Deoxyribose nucleic acid (DNA) is present in the nucleus ofall living organisms. It controls all the chemical changes within the cell anddetermines the kind of organism that is produced. Each cell is identical(unless specialised) and contains the genetic information of the livingorganism. DNA consists of a double strand of nucleotides, the sugar-phosphatechains are parallel to each other, and these chains are held together by bondsbetween the bases. Nucleotides are made up of three parts; a sugar base calledribose, a phosphate groups and an organic/nitrogenous base.
The most commonorganic bases are adenine, thymine, guanine and cytosine. Adenine and guanineare purines meaning large molecule, cytosine and thymine are pyrimidinesmeaning smaller molecule. A small molecule will always bond with a largemolecule. Adenine always pairs with thymine and guanine always pairs withcytosine. REFERENCE.
Sickle cellanaemia (SCA) is the result of a point mutation, a change in just onenucleotide in the gene for haemoglobin. This mutation causes the haemoglobin inred blood cells to distort to a sickle shape when deoxygenated. Thesickle-shaped blood cells clog in the capillaries, cutting off circulation.
REFERENCE. The chemical reactions inside cells are controlled by enzymes.Asubstance that speeds up a chemical reaction without being a reactant is calleda catalyst.
Thecatalysts for biochemical reactions that happen in living organisms arecalled enzymes. Enzymesare usually proteins, though some ribonucleic acid (RNA) molecules act asenzymes too, they never ‘die’ they get recycled being used and usedagain until they are denatured and no longer fit for use. REFERENCE.
Enzymes perform the critical task of lowering areaction’s activation energy, which is the amount of energy that must be put infor the reaction to start. Enzymes work by binding toreactant molecules and holding them in such a way that the chemicalbond-breaking and bond-forming processes take place more readily. Long chainsof amino acids are folded to produce a special shape which is called a tertiarystructure, a tertiary structure enables other molecules to interact with theenzymes. The ability of the enzyme to act as a catalyst depends on theirshape. On the surface of an enzyme there is a region called the active site.The active site gets its properties from the amino acids it’s built out of.
These amino acids may have side chains that are large or small, acidic orbasic, hydrophilic or hydrophobic. The set of amino acids found in the active sitegive the active site a very specific size, shape, and chemical behaviour. REFERENCE. One or more substratemolecules fit the shape of the active site, when the substrate fits into theactive site its forms a temporary union called the enzyme-substrate complex.
Insome reactions, one substrate is broken down into multiple products. In others,two substrates come together to create one larger molecule or to swap pieces.So the substrate enters the active site, making enzyme-substrate complex thenext stage is enzyme-products complex after this the products leave the enzymefor the cycle to happen again. There are competitive inhibitors which arechemicals that resemble an enzyme’s natural substrate to slow down the actionof enzymes. There is also non-competitive inhibitors that are chemicallydifferent from the substrate and do not enter the active site, but they bind toanother part of the enzyme causing it to change shape which in turn alters theactive site. What can speed up the reaction is an enzyme concentration, themore substrate in the solution the greater chance of the enzyme-substratecomplex will form. The opposite is a substrate concentration this also speedsup the reaction, this is when there is a more substrate in the solution thanenzymes, and this increases the chance of a substrate molecule finding anactive site.
REFERENCE. There is twomethods that scientist believe how substrates fit into active sites. The first,is the Lock and Key theory where the enzyme’s active site is the exact shape ofthe substrate to fit together exactly, which seems to be outdated and now thenew believed theory is the Induced Fit model. The Induced Fit model assumesthat the substrate plays a role in determining the final shape of the enzymeand that the enzyme is partially flexible and will mould itself to the shape ofthe substrate. REFERNCE.
There aresome environmental factors that can affect an enzyme. Temperature is one ofthem, the normal human body temperate (37 °) provides a good internalenvironment for enzymes to work efficiently. Enzymes will work in lowertemperatures although much slower but at higher temperatures will see theactive site to break and the enzyme will become denatured at around 65 ° orabove. The pH of the body works in favours of different enzymes. Pepsin theenzyme found in the stomach works at the optimum level between pH 1–4, salivaryamylase found in your mouth which begins the digestive process by breaking downstarch when you chew your food works at an optimum between pH 6-7 and alkalinephosphatase (ALP) which is found in the blood (the main source found in theliver) helps break down proteins in the body and the pH optimum for enzymaticactivity is pH 8-10. REFERNCE. Adenosinetriphosphate (ATP) is a RNA nucleotide which bears three phosphatechains. At the centre of the molecule lies a five-carbon sugar, ribose, whichis attached to the nitrogenous base adenine and to the chain of threephosphates.
There are four main stages of respiration, firstly glycolysis whichis the breaking down of glucose. The glucose is phosphorylated intoglucose-6-phosphate by taking a phosphate from ATP. The glucose-6-phosphatechanges to fructose via isomerisation. This is then phosphorylated for a secondtime, splitting another molecule of ATP, forming fructose-1-6-bisphosphate. Thefructose-1-6-bisphosphate then splits into two molecules called triosephosphate. They each have 3 carbon (C) and 1 phosphate. They are then convertedinto pyruvic acid.
This involves the removal of hydrogen and its transfer to ahydrogen carrier molecule (NAD) to form reduced NAD. Each pyruvic acid yields 2molecules of ATP in the process of its creation. The 2 reduced NAD made goes tothe electron transport chain and the 2 molecules of pyruvate goes into the linkreaction which is the next stage.
The link reaction connects glycolysis to theKreb’s cycle. The pyruvate undergoes decarboxylation and dehydrogenation to produceC02 and H+ which is used to reduce NAD. This forms acetate which taken bycoenzyme A (coA) recycled from Kreb’s cycle to form acetyl coA. No ATP isproduced or used in this stage so the net total of ATP is still 2. There is now4 carbon.
The third stage is the Kreb’s cycle, acetyl coA enters the Kreb’s cycleby combining with a 4C acid to form a 6C compound (citrate). Citrate undergoesdecarboxylation and dehydrogenation to produce C02 and H+ which is used toreduce NAD which creates a 5C compound (Ketoglutaric Acid). Ketoglutaric Acidundergoes decarboxylation and dehydrogenation again producing a 4C compound.This time enough energy was created to synthesis a molecule of ATP. 4C compoundis dehydrogenation to reduce NAD. The cycle runs twice so 2 ATP are made. Theelectron transport chain is the final stage, this takes place in the innermembrane of the mitochondria.
The electrons move along and as they move from onemolecule to another, a molecule of ATP is produced. This happens 17 times, andthis happens twice so in total 34 molecules of ATP are produced. REFERENCE.