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Human cell physiology - Open resources

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Week 2
Any chemical reaction can be written as:A + B C + DOrA + B ABREACTANTSPRODUCTSA + B A-B
In human physiology we can define 3 types of reactionsThese are active in human cellsDecompositionSynthesisExchange
DECOMPOSITIONThis type of reaction breaks a molecule into smaller fragmentsABA+BExample:A complex food molecule is broken down in the digestive system to simpler, smaller molecules so that it can be absorbed into the cells, then into the blood stream.AB is too large to be able to enter the cell
Decomposition reaction cont’dHere,WATERadds itself to the molecule AB:A – B + HOH A-H + B-OHWhenever we haveDecompositionof any sort, in a cell, it is calledCATABOLISM
In the HYDROLYSIS reaction above,TheCOVALENTbond betweenA and B [A-B]has been broken.This releasesENERGYThis is how the cell derives energy for the work/functions it has to do.Energy is needed for vital functions such asgrowth, movementandreproduction
The second type of reaction isSYNTHESISOppositeof decompositionHere, smaller molecules arecombinedto create larger moleculesC + D CDExample: H + OH H2O
Particular example of aSynthesisreaction isDehydrationHere, a Water molecule isremovedfrom a complex:A-H + B-OH A-B + HOHIn general, whenever the cell synthesises a molecule we call itANABOLISM.SYNTHESIS of any type within the cell,usesEnergy.
Third type of chemical reaction isEXCHANGEAB +CDAC+ BDQuestion:What type of chemical reaction have ABandCD undergone individually?
Reversible reactions:Any of the 3 reaction types in cells, can be reversibleA + B ABMany of the biological reactions going on in cells are freely reversible.It is all a matter of EQUILIBRIUM. This is represented by the double as fast as one AB is formed, another AB is broken down
Here is the first question for your portfolio of 5GLUCOSEThis is the only ‘food’ which the cell uses.The molecule is made up of:6 carbons, 12 hydrogens and 6 oxygensFollowing the rules about electron shells, how would you combineallthe C, H and O atoms to make a single glucose molecule?Hint: All the carbon atoms are maximally saturated. (There are no double bonds between the carbon atoms).Ask yourself:How many electrons does carbon have? Oxygen? Hydrogen?Pleaseshow your reasoningto demonstrate how you think the 24 atoms can be combined to make a single molecule of GlucoseAnswers copied from text books, without your individual explanations ofhowyou arrive at a structure, will score zero marks
WHAT ARE ENZYMES?Most chemical reactions in cells DO NOT OCCUR SPONTANEOUSLY. They are too slow.REACTANTShave to beactivatedbefore a reaction will start and proceed to givePRODUCTSThe energy required tostarta reaction is called theACTIVATION ENERGYWhat do enzymes do?They LOWER the activation energy required, so a reaction can start much more easily when an enzyme is present.Enzymes control theRATEof aReversiblereaction
REVERSIBLE REACTIONWe now write it asE+FEFEach type of reaction has itsOWNenzymeEnzymesareveryspecific proteinswhichCATALYSEreactions,ie. Make them go fasterFACT:Because they are proteins, enzymes aredenatured (killed)if the reaction temperature reaches 40degC
Not surprisingly,ideal temperature for enzyme reactions is35 – 37degCAs you all know, NORMAL body temperature is37 - 38.6degCLet’s look at Enzyme Activity in the context of temperature:
Reactions and Energy:EXERGONICreactionsreleaseenergy as heat:Maintain your body temperature
Metabolic PathwayOften, several compounds, (A,B,C and D) take part in a connected pathway with different enzymes controlling each step.ABCDENZ 1ENZ 2ENZ 3Each of the different enzymes is determining theRATEof itsreversiblereactionSo, ifENZ 2becomes inactive, then there will be no C produced.Question:If there is no C being produced , what can we conclude about D?What is happening to B? What is happening to A?
EQUILIBRIUMIn this next reaction, the conversion rate of compoundAto compoundFis being controlled by an enzymeA FENZThe enzyme will catalyse the conversion of A to F until an equilibrium has been reachedAt equilibrium, the amount of A will be equal to the amount of FQuestion: If we then artificially poured in some of the compound F to the reaction, and the enzyme kept on working , what would you expect to see happening to A?
Let’s see what happenswhen we start withonlyreactant A , then add some enzyme, and warm to 37degin a test-tube:A + ENZ ??Question:After say 2 minutes at 37 degrees C, what will the reaction look like?What about after 30 minutes, whenequilibriumhas been reached?
WHAT DOES THE ENZYME ACT UPON and HOW?In the previous slide, theREACTANTcalledAis acted upon by anENZYMEAny reactant which an enzyme acts upon is known as aSUBSTRATEAn enzyme acts upon a Substrate bycombiningwith itThis combination of Enzyme and Substrate causes the Substrate to be changed in such a way that a PRODUCT is producedSUBSTRATE+ ENZSUBSTRATE-ENZ COMPLEXPRODUCT+ ENZ
HOW DOES THE SUBSTRATE INTERACT WITH THE ENZYME?The ENZ has a particular area on it called theACTIVE SITETheACTIVE SITEonly fits thatparticularSUBSTRATEAt the end of the reaction, the ENZ is unaltered and ready to bind the next Substrate molecule
So, overall, we can draw the reaction sequence like this:Substratehas been altered by theEnzyme…………………………………... to give aProduct
Which types ofbiochemical substancesare inside the cell?Sugars, = carbohydratesProteinsLipids, = fatsNucleic acids
SUGARS = carbohydratesContain:Carbon,HydrogenandOxygen atomsRatio?1:2:1Example:GlucoseC6H12O6Question: If there were 8 Carbon atoms in animaginarysugar, how many Hydrogens would there be? How many Oxygens? How would you write it?
PROTEINSChains of Amino Acids: A typical protein is made up of 1000 amino acidsContain: Carbon, Hydrogen, Oxygen and NitrogenShapes: Their shapes determine what they doProteins can be 1. Structural components of cells2. Enzymes. These catalyse the reactions that are vital to life.3. HormonesCoded for by: Messenger Ribonucleic Acid. Messenger RNA is coded for by DNA
LIPIDS = FATSContain:Carbon, Hydrogen and Oxygen atoms(Much less Oxygen than a carbohydrate)Ratio:1 : 2 : xTypical lipid might have:C12H24O2Importance to cells: structural components, energy reserves and hormone-precursors
NUCLEIC ACIDSDNA(De-oxy-ribo-NucleicAcid): contains thegenetic code, determines our characteristics as individualsRNA(Ribo-NucleicAcid): takes information from DNA to the ribosomes in the making of ProteinsNucleic acids are very longchainsof nucleotidesDNAis double-stranded, like two helical chains wound around each anotherRNAis single stranded and not helical
Second formative testWhich4types ofbiochemical substancesare components of cells?We know that certain chemical reactions within cells release energy for the cell’s use. What general name is given to energy-generating reactions?A chemical reaction in a test tube can be made to go faster by heating it. But this is not possible in cells. How does the cell speed up reactions without the need for heat?What is Activation Energy?What is an enzyme?Why do our cells need enzymes?A baby is found to have a temp of 39.5degC. Why is this classified as an emergency?Which types of reactions are controlled by enzymes?What do we mean by Equilibrium in an enzyme-catalysed reaction?
ORGAN SYSTEMSIntegumentary=hair, skin, nails, sweat glandsSkeletal=bones, cartilages, tendons/ligaments, marrowMuscular=skeletal muscles
ORGAN SYSTEMSNeural=brain, spinal cord, peripheral nerves, sense organsEndocrine=pituitary gland, thyroid gland, pancreas, adrenal glands, gonadsCardiovascular=heart, blood, blood vesselsLymphatic=spleen, thymus, lymphatic vessels, lymph nodes, tonsils
ORGAN SYSTEMSRespiratory=lungs, nasal cavities, sinuses, bronchi, trachea, larynxDigestive=teeth, tongue, oesophagus, stomach, small intestine, large intestine, liver, gall bladderUrinary=kidneys, ureters, urinary bladder, urethraReproductive=testes, prostate, penis, ovaries, fallopian tubes, uterus, vagina, mammary glands





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Human cell physiology - Open resources