پاورپوینت
پزشکی و سلامت • شیمی
پاورپوینت Amino Acids and Proteins
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25 بازدید
11 آبان 1403
برچسبها
25 بازدید
11 آبان 1403
برچسبها
Amino Acids and
Proteins
Amino Acids
Amino acids have both
a carboxyl group
-COOH
an amino group
-NH2
in the same
molecule..
Amino Acid
Structure
The general formula of an amino acid
is shown here
The group designated by R is usually
a carbon chain but other
structures are also
possible
Amino Acid Structure
Amino acids may be
characterized as , ,
or amino acids
depending on the
location of the amino
group in the carbon
chain.
are on the carbon
adjacent to the
carboxyl group.
are on the 2nd
carbon
on the 3rd carbon
from the carboxyl
Amino Acids Proteins
Amino acids are the building
blocks of proteins. Proteins are
natural polymers of successive
amino acids
There are 20 different amino
acids that make up human
proteins
amino acids
Amino acids
found in proteins
are amino
acids. The
amino group is
always found on
the carbon
adjacent to the
carboxyl group
Amino Acid
Functions
1.
2.
Amino acids are the building blocks
of proteins
Some amino acids and their
derivatives function as
neurotransmitters and other
regulators
Examples Include
L-dopamine
Epinephrine
Thyroxine
Histidine
Amino Acids and Proteins
Amino acids
forming
proteins may
be
characterized
as Acidic,
Basic, or
neutral
depending on
the character
of the side
chain
attached.
Acidic Amino Acids
There are
two acidic
amino
acids.
There are
two
carboxyl
groups and
only one
amino
(asp)
(glu)
Basic Amino Acids I
These amino
acids are
basic. They
have more
amino
groups than
carboxyl
groups
Basic Amino Acids II
These amino
acids are
also basic.
They have
more amino
groups than
carboxyl
groups
Neutral Amino Acids
I
These amino
Acids are
considered
neutral. There
is one
carboxyl
group per
amino group
(ala)
(gly)
((leu
Neutral Amino Acids
II
(Ser)
(Tyr)
(Val)
(Trp)
(Cys)
(Met)
Neutral Amino Acids
III
(Ile)
(Thr)
(Asp)
(Phe)
(Gln)
(Pro)
Amino Acids and
Optical Isomers
Except for glycine all amino acids have
a chiral carbon. Therefore they can
have optical isomers
The amino acids found in proteins are
all levarotatory or L forms.
Amino Acids are
Amphoteric
Amino acids are amphoteric. They are capable
of behaving as both an acid and a base, since
they have both a proton donor group and a
proton acceptor group.
In neutral aqueous solutions the proton
typically migrates from the carboxyl group to
the amino group, leaving an ion with both a
The Zwitterion
This dipolar ion form is known as a
Zwitterion.
Peptide Bond
When two amino acids combine,
there is a formation of an amide
and a loss of a water molecule
+ H2O
Proteins- Levels of
Structure
Amino acids can undergo condensation
reactions in any order, thus making it
possible to form large numbers of
proteins.
Structurally, proteins can be described in
four ways.
1. Primary
2. Secondary
3. Tertiary
4. Quaternary structure.
Primary Structure
The primary structure of a protein is defined
by the sequence of amino acids, which form
the protein. This sequence is determined
by the base pair sequence in the DNA used
to create it. The sequence for bovine insulin
is shown below
Secondary Structure
The secondary structure describes the way
that the chain of amino acids folds itself due
to intramolecular hydrogen bonding
Two common secondary structures are
the Helix
and the sheet
Secondary Structure- Helix
H-bond
Secondary Structure- Sheet
Oxygen
Nitrogen
Hydrogen
Carbonyl C
Carbon
R Group
H Bond
Tertiary Structure
The tertiary
structure maintains
the three
dimensional shape
of the protein.
The amino acid
chain (in the helical,
pleated or random
coil form) links itself
in places to form the
unique twisted or
folded shape of the
protein.
Tertiary Structure
There are four ways in which parts of the amino
acid chains interact to stabilize its tertiary shape..
include:
I.-- They
Covalent
bonding, for
example disulfide bridges
formed when two cysteine
molecules combine in
which the –SH groups are
oxidized:
II.-- Hydrogen bonding
between polar groups on
the side chain.
III.-- Salt bridges (ionic
bonds) formed between –
NH2 and –COOH groups
Quaternary
Structure
Many proteins are not single strands
The diagram below shows the quaternary
structure of an enzyme having four interwoven
amino acid strands
Denaturing Proteins
The natural or native structures of
proteins may be altered, and their
biological activity changed or
destroyed by treatment that does not
disrupt the primary structure.
Following denaturation, some
proteins will return to their native
structures under proper conditions;
but extreme conditions, such as
strong heating, usually cause
irreversible change.
Denaturing Proteins
Heat
Ultraviolet
Radiation
Strong Acids
or Bases
Urea
Some Organic
Solvents
Agitation
hydrogen bonds are broken by increased
translational
and vibrational energy.(coagulation of egg white
albumin on frying.)
Similar to heat
(sunburn)
salt formation; disruption of hydrogen bonds.
(skin blisters and burns, protein precipitation.)
competition for hydrogen bonds.
(precipitation of soluble proteins.)
(e.g. ethanol & acetone) change in dielectric
constant and hydration of ionic groups.
(disinfectant action and precipitation of protein.)
shearing of hydrogen bonds.
Sickle Cell Anemia
A small
change in
the sequence
of the
primary
structure can
have a
significant
impact on
protein
structure
Ninhydrin Reaction
Triketohydrindene hydrate, commonly
known as ninhydrin, reacts with amino acids
to form a purple colored imino derivative,
This derivative forms a useful test for amino
acids, most of which are colorless.
Protein Tests: Biuret
Biuret reagent is a light blue solution
containing Cu2+ ion in an alkaline
solution. Biuret turns purple when
mixed with a solution containing
protein. The purple color is formed
when copper ions in the biuret
reagent react with the peptide bonds
of the polypeptide chains to form a
complex.
Xanthroprotic Test
Concentrated Nitric acid will form
a yellow complex with tryptophan
and Tyrosine side chains in
proteins
Disulfide Bridge Test
Disulfide bridges will react with
Pb2+ ion from lead acetate in an
acidfied solution. A black
precipitate indicates the presence
of disulfide-bonded cysteine in
proteins.
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