Core Concepts: Biomolecules Flashcards
What are proteins?
- contain elements C, H,O and N (sometimes S or P)
- proteins are polymers made up of monomers (amino acids)
- 20 amino acids, 8 can only be obtained through diet
What are carbohydrates?
Carbohydrates are organic compounds, consisting of carbon, hydrogen and oxygen with the general formula C(H2O)n
- monosaccharides, disaccharides and polysaccharides
What are monosaccharides?
Small organic molecules that are monomers
- general fromula (CH2O)n
- Named according to the number of carbon atoms…
3C = triose (glyeraldehyde)
5C = pentose (ribose and deoxyribose)
6C = hexose (glucose, fructose and galactose)
Draw alpha and beta glucose
Alpha the hydroxyl groups are down, up, down, down
Beta the hydroxyl groups are down, up, down, up
(from carbon 4 to 1)
- 6th carbon is CH2OH
What are the functions of monosaccharides?
A source of energy in respiration
- C-H and C-C bonds break to release energy and make ATP
Building blocks for larger molecules
- glucose used to make starch, glycogen and cellulose
Intermediates in reactions
- trioses intermediates in photosynthesis and respiration reactions
What is glucose?
Glucose exists as 2 isomers, beta and alpha which form different polymers:
- starch, a polymer of alpha glucose (composed of straight-chained amylose and branched amylopectin)
- glycogen, a polymer of alpha (branched structure)
- cellulose, polymer of beta
- chitin, polymer of beta with some hydroxyl groups replaced by nitrogen containing acetylamine groups
How does glucose act as a source of energy?
Glucose is a main source of energy but it’s soluble in water and therefore increases concentration of cell contents, drawing water in by osmosis
To overcome this glucose is converted into a polysaccharide (starch/glycogen) which…
- is insoluble, has no osmotic effect
- can’t diffuse out the cell
- compact molecule
- carries lots of energy in carbon-carbon/carbon-hydrogen bonds (17kJg^-1)
- glucose can be added and removed easily
What is the polysaccharide cellulose?
- structural polysaccharide, present in cell walls
- consists of long parallel chains of beta glucose units joined by 1-4 glycosidic bonds but every other unit is rotated 180°
- H-bonds form between adjacent chains (stability), multiple chains cross-linked form bundles called microfibrils, held in bundles of fibres (strength)
- cellulose fibres are freely permeable (spaces in between)
What is the polysaccharide chitin?
- structural polysaccharide found in the exoskeletons of insects and in the cell walls of fungi
- carbon 2 has an acetylamine group replacing the hydroxyl group
- long chains of beta 1-4 linked glucose monomers, rotated 180° in relation to their neighbour and chains are cross linked by hydrogen bonds forming microfibrils
- lightweight, strong and waterproof
What are the functions of lipids?
- energy source and storage
- protection of delicate organs
- oxidation of triglycerides produces metabolic water
- biological membranes
- waterproofing
- insulation (thermal and electrical)
- hormones
- water source
What happens if someone’s diet is high in unsaturated fats?
- liver increases production of HDLs
- HDL scavenge excess LDLs in the blood and then return them to the liver for disposal
- A higher ratio of HDLs to LDLs decreases risk of cardiovascular and coronary heart diseases
What are saturated fatty acids?
- fats e.g. lard
- tend to be found in animals
- in the hydrocarbon chain all carbon atoms are saturated with hydrogen and all carbons joined by single bonds
- form straight chains
- high melting points so are solid at room temperature
What are unsaturated fatty acids?
- oils e.g. olive oils
- tend to be found in plants
- in the hydrocarbon chain there is at least one carbon-carbon double bond, not saturated with hydrogen
- form bent chains with low melting points
- 1 C=C bond = monosaturated
- 2+ C=C bond = polysaturated
Why are lipids used instead of carbohydrates as an energy store in seeds and animals?
Lipids have a higher yield of energy per gram than carbohydrates
- lipids = 39 kJg^-1
- carbohydrates = 17 kJg^-1
Describe the formation of a dipeptide?
- two amino acids are joined by a condensation reaction
- reaction removes a H2O molecule and forms a peptide bond between the amino group of one amino acid and the carboxyl group of another
- the reverse of a condensation reaction is hydrolysis which splits a dipeptide by adding a H2O molecule
What is a polypeptide chain?
Both ends of a dipeptide can react with another amino acid, building a chain of amino acids, this is a polypeptide chain
What is the primary structure?
The sequence of amino acids held together by peptide bonds
What is the secondary structure?
- folding of the primary structure
- chain coils to form an alpha helix or a beta pleated sheet
- both structures held together by many hydrogen bonds
What is the tertiary structure?
- further folding of the polypeptide chain to give more complex 3D shapes
- stabalised by: hydrogen bonds (OH groups), disulphide bonds (S-S, cysteine), ionic bonds (between charged R-groups) and hydrophobic interactions (between non-polar R-groups)
What is the quaternary structure?
Proteins that are made up of more than one polypeptide chain
What is a fibrous protein?
- fibrous proteins form long fibres
- usually insoluble in water
- generally structural roles (e.g. myosin in muscles and keratin in hair)
- no prosthetic group
What is an example of a fibrous protein?
Collagen - in skin
- a tropocollagen formed of 3 identical polypeptide chains twisted around each other, forming a triple helix
- every 3rd amino acid in the chains is glycine
- chains are linked by hydrogen bonds creating stability
- molecules cross-link to form covalent bonds creating strength
What is a globular protein?
- fold up into a compact ball like shape
- more soluble than fibrous proteins
- metabolic roles (e.g. enzymes)
- can have a prosthetic group
What is an example of a globular protein?
Haemoglobin
- 4 polypeptide chains (2 alpha and 2 beta)
- each chain has a haem group (prosthetic group) which contains a Fe2+ ion
- carries oxygen from the lungs to respiring tissues
Explain why a mistake leading to the insertion of the wrong amino acid during protein synthesis could produce an enzyme that doesn’t function?
- The ‘wrong’ amino acid may not form the same bonds in the tertiary structure as the primary structure has changed
- therefore folding will give the molecule a different shape and a different active site which won’t be complementary to the substrate
Glucose is transported into cells by carrier proteins in the cell surface membrane. How do carrier molecules specifically recognise glucose?
The transport proteins are specific to the thing they transport because of their shape (specific shape bind to the substrate)
What is the food test for starch?
Add dilute iodine solution to a sample and mix well
If positive there will be a colour change from yellowy-brown to blue-black
What are the purposes of proteins?
- enzymes which catalyse reactions
- carrier proteins transport molecules across membranes
- antibodies defend against disease
- structural proteins support cells and tissues
- hormones transmit information
- transport proteins (haemoglobin)
- contractile proteins
What is the food test for reducing sugars?
Add benedict’s reagent to the sample, mix well and then boil for one minute
If present there will be a colour change from blue to brick red precipitate
What is the food test for non-reducing sugar (sucrose)?
- add 1cm^3 of HCl to sample and boil to hydrolyse the sucrose into glucose and fructose
- neutralise solution with an alkali
- check solution is neutral/slightly alkaline with pH indicator paper (green)
- boil for 1 min with benedict’s reagent
if present there will be a colour change from blue to brick-red precipitate
What is the food test for proteins?
Add biuret reagent to the sample and mix well
If present there will be a colour change from blue to purple precipitate
What is the food test for lipids?
- mix absolute ethanol with sample, dissolves any lipids present
- shake with an equal volume of distilled water
- dissolved lipids are insoluble in water so they come out of solution and form an emulsion
if present there will be a colour change from colourless to a cloudy white emulsion
What is meant by the term organic and inorganic?
Organic: molecules that have a high proportion of carbon atoms
Inorganic: a molecule or ion that has no more than one carbon atom
What are the most common elements in living organisms?
hydrogen, carbon, oxygen and nitrogen
What are the roles of magnesium ions (Mg2+)?
- in plants Mg2+ is important component of chlorophyll, therefore essential for photosynthesis (without, chlorosis takes place)
- in mammals Mg2+ is needed for bones
What are the roles of iron ions (Fe2+)?
Fe2+ is an important constituent of haemoglobin (prosthetic group)
- without someone will develop anaemia
What are the roles of phosphate ions (PO4^3-)?
PO4^3- is used for making nucleotide and ATP as well as being a constituent part of phospholipids
What are the roles of calcium ions (Ca2+)?
Ca2+ is a structural component of bones and teeth in mammals as well as being a component of cell walls in plants
How is water a universal solvent?
Wate is a dipole molecule (but no overall charge)
- this allows water molecules to form hydrogen bonds with other H2O molecules (H-bonds are singularly weak but lots makes water molecules hard to separate)
- other polar molecules and ions are attracted to H2O molecules causing them to dissolved in water
Why is water being a universal solvent important in both plants and animals?
Plants -> solutes can dissolve in water to be transported in the xylem and phloem vessels
Animals -> solutes can be dissolved to be transported in the blood plasma
How is cohesion created in water?
individually the H-bonds are weak but because there are many, molecules stick together in a lattice
- this sticking together is called cohesion
How is the cohesion of water important to plants?
Allows columns of water to be drawn up xylem vessels in plants
Why does water have a high specific heat capacity?
- water can absorb a lot of heat energy before the temperature increases
- H-bonds restrict movement, this restricts an increase of kinetic energy, therefore resists an increase of temperature
- prevents fluctuations in temperature
How is a high specific capacity of water important to plants and animals?
- keeps aquatic habitats stable, organisms don’t have to adapt to extremes of temperatures
- enables enzymes to work efficiently
What is meant by water having a high latent heat of vaporisation and what is the importance of this for animals?
Lots of heat energy is needed for water to change state from a liquid to a gas (vapour)
Important in temperature controls:
- excess heat used to vaporise water on the skin (sweat)
- as water evaporates the body cools
Why is ice less dense than liquid water?
- In ice the hydrogen bonds hold the molecules further apart than in liquid water (more space between the molecules)
- Water has a maximum density at 4°C
- When water freezes volume increases but no mass, therefore the density will increase
How is the density of ice important to plants and animals?
ice floats on water forming an insulating layer on the surface of the water, prevents large bodies of water losing heat/freezings, organisms below will survive
How does water play a role as a metabolite?
- Used in many biochemical reactions as a reactant
- hydrolysis (water splitting molecule) and condensation (water is a product)
Why is a high surface tension of water important?
Cohesion between water molecules creates surface tension
- body of an inset can be supported (e.g. pond skater)
What is a phospholipid?
A glycerol, 2 fatty acids and a phosphate group
- has 2 hydrophobic tails and a hydrophilic head
Describe the parts of a lipid molecule in terms of its interactions with water
- glycerol is hydrophilic because of its polar hydroxyl groups
- hydrocarbon chains of fatty acids are hydrophobic (non-polar) whilst the (polar) carboxyl group is hydrophilic (fatty acids are hydrophobic)
- hydrophilic groups are used in forming the ester bond of triglycerides hence the insolubility in water
What are the 2 differences between phospholipids and triglycerides?
- phospholipids have a charged phosphate group, triglycerides don’t
- phospholipids have 2 fatty acids instead of 3
What are the 2 main causes of heart disease?
- fatty deposits in coronary arteries (atheroma)
2. high blood pressure (hypertension)
What are the factors which contribute to heart disease?
- diet high in saturated fats
- smoking
- lack of exercise
- age
What is the basic structure of an amino acid?
Amino group -NH2 (N-terminal) Central carbon Hydrogen atom R group (variant) Carboxyl group -COOH (C-terminal)
What are the monosaccharide combinations for 3 disaccharides?
glucose + glucose = maltose
glucose + fructose = sucrose
glucose + galactose = lactose
Where is maltose, sucrose and lactose found?
maltose -> germinating seeds
sucrose -> transport in phloem of flowering plants
lactose -> mammalian milk
Why is water being transparent important?
Allows for light to pass through so aquatic plants can photosynthesise effectively
What is meant by the terms ‘monomer’ and ‘polymer’?
Monomer - single repeating unit of polymer
Polymer - a large molecule comprising of repeated units (monomers) bonded together
Describe glycogen as a polysaccharide?
- main storage product in animals of alpha glucose
- branched and chain polymer
- more compact than starch
- 1-4 and 1-6 glycosidic bonds
- glycogen is stored as glycogen granules in the liver and muscle cells
Describe starch as a polysaccharide?
- main storage of glucose in plants
- found in high concentrations in seeds and potato tubers
- made of alpha glucose and bonds in two different ways…
1. amylose a linear, unbranched molecule with 1-4 glycosidic bonds, forms a chain coiling into a helix
2. amylopectin a branched polymer with 1-4 glycosidic bonds cross-linked with 1-6 glycosidic bonds of alpha glucose
What are the elements that make up lipids?
carbon, hydrogen, oxygen and phosphorus (as phosphate in phospholipids)
What is a triglyceride and draw the reaction?
- formed by the condensation reaction of one glycerol molecule and 3 fatty acids
- 3 ester bonds are formed and 3 H2O molecules formed
What happens if someone’s diet is high in saturated fats?
- liver increase production of LDLs (low-density lipoproteins)
- atheroma is deposited by LDLs in coronary arteries which restricts blood flow and therefore reduces the amount of oxygen being delivered to the heart muscle
- can result in angina and if the whole vessel is blocked a myocardial infarction
