Biological Molecules - 2016 AQA Specification

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  • Created by: becky
  • Created on: 10-02-16 10:20
How are monomers joined together?
Condensation reactions where a molecule of water is lost
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How are polymers broken down?
Hydrolysis using a water molecule
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General structure of amino acid?
Central carbon, amino group (NH2), acid group (COOH) and an R group
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Name of bond between 2 amino acids?
Peptide bond
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What is formed when 2 amino acids are bonded?
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What is formed when many amino acids are bonded?
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What is the primary structure of a protein?
The sequence of amino acids
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What is the secondary structure of a protein?
It is either folded into an alpha helix or a beta pleated sheet when hydrogen bonds form between amino acids
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What is the tertiary structure of a protein?
The protein becomes 3D when more hydrogen, ionic bonds and disulfide bridges form, this structure determines a proteins use
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What is the quaternary structure of a protein?
Multiple polypeptides are joined together, not all proteins have this structure
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What is a fibrous protein? Examples?
Long, thin molecules that usually have a structural function, eg keratin in hair/nails, collagen in bones, tendon and ligaments
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What is a globular protein? Examples?
Generally rounded in shape and have chemical functions, eg enzymes, hormones, haemoglobin
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What is the test for proteins? Give steps
The biuret test, 1) Add sodium hydroxide to make the solution alkaline, 2) Add copper sulfate solution, if protein is present, the solution will turn from blue to purple
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What is an enzyme?
A globular protein that catalyses reactions by lowering the activation energy needed to make the reaction happen, the enzyme does not get used up
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What is made when a substrate binds to an enzyme?
An enzyme-substrate complex
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What is the lock and key model?
This is the theory that a substrate fits exactly into the enzyme's active site, e.g. the shapes are perfectly complementary
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What is the induced fit model?
The theory that the enzyme and substrate aren't exactly the same shape but the enzyme's active site is slightly fluid and moulds itself around the substrate which puts pressure on the substrate causing it to break
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Two ways that enzyme activity can be measured?
Measuring: 1) how fast product is made or 2) how fast the substrate is broken down
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How does heat affect enzyme activity?
Speeds it up by giving the substrates more energy to collide/make enzyme-substrate complexes but when the heat exceeds optimum, rate slows as the bonds holding the tertiary structure break down and the enzyme denatures
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How does pH affect enzyme activity?
If the pH is too high to too low for the enzyme the hydrogen or hydroxide ions will disrupt the ionic or hydrogen bonds that hold the tertiary structure and the enzyme will become denatured
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How does enzyme concentration affect enzyme activity?
Enzyme conc. increases rate of reaction as more active sites will be available to the substrate but after a point there will be more than enough enzymes to take all substrates at once so the reaction rate will remain the same
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How does substrate concentration affect enzyme activity?
Increasing substrate conc. speeds up rate of reaction as more collisions are likely to take place, too many substrates means the rate will stay the same as all active sites will be occupied at any one time
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What is a competitive enzyme inhibitor?
Molecule that has a similar shape to a substrate or mimics part of one, it binds to an enzymes active site but no reaction takes place, and prevents the actual substrate from fitting into the active site so the enzyme becomes useless
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What is a non-competitive enzyme inhibitor?
Molecule that bonds to an enzyme at an allosteric site (not the active site), this changes the active site shape so it can no longer take the original substrate and the enzyme becomes useless
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Which elements are carbohydrates made from?
Carbon, oxygen and hydrogen
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What are 3 monosaccharides that make carbohydrates?
Glucose, fructose and galactose
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Difference between the two glucose isomers?
Alpha glucose has H above OH on carbon 1, beta glucose has OH above H on carbon 1
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What is the chemical formula for glucose?
C6 H12 O6
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Disaccharides are formed how?
Condensation reaction between 2 monosaccharides
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What bond holds 2 monosaccharides together?
1-4 glycosidic bond
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Name 3 disaccharides?
Sucrose, maltose and lactose
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What is maltose made of?
2 alpha glucose molecules
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What is sucrose made of?
Glucose and fructose
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What is lactose made of?
Galactose and glucose
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What is the test for sugars?
Benedicts test
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What sugars are reducing sugars?
All monosaccharides, maltose and lactose
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What sugars are non-reducing sugars?
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How do you test for reducing sugars?
Add Benedicts reagent to a sample and boil it in a water bath, if it is present there will be a colour change from blue to green, yellow, orange or brick red depending on quantity
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How do you test for non-reducing sugars?
If first test remains blue you add sample to dilute HCl and heat in a water bath, then neutralise with sodium hydrogen carbonate and do the normal Benedicts test
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What are the three polysaccharides?
Starch, cellulose and glycogen
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What is starch?
Plant store for excess glucose, 2 types: amylose (coiled unbranched chain of alpha glucose) and amylopectin (branched chain of alpha glucose for quick glucose release upon breaking of glycosidic bonds)
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What is glycogen?
Animal store of glucose, branched chains of alpha glucose for fast release
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What is cellulose?
Long unbranched chains of beta glucose for structural support in cell walls, layers are linked by hydrogen bonds to form strong microfibrils
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What is the test for starch?
Iodine test, add iodine dissolved in a potassium iodide solution to sample, should go from brown/orange to blue/black
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What is the structure of a triglyceride?
A glycerol molecule attached to 3 fatty acid chains by an ester bond, these hydrocarbon tails are hydrophobic
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What is the difference between saturated and unsaturated fatty acids?
Saturated fatty acids have no double bonds between carbons but unsaturated fatty acids have a double bond between 2 carbons making the chain kink slightly
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What is the structure of a phospholipid?
Phosphate group (hydrophilic) attached to a glycerol molecule and 2 fatty acid chains (hydrophobic)
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What are triglycerides used for?
Mainly used as energy storage molecules as hydrocarbon tails release a lot of energy when broken down, they are insoluble and don't affect the water potential of a cell
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What are phospholipids used for?
Make up phospholipid bilayer in a cell membrane, control entry and exit of substances in cells using hydrophobic tails as water soluble substances can't easily pass through
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How do you test for lipids?
Add sample to ethanol and add the same volume of water, shake and if lipids are present, white opalescent beads of emulsified fat should be suspended in the solution
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What is DNA?
Deoxyribonucleic acid used to store genetic material and instructions
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What is RNA?
Ribonucleic acid, 2 types, messenger and transfer, carries genetic information to ribosomes
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What are the monomers of DNA/RNA called?
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What is the structure of a nucleotide?
Phosphate group, pentose sugar and a nitrogenous base
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What bond is between bases?
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What bond helps form the backbones of DNA?
Sugar-phosphate bond
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What is the structure of DNA?
Two antiparallel polynucleotide strands form a double helix, long and coiled very tightly
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What are the 4 base pairs?
A-T and C-G (or A-U and C-G in RNA)
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How many hydrogen bonds between the bases?
2 between A-T and 3 between C-G
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What are the differences between DNA and RNA?
1) DNA double stranded, RNA single stranded 2) DNA has deoxyribose as pentose sugar, RNA has ribose 3) DNA has thymine, RNA replaces this with uracil 4) DNA is far longer than RNA
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Which enzymes are used in DNA replication?
DNA helicase, DNA polymerase
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How is DNA replicated?
1) DNA helicase breaks H bonds between bases and unwinds double helix 2) The 2 strands act as templates for complementary nucleotides to attach to 3) The bonds are recreated on new strands by DNA polymerase
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Why are the new strands made by DNA replication 'semi conservative?'
Because the new strands still contain half of the original strand, the half that acted as the template is part of the new DNA
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Why does DNA polymerase work on the 2 new strands in opposite directions?
The 2 strands are antiparallel and DNA polymerase can only start at a certain point on DNA, the points on the 2 new DNA molecules are at opposite ends therefore the enzymes go in opposite directions
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What is the evidence that DNA is semi conservative?
Meselson and Stahl: 1) Bacteria had heavy nitrogen or light nitrogen in its DNA 2) In centrifuge, light nitrogen stayed near top of tube, heavy near bottom 3) Bacteria grown in heavy N put in broth with light N and centrifuged 4) DNA stayed in middle
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What is the structure of ATP?
Contains adenine base, ribose sugar and 3 phosphate groups
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How is energy created from ATP?
Broken down into ADP and a single phosphate group by hydrolysis, the energy is released when a phosphate bond is broken by enzyme ATP hydrolase
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How is ATP recreated?
Condensation reaction during respiration and photosynthesis where phosphate group rejoins ADP with enzyme ATP synthase
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Why is energy important?
Required in biological processes eg. active transport, DNA replication and protein synthesis
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Why is water important?
Needed in metabolic reations, condensation and hydrolysis reactions, used as solvent, temperature control and transport mechanism in plants
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What is the structure of water?
1 hydrogen and 2 oxygen ions, H is slightly positive, O is slightly negative making it a polar molecule, hydrogen bonds form between a H of one water molecule and the O of another as the opposite charges attract
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What makes water a metabolite?
Hydrolysis reactions require a water molecule to break the bond and condensation reactions requires loss of water to make them
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What makes water a good solvent?
When other charged compounds are in water, they are separated and dissolved as positive H in water attracts negative ions from the other compounds and vice versa, being dissolved makes things easier to transport around the body
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What is high latent heat of vaporisation and why is it useful?
It takes a lot of energy to break all the hydrogen bonds in water before it evaporates, it means animals can use water loss to cool down as the surface cools when the water evaporates
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What is high specific heat capacity and why is it useful?
Lots of heat energy is used to break hydrogen bonds in water rather than actually warming it, so lots of energy is needed to heat water, this is useful as water doesn't undergo rapid heat change and body temp stays fairly constant
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What is cohesion and why is it useful?
Water is very cohesive as it is polar, this helps water to flow, water is also adhesive so it sticks to other polar molecules which they can then transport eg. in xylem
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What is high surface tension?
Water has stronger bonds on its surface as it has to make less bonds here, this is helpful as it means insects can walk on water
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What are cations and anions?
Cations are ions with positive charge, anions are ions with negative charge
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What is an inorganic ion?
An ion that doesn't contain carbon
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Where are inorganic ions found?
In solutions, cytoplasm and bodily fluids
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What is the role of iron in the body?
It is found in haemoglobin which carries oxygen around the body, the iron is what binds to the oxygen, allowing it to be transported
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What is the role of hydrogen in the body?
pH is determined by the concentration of hydrogen ions that are present, pH in the body affects enzyme controlled reactions
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What is the role of sodium in the body?
Sodium is used in co-transport to allow glucose and amino acids across a membrane
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What is the role of phosphate ions in the body?
DNA, RNA and ATP all contain phosphate groups, the breaking of phosphate bonds in ATP is what releases the energy, phosphate groups in DNA and RNA allow nucleotides to bind together
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Card 2


How are polymers broken down?


Hydrolysis using a water molecule

Card 3


General structure of amino acid?


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Card 4


Name of bond between 2 amino acids?


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Card 5


What is formed when 2 amino acids are bonded?


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