Biological molecules (chemical tests and nucleic acids) proteins and Lipids recap AS Biology [JM}
Biological Molecules - Proteins
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Transcript of Biological Molecules - Proteins
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Unit 3 Structure and
Function of Cells
Proteins
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Proteins are polymers made up of
amino acids
They consist of carbon, hydrogen,oxygen, nitrogen, phosphorus and
sulphur
They perform many functions
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An overview of protein functions
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Polypeptides
PolypeptidesAre polymers of amino acids
A protein
Consists of one or more polypeptidesAll polypeptide chains are polar due to
the presence of the carboxyl group and
amino group at the terminal end
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Amino Acid Monomers
Amino acids
Are organic molecules consisting of anasymmetrical carbon atom attached to a
carboxyl group, an amino group, a hydrogen
atom and a side group, R
Differ in their properties due to differing sidechains, called R groups
There are about 20 types of amino acids in
nature due to 20 different types of R groups
and the specific sequence of amino acids in a
polypeptide chains determines the function of a
protein
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Amino acids
Can form zwitterions in water whenthe amino and carboxyl groups ionize
They are amphoteric in nature acting
as acids and bases at the same time
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Amino acids
20 different amino acids make up
proteins
O
O
H
H3N+ C C
O
O
H
CH3
H3N+ C
H
C
O
O
CH3 CH3
CH3
C C
O
O
H
H3N+
CH
CH3
CH2
C
H
H3N+
CH3 CH3
CH2
CH
C
H
H3N+ C
CH3
CH2
CH2
CH3N+
H
C
O
O
CH2
CH3N+
H
C
O
O
CH2
NH
H
C
O
O
H3N+ C
CH2
H2C
H2N C
CH2
H
C
Nonpolar
Glycine (Gly) Alanine (Ala) Valine (Val) Le cine (Le ) I le cine (Ile)
Methi nine (Met) Phenylalanine (Phe)
C
O
O
Trypt phan (Trp) Pr line (Pr )
H3C
S
O
O
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O
OH
CH2
C C
H
H3N+
O
OH3N
+
OH CH3
CH
C C
HO
O
SH
CH2
C
H
H3N+ C
O
OH3N
+ C C
CH2
OH
H H H
H3N+
NH2
CH2
O
C
C C
O
O
NH2 O
C
CH2
CH2
C CH3N+
O
O
O
Polar
Electrically
charged
O O
C
CH2
C CH3N+
H
O
O
O O
C
CH2
C CH3N+
H
O
O
CH2
CH2
CH2
CH2
NH3+
CH2
C CH3N+
H
O
O
NH2
C NH2+
CH2
CH2
CH2
C CH3N+
H
O
O
CH2
NH+
NH
CH2
C CH3N+
H
O
O
Serine (Ser) Threonine (Thr)Cysteine
(Cys)
Tyrosine(Tyr)
Asparagine(Asn)
Glutamine(Gln)
Acidic Basic
Aspartic acid(Asp)
Glutamic acid(Glu)
ysine ( ys) Arginine (Arg) Histidine (His)
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Amino Acid Polymers
Amino acids - are linked by peptide bonds
produced by condensation reactions to form apolypeptide chainOH
DESMOSOMES
OH
CH2
C
H
C
H O
H OH OH
Peptidebond
OH
OH
OH
H H
HH
H
H
H
H
H
H H
H
SH Side chains
SH
OO
O O O
H2O
CH2 CH2
CH2 CH2 CH2
C C C C C C
C CC C
Peptidebond
Amino end( -terminus)
Backbone
(a)
(b)Carboxyl end(C-terminus)
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Protein Conformation and Function
A proteins specific conformation
Determines how it functions
Proteins can be globular e.g. catalytic
proteins such as enzymes, hormones or
fibrous e.g. structural proteins such as
collagen and keratin
There are 4 levels of protein structure:
1. Primary structure
2. Secondary structure
3. Tertiary structure
4. Quaternary structure
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Primary structure
Is the unique sequence of amino acids in a
polypeptide formed by peptide bonds
Amino acidsubunits
+H3NAmino
end
o
Carboxyl end
oc
GlyProThrGly
Thr
Gly
GluSeu
ysCysPro euMet
al
ys
al
euAsp
Ala
alArgGlySer
ProAla
Gly
lle
SerProPheHisGluHis
Ala
Glu
alalPheThrAla
Asn
Asp
SerGlyPro
ArgArg
TyrThr
lleAla
Ala
eu
euSer
ProTyrSerTyrSerThr
Thr
Ala
al
alThrAsnPro
ysGlu
Thr
ys
SerTyrTrp
ysAla eu
Glu
leAsp
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Secondary structureIs the folding or coiling of the polypeptide into a
repeating configurationIncludes the E helix (e.g. -keratin) and the Fpleated sheet (e.g. silk proteins)
The secondary structures are maintained byhydrogen bonding
O C E helix
F pleated sheet
Amino acidsubunits
NCH
C
O
C N
H
C
O H
R
C N
H
C
O H
C
R
N
HH
RC
O
R
C
H
N
H
C
O H
NC
O
R
C
H
N
H
H
C
R
C
O
C
O
C
N
HH
R
C
C
O
N
HH
C
R
C
O
N
H
R
C
H C
ON
HH
C
R
C
O
N
H
R
C
H C
O
N
HH
C
R
C
O
N H
H C R
N H O
O C N
C
RC
H O
CHR
N H
O C
RC
H
N H
O CH C R
N H
CC
N
R
H
O C
H C R
N H
O C
RC
H
H
C
R
N
H
C
OC
N
H
R
C
H C
O
N
H
C
H H
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Tertiary structureIs the overall three-dimensional shape of a
polypeptide - results from interactions betweenamino acids and R groups
The tertiary structure is maintained by ionic
bonds, disulfide bridges, hydrogen bonds,
hydrophobic and an der Waals interactions
O
O
O
N 3+ -O
O
SS
3
3
3
3
Hydrophobicinteractions and
van der Waals
interactions
Polypeptide
backboneHyrdogen
bond
Ionic bond
CH2
Disulfide bridge
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Quaternary structure
Is the overall protein structure that results from the
aggregation of two or more polypeptide subunitsE.g. collagen and hemoglobin
Polypeptidechain
Coll
F Chains
E ChainsHemoglobin
IronHeme
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The four levels of protein structure
+H3NAmino end
Amino acidsubunits
Ehelix
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What Determines Protein
Conformation?
Protein conformation
Depends on the physical and chemical
conditions of the proteins environment
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DenaturationIs when a protein unravels and loses its native
conformationDenaturation
Renaturation
Denatured proteinNormal protein
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Causes of Protein Denaturation
1. pH2. Temperature
3. Salt concentration
4. Detergents and other chemicals thatdisrupt chemical bonds