Download Proteins - Seattle Central College

Proteins
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
What Are Proteins?
• Proteins: large polymers 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
Amino Acids
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, then use these
to build proteins of our own.
How Are Proteins Made?
Amino Acids -> Protein
• During Translation, AA are joined via
dehydration synthesis
AA chain folds to become a
functional protein
• Shape & function determined by electrochemical
properties of each AA chain (polypeptide)
• H-bonds hold structure together
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.
Clicker Q
• What must be the optimal pH for an
enzyme like salivary amylase?
a) Very basic
b) Very acidic
c) About neutral
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!
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
Complementarity
Legumes and grains in combination
are effective complementary
proteins because they:
a) have the same strengths.
b) balance each others strengths and
weaknesses.
c) have adequate sources of lysine and
tryptophan.
d) taste good when eaten together.
Digestion of Proteins
• Mechanical – mouth
• Chemical
– stomach with HCl & pepsin
• Denatures proteins & activates pepsin
• Pepsin digests proteins into short polypeptides
and amino acids
– small intestines with proteases
• Pancreatic proteases complete into di- and tripeptides & amino acids
Digestion of Proteins
The action of hydrochloric acid
(HCl) on ingested protein results in:
a)
b)
c)
d)
a condensation reaction.
denaturation.
decreased enzyme activity.
an increase in alkalinity.
Protein absorption
• AA & short
peptides
absorbed via
cotransport
• Active transport
into capillaries
• Off to the liver
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
Functions of Proteins
• Enzymes - increase
rates of chemical
reactions
• Hormones - chemical
messengers
– insulin
Functions of Proteins
• Fluid & electrolyte balance
– Negatively charged proteins influence the balance of
fluid and dissolved electrolytes (solutes)
– If concentration of blood proteins becomes low, then
plasma stays in intercellular spaces, producing edema
Functions of Proteins
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
How Much Protein Should We Eat?
• Adequate protein intake depends on:
– Activity level
– Age
– Health status
• People who require more protein include
–
–
–
–
–
Children
Adolescents
Pregnant or lactating women
Athletes
Vegetarians
How Much Protein Should We Eat?
• DRI: 0.8 grams/kg body weight
• 12-20% of total energy intake
Group
Most adults
Protein Intake (g/kg
body weight)
0.8
Nonvegetarian endurance athletes
1.2 – 1.4
Nonvegetarian strength athletes
1.6 – 1.7
Vegetarian endurance athletes
1.3 – 1.5
Vegetarian strength athletes
1.7 – 1.8
Risks of too much protein
• Direct: Possible bone loss
– High protein diets MAY cause excess Ca2+
excretion leading to bone loss
• Ca2+ pulled from bones to reduce blood acidity
Vegetarian Diets
• Eating Vegetarian: restricting diet to
foods of plant origin
– Many versions
– Many reasons to adopt a vegetarian diet
Health Benefits of Eating
Vegetarian
• Associated with lower intake of total
energy
• Lower blood pressure
• Reduced risk of heart disease
• Reduced risk of some types of cancer
• Fewer digestive problems
Challenges of eating
vegetarian
• 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
Protein – Energy
Malnutrition
• Protein-energy malnutrition:
disorders caused by inadequate
intake of protein and energy
• Two common forms:
– Marasmus
– Kwashiorkor
Protein – Energy
Malnutrition
• Marasmus: Severe wasting of muscle
tissue
– Stunted physical growth
– Stunted brain development
– Anemia
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
Genetic Diseases
• Some genetic diseases can result in
protein abnormalities
– Phenylketonuria
– Sickle cell anemia
– Cystic fibrosis
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