Biological Molecules OCR - Proteins & Enzymes

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Quiz On Proteins From Biological Molecules AQA AS

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Name 5 key functions and roles of proteins.
- Structure
- Membrane components
- Enzymes
- Hormones
- Antibodies
What are the monomers of proteins?
Amino Acids
How many types of amino acid are there?
What determines what amino acid each is?
The 'R' Group.
What is the structure of an amino acid?

An amino group, an R group, an Acid group and a carbon inbetween. 
How do plants and animals obtain amino acids?
Plants manufacture them. Animals have to obtain them from thier diet. 
What is deamination, where is it carried out and why?
The process of removing the amino group from the amino acid.
This takes place in the Liver and is because excess amino acids cannot be stored by animals as the amino group makes them too toxic if too much is present.
What are amino acids joined by?
What are amino acids split by?
What bond is made?
What is the name of the molecule formed from 2 amino acids?
What is the name of the molecule formed from 3 or more amino acids?
Why are some amino acids decribed as 'non-essential'?
Because they are not essential parts of the diet. They are still essential for protein synthesis but they can be made in the body from other amino acids. 
What is the structure of a dipeptide molecule?

Where are polypeptides and proteins synthesised?
What is Primary Structure?
The types and sequence of amino acids in the polypeptide or protain chain.
What is the secondary structure and what are the two types?
The shape determined by hydrogen bonds.
Either alpha helix or beta pleated sheet.
What is the tertiary structure?
The shape of the polypeptide backbone determined by hydrogen bonds, hydrophobic interactions, disulphide bridges and ionic bonds.
What is the quaternary structure?
This is how several polypeptide chains interact with each other. 
What are two examples of this?
Haemoglobin and collagen.
Why do all proteins have an amino group at one end and an acid group at the other?
Because they are made from amino acids joined 'end to end'. In all cases, the amino group of one amino acid joins to the acid group of the next and so on. 
Some organisms can survive in hot environments. What bonds are likely to be most common in the proteins of these organisms and why?
Covalent (disulfide) bonds because they are unaffected by heat.
Describe the similarities and differences between Collagen and Haemoglobin. 
Both are proteins with a unique primary, secondary and tertiary structure.
Haemoglobin is a globular protein with a metabolic function and contains a prosthetic group.
Collagen is a fibrous protein with a structural function and does not have a prosthetic group. Collagen also contains fewer amino acids.
What are the similarities between cellulose and collagen?
Both are fibrous molecules, used to give structure and support in an organism. Molecule fibres are strengthed by hydrogen bonds.
Describe the test for proteins. 
Biuret test, colour change from plae blue to lilac as the chemicals in the reagent react with the peptide bonds. 
Name 6 features of enzymes. 
- globular proteins
- usually soluble in water
- act as catalysts
- specific to substrate
- has an active site
- activity is affected by temperature and pH.
Why is the tertiary structure so important in enzymes?
For the shape of the active site. 
What are enzymes also referred to as and why?
Biological catalysts, because they speed up chemical reactions. 
What is the name of the following enzymes?
- Used in the breakdown of sugar.
- used in the breakdown of hydrogen peroxide.
- Lactase.

- Catalase.
What is the name of enzymes that catalyse reactions outside the cell?
What is the name of enzymes that catalyse reactions inside the cell?
What are the advantages of having an internal digestive system compared with secreting enzymes outside the organism.
The enzymes produced are not lost to the environment and so can be retained and recycles. The invironment of the internal system can also be regulated to give the optimum conditions for the enzymes' activity.
Explain why many white blood cells invlolved in phagocytosis contain a high concentration of enzymes.
White blood cells take in and destroy foreign organisms and debris. The destruction of this material is achieved by potent digestive enzymes and the lysosomes of these cells. 
What is the name of the process where phagocytes take in and digest bacteria using lysosomal enzymes?
Why do all organisms have enzymes in their cells?
Enzymes regulate metabolic process by catalysing reactions at a rate apporpriate to the organism. 
What is activation energy and what do enzymes do to this?
The amount of extra energy needed for a reaction to proceed.
Enzymes reduce the amount of activation energy needed to allow a reaction to proceed.
How do enzymes do this?
Enzymes destablise the structure of the molecule needed in the reaction.
What are the two theories behind how they destabalise the molecule stucture?
Lock and Key; hydrophobic R groups are attached to the substrate in the active site which is of a completmentary shape. As the substrate binds to the active site the enzyme splits the substrate into two smaller products.
Induced Fit; the substrate collides with the active site and the enzyme changes shape to fit more closely around the substrate. It is held in place by oppositley charged groups on the substrate and active site forming an ''enzyme-substrate complex''. This destabilises the structure of the substrate making an enzyme product complex that no longer fits and therefore moves away.
How does the lock and key theory of enzyme action differ from induced fit?
In the induced fit hypothesis the enzyme changes shape to fit the substrate whereas in the lock and key hypothesis there is no shape change. 
Explain making an enzyme-substrate complex reduces activation energy.
The enzyme molecule hold the substrate in such a way that the reaction proceeds more easily. 
Why are enzymes essential to living organisms?
Reactions essential to life do not take place at a rate sufficient to sustain life without them. 
What four main external factors effect the function of enzymes?
How does temperature effect molecules in a solution?
Gives more kinetic energy to the molecules and therefore makes collisions more likely. 
What does this do to reaction rate?
Increases it. 
What is denaturisation and why does it happen?
An irreversible change to the tertiary structure of a protein leading to loss of function.
Vibrations caused by the extra kinetic energy puts strain on the bonds that hold the molecules together and eventually break the hydrogen and ionic bonds that hold the tirtiary structure.
What is pH?
The measure of hydrogen ion concentration. 
What would a high value of pH be?
Would a high concentration of hydrogen ions cause a low or high pH reading?
How does pH effect enzyme action?
Hydrogen ions carry a positive charge and interfere with the bonds in tirtiary structure of the enzyme.
Changes to the structure cause shape changes and therefore change the working of the active site.
Is this a permenant change?
How is reaction rate effected when the concentration of substrate is increased if there is a fixed concentration of enzyme molecules?
The more substrate molecules present, the more enzyme-substrate complexes can form and therefore the reaction rate increases. 
Why does a plateau occur?
The enzymes are all 'occupied' and working at a maximum possible rate. 
What is this also known as?
A limiting factor. 
How is reaction rate effected when the concentration of enzymes is increased if there is a fixed concentration of substrate molecules?
The more active sites available the more enzyme-substrate complexes can form, and therefore the reaction rate increases. 
Why does a plateau occur?
There is a maximum reaction rate as eventually all substrates will be occupying active sites. 
What does the initial reaction rate give?
the maximum possible reaction rate for an enzyme under a particular experimental situation. 
Why are enzymes usually kept at low concentrations in cells?
Because they are reusable and this makes them easier to control. 
What are inhibitors (in short)?
Any substance or molecule that slows down the rate of reaction. 
What are the two types of inhibtor?
Competitive and Non-Competitive. 
What is a Competitive inhibitor?
Molecules that have a similar shape to that of the substrate and can form enzyme-inhibitor complexes preventing the molecule from entering.
The number of enzyme-substrate complexes that can form is reduced and therefore so too is the reaction rate.
What would be the effect of increasing the concentration of substrates with a fixed concentration of competitive inhibitors?
Effectivly dilutes the effect of the inhibitor. 
What is a non-competitive inhibitor?
Molecules that attach to the enzyme in another region, distorting the tirtiary stucture of the enzyme.
This leads to a change in the shape of the active site, meaning the substrate no longer fits into the active site.
Complexes cannot form and the reaction rate therefore decreases.
Is the effect of competitive inhibitors permenant?
Is the effect of non-competitive inhibitors permenant?
How can it be determined what type of inhibitor is present?
By carrying out experiments at different substrate concentrations.
If the rate of reaction increases up to the same as that given without an inhibitor present, then it can be determined that it is a competitive inhibitor present.
Individual hydrogen bonds are very weak, how can these weak bonds be responsible for holding the tertiary of an enzyme molecule in place?
There are many hudrogen bonds, each is weak but lots of them together are very stabalising.
What are the names of the two non-protein substances needed by some enzymes to be present in order for them to catalyse reactions?
Cofactors and Prosthetic groups.
What are coenzymes and what is an example of one?
Small organic non-protein molecules that bind breifly to the active site either just before or during the ]bstrate binding. 
They can be reused and are sometimes changed in some way during the reaction.
Can act as a 'middle man' to link enzyme controlled reactions that take place in a sequence.
An example is vitamin B3, which produces a coenzyme used by pyruvate dehydrogenase in respiration.
What are prosthetic groups and what is an example of one?
A conenzyme that is a permenant part of an enzyme molecule.
They contribute to the final 3d shape and to other properties on the molecule including charges.
An example is carbonic anhydrase which contains a zinc based prosthetic group.
What is an example of an inorganic ion cofactor?
Chloride ions.
The enzyme amylase catalyses the breakdown of starch to maltose molecules, but only in the presence of chloride ions.
The recommended daily dietry allowance for nicotinamide is 18mg. Suggest why the RDA is low.
Nicotinamide is a reusable conezyme.
What is the protethic group found in haemoglobin?
Haem group. 
Where in the cell would the addition of prosthetic groups to the enzyme molecules take place?
Golgi body/apparatus.
What effect does potassium cyanide have on an organism (metabolically)?
Acts an a non-competitive inhibitor for a vital repiratory enzyme cytochrome oxidase, found in mitochrondria.  Inhibition of this enzyme decreases the use of oxygen so ATP cannot be made.
The organism can only respire anaerobically, leading to a build up of lactic acid in the blood.
How can cystic fibrosis sufferers be treated with enzymes?
One of the symptoms of cystic fibrosis is that the passage of digestive enzymes is blocked causing problems digesting thier food.
Enzymes in tablet form with an acid resistant coat can be prescribed to overcome this problem.
Why is antifreeze dangerous when taken into the body?
It contains Ethylene Glycol which in itself is not dangerous.
However when taken in by the body it is broken down in the liver by the enzyme, alcohol dehydrogenase. The breakdown product Oxalic acid is extremely toxic and can lead to death.
Why is alcohol intoxication used to treat ethylene glycol intake?
Enthanol acts as a competitive inhibitor of alcohol dehydrogenase. Therefore reducing the production of oxalic acid aloowing ethylene glycol to be excreted harmlessly. 
How does penecillin work to inhibit the growth of microorganisms?
It is an inhibitor of a bacterial enzyme that forms cross-links in the bacterial cell wall of some bacteria. meaning repoduction is halted. 
What four functions do the enzymes present in snake venom do to their prey?
-Interfere with the working of the preys heart causing a fall in blood pressure.
- inhibit enzyme used in nerve transmission, resulting in paralysis.
- break down connective tissue to help toxins penetrate quickly.
- breaking down ATP to disrupt the prey's use of energy.
Why would the enzymes given in tablet form be destroyed by the stomach if not packaged properly?
Enzymes are proteins and the stomach contains potent protease enzymes. The enzymes would be broken down and rendered useless. 
Suggest why glucose does not normally appear in urine, but does appear in individuals with diabetes mellitus.
The kidney is able to retain glucose in the blood when urine is formed. In a diabetic there is so much glucose in the blood that the kidney is unable to retain it and therefore causing some to be lost. 
Many antibiotics are chemicals naturally produced by fungal organisms and released into their environment.  What is the advantage to a fungus of producing and releasing antibiotics?
To detroy other organisms so that they cannot take up its food supply.
What is a metabolic pathway?
A series of enzyme-controlled reactions where the product of one reaction in the substrate to the next. 
Why will the end product often act as a reversible non-competitive inhibitor for the first enzyme in the sequence?
To prevent over production. 
What is an example of a condition where enzyme action is not controlled?
Multiple Sclerosis. 
Explain the effects and treatment of the condition Phenylketonuria.
An inborn error of metabolism resulting from mutated DNA. This causes errors in enzyme structure of Phenylalanine hydroxylase which breaks down excess phenylalanine from the diet to tyrosine.
As this amino acid (phenylalanine) cannot be broken down it builds up and causes irreversible damage to the nervous system.
Affected individuals must have a diet with very little phenylalanine.
ATP is an end-product inhibitor of one of the enzymes that catalyses an early reaction in the sequence of reactions involved in respiration. Explain the advantages to an organism of this inhibition.
ATP production will occur at a rate sufficient to the organisms needs.
Explain why end-product inhibition is usually inhibition of an enzyme at the start of the reaction sequence.
intermediate products in the sequence will then not build up as well as the end product. It gives control over the whole sequence. 
Why is diet restricted only in young people affected by phenylketonuria?
Damage is caused by a build up of phenylalanine in growing nervous tissue. In adults the nervous tissue is mature and so unaffected by higher levels in the blood. 
Tyrosine is normally changed to melanin. Suggest why individuals with PKU usually have very fair hair.
individuals with PKU can't change phenylalanine into tyrosine, so they therefore cannot make melanin which is important for making hair.