Download CHAPTERS 19 AND 20

CHAPTERS 19 AND 20
CONCURRENT
ENROLLMENT
AMINO ACIDS
Alpha-amino acids
– An organic compound containing both an amino
group and a carboxylate group, with the amino group
attached to the carbon next to the carboxylate group
– Overhead
There are 20 natural proteins, they are alpha because
the amino group is attached to the carbon
Page 595 common amino acids 594 has general
structure
L-amino the amino group is on the left
The amino acids found in living systems exist in the L
form
ZWITTERIONS
A dipolar ion that carries both a positive and a
negative charge as a result of an internal acidbase reaction in an amino acid molecule
Amino acid structures varies with the changes of
pH
Pages 596-597
Isoelectric point - the pH at which the zwitterion
forms
Learning check 19.1
Oxidation of cysteine
– The -SH on two cysteines lose the hydrogen's
through oxidation to form a -S-S-(disulfide
bond) and water
PEPTIDE FORMATION
Peptide linkage
– The amide linkage between amino acids that results
when the amino group of one acid reacts with the
carboxylate group of another
– Page 599
Dipeptide
– A compound formed when two amino acids are
bonded by an amide linkage
– Notice that both amino acids are zwitterions page
599
Peptide
– An amino acid polymer of short chain length
Polypeptide
– An amino acid polymer of intermediate chain length
containing up to 50 amino acids
Continue
Protein
– An amino acid polymer made up of more than 50
amino acids
Amino acid residue
– An amino acid that is a part of a peptide, polypeptide,
or protein chain
N-terminal residue
– An amino acid on the end of a chain that has an
unreacted or free amino group
C-terminal residue
– An amino acid on the end of a chain that has an
unreacted or free carboxylate group
– Page 600 learning check 19.2
IMPORTANT PEPTIDES
Disulfide bridge
– A bond produced by the oxidation of -SH groups on
two cysteine residues. The bond loops or holds two
peptide chains together
– Insulin has three disulfide bridges
Prion
– A protein infectious particle capable of causing
disease like mad cow disease
Size of proteins
– Very large 6000 to millions amu’s
– Proteins are too large to pass through cell
membranes and are contained inside the normal
cells, when trauma or disease damage the cell
membrane the proteins leak out, when protein is
found in the urine, this indicates kidney damage
Continue
The tendency for large molecules like proteins to
remain in solution or form a stable colloidal
dispersion depends on the repulsive forces
acting between molecules
These the repulsive forces are smallest at the
isoelectric point, when the net molecular
charges are essentially zero
Protein molecules tend to clump together and
precipitate from solutions in which the pH is
equal to or close to the isoelectric point
PROTEIN FUNCTION
Catalytic function
– Nearly all reactions in living organisms are catalyzed
by proteins called ENZYMES
Structural functions
– Plants have cellulose for structural materials
– Animals structural materials (other than the skeleton)
are composed of proteins. Collagen found in skin and
bone. Keratin found in hair, skin and fingernails
Storage functions
– Proteins provide a way to store small molecules or
ions
– Ovalbumin is a stored form of amino acids found in
embryos of bird eggs
– Ferritin, liver protein, stores iron ions
Continue
Protective function
– Antibodies - a substance that helps protect the
body from invasion by foreign materials known
as ANTIGENS
– Antigens - a foreign substance that can
stimulate the production of antibodies
– Blood clotting is another protective process
carried out by the proteins thrombin and
fibrinogen
Regulatory function
– Body processes are regulated by hormones,
many that are proteins
– Growth hormone - regulates the growth rate of
young animals
Continue
Nerve impulse transmission
– Some proteins behave as receptors of small
molecules that pass between gaps (synapses)
separating nerve cells
Movement function
– Proteins, actin and myosin, are used in the
movement of a muscle. These long-filament proteins
slide along each other during muscle contraction
Transport function
– Small molecules and ions are transported through
the body by binding with proteins
– Hemoglobin carries oxygen
– Ferrin carries iron in blood plasma
CLASSIFICATION
Fibrous protein
– A protein made up of long rod-shaped or stringlike
molecules that intertwine to form fibers
Globular protein
– A spherical-shaped protein that usually forms stable
suspensions in water or dissolves in water
Simple protein
– A protein made up entirely of amino acid residues
Conjugated protein
– A protein made up of amino acid residues and other
organic or inorganic components
Prosthetic group
– The non-amino acid parts of conjugated proteins
PRIMARY STRUCTURE
Linear sequence of amino acid residues in a
protein chain
Every protein has the same backbone of peptide
bonds page 607
Overhead of insulin
Small changes in the amino acid sequence can
alter the function of the protein. This is what
happens if you change a few amino acids in
hemoglobin you cause sickle-cell anemia. The
sixth amino acid glutamate is replaced with
valine
SECONDARY STRUCTURE
The arrangement of protein chains into patterns as a
result of hydrogen bonds between amide groups of amino
acid residues in the chain. α -helix and β -pleated sheet
α -helix
– Discovered by Pauling and Corey
– A single protein chain twists so the it resembles a coiled helical
spring
– Proteins like α-keratin in hair, myosin in muscles, fibrin in blood
clots
β-pleated sheet
– Protein chains are aligned side-by-side in a sheet-like array held
together by hydrogen bonds
– Only silk is made up of just β-pleated sheets
– All other proteins with β-pleated sheet have α -helixes and
random structures OVERHEAD
TERTIARY STRUCTURES
A specific three-dimensional shape of a protein resulting from
interactions between R groups of the amino acid residues in the
protein
Disulfide bridges
– Disulfide linkage between two cysteine residues found in different parts
of the chain
Salt bridges
– Interactions that result in ionic bonds that can form from ionized forms
of an acidic amino acid(-COO-) and a basic amino acid(-NH3+)
Hydrogen bonds
– Formed if you have a -OH, -NH2, or CONH2
– Two serine residues can form a hydrogen bond
Hydrophobic interactions
– When nonpolar groups are attracted or forced together by their mutual
repulsion of water
– This will form a globular protein because the polar groups will point
outward and the nonpolar groups will point inward
QUATERNARY STRUCTURE
Overhead on globular protein
The arrangement of subunits that form a larger protein
– Subunit- a polypeptide chain having primary, secondary, and
tertiary structural features that are a part of a larger protein
Overheads showing the subunits of hemoglobin and
hemoglobin
Protein + water ----> smaller peptides ----> amino acids
H+ or OHH+ or OHNative state
– The natural three-dimensional conformation of a functional
protein
Denaturation
– The process by which a protein loses its characteristic native
structure and function
Continue
The change of egg whites from clear to
white when heated
This is why you pressure cook food it
denatures the protein Clostridium
botulinum that causes botulism
Table 19.7 page 616
ENZYMES
A biomolecule that catalyzes chemical reactions
Catalytic efficiency
– Increase rate of reaction without being used in reaction
– Enzymes speed up the reaction by lowering the activation
energy
– Figure 20.2 page 624
Absolute specificity
– The characteristic of an enzyme that is acts on one and only
one substance
Relative specificity
– The characteristic of an enzyme that it acts on several
structurally related substances
Stereochemical specificity
– The characteristic of an enzyme that it is able to distinguish
between stereoisomers
Regulation
– The cell controls the rates of the reaction and the amount of
product by regulating the enzymes
ENZYME NOMENCLATURE
Substrate
– The substance that undergoes a chemical change catalyzed by
an enzyme
The name of the enzyme is the common name of the
substrate and adding -ase
Hydrolysis reactions the enzyme would be hydrolases
Overhead
Learning check page 627
Cofactor
– A nonprotein molecule or ion required by an enzyme for catalytic
activity
Coenzyme
– An organic molecule required by an enzyme for catalytic activity
Continue
Apoenzyme
– A catalytically inactive protein formed by removal of the cofactor from
an active enzyme
Apoenzyme +
cofactor
--> active enzyme
(coenzyme or inorganic ion)
Typical inorganic ions are Mg2+, Zn2+, and Fe2+ (metals)
Many coenzymes are formed from vitamins found in the body
NAD+ is a coenzyme necessary part for some redox reactions, it is
formed from the vitamin nicotinamide
Table 20.2 page 628
Active site
– The location on an enzyme where a substrate is bound and catalysis
occurs
Enzyme + substrate -> enzyme-substrate -> enzyme + product
complex
Continue
Overhead
Lock and key theory
– A theory of enzyme specificity proposing that a
substrate has a shape fitting tht of the enzyme’s
active site, as a key fits a lock
Overhead
Induced-fit theory
– A theory of enzyme actionproposing that the
conformation of an enzyme changes to accommodate
an incoming substrate
ENZYME ACTIVITY
The rate at which an enzyme catalyzes a reaction
Turnover number
– The number of molecules of substrate acted on by
one molecule of enzymes per minute
Factors affecting enzyme activity
– Enzyme concentration -increase of enzyme will
increase the ES which increases the rate
– Substrate concentration - increase of substrate at
first increases rate until it reaches saturation point
– Temperature - enzymes are proteins, so there is a
temperature limiting called the optimum temperature
usually 25 °C to 40 °C
– Effect of pH - more active in a narrow range of pH,
becomes less active as the pH deviates from the
optimum (usually around 7)
– Overhead
ENZYME INHIBITION
A substance that decreases the activity of an
enzyme
Irreversible inhibitor - forms covalent bond with
a specific functional group of the enzyme and
renders the enzyme inactive
– Cyanide ion interferes with the operation of an ironcontaining enzyme called cytochrome oxidase
– Antibiotics - a substance produced by one
microorganism that kills or inhibits the growth of other
microorganisms - usually contains sulfur
Reversible inhibitor - inhibitor can be removed
from the enzyme by shifting the equilibrium
Continue
Competitive inhibitors can be reversed by
increasing the substrate and letting
LeChâtelier’s principle work
Noncompetitive inhibitor
– Binds to the enzyme at a location other than the
active site
Zymogen or proenzyme
– Inactive precursor of an enzyme, when the enzyme is
needed the zymogen is released from storage and
activated
Read 639-643 take notes will be on test