Download Worksheet 4 Structure and function of protein molecules qa chi

ANDFUNCTION
OF PROTEINS
Worksheet
4 STRUCTURE
Worksheet4
15
Structure and function of protein molecules
Protein moleculesare large polymers made up of gbout 20 common building blocks called amino acids
linked together. Organisms typically, have thousandsof thesemolecules.Humans are thought to have
different proteins, each one with a unique three-dimensional structure that is
between 50,000-100,000
critical for its particular function. Proteins can be placed into 2 main groups, fibrous or strucfural
proteins, and globular proteins.
Protein structure can be studied at four levels
o Primar! structure - the sequenceof amino acids linked by peptide bonds. Each protein is characterised
by its own unique number, type and sequenceof amino acids.Typically proteins are made up of
hundreds to thousands of amino acids,haemoglobin, a transport proteiry is some 400 times bigger in
size than a glucose molecule.
. Secondary
structure - the coiling or folding of the polypeptide chain.
. TertiarAstructure - the three-dimensional strucfure, which is important for binding.
c Quaternarystructure - applies to those proteins with more than one polypeptide strand.
It is the tertiary structure of each specific protein that determinesits specific function. If the delicatethreedimensional shapeof a protein is altered, it usually follows that the function of that protein is also
inhibited, this is called denaturation. The diagram below gives a diagrammatic representationof the
different levels of structure in a molecule of haemoglobin which is a protein found in blood.
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PRIMARY
STRUCTURE
SECONDARY
STRUCTURE
TERTIARY
STRUCTURE
QUATERNARY
STRUCTURE
The structural proteins are more fibrous in nature and tend to have repeating units of amino acid
sequences/whereas the globular proteins eachhave their own unique sequencesgiving them their
particular shapethat is so vital for their function.
Types of proteins.
Proteinscan be placed into groups depending on their particular roles in the organism.
Structural
Examplesinclude those that make up ligaments and tendons, while others assistin movemen! for
example muscle proteins. Keratin is an important structural protein found in organisms, it makes up the
outer layer of skin, and is the main component of hair, nailt wool, beaks and feathers.Proteins
embedded in the cell membrane are vital for the efficient functioning of cells.Somehave roles in acting as
channelproteins allowing certain molecules to enter or leave cells,but not others. Other proteins act as
receptor proteins that can bind to chemicalslike hormones, and thus bring about a particular response.
Defence
Specificprotein molecules,called antibodies, ar€ releasedfrom white blood cells and have a role in the
inactivation and destruction of foreign antigen moleculesthat may invade our tissues.The unique shape
of the protein antibody means that the action of each antibody is specific for a particular antigen; one
particular antibody can only bind with and inactivate one particular antigen.
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@ Cri"ri" e. and GreigD.2008 Att rightsarereseraed,
16
SACE 2 BIOLOGYEssentialsWORKBOOK
Communication
Certain molecules,including some hormones, bring about their specific action by binding to other
molecules.When the hormone insulin binds to receptor proteins in the cell membrane, the cell membrane
increase its permeability to glucose and the cell takes up more glucose to store as glycogen. The diagram
below represents the binding of a hormone to a surface receptor.
Hormonemessenger
molecule
Receptor
moleculeembedded
intothe bi-lipidlayerof
cellmembrane
Bindingleads to activation
Transport
Haemoglobin is a protein molecule found inside human red blood cells.It has a specific role in the
transport of oxygen molecules to the tissuesof the body. The particular shapeof the molecule makes it
ideal for the reversible binding that occurs with oxygen.
The controlof metabolicreactions.
All reactionsinside cells need specific enzyme moleculesto ensure that they proceed. Enzymes are
protein moleculeswith a specific shapethat is critical for the binding of the reactant or substrate
molecules.The three dimensional shapeof the protein gives rise to an active site on the enzyme where an
induced fit binding occurs.
1. Write a concisestatement to explain eachof the following terms:
antibody
arttigen
complementary
strand
denature
enzyrne
haemoglobin
hormone
insulin
polypeptide
protein
surfacereceptor
@ Crierie A. and'Greig D. 2008 AII rights are reseraeil,copying is prohibited by law,
ENZ/IAE5
upo chemicolreoctionby reducingthe omountof
that Speeds
A CATALISTis o substonce
(proteins
ACTIVATIONENER6yneededtostort thot reoction.ENZ/MESore the biologicslmolecules
or RNA)thot oct os cotolystsin o livingorgonism'
to releaseenergYis octuollyo seriesof
simpleoct of breokingdownfood molecules
Theseemingly
wouldnot be
to speedupthesereoctions,energY
reoctions.Without enrymes
dozensofchemicol
duringthe
ore not chonged
Enzymes
to supportoll but the smollestorgonisms.
enough
releasedfost
chemicolreoctionsthot they expedite- so they conbe reusedoverondovercgain'
.LOCKAND KEY,,,IAODEL
OF ENZ/AAEACTION
o keythot is just
Whenyougohomeqt nightondthe dooris locked,conit openitself?Nope.Youneed
workin o similorwoy'
the right shopeto f it in tnot lock.otherwiseyou'restuckin the cold.Enzymes
completevery specificjobs onddo nothingelse.TheyareverYspecificlocksondthe
Enzyrnes
they workwith ore the speciolkeys'
compounds
Thereorefour stepsin the Processof onenzymeworking'
thot the
o 5UBSTRATEore in the ssmeoreo.Thesubstroteis the biologicolmolecule
(1)An enzymeand
willworkon.
enzyme
ontothe substrotewith q specioloreocolledthe ACTIVESrTE.Theoctivesite is
(z) The enzymegrobs
keyholeof
o speciollysnopeaoreoof the enzymethotf its oroundfhe substrote.The octivesite is the
the lock.
It couldbe broken
Cotolysisis whenthe substroteis chonged.
(3) A processcolledcATALysrS hoppens.
new.
to mokesomething
with onothermolecule
downor combined
lets go,it returnsto normol,readyto doanother
go.Bigideo- Whanthe enzyme
(a) The enzymelets
reoction.Thesubstrot" iJno longerthe some.Thesubstroteis nowcolledthe PRoDUCT.
5ubstrate
Activesite
entering
Substrate
activesiteof enzyme
EnqymechangesshaPe
slightlyas substratebinds
€==-=-+
leaving
Froducts
Enzyme/substrate Enzyme/products
of
enzyme
site
active
complex
complex
INDUCEDFIT AAODEL
OF ENZy,IAEAcTIoN
The inducedfit modelof enzyme
octionexpondsonthe lockcnd keymodelby showingthot the shopeof
fhe enzyme
chonges
whenthe substroteottochesto the activesite. The chongein tle shopeof the
enzymecousessomeof the bondsin the substroteto weoken- lessening
the octivotionenergyneeded
to
breokthe bondsondstort the reoction.As with the lockandkeymethod,the ennlmereturnsto its
originofshopeafter releasing
the productsqndconbe usedogoin.
htbi!m{*
,*,ffi
huluc*d fit
ENZYAAE5
AND THEIR ENVTRONAAENT
An enzyme
moynot workif it's environment
is chonged.Bothmodetsof enzymeoctiondependonon
exoctfit between
the octivesiteof onenzyme
ondthe substroteto whichit binds.If onythingwereto
blockthe octivesite or chongethe shopeof the protein(enzyme),
it couldpreventthe enzyme?.ot
workingproperly
(1) TEiAPERATURE:
Proteins(includingenzymes)
chongeshopeos temperotures
chonge.Just think of whot hoppens
to on
egg(mostlyprotein)osyoucookit or yourhoir(protein)whenyouuseo curlingiron. Becouse
so muchof
on enzyme'
s octivityis bosedon its shope,temperoturechonges
conmessupthe processondthe enzyme
won'twork.
(2) pH LEVELS:
fn the samewoytho'ttemperotureconchongethe shapeof proteins,the ocidityof the environment
doesthe something.Remember
thot the pH is o meosur
e of howocidicor bosicsomethingis.
'
(3) rNHrBrToRS:
fnhibitor ore molecules
thot eithersfowdownor stop the octivityof on enzyme.
Theyoften bondto the
- Whenthe shopechonges,
enzyme cousing
the shopeto chonge.Remember
the enzymewill
not work
the samewoy.Exomples
of inhibitorsincludesnokevenomondnervegasfrom WorfdWor I.
&f\qwJw
p{\ 6ep" *r"S. :b' .uF
EnzymeWorksheet
onswerthe followingquestions:
After readingthe informotionon enzymes
1. Whot doeso cotolystdo?
?. Whot is an enzyme?
3. Why do enzymesgenerollybindto onlyonetype of substrote?
similor?
fit" models
4. Howare the "lockondkey"ond"induced
5. Howore the "lockondkey"ond"inducedfit" modelsdifferent?
work? Exploinhoweochthingwouldaffect
6. Whotore 3 thingsthot conoffect the woyenzymes
onenryma
o.
b.
c.