Transcript Enzymes

Introduction
• Food provides the energy and nutrients
that the body needs to stay alive and be
healthy.
• Before the body can make use of it, the
food has to be broken down to release
the nutrients (digested).
• The nutrients are then absorbed into the
bloodstream and taken to the cells where
they can be used.
Digestion
• Digestion is the breakdown of large macromolecules into
smaller components by the action of digestive enzymes.
• CHO  begins in mouth, continues in small intestine
(pancreatic juice and small intestinal enzymes).
• Fats  digested primarily in small intestine:
– liver (bile);
– enzymes in pancreatic juice & small intestine.
• Protein  begins in stomach; continues in small intestine with
enzymes in pancreatic juice & small intestine
Digestion in the Mouth
• Mastication
• Saliva:
– α-Amylase breaks down starch to sugars.
– Mucus to lubricate the food for easier swallowing.
– Lysozyme to kill bacteria .
Digestion in the Stomach
Stomach secretes gastric
juice and HCl.
Gastrin stimulates flow of
stomach enzymes and HCl.
Gastric Inhibitory Peptide
(GIP) inhibits the secretion
of stomach enzymes and
acid.
Pepsinogen
Secreted by chief cells & activated by HCl and
pepsin.
Pepsin digests proteins into peptides and
amino acids.
Hydrochloric acid (HCl)
• Secreted by parietal cells.
• Denatures protein.
• Turns pepsinogen into pepsin & provide a medium
of low pH favoring pepsin action.
• Partially digests dietary protein.
• Kills many swallowed virulent organisms.
• Promotes the secretion of pancreas & bile.
• Promotes the absorption of calcium & ferrous.
Digestion in the Small Intestine
• Duodenum
– Primary site of digestion
• Jejunum
– Some digestion
• Ileum
– Little digestion
Digestion in the Small Intestine
1. Pancreatic juice: Bicarbonate and digestive
enzymes.
2. Bile.
3. Intestinal cells: Digestive enzymes.
Pancreatic Juice
Bicarbonate (HCO3):
Neutralize HCl & provide a weak basic medium favoring
digestive enzyme action.
Pancreatic enzymes:
It contains:
- Proteases.
- Lipases.
- Amylase.
- Nucleases.
Pancreatic Zymogens
- Trypsinogen.
- Chymotrypsinogen.
- Procarboxypeptidase.
- Prophospholipase.
Activation of Pancreatic Zymogens
Trypsinogen
enteropeptidase (enterokinase)
Chymotrypsinogen
enteropeptidase, trypsin
Procarboxypeptidase
Prophospholipase
trypsin
trypsin
Trypsin
Chymotrypsin
Carboxypeptidase
Phospholipase
Hormonal Regulation of Pancreatic secretion
Secretin:
Stimulates the secretion of bicarbonate.
Cholecystokinin (CCK):
Stimulates the release of enzyme rich pancreatic fluids.
Bile secretion (mainly bile salts)
Fat emulsification.
Lipid absorption.
Absorption of fat-soluble vitamins.
Hormonal control of Bile secretion
Cholecystokinin:
Stimulates contraction of gallbladder and flow of bile.
Enzymes of the Small Intestine
Enterokinase: the only one secreted.
Oligopeptidases, oligosaccharidases those are
contained in the epithelial cells.
Digestion in the Small Intestine
 Pancreatic enzymes play the major digestive function:
Complete digestion of starch (pancreatic α-amylase).
Complete digestion of protein (trypsin, etc.).
 Digestion of fat (lipases).
 Digestion of nucleic acids (nucleases).
 Enzymes from the brush border:
 Break down disaccharides into simple sugars.
 Complete some protein digestion.
Sites of Absorption
Oral cavity & Stomach: little
Duodenum & Upper jejunum: most nutrients
Ileum: bile salts & Vit. B12
Colon: water & electrolytes
Sites of Absorption
Types of Absorption
Passive Diffusion:
– Intestinal wall is permeable to the nutrients.
– Going from higher to lower concentration (i.e. down
concentration gradient).
– No energy expended.
Facilitated Diffusion:
– A carrier shuttles substances into the absorptive cells.
– Going from higher to lower concentration (i.e. down
concentration gradient).
– No energy expended.
Active Transport:
– Going from lower to higher concentration (i.e. against
concentration gradient).
– Uses a carrier and ATP .
Types of Absorption
Absorption in the Small Intestine
• The digestion products, sugars, fatty acids, glycerol, amino
acids, and dipeptides are able to enter the intestinal wall.
• The amino acids and sugars then pass from the villi wall into
the bloodstream and go to the liver.
• Most of the fatty acids and monoacylglycerol are then reesterified and incorporated into chylomicrons and go to the
lymphatic system from where they enter the bloodstream.
• The nutrients are then transported in the blood to all the
cells of the body. In this way the cells get the nutrients they
need.
Absorption in the Large Intestine
• Absorption of water, minerals, and vitamins (leaving a
mass in a semi-solid state).
• Almost everything of nutritional value has been
utilized by time it reaches the large intestines -- leaving
only waste (cellulose, pectins, etc..).
• Feces contains some water, dead mucosal cells,
bacteria, non-absorbed remains of digestion (inorganic
matter and lipid).
METABOLISM
• Metabolism is the sum of all biochemical
reactions occurring in living cells.
• These reactions can be divided into two main
groups:
– 1) ANABOLISM
– 2) CATABOLISM
• Involves the
synthesis of complex
molecules from
simpler molecules
which requires energy
input.
• Involves the
breakdown of
complex molecules
into simpler
molecules involving
hydrolysis or
oxidation and the
release of energy.
Regulation of metabolism
Metabolic processes are regulated by
Many factors, most important are:
1- Enzymes
2- Coenzymes
3- Hormones
4-Feed back mechanism
5-Homeostasis
• Enzymes are proteins that catalyze (i.e. accelerate)
and control the rates of chemical reactions.
• In enzymatic reactions, the molecules at the
beginning of the process are called substrates, and
the enzyme converts them into different
molecules, the products.
• Almost all processes in a biological cell need
enzymes in order to occur at significant rates.
ENZYME AS BIOLOGICAL CATALYSTS:
• Enzymes are biological catalysts produced by
living cells.
• Enzymes lower the amount of activation
energy needed.
• They speed up the rate of biochemical
reactions in the cell but remain unchanged at
the end of the reactions.
• Most enzymes are globular protein molecules.
• The chemicals which an enzyme acts on is
called its substrate.
• The enzyme combines with its substrate to
form an enzyme-substrate complex.
• The complex than breaks up into product and
enzyme.
• A metabolic pathway is a number of reactions
catalysed by sequence of enzymes.
How do enzymes work?
• substrate: molecules upon which an
enzyme acts. The enzyme is shaped so
that it can only lock up with a specific
substrate molecule.
enzyme
• substrate -------------> product
• There are approximately 3000 enzymes
which have been characterised.
• These are grouped into six main classes
according to the type of reaction
catalysed.
• At present, only a limited number are used
in enzyme electrodes or for other
analytical purposes.
IEC Classification of Enzymes
Group Name
Type of Reaction Catalyzed
Oxidases or
Oxidation-reduction
Dehydrogenases
reactions
Transfer of functional
Transferases
groups
Hydrolases
Hydrolysis reactions
Addition to double bonds or
Lyases
its reverse
Isomerases
Isomerization reactions
Formation of bonds with
Ligases or Synthetases
ATP cleavage
• A non protein component of enzymes is called the
cofactor.
• If the cofactor is organic, then it is called a
coenzyme.
• Coenzymes are relatively small molecules
compared to the protein part of the enzyme.
• Many of the coenzymes are derived from vitamins.
• The coenzymes make up a part of the active site,
since without the coenzyme, the enzyme will not
function.
• In the graphic on the left is the structure for
the coenzyme, NAD+, Nicotinamide Adenine
Dinucleotide.
• Nicotinamide is from the niacin vitamin.
• The NAD+ coenzyme is involved with many
types of oxidation reactions where alcohols
are converted to ketones or aldehydes.
Vitamin
Coenzyme
Function
niacin
nicotinamide adenine
dinucleotide (NAD+)
oxidation or
hydrogen transfer
riboflavin
flavin adenine
dinucleotide (FAD)
oxidation or
hydrogen transfer
pantothenic
acid
coenzyme A (CoA)
Acetyl group carrier
vitamin B-12
coenzyme B-12
Methyl group
transfer
thiamin (B-1)
thiaminpyrophosphate
(TPP)
Aldehyde group
transfer
• Insulin
• Glucagon
• Adrenaline
• Glucocorticoids
• Growth Hormones
• Thyroxin
These also are regulators of metabolism :
Stimulating or inhibiting certain reactions.
4-Feed back mechanism
When a certain substance increases
in its level in the blood , a certain
message goes to the brain. The brain
will then send a message to the
special organ that forms this
substance to stop producing it.
5-Homeostasis
Keeping the internal
environment(blood ,C S F)constant
(i.e. the level of its constituents
constant) inspire of the changes of
the outside environment and the
chemical changes taking place inside