Proteins

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Proteins
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Proteins are invaluable!

• Cell growth, repair, and maintenance
• Cytoskeleton, channel proteins, carrier proteins
• Enzymes - increase rates of cellular reactions
• Lipase, amylase
• Hormones
• Fluid and electrolyte balance
• Albumin
• pH balance
• Antibodies protect against disease

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What Are Proteins?

• Proteins large polymers composed of amino acids
• Contain C, H, O, N
• Primary source of Nitrogen in our diets
• 20 different amino acids are used to make ALL
  proteins

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Amino Acids
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Types of Amino Acids

• Essential amino acids
• Cannot be produced by our bodies Must obtain
  them from food
• Nonessential amino acids
• transfer amine group to a new, alcohol side
  chain
• We digest proteins into amino acids, to then
  build proteins of our own.

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Proteins made via two processes

• Transcription Copies the information in DNA to
  make mRNA (nucleic acids)
• Translation Converts information in mRNA to an
  amino acids sequence of a protein
• vid

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How Are Proteins Made?
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Amino Acids - Protein

• During Translation, AA joined via dehydration
  synthesis

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AA chain folds to become a functional protein

• Shape function determined by electrochemical
  properties of each AA chain (polypeptide)
• H-bonds hold structure together

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Proteins require specific environments to function

• Proteins work optimally under a narrow range of
  temperature and pH (acidity).
• If conditions are not right (e.g. too hot, very
  acidic) proteins will denature.
• Denaturation is caused by disruption of H-bonds.

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Types of Dietary Protein

• Incomplete protein does not contain all
  essential amino acids
• Not sufficient for growth and health
• Considered a low quality protein
• Complete protein contains sufficient amounts of
  all 9 essential amino acids
• Considered a high quality protein
• Ex meat!

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Proteins in the Diet

• Mutual supplementation Method of eating two (or
  more) incomplete proteins together to make a
  complete protein
• Complementary proteins two (or more) protein
  sources that together supply all 9 essential
  amino acids
• Ex beans and rice PB bread corn tortilla
  beans hummus

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Complementarity
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Legumes and grains in combination are effective
complementary proteins because they

• have the same strengths.
• balance each others strengths and weaknesses.
• have adequate sources of lysine and tryptophan.
• taste good when eaten together.

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Digestion of Proteins

• Mechanical mouth
• Chemical - stomach w/ HCl
• Denatures proteins
• Activates pepsin
• Chemical Pepsin digests proteins into short
  polypeptides and amino acids

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Digestion of Proteins

• Continues in small intestines
• Pancreatic proteases complete digestion of
  proteins into di- and tri-peptides amino acids

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Digestion of Proteins
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The action of hydrochloric acid (HCl) on ingested
protein results in

• a condensation reaction.
• denaturation.
• decreased enzyme activity.
• an increase in alkalinity.

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Protein absorption

• AA short peptides absorbed via cotransport
• Active transport into capillaries
• Off to the liver

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Functions of Proteins

• Cell growth, repair, and maintenance
• Cytoskeleton (structural filaments that give
  cells their shape)
• Microvilli
• Extracellular matrix of bones, cartilage
• Integral contractile fibers of muscle
• Channel proteins regulate passage of ions through
  plasma membrane
• Carrier proteins actively transport molecules
  across membrane

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Functions of Proteins

• Enzymes - increase rates of chemical reactions
• Hormones - chemical messengers
• insulin

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Functions of Proteins

• Fluid electrolyte balance
• Negatively charged proteins influence fluids and
  their dissolved electrolytes (solutes)
• If concentration of blood proteins becomes low,
  then plasma stays in intercellular spaces,
  producing edema

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Functions of Proteins
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Functions of Proteins

• pH balance Proteins have negatively charged side
  chains
• Prevents acidosis by attracting positively
  charged H ions
• Prevents alkalosis by releasing H ions when
  blood becomes too basic
• Antibodies protect against disease
• Energy source
• Protein deamination produces burnable molecules
  AND raw substrates for glucose construction

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How Much Protein Should We Eat?

• Proper protein intake depends on
• Activity level
• Age
• Health status
• Ex each day, a sedentary adult requires 0.8
  grams protein per kg of body weight.

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How Much Protein Should We Eat?

• People who require more protein include
• Children
• Adolescents
• Pregnant or lactating women
• Athletes
• Vegetarians

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How Much Protein Should We Eat?

• Recommended Dietary Allowance (RDA)
• 0.8 grams/kg body weight
• 12-20 of total energy intake should be from
  protein

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Risks of too much protein

• Indirect high cholesterol CHD
• Diets high in animal protein are associated with
  high cholesterol
• Animal proteins contain lots of saturated fats
• Direct Possible bone loss
• High protein diets MAY cause excess Ca2
  excretion leading to bone loss
• Ca2 pulled from bones to reduce blood acidity

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Vegetarian Diets

• Vegetarianism restricting diet to foods of plant
  origin
• Many versions
• Many reasons to adopt a vegetarian diet

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Health Benefits of Vegetarianism

• Lower intake of fat and total energy
• Lower blood pressure
• Reduced risk of heart disease
• Reduced risk of some types of cancer
• Fewer digestive problems

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Challenges of Vegetarianism

• Diets can be low in some vitamins and minerals
• Plant proteins are of lower quality than animal
  proteins.
• Include complementary proteins
• Use soy products as a protein source

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Protein Energy Malnutrition

• Protein-energy malnutrition disorders caused by
  inadequate intake of protein and energy
• Two common forms
• Marasmus
• Kwashiorkor

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Protein Energy Malnutrition

• Marasmus Severe wasting of muscle tissue
• Stunted physical growth
• Stunted brain development
• Anemia

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Protein Energy Malnutrition

• Kwashiorkor Muscle wasting and bloating
• Symptoms
• weight loss muscle wasting
• Edema belly distention
• Retarded growth development
• Kwashiorkor is often seen in children in
  developing countries

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Genetic Diseases

• Some genetic diseases can result in protein
  abnormalities
• Phenylketonuria
• Sickle cell anemia
• Cystic fibrosis

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Sickle Cells Normal Red Blood Cells
Amino acid sequence of normal hemoglobin Val
His Leu Thr Pro Glu Glu Amino acid
sequence of sickle-cell hemoglobin Val His
Leu Thr Pro Val Glu