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Transcript
BIOL. 233 TERM 121
CHAPTER 3
PART 2
Dr. Amjad Khalil
1
3.4 PROTEINS – DIVERSITY IN STRUCTURE AND
FUNCTION
Proteins are the most diverse biological
molecules (examples: there are structural,
nutritious, enzyme, transport, communication,
and defense proteins)
 Cells build thousands of different proteins by
stringing together amino acids according to the
directions found in the DNA
 Key is the flexibility of proteins allowing them to
perform many functions in the organism

2
PROTEINS AND AMINO ACIDS

What is Protein?
 An
organic compound composed of one or more
chains of amino acids joined by peptide bonds
3
PROTEINS STRUCTURE



An amino acid is a small
organic compound with an
amino group (-NH3+) , a
carboxyl group (-COO-,the acid
part ),a hydrogen atom , and
one or more atoms called its R
group .
It is the R group that makes each
of the 20 naturally occurring
amino acids different
In most cases ,these
components are attached to
the same carbon atom (Figure
3.15).
4
PEPTIDE BOND FORMATION AND POLY PEPTIDE
Peptide Bond: A bond between the amino group of one amino
acid and the carboxyl group of another.
A peptide bond from as a condensation reactions joins the amino group of one
amino acid and the carboxyl group of the next in line.
5
PEPTIDE BOND FORMATION AND POLY PEPTIDE
Polypeptide: A chain of amino acids linked by peptide bonds.
Each polypeptide chain consists of three or more amino acids .The carbon
of this chain incorporates nitrogen atoms in this regular pattern: -N-C-C-NC-C- .
6
POLYPEPTIDES FROM AMINO ACIDS
Protein synthesis involves the formation of chain of
joined amino acids (also called a polypeptide)
 Polypeptide

A chain of amino acids bonded together by peptide
bonds in a condensation reaction between the amine
group of one amino acid and the carboxyl group of
another amino acid
 Remember: the condensation bond is made by
extracting water from the two amino acids and thus
linking them together

7
AMINO ACIDS CODED IN DNA

Instructions coded in DNA specify the order in
which any of the twenty kinds of amino acids
will occur in a given protein.
8
PROTEIN STRUCTURE (PRIMARY & SECONDARY)

Primary structure
 The
unique amino acid sequence of a protein
(just the list of amino acids contained in protein)

Secondary structure
 The
polypeptide chain can fold and it forms
hydrogen bonds between the amino acids
9
PROTEIN STRUCTURE (TERTIARY &
QUATERNARY)

Tertiary structure (more complex)
A
secondary structure is compacted into
structurally stable units called domains or unit.
 Forms a functional protein

Quaternary structure (most complex)
 Some
proteins consist of two or more folded
polypeptide chains(units) in close association
 Example: hemoglobin
10
LEVELS OF PROTEIN STRUCTURE
3.5 WHY IS PROTEIN STRUCTURE SO
IMPORTANT?
Just one wrong amino
acid…..
Hemoglobin’s oxygenbinding properties
depend on its structure.
Each of the 4 globin
chains in the hemoglobin
protein forms a pocket
that holds an iron
containing heme group,
figure 3.18.
Hemoglobin made up of
4 globin units, 2 α and 2
β.
ONE WRONG AMINO ACID CAUSE SICKLE CELL ANEMIA
Phenotypic Basis Of Sickle Cell Anemia
Glutamic acid carries a negative charge;
valine carries no charge. This difference
changes the protein so it behaves
differently. At low oxygen levels, HbS
molecules stick together and form rodshaped clumps that distort normally
rounded red blood cells into sickle
shapes. (A sickle
is a farm tool that has a crescent-shaped
blade.)
sickled cell
normal cell
14
Fig. 3-19c, p. 47
PROTEINS UNDONE – DENATURATION
Proteins function only as long as they maintain
their correct three-dimensional shape
 Heat, changes in pH, salts, and detergents can
disrupt the hydrogen bonds that maintain a
protein’s shape
 When a protein loses its shape and no longer
functions, it is denatured;
 a breakfast egg with the “white” set around the
yolk is a familiar example of denatured protein
15
KEY CONCEPTS:
PROTEINS IN GENERAL
Structurally and functionally, proteins are the
most diverse molecules of life
 They include enzymes, structural materials,
and transporters
 A protein’s function arises directly from its
structure

16
3.6 NUCLEOTIDES, DNA, AND THE RNA
Each nucleotide
is made up of
one 5 carbon
sugar,
phosphate
group and one
nitrogen base.
ATP: Adenosine
tri- phosphate.
17
NUCLEIC ACIDS – BLUEPRINT FOR LIFE
Some nucleotides are subunits of nucleic acids
such as DNA and RNA.
 Some nucleotides have roles in metabolism
such as ATP and ADP in cell respiration and in
photosynthesis via energy storage (that’s
adenosine triphosphate and adenosine
diphosphate).

18
NUCLEOTIDES

Nucleotide
A
small organic molecule consisting of a sugar
with a five-carbon ring, a nitrogen-containing
base, and one or more phosphate groups

ATP – adenosine triphosphate
A
nucleotide with three phosphate groups
 Important in phosphate-group (energy) transfer
 ATP is the “energy ATM” of the cell – it is used to
store and release energy as needed
19
ATP STRUCTURE
20
NUCLEIC ACIDS

Nucleic acids
 Polymers
of nucleotides in which the sugar of one
nucleotide is attached to the phosphate group of
the next
 RNA and DNA are very useful nucleic acids
21
RNA – CARRIES OUT DNA INSTRUCTIONS

RNA (ribonucleic acid)
 Contains
four kinds of nucleotide monomers,
including ATP
 Important in protein synthesis
 Is always at direction (and creation of) the DNA
 Is a single helix (helix simply means curved)
22
DNA – ARCHITECT FOR LIFE

DNA (deoxyribonucleic acid)
 Two
chains of nucleotides twisted together into a
double helix with links of hydrogen bonds
 Contains all inherited information necessary to
build/maintain an organism, coded in the order of
the nucleotide bases, with each three base
“letters” forming a genetic code “word”
 All living organisms have DNA
23
NUCLEOTIDES AND NUCLEIC ACIDS
DNA MOLECULE
Hydrogen bonds between
base join the 2 strands along
the length of a DNA
molecule.
DNA sequence of bases has
heritable information on how
to build all the proteins and
RNAs that gives each cell the
potential to grow and
reproduce.
KEY CONCEPTS:
NUCLEOTIDES AND NUCLEIC ACIDS
Nucleotides have major metabolic roles and
are building blocks of nucleic acids
 Two kinds of nucleic acids, DNA and RNA,
interact as the cell’s system of storing,
retrieving, and translating information about
building proteins

26
END OF CHAPTER 3
27