2.1.2 Biological Molecules (Foundations in Biology) Flashcards

Question

Explain the difference between alpha and beta glucose and draw one out

Answer 1

- in α glucose, the OH at C1 is below plane - in β glucose, the OH at C1 is above the plane - leads to very different properties

Answer 2

- in fruit and nectar: attracts animals to disperse seeds/pollen - used by plants to make sucrose (glucose and fructose)

Answer 3

- ribose: component of RNA, ATP and NAD - deoxyribose: component of DNA

Answer 4

- two monosaccharide molecules joined together in a condensation reaction to form a disaccharide - a new covalent bond called a glycosidic bond is formed and water is removed

Answer 5

- soluble in water - taste sweet

Answer 6

- the glycosidic bond is between carbon atom 1 of one molecule and carbon atom 4 of the other - alpha is when the OH on C1 is below the ring - beta is when the OH on C1 is above the plane

Answer 7

- disaccharides and polysaccharides are broken into monosaccharides by a hydrolysis reaction - it requires the addition of water

Answer 8

- a chemical reaction where the covalent bond between two molecules is broken with the addition of a water molecule, separating the two molecules

Answer 9

- large complex organic molecules made up of many hundred monosaccharide subunits there are two types: - homopolysaccharides: made solely of one kind of monosaccharide (e.g. starch) - heteropolysaccharides: made of more than one monosaccharide (hyaluronic acid)

Answer 10

- they are insoluble in water - due to their size - also because regions that could H-bond with water are hidden away inside the molecule - or the molecule (e.g. amylose) may form a double helix, which has a hydrophobic surface

Answer 11

- energy storage and structural roles

Answer 12

- Glycogen: in animals - Starch: in plants - starch is made of amylose and amylopectin

Answer 13

- the energy storage polysaccharide in plants - glucose made by photosynthesis in plant cells is stored as starch - a chemical energy store - a polymer of α-glucose - it is actually a mixture of two different polysaccharides: amylose and amylopectin

Answer 14

- amylose is formed by a series of condensation reactions that bond alpha glucose molecules together into a long chain - forms many alpha 1, 4-glycosidic bonds

Answer 15

- once the amylose chain is formed, the angle of the bond means that the long chain of glucose coils into a helix - this is further stabilised by hydrogen bonding within the molecule - this makes the polysaccharide more compact than glucose molecules - OH groups on carbon 2 are situated inside the coil, making the molecule less soluble

Answer 16

- forms glycosidic bonds between carbons 1 and 4 but in addition it has glycosidic bonds between carbons 1 and 6 - amylopectin also coils into a spiral shape like amylose, held together by H bonds, but with branches emerging from the spiral

Answer 17

- the highly branched amylopectin is wrapped around the amylose to make up starch

Answer 18

- root tubers e.g. potatoes - leaf cells - chloroplasts

Answer 19

- the energy storage polysaccharide in animals

Answer 20

- like amylopectin, with glycosidic bonds between carbon 1 and 4, and carbon 1 and 6 - the 1-4 bonded chains tend to be smaller than in amylopectin, so glycogen has less tendency to coil - however, it does have more branches, which makes it more compact - it is easier to remove monomer units as there are more ends

Answer 21

- muscles: needs to be used when glucose runs out and needs to be converted - liver: many reactions so needs a lot of glucose

Answer 22

- glycogen is more space efficient than starch: due to more branching - more glucose can be released from glycogen than the same amount of starch: so more energy is obtained from it, advantage in animals as they are more metabolically active

Answer 23

- compact due to helix form and doesn't take much space. - occurs in dense granules within the cell - insoluble: keep glucose in the right place (i.e. not used or transported). glucose is stored in a cell as a free molecule would dissolve and reduces the water potential of the cell which would affect osmotic balance - easily hydrolysed by enzymes to release glucose when needed - branched structure provides easy access for enzymes to 'strip off' glucose when needed

Answer 24

- compact due to helix form and doesn't take much space. - insoluble: keep glucose in the right place (i.e. not used or transported). glucose is stored in a cell as a free molecule would dissolve and reduces the water potential of the cell which would affect osmotic balance - easily hydrolysed by enzymes to release glucose when needed - branched structure provides easy access for enzymes to 'strip off' glucose when needed - glycogen is insoluble so doesn't affect the water potential of cell - our muscles and over cells need a store of glucose to use even if we haven't recently eaten sugar

Answer 25

- found in plants, forming the cell walls - a polymer of beta glucose units where each glucose molecule is inverted with respect to its neighbour - the orientation of the beta glucose units places many hydroxyl (OH) groups on each side of the molecule

Answer 26

- every other beta-glucose molecule is rotated by 180 degrees - the two beta-glucose molecules join together to form a beta-1-4-glycosidic bond - it is unable to coil or form branches, so a straight-chain molecule is formed - H-bonding between the rotated b-glucose molecules in different chains gives additional strength - when 60-70 cellulose chains are bound together in this way, they form microfibrils, which are 10-30nm in diameter - these then bundle together into macrofibrils containing up to 400 microfibrils, which are embedded in pectins to form plant cells - macrofibrils run in all directions, criss-crossing the wall for extra strength

Answer 27

cellulose is excellent for cell walls because: - microfibrils and macrofibrils have very high tensile strength, both because of the strength of the glycosidic bonds, but also because of H-bonding between chains - macrofibrils are stronger than steel wire of the same diameter - macrofibrils run in all directions, criss-crossing the wall for extra strength - it is difficult to digest cellulose because glycosidic bonds between glucose molecules are hard to break

Answer 28

- because plant cells do not have a rigid skeleton, so it requires a cell wall to provide support - there is space between the macrofibrils to allow ions and water to get into and out of the cell, making it fully permeable - the wall has high tensile strength, so it prevents the cells from bursting when they are turgid to help support the plant - the wall also protects the delicate cell membrane - macrofibril structure can be reinforced with other substances for extra support or to make the cell walls waterproof - cutin and suberin are waxes that block the spaces in the cell wall and make it waterproof

Answer 29

- provides great tensile strength to cell wall: - prevents cell bursting - enables turgidity: keeps plant upright when hydrated - cell wall is permeable - role in guard cells: opening and closing stomata - can be reinforced to make it more waterproof of for extra support (e.g. cutin, suberin, lignin)

Answer 30

- a group of substances that are soluble in alcohol rather than water - non-polar molecules - they are large complex molecules known as macromolecules, which are not built from repeating units - includes triglycerides, phospholipids, glycolipids and cholesterol

Answer 31

- a lipid made by combining one glycerol molecule with three fatty acids - glycerol is an alcohol - fatty acids are carboxylic acids

Answer 32

- they have a carboxyl group at the end, attached to a hydrocarbon tail - this may be anything from 2 to 20 carbons long - the carboxyl group ionises into H⁺ and COO^-, so it is an acid due to the H⁺ - fatty acids can be saturated or unsaturated

Answer 33

- the tails are hydrophobic (repel water molecules) - they make lipids insoluble in water

Answer 34

- having one or more C=C bond changes the shape and forms a kink - these kinks push the molecules apart slightly, making them more fluid

Answer 35

- triglycerides are synthesised by the formation of an ester bond between each fatty acid and the glycerol molecule - each ester bond is formed by a condensation reaction (in which a water molecule is released) - the process of triglyceride synthesis is called esterification - triglycerides break down when the ester bonds are broken - each ester bond is broke in a hydrolysis reaction (water molecule is used up)

Answer 36

- energy source: triglycerides can be broken down in respiration to release energy and generate ATP - first, hydrolyse ester bonds, then both glycerol and fatty acids can be broken down to CO₂and water. respiration of lipid produces more water than respiration of a sugar - energy store: insoluble in water, so can be stored without affecting the water potential of the cell - 1g of fat releases twice as much energy as 1g of glucose due to a higher proportion of H atoms - insulation: adipose tissue a storage location for whales - lipids in nerve cells act as an electrical insulator. - buoyancy: fat is less dense than water, helps aquatic mammals stay afloat - protection: humans have fat around delicate organs, such as kidneys, to act as a shock absorber - peptidoglycan cell wall of some bacteria is covered in the lipid-rich outer coat

Answer 37

- they are also macromolecules - similar to triglycerides except one fatty acid molecule is replaced by a phosphate group - a condensation reaction between an OH group on a phosphoric acid molecule (H₃PO₄) and one of the OH on glycerol - most fatty acids found in phospholipids have an even number of C atoms (often 16 or 18) - commonly one of these chains is saturated and the other unsaturated

Answer 38

- the phosphate group is polar and the fatty acid tails are non-polar - this is known as amphipathic - in water, they form a later on its surface, with the phosphate heads in the water and the tails sticking out - they are called surface-active agents, or surfactants - they can also form a phospholipid bilayer with all their hydrophobic tails pointing toward the centre of the sheet, protected from the water by the hydrophilic heads - they can also form micelles

Answer 39

- between 20-80% of membranes in plants and animal cells are made of phospholipids - bacterial membranes tend to contain a higher proportion of protein - the individual phospholipids are free to move around in their layer, but will not move into any position where their hydrophobic tails are exposed to water - this gives the membrane some stability - the membrane is selectively permeable - it is only possible for small and non-polar molecules to move through the tails in the bilayer such as oxygen and carbon dioxide - this lets the membrane control what goes in and out of the cell and keeps it functioning properly

Answer 40

- steroid alcohols - another type of lipid - they are complex alcohol molecules, based on a four-carbon ring structure (isoprene units) with a -OH group on one end - they are amphipathic

Answer 41

- cholesterol is a sterol - it is a small and hydrophobic molecule - mainly made in the liver in animals - plants also have a cholesterol derivative in their membranes, called stigmasterol (it has a double bond between carbon 22 and 23)

Answer 42

- steroid hormones such as testosterone, oestrogen, vitamin D - they are small and hydrophobic, so can pass through the hydrophobic part of the cell membrane

Answer 43

- due to being small and hydrophobic, it can sit in the middle of the hydrophobic part of the bilayer - it regulates the fluidity of the membranes, preventing it from becoming too fluid or stiff - steroid hormones testosterone, oestrogen, vitamin D and bile are made from cholesterol - since they are hydrophobic, they can pass through the hydrophobic part of the cell membrane and any other membrane inside the cell

Answer 44

- they are large polymers comprised of long chains of amino acids

Answer 45

- all contain carbon, oxygen, hydrogen and nitrogen - some contain sulfur

Answer 46

- they are linked together by peptide bonds to form dipeptides and polypeptides - the carboxyl group from one amino acid bond with the amine group from another to form a peptide bond - a molecule of water is released during the reaction, called a condensation reaction - when many amino acids are joined together, a polypeptide is formed - this is catalysed by the enzyme peptidyl transferase present in ribosomes

Answer 47

- small intestine: trypsin - stomach: pepsin

Answer 48

- the sequence of amino acids in a protein chain is its primary structure - this is determined by the sequences of bases on a gene - the particular amino acids in the sequence will influence how the polypeptide folds to give the protein's final shape - which in turn will determine its function - a change in one amino acid could lead to a different protein/prevent protein function

Answer 49

- formed when amino acid chain coils or folds - may form an α helix or ß-pleated sheet, or they may not adopt a regular structure, or even have more than one secondary structure - hydrogen bonds holds the structures in place - they are **weak** bonds, but there are **many**, so give great stability - these bonds form between different amino acids in the chain

Answer 50

alpha-helix: - 36 amino acids per 10 turns of the helix - helix is held together by the hydrogen bonds between the NH group of one amino acid and the -CO group of another four places ahead of it Beta-pleated sheet: - a very slight zig-zag structure - hydrogen bonds between the -NH group of one amino acid and the -CO group of another further down the strand hold the sheet together

Answer 51

- the coiled or folded chain of amino acids is often coiled and folded further to form the final 3D shape of the protein - the coiling or folding of proteins in their secondary structures brings R-groups of different amino acids closer together so they can interact and fold further interactions that may occur: - hydrophobic and hydrophilic interactions: weak interactions between polar and non-polar R-groups - hydrogen bonds: weakest of the bonds formed - ionic bonds: stronger than H bonds and form between oppositely charged R-groups - disulfide bonds: these are covalent and the strongest of the bonds, but only form between R-groups that contain sulfur atoms

Answer 52

- some proteins are made of several different polypeptide chains held together by bonds - quaternary structure is the way polypeptide chains are assembled together - it is the interaction between R groups on different chains that hold the quaternary structure in place

Answer 53

- peptide bonds between amino acids

Answer 54

- hydrogen bonds

Answer 55

- ionic bonds: the attraction between negatively-charged R groups and positively-charged R groups on different parts of the molecule - disulfide bonds: the sulphur atom from one cysteine bond and another sulphur atom come close and form a disulphide bond - hydrophobic and hydrophilic interactions: when hydrophobic R groups are close together in the protein, they tend to clump together, meaning hydrophilic R groups are more likely pushed to outside, affecting how proteins fold up into its final structure - hydrogen bonds: weak bonds between slightly positively-charged hydrogen atoms in some R groups and slightly negatively charged atoms in other R groups

Answer 56

- determined by the tertiary structure - can be influenced by all the other levels

Answer 57

- they are compact, water-soluble and have a spherical shape - the hydrophilic R groups on the amino acids tend to be pushed outside the molecule due to hydrophobic and hydrophilic interactions - this makes the globular proteins soluble, so they're easily transported in fluids

Answer 58

- they are globular proteins that contain a non-protein component, called a prosthetic group - proteins without a prosthetic group are called simple proteins - prosthetic groups could include: - lipids - carbohydrates - metal ions - molecules derived from vitamins - haem groups

Answer 59

- the quaternary structure of haemoglobin is made up of four polypeptides: - two alpha-globin chains - two beta-globin chains - on the outside of each chain, there is space for a haem group - the haem group contains an iron ion - in the lungs, an oxygen molecule binds to the iron in each of the four haem groups - when it binds, haemoglobin turns from a purple-red colour to bright red - the oxygen is released when it reaches the tissues

Answer 60

- a globular protein made of two polypeptide chains - A chain begins with a section of alpha-helix and the B chain ends with a section of beta-pleat - both chains fold into a tertiary structure and are then joined together by disulfide links - amino acids with hydrophilic R groups are on the outside of the molecule, making it soluble in water - insulin binds to glycoprotein receptors on the outside of muscle and fat cells to increase their uptake of glucose from the blood, and to increase their rate of consumption of glucose

Answer 61

- a globular protein - an enzyme that catalyses the breakdown of starch in the digestive system - made of a single chain of amino acids - secondary structure contains both alpha helix sections and beta pleated sheet section

Answer 62

- have regular repetitive sequences of amino acids - usually insoluble in water - due to the presence of a high proportion of amino acids with hydrophobic R-groups in their primary structures - tend to have a structural function

Answer 63

- a fibrous protein - a connective tissue found in skin, tendons, ligaments and the nervous system - made up of three polypeptides wound together ina long and strong rope-like structure - bones are made of collagen and then reinforced with calcium phosphate to make them hard

Answer 64

- a group of fibrous proteins found in hair, skin, nails - has a large proportion of sulfur-containing amino acid, cysteine - this results in many strong disulfide bridges - the degree of disulfide bonds determines the flexibility - hair contains fewer bonds than nails, so is more flexible - the unpleasant smell when hair or skin is burnt is due to the presence of large quantities of sulfur

Answer 65

- a fibrous protein found in elastic fibres - elastic fibres are present in the walls of blood vessels and in the alveoli of lungs - they allow these structures to expand but also return to normal size - elastin is a quaternary protein made from many stretchy molecules called tropoelastin

Answer 66

- an ion that doesn't contain carbon

Answer 67

- increases rigidity of bone, teeth and cartilage and is a component of the exoskeleton of crustaceans - important in clotting blood and muscle contraction - activator for several enzymes, such as lipase, ATPase and cholinesterase - stimulates muscle contraction and regulates the transmission of nerve impulses - regulates the permeability of cell membranes - important for cell wall development in plants and formation of middle lamella between cell walls

Answer 68

- involved in regulation of osmotic pressure, control of water levels in body fluid and maintenance of pH - affects the absorption of carbohydrate in the intestine and water in the kidney - contributes to the nervous transmission and muscle contraction - a constituent of the vacuole in plants which helps maintain turgidity

Answer 69

- involved in the control of water levels in body gfluid and maintenance of pH - assists active transport of materials across the cell membrane - involved in synthesis of glycogen and protein, and breakdown of glucose - generates healthy leaves and flowers in flowering plants - contributes to nervous transmission and muscle contraction - component of vacuoles in plants, helping to maintain turgidity

Answer 70

- involved in photosynthesis and respiration - involved in transport of oxygen and carbon dioxide in blood - involved in regulation of blood pH

Answer 71

- a component of amino acids, proteins, vitamins and chlorophyll - some hormones are made of proteins - an essential component of nucleic acids - involved in maintenance of pH in the human body - a component of the nitrogen cycle

Answer 72

- a component of amino acids, proteins, vitamins and chlorophyll - an essential component of nucleic acids - some hormones are made of proteins, which contain nitrogen - a component of the nitrogen cycle

Answer 73

- involved in regulation of blood pH - involved in transport of carbon dioxide into and out of blood

Answer 74

- involved in the chloride shift, maintaining the pH of the blood during gas exchange - acts as a cofactor for the enzyme amylase - involved in some nerve impulses

Answer 75

- involved in photosynthesis and respiration reaction - needed for the synthesis of many biological molecules, such as nucleotides, phospholipids - bone formation - cell membrane formation

Answer 76

- affects the pH of substances (more OH-, more alkali) - catalysis of reactions

Answer 77

- sugars that can reduce another molecule, or donate electrons - all monosaccharides and some disaccharides are reducing sugars

Answer 78

1. Place sample in boiling tube and add equal volume of Benedict's reagent 2. Heat mixture gently in a boiling water bath for five minutes - reducing sugars will react with the copper ions in Benedict's (an alkaline solution of copper(II) sulfate) - this results in the blue Cu²⁺being reduced to red Cu⁺ - the more reducing sugar present, the more precipitate formed and the less blue Cu²⁺ion are left in solution - this test is qualitative

Answer 79

- if the result for reducing sugars is negative, there could still be non-reducing sugars like sucrose - you have to break them down into monosaccharides - get a new sample of solution - add dilute HCl and heat in water bath that is boiling - neutralise with sodium hydrogencarbonate - carry out Benedict's test like for reducing sugar - if it is positive, it will for coloured precipitate

Answer 80

- test strips with reagent

Answer 81

- iodine test add iodine dissolved in potassium iodide - if starch is present, sample changes from orange-brown to dark, blue-black colour - if not, it stays

Answer 82

- biuret test - test solution needs to be alkaline, so first add a few drops of sodium hydroxide solution - then add copper(II) sulphate solution - if protein is present solution turns lilac - if no protein, solution stays blue

Answer 83

- emulsion test - test substance with ethanol then pour solution into water - if lipid present, solution will turn milky - more lipid, more milky - if no lipid, solution stays clear

Answer 84

- distance travelled by spot / distance travelled by solvent