BIO-319 quiz 3

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Four characteristics of protein

Four characteristics of protein

• large, complex molecules

• found in cells of all living things

• organic molecule

• composed of long chain of amino acids (20)

Amino acid structure

• each have the same basic structure

• carbon atom (alpha carbon) with:

  • amino group (NH2)

  • Carboxylic acid (COOH)

  • H atom

  • Side chain (R group)

How are amino acids linked together

peptide bonds

Dipeptide

2 amino acids

Tripeptide

3 amino acids

Polypeptide

more than 3 amino acids

protein

70 or more amino acids

What is protein denaturation

• proteins uncoil and lose their shape

• protein function is lost (shape=function)

what causes protein denaturation

• temperature

• pH

• enzymes

• alcohol

Essential amino acids

• cannot be produced in sufficient quantities to meet physiological needs

• must be obtained from food

• total of 9 essential amino acids

• support normal body growth-maintenance repair

Non-essential amino acids

• can be synthesized by the body in sufficient quantities

• Total of 11 non-essential amino acids

Conditionally essential amino acids

• non-essential amino acid become essential in the diet

• phylketonuria (PKU): tryosine becomes a conditionally essential amino acid

Transamination

• transfer amine group (NH2) from essential amino acid to a different acid group and R group

• used to make nonessential amino acids

How do we determine protein quality ?

• determine how well a protein from food matches the body’s requirements and, therefore, how useful the protein is for our body

  • amino acid composition

  • protein digestibility

Amino acid composition: complete proteins

• contain all 9 essential amino acids

• adequate amounts for growth and maintenance of body tissue

• all animal products are complete proteins except gelatin

Amino acid composition: incomplete proteins

• lack one or more of the 9 essential amino acids

• cannot support either maintenance or growth of body tissues

• most of the plant proteins are incomplete

amino acid composition: partially complete protein

• contains all 9 essential amino acids, but one or more is limited

• limiting amino acid

• limits the amount that all amino acids can be used to produce protein

  • can support maintenance but not growth of tissues

Limiting amino acids

an essential amino acid supplied in less than the amount needed to support protein synthesis

Amino acid composition: complementary protein

• combining two incomplete protein sources

• amino acids in one food makeup for those lacking in the other food

• vegetarian must mix protein-rich plant foods to get amino acid balance, ex.- rice and beans

Protein digestibility

• digestibility of a protein varies between foods

• amino acids from animal sources are digested more easily

  • animal proteins: 90-99% digested and absorbed

  • plant proteins: 70-90% digested and absorbed

  • Soy and legumes: >90% digested and absorbed

protein quality: reference proteins

• a standard against which to measure the quality of other proteins

• compares amino acid composition with essential amino acid requirements of preschool-age children

• Reference proteins:

  • highest protein quality and digestibility

  • sustain maximal growth rates

Protein quality: biological value (BV) (high and low)

• nitrogen is retained/ absorbed

• high biological value

  • more nitrogen is retained/ absorbed

  • generally animal proteins (Ex. eggs)

• Low biological value

  • less nitrogen is retained/ absorbed (more is exerted)

  • generally plant proteins

Protein function

• growth and maintenance

• body processes

• energy

• fluid and electrolyte balance

Protein function: growth and maintenance

• involved whenever body is growing, repairing, or replacing tissues

• form the building blocks of muscles, blood, and skin

• collagen is a structural protein that makes scars, tendons, ligaments, foundations of bones and teeth

• replace dead cells → avg. life span of skin cell 30 days and cells of GI tract are replaced every few days

Protein function: body processes

• enzymes→ digestion, DNA synthesis

• hormones→ messenger molecules that tell something to happen (insulin, glucagon)

• antibodies→ large proteins that are produced by your immune system to fight viruses

• transport proteins→ brining important substances in and out of your cells, lipoproteins

Protein function: energy

• they are sacrificed to provide energy and glucose during times of starvation or insufficient carb intake

• tissue proteins are broken down to make amino acids available for energy or glucose production- known as GLUCONEOGENESIS

• protein can maintain blood glucose levels, but at the expense of losing lean body tissue

• 4 kcal per gram

Protein function: fluid and electrolyte balance

• protein attracts water, protein in the blood creates an osmotic pressure and keeps fluid from seeping out into extracellular space

• during critical illness or protein malnutrition, plasma proteins can leak out of the blood vessels into the spaces between the cells

• due to protein attracting water, fluid can accumulate and cause swelling (edema)

• also accepts and releases hydrogen ions, thus acting as buffers in the blood- maintaining acid- base balance - pH balance

• failure of any part of the fluid balance system causes edema (protein deficiency)

Sickle cell disease

• two of hemoglobin’s four polypeptide chains have a normal sequence of amino acids, but the other chains do not

• changes shape of hemoglobin

• loses its ability to carry oxygen effectively

Protein digestion: where?

• stomach: <10% of protein is digested

• small intestine: >90% of protein is digested

protein digestion: how?

• stomach: pepsin and HCl (acid)

• small intestine: chymotrypsin and trypsin

Protein digestion

• protein foods denatured by stomach acids (HCl)

• enzymes from stomach, pancreas, and small intestine digest proteins

• free amino acids are formed

Protein absorption

• amino acids absorbed by villi

• delivered to cells via blood

• amino acids rebuilt as needed into new protein in the cells

Protein balance

• balance of protein output and protein intake

• nitrogen balance: the amount of nitrogen consumed compared to the amount of excreted in a given time period

  • equilibrium or nitrogen balance: intake = output

  • positive nitrogen balance: intake > output

  • Negative nitrogen balance: intake < output

protein balance: positive nitrogen balance

• growth (infant and children)

• pregnancy and lactation

• recovery from illness

• athletes

protein balance: negative nitrogen balance

• when muscles or other protein tissue breaks down and is lost (illness

• inadequate protein intake (fasting)

• inadequate energy intake

• deficiency in essential amino acids

RDA protein requirement

0.8 grams per kg healthy body weight

AMDR protein requirement

10-35% total kcals

Kwashiorkor

• protein malnutrition, disease resulting from low protein intake

• occurs often when child taken off breast milk and fed starchy liquid

• usually develops rapidly

• will cause symptoms of EDEMA→ swollen belly

Marasmus

• protein-energy malnutrition

• extreme starvation; occurs during famine, especially in infants

• resulting from chronic underfeeding, both inadequate energy as well as protein

• symptoms:

  • weakening of the muscles

  • stunted brain development and learning

  • depressed metabolism

  • stunted physical growth

  • growth ceases

  • death

Excessive protein intake

• often associated with obesity

• high cholesterol and heart disease

• contribution to bone loss

• kidney disease

Triglycerides (TG)

• fats and oils

• 90-95% lipids in food

phospholipids

2-3% lipids in food

sterols

2-7% lipids in food

types of lipids

• triglycerides

• phospholipids

• sterols

Triglycerides basic structure

• glycerol backbone

• 3 fatty acids

Fatty acid structure

• C-H chain

• COOH (acid group)

• CH3 (methyl group)

fatty acid differences

• length of carbon chain

• number of double bonds

• location of double bonds

Fatty acid differences: length of carbon chain

• most contain even number of carbons- up to 24

• long chain fatty acids

  • 12-24 carbons

  • meats, seafood, vegetable oils

  • most common in diet

• Medium- chain fatty acids

  • 6-10 carbons

• Short-chain fatty acids

  • less than 6 carbons

• medium and short primarily in dairy products

Fatty acids differences: number of double bonds→ saturated fatty acids

• carbon is “saturated” with hydrogens

• no double bond

• solid at room temp

• primarily from animal sources

• some plant sources

• associated with health risks

Fatty acids differences: number of double bonds→ unsaturated fatty acids

• carbon lacks hydrogen atoms

• at least one double bond between carbons

• point of unsaturation

• liquid at room temperature (oils)

• primarily from plant sources

• double bonds are “reactive”

Monounsaturated fatty acids

• one double bond

• “cis” formation

• sources: olive, peanut, canola oils

  • mediterranean diet

• usually omega-9 group

  • only double bond 9 carbons from methyl end

• oleic acid (18 carbons, omega 9)

polyunsaturated fatty acids

• two or more double bonds

• “cis” formation

• two basic forms

  • Linoleic acid→ Omega 6

  • Linolenic acid→ Omega 3

polyunsaturated fatty acid: omega-6

• omega 6= linoleic acid

• 18 carbon chain

• two double bonds

• essential in our diet

• sources: vegetable oils, nuts, poultry

polyunsaturated fatty acid: omega-3

• omega 3= linolenic acid

• 18 carbon chain

• three double bonds

• EPA (food form, essential)

  • may lower cholesterol and decrease risk of heart disease, HTN, cancer, arthritis

  • reduce inflammation, blood clotting, plasma TG

  • sources: vegetable oils, nuts, poultry

Fatty acids differences: location of double bonds

identified by closest double bond to methyl end of the carbon chain

characteristics of fats

• lipids that are solid at room temperature

  • most saturated animal fats

characteristics of oils

• lipids that are liquid at room temperature

  • most unsaturated plant fats

  • cocoa butter, palm oil, palm kernel oil, coconut oil have higher saturated fat content

characteristics of fats and oils: degree of unsaturated affects stability

• spoiled (rancid) when exposed to oxygen

• polyunsaturated fats spoil most readily- double bonds are unstable

• saturated fats least likely to turn rancid

characteristics of fats and oils: manufacturers protect fat-containing products

1. air-tight containers, protected from light, refrigerated

2. antioxidant additives

3. hydrogenation-cis→ trans fatty acids

hydrogenation

• the process of adding hydrogen to double bonds

• converts double bonds → single bonds

• may be partially or fully hydrogenated

• makes oils more solid and more saturated

• improves shelf life

• increases risk of cardiovascular disease

hydrogenation pros

• decrease food spoilage

• can use oils as solid fats

• better cooking qualities

hydrogenation cons

• increase saturation of fats

• produce trans fats

• “unnatural” reaction

triglycerides and condensation reaction

• few fatty acids occur free in foods or in the body

• most are incorporated into triglycerides

• most contain a mixture of more than one type of fatty acid

• formed via condensation reactions

  • H from glycerol + OH from fatty acid → triglyceride + H2O

Diglycerides

• two fatty acids +glycerol

• generated during digestion of triglycerides

• added to foods as an emulsifier

monoglycerides

• one fatty acid +glycerol

• also generated during digestion and used as emulsifier in foods

Phospholipid structure

• glycerol backbone

• two fatty acids

• phosphorus-containing side group

• polar head and nonpolar tail

phospholipids manufactures in our bodies

not essential in our diet

phospholipid functions

• major component of cell membranes

• important transport forms of lipids in the blood

best known phospholipid

lecithin

phospholipid supplements not needed

• can cause GI distress, loss of appetite

• liver makes phospholipids for the body

phospholipid food sources

eggs (yolks only), liver, soybean, wheat germ, peanuts

sterol structure

multi-ring structure

most well known sterol

cholesterol

sterols are in foods derived from ____

• plants/ animals

• plant sterols interfere with cholesterol absorption and lower blood cholesterol levels

cholesterol is in foods derived from ____

• animals only

• body can make all the cholesterol we need; no dietary requirement

• associated with heart disease

Sterol function

• bile acids

• sex hormones (testosterone, androgen, estrogen)

• vitamin D

• adrenal hormones (cortisol, cortisone, aldosterone)

• cholesterol is structural component of cell membranes

  • more than 90% of all body’s cholesterol is found in cells

Cholesterol sources

• endogenous (made by the liver)→ up to 1500 mg/day

• exogenous (from animal food)→ 200-300 mg/day

the role of lipids in diet

• energy source

• essential fatty acids

• carrier of fat-soluble vitamins

• palatability

the role of lipids in the body

• energy reserve

• insulates to prevent loss of body heat

• regulates body functions

  • cell membrane structure and activity

  • precursor of hormone-like substances (eicosanoids)

Fat absorption: glycerol and short/medium-chain fatty acids

• absorbed into blood

• go directly to liver

• made into VLDL (form of lipoprotein)

Fat absorption: monoglycerides and long-chain fatty acids

• form micelles in the small intestine

• absorbed into small intestinal cells

• repackaged into new TG

• packed into chylomicrons

• chylomicrons enter lymph

how to differentiate Saturated and unsaturated fatty acids

• Saturated will be saturated with hydrogen

• unsaturated will have double bonds

Lipoproteins

clusters of lipids, proteins, cholesterol, and triglycerides that act as “transport vehicles” for fats

Four different types of lipids in order from largest and least dense to smallest and most dense

1. Chylomicrons

2. Very low density lipoproteins (VLDL)

3. Low density lipoproteins (LDL)

4. High density Lipoproteins (HDL)