BPK 110 CH 7 PROTEINS

Proteins are:

Folded amino acid chains

Amino acids (AAs) have three main groups:

– A nitrogen-containing amine group

– A carboxylic acid

– A side chain (Rx)

There are __ amino acids, that make up….

21, proteins

Structurally, they differ only in their __.

side chain

How many amino acids are found in nature?

500

How many essential amino acids are there? What are they?

9, essential amino acids are non-essential amino

acids that become essential when the body cannot

synthesize enough of them

How are non-essential amino acids made? What’s the process?

modifying other amino acids

– Through process of transamination

Complete vs Incomplete Proteins

• Complete proteins are foods that have all nine

essential amino acids

– All animal sources are complete, as are soy, quinoa, buckwheat, hemp seeds, chia seeds, pistachios

• Incomplete proteins are foods that are missing one or more essential amino acids (most commonly absent:lysine)

– Plant sources are typically incomplete

– The amino acid that is lacking is the limiting amino acid

Animal Sources of Protein

• Are complete proteins

• Are typically higher in total protein content

• Have B (12) vitamins, iron, zinc, calcium

• Tend to be lower in fiber, higher in saturated fat and cholesterol

– Increase risk of heart disease

Plant Sources of Protein

• Are typically incomplete proteins (ex. Legumes —> deficient in sulfur containing amino acids, high in lysine)

• Contain some B vitamins, iron, zinc, calcium

– but they are less available in the body

• These sources tend to be high in fiber, unsat fats and phytochemical

Complementing Proteins

By eating lots of plant sources of protein, all essential amino acids can be consumed = complementing proteins

– (N.B. Doesn’t have to be eaten at same meal)

• multiple sources of plant proteins

• Ex. Rice (limiting lysine) + beans (high in lysine)

Protein Synthesis

• To become part of a fully functional protein, amino

acids must bind together in a specific order

– Our DNA holds the instructions for the sequence of amino acids needed in order to build specific proteins

– We draw on the amino acid pool to make these

chains

Primary Structure of a Protein

• The first level of protein structure arises from

adjacent amino acids binding to each other

• Peptide bonds lead to the formation of a polypeptide

• This polypeptide is not yet a protein

• Must fold into secondary, tertiary, perhaps quaternary structure

• Water released in process (condensation reaction)

• Structure affects function of protein

Secondary Structure of a Protein

Hydrogen bonds between non-adjacent

amino acids lead to the formation of:

– Alpha helices (coil into, hydrogen bond between every 4th amino acids)

– Beta-pleated sheets (fold into, hydrogen bond form at stability to proteins)

Tertiary Structure of a Protein

• Interactions between amino acids side chains leads to further folding of the polypeptide chain

• This may result in a functional protein

• 3D shape: functional subunit

• Hydrophilic exterior: forms binding sites

Quaternary Structure of a Protein

• Some proteins have a quaternary structure

• Several proteins in their tertiary structure bind together to form the final protein

• Each of these is called a protein subunit

• 4 tertiary structure: 2 alpha helix, 2 beta sheet

Denaturation of a Protein

• A protein is denatured when it loses its folded

three-dimensional structure

– Also loses its function

• Acids, heat, agitation can all denature proteins

– This is sometimes desirable (ex. Food preparation)

Proteolysis

Breakdown of proteins into amino acids by enzymes

Protein Digestion and Absorption (Mouth, stomach, small intestine, villi)

Mouth: no enzymes that digest

Stomach: protein digestion starts (pepsinogen into pepsin)

Small intestine: most digestion occurs

Villi: further breakdown of polypeptide chains

What must happen to proteins for it to be absorbed?

The protein’s 3D structure must first be denatured

and the polypeptide must be broken down into

individual AAs to be absorbed

How are AAs absorbed?

• AAs are then absorbed into the SI by active

transport (requires energy to absorb)

– Similar AAs use the same transporter

– Therefore if there is an overabundance of one AA, it may block the absorption of another!

• over consume 1 amino acids: may block an of other amino acids

• Ratio of amino acids:ATP - 1:1

Body Structure

• Bones, muscles, skin, and every organ in the

body contain protein

• Collagen is the main structural protein (28 types of—> type 1-5 is most common —> type 1 is most common)

• Elastin is another key structural protein

– Permits elasticity, less strength, can be stretched 150%

Collagen Fibres in Tendon

Very stiff —> can transmit forces,

Transport

• Protein tracks in cells allow substances to walk along them, permitting transport around the cell

• The blood protein hemoglobin transports oxygen around the body

• Protein channels & pumps regulate movement of ions and

molecules into and out of the cell

• cell membranes: have protein transporters

Enzymes

• Most enzymes are proteins

• Recall: They speed up the rate of reactions

• Allows creation of unique active sites

Movement

• Myosin and actin are proteins found in muscle

• When myosin proteins attach to actin proteins and kink their heads, muscle contraction occurs

– Allows our bodies to produce movement

Fluid Balance

• Water is attracted to the positive and negative charges of the amino acids found in blood proteins

– This draws water into the blood and out of the extracellular space (controls movement)

– If blood proteins are low, fluid can build up in the extracellular space, leading to edema

Albumin: 75-80% of blood plasma (too large to leave blood….)

Protection from Disease

• Collagen in skin helps to restrict what can enter the body

• If infectious agents enter, proteins called antibodies (created by immune system) stick to these agents, promoting their removal and limiting the harm they can cause

• they can clump together, making it easier for immune system cells to find + remove them

• Our skin protects us

Energy

Protein is our last resort ( using common amino acids is wasteful)

• While proteins provide 4 kcal/gram, they are a minor sources of energy to the body

• It is wasteful to deaminate an amino acid so it can be

  metabolized to generate ATP

  – The body prefers to use protein for all its various other functions

What’s the UL protein?

There isn’t one

Protein Deficiency

(Protein energy malnutrition —> lack of all nutrients)

• Marasmus

– Wasting syndrome

– Occurs when energy and protein are deficient

– Promotes anemia, dehydration, heart irregularities, body temperature dysregulation

• Kwashiorkor

– Believed to occur when protein is deficient, but energy is

sufficient (eating a lot of one nutrients, incomplete)

– Evidenced by a distended, swollen abdomen and an

otherwise slim appearance

Protein and Body Weight

• The primary dietary factor that promotes weight gain is a caloric intake that is consistently above the body’s needs

– Whether a high/low-protein diet leads to weight gain depends on the total calories consumed

• However, protein may promote a caloric deficit by:

– Promoting fullness

– Contributing to carbohydrate and lipid metabolism

– Requiring more energy to digest and absorb it

• i.e. it has a higher thermic effect

Over consume: proteins —> fatty acids

Protein and Muscle Growth

• Protein is important for the repair and growth of muscle

• Protein muscle synthesis increases in the 24 hours following weight training

– 10 g of essential amino acids in the first 2 hours following exercise encourages muscle growth

– Milk-based proteins, for instance, increases muscle strength and improves body composition

• Athletes have a higher overall protein requirement

– ACSM recommends increasing intake from 0.8 g/kg to 1.2-2.0 g/kg, depending on the intensity and load of training (strength/power: 1.6-1.7, endurance:1.1-1.4?)

• eat protein to make protein

• Consume protein right after exercise

How many grams of protein can the body handle at a time?

30

Protein and Bone Health

• In bone, collagen forms a matrix that minerals (ex.

Calcium) harden

• However, high protein diets can promote calcium excretion

• Overall, high protein diets do not seem to negatively affect

bone health

Protein metabolism: increased carbon load?

Protein and Kidney Health

• High protein diets tax the kidneys because they have

more waste products to excrete

• For those with reduced kidney function, consuming protein at the recommended intake level (0.8 g/kg), and not beyond it, is recommended

• Increased protein consumption: no negative impact on kidneys

Protein Quality

Typically refers to two factors:

– How well a protein is digested

– How the types and quantities of amino acids in that protein

source match the body’s requirements (what it makes compared to what we need)

Ways to Assess Protein Quality

• Protein digestibility corrected amino acid score (PDCAAS)

– Compares the amino acid content of a food against a standard amino acid profile, the highest score that can be achieved is 1.0 (Based on rats —> rat feces: what’s left of protein/not digested into rat)

– Takes into account the digestibility of the protein

– This is the industry standard

• Digestible indispensable amino acid score (DIAAS)

– Measures how well amino acids are digested in the ileum and more closely estimates the amount of amino acids absorbed by the body

– Database is still being built

• Protein efficiency ratio (PER)

– How much weight an animal gains when consuming a specific amount of protein, divided by the amount of food it consumed

– Used in Canada

• animal PDCAAS sources: 90-91% or 0.90-0.91

• Plant: legumes - 0.5-0.6, soy - 0.65-0.75

Protein Supplements

• Protein supplementation can be from whole sources and from protein supplements (ex. Protein powders, shakes)

• Strength and muscle size increases with protein supplementation, especially in younger people who train regularly

– However, excessive supplementation (>1.62 g/kg body weight) does not promote further gains

– Doesn’t have to come from supplements!

• NOVA group 4

• Easy access to protein

• Protein powders: not regulated by government —> some have substances not listed on label

Branched-Chain Amino Acids

• BCAAs are essential amino acids that have a branched side chain

• They account for 35-40% of the dietary essential amino acids found in body protein

• Have been shown to reduce muscle damage associated with weight training

• Can be consumed from whole sources, do not have to come from supplements!

• All side chains are more branched

Animal Sources of Protein

• Animal proteins have more total protein, a higher PDCAAS and are complete proteins (more easily digested)

• Also, they have vitamin B12 and are higher in vitamin D, iron, zinc, and omega-3 fatty acids

• However, they are also higher in saturated fat and are

absent in fibre, phytochemicals

• Also, processed animal products (ex. Deli meats, bacon)

increase CVD risk/mortality

Consuming animal products has a significant __ impact.

Environmental. Grown + cultivated for consumption

Omnivore

A person who consumes a variety of both animal and plant products

Semi-vegetarian

A person who restricts one or more type of animal product. For instance, a semi vegetarian might avoid all red meat.

Pescatarian

A person who restricts most or all animal products except fish.

Plant-based diet

A diet that is mostly or entirely based on plant-derived foods and ingredients. However, there is no clear definition of this term. Vegetarian and vegan diets are plant based.

Vegetarian

A person who avoids some or all animal-related food and ingredients.

Lacto-ovo vegetarian

A person who avoids animal flesh, but consumes milk products (lacto) and eggs (ovo).

Lacto-vegetarian

A person who avoids animal flesh and eggs, but consumes milk products.

Vegan

A person who excludes all animal products, including eggs and milk. This may also include any animal-involved products, such as honey.

Health Benefits of Vegetarian Diets

• Diets are high in fibre and phytochemicals and low in

saturated fats

• Vegetarians are more likely to have lower BMIs, total cholesterol and LDL

• They are also at lower risk for heart disease, cancer, and CVD mortality

• Lower body mass index (epidemiological studies)

Risks of Vegetarian Diets

• They are lower in vitamin D, omega-3 fatty acids, calcium, iron, and zinc

• Vitamin B12 is only found in animal products (with the exception of nutritional yeast)

• Supplementation is recommended if these are not sufficient in diet

Balancing Protein Intake and Losses

By measuring nitrogen intake in the diet (ie. By measuring protein intake), and nitrogen output in the urine, you can assess whether someone is in a state of negative nitrogen balance (net protein breakdown), positive nitrogen balance (net protein deposition) or nitrogen balance (protein content of body remains the same)

Consume most protein from __ sources

Whole

Name plant and unprocessed animal proteins that satisfy protein needs while promoting health.

plant proteins: nuts, beans, and legumes

unprocessed animal products: fish and lean meats

Based on body weight, what’s the protein recommendation per day for those 19 years of age and older?

0.8 g/kg body weight

Why do children and infants have higher protein requirements?

• To support their growth and development

• Soft tissue development

DRI of protein needs for pregnant and lactating women

Pregnant women: 1.1 g/kg body weight

Lactating women: 1.3 g/kg body weight