NTR 108 test 2

Amino acid

basic unit of protein

Structure of amino acids

• central carbon with hydrogen (backbone)

• amine group (always has nitrogen)

• acid group

• R-group (side chain)

R-group

• side chain

• differentiates one amino acid from another

• determines structure + function

Peptide bond

• links 2 amino acids together

• needs to be broken during digestion

Dipeptides

2 amino acids bonded together

Polypeptide

many amino acids bonded together

Protein structure

• structure & function determined by amino acid sequence

• 20 different amino acids

• a lot of different structures/ sequences can be produced in the body

• each unique amino acid sequence is encoded in cellular data

Protein production in DNA

• DNA in nucleus copied onto mRNA (transcription)

• ribosome attaches to mRNA and “scans” code

• tRNA creates new peptide chain (translation)

Double helix

description of molecular shape of double-stranded DNA molecule

4 levels of protein structure

as peptide chain grows in length, twists around itself

1. primary structure

2. secondary structure

3. tertiary structure

4. quaternary structure

Tertiary structure

• 3D structure

• most important for biological structure & function

• “faraway“ amino acids bond with each other

Quartenary structure

• when tertiary proteins interact with each other and twist around each other

• e.g. muscle contraction, hemoglobin

Essential amino acids

• 9 EEAs

• cannot be made by body

• must be included in diet to maintain optimal protein status

• provide source of nitrogen for other compounds

• can be used as energy source

• ALL must be present in sufficient amounts to make protein

Non-essential amino acids

• 11 NEEAs

• body can make these from other substances in diet

• provide source of nitrogen for other compounds

• can be used as energy source

Protein functions

• structural (muscle)

• growth (infancy, pregnancy)

• maintenance & repair of body tissues

• energy (4 kcal/g)

• hormone production: insulin, glucagon, CCK, secretin

• blood proteins

• enzymes: speed up & control chemical reactions like digestion, absorption & metabolism

• immune function

Role of blood proteins

• regulation of fluid balance (prevents edema)

• maintenance of acid-case balance

• involved in blood-clotting

• delivers oxygen to tissues

• transport proteins e.g. albumin, lipoproteins

Denaturation

heat/acid/alkaline/enzymes resulting in alteration of protein’s 3D structure

Protein digestion

1. Denaturation results in a loss of protein function and exposure of peptide bonds for digestion

2. Protein in food is broken down into individual amino acids

3. Body uses pool of amino acids to make new tissues and to maintain existing tissues

Protein digestion in stomach

• protein with 3D structure denatured (exposes bond) with acid

• acid breaks some bonds

• pepsin breaks more bonds

Protein digestion in small intestine

• proteases from pancreas & small intestine digest polypeptides

• amino acids & di/tripeptides absorbed into enterocyte where peptidases digest them into single amino acids

Protein absorption into enterocytes

1. secondary active transport (sodium)

2. use different transporter based on R group (can affect protein quality if very unbalanced)

3. released as amino acids into capillaries which go to portal vein to liver

Competitive inhibition

Taking high amounts of one amino acids can block absorption of another amino acid

Protein absorption in liver

1. amino acids can be taken up before rest of the body gets a chance

2. regulates level of amino acids in blood

Transamination

• transfer of an amine group from an amino acid to carbon skeleton to form a new different amino acid

• used for formation of NEAAs

• vitamin B6 needed - without it, all amino acids are essentials

Deamination

• removal of amine group from amino acids

• used for energy production from amino acid & gluconeogenesis (nitrogen excreted)

• vitamin B6 dependent

Nitrogen excretion

• excess nitrogen (from amine group) synthesized into urea in liver

• urea transported to kidney & excreted in urine

• nitroge is also lost through feces, skin, hair, nails

Functions of vitamin B6/pyridoxine

• amino acid metabolism (transamination to make NEAA)

• carbohydrate metabolism (glycogen to glucose, gluconeogenesis)

• immune function (lymphocytes & antibodies)

• heme synthesis - hemoglobin in red blood cells

Vitamin B6 deficiency

• anemia

• convulsions

• depression

• confusion

Vitamin B6 sources

• meat (incl. poultry & seafood)

• eggs

• dairy

• peanut butter

• potatoes

• green vegetables

• bananas

• whole grain cereals

Vitamin B6 supplements

• used to treat PMS & carpal tunnel syndrome

• excess could lead to toxicity: nerve damage & skin lesions

Protein requirements

based on goal of nitrogen balance i.e. intake = output

Protein intake

• amount of protein

• protein quality

Amount of protein (intake)

• better usage when lower (to a point)

• poorer usage when high (used for energy)

Factors affecting protein quality

• digestibility

• amino acid content

Digestibility of proteins

• animal proteins & soy: 90% of amino acids absorbed

• legume: 70-80%

• grains & vegetables 60-90%

Amino acid content

based on amount of EAA in lowest proportion

Nitrogen balance

found in healthy adults who are not pregnant

Positive nitrogen balance

higher protein needs for

• growth

• pregnancy

• recovery from illness

• protein deficiency

Types of vegetarianism

• vegan (no animal products)

• lacto-vegeterian (will consume dairy)

• lacto-ovo-vegeterian (will consume dairy & egg)

• pescovegetarian (will consume dairy, egg & seafood)

• semivegetarian (plant-based, flexitarian)

Benefits of vegan diet

• low in saturated fats

• high in fiber & most vitamins

• phytochemicals

• rich in low energy density foods

Potential concerns for vegan diet

• low in iron & calcium

• low energy & protein density (children & pregnant people)

• low in vitamin B12

Anabolism

building body compounds by putting together smaller units

Catabolism

breaking down compounds to basic units for energy & excretion

ATP

• adenosine triphosphate

• high energy compound cells use for fuel

Anaerobic glycolysis

• without oxygen

• takes place in cytosol of cells

• broken down into 2 pyruvic acid molecules

• 2 ATP formed

• lactic acid produced - muscle fatigue

Aerobic glycolysis

• oxygen needed

• pyruvic acid goes to citric acid cycle

• takes place in mitochondria of cells

• 36-38 ATP formed

• CO2 formed - no lactic acid

• slower than anaerobic

Amino Acid Metabolism

• when not enough carbohydrates in diet

• almost all amino acids can be converted to glucose

• anaerobic in cytosol, aerobic in mitochondria

• urea (from nitrogen) formed in liver

Lipid metabolism

• aerobic - requires oxygen

• takes place in mitochondria

Lipid metabolism with glucose

• beta oxidation as major pathway (products go to citric acid cycle)

• complete oxidation to CO2

• lots of ATP formed

Lipid metabolism without glucose

• ketones formed in liver (ketogenesis)

• sent to peripheral tissues for energy

• some ATP formed

Alcohol

• 7 kcal/g

• 5% of US caloric intake

Alcohol metabolism

• metabolised in liver by ADH (alcohol dehydrogenase)

• acetaldehyde (toxin) is intermediate

• converted to fatty acids or ATP

• CO2 released

Vitamins’ involvement in metabolism

• direct or indirect involvement

• needed for conversion of glucose, fatty acids, amino acids & alcohol to chemical intermediates

• co-enzymes in generation of ATP

Functions of thiamin (vit B1)

• co-enzyme for carbohydrate & amino acid metabolism

• plays role in production of neurotransmitters

Thiamin deficiency

• beriberi

• dementia & amnesia (due to alcohol weakness)

• overall weakness

Symptoms of beriberi

• reduced cognitive function

• heart failure

• fatigue

• paralysis

Groups at risk of thiamin deficiency

• alcoholics (thiamin lost through liver)

• polished rice as main food (lost during removal of rice germ and making of white flour)

• malabsorption (AIDS)

Dietary sources of thiamin

• whole grains (with germ)

• enriched flour

• green leafy vegetables

• beans & legumes

• pork

Special notes on Thiamin

• no toxicity (excess lost in urine)

• increase in intake requirement with increase in physical activity

• lost in cooking water (most water-soluble vitamins)

Function of riboflavin (vitamin B2)

co-enzyme for carbohydrate & fat metabolism

Riboflavin deficiency

• weakness

• fatigue

• cracks at corners of mouth

• magenta tongue

Groups at risk for riboflavin deficiency

• alcoholics

• liver disease

• diabetics

Dietary sources of riboflavin

• enriched flour products

• milk

• green leafy vegetables

Special note on riboflavin

very photosensitive, can be lost in glass milk bottles

Functions of niacin (vitamin B3)

• co-enzyme for carbohydrate & fat metabolism

• fatty acid synthesis

• DNA replication

Niacin deficiency

Pellagra

• dermatitis

• diarrhea

• dementia

• death

Groups at risk of niacin deficiency

• alcoholics

• low protein intake (can be made from EEA tryptophan)

Dietary sources of niacin

• whole grains

• enriched flour

• meat & fish

• made in liver from tryptophan (from milk)

Special notes on niacin

• can be used as hypercholesterolemia drug (lowers blood cholesterol)

• can be toxic at high levels (flushing, liver damage)

Functions of pantothenic acid

• co-enzyme energy metabolism (esp impt for fat)

• fatty acid synthesis

Pantothenic acid deficiency

• weakness

• fatigue

Groups at risk of pantothenic acid deficiency

• very rare to have deficiency

• malabsorption

Dietary sources of pantothenic acid

“pan” found everywhere

• whole grains

• meat

• milk

Function of biotin

co-enzyme for metabolism of all macronutrients

Biotin deficiency

• red, scaly rash around eyes, nose & mouth

• lethargy/weakness

Groups at risk of biotin deficiency

• deficiency very rare

• people that eat a lot of raw egg whites (contains protein that binds biotin and makes it unabsorbable)

Dietary sources of biotin

• meat

• egg yolks

• nuts

• legumes (peanuts)

• some produced in intestine

Minerals involved in energy metabolism

co-factors in metabolism

• chromium

• iodine

• iron

• copper

• zinc

Function of chromium

• enhances ability of insulin to move glucose from blood into cells

• glucose tolerance factor

Chromium deficiency

• rise in blood glucose levels

• uncommon in US

Dietary sources of chromium

• whole grains

• mushrooms

• nuts

• dark chocolate

Chromium picolinate

• chromium supplement

• may cause organ damage

• no evidence for claim to enhance muscle mass & reduce body fat

Function of iodine

synthesis of hormone thyroid, which regualte body temperate & metabolic rate

Iodine deficiency

• Goiter: swollen thyroid gland

• weight gain

• weakness/fatigue

Groups at risk of iodine deficiency

• lack of iodized salt intake

• people in areas with low iodine content

Dietary sources of iodine

• iodized salt (not very high in sea salt)

• seafood

• dairy foods (iodine used to clean equipment for processing milk)

• depends on iodine in soil

Iodine deficiency during pregnancy

• infant risk of cretinism - mental impairment

• major cause of preventable brain damage worldwide

Energy balance

the relationship between energy intake & expenditure (individualized)

Balance

• intake = expenditure

• weight stable

Energy deficit

• intake < expenditure

• weight loss

Energy excess

• intake > expenditure

• weight gain

Energy equivalence

• 1 lb body fat = 3500 kcal

• 10 extra kcal/day = 1 lb gained per year (in theory)

Hunger

• physiological drive to eat

• caused by lack of food in GI tract

Appetite

• psychological drive to eat

• caused by thought, smell & sight

Satiety

• state in which both physiological & psychological drives are satisfied

• no longer have desire to eat

Hypothalamus

group of cells at base of brain which participate in many regulatory functions, incl. hunger

Components of energy expenditure

1. basal metabolic rate (60-75%)

2. physical activity (15-35%)

3. thermic effect of food (5-10%)

Basal Metaboic Rate (BMR)

resting energy expenditure (REE) measured soon afer waking up in the morning, at least 12h after last meal

Factors affecting BMR

high individual variation

• males need more

• lower lean body mass (LBM) i.e. muscle = lower B<R

• age (decrease about 1-2% per decade after 30; hormones & decline in LBM due to inactivity)

• shorter height = lower BMR

• nutritional status: starvation & dieting reduce BMR

• fever increases BMR

• pregnancy & lactation increase BMR

• extreme environmental temperate increase BMR

Physical activity

• planned/conscious activity

• NEAT (non-exercise activity thermogenesis): activities of daily living, spontaneous physical activity

• kcal per kg body weight per min

• continues after activity