphipathic molecule due to the hydrophilic phosphate head and wo hydrophobic hydrocarbon / fatty acid chains The phosphate head is hydrophilic as it is charged
Thus the head of the molecule is soluble in water but the tails are insoluble in water
When placed in water, forms micelles and membrane bound.
What is the structure of an amino acid?
The central carbon atom, known as the a-carbon is bonded to 4 different groups of atoms:
hydrogen atom
basic amino group (-NH:) which accepts protons
acidic carboxyl group (-COOH) which donates protons
R group/ side chain which is unique to each amino acid
Amino acids are classified into uncharged and charged R groups. Uncharged amino acids can be non-polar (glycine) or polar (cysteine). Charged R groups can be basic or acidic.
What are the properties of amino acids?
Insoluble in organic solvents but can dissolve in water to form zwitterions.
Properties of amino acids
Dipolar as they carry a positive charge on the basic group and a negative charge on the acidic group.
Amphoteric, as they contain both acidic and basic groups. They are able to resist slight changes in pH, thus are able to act as pH buffers
What is the peptide bond and how are they broken?
A peptide bond is the covalent bond between two amino acids. Peptide bonds are formed between the carboxyl group of one amino acid and the amino group of another in a condensation reaction with the removal of one molecule of water.
Peptde bonds can be broken by hydrolysis reactions using enzymes or acid hydrolysis The peptide bond is broken between two amino acids (in a dipeptide) in a hydrolysis reaction with the addition of one molecule of water, to form the amino group and the carboxyl group on two different amino acids.
What are the 4 levels of structural organisation in proteins?
There are 4 levels of structural organisation in proteins: primary, secondary, tertiary and quaternary.
Describe the primary level of protein organisation.
The primary structure is the specific number and sequence of amino acids joined by peptide bonds in a polypeptide chain.
Every protein molecule has a unique sequence of amino acids which is determined by base sequence of DNA. The unique sequence of amino acids with its side chains of different chemical and physical properties determines the three-dimensional conformation of the protein.
Every polypeptide possesses a carboxyl terminus (C-terminus) and amino terminus (N-terminus). The possible amino acid residues in a polypeptide chain can be of any number and arrangements of the 20 common amino acids.
(The total possible number of different combinations of polypeptide chains can be denoted as n’, wheren = number of different amino acids and r = number of residues in polypeptide chain.)
Describe the secondary structure.
Secondary structure refers to the local spatial conformation of a polypeptide backbone, excluding the side chains of its amino acids. The secondary structure is the repeated coiling and folding of a polypeptide chain, maintained by hydrogen bonds fomed between peptide bonds
Hydrogen bonds are formed between N-H group in a peptide bond of an amino acid and C=O group in a peptide bond of another amino acid.
There are two main forms of secondary structures, namely a-helix and B-pleated sheets.
A-helix and B-pleated will be gone through in other cards.
Describe the structure of an A-helix.
Unbranched polypeptide chain tightly coiled into a spiral Each turn of the helix consists of 3.6 amino acids Held by intra-chain hydrogen bonding between N-H group in a peptide bond of an amino acid and C=O group in a peptide bond of another amino acid four amino acids away.
The numerous hydrogen bonds make the a-helix structurally strong and inelastic but flexible.