Biological Molecules AS Flashcards
Define monomer and give examples
small basic molecular units that can form a polymer
examples include monosaccharides, amino acids and nucleotides
What is the name of the reaction which forms polymers?
condensation reaction where a molecule of water is removed
Breaking down polymers by ________ reaction
hydrolysis = addition of water molecule
What are the monomer which form carbohydrates and give examples?
monosaccharides
examples are glucose, galactose and fructose
Glucose is a hexose sugar - alpha and bets glucose are the isomers - what is the difference ?
alpha glucose has the OH group on the BOTTOM and beta glucose has the OH group on the TOP
How is a disaccharide formed ?
2 monosaccharides are joined by a condensation reaction forming a glycosidic bond
Maltose + maltose =
alpha glucose
fructose + glucose =
sucrose
glucose + galactose =
lactose
The Benedicts test is used for sugars, how do you test for reducing sugars ?
- Add Benedicts reagent to a sample and heat in a water bath that has been brought to a boil
- the sample will stay blue if no reducing sugar is present
- if positive the sample forms green –> yellow –> orange –> brick red precipitate
- the higher the concentration of reducing sugar the further the colour change
What is the problem with the benedicts test?
qualitative data is subjective to make it objective use colorimetry to filter and measure wavelength of absorbance
How to test for non reducing sugars?
- you need to break them down into monosaccharides to do this you get a new sample of test solution and add dilute hydrochloric acid and carefully heat in a water bath that has been brought to a boil
- Then neutralise with sodium hydrogen-carbonate and check pH with red litmus paper
- carry out test as normal
- if negative sample stays blue
- if positive sample forms green –> yellow –> orange –> brick red ppt
Polysaccharides are formed when ____ _____ ____ monosaccharides are joined by _____ reactions
more than two
condensation
Starch - cells get _____ from glucose, plants store excess glucose as ____
energy
starch
Starch is a mixture of two polysaccharides of alpha glucose - amylose and amylopectin - explain both
Amylose
- long unbranched chain of a glucose
- the 1-4 glycosidic bonds give a coiled compact structure for storage
Amylopectin
- long branched chain of a glucose
- the 1-4 and 1-6 glycosidic bonds allow for the side branched to be hydrolysed easily by enzymes for quick release of glucose/energy
Why is starch good for storage?
Starch is insoluble i water and doesn’t affect water potential
Glycogen - animal cells get energy from glucose too but animals store excess glucose as glycogen - another polysaccharide of alpha glucose
Explain the structure and importance of glycogen
structure is similar to amylopectin except it has a lot more side branches coming off it
Loads of branches means that stored glucose can be released quickly - it is also very compact for good storage
Found in muscles and packed with mitochondria
1-4 and 1-6 glycosidic bonds
Cellulose is made of long unbranched chains of ____ glucose
explain what happens when these bond
beta
When beta glucose molecules bond, they form straight cellulose chains linked together by hydrogen bonds to form strong fibres called microfibrils.
The strong fibres mean cellulose provides structural support for cells
High tensile strength so able to withstand turgor pressure and stretch
Describe how to test for starch
Add iodine dissolved in potassium iodide solution to the test sample
If positive = dark blue/black colour
If negative = orange/brown colour
Describe the structure of triglycerides
one molecule of glycerol and 3 fatty acids
fatty acid long tails made from hydrocarbons = hydrophobic
What are saturated fatty acids?
don’t have any double bonds between their carbon atoms
the fatty acid is saturated with hydrogen
What are unsaturated fatty acids?
have double bonds between carbon atoms, which cause the chain to kink
How is a triglyceride formed and what bond is formed?
formed by condensation reactions - this happens 3x to form a triglyceride
an ester bond is formed
What are the lipids found in cell membranes called?
phospholipids
Explain the structure of a phospholipid
glycerol backbone with 2 fatty acids and one phosphate group
fatty acid tails are hydrophobic
phosphate group is hydrophilic
Properties of triglycerides?
clue:
energy
water
- Mainly used as energy storage molecules they are good for this as the long hydrocarbon tails of the fatty acids contain a lot of chemical energy - a lot of energy is released when broken down
- insoluble in water so don’t effect water potential
- triglycerides bundle together as insoluble droplets in cells as fatty acid tails are hydrophobic - tails face inwards shielding themselves from water with their glycerol heads
Properties of phospholipids?
- make up the bilayer of cell membranes - this controls what enters and leaves a cell
-heads are hydrophilic and tails are hydrophobic so they form a double layer with heads facing outwards
- the centre of the bilayer is hydrophobic so water soluble substances cant easily pass through - the membrane acts as a barrier to those substances
How to test for the presence of lipids ?
Emulsion test
- Shake test substance with ethanol for a minute, then pour the solution into water
- any lipid will show as a milky emulsion
- the more lipid there is the more noticeable the milky colour will be
what are the monomers of proteins?
amino acids
A ________ is formed when two amino acids join together
dipeptide
A __________ is formed when more than 2 amino acids join together
polypeptide
Proteins are made up of one or more ______
polypeptides
How are amino acids linked together and what is the bond formed called ?
condensation reactions
peptide bond
Primary structure of a protein?
sequence of amino acids in the polypeptide chain
Secondary structure of a protein?
Hydrogen bonds form between amino acids in the chain
This makes it automatically coil into alpha helix or beta pleated sheet
Tertiary structure of a protein?
More bonds form between different parts of the polypeptide chain including hydrogen bonds and ionic bonds.
Disulfide bridges also can form
For proteins with one polypeptide chain, this is their final 3D structure
Quaternary structure of a protein?
Some proteins are made of several polypeptide chains held together by bonds. The way these are held is the quaternary structure
e.g. haemoglobin, insulin and collagen
final 3D structure
Give an example of how a proteins shape effects its function
Haemoglobin is compact and soluble which makes it easy for transport. This makes them good for transport of oxygen
Antibodies = two light and 2 heavy polypeptide chains - these have variable regions
Enzymes = roughly spherical in shape due to tight folding, soluble and often have roles in metabolism and other enzymes help to synthesise large molecules
How to test for proteins?
- test solution needs to be alkaline, so first you add a few drops of sodium hydroxide solution
- then you add some copper (II) sulfate solution
if positive purple colour
if negative solution stays blue
Enzymes speed up chemical reactions by acting as biological ______
catalysts
Enzymes are ________
Explain the structure of an enzyme
proteins
Enzymes have an active site which has a specific shape. This is where the substrate molecule binds to the enzyme. Enzymes are highly specific due to tertiary structure.
How do enzymes speed up the rate of reaction?
Lower the activation energy by providing an alternative pathway
When a substrate fits into the enzymes active site it forms an enzyme substrate complex - its this that lowers the activation energy .
Give 2 reasons why
- if two substrate molecules need to be joined, being attached to an enzyme holds them close together, reducing any repulsion between the molecules so they can bond more easily
- if the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate so the substrate molecule breaks up more easily
Explain the lock and key model
Substrate fits directly into the enzyme the way a key fits into a lock - the active site and substrate have a complimentary shape
Explain the induced fit model
The substrate doesn’t only have to be the correct shape to sit the active site, it has to make the active site change shape as well
As the substrate binds to the active site, the active site changes shape slightly
Each different enzyme has a different _______ structure and therefore a different shaped active site
tertiary
What happens id the tertiary structure is altered and how can this happen?
The shape of the active site will change and the substrate will therefore not be able to fit into active site - preventing the formation of an enzyme-substrate complex and the enzyme cannot carry out the function.
The structure may be altered by pH or temperature
If there is a mutation in a gene in the primary structure it could change the tertiary structure of the enzyme produced
How can you measure the rate of enzyme activity/rate of reaction?
- how fast the product is made - measure amount of end product present at different times in the reaction
- how fast the substrate is broken down - measure amount of substrate molecules present at different times in the reaction
Explain how temperature can effect enzyme activity
Increased temp means more kinetic energy so the substrate molecules are more likely to collide with the enzyme active sites. The energy of these collisions also increases which means each collision is likely to result in a reaction.
If temp goes too high, the active site changes shape and the enzyme substrate can no longer fit - the enzyme is denatured and no longer can function as a catalyst
Explain how pH can effect enzyme activity
All enzymes have an optimum pH value, most human enzymes work at pH 7 but others are an exception such as pepsin which is pH 2
Levels above and below the optimum pH can disrupt the ionic and hydrogen bonds that hold the enzymes tertiary structure in place
The enzyme become denatured and the active site changes
Explain how substrate concentration can effect enzyme activity
The higher the substrate concentration the faster the reaction as more collisions between substrate and enzyme
After the saturation point, there is not enough enzymes to cope with all of the substrates so adding more makes no difference
Explain how enzyme concentration effects enzyme activity
More enzymes = more likely a substrate will collide to form an enzyme substrate complex therefore increasing rate of reaction
If amount of substrate is limited, there aren’t enough to bind with all of the enzymes - so adding more enzyme has no further effect
How do competitive inhibitors work?
Have a similar shape to the substrate molecule. They compete with the substrate molecules to bind to the active site so no reaction takes place.
They prevent substrates binding by blocking the active site
Increasing the concentration of substrate will increase the rate of reaction as the substrate will have better chance at binding with the substrate.
How do non competitive inhibitors work?
Bind to the enzymes away from the active site which causes the active site to change shape so the substrate molecules can no longer bind to it.
Increasing the conc of substrate will have no effect as they don’t compete with the substrate.
