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Protein: Amino Acids
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Protein and Amino Acids
Protein: a compound composed of C, H, O and
N atoms, arranged into amino acids linked in a
chain.
Amino acid: a building block of protein, a
compound containing amino group and anacid group attached to a central carbon atom.
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Structure of Amino Acids
Central C is connected to three compounds:
amino group (NH2), acid group (COOH), and
hydrogen (H).
Central C is also another atom or group of
atoms that varies one amino acid to another.
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Structure of Amino Acids
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20 Amino Acids
G Glycine Gly P Proline Pro
A Alanine Ala V Valine Val
L Leucine Leu I Isoleucine Ile
M Methionine Met C Cysteine Cys
F Phenylalanine Phe Y Tyrosine Tyr
W Tryptophan Trp H Histidine HisK Lysine Lys R Arginine Arg
Q Glutamine Gln N Asparagine Asn
E Glutamic Acid Glu D Aspartic Acid Asp
S Serine Ser T Threonine Thr
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Aromatic Amino Acids
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Amino Acid Sequence
Dipeptide: two amino acids bonded together
by peptide bond.
Tripeptide: three amino acids bonded
together by peptide bond.
Polypeptide: many (ten or more) amino acids
bonded together by peptide bond.
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Amino Acid Sequence
Oligopeptide: an intermediate string of
between four to ten amino acids bonded by
peptide bond.
Peptide bond: a bond between amine group
of one and carboxyl group of another aminoacid.
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Amino Acid Sequence
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61
91
121
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60
90
120
150
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Structure of Protein
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Structure of Protein
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Protein Synthesis
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Complete and Incomplete Proteins
Complete proteins, meaning that all
indispensable AAs are present.
Incomplete proteins, meaning that one or
more of the indispensable AAs was absent.
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Dispensable and Indispensable Amino
Acids
Dispensable alanine
glutamic acid
aspartic acid
Glycine
serine
proline
glutamine(a)
asparagine
cysteine (b)
tyrosine (b)
Indispensable Lysine
isoleucine (c)
leucine (c)
valine
Histidine
Threonine
Methionine
Phenylalanine
tryptophan
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Dispensable and Indispensable Amino
Acids
a. Conditionally indispensable under times of
severe bodily stress
b. Conditionally indispensable if methionine
and phenylalanine are not available
c. Leucine, isoleucine, and valine are called
branch chain amino acids (BCAAs) because
of their structure.
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Complex proteins
Lipoproteins contain lipid subunits in addition to the
amino acid.
Glycoproteins contain carbohydrate subunits.
Phosphoproteins contain phosphoric acid, and
nucleoproteins contain nucleic acids.
Some proteins have important smaller molecules,
known as prosthetic groups, attached to their
surfaces.
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Enzymes: A Function of Protein
Protein catalysts
Enzymes are protein molecules that regulate
the metabolism of proteins, carbohydrates
and fats.
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Roles of Protein
Fluid and acid-base balance,
Antibodies and hormones,
Nutrient transportation,
Blood clotting,
Muscle contraction,
Blood vessel expansion,
Contraction to maintain normal blood pressure,
Connective tissues,
Visual pigments
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Biologically Active Peptides
Peptides that are inactive in the sequence of
the parent protein, but can be released duringenzymatic digestion or food processing, and
have health benefits to the body.
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Biologically Active Peptides
Antihypertensive activity,
Antibacterial activity,
Mineral-binding activity,
Enhancement of intestinal activity
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Peptide Sequences Showing
Antihypertensive Effect
Milk protein (casein, sour milk, whey protein)
Poultry (chicken muscle, ovalbumin)
Several kinds of fish (sardine, bonito, salmon)
Porcine skeletal muscle protein (actin, myosin,troponin)
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Protein Quality
Essential amino acid: an amino acid that the
body cannot synthesize in amounts sufficientto meet physiological need.
Non essential amino acid: an amino acid that
can be synthesized in the body.
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Protein Quality
Complete protein: a protein containing all the
essential amino acids in human nutrition in
amounts of adequate for human use.
High-quality protein: an easily digestible
complete protein that amino acids fit theprotein needed by human body.
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Protein Quality
Limiting amino acid: the essential amino acid
found in the shortest supply relative to the
amounts needed for protein synthesis in the
body.
Digestibility: the measure of the amount of
amino acids absorbed from protein intake.
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Protein Digestibility
Food source Protein digestibility (%)
Egg 97
Milk and cheese 97
Mixed US diet 96
Peanut butter 95
Meat and fish 94
Whole wheat 86
Oatmeal 86
Soybeans 78
Rice 76
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Protein Quality
Reference protein: egg protein is used as a
standard against which to measure the quality
of other proteins.
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Protein Quality
Reference protein: egg protein is used as a
standard against which to measure the quality
of other proteins.
Nitrogen balance: the amount of nitrogen
consumed (N-in) as compared to the amount
of nitrogen excreted (N-out).
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Protein Quality
The average amino acid weight is about 6.25
times as much as the nitrogen it contains, sothe scientists can estimate the amount of
protein in a sample of food, body tissue, or
excrete by multiplying the weight of nitrogen
in by 6.25.
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Nitrogen Balance
Nitrogen equilibrium/zero nitrogen balance:
N-in = N-out
Positive nitrogen balance: N-in > N-out
Negative nitrogen balance: N-in < N-out
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Measures of Protein Quality
Chemical score: a rating of the quality of a test
protein arrived at by comparing its amino acid
pattern with that of a reference protein.
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Reference Pattern for Chemical Score of
Protein
Essential amino acids Whole egg
mg AA per g N
Histidine 148
Isoleucine 340
Leucine 540
Lysine 440
Methionine 355
Phenylalanine 580
Threonine 294
Tryptophan 106
Valine 410
Total 3,210
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Measures of Protein Quality
Biological value (BV): the amount of protein
nitrogen that retained from a given amount of
protein that has been digested and absorbed.
BV = [Food N (Fecal N Metabolic N) (Urinary N
Endogenous N)] / [Food N (Fecal N Metabolic N)]
x 100
BV = N retained / N absorbed x 100
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Biological Value of Proteins
Protein Biological Value
Egg 100
Milk 93
Rice 86
Beef, fish 75
Corn 72
Peanut flour 56
Wheat gluten 44
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Measures of Protein Quality
Net protein utilization (NPU): the amount of
protein nitrogen that is retained from a givenamount of protein nitrogen eaten.
NPU = [Food N (Fecal N Metabolic N) (UrinaryN Endogenous N)] / Food N x 100
NPU = N retained / N intake x 100
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Measures of Protein Quality
Protein efficiency ratio (PER): the weight
gained from protein intake.
PER = Weight gain (g) / Protein intake (g)
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Protein-kCalorie Malnutrition
Kwashiorkor: a malnutrition caused by protein
deficiency in the presence of adequate
kcalories.
Marasmus: a malnutrition caused by
inadequate kcalories.
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Recommended Protein Intakes
RDA = 0.8 g/kg body weight.
Factors are considered in establishing
recommended protein intake:
Body weight
Lean body
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Protein Sources
Animal foods
Cereals
Vegetables
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Protein Digestion and Absorption
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Digestion
Process that breaks down food into molecules
small enough to absorb.
Break polymers into monomers that are easier
to absorb and that can be used to synthesize
new polymers required by the organism.
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Absorption
Cells that line tract take up nutrients
Nutrients move to cells where they are
Incorporated into the cells
Converted to energy which may be used
immediately or stored until needed
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Di dalam Mulut
Tidak terjadi digesti protein yang signifikan di dalam
mulut, hanya membasahi jaringan konektif (protein
kolagen).
Distimulasi dengan timbulnya bau, indra penglihatan
dan rasa, atau pemikiran mengenai makanan,
menyebabkan saliva tersekresi.
Saliva mengandung: mucin (a glycoprotein lubricant),
amylase (untuk memecah KH dan glikogen)
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Di dalam Lambung (Stomach)
Distimulasi dengan aliran makanan, menyebabkan neurotransmitters acetylcholine
dan histamine dihasilkan oleh sel-sel dalam lambung (stomach)
Distimulasi dengan adanya makanan di dalam lambung, mengakibatkan hormone
gastrin tersekresi.
Kombinasi acetylcholine, histamine dan gastrin menyebabkan cairan lambung(gastric juices) tersekresi.
mucin selalu disekresikan dalam stomach
HCl - pH 0.8-2.5 (disekresikan parietal cells)
pepsinogen (zymogen, disekresikan oleh chief cells)
gastric lipase (enzyme yang meemecah lemak, tetapi aktif di intestine)
Protein terdenaturasi akibat pH rendah
Nilai pH yang rendah berfungsi sebagai antiseptik, dan membunuh bakteri dan sel
asing.
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Digesti dalam lambung
Zymogen Pepsinogen (MW=40,000) yang dihasilkan
di dalam lambung diaktivasi oleh adanya enzim
pepsin dan asam lambung. Pepsinogen memiliki 42
potongan asam amino untuk menjadi enzim pepsin
(MW=33,000) dan fragmen peptida yang akan
terdegradasi. Pepsin akan mendigesti secara parsial dengan
memotong ikatan peptida pada ujung N asam amino
aromatis (Phe, Tyr, Trp)
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Digesti dalam Duodenum
Cairan lambung yang disebut Chyme masuk ke duodenum, pH
rendah memicu sekresi hormon secretin dalam darah. Asam amino
menstimulasi sekresi cholecystokinin.
Secretin menstimulasi pankreas untuk mensekresikan bicarbonat ke
dalam usus kecil (small intestine), (pH changes to about 7).
Cholecystokinin menstimulai sell exocrine pancreas untuk
mensekresikan trypsinogen, chymotrypsinogen dan
procarboxypeptidase ke dalam intestine. (Sel exocrine juga
mengandung protein trypsin inhibitor untuk melindungi diri dari
free trypsin).
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Digesti dalam Duodenum
Sel-sel intestinal mensekresikan enzim yang disebut enteropeptidase yangbertugas pemotongan trypsinogen menjadi trypsin.
Trypsin merubah chymotrypsinogen menjadi chymotrypsin,procarboxypeptidase menjadi carboxypeptidase dan proelastase menjadielastase (belum diketahui asal-nya dari mana), dan trypsinogen menjaditrypsin.
Trypsin memotong peptida pada ujung karboksil asam amino Lys dan Arg.
Chymotrypsin memotong ujung karboksil asam amino aromatis Phe, Tyr
dan Trp.
Enzim yang membutuhkan Zn.
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Digesti dalam Duodenum
Carboxypeptidase memotong semua asam amino pada fragmen
yang masih memiliki satu asam amino pada ujung karboksil (akan
memotong pada sisi ujung N dari ujung C asam amino).
Elastase memotong derivat asam amino, desmosine.
Aminopeptidase merupakan sekresi sel usus halus dan bertugas
memotong ujung N asam amino pada semua peptida.
Banyak protein terdigesti secara sempurna menjadi asam amino,diserap dan kemudian diangkut ke dalam darah menuju sel-sel
dalam tubuh.
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Digesti dalam Duodenum
Keratin dan protein fibrosa lainnya sulit untuk
didigesti (hanya lewat).
Kebanyakan protein tanaman tertutup
selulosa dan tidak dapat didigesti.
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Component of Gastrointestinal
System
Mouth
Oral cavity
Tongue
Pharynx
Salivary Glands
Esophagus
Stomach
Liver
Gall Bladder
Pancreas
Small Intestine
Large Intestine
Rectum
Anus
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Oral Cavity
Food enters the mouth and is reduced in size
by teeth and tongue.
Salivary glands secrete saliva which
Lubricates
Buffers
Contains antimicrobial substances
Contains amylase to digest starch
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http://www.vh.org/Providers/Textbooks/motilitygastro/7.htmlhttp://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/pregastric/salivary.htmlhttp://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/pregastric/salivary.htmlhttp://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/pregastric/esophagus.htmlhttp://www.ee.ualberta.ca/~mintchev/stomach.htmlhttp://www.vh.org/Providers/Textbooks/LiverPathology/Text/AtlasLiverPathology.htmlhttp://www.cag-acg.org/patinfo/gall_bladder.htmhttp://www.fda.gov/fdac/features/896_panc.htmlhttp://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/smallgut/index.htmlhttp://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/largegut/index.htmlhttp://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/largegut/index.htmlhttp://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/smallgut/index.htmlhttp://www.fda.gov/fdac/features/896_panc.htmlhttp://www.cag-acg.org/patinfo/gall_bladder.htmhttp://www.vh.org/Providers/Textbooks/LiverPathology/Text/AtlasLiverPathology.htmlhttp://www.ee.ualberta.ca/~mintchev/stomach.htmlhttp://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/pregastric/esophagus.htmlhttp://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/pregastric/salivary.htmlhttp://www.vh.org/Providers/Textbooks/motilitygastro/7.html -
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Swallowing
Food passes to pharynx which contains both
trachea and esophagus
Epiglottis prevents food from entering trachea
Food passes through esophagus into the
stomach
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Stomach
Stores and digests food
Contains pits leading to Gastric glands with
three types of cells:
Mucous cells - produce mucous which lubricates
and protects lining. Parietal cells - secrete hydrochloric acid
Chief cells - secrete pepsinogen
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Small Intestine
Receives food from stomach
Bile from liver via the Gall bladder (kantung
empedu)
Enzymes from pancreas
Site of most digestion
Site of most absorption
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Duodenum
First 25 cm of small intestine
Receives enzymes from pancreas
Neutralizes acid from stomach
Site of most chemical changes in food
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Enzymes
Fat + bile and lipase = Fatty acids + glycerol
Starch + Amylase = simple sugars
Maltose + maltase = glucose + glucose
Sucrose + sucrase = glucose + fructose
Lactose + lactase = glucose + galactose
Protein + protease = amino acids
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Pancreas
Releases critical enzymes for digestion
Neutralize acid by releasing bicarbonate
Insufficient pancreatic function can lead to
starvation
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Liver
Produces bile
No digestive enzymes, but contains bile salts
Emulsifies fats
Made from cholesterol
Stored in Gall Bladder
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Enzymatic Action - Carbohydrates
Starch broken down into the disaccharide , maltose, by
pancreatic amylases.
Disaccharides converted to monosaccharides
Maltose is hydrolyzed by Maltase to give Glucose + Glucose
Sucrose is hydrolyzed by Sucrase to give Glucose + Fructose
Lactose is hydrolyzed by Lactase to give Glucose + Galactose
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Absorption
Following enzymatic action in the duodenum,
food is absorbed in the remainder of the small
intestine
Has a very large surface area
Contains Villi and microvilli
Rich in capillaries and lymph vessels
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Large Intestine
Material not be digested or absorbed passes
into the large intestine.
90% of the water is absorbed into blood
Some vitamins are produced by bacteria and
are absorbed
Residue is stored in rectum
Eliminated through the anus
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How are proteins absorbed?
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How are proteins absorbed?
The absorptive cells of the small intestine can only
absorb individual amino acids, dipeptides ortripeptides.
Once transported inside the cells all di/tripeptides are
broken down into individual amino acids by proteases
within the cells.
Like monosaccharides, the amino acids are transported
out of the absorptive cells and diffuse into the
capillaries to move into general circulation.
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THANK YOU
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