Cell Biology and Biochemistry for Veterinary Science and Agriculture (TV1102:03)

12/06/2024, 00:29 Lecture notes, lecture All



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Semester'1'2015' Subject:'TV1102' ' 1' '
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Topic:'Cell'Structure'&'Function' ' ' Date:'Tuesday'24/2/15'
Life'–'The'Science'of'Biology:'Chapter(5(–(Cells:(the(working(units(of(life(pgs(78(8103(
(
5.1:(What(features(make(Cells(the(fundamental(units(of(life?(
(
Cell(Theory:(
(
• 100(years(after(Hooke’s(discovery(of(“cells”(their(importance(is(not(fully(understood(
• 1838(–(M.(J(Schneider(and(Theodore(Schwann(independently(proposed(the(‘Cell(Theory’(of(
life.(Both(postulated(that(ALL(life(is(composed(of(cells(
• The(cell(theory(states:(
1. Cells(are(the(fundamental(units(of(life(
2. All(living(organisms(are(composed(of(cells(
3. All(cells(come(from(pre8existing(cells(
• Cells(contain(70%(water(and(other(small(and(large(molecules(
• The(cell(theory(has(three(important(applications:(
1. Principles(that(underlie(the(functions(of(a(single(cells(of(bacterium(are(similar(to(those(
governing(multi(cellular(organisms(
2. Life(is(continuous.(
3. The(origin(of(life(on(earth(was(marked(by(the(origin(of(the(first(cells(
(
Cell(size(is(limited(by(SA:V(ratio(
(
• Volumes(of(cells(range(from(1(–(1000um3(
• Small(cell(size(is(a(necessity(arising(from(the(change(in(SA:V(ratio(of(any(object(as(it(increases(
in(size(
• As(an(object(increases(in(V,(it(also(increases(in(SA(but(in(a(different(ratio.(This(phenomenon(
has(biological(significance(for(two(reasons:(
1. V(of(a(cell(determines(the(amount(of(chemical(activity(it(carries(out(
2. SA(of(a(cell(determines(the(amount(of(substances(that(can(enter(ut(from(the(outside(
enviro,(and(the(amount(of(waste(products(that(can(exit(
• As(a(living(cell(grows(larger,(chem(activity(increases(faster(than(its(SA.(Substances(must(also(
move(from(one(site(to(another.(Therefore,(the(smaller(the(cell,(the(more(efficiently(processes(
occur.(
(
(
(




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Semester'1'2015' Subject:'TV1102' ' 2' '
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Microscopes(reveal(the(features(of(Cells:(
(
• Living(things(are(either:(
8 Unicellular((
8 Multicellular((
• Microscopes(do(two(things:(
1. Magnify(–(increase(the(size(of(the(object(
2. Resolve(–(increase(resolution 1(so(that(cells(an(their(internal(structure(can(be(seen(clearly((
• There(are(two(basic(types(of(microscopes:(
8 Light(microscopes(
8 Electron(microscopes(
(
Light(microscopes:(
(
• Most(commonly(encountered(microscope(in(bio(
• Light(passes(through(the(specimen(
• Lenses(magnify(the(image(
• Modern(compound(microscopes(have(one(lens(in(eyepiece(
and(another(lens((objective)(near(specimen(
• Glass(lenses(and(visible(light(are(used(to(form(an(image(
• Resolution(is(about(0.2um,(which(is(1000(x(greater(than(that(
of(the(human(eye(
• Allows(visualisation(of(cell(size(and(shapes(and(some(internal(
structures(
• Internal(structures(are(hard(to(see,(so(cells(are(often(
chemically(treated(and(stained(with(various(dyed(to(make(
certain(structure(stand(out(

(




!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
1!Resolution!is!defined!as!the+minimum+distance+two+objects+can+be+apart+and+still+be+seen+

as+two+objects!




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Semester'1'2015' Subject:'TV1102' ' 3' '
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• Total&magnification&=&eye&piece&magnification&X&objective&magnification(
(
Electron(microscopes:(
(
• Electromagnets(are(used(to(focus(an(electron(beam(
• Electron(microscope(directs(electrons(through(a(vacuum(at(a(fluorescent(screen(or(
photographic(film(to(create(a(visible(image(
• Resolution(is(about(2nm,(100000(x(greater(than(the(human(eye(
• Resolution(permits(the(details(of(many(subcellular(structures(
• Only(dead,(dehydrated(cells(are(visualised.(Therefore,(the(prep(of(cells(may(alter(them,(and(
this(must(be(taken(into(account(when(interpreting(images(
• There(are(three(main(types(of(electron(microscopes:(
1. Transmission(electron(microscopy((TEM)(
2. Scanning(electron(microscopy((SEM)(
3. Freeze8fracture(microscopy(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(




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Semester'1'2015' Subject:'TV1102' ' 4' '
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SEM:(
• A(beam(of(electrons(is(produced(at(the(top(of(the(microscope(
• Magnets(and(coils(are(used(to(focus(the(beam(
• Directs(electrons(to(the(surface(of(the(sample,(where(they(
cause(other(electrons(to(be(emitted.(These(electrons(
(backscattered(and(secondary(electrons)(are(ejected(and(
detected(to(produce(an(image(
• Three8dimensional(surface(of(the(object(can(be(visualised(
• Sample(must(be(coated(with(a(metal(–(E.g.(gold(or(platinum(–(
to(make(the(electrons(bounce(off(
(
(
(
(
(
(
(
(
(
TEM:(
• Looks(‘through’(the(cell(
• A(beam(of(electrons(is(produced(at(the(top(of(the(
microscope(
• A(beam(of(electrons(is(focused(on(the(object(by(
magnets(and(coils(
• Electrons(pass(through(a(VERY(thinly(sliced(sample((~(
100nm(=(0.1um)(
• Objects(appear(darker(if(they(absorb(electrons(
• If(the(electrons(pass(through(they(are(detected(on(a(
fluorescent(screen((
• Samples(must(be(specifically(prepared(to(contain(
electron8absorbing(metal(salts(
(
(
(
(
(
(
(
Freeze8Fracture(Microscopy:(
(
• Cells(are(frozen(and(then(a(knife(is(used(to(crack(them(open.(
• The(crack(often(passes(through(the(interior(of(plasma(and(internal(membranes(
• The(“bumps”(that(appear(are(usually(large(proteins(or(aggregates(embedded(in(the(interior(
of(the(membranes( (




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