Protein are the important tissue builders in body which it can help in the cell structure, functions, hemoglobin formation to carry oxygen, enzyme for metabolic reaction and other functions in the body. Also in supply the nitrogen for the DNA and RNA genetic materials and the energy production. This is because, protein contain long chain of amino acids Protein metabolism is the process to breakdown foods are used by During protein metabolism, some of the protein will converted into glucose through gluconeogenesis process.

1. Prepared By: Rabia Khan Baber
Course Title : Biochemistry

2. INTRODUCTION TO METABOLISM
WHAT IS PROTEIN METABOLISM
INTRODUCTION TO AMINO ACID POOL
KNOW THE IMPORTANCE OF ESSENTIAL AMINO ACIDS
KNOW THE SOURCES AND FUNCTION OF COMMON PROTEINS IN THE DIET
WHAT IS AMINO ACID METABOLISM
METABOLIC USES OF AMINO ACIDS

3. Metabolism is the chemical reactions that are involved to maintain
the cell and organisms. For human, metabolism process is very
important because it requires the cellular metabolism which
involves the complex biochemical reactions. These metabolic
pathways are important in breaking down the nutrients in order to
produce energy.

4. CATABOLISM :
​​The process that is breaking down
of things. A series of degradative
chemical reactions that break
down complex molecules into
smaller units, and does not require
energy because it is releasing
energy.
ANABOLISM :
​The process to building up of
things. Chemical reaction that
synthesizes molecules from the
smaller components and usually
require energy in process

6. Protein are the important tissue builders in body which it can help in
the cell structure, functions, hemoglobin formation to carry oxygen,
enzyme for metabolic reaction and other functions in the body. Also in
supply the nitrogen for the DNA and RNA genetic materials and the
energy production. This is because, protein contain long chain of
amino acids
Protein metabolism is the process to breakdown foods are used by
During protein metabolism, some of the protein will converted into
glucose through gluconeogenesis process.

7.  Protein is a nitrogen-containing compound found in all plants and animals.
There is a continuous need for protein to make hormones, enzymes,
antibodies, and to produce new tissue (growth) and repair damaged tissues
(maintenance). About 75% of human body tissue is made of protein. From
1-2% of the body's total protein is broken down each day into amino
acid and recycled into new proteins. About60-70% of the amino acids the
body needs come from this recycling process. The rest must be supplied by
diet.

8.  The main sources of amino acids for the human body are the proteins in
our diet, the non-essential amino acids synthesized by the liver plus the
amino acids that come from the own's body protein, which are being
constantly degraded and resynthesized.
 Protein digestion begins in the stomach , where the action of gastric juice
hydrolyzes about 10% of the peptide bonds. Gastric juice is a mixture of
water (more than 99%), inorganic ions, hydrochloric acid, and various
enzymes and other proteins. The pain of a gastric ulcer is at least partially
due to irritation of the ulcerated tissue by acidic gastric juice.

9.  Catabolism, or the breakdown of nutrients obtained from food, releases
energy that drives all metabolic activities in the body. For example, glucose
is broken down to provide energy for cellular respiration that allows
functions such as muscle movement. Proteins are broken into amino acids
then re-synthesized into hormones and enzymes to regulate chemical
reactions in the cell, and molecules used for tissue growth and repair.
Carbohydrates and fats are the preferred sources of energy for cellular
metabolism. When the supply of fats and carbohydrates is insufficient to
meet the body' needs, proteins can be broken down to supply energy. This
accounts for the loss of muscle seen in prolonged cases of starvation.

10.  Proteins are complex nitrogen-containing molecules formed by a
combination of about 20 amino acids. These twenty amino acids can be
connected in thousands of different combinations to form all the different
proteins in the body. During protein formation the amino acids are
connected in long chains called polypeptides that fold into three-
dimensional shapes. The combinations of amino acids produce proteins
with unique shapes that perform specific functions in the body such as
catalyzing metabolic reactions, repairing tissue, or stimulating glands to
produce other proteins.

11.  Protein metabolism consists of a cycle of breaking down proteins,
synthesizing new ones and removing nitrogenous waste products that result
from these reactions. The amount of protein needed to balance this cycle
changes throughout an individual' life. Growing children who are creating
new muscle and bone, for example, have higher protein needs than adults.

13.  The digestion of proteins begins in the stomach where the hormone pepsin is
secreted by the stomach. Pepsin breaks the long polypeptide molecules into
smaller peptides. The mechanical churning of the stomach assists digestion by
mixing food with gastric secretions. When the contents of the stomach reach a
certain degree of acidity, the muscle that separates the stomach from the small
intestine, opens. The stomach contents, called chyme, flow into the duodenum, or
upper part of the small intestine. As chyme moves through the small intestine,
enzymes break the chemical bonds in the peptides, reducing the proteins to their
component amino acids. Amino acids molecules are small enough that they can
move though the intestinal wall and into blood where they (along with glucose,
fatty acids, and the other products of digestion) are carried by a large blood
vessel to the liver.

14.  The liver is at the heart of protein metabolism. It has both anabolic and
catabolic functions. In the liver, amino acids are synthesized into larger
proteins that circulate through the body performing a huge variety of tasks
including stimulating production of other proteins. The liver also breaks
down proteins, for example, hemoglobin found in dead red blood cells. The
liver cleanses the blood by removing cellular debris and processing excess
nitrogen that is produced by chemical reactions within cells. This excess
nitrogen is initially in the form of ammonia (NH3). If allowed to remain in
the blood, it would rapidly become toxic to the body. The liver converts
ammonia to non-toxic urea that is removed from the body in urine. This
lost nitrogen must then be replaced through diet.

15.  The hydrochloric acid (HCl) in gastric juice is secreted by glands in the
stomach lining. The pH of freshly secreted gastric juice is about 1.0, but
the contents of the stomach may raise the pH to between 1.5 and 2.5. HCl
helps to denature food proteins; that is, it unfolds the protein molecules to
expose their chains to more efficient enzyme action. The principal
digestive component of gastric juice is pepsinogen, an inactive enzyme
produced in cells located in the stomach wall. When food enters the
stomach after a period of fasting, pepsinogen is converted to its active
form pepsin in a series of steps. Pepsin catalyzes the hydrolysis of peptide
linkages within protein molecules. It has a fairly broad specificity but acts
preferentially on linkages involving the aromatic amino acids tryptophan,
tyrosine, and phenylalanine, as well as methionine and leucine. Protein
digestion is completed in the small intestine.

16.  The amino acids available for protein synthesis at any given time; the
liver regulates the blood level of amino acids based on tissue needs and
converts excess amino acids to carbohydrates for energy production.
 The "Amino Acid Pool" is a grand mixture of amino acids available in
the cell derived from dietary sources or the degradation of protein. Since
proteins and amino acids are not stored in the body, there is a constant
turnover of protein.

17. Once the proteins in the diet have been hydrolyzed, the free amino acids
join the non-essential amino acid synthesized in the liver and the amino
acids recycled from the body's own proteins, constituting the amino acid
pool now available for metabolic processes. Most of the amino acid pool is
used for the synthesis of protein and other nitrogen-containing compounds
such as DNA bases, neurotransmitters, hormones, etc. Under certain
metabolic situations, amino acids can also be used as a source of energy by
the body. It is worth mentioning that the human body cannot store amino
acids. If the amino acids in the amino acid pool are not used for biological
processes, they are degraded and the nitrogen excreted in the urine as urea.

19. Non Protein
Nitrogen

20. Amino acids are classified into three
groups namely: essential amino acids
and nonessential amino acids
ESSENTIAL AMINO ACIDS
Essential amino acids cannot be made
by the body. As a result, they must come
from food.
NONESSENTIAL AMINO ACIDS
Nonessential means that our bodies
produce an amino acid, even if we do
not get it from the food we eat.

21.  Based on this classification of amino acids, proteins can also be classified
as either complete or incomplete. Complete proteins provide adequate
amounts of all nine essential amino acids. Animal proteins such as meat,
fish, milk, and eggs are good examples of complete proteins. Incomplete
proteins do not contain adequate amounts of one or more of the essential
amino acids. For example, if a protein doesn't provide enough of the
essential amino acid leucine it would be considered incomplete. Leucine
would be referred to as the limiting amino acid, because there is not enough
of it for the protein to be complete. Most plant foods are incomplete
proteins, with a few exceptions such as soy.

22.  Even though most plant foods do not contain complete proteins, it does not
mean that they should be sworn off as protein sources. It is possible to pair
foods containing incomplete proteins with different limiting amino acids to
provide adequate amounts of the essential amino acids. These two proteins
are called complementary proteins, because they supply the amino acid(s)
missing in the other protein. A simple analogy would be that of a 4 piece
puzzle. If one person has 2 pieces of a puzzle, and another person has 2
remaining pieces, neither of them have a complete puzzle. But when they
are combined, the two individuals create a complete puzzle.

24.  The Daily Reference Intake (DRI) for protein changes with age. The DRI is
a United States government-determined measure of the amount of a nutrient an
individual should consume daily and replaces the recommended daily amount
(RDA) measurement. Current DRI guidelines call for children ages 1-3 to
consume 1.1 grams of protein per kilogram of body weight (g/kg body weight) or
roughly 17 g/day. Children ages 4-13 should receive 0.95 g/kg body weigh, and
children 14-18 should receive 0.85 g/kg body weight. For reference, 3 ounces of
lean beef provide about 30 grams of protein; milk provides about 1 g/ounce or 8
grams per cup; an egg contains about 6 grams of protein. Adolescent boys have
higher protein requirements than adolescent girls, and pregnant women have
higher protein requirements than non-pregnant women.

25.  The concept of nitrogen balance is that the difference
between nitrogen intake and loss reflects gain or loss of total body protein.
If more nitrogen (protein) is given to the patient than lost, the patient is
considered to be anabolic or “in positive nitrogen balance”.
 “A negative nitrogen balance” occurs when a person loses (through
excretion) more protein than is provided through diet. Negative nitrogen
balance is often associated with inadequate caloric intake and not just
inadequate protein intake.

27.  Building blocks for protein synthesis
 Precursors of nucleotides and heme
 Source of energy
 Neurotransmitters
 Precursors of neurotransmitters and hormones

28.  Health conditions related to protein metabolism are generally caused by the
amount of dietary protein consumed. Inadequate protein intake is rarely an
issue in the United States because most people routinely eat food
containing far more than the recommended protein DRI. People who eat
too much protein are at risk of gaining weight since excess protein is
converted to fat. Meat, a good source of protein, also contains fat and
cholesterol. A diet with too much protein from fatty meat can result in high
cholesterol, and an increased risk for heart disease.

29.  In addition, excessive protein consumption increases the amount of calcium
excreted in urine. Calcium is crucial to bone health, so bone strength may
be affected by a prolonged high-protein diet. Excess dietary protein can
also damage the liver and kidneys. Furthermore, recommended daily intake
of protein for healthy individuals is harmful to people with cirrhosis of the
liver, therefore, people with liver or kidney damage may be placed on low-
protein diets.

30.  Inadequate protein intake can inhibit growth, reduce muscle mass weaken the
immune system. Over time, it can strain the heart and cause death. Severe lack of
protein, known as protein energy malnutrition, can be caused by eating
disorders such as anorexia and bulimia.
 Starvation is another cause of low-protein intake. Starvation (intake of inadequate
calories) may be the result of a famine, economic conditions, or caregiver abuse.
In poor countries, severe protein malnutrition causes a disorder called
kwashiorkor. This condition primarily affects children between the ages of 1 and
3. Once these children are weaned and no longer receiving breast milk, their diets
consist of foods containing little protein. Symptoms of this condition include
impaired growth, a swollen stomach, and fatigue. Treatment consists of slowly
reintroducing a balanced, higher calorie diet. If not treated, kwashiorkor can
result in liver damage and death.

31.  Protein digestion begins in the stomach where hydrolysis of the protein linkages
occurs with the action of gastric juices (mainly HCl ) and the active enzyme
pepsin. Protein digestion is completed in the small intestine wherein other protein
digesting enzymes are involved.
 Essential amino acids cannot be made by the body and must come from food.
 Complete proteins provide adequate amounts of all nine essential amino acids.
 Protein turnover refers to the replacement of amino acids in older proteins
 The amino acid pool is the total amount of amino acids from the diet, protein
recycling, and non-essential amino acids produced by the body that is available
for metabolic processing.