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Biology > Nucleic acids and Enzymes > Flashcards

Nucleic acids and Enzymes Flashcards

1
Q

What are nucleotides

A

-form monomers of nucleic acids DNA and RNA
-in RNA the nucleotide pentose sugar is ribose
-in DNA the nucleotide sugar is deoxyribose
-one phosphate group e.g ADP and ATP is an energy rich end product of most energy releasing biochemical pathways and used to drive energy requiring metabolic processes
-may be components of coenzymes

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2
Q

Describe DNA as a nucleic acid

A

-DNA is found in the nuclei of all eukaryotic cells within cytoplasm of prokaryotic cells and inside some viruses
-it is hereditary material and carries coded instructions used in development and functioning of all known organisms
-DNA is an important macromolecule that makes up the structure of all living organisms, others being proteins, carbohydrates and lipids

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3
Q

Describe structure of DNA

A

-DNA is a polymer as its made up of many nucleotides
-a molecule DNA consists of 2 polynucleotide strands run in opposite directions ‘antiparallel’
-covalent bond between sugar residue and phosphate group is called phosphodiester - these are broken when polynucleotides breakdown and formed when polynucleotides are synthesised
-DNA molecules long and carry encoded genetic information

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4
Q

Purines and pyrimidines

A

PURINES= adenine, guanine
PYRIMIDINES= thymine, cytosine

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5
Q

What is the importance of hydrogen bonds

A

-adenine always pairs with thymine by 2 hydrogen bonds
-guanine always pairs with cytosine by 3 hydrogen bonds
-a purine always pairs with a pyrimidine giving equal sized rungs of DNA ladder
-it can twist around an imaginary axis to form a double helix - gives the molecule stability
-hydrogen bonds allow molecules to unzip for transcription and replication

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6
Q

How is DNA organised in eukaryotic cells

A

-majority of DNA content of genome is in nucleus
-each large molecule of DNA is tightly wound around special histone proteins - each chromosome therefore is a molecule of DNA
-there is also a loop of DNA without histone proteins inside mitochondria and chloroplasts

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7
Q

How is DNA organised in prokaryotic cells

A

-DNA is in a loop and is in within cytoplasm not enclosed in a nucleus
-it is not wound around histone proteins - is described as naked
-viruses that contain DNA also have it in the form of a loop of naked DNA

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8
Q

How is DNA a self replicating molecule

A

-all DNA within a cell (the genome) and within every cell of an organism carries the coded instructions to make and maintain that organism
-every time a cell divides the DNA has to be copied so that each new daughter cell receives full set of instructions
-each molecule of DNA replicates
-this replication takes place during interphase
-in eukaryotes this results in each chromosome having an identical copy of itself
-as first they are joined together by centromere forming two sister chromatids
-the DNA within mitochondria and chloroplasts also replicates each time these organelles divides

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9
Q

Describe semi-conservative replication

A

-to make a new copy, each DNA molecules
-unwinds so the double helix is untwisted a bit at a time, catalysed by gyrase enzyme
-unzips - hydrogen bonds between the nucleotide bases are broken - this is catalysed by DNA helicase and results in two single strands of DNA with exposed nucleotide bases
-free phosphorylated nucleotide present in nucleoplasm within nucleus are bonded to exposed bases following complementary base pairing rules
-the enzyme DNA polymerase catalyses the addiction of new nucleotide base sin the 5’ to 3’ directions to the single strand of DNA; it uses each unzipped DNA stand as a template
-the leading strand is synthesised continuously whereas the lagging strand is in fragments (discontinuous) that are later joined catalysed by ligase enzymes
-hydrolysis of the activated nucleotides to release the extra phosphate groups supplies the energy to make phosphodiester bonds between the sugar residue of one nucleotide and phosphate group of next nucleotide
-the product of replication is 2 DNA molecules identical to each other and parent molecule

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10
Q

Why is it called semi conservative replication

A

-each of the new DNA molecules contains one old strand and one new strand

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11
Q

How do mutations occur

A

-during DNA replication errors may occur and wrong nucleotide may be inserted
-this is estimated to occur 1 in 10^8 base pairs
-this could change genetic code and example of point mutation
-during replication process there are enzymes that can proof read and edit out such incorrect nucleotides reducing rate of mutations produced
-not all mutations are harmful - some appear to give neither advantage or disadvantage - e.g. rolling tongue
-some can be advantageous - white coat in winter for camouflage

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12
Q

RNA structure in comparison to DNA

A

-the sugar molecule in each nucleotide is ribose
-the nitrogenous base is uracil which is pyrimidine, places pyrimidine base thymine
-polynucleotide chain usually single stranded
-polynucleotide chain shorter
-3 forms of RNA - messenger RNA, transfer RNA and ribosomal RNA

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13
Q

What is transcription and translation

A

TRANSCRIPTION
-process of making messenger RNA from DNA template
TRANSLATION
-formation of a protein at ribosomes by assembling amino acids into a particular sequence according to coded instructions from DNA to ribosome by mRNA

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14
Q

What are genes

A

-on each chromosome there are specific lengths of DNA called genes
-each gene contains code that determines sequence of amino acids in particular protein
-some proteins as structural e.g. cytoskeleton where as others are metabolic such as enzymes
-within each gene there is sequence of DNA base triplets that determine amino acid sequence or primary structure of polypeptide
-as long as primary structure correct, it will fold correctly and carry out unction

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15
Q

Why must transcription occur

A

-as instructions inside genes, on chromosomes, cannot pass out of nucleus, a copy of each gene has to be transcribed into length of mRNA
-in this form sequence of base triplets now called codons can pass out of nucleus to ribosome ensuring coded instructions translated and protein assembled correctly

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16
Q

Describe the nature of the genetic code

A

-the genetic code is near universal because in almost all living organisms the same triplets of DNA bases codes for same amino acid
-genetic code described as degenerate because for all amino acids, except two, there is more than one base triplet - this may reduce effect of point mutations as a change in one base of triplet could produce another base triplet that still codes for same amino acid
-genetic code is non overlapping and it’s read from fixed point in groups of 3 bases
-if base added or deleted causes frame shift as every base triplet is changed

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17
Q

Describe transcription

A

-a gene unwinds and unzips
-hydrogen bonds between complementary nucleotide bases break
-enzyme RNA polymerase catalyses formation of temporary hydrogen bonds between RNA nucleotides and complementary unpaired DNA bases
-A to T, C to G, U to A on one strand of unwound DNA
-this stand called template strand
-length of RNA that is complementary to template strand of gene produced
-it is therefore copy of other DNA strand - coding strand
-mRNA now passes out of nucleus through nuclear envelope and attaches to ribosome

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18
Q

How are ribosomes made

A

-ribosomes made in nucleolus in two smaller subunits
-these pass separately out of nucleus through pores in nuclear envelope then come together to form ribosome
-magnesium ions help bind two subunits together
-ribosomes made of ribosomal RNA and protein

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19
Q

Describe translation

A

-transfer RNA molecules are made in nucleolus and pass out of nucleus into cytoplasm
-they are single stranded in polynucleotide
-at one end of trionucleotide base that recognises and attaches to specific amino acid
-at loop of hairpin is another triplet of bases called anticodon that is complementary to specific codon

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20
Q

Describe translation at ribosome

A

-transfer RNA bring amino acids and find place when anticodon binds by temporary hydrogen bonds to complementary codon on mRNA
-as ribosome moves along length of mRNA it reads code and when two amino acids adjacent to each other a peptide bond forms
-energy from ATP needed for polypeptide synthesis
-amino acid sequence for polypeptide determined by sequence of triplet nucleotide bases on length of DNA - gene
-after polypeptide assembled mRNA breaks down- its component molecules can be recycled into new lengths of mRNA with different codon sequences
-newly synthesised polypeptide helped by chaperone proteins to fold correctly into 3D shape or tertiary structure to carry out functions

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21
Q

What are enzymes

A

-enzymes are biological catalysts as they speed up metabolic reactions
-at end they remain unchanged and reusable
-small amount catalyst can catalyse conversion of large number of substrate molecules to product molecules
-number of reactions that enzyme can catalyse per second is turnover number

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22
Q

Compare biological and chemical catalysts

A

-chemical enzymes usually need very high temperatures, increased pressures and extreme pH where as biological enzymes speed up metabolic reactions by up to 10^12 times at lower temperatures, neutral pH and normal pressure - hence can function in conditions that sustain life
-enzymes more specific than chemical catalysts
-do not produce unwanted by products and rarely make mistakes
-cells in which they are made and/or act can regulate their activity and production

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23
Q

How does enzyme structure determines function

A

-for enzymes to catalyse some reactions they may need help from cofactors
-the instructions for making enzymes are encoded in genes
-if gene has mutation that alters the sequence of amino acids in the protein then this may alter enzymes tertiary structure and prevent it from functioning
-if enzyme catalyses formation of organisms structural components such as collagen in bone, cartilage, blood vessel walls, joints and connective tissue
-genetic disorders cause malformation of connective tissue and can be very harmful such as stone man syndrome

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24
Q

Describe the active site of enzymes

A

-enzymes are large molecules with specific area, an indentation or cleft on surface of molecule called active site
-this consists of just few amino acids
-tertiary structure of active site is crucial as its shape is complementary to shape of substrate molecule
-each type enzyme is highly specific in its function as it can only catalyse reaction involving particular type of substrate molecules
-shape of enzymes active site can be altered by changes in temperature and pH as these affect tertiary structure

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25
Q

Describe intracellular enzymes

A

-each metabolic pathway in living cell is series of consecutive reactions, catalysed by specific enzyme that produces specific product
-various reactants and intermediates act as substrates for specific enzymes
-the reactants, intermediates and products are known as metabolites
-in some metabolic pathways described as anabolic, energy used to synthesis larger molecules from smaller molecules
-in others, described as catabolic, metabolites broken down to smaller molecules and release energy

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26
Q

What is catalase

A

-found in nearly all living organisms that are exposed to oxygen
-it is a very important enzyme as it protects cells from damage by reactive oxygen by quickly breaking down hydrogen peroxide, a potentially harmful by product of many metabolic reactions to water and ocygen
-catalase consists of four polypeptide chains and contains a haem group with an iron
-in eukaryotic cells, catalase is found inside small vesicles called peroxisomes
-then white blood cells ingest pathogens they use catalase to help kill invading microbe
-the optimum pH for human catalase is around pH 7

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27
Q

Describe extracellular enzymes

A

-some enzymes are secreted from the cells where they are made and act on their substrates extracellularly
-fungi such as bread mould release the hydrolytic enzymes from their thread-like hyphae enzymes digest carbohydrates, proteins, and lipids in bread
-glucose, amino acids, glycerol and fatty acids are absorbed into the fungal hyphae for use in respiration and growth

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28
Q

Describe digest enzymes

A

-in our digestive system many enzymes are secreted from cells lining the alimentary canal into the gut lumen
-they extracellularly digest the large molecules such as proteins, lipids, carbohydrates and nucleic acids found in food
-the products of digestion are then absorbed via epithelial cells of gut wall into bloodstream in order to be used for respiration, growth and tissue repair
-amylase is produced in the salivary glands and acts in the mouth to digest the polysaccharide starch to disaccharide maltose
-it is also made in the pancreas and acts to catalyse the same reaction in the lumen of the small intestine
-trypsin is made in the pancreas and acts in the lumen of the small intestine to digest proteins into smaller peptides by hydrolysing peptide bonds
-its optimum pH is between 7.5-8.5

29
Q

Steps of translation

A

-transfer RNA (tRNA)
-made in the nucleus and passes into the cytoplasm through nuclear pore
-tRNA brings amino acids to form polypeptide chain
-peptide bonds form between amino acids
1) anticodon binds with temporary H bonds to the codon
2) peptide bond forms between 2 amino acids
3)ATP required
4) DNA triplet - mRNA codon- tRNA codon - amino acid sequence
5) secondary/tertiary structure depends on correct sequence

30
Q

What is the lock and key hypothesis

A

-the substrate molecules fit to the active site due to the tertiary structure of the active site; gives it a shape that is complementary to that of substrate molecule
-this idea about how enzymes work is called lock and key hypothesis

31
Q

Steps of lock and key hypothesis

A

1) substrate molecule fits into enzyme active site. Temporary hydrogen bonds hold 2 together and form enzyme substrate complex
2) substrate molecule is broken into smaller product molecules that leave active site
3)substrate molecules fit into the active site forming an enzyme-substrate complex
4) bonds form between substrate molecules and form enzyme product complex
5)larger product molecule leaves active site

32
Q

Describe the induced fit hypothesis

A

-the active site still has a shape complementary to shape of substrate molecule; on binding the subtle changes of shape of side chains of amino acids that make up active site give a more precise conformation that exactly fits substrate molecule
-this moulding enables substrate to bind more effectively to active site
-an enzyme substrate complex is formed and non covalent forces such as hydrogen bonds, ionic attractions, hydrophobic interactions bind the substrate molecule to active site
-when substrate molecule have been converted to product molecules and these are still in the active site, they form an enzyme product complex
-as product molecules have a slightly different shape from substrate molecule, they detach from active site
-the enzyme molecule is now free to catalyse another reaction with another substrate molecule of same type

33
Q

Who developed the induced fit theory

A

-1958, Daniel Koshland modified lock and key hypothesis by suggesting active site of enzymes is not rigid, fixed structure but that presence of substrate molecule induces a shape change, giving it good fit
-suggested that: when substrate molecules fit into the enzymes active site, the active site changes shape slightly to mould itself around substrate molecule

34
Q

How do enzymes lower activation energy of a reaction

A

-chemical reactions need energy to activate/ begin
-many chemicals can use heat- this increase kinetic energy of molecules so move more and therefore more likely to successfully collide and react together
-in living cells the temperature cannot be raised too much or proteins within it denature and lipids melt
-because enzymes have active specific to only substrate molecules they bring substrate molecules close enough together to react without need of excessive heat
-therefore lower activation energy and hence speed up metabolic reactions

35
Q

How does heat effect kinetic energy

A

-it substance is heated-
-extra energy in form of heat cause molecules to move faster
-increase rate of collisions between molecules
-also increases force with which collide due to moving faster

36
Q

How does temperature effect the collisions between enzymes and substrate molecules

A

-if reactant mixture containing enzyme and substrate heated
-both types molecule gain kinetic energy and move faster - increase rate of successful collisions
-rate of formation of ES complexes increase and rate of reaction increases - increase number of enzyme-product complexes per second up to a point
-at particular temperate (enzymes optimum temperature) rate of reaction is at its maximum

37
Q

How is vibration effected by heat

A

-this may make some of weak bonds break such as hydrogen and ionic that hold tertiary structure of enzymes active site
-as active site changes, substrate molecules that will not fit in so well and rate of reaction begins to decrease
-as more heat applied, enzymes active site changed completely and irreversible so its no longer complementary reaction cannot proceed at all
-enzyme is denatured - heat doesn’t break peptide bonds between amino acids so primary structure is not altered

38
Q

Describe the optimum temperature

A

-temperature at which enzyme works best - maximum rate of reaction
-some enzymes work best at cool temperatures - for example psychrophilic bacteria
-some organisms, like thermophilic bacteria in hot springs live at very high temperatures
-their enzymes are heat stable due to more disulfide bonds that do not break with heat and keep shape of protein molecules stable

39
Q

What is the temperature coefficient Q10

A

-refers to increase in rate of process when temperature increased by 10 degrees
Q10= rate of reaction at T+10/ rate of reaction at T

40
Q

What is pH

A

-pH indicates whether substance acidic, alkaline or neutral
0-6= acidic
7=neutral
8-14=alkaline
-acids such as hydrochloric acids and sulfuric acids dissociated into protons and negatively charged ion
-organic acids are also proton donors -
-lactic acids dissociates into H+ and lactate
-pyruvic acid dissociates into H+ and pyruvate

41
Q

Describe buffers

A

-a buffer is something that resists changes in pH
-there are certain chemicals in blood that help resist changes in pH so it stays close to 7.4
-they donate or accept hydrogen ions

42
Q

How do changes in pH affect molecule bonds

A

-a hydrogen ion has a positive charge so it is attracted towards negatively charge ions. molecules or parts of molecules
-hydrogen bonds and ionic forces between amino acids hold tertiary structure of an enzyme, particularly active site, in correct shape
-excess hydrogen ions will interfere with hydrogen bonds and ionic forces so active site changes shape
-if substrate molecule doesn’t fit well to active site, rate of reaction that enzyme catalyses will be lowered
-increasing concentration of hydrogen ions will also alter changes on active site of enzyme molecules as more protons will cluster around negatively charged groups in active site- this interferes with binding of substrate to active site
-hydrogen bonds hold structures like an alpha helix in place in protein molecules

43
Q

Why can there only be narrow changes in pH

A

-small changes of pH either side of the optimum, slow rate of reaction because shape of active site is disrupted
-however if normal optimum pH restored, hydrogen bonds can reform and active site shape is restored
-extremes of ph, the enzymes active site may be permanently changed- when enzyme is thus denatured it cannot catalyse the reaction

44
Q

How do different enzymes have different optimum pH

A

-intracellular enzymes=optimum close to 7
-during digestion amylase enzymes that digest starch to maltose work best at pH 6.8
-as food passes to stomach, hydrochloric, acid is secreted giving a very low pH- one of acids function is to kill pathogens
-the protease enzyme pepsin works best at pH levels between 1-2; it digests large protein molecules into smaller peptide molecules
-as partly digested food moves into small intestine, salts in bile (made in liver) neutralise it and raise pH to around 7.8
-this optimal for protein digesting enzymes trypsin and enterokinase that catalase further digestion of peptides to amino acids

45
Q

Effect of substrate concentration on rate of enzyme-catalysed reactions

A

-when substrate concentration increases the rate of reaction increases
-because more enzyme-substrate complexes can form
-as a result the more product molecules formed
-substrate concentration is limiting the reaction because as it increases, the rate of reaction is increasing
-however any further increases will cause the maximum rate to be met
-adding more substrate molecules to increase substrate concentration will not increase rate of reaction
-because all enzymes active site are occupied with substrate molecules
-if more substrate molecules added, they cannot successfully collide with and fit into enzymes active site

46
Q

What does the availability of enzymes depend upon

A

-enzyme synthesis=gene coding for particular enzymes can be switched on or off
-enzyme degradation=quantity of enzymes can be regulated by digesting old enzymes

47
Q

Types of cofactors

A

-prosthetic group= carbonic anhydrase, Zn2+
-inorganic ions= amylase, Cl-
-coenzymes= NAD, NADP, ATP

48
Q

What are the advantages of enzyme degradation

A

-elimination of abnormally shaped proteins that might otherwise accumulate and harm cell
-regulation of metabolism in cell by eliminating any superfluous (surplus to requirement) enzymes
-therefore for cell to regulate its metabolism properly, the control of enzyme degradation is equally as important as enzyme synthesis

49
Q

What is the effect of increasing enzyme concentration on rate of reaction

A

-more active sites of enzymes becomes available
-more successful collisions between substrate and enzymes occur
-more enzyme substrate complexes (ESC) can form per unit time so rate of reaction increases
-enzyme concentration is the limiting factors- as it increases so does the rate of reaction
-if the substrate concentration is fixed of limited all the substrate molecules is occupying an active site or will have occupied and active site and been releasing product molecules
-the reaction is at maximum rate for fixed substrate concentration
-if enzyme concentration increase further there will be no increase in rate because active site of extra enzymes will not be occupied by substrate molecules
-enzyme concentration is no longer limiting factor - substrate concentration is

50
Q

What is the initial rate of reaction

A

-at beginning of a reaction, when enzyme and substrate molecules are first mixed and are moving randomly, there is great chance of substrate molecule successfully colliding with an enzymes active site
-as reaction proceeds substrate molecules are used up as they are converted to product molecules so concentration of substrate drops
-as a result, the frequency of successful collisions between enzymes and substrate molecules decrease because some enzymes may collide with product molecules so rate of reactions slows down
-thus initial rate of reaction gives maximum rate for an enzyme

51
Q

What are cofactors

A

-some enzymes, particularly those involved in catalysed oxidation-reduction reactions can only work if another small non protein molecule is attached to them
-they are called cofactors
-they help ensure the reaction takes place at the appropriate time

52
Q

COFACTORS: prosthetic groups

A

-a cofactor that is permanently bound, by covalent bonds, to an enzyme molecule is called a prosthetic group
-enzyme carbonic anhydrase contains a zinc ion permanently bound as a prosthetic group to active site
-this enzyme is found in erythrocytes and catalyses the interconversion of carbon dioxide and water to carbonic acid which then breaks down to protons and hydrogencarbonate ions
-this reaction may proceed in either direction, depending on concentration of substrate or product molecule
CO2+ H2O—carbonic anhydrase—H2CO3 -H+ + HCO3
-the reaction is vitally important as it enables carbon dioxide to be carried in the blood from respiring tissues to the lungs

53
Q

COFACTORS: mineral ions

A

-some enzymes work better in the presence of ions that are not permanently bound to them
-during an enzyme catalysed reaction, the enzyme and the substrate molecules temporarily bind together to form an enzyme substrate complex
-the presence of certain ions may temporarily bind to either substrate or enzyme which may ease formation of ESC and therefore increase the rate of reaction
-some cofactors act as co-substrates- they and the substrate together form correct shape to bind to active site of enzyme
-some cofactors change charge distribution of surface of substrate molecule or on surface of enzyme active site and make temporary bonds so ESC easier to form

54
Q

COFACTORS: coenzymes

A

-coenzymes are small organic non protein molecules that bind temporarily to active site of enzyme molecules either just before or at same time the substrate binds
-the coenzymes are chemically change during reaction and need to be recycled to original state, sometimes by a different environment

55
Q

Vitamin sources of coenzymes

A

-B12- cobalamin- pernicious anaemia
-folic acid-tetrahydrofolate-megablastic anaemia
-B3 - NAD, NADP- pellagra
B1-thiamine pyrophosphate- beriberi

56
Q

What are inhibitors

A

-substances that reduce activity of an enzyme
-they do this by combining with the enzyme molecule in a way that influences how substrate binds to enzymes or effect enzyme turnover number
-some may block active site and some change shape of active site
-both inhibit formation of ES complexes and therefore product formation

57
Q

What are competitive inhibitors

A

-they have similar shape to substrates
-they fit into active site so substrate cannot fit
-amount of inhibition depends on relative concentration of substrate and inhibitor molecules - more inhibitor molecules means more inhibitors collide with active sites so effect of inhibition greater
-increasing substrate concentration ‘dilutes’ effect of inhibitor- if enough substrate added, inhibitor unlikely to collide with enzyme

58
Q

Describe the mechanism of competitive inhibitors

A

-compete directly with substrate molecules for a position on enzymes active site forming enzyme-inhibitor complexes that are catalytically inactive
-once on active site, inhibitor is not changed by enzyme as normal substrate molecule would be
-presence of inhibitor prevents substrate molecules from joining to active site- this reduces rate of formation of ESCs and product molecules
-a competitive inhibitor reduces the number of free enzyme active sites available for substrate to bind and form ESC
-most enzyme inhibition by competitive inhibitors is reversible
-as collisions between enzyme and substrate or inhibitor molecules are random, increasing substrate concentration would reduce effect of reversible competitive inhibition as there would be more chance of enzyme colliding with substrate than inhibitor
-if competitive inhibitor binds irreversibly, known as inactivator

59
Q

Describe non competitive inhibition

A

-binds somewhere other than active site
-do not compete with substrate molecule for place on enzymes active site
-they attach to enzyme molecule in region (allosteric site) away from active site and in doing so, disrupt enzyme tertiary structure and changes its shape
-this distortion changes shape of active site so no longer complementary to shape of substrate molecule and substrate molecule cannot bind to enzymes active site - ESC cannot form
-the maximum rate of reaction is reduced by presence of non competitive inhibitors
-adding more substrate might allow reaction to attain this new lower rate, but even very high concentrations of substrate will not allow rate of reaction to return to uninhibited maximum
-the more inhibitor molecules present=greater degree of inhibition because more enzyme molecules distorted and cannot form ESC
-can bind reversibly or irreversibly

60
Q

What is end product inhibition

A

-one way which enzyme catalysed reactions may be regulated it by end product inhibition
-after the catalysed reaction has reached completion, product molecules may stay tightly bound to enzyme
-in this way, enzyme cannot form more of the product than the cell needs
-for example, negative feedback

61
Q

Describe the control of metabolic sequences

A

-the product of one enzyme catalysed reaction becomes the substrate for the next enzyme catalysed reaction in metabolism
-cells do not need to accumulate too much of end product, so product of last enzyme catalysed reaction in metabolic pathway may attach to part of first enzyme in pathway but not active site
-this binding changes shape of enzyme active site, preventing pathway from running
-this is reversible, non competitive inhibition
-when the concentration of this product with cell falls, molecules will detach from enzyme 1 and allow its active site to resume normal shape, the metabolic pathway can run again

62
Q

What are multi enzyme complexes

A

-multi enzyme complexes increase the efficiency of metabolic reactions without increasing substrate concentration as they keep enzyme and substrate molecules in same vicinity and reduce diffusion time
-many metabolic reactions are carried out in particular regions or organelles in cells
-this also increases efficiency of metabolism
-some enzymes within organelles are bound in organelle membranes

63
Q

POISON: cyanide

A

-potassium cyanide KCN is highly toxic because it inhibits aerobic respiration- also inhibits catalase
-when ingested KCN is hydrolysed to produce hydrogen cyanide a very toxic gas that can readily dissociate into H+ and CN- ions
-the CN- ions bind irreversibly to enzymes found in mitochondria and inhibit final stage of aerobic respiration
-because final stage is inherited, early stages cannot run and aerobic respiration stops

64
Q

POISON: snake venom

A

-the venom of green mamba snake contains a chemical that inhibits the enzyme acetlycholinesterase AChe
-this enzyme is important at neuromuscular synapses to break down the neurotransmitter acetylcholine ACh
-if this enzymes is inhibited the ACh stays attached to the receptors on the muscle membrane and keeps muscle contracted
-this causes paralysis as movement depends on muscles being able to contract and relax alternately
-if muscles involved in breathing are paralysed then victims die from suffocation

65
Q

DRUGS: aspirin

A

-drug that has been used for over 3000 years and marketed as aspirin since late 19th century
-1971, Professor John Vane and team discovered salicylic acid binds to enzymes that catalyse formation of prostaglandins
-thus it prevents the formation of prostaglandins that are cell signalling molecules produced by cells when tissues are infected or damaged
-prostaglandins make nerve cells more sensitive to pain and increase swelling during inflammation
-aspirin can also reduce risk of blood clots forming in blood vessels and many people take low dose to reduce risk of strokes
-children under 12 should not take aspirin as it can damage stomach lining

66
Q

DRUGS: ATPase inhibitors

A

-extract from purple foxglove leaves have been used to treat heart failure and atrial arrhythmia (abnormal atrial heart beat)
-chemicals identified as cardiac glycosides also known as digitalis, digitoxin, digoxin
-they inhibit sodium potassium pump in cell membranes of heart muscle cells and allow more calcium ions to enter cell
-calcium ions increase muscle contraction and this strengthens heartbeat

67
Q

DRUGS: ACE inhibitors

A

-medical drugs that inhibit angiotensin converting enzyme which normal operates in metabolic pathway that ultimately increases blood pressure used for:
-lower blood pressure in patients with hypertension who cannot take beta blockers
-treat heart failure - a low dose given at first and patients blood pressure is checked in case it falls too low
-minimise risk of a second heart attack or stroke in patients who suffered myocardial infarction

68
Q

DRUGS: protease inhibitors

A

-protease inhibitors such as amprenavir and ritonavir used to treat some viral infections
-they prevent replication of virus particles within host cells by inhibiting protease enzymes so that viral coats cannot be made
-these inhibitors often inhibit viral protease enzymes by competitive inhibition

69
Q

DRUGS: nucleoside reverse transcriptase inhibitors

A

-many of antiviral drugs such as abacavir and zidovudine used to treat patients who are HIV positive are nucleoside reverse transcriptase inhibitors
-they inhibit enzymes involved in making DNA using viral RNA as templates

Biology (16 decks)

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