1. Chapter 1 - Three Societies on the Verge of Contact
Copyright ©2016 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.

2. Learning Outcomes
Define the basic building blocks of a protein and describe what makes each protein unique.
Describe the process by which cells make proteins.
Explain the significance of a protein’s shape.
Define and understand genetics and epigenetics and how they relate to protein synthesis.
Explain protein digestion, absorption, and circulation.

3. Learning Outcomes
6 Describe the major functions of proteins in the body. 7 Explain how the body recycles and reuses amino acids. 8 Calculate the amount of protein you need on a daily basis. 9 Describe vegetarianism and variations of vegetarian diets. 10 Know the consequences of protein deficiency and excess.

4. Nitrogen-containing macronutrient
What Are Proteins?
Nitrogen-containing macronutrient
Amino acid subunits
Peptide bond
Most abundant organic substance in body
Classification
Number of amino acids

5. What Are Proteins? Amino acid structure Common components
Central carbon bonded to hydrogen
Amino group
Nitrogen
R-group
Carboxylic acid group
Shape of protein imparts its function

6. FIGURE 5.1 Components of an Amino Acid
The structure of the R-group makes
one amino acid different from another.
These 3 components are the
same for all amino acids.
Amino acids have four parts: an amino group, a central carbon, a carboxylic acid group, and an R-group. 6

7. What Are Proteins? Amino acids Essential Nine Nonessential Eleven
Transamination
Conditionally essential
Six
PKU
Animal-derived foods
such as meat, milk, fish,
and eggs are considered
complete protein
sources because
they contain all
of the essential
amino
acids.

8. TABLE 5.1 Essential, Nonessential, and Conditionally Essential Amino Acids

9. Proteins of animal origin Proteins found in plant-derived foods
What Are Proteins?
Proteins of animal origin
Proteins found in plant-derived foods
Complete protein source
Balanced amount of essential amino acids
Incomplete protein source
Limiting amino acid
Protein complementation
Different incomplete proteins

10. How Do Cells Make Proteins?
Protein synthesis
Step 1: Cell signaling
Cellular needs conveyed to cell nucleus
Step 2: Transcription
mRNA is constructed using DNA as a template
Exits nucleus
Chromosome
Gene

11. How Do Cells Make Proteins?
Protein synthesis
Step 3: Translation
mRNA binds to a ribosome
tRNA
Carry amino acids to the ribosome
Peptide is released from ribosome

12. FIGURE 5.2 Protein Synthesis
1. Cell signaling
Cell signaling communicates
the need to synthesize a protein
to the nucleus.
2. Transcription
Transcription of a gene in
the nucleus results in the
synthesis of a strand of mRNA.
3. Translation
The mRNA strand leaves
the nucleus and binds to
ribosomes in the cytoplasm.
tRNA translates the information
carried by mRNA by delivering
amino acids in the correct
sequence to the ribosome,
resulting in the production of
a polypeptide strand.
The steps involved in protein synthesis are three-fold: cell signaling, transcription,
and translation. 12

13. Why Is a Protein’s Shape Critical to Its Function?
Primary structure
Number and sequence of amino acids in a single chain
Determined by DNA code
Critical to function
Sickle cell anemia

14. FIGURE 5.3 Primary Structure of a Protein
The number and sequence of amino acids in a single polypeptide chain is referred to as
a protein’s primary structure. 14

15. Why Is a Protein’s Shape Critical to Its Function?
Secondary structure
α-helix
β-folded sheet
Tertiary structure
Interactions between R-groups

16. FIGURE 5.4 Secondary Structure of a Protein
Weak bonds between
carboxylic acid and
amino groups cause
the protein to fold into
a secondary structure.
Weak chemical bonds fold proteins into three-dimensional spiral- and fan-like shapes,
resulting in secondary structures 16

17. Why Is a Protein’s Shape Critical to Its Function?
Quaternary structure
Two or more peptide chains join together
Not all proteins have this structure
Prosthetic groups
Often contain minerals
Denaturation
Denaturing agents

18. FIGURE 5.5 Quaternary Structure and Prosthetic Groups of Hemoglobin
Hemoglobin is made from four polypeptide chains and four
iron-containing prosthetic groups called heme. 18

19. What Is Meant by Genetics and Epigenetics?
Genotype
DNA
Phenotype
Physical or biochemical characteristics
Mutations
Alteration in a gene
Inherited if present in DNA of egg or sperm

20. What Is Meant by Genetics and Epigenetics?
Inheritable changes in gene expression not involving DNA sequence
May be passed on to next generation
Nutritional status
May impact long-term epigenetic modifications

21. How Are Proteins Digested, Absorbed, and Circulated?
Digestion
Begins in the stomach
Gastrin
Hydrochloric acid
Disrupts chemical bonds
Converts proenzyme pepsinogen to pepsin
Pepsinogen
Proenzyme for pepsin

22. How Are Proteins Digested, Absorbed, and Circulated?
Digestion
Small intestine
In lumen and within cells
Secretin
Stimulates pancreas to release bicarbonate
Cholecystokinin (CCK)
Stimulates release of proenzymes from pancreas

23. FIGURE 5.6 Overview of Protein Digestion
1. Stomach cells release the hormone gastrin,
which enters the blood, causing the release
of hydrochloric acid (HCl) and pepsinogen
from other cells in the stomach.
2. Hydrochloric acid denatures proteins and
converts pepsinogen to pepsin, which begins
to digest proteins.
3. Partially digested proteins
enter the small intestine
and cause the release of the
hormones secretin and
cholecystokinin (CCK).
4. Secretin stimulates the pancreas to release
bicarbonate and proenzymes into the intestine.
Bicarbonate neutralizes chyme. CCK also
stimulates the pancreas to release proenzymes
into the small intestine
5. Pancreatic proenzymes are
converted to active enzymes
in the small intestine. These
enzymes digest polypeptides
into tripeptides, dipeptides, and
free amino acids.
6. Intestinal enzymes complete protein digestion.
Protein digestion occurs in both the stomach and small intestine via pepsin, pancreatic proteases, and intestinal proteases. 23

24. How Are Proteins Digested, Absorbed, and Circulated?
Absorption
Amino acids are absorbed in the duodenum
Amino acids enter the bloodstream
Circulation
Travel to the liver for processing

25. How Are Proteins Digested, Absorbed, and Circulated?
Food allergy
Major allergens
Food labels
Immune response
Common signs and symptoms
Anaphylaxis
Food intolerance or sensitivity
Lactose intolerance

26. Why Do You Need Proteins and Amino Acids?
Structure
Structural materials of the body
Growth and development
Enzymes
Biological catalysts
Movement
Contraction and relaxation of muscles
Voluntary and involuntary movements
Actin and myosin

27. Why Do You Need Proteins and Amino Acids?
Transport
Escorting substances into and around the body
Secondary malnutrition
Communication
Hormones
Cell-signaling proteins
Protection
Antibodies

28. Why Do You Need Proteins and Amino Acids?
Fluid balance
Albumin
Edema
Regulation of pH
Source of glucose and energy
Proteolysis
Gluconeogenesis
Lipogenesis
Other purposes
Because protein is needed for fluid balance, severe
protein deficiency can cause edema. Pressure has
been applied to the tops of these feet, demonstrating
what is referred to as pitting edema.

29. FIGURE 5.7 Regulation of Fluid Balance by Albumin
1. Blood is pumped
out of the heart
and into blood
vessels.
2. The narrow diameter of the blood
vessels surrounding organs and
tissues causes blood pressure to
increase. This forces fluid and
nutrients (but not albumin) out of
the capillary vessels.
3. The increased concentration of albumin
causes water to be drawn back into
the blood. When this does not
happen, edema can occur. Edema
is common in protein deficiency
when albumin synthesis is limited.
Albumin is a protein in the blood that helps regulate fluid balance within and around tissues.
© 2014 Cengage Learning® 29

30. TABLE 5.2 Major Functions of Proteins in the Body

31. How Does the Body Recycle and Reuse Amino Acids?
Protein turnover
Adaptation to periods of growth and development
Nitrogen excretion
Ammonia
Liver converts to urea
Nitrogen balance and protein status
Negative nitrogen balance
Positive nitrogen balance

32. How Much Protein Do You Need?
Reasons to consume dietary protein
For adequate amounts of essential amino acids
For nitrogen
DRIs for amino acids
Milligrams per kilogram per day (mg/kg/day)
Set relative to body size
No ULs

33. FIGURE 5.8 RDAs for the Essential Amino Acids in Adults
Source: Institute of Medicine. Dietary Reference Intakes for energy, carbohydrate, fiber, fatty acids, cholesterol, protein, and
amino acids. Washington, DC: National Academies Press; 2005. 33

34. How Much Protein Do You Need?
DRIs for protein
Expression
Grams per day (g/day)
Grams per kilogram body weight per day (g/kg/day)
Times for greater protein intake
No UL
Athlete protein needs
AMDRs

35. Can Vegetarian Diets Be Healthy?
Forms of vegetarianism
Lacto-ovo-vegetarian
Lactovegetarian
Vegan
Micronutrient deficiencies
Special recommendations for vegetarians
Enjoy assortment of foods
Consume foods in moderation

36. What Are the Consequences of Protein Deficiency and Excess?
Protein-energy malnutrition (PEM)
Micronutrient deficiencies
Risk for infection and illness
Marasmus
Severe, chronic, overall malnutrition
Kwashiorkor
Severe edema in extremities
Ascites
Children with kwashiorkor often have distended
abdomens (ascites), edema in their hands and feet,
cracked and peeling skin, and an apathetic nature.
These children are at especially increased risk for
infections.

37. What Are the Consequences of Protein Deficiency and Excess?
Adults
Rarely experience kwashiorkor
Extreme muscle loss
Protein excess
High intakes of protein accompany high intakes of fat, saturated fat, and cholesterol
Red meat consumption
Cancer risk