2.1.2 Biological Molecules (Foundations in Biology) Flashcards
What’s the role of water in the body?
- provide a medium for reactions to occur
- transport medium e.g. blood
- maintain osmotic balance
- cooling mechanism i.e. sweating
- waste removal
- formation of urine
What are the roles of carbohydrates in the body?
Simple Sugars (monosaccharides and disaccharides):
- use in respiration to provide energy for cells
- other roles e.g. attracting animals to eat fruit
Complex Carbohydrates (polysaccharides):
- starch and glycogen are energy stores
- cellulose: plant cell walls
What are the roles of lipids in the body?
Fats and Oils (triglycerides):
- insulation
- protection of organs
- stored energy
Cholesterol:
- component of cell membranes
Steroid Hormones:
- testosterone, oestrogen, progesterone (sex hormones)
What are the roles of proteins in the body?
- enzymes
- some hormones
- antibodies
- blood clotting
- muscles
- structural roles e.g. keratin in hair and collagen in skin
- channel protein and protein pumps
- haemoglobin (transports oxygen)
What are the role of nucleic acids in the body?
DNA: - stores genetic info
- codes for proteins
RNA: - protein synthesis
Draw a water molecule
What is meant by ‘water is a polar molecule’?
- it has negative and positive regions
What are hydrogen bonds?
- a weak interaction which happens between slightly negatively charged atom and slightly positively charged hydrogen
- they form between adjacent water molecules
- weaker than covalent bonds
Draw how water molecules are joined by hydrogen bonds
Name six properties of water related to its importance for organisms
- liquid at room temperature
- density
- solvent
- cohesion and surface tension
- high specific heat capacity
- high latent heat of vaporisation
Describe and Explain why water being a liquid of room temperature is important to organisms
- as the water molecules move, they continually make and break hydrogen bonds
- the hydrogen bonds make it more difficult for them to escape to become a gas
- even with H bonds, water has quite a low viscosity so flows easily
- provides habitats
- provide a medium for chemical reactions
- major componenet of tissues in organism
Describe and Explain why the density of water is important to organisms
- water behaves differently from other liquids
- as it goes from 4 degrees celsius to freezing point, due to its polar nature, the water molecules align themselves in a structure which is less dense than liquid water
- aquatic animals live in a stable environment
- bodies of water are insulated against extreme cold, layers of ice reduce rate of heat loss
- organisms can live on ice
Describe and Explain why water being a solvent is important to organisms
- water is a good solvent for many substances found in living things (e.g. ionic solutions NaCl)
- since water is polar, positive and negative parts of water molecules are attracted to the negative and positive parts of the solute
- water molecules cluster around these parts of the solute molecules or ions and will help separate them and keep them apart
- so they dissolve and a solution is formed
- molecules and ions can move around and react together in water e.g. in cytoplasm of cell
- molecules and ions can be transported around living things whilst dissolved in water
Describe and Explain why cohesion and surface tension of water is important to organisms
- water molecules show cohesion, which is when H bonds between them pull them together
- this happens at the surface of the water as well: surface of the water contracts as molecules are pulled inwards and gives the surface of the water the ability to resist forced applied to it surface tension
- transport in the xylem relies on cohesions between water molecules sticking together
- surface tension allows small insects to walk on water
Describe and Explain why high specific heat capacity of water is important to organisms
- water require a lot of energy to increase its temperature
- a lot of energy is needed to break the hydrogen bonds between water molecules
- this means that water does not change temperature easily
- organisms need a stable temperature for enzyme-controlled reactions to happen properly
- aquatic organisms need a stable environment to live
Describe and Explain why high latent heat of vaporisation of water is important to organisms
- when water evaporates, heat energy, the latent heat of vaporisation, helps the molecules to break away from each other to become a gas
- because the molecules are held together by hydrogen bonds, a relatively large amount of energy to needed fro water molecules to evaporate
- water can help to cool living things and keep their temperature stable
- liquid water remains as liquid despite temperature changes e.g. oceans exist
What are carbohydrates?
- they are molecules made up of sugar units
- general formula: CnH2nOn
- include sugars, starch/glycogen and cellulose
What are monosaccharides?
- carbohydrates whose molecules contain just one sugar unit
- monosaccharides are the monomers of carbohydrates
How are larger carbohydrates made?
- by joining monomers, the monosaccharides, together
- a condensation reaction occurs to form a glycosidic bond
What are the properties of monosaccharides?
- sweet-tasting
- soluble
- crystalline
How are monosaccharides grouped?
- grouped according to the number of carbon atoms in the molecules
- e.g. triose sugars have 3 carbon atoms
- pentose 5
- hexose 6
What is the most common monosaccharide group?
- hexoses
- includes glucose, fructose and galactose
What is the role of glucose?
- used in respiration to release energy
What is the role of fructose?
- in fruit and nectar attracts animals to disperse seeds/pollen
- used by plants to make sucrose (glucose and fructose)
Give two important pentose sugars
- ribose (a component of RNA)
- deoxyribose (component of DNA)
Explain the difference between alpha and beta glucose and draw one out
- 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
Draw the structure of ribose
What are disaccharides?
- two monosaccharide molecules can join together in a condensation reaction to form a disaccharide
- a new covalent bond called a glycosidic bond is formed and water is removed
What are the properties of disaccharides?
- soluble in water
- taste sweet
What is α glucose + α glucose?
- maltose
What is ß glucose + galactose?
- lactose
What is α glucose + fructose?
- sucrose
What is an alpha 1,4-glycosidic bond?
- the glycosidic bond is between carbon atom 1 of one molecule and carbon atom 4 of the other
What happens when carbohydrates are digested and what is that called?
- glycosidic bonds are broken by carbohydrases (enzymes)
- this is a hydrolysis (meaning water breaking apart) reaction using a water molecule
Define monomer
- a single, small molecule that may combine with other monomers to build up larger molecules called polymers
Define polymer
- a large molecule built up from many similar monomers joined together by covalent bonds to form a chain or a branched chain
Define condensation reaction
- a chemical reaction where two molecules are joined together by a covalent bond, forming a larger molecule and releasing one molecule of water
Define hydrolysis
- a chemical reaction where the covalent bond between two molecules is broken with the addition of a water molecule, separating the two molecules
What are polysaccharides?
- large complex organic molecules made up of many hundred monosaccharide subunits
there are two types:
- homopolysaccharides: made solely of one kind of monosaccharidge (e.g. starch)
- heterepolysaccharides: made of more than one monosaccharide (hyaluronic acid)
What differs in polysaccharides from monosaccharides and disaccharides?
- they are insoluble in water
What roles do polysaccharides provided in plants and animals
- storage and structural roles
What are the stores of potential energy?
- starch and glycogen
What is starch?
- the energy storage polysaccharide in plants
- a polymer of α glucose
- it is actually a mixture of two different polysaccharides: amylose and amylopectin
How is amylose formed?
- 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
What shape is amylose in and why?
- once the amylose chain is formed, it coils into a helix
- it stays in a helix because of the hydrogen bonding between molecules, keeping the helix in place
- it is more compact and stores more glucose
What is amylopectin?
- amylopectin consists of a straight chain of alpha glucose units with branch points along the chain
- also coils into a spiral shape, held together by H bonds, but with branches emerging from the spiral
How is starch made?
- the highly branched amylopectin is wrapped around the amylose to make up starch
Where in plants is starch stored?
- root tubers e.g. potatoes
- leaf cells
- chloroplasts
What makes starch and glycogen good storage materials?
- 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
What is glycogen?
- the energy storage polysaccharide in animals
What is the glycogen’s structure same as?
- same overall structure as amylopectin, but there is more branching in glycogen
Where is glycogen stored?
- muscles: needs to be used when glucose runs out and needs to be converted
- liver: many reactions so needs a lot of glucose
Explain the importance of the difference in structure between glycogen and starch
- 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
If glucose is needed for fuel, why store it as glycogen?
- 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
What is cellulose?
- 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
Describe the structure of cellulose
- 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
- many parallel chains of beta glucose units form and each chain forms hydrogen bonds between the OH groups of adjacent chains
How does cellulose form the plant cell wall?
- cellulose chains that align parallel have H bonds between them
- when 60-70 chains are bound, they form microfibrils (10-30nm in diameter)
- up to 400 microfibrils are bundles together into macrofibirls
- it is then embedded in pectoris to form plant cell walls
- macrofibrils run in all directions, criss-crossing the wall
What are triglycerides?
- fats and oils
- made up of glycerol and three fatty acids
What elements are in all lipids?
- carbon
- hydrogen
- oxygen
What are the fatty acid molecules made of?
- hydrocarbons
- they can vary from 2 to 20 carbons long
- contain a carboxyl group
- rest of molecule is a hydrocarbon chain
What are the properties of fatty acids?
- the tails are hydrophobic (repel water molecules)
- they make lipids insoluble in water
How are triglycerides formed?
- 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)
What are saturated fatty acids?
- they don’t have any double bonds between their carbon atoms
- fatty acid is saturated with hydrogen
What are unsaturated fatty acids?
- they have at least one double bond between carbon atoms, which cause the chain to kink
- these kinks push the molecules apart slightly, making htem mor fluid
What are phospholipids?
- 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 phophoric acid molecule (H3PO4) and on of the OH on glycerol
Are phospholipids hydrophobic or hydrophilic?
- the phosphate group is hydrophilic
- but the fatty acid tails are hydrophilic
- meaning the molecule is amphipathic
What are the functions of triglycerides?
- energy source: triglycerides can be broken down in respiration to release energy and generate ATP
- hydrolyse ester bonds, then both glycerol and fatty acids can be broken down to CO2 and water. respiration of lipid produces more water than respiriation sugar.
- energy store: insoluble in water, so can be stored without affecting water potential of cell. 1g of fat releases twice as much energy as 1g of glucose due to higher proportion of H atoms
- insulation: adipose tissue a storage location for whales. lipiids in nerve cells act as 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 shock absorber. peptidoglycan cell wall of some bacteria is covered in lipid-rich outer coat
What are the functions of phospholipids?
- phospholipids are found in the cell membranes of all eukaryotes and prokaryotes
- they make the phospholipid bilayer, which controls what enters and leaves the cell
- the phospholipid heads are hydrophilic and tails are hydrophobic so they form a double layer with head facing out
- the centre of the bilayer is hydrophobic so water soluble substances can’t easily pass through it, acting as a barrier to these substances
What is cholesterol and its structure?
- a steroid alcohol
- a type of lipid not made from glycerol and fatty acids
- has a hydrocarbon ring structure attached to a hydrocarbon tail
- ring structure has a polar hydroxyl (OH) group attached to it
- mainly made in the liver in animals
What is the function of cholesterol?
- in eukaryotic cells, cholesterol molecules help strengthen the cell membrane by interacting with the phospholipid bilayer
- cholesterol has a small size and flattened shape, allowing it to fit between phospholipid molecules in the membrane
- they bind to the hydrophobic tails of phospholipids, causing them to pack more closely together, making the membrane less fluid and more rigid
What are proteins?
- they are large polymers
- comprised of long chains of amino acids
What are the monomers of proteins?
- amino acids
What is a polypeptide?
- when more than two amino acids join together
What differentiates one amino acid from another amino acid
- all amino acids have the same general structure
- a carboxyl group (-COOH) and an amino group (NH2) attached to a carbon atom
- the difference is the variable group (R)
What chemical elements are in amino acids?
- all contain carbon, oxygen, hydrogen and nitrogen
- some contain sulfur
How are amino acids joined together?
- 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
- the reverse is the hydrolysis reaction, which is when a molecule of water is added to break the peptide bond
What are the four protein structural levels?
- primary
- secondary
- tertiary
- quaternary
Describe the primary structure of proteins
- the sequence of amino acids in a protein chain is its primary structure
- this is determined by the sequences of bases on a gene
- a change in one amino acid could lead to a different protein/prevent protein function
Describe the secondary structure of proteins
- formed when amino acid chain coils or folds
- either to form an α helix or ß-pleated sheet
- 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
Describe the tertiary structure of proteins
- the coiled or folded chain of amino acids is often coiled and folded further to form the final 3D shape of the protein
- structure is held in place by a number of different bonds between R-groups
- vital to the function of protein as it gives it the specific shape
Describe the quaternary structure of proteins
- 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
What can computer modelling do?
- it can create 3D interactive images of proteins
- good for investigating different levels of structure in a protein molecule
- predicts the occurrence of binding sites on a protein can help identify new medicines
What kind of bonds hold together the primary structure of proteins?
- peptide bonds between amino acids
What kind of bonds hold together the secondary structure of proteins?
- hydrogen bonds
What kind of bonds hold together the tertiary structure of proteins?
- ionic bonds: attraction between negatively-charged R groups and positively-charged R groups on different parts of 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
What kind of bonds hold together the quaternary structure of proteins?
- determined by the tertiary structure - can be influenced by all the other levels
Describe the structure of globular proteins
- 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
Describe the function of the haemoglobin protein
- a globular protein that carries oxygen around the bond in red blood cells - a conjugated protein (protein with a non-protein group attached) - the attached is a prosthetic group, and it binds to haemoglobin, which contains iron, which O2 binds to
Describe the function of the protein hormone insulin
- secreted by pancreas - helps to regular blood glucose level - soluble is important - can be tranported in the blood to tissues - consists of two polypeptide chains, held together by disulphide bonds
describe the function of the protein amylase
- 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 - globular
What are fibrous proteins?
- they’re structural proteins - fairly unreactive - are insoluble and strong
Describe the function of the protein collagen
- found in a animal connective tissues, such as bone, skin muscle - very strong molecule - minerals can bind to the protein to increase its rigidity
Describe the function of the protein keratin
- found in many of the external structure of animals such as skin hair nails - can either be flexible or hard and tough
Describe the function of elastin
- found in elastic connective tissues, such as skin, large blood vessels and some ligaments - elastic, so allows tissues to return to their original shape after stretched
What is an ion?
- an atom that has an electric charge
What is an ion with +
- cation
What is an ion with -
- anion
What is an inorganic ion
- an ion that doesn’t contain carbon
What is the role of calcium in biological processes?
- Ca2+ - involved in the transmission of nerve impulses and the release of insulin from the pancreas - a cofactor for many enzymes - important for bone function
What is the role of sodium in biological processes?
- Na+ - important for generating nerve impulses, for muscle contraction and regulating fluid balance in body
What is the role of potassium in biological processes?
- K+ - generating nerve impulses, muscle contraction and regulating fluid balance in body - activates essential enzymes needed for photosynthesis in plant cells
What is the role of hydrogen in biological processes?
- H+ - affects the pH of substances (more H+, more acidic) - important for photosynthesis reactions
What is the role of ammonium in biological processes?
- NH4+ - absorbed from the soil by plants - an important source of nitrogen
What is the role of nitrate in biological processes?
- NO3- - absorbed from the soil b plants - important source of nitrogen
What is the role of hydrogencarbonate in biological processes?
- acts as a buffer, helping to maintain pH of bloof
What is the role of chloride in biological processes?
- involved in the chloride shift, painting the pH of the blood during gas exchange - acts as a cofactor for the enzyme amylase - involved in some nerve impulses
What is the role of phosphate in biological processes?
- involved in photosynthesis and respiration reaction - needed for the synthesis of many biological molecules, such as nucleotides, phospholipids
What is the role of hydroxide in biological processes?
- affects the pH of substances (more OH-, more alkali)
How do test for reducing sugars>
- reducing sugars include all monosaccharides and some disaccharides - add benedictus reagent (blue) and heat above 90 degrees for at least 5 mins - blue to green to yellow to orange to brick red - a colour precipitate will form if positive - you can compare by weighting or looking at colour or colorimetert
How to test for non-reducing sugars?
- 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
How to test for glucose?
- test strips with reagent
How to test for starch?
- iodine test - add iodine dissolved in potassium iodide - if starch is present, sample changes from orange brqwn to dark, blue black colour - if not, it stays
How to test for proteins?
- biuret test - test solution needs to be alkaline, so first add 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
How to test for lipids
- emulsion test - test substance with ethanal then pour solution into water - if lipid present, solution will turn milky - more lipid, more mily - if no lipid, solution stays clear
What is the Rf value?
- distance travelled by spot / distance travelled by solvent
Draw deoxyribose
What are the properties and functions of cellulose?
- 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)
What are lipids?
- a group of substances that are soluble in alcohol rather than water
- includes triglycerides, phospholipids, glycolipids and cholesterol
Draw a glycerol molecule
What hormones are made from cholesterol and why is that helpful?
- steroid hormones such as testosterone, oestrogen, vitamin D
- they are small and hydrophobic, so can pass through the hydrophobic part of the cell membrane
Draw the structure of an amino acid
How many naturally occurring amino acids are there?
- 20
What bond joins amino acids together?
- a peptide bond
- covalent
Which enzymes catalyse the breakdown of polypeptides in humans?
- small intestine: trypsin
- stomach: pepsin
