Proteins and Amino Acids

Chapter 6-Proteins
and Amino Acids
FCNS 201-Human Nutrition
Joan E. Quinn, MEd., RD

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LEARNING OBJECTIVES OF THE
CHAPTER
Describe the structure of proteins
and explain why adequate amounts
of all essential amino acids are
required for protein synthesis
 Summarize the processes of protein
digestion and absorption in the body.
 Explain the roles of proteins in the
body


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Learning objectives, CONT.
Discuss the importance of protein
quality and mutual supplementation
 Calculate your individual protein RDA

and describe how nitrogen balance
studies are used in determining the RDA
for protein
 Compare the positive health aspects of a
vegetarian diet with those of a diet that
includes meat and describe ways each
diet can include adequate nutrients



PROTEIN PERCEPTION

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GENERAL INFORMATION






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Protein means TO
TAKE FIRST PLACE
Carbohydrates
and fats = energy

Proteins =
growth,
maintenance, and
repair

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WHERE ARE PROTEINS
FOUND?


In the body-1/2 of all dry material
of body is protein
 20%

body weight

– 1/3 muscle
– 1/5 bone and cartilage
– 1/10 skin
– remaining 1/5 other tissues + fluids

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WHERE ARE PROTEINS
FOUND?, CONT.



All enzymes are proteins
 many

hormones
 all viruses


Made by both plants and animals
 each

species builds proteins
characteristic to that specific species

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THE STRUCTURE OF
PROTEINS
Chains of amino acids join together
to form proteins
 There are 20 different naturally
occurring amino acids


 Each

contain an Amino group-NH2

 Each

contain a Acid group-COOH
 Each contain a side chain--which
distinguished one AA from another
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THE STRUCTURE OF
AMINO ACIDS
side chain

amine group

acid group

NH2

9

COOH

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PROTEINS ARE

CHARACTERIZED BY:





types of amino acids within
# of times AA is repeated
order of the AA’s
spatial structure
coil-rope like---strong flexible
 rod-insoluble & very strong-bones,
tendons, connective tissue
 globular-blood proteins
 amount of cross linking between AA’s


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PROTEINS CAN BE
DENATURED BY:





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heat
alcohol
acids
salts or heavy
metals

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Denaturation of Proteins

Heat/acid/alkaline/enzymes
Result in alteration of the
protein’s
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three dimensional
structure
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PROTEIN QUALITY IN THE
FOODS WE EAT




Meals need to have
all necessary amino
acids within them to

be used for building
essential proteins in
the body
Amino acids are
essential (9) or
nonessential (11)


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20 total amino acids
have been identified


Essential and Nonessential
Amino Acids (Table 6-1)

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Measuring Protein Quality


High-quality
 complete



Low-quality
 incomplete

All-or-none principle in protein
synthesis
 Limiting amino acid
 Complementary protein


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Limiting Amino Acid
C is the limiting amino acid in this example

CCCCC
AAAAAAAA
RRRRRR

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CAR CAR CAR
CAR CAR
R
A A A
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Complementary Protein
Beans (legumes)
Grains

Nuts/seeds

Vegetables
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DIGESTION OF A PROTEIN


STOMACH

acids uncoil protein strands and
activate stomach enzymes
– protein
+ pepsin & HCL
smaller polypeptides



SMALL INTESTINE


Pancreatic & small intestinal
enzymes split polypeptides further
– polypeptide
+pancreatic and
intestinal proteases

dipeptides, tripeptides, & AA

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DIGESTION OF A PROTEIN,
CONT.,


Enzymes on the surface of the small
intestinal cells hydrolyze these
peptides and the cells absorb them:
 Peptides
+ intestinal
dipeptidases
and tripeptidases


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amino acids absorbed

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Protein Absorption







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Active absorption
Whole proteins are broken down at the
microvilli surface and within the
absorptive cells
Whole proteins are eventually broken
down to amino acids
Many different amino acid transport
mechanisms
Amino acids are sent to the liver via portal
circulation

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TRANSPORT OF A PROTEIN


transported to liver


one of 3 fates
– AA’s released into circulation
– Liver produces plasma proteins
– AA’s not needed are
deaminated



excessive protein intake
(especially with low fluids)
may tax kidneys
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STORAGE OF PROTEINS
THERE IS NONE!
 Short term storage


 mostly

in liver
 also blood and other body cells have
a small amount

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SUMMARY OF PROTEIN
UTILIZATION
Protein ingested--broken down into
AA’s
 AA’s transported to cells and
assembled into new proteins
 AA’s not used for protein synthesis
are deaminated and utilized as an
energy source or stored as fat


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FACTORS AFFECTING
PROTEIN UTILIZATION






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AA balance
Caloric intake
Immobility
Injury

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